Journal of the Korean Society for Heat Treatment (열처리공학회지)

The Korean Society for Heat Treatment (한국열처리공학회)
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Heat Treatment for Improvement of Hardness Uniformity of Standard Hardness Blocks

경도 기준편의 경도 균일성 향상을 위한 열처리

  • Hahn, J.H. (Materials Properties Lab., Korea Standards Research Inst.) ;
  • Hwang, N.M. (Materials Properties Lab., Korea Standards Research Inst.) ;
  • Kim, J.J. (Materials Application Lab., Korea Standards Research Inst.) ;
  • Moon, H.G. (Materials Application Lab., Korea Standards Research Inst.)
  • 한준희 (한국표준연구소 재료물성연구실) ;
  • 황농문 (한국표준연구소 재료물성연구실) ;
  • 김종집 (한국표준연구소 재료응용연구실) ;
  • 문한규 (한국표준연구소 재료응용연구실)
  • Published : 1989.06.30
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Abstract

In order to improve hardness uniformity of standard-hardness blocks. experimental procedure was designed using Taguchi Method. For this purpose the following factors were studied: austenitizing temperature, tempering condition, grinding condition, subzero treatment, lapping time, $15{\mu}m$ 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 uniformity 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%.

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