Weldability of Metals and Their Alloys

The weldability, also referred to as joinability, of a material represents it's ability to be welded. Several metals and thermoplastics can be welded, however, many are easier to weld as compared to others. A material's weldability is required to determine the welding technique and also to compare and contrast the final weld quality to other materials.

Weldability is usually complicated to define quantitatively, consequently the majority of standards define it qualitatively. For instance, the International Organisation for Standardisation (ISO) defines weldability in ISO standard 581-1980 as:

"Metallic material is considered to be susceptible to welding to an established extent with given processes and for given purposes when welding provides metal integrity by a corresponding technological process for welded parts to meet technical requirements as to their own qualities as well as to their influence on a structure they form."

One of the main objectives in welding is to produce a joint which is without any cracks and therefore can withstand the stresses placed on it. If practically any sort of welding process can be used on a metal and minimal effort is required to produce a sound weld, the metal is said to possess “good weldability”. In situations where a welder can select from only a limited number of welding processes and additionally must carefully prepare the joint and carryout the welding procedure to produce a strong weld, the metal is regarded to have “poor weldability”.

Weldability is recognised as the ease of accomplishing a satisfactory weld joint and can be determined through the quality of the weld joint, effort and cost necessary for producing the weld joint. Quality of the weld joint on the other hand, can be determined by several factors although the weld must satisfy the service requirements. The characteristics of the metal determining the quality of weld joint includes predisposition to cracking, hardening and softening of heat affected zone (HAZ), oxidation, evaporation, structural modification and affinity to gases. Whereas efforts necessary for producing sound weld joint are generally determined by the properties of metal system in consideration particularly melting point, thermal expansion coefficient, thermal and electrical conductivity, defects inherent in base metal and surface condition. Each of the factors detrimentally impacting on the weld quality and increasing the efforts and skill necessary for producing a satisfactory weld joint will consequently be decreasing the weldability of metal.

In view of previously mentioned, it could be stated that weldability of metal is not an intrinsic property considering that it is influenced by,

• All steps related to the welding procedure
• Purpose of the weld joints
• Fabrication conditions etc.

Welding of a metal making use of a particular process might exhibit poor weldability for instance aluminium welding using SMA welding process and good weldability when the same metal is welded using some other type of welding process for instance aluminium welding using TIG/MIG. Furthermore, a steel weld joint could possibly perform well under normal atmospheric conditions and the same may possibly demonstrate very poor toughness and ductility at very low temperature condition. Steps of the welding procedure particularly preparation of surface and edge, preheating, welding process, welding parameters, post weld treatment including relieving the residual stresses, can have an impact on the weldability of metal appreciably. Consequently, weldability associated with a metal is considered as a relative term.

Factors Affecting Weldability

There are various factors that have an impact on the weldability of metals. Listed here are some of the most significant ones.

• Metallurgy – The science of heating or manipulating metals to produce desired properties or shapes within them.
• Welding Process – There are more than 67 welding processes. A variety of factors set them apart: the way the heat and pressure are applied, the amount of heat and pressure applied, and also the type of equipment employed.
• Joint Design – The combination of the dimensions necessary for the welded joint along with the geometry of the joint.
• Weld Preparation – Weld preparation is a collection of techniques to carryout in advance of welding to prevent defects in the weld. For instance, one process is to clean the base metal prior to welding.
• Melting Point – The temperature that needs to be attained for a solid substance to melt or fuse. Whenever a metal possesses a medium melting point, it has better weldability.
• Electrical Resistance – A metal’s opposition, or resistance, to the flow of electrical current. Metals having a high electrical resistance require more heat energy to weld which makes them possess poor weldability.

Improving Weldability

The heating and cooling cycles inherent to the majority types of welding can produce strains and stresses in the weld. Additionally, they have an impact on physical, chemical, and metallurgical changes in the metal. When these kinds of changes make a metal susceptible to poor weldability, adjustments are generally made to improve the quality of the weld.

• Shielding Gas – Some types of metals, including copper and aluminium, require a gas to shield them from atmospheric contaminants during welding. Choosing the suitable shielding gas for the application in the right quantity will minimise the chance of weld defects.
• Welding Process – Welding charts are obtainable to employ as a reference for which process to choose for a metal.
• Filler Metal – Choosing the incorrect filler metal can result in defects in the weld, including cracks and porosity. An effective general principle is to select a filler metal which is stronger ın comparison to the base metal.
• Preheat and Postheat – Brittle metals are susceptible to cracking during welding. Heating the metal before welding and additionally afterwards can alleviate this problem.
• Welding Procedure – Weld quality could be dependent upon the number of welds, their length, along with the size of the weld bead. A number of small welds may be more effective compared to a few large welds.

While all metals can be welded, several fuse more readily than others. Nevertheless, an understanding of the factors which influence weldability and the techniques to improve it will help a welder consistently produce strong and sound welds.

Process Factors

While weldability could be typically defined for various materials, some welding processes are more effective for specific material as compared to others. Even within a particular process the quality of the weld may vary considerably depending on parameters, for instance the electrode material, shielding gases, welding speed, and cooling rate.

Weldability of Aluminium

Aluminium and its alloys are widely used metals because of their low weight, good corrosion resistance, and weldability. Despite the fact that they generally possess low strength, certain alloys can have mechanical properties comparable to steels. Aluminium alloys can be joined using a wide range of methods. However they additionally possess several properties that need understanding depending on which method is used.

Aluminium Alloys

Pure aluminium is a comparatively soft metal. However , when combined with alloying elements it can produce a wide variety of mechanical properties. These kind of alloys are categorised into families in accordance with the principal alloying elements using a four-digit identification system.

The following is an overview of the prevalent families of aluminium alloys and their weldability characteristics in conjunction with common filler metals:

1000 series alloys:

Almost pure aluminium, at 99% with trace elements making up the rest. This particular family is used to transport electrical current or for corrosion resistance in particular environments. 1000 series Aluminium alloys are conveniently weldable with 1100 filler metal.

2000 series alloys:

This is a family of high-strength aerospace alloys. They are extremely susceptible to hot cracking and tend to be the least weldable aluminium alloys. Specifically, 2024 is the least weldable. Nonetheless there are several exceptions, 2219 and 2519, that can be readily welded with 2319 or 4043 filler metal.

3000 series alloys:

A collection of medium-strength aluminium alloys. They are extremely formable consequently they are typically used for heat exchangers and air conditioners. 3000 series aluminium alloys are conveniently weldable with either 4043 or 5356 filler metal.

4000 series alloys:

These are generally used as welding or brazing filler alloys instead of base materials. However, when they are utilized as base materials, 4000 series aluminium alloys are readily welded with 4043 filler metal.

5000 series alloys:

A family of high-strength sheet and plate alloys. 5000 series aluminium alloys are conveniently welded with 5356 filler metal. Nevertheless, with stronger alloys which include 5083, 5183, or 5556, filler metals need to be used.

6000 series alloys:

6000 series aluminium alloys are challenging to weld because they are susceptible to cracking. Nevertheless, together with the proper techniques, they can be conveniently welded using 4043 or 5356 filler metals.

7000 series alloys:

Another group of high-strength aerospace alloys. These alloys are primarily unweldable because of their susceptibility to hot-cracking and stress-corrosion. 7075 is particularly susceptible. The exceptions are 7003, 7005, and 7039, which are conveniently weldable with 5356 filler. The alloys are generally further classified according to being non-heat-treatable or heat-treatable alloys.

Weldability of Aluminium Alloys

TIG (Tungsten Inert Gas), MIG (Metal Inert Gas), and oxyfuel processes are appropriate processes for fusion welding the vast majority of wrought grades in the 1XXX, 3XXX, 5XXX, and 6XXX series; the 5XXX alloys especially possess excellent weldabilty. These kind of processes are likewise suitable for medium strength 7XXX series alloys. Fusion welding is not recommend for high strength alloys, such as 7010, 7050, and a majority of the 2XXX alloys, since they are susceptible to liquidation and solidification. The Friction Stir Welding technique is particularly suited for producing sound welds in aluminium alloys. This technique is an effective option for heat-treatable alloys that happens to be susceptible to hot cracking.

Below is a practical breakdown of the weldability of aluminium alloys in heat-treatable and non-heat-treatable variants and which fillers the base metals are generally best combined with:

Non Heat-Treatable Aluminium Alloys

For non-heat-treatable alloys, the material strength of alloys is dependent upon the effect of work hardening and solid solution hardening of alloy elements including magnesium and manganese. These are typically found in the 1000, 3000 and 5000 series aluminium alloys. When welded, these kind of alloys might lose the effects of work hardening and cause softening of the heat affected zone adjacent to the weld.

Heat-Treatable Aluminium Alloys

The material hardness and strength of heat-treatable alloys be determined by their composition and the heat treatment. The primary alloying elements of these kind of materials are defined in the 2000, 6000 and 7000 series aluminium alloys. Observe that when fusion welding heat-treatable alloys, the hardening constituents in the heat affected zone (HAZ) is redistributed and leads to a reduction in material strength inside the local area.

Guide to the Selection of Filler Metal for Aluminium Welding

Weldability of Steel

Steel is among the most prevalent materials in the world. It is widely used because of its high tensile strength and unparalleled versatility. Employed in everything from structural construction to comprehensive aesthetic designs, steel is supplied in a vast range of grades. Each grade has specific strengths and is optimised for a certain type of project.

The weldability of steel grades is dependent mostly on how hard it is. Consequently, this is dependent upon the material’s chemical composition, particularly its carbon content. Other alloying elements that have a lesser effect on the hardness of steel include manganese, molybdenum, chromium, vanadium, nickel and silicon. Accordingly, in order to successfully weld this versatile material it is essential to understand the various types of steels and their properties.

Types of Steel

According to the American Iron & Steel Institute (AISI), Steel is supplied in four main groups based on the chemical compositions. Each group differs in carbon content and for that reason possess different weldabilities. The four groups are Carbon Steel, Alloy Steel, Stainless Steel, and Tool Steel.

Carbon Steel

The ease of welding carbon steel primarily is dependent upon the quantity of carbon present. As the carbon content increases, the weldability has a tendency to decrease. For the reason that the increase in hardness makes the steel more prone to cracking. Nevertheless, the majority of carbon steels are still weldable.

Low Carbon Steel (Mild Steel)

These steels characteristically contain less than 0.3% carbon content and upto 0.4% manganese. Low carbon steels with 0.15-0.3% carbon and up to 0.9% manganese posses good weldability. Those with less than 0.2% carbon are generally most suitable.

On condition that the impurities are maintained low, these metals rarely present complications during the welding process. Steels with carbon over 0.25% are susceptible to cracking in certain applications. In contrast, steels with less than 0.12% carbon may be susceptible to porosity. All low carbon steel can be welded by using any of the common welding processes. But the steels with more carbon content are best welded with a low-hydrogen process or using low-hydrogen fillers.

Medium Carbon Steel

Medium carbon steels contain 0.30-0.60% carbon and 0.60-1.65% manganese. These are stronger when compared to low carbon steel, but tend to be more challenging to weld. This is because they are more susceptible to cracking. Medium carbon steels must always be welded using a low-hydrogen welding process or controlled hydrogen fillers.

High Carbon Steel (Carbon Tool Steel)

High carbon steels contain 0.60-1.0% carbon and 0.30-0.90% manganese. They are very hard and strong, but additionally possess poor weldability and tend to be complicated to weld without cracking.

Once heat treated, these are extremely hard and brittle. If welded, high carbon steels require preheating, careful interpass temperature control, and additionally post weld stress relief. Low-hydrogen processes to low-hydrogen fillers are essential when welding these kind of steels.

Carbon-Manganese Steels

Carbon-Manganese steels have 0.15-0.5% carbon and 1.0-1.7% manganese. Typically these steels are weldable, however some steels will require controls on preheat and heat input. When welding carbon-manganese steels using higher amounts of carbon, it is recommended to utilise low-hydrogen welding processes or controlled hydrogen fillers.

Comparable to various other carbon steels, several low alloy steels are weldable. However , their weldabilty again deviates with its carbon content. Particularly, the weldabilty of alloy steels depend upon the carbon equivalent to it's alloying inclusions: manganese, chromium, molybdenum, vanadium and nickel.

Alloy Steel

This category includes a wide range of metals. They are carbon steels that are subsequently alloyed heavily with other elements, typically chromium, cobalt, manganese, molybdenum, nickel, tungsten, vanadium, and chromium-vanadium.

Alloy Steels frequently have superior hardness, higher corrosion resistance, yet poor weldability. They are susceptible to cracking when welded unless particular attention is paid to preheat, interpass temperature, cooling rate and post-weld treatment. Similar to the other hardenable steels, low hydrogen processes or hydrogen controlled filler are recommended to lessen the risk of cracking.

Nickel Steel

Nickel steel is a specific type of Alloy Steel that is unusual enough that it receives a unique entry. Alloys containing 1-3% nickel can be cautiously welded with low hydrogen welding processes. As the nickel content increases, the steel’s hardness increases. Like carbon, it indicates the weldability of these steels becomes worse. Steels containing 5-9% nickel possess poor weldability. They are too hard to be welded without the risk of cracking.

When welding nickel steel, it is crucial to utilize a low-hydrogen process or controlled hydrogen fillers.

Stainless Steel

Stainless Steels are a category of high alloy steels that contain a minimum of 10.5% chromium. They are widely-preferred for their performance in even the most aggressive environments. Stainless steels are typically alloyed with a number of other elements to enhance heat resisting properties, enhance mechanical properties and/or fabricating characteristics, and also to enhance corrosion resistance. These alloying elements additionally influences their weldability.

Tool Steel

As with carbon steels, the weldability of steels with more than 0.2% carbon is regarded to be poor. This is because of their hardness and risk of cracking when welded. Tool Steels, which contain 0.3–2.5% carbon, are accordingly challenging to weld and many steel manufacturers will essentially recommend against it. Nevertheless, with advancements in welding equipment, techniques, procedures, tool steel and fillers, it is possible.

Steel Classification

Steel Grade Classification

Carbon steels and alloy steels are designated a four digit number, whereby the first digit indicates the main alloying element(s), the second digit indicates TG (top grade) element(s), and the last two digits indicate the amount of carbon, in hundredths of a percent (basis points) by weight. As an illustration, a 1060 steel is a plain-carbon steel containing 0.60 wt% C. An "H" suffix can be added to any designation to denote hardenability as a major requirement. The chemical requirements are loosened but hardness values defined for various distances on a Jominy test.

Carbon Equivalent Based Weldability Classification

The equivalent carbon content concept is employed on ferrous materials, commonly steel and cast iron, to ascertain various properties of the alloy when more than just carbon is used as an alloyant, and that is frequent. The concept is to convert the percentage of alloying elements with the exception of carbon to the equivalent carbon percentage, considering that iron-carbon phases are better understood as compared to other iron-alloy phases. Typically this concept is employed in welding, nevertheless it is also applied when heat treating and casting cast iron.

In welding, equivalent carbon content (C.E) is needed to comprehend how the different alloying elements have an impact on the hardness of the steel being welded. This is then directly related to hydrogen-induced cold cracking, which is the most prevalent weld defect for steel, thus it is most commonly used to determine weldability. The AWS states that for an equivalent carbon content above 0.40% there exists a potential for cracking in the heat-affected zone (HAZ) on flame cut edges and welds.

The classification of steels on the basis of weldability is presented below:

Welding of Various Steel Grades

Low-Carbon Steels and Low-alloy Steels

Low-carbon steels include those in the AISI series C-1008 to C-1025. Carbon ranges from 0.10 to 0.25%, manganese ranges from 0.25 to 1.5%, phosphorous is 0.4% maximum, and sulphur is 0.5% maximum. Steels in this range are most widely used for industrial fabrication and construction. These steels are usually easily welded by means of any of the arc, gas, and resistance welding processes.

The low-alloy high-strength steelsrepresent the majority of the remaining steels in the AISI designation system. These steels are welded by means of E-80XX, E-90XX, and E-100XX class of covered welding electrodes. It is additionally for these types of steels that the suffix to the electrode classification number is used. These steels include the low-manganese steels, the low-to-medium nickel steels, the low nickel-chromium steels, the molybdenum steels, the chromium-molybdenum steels, and the nickel-chromium-molybdenum steels. These alloys are included in AISI series 2315, 2515, and 2517. Carbon ranges from 0.12-0.30%, manganese from 0.40-0.60%, silicon from 0.20-0.45% and nickel from 3.25-5.25%. If the carbon doesn't exceed 0.15% preheat is not necessary, with the exception of extremely heavy sections. If the carbon exceeds 0.15% preheat of up to 260°C, dependant upon thickness is required.

For the shielded metal arc welding process, attention was directed towards the selection of the class of covered electrodes determined by their usability factors. All the electrodes described in AWS specification A5.1 are applicable to the mild and low-alloy steels. The E-60XX and E-70XX classes of electrodes provide adequate strength to produce 100% weld joints in the steels. The yield strength of electrodes, in these classes, will overmatch the yield strength of the mild and low alloy steels. The E-60XX class should be utilized for steels having yield strength below 350 MPa and the E-70XX class should be used for welding steels possessing yield strength below 420 MPa. Low-hydrogen electrodes should be used and preheat is advisable when welding heavier materials, or restrained joints. The electrode that provides the desired operational features should be selected.

When welding the low-alloy high-strength steels, the operating characteristics of the electrode are not considered considering that E-80XX and higher-strength electrodes are all of the low-hydrogen type. There does exist a particular exception, which is the E-XX10 class. These are shown in the AWS specification for low-alloy steel-covered arc welding electrodes, AWS 5.5. This specification is more complex compared to the one for mild steel electrodes, despite the fact that there are only two basic classes in each strength level. The lower strength level includes the E-8010, E-XX15, E-XX16, and the more popular E-XX18 classes.

This allows the selection of the covered electrode to match not only the mechanical properties of the base metal, but additionally to approximately match the composition of the base metal. The base metal composition and the mechanical properties needs to be known so as to choose the correct covered electrode to be utilised. The only E-80XX or higher-strength electrodes that do not have low-hydrogen coverings are the E-8010 type electrodes which are designed specifically for welding pipes.

These high strength, cellulose-covered, electrodes are matched to specific alloy of the steel pipes. The deep penetrating characteristics of the cellulose-covered electrodes make them well suited for cross-country pipe welding. The theory and practice is that alloy steel pipe is comparatively thin and it is welded with cellulose-covered electrodes at relatively high currents. Additionally, each welding pass is very thin and the weld metal is aged for a substantial period of time in advance of placing the pipeline into service. This permits for hydrogen, which might be absorbed, to escape from the metal and not detrimentally have an impact on the service life of the pipeline.

Medium-Carbon Steels

The medium-carbon steels include those in the AISI series C-1020 to C-1050. The composition is comparable to low-carbon steels, with the exception that the carbon ranges from 0.25 to 0.50% and manganese from 0.60 to 1.65%.

With higher carbon and manganese, the low-hydrogen type electrodes are recommended, specifically in thicker sections. Preheating could possibly be needed and should range from 150-260°C. Postheating is often specified to relieve stress and help reduce hardness which might have been caused by rapid cooling. Medium-carbon steels are readily weldable provided the above mentioned precautions are observed.

These steels can be welded with all of the processes.

High-Carbon Steels

High-carbon steels include those in the AISI series from C-1050 to C-1095. The composition is comparable to medium-carbon steels, with the exception that carbon ranges from 0.30 to 1.00%.

Special precautions are recommended to be taken when welding steels in these classes. The low-hydrogen electrodes must be employed and preheating of from 300-320°C is necessary, particularly when heavier sections are welded. A postheat treatment, either stress relieving or annealing, is typically stipulated.

High-carbon steels can be welded with all the same processes mentioned earlier.

Low-Nickel Chrome Steels

Steels in this group include the AISI 3120, 3135, 3140, 3310, and 3316. In these steels, carbon ranges from 0.14-0.34%, manganese from 0.40-0.90%, silicon from 0.20-0.35%, nickel from 1.10-3.75% and chromium from 0.55-0.75%.

Thin sections of these steels in the lower carbon ranges can be welded without the need of preheat. A preheat of 100-150°C is necessary for carbon in the 0.20% range, and additionally for higher carbon content a preheat of up 320°C must be used. The weldment is required to be stress relived or annealed after welding.

Low-Manganese Steels

Included in this group are the AISI type 1320, 1330, 1335, 1340, and 1345 designations. In these kind of steels, the carbon ranges from 0.18-0.48%, manganese from 1.60-1.90%, and silicon from 0.20-0.35%.

Preheat is not essential at the low range of carbon and manganese. Preheat of 120-150°C is advisable as the carbon approaches 0.25%, and mandatory at the higher range of manganese. Thicker sections must be preheated to double the above mentioned figure. A stress relief postheat treatment is recommended.

Low-Alloy Chromium Steels

Included in this group are the AISI type 5015 to 5160 and the electric furnace steels 50100, 51100, and 52100. In these steels carbon ranges from 0.12-1.10%, manganese from 0.30-1.00%, chromium from 0.20-1.60%, and silicon from 0.20-0.30%. When carbon is at low end of the range, these steels can be welded without the need of special precautions. As the carbon increases and as the chromium increases, high hardenability results and a preheat of as high 400°C would be necessary, specifically for heavy sections.

When utilizing the submerged arc welding process, it is additionally recommended to match the composition of the electrode along with the composition of the base metal. A flux that neither detracts nor adds elements to the weld metal must be used. Typically, preheat could be reduced for submerged arc welding due to the higher heat input and slower cooling rates involved. To make certain that the submerged arc deposit is low hydrogen, the flux has to be dry and the electrode and base metal is required to be clean.

When making use of the gas metal arc welding process, the electrode must be selected to complement the base metal and the shielding gas must be chosen to avoid excessive oxidation of the weld metal. Preheating with the gas metal arc welding (GMAW) process ought to be in the same order as with shielded metal arc welding (SMAW) considering that heat input is comparable.

When utilizing the flux-cored arc welding process, the deposited weld metal that is generated by the flux-cored electrode must match the base metal being welded. Preheat requirements would be comparable to gas metal arc welding.

When low-alloy high-strength steels are welded to lower-strength grades the electrode needs to be selected to match the strength of the lower-strength steel. The welding procedure, that is, preheat input, etcetera, ought to be appropriate for the higher-strength steel.

Weldability of Stainless Steel

Known because of its corrosion resistance and wide range of applications in food handling, cutlery, and several additional applications, stainless steel is among the most widely used metals being used today. The a wide selection of alloy variants produce welding stainless steel more complicated when compared with welding traditional carbon steel. Nonetheless, whereas stainless alloys were once considered a major challenge to weld, at present they are referred to as “different” instead of “difficult”.

Stainless Steels are high alloy steels containing a minimum of 10.5% chromium. They are also typically alloyed with other elements to enhance heat resistance, mechanical properties, and fabricating characteristics. These kind of alloying elements additionally modify and impact the weldability of stainless steel.

To effectively weld stainless, it is recommended to fully understand the various types of stainless and their properties. They are divided into five main types: ferritic, martensitic, precipitation hardening, duplex, and austenitic.

Types of Stainless Steel

Austenitic Stainless Steel

This class of stainless is highly corrosion resistant, strong, and highly formable. However , it is additionally susceptible to stress cracking. These are typically regarded as the most easily weldable of the stainless steels. There is no requirement for pre or post-weld heat treatment.

Austenitic alloys are typically welded using fillers with matching composition to the base material. There are some exceptions nonetheless; 308 filler is used for alloys 302 and 304 and type 347 filler used for 321.

Ferritic Stainless Steel

All ferritic alloys are in the 400 family, but not all 400s are ferritic. They have lower ductility, are more brittle, susceptible to hot cracking, and posses lower corrosion resistance compared to the austenitic grades. Nonetheless they offer higher resistance to stress corrosion cracking. This type is normally considered to possess poor weldability considering that at high temperatures it undergoes rapid grain growth. This results in brittle, heat affected zones.

If ferritic alloys are being welded, it happens to be in sections less than 6mm thick. Any loss of toughness is negligible in a piece that thin. When welding the ferritic stainless, filler metals must be used that match or exceed the chromium level of the base alloy. 409 and 430 are typically made use of as fillers, and austenitic types 309 and 312 for dissimilar joints.

Martensitic Stainless Steel

The 400 and 500 series comprise the martensitic grades. These alloys possess higher strength, wear resistance and fatigue resistance than the austenitic and ferritic grades. However they are less corrosion resistant. This grade becomes hard and brittle upon cooling, making it a great material for wear resistance but more challenging to weld considering that it has a tendency to weld crack on cooling.

However, martensitic stainless can be welded using careful precautions. The filler metals should generally match the chromium and carbon content of base martensitic metal. Type 410 filler is utilized to weld types 402, 410, 414 and 420 steels. Austenitic types 308, 309 and 310 are likewise used to weld martensitic steels to themselves or dissimilar metals.

Precipitation-Hardening Stainless Steel

Precipitation-hardening stainless steels contain both chromium and nickel. These metals provide a combination of the properties of martensitic and austenitic grades. They can be hardened through heat treatment to levels comparable to Martensitic steels while additionally being corrosion resistant like austenitic steels.  

P-H steels can be readily welded by using procedures comparable to those for 300-series stainless steels. Grade 17-4 is frequently welded with 17-7 filler and can be welded without preheating. Similar to many other alloys, achieving a similar mechanical properties in the weld as in parent material is difficult for P-H steels. Irrespective of whether utilizing a matching filler, it requires certain careful preparation. Heat treating subsequent to welding can be used to enable the weld achieve close similarities to the parent metal.

Duplex Stainless Steel

Duplex stainless steels are “duplex” since they possess a two-phase microstructure. This contains grains of both ferritic and austenitic stainless steel. These steels have considerably improved toughness and ductility than ferritic grades. Nevertheless, they don't attain the excellent values of austenitic grades. However they share a comparable corrosion resistance to the austenitic steels.

Modern duplex steels are conveniently weldable. But the procedure to maintain the heat input range must be strictly followed. As a result of the material’s complex chemical composition, an excessive amount of heat also adversely affects duplex stainless steels. Similarly, selecting a filler metal is slightly more complicated. Various types of duplex stainless base metals are not available as filler metals because of the fact that filler metal cools much more rapidly ın comparison to the base metal.

Welding of Stainless Steel

As in any type of welding, it is essential to clean stainless steel prior to welding it. What is not necessarily evident is precisely how sensitive the stainless weld is to the presence of any carbon steel. Ensure that any tools used to clean the stainless steel are only used to clean stainless steel. For instance, if using a stainless steel brush to clean carbon steel, don’t use it again on any stainless steel. The same will also apply to stainless hammers and clamps.

Trace amounts of carbon steel can transfer to the stainless, causing it to rust. Likewise, grinding carbon steel in proximity to stainless steel can lead to complications. Carbon steel dust suspended in the air may well land on nearby stainless steel and result in rusting. Its for these reasons, it’s recommended to keep carbon steel and stainless steel work areas separate.

The procedure for welding stainless steel isn’t immensely different from that of welding mild steel. The majority of all stainless steels can be joined through various types of welding. In order to assist to find the best one for a given material, listed here is a breakdown of the ratings for the weldability of stainless steel and other fabrication properties for each type of stainless.

Weldability of Copper & its Alloys

Copper and its alloys of Brass and Bronze are widely used. Bronzes are typically copper with tin as main alloying element, while brass has zinc as the alloying element. Because of their excellent corrosion resistance and ability to be strengthened, they are extremely versatile and used in numerous environments. Additionally, Copper possesses exceptional electrical and thermal conductivity.

When welding copper and its alloys, it is suitable to maintain the desirable corrosion resistance, mechanical properties, and to avoid introducing defects to the welds.

Types of Copper Alloys

Copper-based alloys are categorised into families based on their chemical makeup. UNS assigns a number designation based on this. These numbers range from 10000 to 99999. Also these kind of alloys frequently have a C in their name, for instance, C11000. Wrought metals fall between 10000 and 7999. Cast metals are between 80000 and 99999.

These numbers are often stylised by dropping the last two zeroes off. This approach makes them easier to read and consume less space in writing. For instance, Copper C10100 listed simply as Copper 101.

Wrought 101 to 130 | Cast: 801 to 812

These alloys are functionally pure copper. Consequently they are soft and weld fair. Oxygen-free coppers, such as 101, are easily welded. However, oxygen-bearing copper must not be welded as high temperatures drastically reduce the metal’s strength and ductility.

Fusion welding is not suggested for free-machining copper since they are susceptible to cracking. Neither is it advised for precipitation-hardenable copper alloys. High temperatures will weaken the heat affected zone.

Commonly weldable coppers are generally paired with Cu 1897 and Cu 1898 filler metal.

Types of Brass Alloys

Wrought: 205 to 28580 | Cast: 833 to 858

All brasses are weldable with the exception of the alloys containing lead. Nonetheless, the lower the zinc content, the more easily welded it is. Low-zinc brasses with less than 20% zinc possess good weldability. In comparison, high-zinc brasses with over 20%, possess only fair weldability. Finally, cast brasses are only marginally weldable.

The recommended fillers for low-zinc brasses are Cu 6328 and Cu 6560.

Wrought: 404 to 486 | Cast: 833 to 848 “Tin Brass”

Unleaded tin brass alloys possess fair weldability. Nonetheless, they are susceptible to hot cracking and forming oxide films on the weld pool. Consequently, high welding heat inputs, high preheat, and slow cooling rates must be avoided. Leaded tin brass alloys are typically regarded as unweldable.

Types of Bronze Alloys

Wrought: 501 to 524 | Cast: 902 to 917 “Phosphor Bronze”

Unleaded Phosphor Bronze alloys possess fair weldbility. However, under stressed conditions they are cause to undergo hot cracking. Consequently like Tin Brass, high heat inputs, high preheat, and slow cooling rates must be avoided. It is possible to carefully weld leaded Phosphor Bronze by using SMAW. Take into account that weldability of copper alloys decreases as lead content increases.

The most regularly used phosphor bronze alloy is best suited to Cu 5180 filler metal.

Wrought: 608 to 64210 | Cast: 952 to 959 “Aluminium Bronze”

These metals possess low electrical and thermal conductivity, that improves weldability. On the other hand, is it important to remove all aluminium oxide on the surface of the material prior to welding.

For Aluminium Bronze alloys with less than 7.8% aluminium, Cu 6240 and Cu 6100 are most suitable filler metals. Whereas alloys with aluminium content greater than 7.8% are more suitable with Cu 6180 and Cu 6100. 642 Aluminium Silicon Bronze is best matched with Cu 6100.

Wrought: 647 to 661 | Cast: 870 to 87999 “Silicon Bronze”

These are certainly the easiest of all the bronzes to weld. As opposed to some other copper alloys, their thermal conductivity is comparatively low and high welding speeds can be used. Silicon Bronze alloys must be stress relieved or annealed in advance of welding. Following that, they must be slowly and gradually heated to the desired temperature. Subsequently rapidly cooled through the critical temperature range.

Silicon bronzes are conveniently weldable with Cu 6560 filler metal.

Wrought: 701 to 72950 | Cast: 962 to 969 “Copper Nickel”

These alloys are typically utilised in welded fabrication projects. Phosphorus and sulphur levels ought to be less than 0.02% to ensure good welds. Most Copper Nickel alloys never contain a deoxidiser. Consequently, fusion welding necessitates the inclusion of a deoxodised filler metal. This approach reduces the risk of porosity in the weld.

For copper nickel with a 10% nickel composition, Cu 7071 or Cu 7158 fillers are recommended. For copper nickel with a 30% nickel composition, a Cu 7158 filler is recommended.

Types of Nickel Silver Alloys

Nickel Silver is neither nickel nor silver. Essentially, it's actually a brass alloy. However , due to the fact that people typically list Nickel Silver as a unique category, the same is done here.

Wrought: 735 to 799 | Cast: 973 to 978 “Nickel Silver”

These alloys possess a weldability comparable to other brasses. Additionally, the weld quality decreases if lead is present. Unleaded Nickel Silver alloys are considered suitable to weld. However , leaded alloys are not. Additionally much like other brasses, alloys with lower zinc content possess better weldability.

These low-zinc alloys are readily weldable with Cu 6328 and Cu 6560 filler metals.

Welding of Copper, Brass and Bronze Alloys

It is feasible to connect copper and its alloys by a variety of methods of welding, brazing and soldering. In order to find the right one method, listed here is a breakdown of the weldability ratings and fabrication properties for the most common copper, brass, and bronze alloys.

Weldability of Titanium and Titanium Alloys

Titanium is probably the most fascinating metals. It has strength comparable to steel, nevertheless it is 45% lighter. Moreover, it maintains it's mechanical properties at a wide range of temperatures. Titanium will continue to work in below freezing temperatures without losing its toughness. And yet in addition, it resists creep and oxidation at temperatures up to 600°C.

Titanium is actually a reactive metal and forms a thin layer of titanium dioxide on its surface. This oxide layer provides excellent corrosion resistance and endures indefinitely in acidic, chloride, and saltwater environments. Although expensive initially, the lifetime cost of titanium is actually quite low due to its extensive service life and reduced (or even non-existent) maintenance and repair costs.

Types Of Titanium

There are 31 grades of titanium based on mechanical and chemical properties. These grades are divided up into four classes: Commercially Pure (CP, or unalloyed), Alpha, Alpha-Beta, and Beta.

The elements in the titanium determine the crystal structure of the material. Oxygen, nitrogen, and aluminium encourage an alpha structure. In contrast vanadium, molybdenum and silicon act as beta stabilisers. The inclusion of other elements to the alloy will precisely control the crystal structure. Therefore, the alloy’s properties and weldability can be controlled.

Consequently, the initial step to successful titanium welding should be to understand the various alloys, their properties, and the issues to consider in choosing filler metal for each.

Commercially Pure

Commercially Pure Titanium contains 98-99.5% titanium. The small additions of oxygen, nitrogen, carbon, and iron improve strength. CP alloys possess the best weldability of titanium grades. This is because of their combination resulting in excellent corrosion resistance, good ductility and excellent weldability.

The most widespread CP grades are Grades 1, 2, 3 and 4. The difference between these is the amount of oxygen and iron that are alloyed in them. Grade 1 is the most pure and also the weakest. Remember the fact that the mechanical properties increase with the grade number. Grades with more oxygen and iron possess higher strength but lower ductility and weldability.

When welding CP Titanium, a filler should be used that is one or two PSI strength grades lower than the parent metal. The weld dilution along with the base metal will increase in the strength of the weld metal.

Alpha Alloys

Alpha titanium alloys commonly contain aluminium, tin, and trace amounts of oxygen, nitrogen, and carbon. Additionally, they also have medium strength in comparison to other titanium alloys. Furthermore, they have reasonably good ductility and excellent mechanical properties at cryogenic temperatures. And finally, they are extremely weldable and are always welded in the annealed condition.

Alpha alloys don't respond to heat treatment. Nevertheless, they can be strengthened by cold working. In addition to the CP Titanium grades, Alpha alloys possess the highest corrosion resistance of the Titanium groups.

Alpha-Beta Alloys

As the name indicates, Alpha-Beta Titanium alloys contain both crystal structures. They are formed through the addition of less than 6% aluminium and varying amounts of the Beta forming elements. Included in this are vanadium, chromium and molybdenum.

These alloys possess medium to low strength in comparison to the other Titanium grades. As opposed to CP and Alpha alloys, that can solely be strengthened by cold work, Alpha-Beta alloys are heat treatable. Consequently, these grades can proceed through machining while the material is still ductile. Then they can be heat treated to further strengthen the material.

Alpha-Beta alloys are typically weldable. Nonetheless, their weldability is dependent on the amount of Beta present. The higher the Beta elements, the lower the weldability of titanium grades. Moreover, the higher the Beta elements, the more brittle the welds become. High-Beta grades are extremely strong and rarely welded.

Alpha-Beta alloys can be welded with a variety of filler metals. It's quite common to make use of filler metal of an equivalent grade, particularly for the lower alloyed materials. An additional choice is one grade lower to guarantee good weld strength and ductility.

Beta Alloys

Beta titanium alloys are the smallest group of titanium alloys. They are high strength, low weight, and highly corrosion resistant. Beta alloys are fully heat treatable, possess good hardenability, and are generally weldable.

Beta alloys are slightly denser as compared to other titanium alloys. However, they have the highest strength and good creep resistance. These grades are welded in the annealed or solution heat treated condition. When welded, the joint has a low strength and yet is ductile. Following that, they are cold-worked, subsequently solution treated and aged. This approach increases strength but avoids embrittlement.

These alloys are welded by using filler wire of matching composition. However, whenever welding higher strength titanium alloys, fillers of a lower strength are occasionally useful to maintain weld metal ductility.

Titanium Welding Processes

Titanium and most titanium alloys are readily weldable, by using several welding processes. Properly made welds in the as-welded condition are ductile and additionally, in the majority of environments, are as corrosion resistant as base metal. Improper welds, in contrast, might be embrittled and less corrosion-resistant in comparison to base metal.

The techniques and equipment utilised in welding titanium resemble those necessary for other high-performance materials, which include stainless steels or nickel-base alloys. Titanium, on the other hand, demands greater attention to cleanliness and to the utilization of auxiliary inert gas shielding as compared to these materials. Molten titanium weld metal is required to be totally protected from contamination by air. Moreover, hot heat-affected zones and root side of titanium welds ought to be shielded until temperatures drop below 800°F (427°C).

Titanium reacts readily with air, moisture, grease, dirt, refractories, and most other metals to form brittle compounds. Reaction of titanium with gases and fluxes makes standard welding processes including gas welding, shielded metal arc, flux cored arc, and submerged arc welding unsuitable. Similarly, welding titanium to the majority of dissimilar metals isn't feasible, considering that titanium forms brittle compounds with the majority of metals; nonetheless, titanium can be welded to zirconium, tantalum and niobium.

Irrespective of the precautions, that must be taken, many fabricators tend to routinely and economically welding titanium, producing sound, ductile welds at comparable rates to numerous other high performance materials. Amongst the significant benefits of welding the commercially pure grades of titanium is that they are in excess of 99% pure titanium and additionally there's no concern for segregation. Precisely the same will also apply to weld wire or rod in commercially pure grades.

As a consequence of diverse weldability of titanium alloys, it can be welded in a number of different ways.

• Gas-tungsten arc welding is the most widespread process for joining titanium. Nevertheless, it should never be used when welding parts with thick sections. Joints may be welded without the need of filler metal in base metals as much as 2.5 mm thick. For thicker base metals, a filler metal becomes necessary plus the joint must be grooved. It's essential that weld pool is adequately shielded from the atmosphere to circumvent contamination with oxygen, nitrogen, and carbon, which could result in embrittlement.
• Laser-beam welding is becoming more and more preferred for joining titanium and titanium alloys. This technique doesn't involve the usage of vacuum chambers, although gas shielding will be needed. This technique is more limited when compared to some others, because the base metal thickness cannot typically exceed 13 mm.
• Gas-metal arc welding is employed to join titanium and titanium alloys thicker than 3 mm, by using pulsed current or the spray mode. This technique is less expensive as compared to GTAW, particularly when a considerable thick base metal thickness (>13 mm).
• Plasma arc welding is an alternative feasible technique for joining titanium and titanium alloys. It's faster as compared to GTAW and additionally comparable to gas-metal arc welding, it can also be used on thicker sections.
• Friction welding is practical in joining titanium tubes, pipes, or rods, as joint cleanliness can be accomplished without the need of shielding.
• Resistance welding is employed to join titanium and titanium alloy sheet by either spot welds or continuous seam welds. Despite the fact that it's not recommended, this technique is additionally employed for welding titanium sheet to dissimilar metals, including carbon or stainless steel plate.

Filler alloys

Commonly used filler alloys are listed in the table underneath along with the appropriate ASTM grade, the internationally recognised designation.

Titanium and its alloys can be welded utilizing a matching filler composition; compositions are shown in The American Welding Society specification AWS A5.16-2004. Recommended filler wires for the frequently used titanium alloys are likewise provided in the table above.

When welding higher strength titanium alloys, fillers of a lower strength are occasionally useful to accomplish acceptable weld metal ductility. For instance, an unalloyed filler ERTi-2 could be used to weld Ti-6Al-4V and Ti-5Al-2.5Sn alloys in order to balance weldability, strength and formability requirements.

Weldability of Nickel and Nickel Alloys

Nickel is a relatively simple metal. It's face centred cubic and experiences no phase changes while it cools from melting point to room temperature; comparable to a stainless steel. Nickel and its alloys cannot consequently be hardened through quenching, hence cooling rates are less significant than with, to illustrate, carbon steel and preheating, in the event the ambient temperature is above 5°C, is hardly ever required. Nickel and its alloys are widely-used in a very wide range of applications - right from high temperature oxidation and creep resistance service to aggressive corrosive environments and very low temperature cryogenic applications. Nickel can also be used in a commercially pure form although it is usually more often combined with other elements to produce two families of alloys - solid solution strengthened alloys and precipitation hardened alloys.

The joining of nickel and nickel alloys can be consistently accomplished pursuing the various welding methods. The ductile and solution strengthened nickel and its alloys can be weldable and specifically these are typically suitable with all types of welding procedures. The weld forming of these alloys is easy plus they typically don't require heating prior to and following the process, and also the interpass temperature control while welding isn't significantly crucial. The precipitation hardenable alloys are unlikely to be weldable and as a consequence of the availability of gamma prime reinforcing phase, they become susceptible to strain age cracking. They're typically welded in annealed or solution annealed conditions and tend to be postweld heat processed to precipitate gamma prime phase as an eventual or almost ultimate formation step. The precipitation hardenable alloys are likewise typically welded by brazing.

The physical properties of solid solution nickel alloys, Groups I, II, and III, are fairly comparable to the 300 Series austenitic stainless steels. The solid solution nickel alloys cannot be strengthened by heat treatment, only by cold working. Group IV alloys, the precipitation hardening nickel alloys, are strengthened by special heat treatments comparable to those for the precipitation hardening (PH) stainless steels. Although the solid solution alloys, Groups I, II, and III are predominately intended for corrosion resistant services, the Group IV alloys are used where higher strength is needed, nevertheless with generally certain minor sacrifice of corrosion resistance.

All the conventional welding processes could be used to weld nickel and its alloys and matching welding consumables are obtainable. As mentioned previously, nickel and its alloys are comparable in many aspects to the austenitic stainless steels; welding procedures are in the same way equally similar. Nickel, nonetheless, possesses a coefficient of thermal expansion lower than that of stainless steel consequently distortion and distortion control measures resemble those of carbon steel.

Nickel alloys can be welded by using all the conventional arc welding and power beam processes, the most typical techniques being TIG or MIG along with pure argon, argon/hydrogen or argon/helium mixtures as shield gases and MMA wherever basic flux coatings supply the best properties. Nearly all nickel alloys are best welded in the annealed or solution treated condition, especially when the alloys have already been cold worked.

Nevertheless, if argon/helium mixes are being used its only when there exists in excess of 40% helium that any sort of significant benefits regarding penetration and enhanced fusion is going to be noticed. Submerged arc welding is restricted to welding solid solution alloys utilising basic fluxes. Matching welding consumables are available for the majority of the nickel alloys.

For the majority of alloys, heat input must be regulated to moderate levels (say 2kJ/mm maximum) to limit grain growth and HAZ size even though for some Alloys 718, C22, and C276 for instance, a maximum heat input of 1kJ/mm is recommended.

Alternatively, in the event that very fast travel speed is employed in an effort to maintain a low heat input, this could result in a narrow weld bead sensitive to centre line cracking. Sufficient testing in the course of welding procedure development must be employed to optimise the range of suitable welding parameters.

The solid solution alloys including Alloy 200 or 625 don't necessitate post weld heat treatment to maintain corrosion resistance although might be susceptible to PWHT either to reduce the risk of stress corrosion cracking in case the alloy will be employed in caustic soda service or in contact with fluoro-silicates or to provide dimensional stability.

A widespread stress relief treatment could be 700°C for ½ an hour for Alloy 200; 790°C for four hours for the higher chromium content alloys including Alloy 600 or 625.

The nickel-molybdenum alloys are identified using the prefix B like B1, B2, etc. and are used in reducing environments, which includes hydrogen chloride gas and sulphuric, acetic and phosphoric acids. Alloy B2 is the most frequently utilised alloy and matching filler metals are obtainable. As opposed to Alloy B1, Alloy B2 doesn't form grain boundary carbide precipitates in the weld heat affected zone, therefore it can be used practically in most applications in the as-welded condition.

Alloy 400, a 70Ni-30Cu alloy, provides excellent corrosion resistance when exposed to hydrofluoric acid, strong alkaline solutions and sea water. A matching filler metal, Alloy 190, is available although this could become anodic in salt solutions, resulting in galvanic corrosion and it is advisable that one of the Ni-Cr alloy fillers including Alloy 600 or 625 is used in such a environment.

The age hardened alloy K-500 does not possess a matching filler metal and is typically welded using the Alloy 190 filler, the reduction in strength being taken into consideration through the design phase.

Precipitation hardened alloys are best welded in the solution treated condition; welding these kind of alloys in the age hardened condition probably will induce HAZ cracking. The ageing process in the alloys is sufficiently sluggish that the components could be welded in the solution treated condition thereafter aged at approximately 750°C without the mechanical properties being degraded. A solution treatment of the welded piece accompanied by ageing will offer the highest tensile strength.

The sensitivity of the age hardened alloy to cracking results in complications as soon as attempts are made to repair items, especially when these have been in high temperature service and additional precipitation on the grain boundaries has developed.

Little is possible to overcome this difficulty beyond a full solution heat treatment nevertheless this is often unrealistic with a fully fabricated component. If repair is to be attempted, small weld beads and controlled low heat input welds are recommended.

If the design enables, a low strength filler metal, for example Alloy 200 or 600, are useful to reduce the risk. Buttering the faces of the repair weld preparation, occasionally combined with a peening operation, has been effective.

Many of the nickel alloy filler metals are generally utilized for producing dissimilar metal joints with excellent results; dilution when welding joints involving ferritic, stainless and duplex steels being less significant than when working with a type 309 stainless steel filler.

Nickel also offers a coefficient of thermal expansion between that of ferritic and austenitic steels and for that reason experiences less as a result of thermal fatigue when high temperature plant is thermally cycled. Alloy 625 is a common choice, the weld tensile strength corresponding or exceeding that of the parent metal. There are limitations to this particular approach, and additionally caution is required to be practiced when choosing a suitable filler. To illustrate, Alloy 625 happens to be extensively utilized for welding dissimilar joints in austenitic and duplex steels.

Using of this particular filler metal has resulted in the formation of niobium rich precipitates adjacent to the fusion line and has long been discontinued. Alloy 59 or C22 filler metals have replaced Alloy 625 as being the filler of preference.