0Cr18Ni9不锈钢的高温疲劳裂纹扩展规律

研究奥氏体不锈钢0Cr18Ni9在高温(550℃)下的疲劳裂纹扩展规律。测试采用标准CT(compact tension)试样,最大载荷范围为6.5 kN～14 kN,应力比为0.1(室温)和0.05(550℃)。裂纹扩展过程通过QUESTAR长焦距显微镜直接观测,同时采用COD(crack opening displacement)规记录加载线位移。由于在高温条件下,测试终止时试样的裂纹前缘呈明显弧形,故此给出实测表面处裂纹长度有效值的修正方法。对高温疲劳裂纹扩展问题,采用应力强度因子范围ΔK作为裂纹扩展驱动力参数,同时考虑高ΔK和低ΔK值对裂纹扩展规律的影响,得到0Cr18Ni9不锈钢在550℃下的疲劳裂纹扩展规律表征模型,给出裂纹扩展率的上限结果。

FATIGUE CRACK GROWTH BEHAVIOR OF 0Cr18Ni9 STAINLESS STEEL AT HIGH TEMPERATURES

For austenitic stainless steel 0Cr18Ni9,fatigue crack grow law are studied at 550 ℃.The crack growth tests adopt the standard compact tension(CT) specimens.The applied maximum loads are from 6.5 kN to 14 kN and the stress ratios are 0.1(at room temperature) and 0.05(at 550 ℃).The crack growth length is directly measured by QUESTAR long focus microscope system and the load-line displacement is simultaneously recorded by using crack opening displacement(COD) gauge.Because of the good ductility of 0Cr18Ni9 at high temperatures,the crack front curves on fracture surface of the specimens are complex.In order to get an effective crack size,a modified method for crack length inspected on the surface is proposed.The stress intensity factor range ΔK is used as the driving force parameter of fatigue crack growth.Considering the high ΔK and the low ΔK effects on the fatigue crack growth law,the fatigue crack growth law is obtained for stainless steel 0Cr18Ni9 at room and high temperatures and the upper bound to the crack growth rate is given.