Effect of Heat Treatment Processes on Fatigue Crack Growth Rates of Hardened-tempered 8Cr4Mo4V Steel

The fatigue crack growth rates and the fatigue fracture surfaces had been investigated about four groups of 8Cr4Mo4V steel specimens with different heat treatment processes. The result show that at room temperature the fatigue crack steady growth rates of the hardened-tempered 8Cr4Mo4V steel accorded with Paris relation. The fatigue crack growth rates related with the heat treatment process, depended mainly on carbon conten in the martensite, and did not obviously related with the cold treatment. The main microscopic appearance of the fatigue fracture surfaces was quasi-cleavage. The narrower the X-ray FWHM of the martensite(211) was, the lower the crack growth rate was, and the greater the tensile residual stress on the fracture surface was.