【作者】 胡心彬；

【导师】 李麟；

【作者基本信息】 上海大学 ， 材料学， 2005， 博士

【摘要】 AISI H13钢是目前应用极为广泛的一类热作模具钢,主要应用于压铸模、热挤压模和热锻模等。热疲劳是这类钢的主要失效形式。本文研究了微量Nb对H13钢热疲劳行为的影响,初步探明了Nb微合金化H13钢的热疲劳裂纹萌生、扩展的主要方式及其热疲劳循环软化的表现形式,并提出相应的热疲劳寿命预测模型;同时对热疲劳过程中多元合金钢的碳化物粗化动力学行为也进行了初步探讨。主要结论如下:1、借助Thermo-calc热力学计算软件和TEM&EDS等手段,研究了微量铌对H13钢的显微组织结构、碳化物的类型、大小和分布的影响。研究表明,在相同的奥氏体化温度下,添加微量的Nb可以有效细化H13钢的奥氏体晶粒,甚至添加0.07wt%Nb的H13钢在1120℃奥氏体化后的晶粒大小与普通H13钢1030℃奥氏体化时的晶粒大小相当;同时碳化物细小且更加弥散。2、对铌微合金化H13钢的室温及高温力学性能研究表明,添加微量Nb对H13钢的抗拉强度和屈服强度的贡献不显著,而且对塑韧性的改善也有限。回火软化抗力和热稳定性的研究结果表明,微量铌的添加改善了H13钢的回火软化抗力和热稳定性,其中添加0.07wt%Nb的效果好于添加0.014wt%Nb的效果。3、添加微量的Nb使H13钢的热疲劳裂纹萌生细小、均匀,裂纹扩展缓慢;热疲劳后的硬度梯度下降缓慢,软化层较浅,从而显著提高了H13钢的热疲劳性能。其中含0.07wt%Nb的H13钢热疲劳性能最好。奥氏体化温度对所研究钢的热疲劳性能有明显的影响。随奥氏体化温度升高,钢的热疲劳性能先增加后降低,在1080℃奥氏体化时钢具有最好的热疲劳性能。4、对Nb微合金化H13钢和普通H13钢热疲劳后的表层硬度测试发现,在热疲劳过程中的表层硬度随循环次数的增加呈类震荡周期变化。在热疲劳循环起始阶段,表层硬度急剧下降,类震荡频率较快;在热疲劳后期,类震荡频率趋缓,表层硬度总体表现为循环软化特性。TEM&EDS分析显示,热疲劳初期表层硬度的急剧下降与M23C6碳化物的迅速粗化有关;而表层硬度的类震荡周期变化与位错密度的变化密切相关。5、对几种H13类钢的碳化物形态和弥散分布程度的比较分析发现,热疲劳更多还原

【Abstract】 AISIH13 hot work tool steel is widely used for hot forging, hot-extrusion and die-casting because of its high temperature strength, impact toughness, heat checking resistance and wear resistance etc. The thermally induced surface damage, i.e., thermal fatigue, is believed to be controlled by the magnitude of the imposed cyclic strain. The thermal fatigue on the surface of hot working die, which is responsible to the initiation of the cracks, is reported to result in more than 80% of the failure of dies.In this paper, aimed to suppress the crack generation and improve the heat checking resistance, niobium is added into the H13 steel. The mechanical properties, the resistance to temper softening, thermal stability, the cyclic softening and the thermal fatigue life prediction for H13 steel with and without niobium are investigated. The coarsening kinetics of M23C6 carbide in H13 steel during thermal fatigue is also studied. And the main results are summarized as follows:1. The influence of the niobium on the microstructure and the type, size and distribution of carbides in AISI H13 steel have been investigated by means of Thermo-calc software and TEM&EDS. It is shown that austenitic grains of H13 steel containing niobium are smaller than those without niobium. Experimental results indicate that the 0.07 pct niobium in H13 steel is sufficient to suppress grain growth at the austenitizing temperature up to 1120℃. After microalloyed by 0.07pct niobium, the carbides become smaller and its distribution become much more dispersive in the更多还原