According to the phenomenon of segregation and conglomeration of carbides in annealed steel 3Cr17Mo (/%: 0.25C

16.5Cr

0.60Mn

0.60Si

1.0Mo

0.020P

0.005S)

the orthogonal experiments and discrete data analysis on effect of pre-cooling heating temperature (870~960°C.

oil-cooling to 450℃)

pre-cooling times (1~4) and holding time (1~4h) on structure of steel have been carried out to study the effect of repeated pre-cooling heat treatment on spheroidizing structure of steel 3Cr17Mo. It is obtained that 900~910℃ double pre-cooling heat treatment is available to decrease the time of heat treatment and get structure with uniform and fine carbides. The test results show that as compared with normal annealing process-860°C for 4h

furnace cooling to 500℃

air cooling

the spheroidizing carbides in steel with double 900~910°C. for 30min

oil-cooling to 450℃+ annealing at 730℃ 2h and furnace cooling to 400°C air cooling is more uniform and fine

its comprehensive mechanical properties improve obviously.