Ｃｒ‐Ｍｏ鋼熱影響部の焼もどし脆化に関する研究 ５ ９００Ｋ以下の温度域におけるＨＡＺ焼もどし脆化の発生原因

Abstract

The authors have pointed out in preceding papers that four types of temper arise in temperature range below 900 K when heat affected zone of 2 1/4Cr-lMo steel is reheated. The causes of these temper embrittlements were examined in present paper.The first type of which arises at 775 K was compared with the low temperture temper embrittlement which has been known to arise at 575 K and to be caused by fine precipitates of cementite. Experimental results on a series of specimens which were tempered at each temperature from 575 K to 775 K showed that both types of temper are identical.The second type of embrittlement, which arises at 825 K in short term range and produces cleavage fracture by impact test, was found to be caused by hardening of ferrite which was induced by fine precipitates of Mo2C type carbide.The thirdd type of arises at temperatures around 825 K and produces intergranular fracture by impact test. A new technique for analyzing grain boundary revealed that segregation of phosphorus caused this embrittlement.The fourth type of embrittlement, which arises at 875 K in long term range and produces cleavage fracture, was found to be caused by large sized particles of Mo2C type and Cr, C, type carbide. In impact test, fracture occurred preferentially along planes in which carbide particles of large size exist.The proper terms of first to fourth types of were proposed by authors : low-temperature-, short-term-, intergranular- and long-term temper embrittlement.