Differences Between 8640 & 4037 Steel


American Iron and Steel Institute 8640 steel has many similarities to AISI 4037 steel. Both are high alloy, complex steels in terms of chemistry; however, there are differences in both the exact proportions of elements and in the uses for the steels. Due to the differences in chemistry, the steels also have slightly different mechanical and physical properties.


  • In terms of chemistry 8640 is a more complex steel, containing eight elements compared to the six found in 4037.

    AISI 4037 contains carbon (0.35 to 0.40 percent), manganese (0.70 to 0.90 percent), silicon (0.15 to 0.30 percent) and molybdenum (0.20 to 0.30 percent).

    AISI 8640 also contains chromium (0.40 to 0.70 percent) and nickel (0.40 to 0.70 percent). Additionally, 8640 contains slightly higher carbon and manganese, and slightly less molybdenum and silicon. Both steels have a maximum threshold for the impurities of sulfur and phosphorous at 0.04 and 0.035 percent respectively.

Physical Properties

  • In terms of physical properties 8640 has a density of 7.7 to 8.03 kilograms per cubic meter, the same as 4037. The steels also share the same Poisson's Ratio of 0.27 to 0.30 and elastic modulus of 190 to 210. However, 8640 has a higher elongation percentage (10 percent) than 4037 (6 percent).


  • Generally, 8640 has a higher tensile strength (1,862 MPa) compared to 4037 (1,027 MPa). The yield strength for 8640 (1,669 MPa) is also higher than 4037 (758 MPa). The hardness at 25 degree Celsius of 8640 is 505 HB compared to the 310 HB for 4037.

Thermal Properties

  • Both steels have the same specific heat of 0.475 Joules per gram per degree Celsius. AISI 4037 has a slightly higher thermal conductivity of 48.1 Watts per meter Kelvin. AISI 8640 has a thermal conductivity of 46.6 W/m-K.

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