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 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: Yield strength is the amount of pressure a material will accept before becoming permanently deformed.
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:
|
C |
Mn |
Si |
P |
S |
Cr |
Ni |
Mo |
Other |
8630 |
0.25-0.35 |
0.65-0.85 |
0.70 |
0.04 |
0.04 |
0.40-0.70 |
0.40-0.70 |
0.20-0.30 |
— |
4140 |
0.38-0.43 |
0.75-1.00 |
0.035 |
0.04 |
0.15-0.35 |
0.8-1.10 |
— |
— |
— |
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.