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.
300M Spec.:
AMS 6417 (Replaces MIL-S-83135)
AMS 6419
AMS 6257 (Replaces MIL-S-8844 REV D CLASS 3)
AMS 2300 Premium Aircraft Quality Cleanliness
BMS 7-26
BE1036
CE-0896
C-05-1190
DMS 1935
GM1012
MTL 1201
S155
MAT 137
SAE 434M
IGQ 41-11
LAT 1.9042
ZFNL 9207
ASTM A646
AMS 6417 Macrostructure standards
Class
Condition
Severity
1
Freckles
A
2
White Spots
A
3
Radial Segregation
B
4
Ring Pattern
B
Minimum Longitudinal Tensile Properties per AMS 6417:
Property
Value
Tensile Strength
270 ksi
Yield Strength 0.2% offset
220 ksi
Elongation
8%
Reduction of Area
30%
Minimum Transverse Tensile Properties per AMS 6417
Cross-section Area
Tensile Strength
Yield Strength 0.2% Offset
Avg. Reduction of Area
Individual Reduction of Area
Up to 100 in2, incl
270 ksi
220 ksi
30%
25% min
Over 100 in2, incl
270 ksi
220 ksi
25%
20% min
Over 144 in2, incl
270 ksi
220 ksi
20%
15% min
Over 225 in2
270 ksi
220 ksi
15%
10% min
Melted process
AOD + VAR
VIM + VAR
300M, UNS K44220, 4340MOD Low Alloy Steel - Chemical composition WT %
Grade
Chemical Composition WT %
C
Mn
Si
P
S
Cr
Ni
Mo
V
Fe
300M
0.40-0.46
0.65-0.90
1.45-1.80
Max 0.035
Max 0.03
0.70-0.95
1.65-2.0
0.30-0.45
Min 0.05
93.4-94.8
UNS K44220
0.38-0.46
0.60-0.90
1.45-1.80
Max 0.010
Max 0.010
0.70-0.95
1.65-2.0
0.30-0.65
Min 0.05
Bal
Mechanical Property of 300M, UNS K44220, 4340MOD Low Alloy Steel
Properties
Metric
Imperial
Shear modulus (typical for steel)
80 GPa
11600 ksi
Elastic modulus
205 GPa
29700 ksi
Poisson's ratio
0.28
0.28
Physical Property of 300M, UNS K44220, 4340MOD Low Alloy Steel
Properties
Metric
Imperial
Density
7.87 g/cm3
0.284 lb/in³
Melting point
1422°C
2590°F
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
Process
Normalize
1700° F +/- 25° F (927° C +/- 14° C), then air cool
Harden
1600° F +/- 25° F (871° C +/- 14°C), quench in oil
Temper
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