Internal cracks in 30Cr2Ni4MoV steel were produced by compressing cylindrical sample with drilled hole. In order to consider the effects of deformation degree, temperature, strain rate and holding time on the crack healing, the hot compression tests were performed on Gleeble-1500 thermo-simulation machine under different process conditions. By in situ observation under optical microscope and scanning electron microscope, effects of process condition on crack healing and the behaviours of crack healing were revealed successfully: (1) the result of crack healing improves as the melt temperature, reduction and holding time increase, (2) the effect of crack healing decreases as the strain rate increases. By the energy dispersive spectroscopy, it is also found that the chemical composition of the healed crack area is different from that of the matrix.

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