4340 hot rolled alloy structural steel plate

C

Si

Mn

P≤

S≤

Cr

Ni≤

Mo

0.37~0.45

0.10~0.35

0.55~0.90

  0.025    

  0.025    

0.65~0.95

2.00

0.20~0.35

Chinese

American

German

Swedish

Japanese

GB

AISI

DIN

ASSAB

JIS

42CrNiMo

4340

1.6511/34nicrmo4

SNCM439

   Round bar 

Diameter(mm)

   Length (mm)

     10~500

   2000~6000

   plate/sheet    

Thickness(mm)   

    Width (mm)       

  Length (mm)    

     10~500

     80~2300

   2000~6000

Preheat the steel carefully, then raise the temperature to 1150-1200°C for forging. Do not forge below 850°C.

Heat the AISI 4340 slowly to 800-850°C and allow enough time for the steel to be thoroughly heated. Cool slowly in the furnace to 480°C followed by air cooling.

When parts are heavily machined, ground or otherwise subject to cold work, stress relieving will be beneficial prior to hardening. 

AISI 4340 steel is usually supplied ready heat treated to 18-22HRC. If further heat treatment is required annealed AISI 4340 should be heated slowly to 840-875°C and after adequate soaking at this temperature quench in oil. Temper as soon as the tools reach room temperature.

Heat the AISI 4340 carefully to a suitable temperature selected by reference to a tempering chart or table (usually between 550-700°C, soak at the temperature for 2 hours per 25mm of ruling section, then allow to cool in air. Tempering between 250-375°C is not advised as tempering within this range will seriously reduce the impact value.

Heat treatment temperatures, including rate of heating, cooling and soaking times will vary due to factors such as the shape and size of each AISI 4340 steel component. Other considerations during the heat treatment process include the type of furnace, quenching medium and work piece transfer facilities. Please consult your heat treatment provider for full guidance on heat treatment of alloy steel.