Materials

Carburizing steels are used for applications that require the surface of parts to be hard and wear-resistant while maintaining a softer, more ductile core. Carburizing and ferritic nitrocarburizing are two techniques we apply for case hardening of carburizing steels, while some parts made from this material require through hardening. Parts made from carburizing steel that we typically encounter include stampings, machined components, automotive parts, and agricultural implements.

Two common types of carburizing steels we see are:

• 8620 steel. 8620 is a common carburizing steel that is often used for medium-strength applications such as camshafts, gears, and more.
• 1018 steel. 1018 is a low-carbon steel that features excellent formability and produces a case with uniform hardness once heat treated; it is often used to produce fasteners.

There are three main categories of carbon steel, which we differentiate from other steels that contain more alloy content.

• Mild or low-carbon steels containing 0.05–0.30% carbon. 
• Medium-carbon steels such as 1035 and 1045 containing between 0.3% and 0.5% carbon. 
• High-carbon steels such as 1050 contain 0.5–1.70% carbon by weight.

Carbon steels are often used for springs, stampings, small machine components, knives, and more. The most common thermal process we run on carbon steels is through hardening (also known as neutral hardening).

These metals are called maraging steels by combining the words “martensitic” and “aging.” They comprise a classification of low-carbon, nickel-cobalt-molybdenum alloys with ultra-high strength and toughness that can still maintain excellent ductility. 

Maraging steels are first annealed before undergoing precipitation hardening, a process also known as aging. The precipitation of intermetallic compounds throughout the material is what lends maraging steels their superior strength (as opposed to carbon content in carbon steels). 

We encounter maraging steels such as Vascomax mainly in specialized aerospace applications like helicopter rotor masts.

Often known simply as alloy steels, these materials contain iron, carbon, and other alloying agents in their chemical makeup. Popular additives include chrome, manganese, molybdenum (moly), and nickel. These materials are used in applications that require high strength and ductility.

The combination and content of different alloying agents greatly affects the properties of the material and subsequently, the heat treatment requirements. A few of the most common alloy steels we process include:

• 4140 steel, a chromium- and molybdenum-containing low alloy steel that is widely used across the entire industrial spectrum. 

• 4130 steel, a low-alloy formula featuring chromium and molybdenum. This material is often vacuum arc remelted (VAR) to eliminate impurities and make it more chemically homogenous. 

• 6150 steel is a chromium-vanadium steel commonly used for shafts, gears, and pinions. 

The most common thermal process we apply to alloy steels is through hardening. Alloy steels are often selected for applications that require fully hardened parts with a thickness greater than ¼”. Carbon steels generally will not fully harden when thickness exceeds ¼”.

Spring steels are generally medium- to high-carbon steels with manganese alloy that feature a very high yield strength. Higher carbon content is common among this family of steels to prevent creep (the tendency to deform under persistent mechanical stress). A few of the most common spring steels we encounter include:

• 1075 steel is a high-carbon steel mainly used to manufacture cutting blades (knives, saws, even swords) and springs. 
• 5150 steel is a medium-carbon, chromium steel with good strength, toughness, and hardenability. 
• 5160 steel is also known as chrome steel because of its alloying elements. It features high ductility, excellent toughness, and high tensile-yield ratio.
  As part of the through hardening process, spring steel is typically quenched in oil prior to tempering.

The corrosion resistance of stainless steel thanks to its greater chromium content makes it an obvious choice for parts that require protection against oxidation. There are four main types of stainless steel:

• Austenitic stainless steels. Materials such as 304 and 316 are the most corrosion resistant of all stainless steels. Heat treatment cannot increase the hardness of austenitic stainless steel, but it can be heat treated to enhance corrosion resistance. Austenitic stainless steels are often annealed to enhance toughness, ductility, and machinability.
• Ferritic stainless steels such as 430, like austenitic stainless steels, may be heat treated to improve corrosion resistance but not to increase hardness. Ferritic stainless steels can also be annealed to impart the same benefits described above.
• Martensitic stainless steels like 410, 416, and 420 have higher carbon content than their austenitic counterparts and can be through hardened. 
• Precipitation hardening stainless steels such as 17-4 and 13-8 provide more corrosion resistance than martensitic stainless steels but not as much as the austenitics. After annealing, these materials are “aged,” a process also known as precipitation hardening, which gives them their name. This means that the material hardens as a result of particles precipitating out of the intermetallic structure.

Stainless steel is used in a large range of applications including stampings and machined parts and is most often chosen for its corrosion resistance.

Heat treating aluminum parts is usually required for lightweight structural components for aerospace, in addition to some motorcycle and automotive parts.

The aluminum alloys we typically encounter are:

• 6061 aluminum is the most commonly available aluminum alloy and responds the best to heat treatment when compared with others.  
• 2024 aluminum alloy has a high strength-to-weight ratio and good fatigue resistance.

The main thermal processes for aluminum are solution treating and aging/precipitation hardening.

Most of the copper, brass, and bronze materials we see are used in electrical components for power distribution or for ammunition. While most of these materials can only be made softer through annealing, there is one notable exception.

Beryllium copper is used for non-sparking hand tools produced specifically for oil & gas or other sensitive environments. This material can be hardened up to the mid-30s on the Rockwell hardness scale by aging in a tempering furnace.

For high strength, lightweight, and the ability to withstand higher temperatures, nothing beats titanium. We often see the titanium alloy Ti6Al4 in structural areas of airplanes, medical implants, and firearms components. This material is processed by solution treating and aging/precipitation hardening in a vacuum furnace.

For applications requiring high-temperature resistance without creep (such as jet engine parts, turbine blades, vanes, combusters, igniters, and hot section components) nickel-based superalloys provide performance. A few examples of nickel-based alloys we encounter are Inconel 718 and Rene-80. These materials are usually treated by vacuum solution treating and aging/precipitation hardening.