Comparative Study on Microscopic Evaluation Methods for Non-Metallic Inclusions in Steels for Spring Use

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  • ばね材料における非金属介在物評価のための各種検鏡法の比較
  • ばね材料における非金属介在物評価のための各種検鏡法の比較--非金属介在物評価法調査委員会報告
  • バネ ザイリョウ ニ オケル ヒキンゾク カイザイブツ ヒョウカ ノ タメ ノ
  • Report of Committee for Evaluation of Non-Metallic Inclusions, JSSR
  • 非金属介在物評価法調査委員会報告

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It is known that an adequate control of non-metallic inclusions (nmi) is one of the key factors for modern spring materials to ensure their advanced fatigue performances. The research activities including questionnaire due to this committee have revealed that the microscopic testing method in the Japanese Industrial Standard (JIS) is not enough valid for the assessment of spring steels from fatigue point of view, while the method is most widely used for quality control purposes in steel making industries.<br>In view of obtaining a common basis for the establishment of a new method of evaluation particularly applicable to nmi in the spring steels, a round robin test was undertaken to compare several existing microscopic methods using two heats of SAE 9254 steels with different nmi levels. Analyses of the results was resumed as in the following:<br>(1) method by JIS is not adequate for very low levels of nmi besides the lack of informations about the size, <br>(2) a commercial method known as Michelin's can evaluate both size and quantity of nmi and would be a practical one if the procedure is well standardized, <br>(3) method D by ASTM is effective but cannot result in a single value: it is difficult and requires long time for operation, <br>(4) another commercial method called Bekaert's seems to be a good one and would be also effective if well standardized but scarcely known at present, <br>(5) method M by VDEh cannot give a single value but seems possible to become so if some modifications and simplification are applied, and<br>(6) automatic image analysers used for evaluation of nmi needs more improvement to be practiced to materials with very low level of nmi like spring steels.

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