本文研究铁素体-马氏体复相钢中铁素体含量对裂纹萌生、扩展和裂纹尖端塑性变形的影响。在24.2—41.5％的铁素体含量范围内,以33.8％含量的复相钢裂纹萌生期N_0较长、门槛值ΔK_(th)高、并有低的扩展速率和较高的闭合应力强度因子K_(Cl)。 三种铁素体含量复相钢的dα/dN-ΔK_(eff)一致的事实,表明裂纹闭合对低速扩展的重要作用,且闭合程度(K_(Cl)/K_(max))随裂纹尖端ΔK的降低而提高,在ΔK_(th)时达到最大。铁素体含量为33.8％的K_(Cl)/K_(max)值最高达0.7。
The effect of ferrite content in ferrite-martensite dual-phase steel onthe initiation and propagation of fatigue crack and the plastic deformation at cracktip has been studied. In a range of ferrite content from 24.2 to 41.5%, the opti-mum seems to be 33.8%, of which the crack initiation will be prolonged, the thre-shold value increased, the propagation rate decreased and the closure stress intensityfactor increased. As the propagation force is described by effective stress intensityfactor, three steels with various ferrite contents will show the same propagationbehaviour on da/dN vs △K_(off) curve. It is shown that the closure effect increaseswith the decrease in △K at the fatigue crack tip. When △K equals to △K_(th), theclosure effect reaches a maximum value of 0.7 in a dual-phase steel with 33.8%ferrite.
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