Study on the Hot Ductility of High Nb and Ti Micro-alloyed Steel
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摘要: 采用光学显微镜、扫描电镜、透射电镜以及显微硬度仪对高Nb、Ti微合金钢的高温热塑性拉伸试样进行检测。结果显示，高Nb、Ti微合金钢在600~1 200℃的断面收缩率呈“V”形；在800℃时断面收缩率最小，在1 200℃断面收缩率达到最大值。其第Ⅲ脆性区间为680~910℃，脆化的主要原因是大尺寸碳氮化物和先共析铁素体在晶界析出，弱化了晶界结合力，为裂纹的产生和扩展提供了条件。而试样中普遍存在的微米级TiN颗粒，是造成高Nb、Ti微合金钢断面收缩率整体偏低的主要原因。提高应变速率，缩短先共析铁素体析出和TiN颗粒长大的时间，减弱拉伸过程中的应力集中，可改善试样在第Ⅲ脆性区间的高温热塑性。
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关键词:
- 高Nb、Ti微合金钢 /
- 高温热塑性 /
- 碳氮化物 /
- 先共析铁素体 /
- 应变速率
Abstract: The hot ductility of high Nb and Ti micro-alloyed steel had been investigated through the high temperature tensile test and optical microscopy,scanning electron microscopy,transmission electron microscopy and micro-hardness tester.The results show that the relationship between the rate of reduction in area and the temperature range from 600~1 200℃ was V-shape for the high Nb and Ti micro-alloyed steel.The rate of reduction in area was the lowest at 800℃ while that was the highest at 1 200℃.The third brittle zone for the high Nb and Ti micro-alloyed steel was 680~910℃.The main reason for the embrittlement was the large-size carbonitrides and pro-eutectoid ferrite precipitated at the grain boundaries which weakened the grain boundary bonding force and provided conditions for crack generation and expansion.The micron-sized TiN particles in the sample were the main reason for the low rate of reduction in area of the high Nb and Ti micro-alloyed steel.The hot ductility at the third brittle zone can be improved by increasing the strain rate,shortening the time for the precipitation of pro-eutectoid ferrite and the growth of TiN particles and weakening the stress concentration during the tensile test. -
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