3Cr2W8V、4Cr5MoSiVl钢热疲劳机理及热疲劳抗力的差异

THE DIFFERENCE OF THE THERMAL FATIGUE MECHANISM AND RESISTANCE BETWEEN 3Cr2W8V AND 4Cr5MoSiV1

对淬火、回火后的3Cr2W8V钢、4Cr5MoSiV1钢缺口板状试样,进行了50～650℃ Coffin型热疲劳试验。根据试验结果,分析了热疲劳裂纹萌生和扩展过程,以及此过程中试样上应力的变化。结果表明:试样在升温时产生塑性压缩应变,在降温时产生弹性拉伸应变,呈现出弹塑性应变循环的特征;热疲劳裂纹沿滑移线场方向,在最大应变区形核,在形核数量上,4Cr5MoSiV1钢为3Cr2W8V钢的十几倍;裂纹扩展驱动力主要受材料高温强度和组织的热循环稳定性控制,同时也受材料对拉应力松驰能力的影响;裂纹扩展阻力主要取决于热循环后的材料断裂韧性水平、强度水平和氧化腐蚀抗力的合理配合。根据以上分析结果,从机理上解释了4Cr5MoSiV1钢热疲劳抗力优于3Cr2W8V钢的原因。

The test of 50--650℃ Coffin model thermal-fatigue has been made, usingnotched plate specimen of the hot-working tool steels 3Cr2W8V and 4Cr5MoSiV1after quenching and tempering, It was shown that the specimens appeared plasticcompression strain with the temperature increasing and elastic tensil strain withthe temperature decreasing. A feature of elastic plastic strain cycle has emerged. The thermal-fatigue cracks nucleate in the areas of maximum strain alongthe direction of the slip line field. The nucleating number of 4Cr5MoSiV1 steelis above ten times of the 3Cr2W8V steel. The driving force of the cracks prop-agation was controlled mainly by the high temperature strength and the stabilityof the microstructure in temperature cycles. It was also affected by the relaxat-ion of the tensil stress. The resistance of the cracks propagation was determinedby equitable cooperation of the fracture toughnss, the strength and the resistanceof the oxidation corrosion after temperature cycles. In this paper the causes ofthat thermal-fatigue resistance in 4Cr5MoSiV1 steel being better than that in3Cr2W8V steel were also explained.