Welding & Joining Technology: Weldability of Metals

Metal Profile: Nickel 

All about nickel

Guide to Nickel Welding and Soldering 

Guide to Nickel Welding and Soldering from Weld Guru

Types of Welding Metals 

All about metals for welding

A Guide to Aluminum GMAW Welding 

A guide to welding aluminum in GMAW

International Titanium Association (ITA) 

Trade association dedicated to the titanium metal industry. 

International Zinc Association (IZA) 

Only organization dedicated exclusively to the interests of zinc and its users

Amercian Iron and Steel Institute 

AISI serves as the voice of the North American steel industry in the public policy arena and advances the case for steel in the marketplace as the preferred material of choice

Copper Development Association

American Zinc Association

Weldability of Metals

The term weldability has been coined to describe the ease with which a metal can be welded properly

In terms of weldability, commonly used materials can be divided into the following types:

• Steels
• Stainless steels
• Aluminium and its alloys
• Nickel and its alloys
• Copper and its alloys
• Titanium and its alloys
• Cast iron

Several factors influence the weldability of metals. Below is a list of the most common factors.

• Metallurgy: The science of heating or manipulating metals to produce desired properties or shapes in them. 
• Welding Process: there are several types of processes in welding. Various factors set them apart: how the heat and pressure are applied, how much heat and pressure are used, and the type of equipment employed.
• Joint Design: The combination of the dimensions required for the welded joint and the geometry of the joint.
• Weld Preparation: a set of techniques to execute prior to welding to prevent defects in the weld. 
• Melting Point: The temperature that must be reached for a solid substance to melt or fuse. 
• Electrical Resistance: A metal’s opposition, or resistance, to the flow of electrical current. 

Carbon and alloy steels

Steels alloyed with carbon and only a low concentration of silicon and manganese are known as plain carbon steels

Alloy steels contain specified larger proportions of alloying elements. 

Low-Carbon or Mild Steel have carbon content of less than 0.30%. These steels can be welded easily by all welding processes. 

Medium-carbon steels have carbon content of 0.30% to 0.50%

High-carbon steels usually have a carbon content of 0.50% to 0.90%. These steels are much more difficult to weld than either the low- or medium-carbon steels. Because of the high carbon content, the heat-affected zone can transform to very hard and brittle martensite. 

Tool steel has a carbon content from 0.8% to 1.50%, and is very difficult to weld. 

High-manganese steel contains 12% or more manganese and a carbon content ranging from 1% to 1.4%. 

Low-alloy steels are used increasingly because of requirements for high strength with less weight. These types of steel are readily weldable by all of the common welding processes. 

Chromium-molybdenum steel is used for high-temperature service and for aircraft parts. It can be welded by the following processes: shielded metal arc, gas tungsten arc, gas metal arc, flux cored, and submerged arc. 

Maraging Steel, which combines nickel and elements such as cobalt, titanium, molybdenum or aluminum. With a lower carbon content, this type of steel is known for its high yield strength

Stainless steels consist of four groups of alloys:

• Austenitic:  The austenitic group is by far the most common. Its chromium content provides corrosion resistance, and its nickel content produces the tough austenitic microstructure. 
• Ferritic: contain almost no nickel
• Martensitic: Martensitic stainless steels are also low in nickel but contain more carbon than the ferritic
• Precipitation hardening: Can be much stronger than the austenitic, without losing toughness. Their strength is the result of a special heat treatment used to develop the precipitate. 

Characteristics of Aluminum

• High thermal conductivity: Higher welding current is needed to assure fusion 
• High solidification shrinkage: Aluminum shrinks about twice as much as steel during solidification due to its high coefficient of thermal expansion. Causes higher buildup of residual stresses around the weld and greater distortion.  Shrinks approximately 6% in volume
• High hydrogen solubility: In molten state, aluminum has a very high hydrogen solubility.
• Oxide coating: One of the characteristics of aluminum and its alloys is that it has a great affinity for oxygen. Aluminum forms an oxide layer when it comes in contact with air and combines oxygen. This aluminum-oxide layer is very porous and traps moisture, grease, oil and other contaminants.

Pure aluminum melts at 1200°F (650°C). The oxide that protects the metal melts at 3700°F (2037°C). The metal must be cleaned prior to welding.

Aluminum can be arc welded using aluminum welding rods. 

There are many different types of copper alloys. Copper is often alloyed with other metals such as tin, zinc, nickel, silicon, aluminum, and iron. Copper and copper alloys can be joined by most of the commonly used methods such as gas welding, arc welding, resistance welding, brazing, and soldering. 

When you are welding copper, the welding current should be considerably higher than when welding steel. 

Types of Cast Iron:

• Gray cast iron is the most widely used type. It contains so much free carbon that a fracture surface has a uniform dark gray color. Gray cast iron is easily welded, but because it is somewhat porous it can absorb oils into the surface, which must be baked out before welding.
• White cast iron is the hardest and most brittle of the cast irons because almost all of the carbon atoms are combined with the iron atoms.  White cast iron is practically unweldable. 
•  Malleable cast iron is white cast iron that has undergone a transformation as the result of a long heat-treating process to reduce the brittleness. Malleable cast iron can easily be welded. To prevent it from reverting back to white cast iron, do not preheat above 1200°F (650°C).
•  Alloy cast iron has alloying elements such as chromium, copper, manganese, molybdenum, or nickel added to obtain special properties. 

Titanium is a silver-gray metal weighing approximately half as much as steel or approximately one and one-half times as much as aluminum.

properties of titanium

• Extremely high strength-to-weight ratio (in alloy form)
•  corrosion resistance.

Titanium alloys, unlike most other light metals, retain their strength at temperatures up to approximately 800°F (426°C). 

Nickel is a strong, lustrous, silvery-white metal 

Nickel alloys can be joined reliably by all types of welding processes or methods, with the exception of forge welding and oxyacetylene welding.

Welding of Cast Nickel Alloys: Cast nickel alloys can be joined by the GTAW, GMAW and SMAW processes. For optimum results, casting should be solution annealed before welding to relieve some of the casting stresses and provide some homogenization of the cast structure.