Properties of Steel: Steel Grading, Hardness, Yield Strength, and Alloys

What is Carbon Steel?

Carbon steel is steel that has properties made up mostly of the element carbon, and which relies upon carbon content for its structure. The most perfect carbon structure in the world is a diamond, which is 100% carbon. Carbon is present in all steel and is the principal hardening element, determining the level of hardness or strength attainable by quenching. It raises steel yield strength, tensile strength, hardness, and resistance to wear and abrasion as the carbon content of steel is increased. It lowers ductility, toughness, and machinability.

Cold Drawn carbon steel is typically numbered with the prefix “10” in the AISI numbering system, followed by two numbers that represent the nominal percentage of carbon in the product (up to 100%). For example, C1018 has 0.18% carbon, while C1045 has 0.45%.

Generally carbon adds hardness to the material which improves wearability. Carbon steel with lower levels of carbon (0.05 to 0.25%) is known as mild steel. For carbon contents above 0.30%, the product may be direct hardened (“through hardened”). Carbon steel beneath this level typically require carburizing when heat treated in which carbon molecules are introduced so that a hardened “skin” is able to be developed on the surface, or “case.” This is where the concept of case hardening is found.

Carbon is maximized at under 1.00% of steel because for levels above this percentage material can become brittle. Generally, the higher the carbon content, the more difficult carbon steel is to machine.

Carbon steel is used to manufacture a wide range of fasteners and machine parts, including:

• Nuts, bolts, and screws
• Lifting and rigging hardware
• Key stock and machine keys
• Pins and wireforms

With over 1 million pounds of square and flat stock on hand, G.L. Huyett is competitive at any quantity.

Alloy steels are derivatives of carbon steels where elements are added or deleted to yield certain properties. Typically these properties include machinability, wearability, yield strength, and tensile strength. An iron-based mixture is considered to be an alloy steel when manganese is greater than 0.165%, silicon over 0.5%, copper above 0.6%, or other minimum quantities of alloying elements such as chromium, nickel, molybdenum, or tungsten are present.

Iron alloys are the most common ferrous alloy. Steel is a solid solution of iron and carbon, the carbon is dissolved in the iron; iron is the solvent and carbon is the solute.

Steel, like water, can go through phase changes. With water, the phases are solid, liquid, and gas. With carbon steel the phases are liquid, austenite, and ferrite. If salt is added to water, the temperature of all the phase changes are altered. This is why salt is a common ice melt compound. Salt will lower the transition temperature of the liquid to gas, and lowers the temperature of liquid to solid as well. When carbon is added to iron, the temperatures are altered in the same way.

The more carbon that is added (to a point), the lower the temperature of the phase change will occur. Carbon also creates new phases that don’t exist in iron by itself. Pearlite is a mixture of cementite (Fe₃C) plus ferrite. The most carbon that can be dissolved in austenite is 0.80%. This is called “eutectic.” Other alloys can be described as being eutectic alloys. These alloys have the maximum amount of the alloying element that can be dissolved into the parent material. The more carbon you add to steel (above 0.20%), the more pearlite you get, up to the 0.80%. Above 0.80% you get carbides. If a steel has less that 0.20% carbon, all you can get is ferrite. If a steel has 0.40% carbon, you get pearlite and ferrite. If a steel has 0.90% carbon, you get pearlite and carbides.

Steel Grading

To know the chemistry of a steel by knowing its steel grade, remember the following rules: plain carbon steels are 10xx grades. 10 is plain carbon and the next two numbers are the carbon content. All 10 steel grades also have manganese, phosphorus, and silicon. The last two numbers of ALL grades designate the carbon content. If a grade is 12L14 or 10B21, the L means it contains lead for machinability and the B means it has boron for increased hardenability. If you know the chemistry of the alloy, you will know its hardness, strengths, and if a thermal treatment will work at all.

Learn more about carbon steel and alloy steel from Carbon and Alloy Steels: Part One and Carbon and Alloy Steels: Part Two.

The following information should be considered only as a guideline. For specific applications, proper testing is required. The hardness of a metal is determined by its resistance to deformation, indentation, or scratching. Rockwell hardness testing is the most common measure of a metal’s hardness. Soft steels are usually measured using the Rockwell B scale while harder steels and deep case-hardened steels are usually measured on the Rockwell C scale. In some cases, one object may fall within more than one scale (see the hardness comparison chart). For example, a typical steel spring has a Rockwell hardness of 110 on the B scale and 38 on the C scale.

Note: The yield strength of steel is the amount of pressure steel will accept before becoming permanently deformed. In contrast, the tensile strength of steel, more properly known as steel's ultimate tensile strength (UTS), is the amount of tensile load—stretching or pulling force—a steel alloy will bear before fracturing.

1018 – Heat treating in contact with carbon (carburizing) hardens the surface of this low-carbon steel. It’s easy to cold form, bend, braze, and weld. Max. attainable Rockwell hardness is B72. Melting point is 2800° F. Yield strength is 77,000 psi.

1045 – This medium-carbon steel is stronger than 1018 and is more difficult to machine and weld. Max. attainable Rockwell hardness is B90. Melting point is 2800° F. Yield strength is 77,000 psi.

A36 – General purpose carbon steel is suitable for welding and mechanical fastening. Max. attainable Rockwell hardness is B68. Melting point is 2000° F. Yield strength is 36,000 psi.

12L14 – A low-carbon steel that has excellent machining characteristics and good ductility that makes it easy to bend, crimp, and rivet. It is very difficult to weld and cannot be case hardened. Max. attainable Rockwell hardness is B75-B90. Melting point is 2800° F. Yield strength is 60,000-80,000 psi.

1144 – A medium carbon, resulferized steel with free-machining qualities. 1144 steel heat treats better than 1045 steel. Stress relieving allows it to obtain maximum ductility with minimum warping. Max. attainable Rockwell hardness is B97. Melting point is 2750° F. Yield strength is 95,000 psi.

4140 Alloy – Also called “chrome-moly” steel. Ideal for forging and heat treating, 4140 alloy is tough, ductile, and wear resistant. Max. attainable Rockwell hardness is C20-C25. Melting point is 2750° F. Yield strength is 60,000-105,000 psi.

4140 ASTM A193 Grade B7 Alloy – Similar to 4140 alloy, but it’s already quenched, tempered, and stress relieved. Rockwell hardness is C35 max.

8630 Alloy – This alloy is tough yet ductile. It responds well to heat treating, exhibits superb core characteristics, and has good weldability and machining properties. Max. attainable Rockwell hardness is B85-B97. Melting point is 2800° F. Yield strength is 55,000-90,000 psi.

One of the more common alloys is 1144, a carbon steel in which alloying elements enhance machining. 1144 stress-proof, a product of LaSalle Steel, is an example of an alloy with good machining and hardenability features that possesses high strength and can be through hardened.

Chrome alloy steels, such as 4130, 4140, and 4340 are so named because chromium content is high (around 1%), and is the primary alloying element. As one can see, chrome alloy steels begin with “40” prefix and end in two numbers that account for the nominal percentage of carbon. For example, 4140 has 0.40% of carbon and 0.1% chromium.

Nickel alloy steels substitute nickel in place of roughly half of standard chromium contents for chrome alloys. For example, whereas 4140 has 0.0% nickel and 0.1% chromium, 8630 has 0.60% nickel and 0.50% chromium. These alloys are normally prefixed with “80” numbers. 8630 compare to 4140 as follows:

It is difficult to make mechanical comparisons between chrome alloys and nickel alloys as they are similar but unique to a grade. Generally nickel alloys can be drawn to a more precise finish size and therefore are more common in end use steels such as keystock.

Because of the relevance of these grades to the G.L. Huyett product line, we are giving separate coverage here. Bright steels typically refer to a class of cold finished square and rectangle bars that are drawn to more exacting tolerances; they possess sharp corners, perpendicular and parallel sides, and may be bead blasted to make them “bright.” Bright steels are also known as key stock, which is primarily used to make machine keys.

Key stock squares and rectangles are more difficult to draw than rounds because of the 90° angled corners. Bars must be straight and true and the width must be in a perpendicular plane with the height. The surface finish of key stock must be free of pits and stresses so that installation is smooth and efficient. Most customers prefer sharp corners for increased key way contact (and minimal rocking), but edges must be sufficiently deburred for ease of use.

The definition of key stock has been elusive because no single standard exists. Most technicians refer to “bar stock” or “key bar stock” as cold finished material drawn from market-ready grades to market-ready tolerances. “Key stock” refers to bar stock carefully drawn to ANSI Class 2 fits.

ANSI sets forth two key stock types with the following tolerance specifications:

Many users of key stock have used the above specifications in their own product designs, which has led to two problems. First, because ANSI does not specify a grade, there is confusion. Second, most American mills will not produce to the Class 2 Fit. Tolerance is too low compared to other cold finished forms, and the draw is overly technical. As a result, there is often a difference between what customers want and what is available.

G.L. Huyett has pioneered the development of new cold drawing technologies. Working in concert with steel mills in both the United States and abroad G.L. Huyett has put together the most complete line of key stock steel anywhere in the world.

Stainless steel is the term used for grades of steel that contain more than 0.10% chromium, with or without other alloying elements. Stainless steel resists corrosion, maintains its yield strength at high tolerances and is easily maintained. The most common grades are:

TYPE 304 – The most commonly specified austenitic (chromium-nickel stainless class) stainless steel, accounting for more than half of the stainless steel produced in the world. This grade withstands ordinary corrosion in architecture, is durable in typical food processing environments, and resists most chemicals. Type 304 is available in virtually all product forms and finishes.

TYPE 316 – Austenitic (chromium-nickel stainless class) stainless steel containing 0.2%-0.3% molybdenum (whereas 304 has none). The inclusion of molybdenum gives 316 greater resistance to various forms of deterioration.

TYPE 409 – Ferritic (plain chromium stainless category) stainless steel suitable for high temperatures. This grade has the lowest chromium content of all stainless steels and thus is the least expensive.

TYPE 410 – The most widely used martensitic (plain chromium stainless class with exceptional strength) stainless steel, featuring the high level of strength conferred by the martensitics. It is a low-cost, heat-treatable grade suitable for non-severe corrosion applications.

TYPE 430 – The most widely used ferritic (plain chromium stainless category) stainless steel, offering general-purpose corrosion resistance, often in decorative applications. 430 stainless is a martensitic stainless with higher levels of carbon (.15%) that allow it to be heat treated. 430 is also highly magnetic.

Stainless steel is used to manufacture a wide range of corrosion-resistant fasteners and parts, including stainless steel nuts, stainless steel key stock, and stainless steel dowel pins, among many others.

Tool steels serve primarily for making tools used in manufacturing and in the trades for the working and forming of metals, wood, plastics, and other industrial materials. Tools must withstand high specific loads, often concentrated at exposed areas, may have to operate at elevated or rapidly changing temperatures and in continual contact with abrasive types of work materials, and are often subjected to shocks, or may have to perform under other varieties of adverse conditions. Nevertheless, when employed under circumstances that are regarded as normal operating conditions, the tool should not suffer major damage, untimely wear resulting in the dulling of the edges, or be susceptible to detrimental metallurgical changes.

Tools for less demanding uses, such as ordinary hand tools, including hammers, chisels, files, mining bits, etc., are often made of standard AISI steels that are not considered as belonging to any of the tool steel categories. The steel for most types of tools must be used in a heat-treated state, generally hardened and tempered, to provide the properties needed for the particular application. The adaptability to heat treatment with a minimum of harmful effects, which dependably results in the intended beneficial changes in material properties, is still another requirement that tool steels must satisfy.

To meet such varied requirements, steel types of different chemical composition, often produced by special metallurgical processes, have been developed. Due to the large number of tool steel types produced by the steel mills, which generally are made available with proprietary designations, it is rather difficult for the user to select those types that are most suitable for any specific application, unless the recommendations of a particular steel producer or producers are obtained.

Substantial clarification has resulted from the development of a classification system that is now widely accepted throughout the industry, on the part of both the producers and the users of tool steels. That system is used in the following as a base for providing concise information on tool steel types, their properties, and methods of tool steel selection.

G.L. Huyett stocks a comprehensive selection of tool steel flat stock and bar stock, as well as many other parts manufactured from tool steel.

Steel grades indicate the composition and metallurgical properties of types of steel. A steel grade chart helps customers to select the right type of steel for their application.

Grade W1 (Water-Hardening Steel) – This water-quenching steel heat treats evenly and provides good toughness and maximum wear resistance. High carbon content and fine grain structure make it ideal for general use, even without heat treating. Max. attainable Rockwell hardness is C57-C60. Melting point is 2800° F. Yield strength is 55,000-100,000 psi.

Grade O1 (Oil-Hardening Steel) – A non-shrinking, general purpose tool steel with good abrasion resistance, toughness, and machinability. It is extremely stable with minimal deformation after hardening and tempering. Max. attainable Rockwell hardness is C57-C62. Melting point is 2800° F. Yield strength is 50,000-99,000 psi.

Grade M2 (High-Speed Steel) – This steel resists softening when heated, maintaining a sharp cutting edge. It is easy to heat treat and has minimal loss of carbon (decarburization) after heat treating. Max. attainable Rockwell hardness is C65. Melting point is 2580° F. Yield strength is 105,000 psi.

Grade A2 (Air-Hardening Steel) – Made of a very fine grain structure, this steel has excellent abrasion and wear resistance. Ideal for thin parts that are prone to cracking during heat treating. Supplied in non-resulferized condition. Max. attainable Rockwell hardness is C62-C65. Melting point is 2620° F. Yield strength is 108,000 psi.

Grade D2 (High-Chrome Air-Hardening Steel) – The high chromium and carbon content in this steel provides superior wear resistance and toughness. A low sulfur content makes it difficult to machine. Max. attainable Rockwell hardness is C62-C65. Melting point is 2525° F. Yield strength is 111,000 psi.

Grade S7 (Shock-Resistant Air-Hardening Steel) – Strong and ductile, this steel is known for its ability to resist failure from shock. It combines high-impact strength with average wear and abrasion resistance. Max. attainable Rockwell hardness is C59-C61. Melting point is 2640° F. Yield strength is 105,000 psi.

Grade A6 (Low-Temperature Air-Hardening Steel) – Heat treat this steel at low temperatures (1525° to 1575° F). It experiences almost no dimensional changes after heat treating. Max. attainable Rockwell hardness is C61-C62. Melting point is 2600° F. Yield strength is 110,000 psi.

Grade 4142 – This steel exhibits good wear resistance, toughness, machinability, and high mechanical properties. Prehardened to a Rockwell hardness of C30. Melting point is 2790° F. Yield strength is 130,000 psi.

Grade P20 – This hardened, general purpose mold steel is suitable for production of machined or EDM plastic mold and zinc die casting components. Supplied prehardened to a Rockwell hardness of C32. Melting point is 2790° F. Yield strength is 130,000 psi.

The following charts summarize the metallurgical properties of the various grades of tool steel available. The first step in applying data from the chart is to examine the specific application for the important properties involved. For example, an ejector pin for die-casting requires top toughness with good wear resistance and hot hardness – the chart indicates VDC as a logical start. If the VDC part wears too rapidly, the next move would be to Bearcat. Another application might involve a part for a short run cold forming die setup. Considering die life and steel cost, carbon would be first source – if wear or size change in heat treatment becomes a problem, the next step would be to use Select B but if size change in heat treat was the only problem, then Badger should be tried.

DIMENSIONAL STABILITY IN HEAT TREATMENT

The dimensional stability of steel is the ability of a particular type of steel to maintain its original shape and size while in use.

LowHigh

• OLYMPIC (D-2)
• SELECT B (A-2)
• VDC (H13)
• BEARCAT (S-7)
• DOUBLE SIX (M-2)
• BADGER (O1)
• CARBON (W1)

Viscount 44 is pre-hardened.

TOUGHNESS

Steel toughness is the amount of force steel can absorb before it fractures. Steel often contains tiny cracks, which may propagate under load, causing the part to fracture. Tougher steels are more capable of plastic deformation which resists crack propagation and fracture. A steel's toughness generally decreases as tensile strength increases.

LowHigh

• VDC (H13)
• VISCOUNT 44 (H13 MODIFIED)
• BEARCAT (S-7)
• BADGER (O-1)
• CARBON (W-1)
• SELECT B (A-2)
• DOUBLE SIX (M-2)
• OLYMPIC (D-2)

WEAR RESISTANCE AT ROOM TEMPERATURE

Steel wear resistance, which is also known as abrasion resistance, indicates a steel's resistance to wear when subjected to abrasion or friction.

LowHigh

• DOUBLE SIX (M-2)
• OLYMPIC (D-2)
• SELECT B (A-2)
• BADGER (O-1)
• CARBON (W-1)
• BEARCAT (S-7)
• VISCOUNT 44
• VDC (H13)

MACHINABILITY

Steel machinability indicates how easy it is to remove material without excessive wear on tools while leaving an acceptable surface finish. The most machinable steels are those with medium quantities of carbon. Softer low-carbon steel and harder high-carbon and alloy steels are more difficult to machine.

LowHigh

• CARBON (W-1)
• BADGER (O-1)
• BEARCAT (S-7)
• VDC (H13)
• SELECT B (A-2)
• DOUBLE SIX (M-2)
• OLYMPIC (D-2)
• VISCOUNT 44

HOT HARDNESS

Steel hot hardness, which is also known as red hardness, indicates the hardness of a steel material at high temperatures.

LowHigh

• DOUBLE SIX (M-2)
• VDC (H13)
• VISCOUNT 44 (H13)

Hot hardness not applicable to cold work steels such as Olympic, Select b, Badger, Carbon and Bearcat.

This steel grading chart indicates the quantity of various materials steel can contain within each grade.

Other metals and non-metals are added to steel to change its properties. The following table lists various materials that can be alloyed with steel and their impact on its properties.

The four-digit AISI/SAE steel grading system describes the chemical composition of carbon steel and alloy steel. The following table shows the steel grade and composition of steel alloys. The first two digits refer to the alloying element and the "XX" is a placeholder for the carbon content.

Note: Alloying elements are in weight percent, XX denotes carbon content.

There are many ways of measuring the hardness of materials. Steel hardness in the United States is commonly measured using the Rockwell C scale (HRC). The higher the number on the HRC steel scale, the harder the steel. Hardness should not be confused with brittleness. HRC steel hardness is about how the material reacts when tested to see how deep a diamond tip indenter penetrates under a 150 kg load.