40Cr steel is one of the most widely used steels in the machinery manufacturing industry. After quenching and tempering, it has good comprehensive mechanical properties, 

good low-temperature impact toughness and low notch sensitivity. The steel has good hardenability, and can be hardened to 28-60mm in water quenching and 15-40mm in oil quenching. 

In addition to quenching and tempering, this steel is also suitable for cyaniding and high-frequency quenching. The cutting performance is good. When the hardness is 174-229HB, the relative 

cutting processability is 60%. This steel is suitable for making medium-sized plastic molds.

40Cr quenching 850℃, oil cooling; tempering 220℃, water cooling, oil cooling, air cooling. The surface quenching hardness of 40Cr is 52-60HRC, and flame quenching can reach 48-55HRC. 

After quenching, cubic boron nitride blades can be used for turning.

Tempering troostite to improve the mechanical properties of the core and the quality of the nitride layer.

Hardened structure (martensite structure) that is very sensitive to cold cracks. When the cooling rate of the overheating zone is high, it is easy to form hard and brittle high-carbon martensite, 

which makes the overheating zone embrittled.

Key points of welding process:

1. Generally, welding is carried out in the annealing (normalizing) state.

2. The welding method is not restricted

3. Use a larger line energy and appropriately increase the preheating temperature. Generally, the preheating temperature and interlayer temperature can be controlled between 250 and 

300 ° C.

4. The welding material should ensure that the composition of the deposited metal is basically the same as that of the parent material, such as J107-Cr

5. Tempering heat treatment should be carried out in time after welding. If it is difficult to carry out tempering treatment in time, intermediate annealing can be carried out or the temperature 

can be kept at a temperature higher than the preheating temperature for a period of time to eliminate the diffused hydrogen and soften the structure. For products with complex structures 

and more welds, an intermediate annealing can be carried out after a certain number of welds are welded.

Pig iron chip protection swing tempering specification

(670±10)℃×2h, heating up with the furnace, (710±10)℃×2h, cooling down with the furnace,

(670±10)℃×2h, heating up with the furnace, (710±10)℃×2h, cooling down with the furnace,

(670±10)℃×2h, heating up with the furnace, (710±10)℃×2h, cooling down with the furnace,

(670±10)℃×2h, heating up with the furnace, (710±10)℃×2h, cooling down with the furnace,

3 cycles in total, then cooling down to 550℃, air cooling out of the furnace. Hardness after treatment is 153HBS.