300M, UNS K44220, 4340MOD Low Alloy Steel - Introduction and Application
300M high strength low alloy steel comparable to 4340 with increased alloying elements such as vanadium and silicon giving it slightly higher strength and toughness, modified version of AISI 4340 steel, It has high content of molybdenum and silicon than that of AISI 4340 steel. It has high strength, good toughness, fatigue strength and ductility. The following datasheet gives more details about the 300M low alloy steel main used in a wide array of aerospace applications including landing gear for many commercial airplanes.
AMS 6417 (Replaces MIL-S-83135)
AMS 6257 (Replaces MIL-S-8844 REV D CLASS 3)
AMS 2300 Premium Aircraft Quality Cleanliness
AMS 6417 Macrostructure standards
Minimum Longitudinal Tensile Properties per AMS 6417:
Yield Strength 0.2% offset
Reduction of Area
Minimum Transverse Tensile Properties per AMS 6417
Yield Strength 0.2% Offset
Avg. Reduction of Area
Individual Reduction of Area
Up to 100 in2, incl
Over 100 in2, incl
Over 144 in2, incl
Over 225 in2
AOD + VAR
VIM + VAR
300M, UNS K44220, 4340MOD Low Alloy Steel - Chemical composition WT %
Chemical Composition WT %
Mechanical Property of 300M, UNS K44220, 4340MOD Low Alloy Steel
Shear modulus (typical for steel)
Physical Property of 300M, UNS K44220, 4340MOD Low Alloy Steel
Heat Treatment of 300M, UNS K44220, 4340MOD Low Alloy Steel
300M, UNS K44220 Low Alloy Steel is normalized at 927°C (1700°F). It is then heated at 872°C (1600°F) followed by oil quenching oil and tempering.
AMS 6417 Heat Treatment
Type of Heat Treating
1700° F +/- 25° F (927° C +/- 14° C), then air cool
1600° F +/- 25° F (871° C +/- 14°C), quench in oil
Double temper 400° – 1200° F (204° – 649° C) depending on desired strength and hardness.
Welding of 300M, UNS K44220, 4340MOD Low Alloy Steel
300M, UNS K44220 Low Alloy Steel can be welded using flash resistance welding or fusion welding methods. Approved procedures such as including pre and post-heating practice are followed for performing the fusion welding method because this alloy can be air-hardened due to the heat produced by welding. This process is followed by re-normalizing, or re-normalizing and tempering before heat treatment.
Machining of 300M, UNS K44220, 4340MOD Low Alloy Steel
300M, UNS K44220 Low Alloy Steel can be easily machined in normalized, or normalized and tempered conditions. Due to hardness of the heat treated alloy, the grinding process is performed with extreme care. After grinding, stress relief annealing is performed at 288°C (550°F).
Equivalent grades of 300M, UNS K44220, 4340MOD Low Alloy Steel