精炼12Cr钢高温低周疲劳循环特性试验研究

Experimental Research of the High Temperature Low Cycle Fatigue Characteristics of 12Cr Purified Steel

为研究高温寿命损耗过程中材料低周疲劳特性的变化规律,在540℃和593℃下对3种精炼12Cr转子钢进行总应变控制的低周疲劳试验,分析了其循环弹性模量E*、循环强度系数K和循环应变硬化指数n随循环周次变化的规律。试验结果表明:循环初始阶段(N/N f<0.1),循环弹性模量E*迅速变化,多数试样表现为下降趋势,个别试样存在硬化现象;循环稳定阶段(0.1<N/N f<0.8),E*较为稳定;循环末期(N/N f>0.8),E*急剧降低;当N/N f<0.8时,循环强度系数K和n随循环周次的变化规律均可用系数为正、指数为负的幂函数曲线拟合,寿命损耗过程中,K和n具有相似的变化趋势。同时,控制应变幅和温度对上述3个参数有重要影响。最后,分析了弹性模量劣化对寿命估算的影响,结果表明:与传统寿命估算方法相比,弹性模量修正后的寿命估算精度在较低温度下(540℃)明显提高,而在较高温度时(593℃)精度提高不明显。

To study the variation law governing the low cycle fatigue characteristics of materials in the process of high temperature life loss,at 540 ℃ and 593 ℃,a low cycle fatigue experiment was performed of three kinds of 12Cr purified rotor steel with the total strain being controlled. On this basis,the variation law of the cyclic frequency with the cyclic elastic modulus E*,cyclic strength coefficient K and cyclic strain hardening index n was analyzed. The test results show that at the initial stage of the cycling( N / N f < 0. 1),the cyclic elastic modulus E*changes rapidly and the majority of the specimens exhibits a descending tendency and individual specimens produce a hardening phenomenon. In the stable stage of the cycling( 0. 1 < N / N f < 0. 8),the cyclic elastic modulus E*shows a relatively stable state. In the last stage of cycling( N / N f > 0. 8),the cyclic elastic modulus E* declines sharply. When N / N f < 0. 8,the variation law of the cyclic strength coefficient K and cyclic strain hardening index n with the cyclic frequency can be fitted by using a power function curve with its coefficient being positive and its exponent being negative. In the process of life loss,K and n exhibit a similar variation tendency. In the meantime,to control the strain magnitude and temperature can exercise an important influence on the foregoing three parameters. Finally,the influence of the degradation of the elastic modulus on the life estimation was also analyzed. It has been found that compared with the traditional life estimation method,the life estimation precision after a correction by using the elastic modulus can be obviously enhanced at a relatively low temperature( 540 ℃) and enhanced not obviously at a relatively high temperature( 593 ℃).