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利用复合型(Ⅰ+Ⅲ型)试样研究了应力状态对氢致表观屈服应力(它是产生局部宏观塑性变形所需的外应力)的影响,探讨了Ⅲ型裂纹试样产生氢脆(即氢致裂纹)的可能性。结果表明,对Ⅲ型裂纹试样,即使严重充氢也不会使表观扭转屈服应力下降。从而也不会沿原裂纹面产生氢致滞后裂纹。对复合型试样,只有当K_Ⅰ本身就能使原裂纹面产生滞后塑性变形时才能使表观扭转屈服应力随K_Ⅰ增大而下降。对充氢的纯Ⅲ型裂纹试样,当扭矩大于临界值后保持一定时间就能在和原裂纹面成3/4π或-45°的面上产生氢致滞后裂纹,它导致典型的沿晶断口。如充氢试样直接扭断则得沿原裂纹面断裂的平剪切断口。当钢的强度和氢含量低于临界值就不会产生沿3/4π面的滞后裂纹。计算了Ⅲ型裂纹应力场和氢应变场的互作用能。结果表明,在和原裂纹面成3/4π的诸平面上互作用能有极小值,从而导致氢向该面浓集而形成氢致滞后裂纹。
The effect of the stress state on the hydrogen induced apparent yield stress (which is the external stress required to generate local macroscopic plastic deformation) was investigated by means of composite (type I + Ⅲ) specimens. The effects of type Ⅲ crack on hydrogen embrittlement Ie hydrogen induced cracking). The results show that for Type Ⅲ cracked specimens, the apparent torsional yield stress does not decrease even under severe hydrogen charging. Thus, hydrogen-induced hysteresis cracking does not occur along the original cracked surface. For composite samples, the apparent torsional yield stress decreases with the increase of K_Ⅰ only when K_Ⅰ itself can make the plastic deformation of the original crack surface. Hydrogen-induced pure Type III cracked specimens, when the torque is greater than the critical value for a certain period of time, can produce hydrogen-induced hysteresis cracks on the surface that is 3 / 4π or -45 ° to the original crack surface, resulting in a typical intergranular Fracture. Such as direct hydrogen charging sample is broken along the original cracked plane shear fracture. When the steel strength and hydrogen content below the critical value will not produce hysteresis along the 3 / 4π plane crack. The interaction energy between type III crack stress field and hydrogen strain field is calculated. The results show that there is a minimum value of the interaction on the plane of 3 / 4π with the original crack surface, which leads to the concentration of hydrogen to the surface to form a hydrogen induced hysteresis crack.