It has been recently shown, [Liu and Mittal 1995, 1996] that it is feasible to eliminate the needs for grinding and superfinishing by turning, in selected conditions, directly on hardened steel up to a hardness of 64 RC, for a surface finish of Ra smaller than 8 μ in. Furthermore, it was shown that hard turning is capable of pre-stressing the machined surface so that it may partially “compensate” the surface load for improved fatigue life. A preliminary study has indicated a potential improvement of over 200% in fatigue life is possible. It also offers a prospect that it is possible to produce a component which will never fail due to fatigue. Therefore, it is desirable to explore the capability of pre-stressing by finish hard turning in broad machining condition, thus this study. The purpose of this study is to investigate the residual stress after finish machining of hardened AISI 52100 steel with hardness of 60–62 HRC using CBN inserts. The effect of tool, feed rate, and depth of cut on the residual stress distribution are studied. Surface finish better than 8 μ in. was produced comparable to that produced by grinding and superfinishing. The round tool (0.5 inch radius) was found to give more compressive stress than the 0.0623 inch nose radius diamond-shaped tool. The smaller feed rate gave more compressive residual stress.

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