Alloy composition (by weight)[1]

SAE grade

 % Cr

 % Mo

 % C *

 % Mn

 % P (max)

 % S (max)

 % Si

4118

0.40–0.60

0.08–0.15

0.18–0.23

0.70–0.90

0.035

0.040

0.15–0.35

4120

0.40–0.60

0.13–0.20

0.18–0.23

0.90–1.20

0.035

0.040

0.15–0.35

4121

0.45–0.65

0.20–0.30

0.18–0.23

0.75–1.00

0.035

0.040

0.15–0.35

4130

0.80–1.10

0.15–0.25

0.28–0.33

0.40–0.60

0.035

0.040

0.15–0.35

4135

0.80–1.10

0.15–0.25

0.33–0.38

0.70–0.90

0.035

0.040

0.15–0.35

4137

0.80–1.10

0.15–0.25

0.35–0.40

0.70–0.90

0.035

0.040

0.15–0.35

4140

0.80–1.10

0.15–0.25

0.38–0.43

0.75–1.00

0.035

0.040

0.15–0.35

4142

0.80–1.10

0.15–0.25

0.40–0.45

0.75–1.00

0.035

0.040

0.15–0.35

4145

0.80–1.10

0.15–0.25

0.43–0.48

0.75–1.00

0.035

0.040

0.15–0.35

4147

0.80–1.10

0.15–0.25

0.45–0.50

0.75–1.00

0.035

0.040

0.15–0.35

4150

0.80–1.10

0.15–0.25

0.48–0.53

0.75–1.00

0.035

0.040

0.15–0.35

4161

0.70–0.90

0.25–0.35

0.56–0.64

0.75–1.00

0.035

0.040

0.15–0.35

* The carbon composition of the alloy is denoted by the last two digits of the SAE specification number, in hundredths of a percent