Popular Metals for Welding

Welding is a complicated process, and there can be several pitfalls on the way to completing a successful weld. The choice of welding method, how carefully all materials are cleaned before proceeding, the experience of the welding operator: just a few of the many factors that can make or break a welding job. But one of the most important is your choice of metal. Working with metals that are more compatible to welding will make this process much easier to complete, and boost your chances of a good outcome.
During its exposure to the intense heat used during welding, metal begins to expand and soften. Welding involves connecting those softened edges together, with the use of a filler metal to create a join. Doing this quickly helps reduce the risk of the metal heating to the point of melting, which can thin the material and create a weaker join. So from the start, choosing a metal more compatible to welding helps reduce the risk of a bad weld.

The Four Most Popular Welding Metals
1. Low Carbon (Mild) Steel
Mild steel is one of the most weldable metals available, and this is due to the very quality featured in its name: its low percentage of carbon. In other circumstances, carbon is a great benefit when it comes to alloying steel; it reinforces the strength and hardness of the material, making it less ductile. However, that strength can become a downfall when it comes to welding. The higher the carbon content in the steel, the greater the risk that the heat of welding will create microstructures such as martensite within the material. These microstructures are more brittle than the surrounding metal crystal structures, and end up weakening the metal’s overall strength.
The more ductile a metal, the less likely it is to develop these microstructure flaws within the material. Mild steel is the most ductile of the steel family, so it takes easily to the welding process. Choosing low carbon steel means eliminating much of the risk of a disappointing weld before the process even starts.

2. Cast Iron
On the other side of the spectrum from mild steel, cast iron has an extremely high carbon content — about 2% of its overall formulation is carbon. Just as in steel, the high amount of carbon makes the metal quite strong but also very brittle. However, cast iron is still a good candidate for welding because of its relatively low melting point. This quality means a shorter period of sustained heat is used during welding, which prevents heat damage or burn-through.

3. Stainless Steel
Welding is already a complicated process, and the complex chemical composition of stainless steel can make it even more tricky. The chromium in stainless is what produces the metal’s distinctive shine and excellent corrosion resistance, but the same element can be a stumbling block during welding. The intense heat of welding leads to chromium bonding with the carbon in stainless steel, leading to warping and making it more vulnerable to rust.

It’s important to properly identify the grade of stainless before processing begins, because the formulation of stainless steel will help best determine what type of welding method should be used. Ferritic and austenitic stainless steels can be more easily welded. Martensitic stainless steel grades, which are primarily alloyed with chromium, are more prone to cracking. However, with careful attention paid throughout the process, especially with monitoring welding torch temperature, stainless steel can be welded successfully.

4. Aluminum
Aluminum welding is a balancing act, because the metal possesses qualities that are both beneficial and risky to welding. Its ductility makes it easy to weld, but its high degree of thermal conductivity is an obstacle. The heat during welding can easily spread throughout the metal, making it expand more significantly than heated steel. Then during its cooling period, the aluminum must be monitored to prevent the development of craters and cracking as it shrinks back to its original size.
Yet despite the difficulties, aluminum is one of the most popular welding metals. Its appealing properties such as corrosion resistance, durability, and relative low cost make it worthwhile to take the extra care during welding.

What is Tool Steel?

As you might guess, tool steel earns its name by being primarily used for tools. If you then picture a steel screwdriver, pliers, or a wrench, you’d be right – but the items created of tool steel group consist of much more. Within the steel industry, tool steel also refers to machine tools, including those used to manufacture other metal products. To meet the standards of this demanding usage, tool steel is known for being extremely hard, resistant to abrasion and deformation, and its ability to hold a cutting edge. While the steel’s chemical composition is important, the method of production must be carefully controlled to achieve the proper qualities expected in tool steel.

Tool Steel Groups
Tool steel is classed into six groups, all made of carbon steel alloyed with one or more of these main elements: molybdenum, tungsten, chromium, and vanadium. Most tool steel originates from recycled steel scrap, but not all steel scrap is suitable for tool steel. Alloy scrap containing elements which resist oxidation (such as nickel, cobalt or copper) will impede the development of carbides in the metal’s structure, and carbides are crucial to creating tool steel. To ensure the metal will be an optimal mix, tool steel will typically consist of 75% mill scrap supplemented by purchased steel scrap.
The first step is primary melting, where the scrap is heated until molten. Most often this is done in an electric arc furnace (EAF) due to it being a lower-cost production method. However, it is key to avoid contamination during the melting process to create the highest-quality steel. While the EAF is widely used for tool steel, there is some risk of contamination from dust or traces of oxidation-resistant metals from previous batches. For top notch tool steel, an alternate method known as electroslag refining (ESR) is used to melt the steel. Instead of a furnace, ESR uses electric currents to superheat and slowly melt the metal. While a more expensive process, ESR will produce a more refined type of steel without apparent surface imperfections.
After melting and alloying, the steel is poured into ingot molds and then forged into the desired shapes. This is where the six groups of tool steel are determined by their processing:

• Water hardening: Also known as W-group tool steel, this group’s defining property is being water quenched. Quenching in water does risk warping or cracking steel with its rapid cooling, and results in a relatively brittle metal. For this reason, water-hardened tool steel is not considered appropriate for high-temperature industrial uses; once the temperature nears 300 degrees Fahrenheit, there is noticeable softening of the steel parts. Typical items made of W-group steel include scissors, smaller hand tools, and springs.

• Shock-resisting: S-group tool steel is notable for its toughness and ability to withstand repeated impact. This is achieved by using low carbon steel during its production, since higher carbon content results in a harder but more brittle product. Alloying with silicon, tungsten, and chromium gives additional wear resistance and tensile strength. It’s then quenched in oil, which allows for a gentler cooling than water and helps produce a metal with a high degree of durability. Items made of S-group tool steels include tableware dies, impact hammers for nails guns, and shear blades used in cutting heavy steel plate.

• High speed: This group is mainly used for cutting tools, which requires a very hard and abrasion-resistant type of steel. Tungsten, chromium, and vanadium allow HS steel to withstand very high temperatures, such as the heat friction created while cutting other metals. It also manages to hold a cutting edge with repeated use, allowing for higher speeds while cutting without having to pause to resharpen. HS steel can be found in various cutting tools such as drill bits, saw blades, and milling cutters.

• Hot work: Hot-working (H-group) steels are used to cut and shape materials at very high temperatures. To achieve a steel that can withstand prolonged exposure to intense heat, H-group steels are made of a low carbon steel with a higher percentage of alloying content. This produces a tool steel with a high amount of carbides, giving it good overall toughness and wear resistance. The most common use for hot work steel is to produce other metal items because it can withstand the heat needed to forge and cast other metals. It’s used in machinery such as pressure dies, extrusion, and forging equipment.

• Cold work: This tool steel type is narrowed down further into three groups known as the A series (air-hardened), O series (oil-hardened), and D series (high carbon/chromium). All three are intended to be used to cut or form materials at low temperatures.

1. A-series: As the name suggests, steel in this series is hardened via air. Because of the quenching method and its high chromium content, A-series cold work steel is known for low distortion during heat treatment. This makes it a good fit for machining purposes, and so can be found in dies, forming tools, and gauges.

2. O-series: Oil-quenching avoids the cracking and warping risks brought on by water-quenching, and is used for larger parts which require minimal distortion. It offers good wear resistance and toughness, lending itself to a wide range of applications as a general-use cold work steel. Typical uses of O-series tool steel include stamping dies, bushings (metal parts used to absorb vibration and friction), shear blades, and other cutting tools.

3. D-series: Made of a high-carbon steel with a high alloy percentage of chromium, this can also be categorized as a type of stainless steel. However, unlike typical stainless steel, its corrosion resistance is limited and thus is not used to make consumer products. Instead, D-series tool steel applications include cutters, dies, plastic injection molds, and machining rollers.

• Special purpose: this group includes tool steels with alloying elements such as nickel, which typically resist the formation of carbides. The extra time and effort needed to produce these tool steels makes them too expensive for general purposes, so they are manufactured for specific use. Special purpose tool steel can be found in plastic molding dies, zinc die casting, and drills.

Heat’s Effect on Metal Properties

Often when we speak of heat, it concerns scenarios we’d rather avoid: getting sweaty and sunburnt from the summer sun, overheating laptops or car engines, maybe singeing your hair after leaning too close to a candle. And rightly so! In all these cases heat can be damaging, whether to your possessions or your own self.

Yet despite some risks, heat is greatly beneficial. The sun’s beams feel warm and pleasant after a cold winter. The flames of a stove burner or grill cook your food. And when it comes to metal, heat is no different. Too much heat can damage metal to the point of weakening or destroying it. But heat is also a transformative force, from forging the metal to hardening it and modifying its mechanical properties.

There are four ways the application of heat affects metal:

  • Structural
  • Electrical Resistance
  • Magnetism
  • Thermal Expansion


Heat is a crucial part of the metal making process, with furnaces heated to such high temperatures that metal ore turns molten. However, it’s not always necessary to go to such extremes to affect the properties of the metal. Any time metal is heated, the atoms making up the metal or alloy begin to move. Given enough heat and then carefully cooled, the crystal structure of the metal can be reshaped into a lattice that is much stronger than prior to heat treatment. In the case of high carbon steels, heat application allows the iron to absorb additional carbon, which produces an exceptionally hard and strong steel.

Electrical Resistance

As metal is heated, the electrons within it will absorb energy and move faster. The faster the electrons move, the more likely they are to collide with the metal’s atoms and scatter them. Electrical resistance measures how strongly the metal works against this potential scattering as the temperature rises. That means the higher the electrical resistance of a metal, the lower its conductivity.


There are three elements with naturally magnetic properties, known as ferromagnetic metals: iron, cobalt, and nickel. But once heat is applied – and especially as the temperature goes up – the metal’s natural magnetism is reduced. If heated to a certain point known as the metal’s Curie temperature, its magnetic property will be reduced completely.

Thermal Expansion

As metal is heated, it begins to expand; its volume, length and overall surface area will grow as it continues to absorb more heat. This is due to the atoms making up the metal, which increase their movement as the temperature rises. This movement creates vibrations within the metal’s structure to the point that it swells, an occurrence which is known as thermal expansion. For safety reasons, any metal structure such as bridges or buildings must be designed to accommodate a certain degree of thermal expansion and contraction. Otherwise, you run the risk of damaging the metal as it warms and cools.

MTR: Mill Test Reports

Each day, we take for granted that the metals we encounter and use in our ordinary lives are safe. The steel framing in apartments and high-rise buildings, the aluminum fuselage of a passenger plane, the metal making up our cars and appliances: very rarely do we question the composition of the metal itself. Our lives go smoothly because we can trust these metals are safe and sturdy. We’re able to make that assumption because of the quality controls practiced by the metal industry, and that quality assurance rests largely on the mill test report (MTR).
At every step of the manufacturing process, the metal is accompanied by its MTR. From the mill forging the material, to the service center performing heat processing and finishing, to the company purchasing the items, the MTR passes from hand to hand. But what exactly is included in a mill report that makes it so important?

Mill Test Report
¬As might be expected, most mills will have their own style and layout for an MTR. They may not even call it a Mill Test Report at all: MTR is industry jargon that can also refer to a Material Test Report, a Mill Certification, or Mill Inspection Certificate. But whatever the name, the information the MTR includes is standard across the industry. When reviewing the document, you can expect it to list the following:

• Production information: the metal’s country of origin, melt location, and manufacturer’s name

• Product description: the item’s alloy, temper, grade, finish, width, thickness, and weight

• Material heat number: also referred to as the heat lot, this is an identifying code that is stamped directly onto the metal itself. As each lot of metal is produced, it is assigned a unique code to identify it as part of that batch. This provides a high degree of traceability, no matter where the metal might end up or its purpose. If there is any type of recall or issue with the metal, this number allows it to be traced back to its origin.

• Mechanical and physical properties: this states the metal is compliant with the criteria set by an international standards organization, such as ASME or ANSI. It is especially important in the case of alloys, because it certifies the chemical makeup of the metal. This is where the “test” portion of the MTR applies. While the metal is molten, a sample is drawn from each batch for metallurgical chemical analysis. Once the item is forged, mechanical testing is then performed on the finished item. Putting items such as steel plate through hardness, tensile and impact tests establish that the material will perform to the necessary standards under specific conditions.

• Inspection: in addition to the mill’s test information, the metal requires certification from an independent inspector. This means the MTR typically includes two signatures verifying the material’s makeup: one from the mill itself while producing the metal, and a second from the inspection agency. This third party inspection provides additional authentication of the metal’s physical and mechanical properties, along with confirmation that the heat number matches the actual item. If all information is correct, the inspector signs off on the report as a final step.

Do I Need the MTR?
For companies involved in the industrial side of manufacturing, distribution, and use of metals, MTRs are a necessity. These standards ensure that the metals will be appropriate for their intended use, and able to measure up successfully to further processing such as welding with compatible metals. If the finished goods or structures later experience some type of metal failure, the information provided by the MTR enables every item can be traced back to its source.
However, MTRs aren’t a necessity for the average consumer. Buying from reputable mills and distributors means that they have done the groundwork for you by collecting the MTRs for their products. Companies are required to keep their MTR documentation for a minimum of three years. However, many companies keep their records for much longer, priding themselves on being able to trace back their materials whenever the occasion may arise.

Reliance Steel & Aluminum Co. Launches FastMetals E-Commerce Platform

LOS ANGELES, Feb. 19, 2020 (GLOBE NEWSWIRE) — Reliance Steel & Aluminum Co. (NYSE: RS) today announced the launch of its new e-commerce business, FastMetals, Inc. (www.fastmetals.com), which offers a catalogue pricing model for a diverse selection of metal products including carbon, stainless, aluminum and specialty alloy steels. Located in Massillon, Ohio, FastMetals ships nationwide and has direct access to Reliance’s vast network of metals service center locations which carry over 100,000 products.

“FastMetals was created in response to the growing demand for digital purchasing solutions from metalworkers of all backgrounds,” commented Jim Hoffman, President and Chief Executive Officer of Reliance. “Consistent with Reliance’s core business strategy, FastMetals specializes in small orders with quick-turn around and best-in-class customer service. We are excited to launch this new, innovative venture that differs from our traditional sales model as simply another option for customers to purchase metal from us. Many of our existing service centers presently offer online capabilities and continue to receive inquiries via phone, email or other means based on the individual customer’s preference. FastMetals is yet another channel to experience Reliance’s unique, customer-focused service.”

FastMetals’ model is tailored to smaller, specialized end-users including artists, fabricators, machine shops, hobbyists, and do-it-yourself practitioners. Customers can choose from standard shapes and sizes or select specific dimensions to satisfy unique project requirements. FastMetals provides instant pricing, same-day shipping, no minimum order quantity and direct fulfillment to the individual customer.

About Reliance Steel & Aluminum Co.
Reliance Steel & Aluminum Co. (NYSE:RS), headquartered in Los Angeles, California, is the largest metals service center company in North America. Through a network of more than 300 locations in 40 states and thirteen countries outside of the United States, Reliance provides value-added metals processing services and distributes a full line of over 100,000 metal products to more than 125,000 customers in a broad range of industries. Reliance focuses on small orders with quick turnaround and increasing levels of value-added processing. In 2018, Reliance’s average order size was $2,130, approximately 49% of orders included value-added processing and approximately 40% of orders were delivered within 24 hours. Reliance Steel & Aluminum Co.’s press releases and additional information are available on the Company’s website at www.rsac.com.

Brenda Miyamoto
Investor Relations
(213) 576-2428

or Addo Investor Relations
(310) 829-5400