|4140 High Tensile Steel, SCM440, 42CrMo4, ASSAB 709, 7225, EN19, SCM4|
|4140 is a 1% chromium – molybdenum medium hardenability general purpose high tensile steel – generally supplied hardened and tempered in the tensile range of 850 – 1000 Mpa (condition T).
AISI 4140 is now available with improved machinability, which greatly increases feeds and/or speeds, while also extending tool life without adversley affecting mechanical properties.
Pre hardened and tempered 4140 can be further surface hardened by flame or induction hardening and by nitriding.
1.7225 is used extensively in most industry sectors for a wide range of applications such as:
Common 4140 Steel Specifications
|Standard||ASTM A29||DIN 17200||BS 970||JIS G4105||GB/T 3077||AS 1444|
MECHANICAL PROPERTY REQUIREMENTS IN CONDITION “T” – to AS 1444-1996
|Section mm||0.2% Proof Stress MPa||Tensile Strength MPa||Elongation on 5.65√So
|Impact Izod Charpy
|*up to 63||680 n||850 – 1000||14||– –||248 – 302|
|*up to 100||665 min||850 – 1000||15||54min 50min||248 – 302|
*Applies only to bars bright drawn after hardening and tempering
TYPICAL MECHANICAL PROPERTIES – Hardened and tempered in section size listed
|Section mm||Yield Strength MPa||Tensile Strength MPa||Elongation
|Impact Izod J||Hardness HB|
Typical Mechanical Properties for guidance only
|Heat to 800 oC – 850 oC, hold until temperature is uniform throughout the section and cool in furnace.|
|Flame or Induction Hardening|
|7225 hardened and tempered bar can be further surface hardened by either the flame or induction hardening methods resulting in a case hardness in excess of Rc 50.
Parts should be heated as quickly as possible to the austenitic temperature range (840 C – 870 C) and “required case depth followed by an immediate oil or water quench, depending upon hardness required, workpiece” size/shape and quenching arrangements.
“Following quenching to hand warm, most components should be tempered between 150 C – 200 C to remove” quenching stresses in the case. This will have little effect on case hardness and will reduce the risk of grinding cracks.
|Heat to 840 oC – 875 oC, hold until temperature is uniform throughout the section, soak for 10 – 15 minutes per 25 mm section, and quench in oil, water, or polymer as required.
*Temper immediately while still hand warm.
|EN19 hardened and tempered bar can also be successfully nitrided, giving a surface hardness of up to Rc 60. Nitriding is carried out at 490 oC – 530 oC, followed by slow cooling (no quench) reducing the problem of distortion. Parts can therefore be machined to near final size, leaving a grinding allowance only. The tensile strength of the core is usually not affected since the nitriding temperature range is generally below the original tempering temperature employed.|
|Heat to 870 oC – 900 oC, hold until temperature is uniform throughout the section, soak for 10 – 15 minutes and cool in still air.|
|Heat to 680 oC – 700 oC, hold until temperature is uniform throughout the section, soak for 1 hour per 25 mm section, and cool in still air.|
|Re-heat to 550 oC – 700 oC as required, hold until temperature is uniform throughout the section, soak for 1 hour per 25 mm of section, and cool in still air.|
|Notes on Heat Treatment|
|Heating temperatures, rate of heating and soaking times will vary due to factors such as work piece size/shape also furnace type employed, quenching medium and work piece transfer facilities etc.. Please consult your heat treater for best results.|
|42CrMo4 in the hardened and tempered as supplied condition has good to very good machinability and operations such as sawing, turning, drilling, broaching, hobbing, milling and tapping can be carried out satisfactoraly using machine manufacturers recommendations for suitable tool type – feeds and speeds.|
|Welding of AISI4140 in the hardened and tempered condition (as normally supplied), is not recommended and should be avoided if at all possible, as the mechanical properties will be altered within the weld heat affected zone. It is preferred that welding be carried out on 4140 while in the annealed condition, and that the work piece, immediately on cooling to hand warm, is then stress relieved at 595 oC – 620 oC prior to hardening and tempering.
If welding in the hardened and tempered condition is really necessary, then the work piece, immediately on cooling to hand warm, should be if possible stress relieved at 15 oC below the original tempering temperature (if known).