Common defects and countermeasures of flame surface quenching

cracking

Causes:

1, overheating, such as the high carbon content of the gear, flame quenching, because the tooth top temperature is high, cooling and too intense, easy to cause cracking

2, repeated quenching, such as the ring workpiece, at the beginning of the quenching and the end of the quenching, there is often repeated quenching phenomenon, where the quenching crack is easy to produce

3. The heat treatment furnace did not temper in time

Solutions:

1. Reduce the heating temperature and cooling speed, and adopt self-tempering or timely tempering to control the generation of overheating cracks

2, at the beginning of quenching, reduce the heating temperature, so that it becomes a quenching low hardness zone; When quenching is completed, once the nozzle enters the zone, the flame shall be closed immediately and the cooling water shall be increased

3. Temper it

Insufficient hardness

Causes:

1. Steel has low carbon content and poor hardness

2. Slow operation, not timely cooling, resulting in heat transfer, surface temperature drop

3. Insufficient cooling water or water pressure, reduce quenching cooling speed

4. Low heating temperature

Solutions:

1. (C) steel less than 0.3% is not suitable for surface quenching

2. Quick operation, timely cooling

3. Increase cooling water

4. The heat treatment furnace raises the heating temperature

burning-out

Causes: nozzle fire hole deformation, mistakenly open the oxygen valve or quenching machine suddenly stop caused by

Solution: repair by grinding with grinding wheel, scrap the badly burned workpiece

distortion

Causes: uneven heating or cooling

Solution: improve nozzle shape and size, improve heating and cooling conditions, control quenching distortion, such as rotary quenching instead of static quenching, or increase the workpiece rotation speed