STUDY OF QUENCH CRACKING OF A HIGH CARBON AND CHROMIUM STEEL BAR (3RD REPORT, EFFECTS OF CLOUDING POINT OF POLYMER QUENCHANT ON QUENCH CRACKING).

A preceding paper has shown that the increase of polyaklylene glycol (PAG) polymer concentration results in a decrease of fin cracks and an increase of vertical cracks, because of the clouding point (81 degree C) of PAG sol. This paper deals with the effects of the clouding points of quenchant on the quench cracking of a SUJ 2 bar. The clouding point is affected enormously over pH 13. 0 of the PAG quenchant and goes down to 43 degree C at pH 13. 5. The high cooling rate of the PAG quenchant is obtained by the low clouding point quenchant. Therefore, the behavior of quench cracking in the pH 13. 5 PAG sol. is similar to that of water. When SUJ 2 was quenched from austenitizing temperature 800 degree C, a considerable tensile stress existed on the surface area of all specimens, regardless of their pH values. A gel permeation chromatogram shows that the thermostability of PAG quenchant is excellent under severe conditions.