The Effect of Forging Reduction on the Properties of a Die Steel

The literature dealing with the effect of forging reduction upon mechanical properties and service performance, with particular reference to hot work steels, has been reviewed. The effect of forging reduction on mechanical properties and the service performance of BSS.224 No. 5. nickel-chromium-molybdenum hot work die steel has been studied by processing a 34=ton electrically melted ingot, forged in three stages, with forging reductions of 2.92, 9.0 and 18.5/1 respectively. From each bloom six die inserts were manufactured to a hardness range of 363/388 B.H.N. The life of the die inserts was compared with routine production data. The effect of forging reduction on mechanical properties, measured in three mutually perpendicular testing directions, was investigated at room temperature. The variation of properties is related to the distribution and form of non-metallic inclusions, and not to heterogeneity which, although apparently present on metallographic examination, was not confirmed by chemical and micro-probe analyses. Even so the micro hardness varied in a random manner. Increasing forging reductions did not affect mechanical properties measured in the longitudinal direction. Transverse and depth properties were impaired by heavier amounts of forging, but not to the same extent that other workers have previously reported. Forging had no influence upon die life except that heavy reduction minimised scatter. Room temperature mechanical properties do not appear to have a bearing on die life. The published conversion tables of hardness and tensile strength were found to be inapplicable to the range of hardness studied