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한준희,황농문,김종집,문한규 ( J . H . Hahn,N . M . Hwang,J . J . Kim,H . G . Moon ) 한국열처리공학회 1989 熱處理工學會誌 Vol.2 No.2
In order to improve hardness uniformity of standard-hardness blocks, exprimental procedure was designed using Taguchi Method. For this purpose the following factors were studied : austenitizing temperature, tempering condition, grinding condition, subzero treatment, lapping time, 15㎛ polishing time, final polishing time. These factors were processed and then ten hardness values were measured on each specimen, SN (signal to noise) ratio for each condition was calculated with standard variations of these values. Finally, from the calculated value of ANOVA on SN ratios, the lapping time was found to be the main factor. Better uniformity with longer lapping time implies that residual stress that was formed after quenching is a dominent parameter that affects on the unformity of hardness. Therefore, step-quenching method was adapted to minimize the residual stress. By this modification of quenching procedure, the hardness uniformity was improved remarkably and the yield ratio was increased from 55% to 88%.