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结合室温、高温冲击试验及700℃时效试验,利用光镜、扫描电镜、透射电镜、电子探针等手段对服役态及供货态典型奥氏体耐热钢HR3C的脆化机理进行了研究。结果表明,服役近4万小时后HR3C钢室温及650℃均出现了明显脆化现象,冲击韧性大幅度下降,700℃时效试验结果与此类似。组织分析表明,服役近4万小时的HR3C钢在晶界析出连续片状分布的M_(23)C_6相、沿晶界向晶内生长出针(条)状M_(23)C_6相、晶界周边析出纳米级立方状M_(23)C_6相及弥散Nb Cr N相,Cr、C,P、S 4种元素在晶界明显偏聚。在700℃时效不同时间后相关试验表明HR3C钢在冲击韧性快速下降阶段微观组织中碳化物在晶界已成连续片状分布,未见其余析出相,晶界仅有微量S元素偏聚。M_(23)C_6在晶界的连续片状析出是造成HR3C钢时效脆化的主要原因。
Combining with room temperature, high temperature impact test and aging test at 700 ℃, the embrittlement mechanism of serviceable and supplied typical austenitic heat-resistant steel HR3C was studied by means of light microscope, scanning electron microscope, transmission electron microscope and electron probe. The results showed that the HR300 steel exhibited obvious embrittlement at room temperature and 650 ℃ for nearly 40,000 hours, and the impact toughness decreased sharply. The results of aging test at 700 ℃ were similar. The microstructure analysis showed that HR3C steel with a service life of nearly 40,000 hours precipitated a continuous platelet-like M_ (23) C_6 phase in the grain boundary and grew into a needle-like M_ (23) C_6 phase along the grain boundary. Around the nanocrystalline cubic M_ (23) C_6 phase and the dispersed Nb Cr N phase precipitated, Cr, C, P and S elements segregated significantly at the grain boundaries. At 700 ℃ aging at different times after the relevant tests showed that HR3C steel in the rapid decline of impact toughness in the microstructure of carbides in the grain boundary has become a continuous sheet distribution, no other precipitates, grain boundary segregation of only a small amount of S elements. The continuous sheet-like precipitation of M_ (23) C_6 in the grain boundary is the main cause of aging embrittlement of HR3C steel.