Detailed Explanation of 40Cr Steel Grade

Detailed Explanation of 40Cr Steel Grade

40Cr is a standard steel grade under China's GB (National Standard). Cowinns as one high pressure dual plate check valve manufacturer we can design and manufacture different special material valves, 40Cr material widely used in machinery manufacturing, 40Cr steel exhibits excellent comprehensive mechanical properties after quenching and tempering, including good low-temperature impact toughness and low notch sensitivity. It has good hardenability: water quenching can harden up to Ф28–60 mm, while oil quenching can harden up to Ф15–40 mm. This steel is suitable for cyaniding, high-frequency quenching, and machining (with a relative machinability of 60% at 174–229 HB hardness). It is commonly used for medium-sized plastic molds.

Chemical Composition
C:0.37~0.44
Si:0.17~0.37
Mn:0.50~0.80
Cr:0.80~1.10
Ni:≤0.30
P:≤0.030
S:≤0.030
Cu:≤0.30
Mo:≤0.10

Mechanical Properties
Sample Blank Size (mm):25

Heat Treatment：
First Quenching Temperature：850；Cooling Medium: Oil
Second Quenching Temperature（℃）：-
Tempering Temperature（℃）:520；

Tensile Strength（σb/MPa）：≥980
Yield Point（σs/MPa）：≥785
Elongation After Fracture（δ5/%）：≥9
Reduction of Area（ψ/%）：≥45
Impact Absorption Energy（Aku2/J）：≥47
Brinell Hardness（100/3000HBS）（Annealed or High-Temperature Tempered）：≤207

Basic Attributes
China GB: 40Cr
German DIN: 1.17035/1.7045, 41Cr4/42Cr4
British EN/BS: 18, 41Cr4
French AFNOR/NF: 42C4, 38Cr4/41Cr4
Italian UNI: 41Cr4
Belgian NBN: 42Cr4
Swedish SS: 2245
American AISI/SAE/ASTM: 5140
Japanese JIS: SCr440(H)/SCr440
ISO: 41Cr4

【Critical Point Temperatures】（Approx.） Ac3=780℃
【Normalizing】
Temperature 850~870℃，Hardness179~229HBS。
【Cold Pressed Blank Softening:】
Temperature: 740–760°C, hold 4–6 h
Cooling Rate: 5–10°C/h to ≤600°C, then air cooling
Pre-Treatment Hardness: ≤217 HBS → Post-Treatment Hardness: ≤163 HBS
【Protective Annealing with Iron Chips】
Cyclic Process: (670±10)°C × 2h → (710±10)°C × 2h (3 cycles) Final Cooling: 550°C → Air cooling Resulting Hardness: 153 HBS 
Quenching and Tempering: Quenching: 850±10°C (Oil Cooling) Tempering: 520±10°C (Water/Oil/Air Cooling) Post-Treatment Hardness: 32–36 HRC (≈301–340 HB) 

Hardness After Tempering 
Tempering Temperature (°C)    Hardness (HRC
150                                              55
200                                              53
300                                              51
400                                              43
500                                              34
550                                              32
600                                              28
650                                              24
Applications 40Cr steel is ideal for manufacturing medium-sized plastic molds, gears, shafts, and other components requiring high strength, toughness, and wear resistance after heat treatment. Its versatility in processes like cyaniding and high-frequency quenching further expands its industrial applications.