Jambor Michal, Vojtek Tomáš, Pokorný Pavel, Šmíd Miroslav
CEITEC IPM, Institute of Physics of Materials, Czech Academy of Sciences, Žižkova 22, 616 62 Brno, Czech Republic.
Institute of Physics of Materials, Czech Academy of Sciences, Žižkova 22, 616 62 Brno, Czech Republic.
Materials (Basel). 2021 Mar 10;14(6):1331. doi: 10.3390/ma14061331.
Fatigue crack propagation in near-threshold regime was studied in the 304L austenitic stainless steel in two microstructural states: as-received (AR) with finer microstructure and low susceptibility to the transformation-induced plasticity (TRIP) effect, and solution-annealed (SA) with coarser microstructure and higher susceptibility to TRIP. At the load ratio = 0.1 the threshold was higher in the SA state than in the AR state due to coarser grains and possibly the TRIP effect. In order to clarify the role of crack closure, experiments at = 0.7 were done. The threshold in the SA state was still higher by 1 MPa·m. This effect was identified as crack tip shielding induced by phase transformation, an example of a non-closure shielding effect. Higher resistance to crack growth in the SA state was attributed to promoted martensitic transformation in non-favorable oriented grain families rather than thicker martensite layers in the crack path area. The conclusions were verified by experiments at = 0.7 and temperature 150 °C > M which did not reveal any notable difference in thresholds. However, the threshold values were affected by the load-shedding gradient = -dΔK/da, which had to be equalized in both experimental setups inside and outside the furnace.
研究了304L奥氏体不锈钢在两种微观结构状态下近门槛区的疲劳裂纹扩展：一种是原始态（AR），其微观结构更细，对相变诱发塑性（TRIP）效应的敏感性较低；另一种是固溶退火态（SA），其微观结构更粗，对TRIP的敏感性较高。在载荷比R = 0.1时，由于晶粒更粗以及可能存在的TRIP效应，SA状态下的门槛值高于AR状态。为了阐明裂纹闭合的作用，进行了R = 0.7时的实验。SA状态下的门槛值仍然高出1 MPa·m。这种效应被确定为由相变引起的裂纹尖端屏蔽，这是一种非闭合屏蔽效应的例子。SA状态下对裂纹扩展的更高抗性归因于在不利取向的晶粒族中马氏体转变的促进，而不是裂纹路径区域中更厚的马氏体层。在R = 0.7和温度150 °C > M的实验验证了这些结论，这些实验没有显示出门槛值有任何显著差异。然而，门槛值受卸载梯度dK/da = -dΔK/da的影响，在炉内和炉外的两个实验装置中都必须使该梯度相等。
