AISI 4140

A prehardened mold steel (311-345 HB / 33-37 HRC) with improved machinability

4140 is a chromium-manganese-molybdenum grade designed for plastic mold industry. This grade is normally delivered in a prehardened condition at a hardness level of 33/37HRC. The grade has a fully homogeneous martensite-bainite microstructure. 4140 grade has specific sulfur addition (0.060% typical) in order to increase strongly its machinability. Compared to AISI P20 grade, 30% increase in milling speed and 300% increase in drilling speed can be expected. At constant cutting speed, tool life is multiplied a least by 5 when replacing P20 by 4140 grade.
4140 is not suitable for polishing requirements.

This grade is typically used for:

  • plastic injection molds for thermoplastics
  • extrusion dies for thermoplastics
  • compression molds

Chemical analysis

Typical values (weight%).

C S P Si Mn Cr Mo
0.4 0.060 0.01 0.3 1.5 1 0.2

Mechanical properties

Typical values for plates air quenched and tempered (thickness 45 mm – 1.8”).

Hardness YS 0.2 UTS Elongation Reduction
of area
Elastic modulus
HB MPa ksi MPa ksi % Z% GPa ksi
320 920 133 1075 156 9 40 205 29745
320 900 131 1060 154 8 35 205 29745

Dimensional program

Typical delivery sizes

Thickness Width
20 – 600 mm
(.79″ – 23.6″)
1500 – 2500 mm
(59″ – 98.4″)


Technical data and information are to the best of our knowledge at the time of publication. However, they may be subjected to some slight variations due to our ongoing research programmes. Therefore, we suggest that information be verified at time of enquiry or order. Furthermore, in service, real conditions are specific for each application. The data presented here are for the purpose of description only, and can be considered as guarantees only when written formal approval has been provided by our company. Industeel reserves the right to change its product range at any time without prior notice.