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High-Temperature Crack Tip Deformation and Crack Propagation in Heat-Resistant Steels

耐热钢的高温裂纹尖端变形和裂纹扩展

基本信息

批准号：
62550515
负责人：
HASEGAWA Tadashi
金额：
$ 1.02万
依托单位：
Tokyo University of Agriculture and Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1987
资助国家：
日本
起止时间：
1987 至 1988
项目状态：
已结题

项目摘要

Behavior of crack propagation and local deformation near the crack tip during high-temperature straining (T=923K, =-5x10^<-6>/s) was examined in three types of heat-resistant steel ( 316H austenitic steel, 9Cr-lMo martensitic steel and 2(1/4)Cr-lMo ferritic steel), in order to make clear the mechanism of creep crack propagation. Main results and conclusions are summarized as follows: (1) The rate of crack propagation and frequency of cavitation near the crack tip decreases in the order of austenititic steel, martensitic steel and ferritic steel, though the crack tip opening becomes larger in this order. (2) Even in the austenitic steel which exhibits typical intergranular crack growth with grain-boundary cavitation and is brittle macroscopically, the degree of stress concentration at the crack tip is quite small (1.2-1.3), indicating that a stress concentration at the crack tip is relaxed extensively by local plastic deformation near the crack tip. (3) With increasing degree of biaxial tensile state of stress, the crack propagation rate increases, being accompanied by an increase in the degree of stress concentration and the frequency of cavitation and also by decrease in the size of crack tip area where work-hardening and cavitation are concentrated. (4) The results (1)-(3) indicate that crack propagation depends on the establishment of critical states of both work-hardening and cavitation in crack tip area. Crack propagation rate in a material, which exhibits work-softening during deformation, is very low.

研究了三种耐热钢(316H奥氏体钢、9Cr-lMo马氏体钢和2(1/4)Cr-lMo铁素体钢)在高温应变(T=923K,=-5x10^<-6>/s)过程中裂纹扩展和裂纹尖端附近的局部变形行为，以明确蠕变裂纹扩展的机理。主要结果和结论如下： (1)裂纹扩展速率和裂纹尖端附近的空化频率按照奥氏体钢、马氏体钢和铁素体钢的顺序减小，但裂纹尖端开口逐渐增大。 (2)即使是具有晶界空化的典型沿晶裂纹扩展且宏观脆性的奥氏体钢，裂纹尖端的应力集中程度也相当小(1.2-1.3)，这表明裂纹尖端的应力集中通过裂纹尖端附近的局部塑性变形得到了广泛的松弛。 (3) 随着双轴拉伸应力状态程度的增加，裂纹扩展速率增大，应力集中程度和空化频率增加，加工硬化和空化集中的裂纹尖端区域尺寸减小。 (4) 结果(1)-(3)表明裂纹扩展取决于裂纹尖端区域加工硬化和空化临界状态的建立。在变形过程中表现出加工软化的材料中的裂纹扩展速率非常低。