STUDY OF QUENCH CRACKING OF A HIGH CARBON AND CHROMIUM STEEL BAR (2ND REPORT, EFFECTS OF INTERRUPTED QUENCHING AND DELAYED QUENCHING ON QUENCH CRACKING).

The preceding paper has reported that the increase of polyalkylene glycol (PAG) polymer concentration results in the decrease of fin cracks and increase of vertical cracks because of the low cooling rate of the quenchant. This papers deals with the effects of interrupted quenching and delayed quenching on quench cracking. The residual stress and hardness were measured by the X-ray diffraction method and Rockwell hardness tester, respectively. The interrupted quenching method is more effective to prevent cracking in PAG solutions. Immersed for 6 seconds in 5% PAG sol. and for 15 seconds in 15% PAG sol. , the steel bars exhibited high hardness and residual stress. Delayed quenching is less effective to prevent cracking. As the crack percentage decreases, the hardness and residual stress become lower in the delayed quenching.