应变幅对SDHC钢热机械疲劳行为及微观组织演变的影响

Effect of strain amplitude on thermo-mechanical fatigue behavior and microstructure evolution of SDHC steel

采用MTS热机械疲劳液压伺服试验机研究不同机械应变幅(0.7%,0.9%,1.1%)下SDHC(4Cr5Mo2VCo)热作模具钢的热机械疲劳行为,借助扫描电镜、透射电镜等微观检测手段探讨材料热机械疲劳过程中的微观组织演变规律。结果表明:SDHC钢热机械疲劳应力-应变滞后回线关于原点呈非对称分布,应变幅值越大,滞回环面积越大,材料受到的损伤越严重;在应力循环响应曲线中,材料受到高应变幅作用时,能量损耗增加,寿命周期变短;应变幅值增加,位错缠结减弱,偏聚的位错逐渐散开,导致位错密度下降;组织中主要存在M_(23)C_(6),M_(7)C_(3),M_(2)C和MC型(M=Cr,Mo,V,Fe等)碳化物,应变幅值较小时,碳化物的析出与长大现象更为明显。

The thermo-mechanical fatigue behavior of SDHC(4Cr5Mo2VCo)hot working die steel under different mechanical strain amplitudes(0.7%,0.9%,1.1%)was studied by MTS thermo-mechanical fatigue hydraulic servo testing machine.The microstructure evolution of the material during thermomechanical fatigue was discussed by means of scanning electron microscopy and transmission electron microscopy.The results show that the thermo-mechanical fatigue stress-strain hysteresis loop of SDHC steel is asymmetrically distributed about the origin.The larger the strain amplitude is,the larger the hysteresis loop area is,and the more serious the material is damaged.In the stress cycle response curve,when the material is subjected to high strain amplitude,the energy loss increases and the life cycle becomes shorter;as the strain amplitudes increase,the dislocation tangles weaken,and the segregated dislocations gradually disperse,resulting in a decrease in dislocation density.There are mainly M_(23)C_(6),M_(7)C_(3),M_(2)C and MC(M=Cr,Mo,V,Fe)carbides in the microstructure.When the strain amplitude is small,the precipitation and growth of carbides are more obvious.