【摘要】 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。更多还原

【Abstract】 The effect of the stress state on the apparent yield stress, which is the external stress required to cause the local macroscopic plastic deformaton, is investigated with combined type（Ⅰ+Ⅲ）specimen. The possibility of hydrogen embrittlement, i. e. hydrogen induced cracking of the type Ⅲ specimen is investigated. The results show that the apparent torsional yield stress of the severely charged type Ⅲ specimens does not decrease, and then the hydrogen induced delayed crackingand fracture cannot occur on the original crack plane. For combined type （Ⅰ+Ⅲ）specimen, the apparent torsional yield stress can be decreased only when K₁ is so large that hydrogen induced delayed plastic deformation can occur under the action of K₁ itself. For the charged type Ⅲ crack or notch specimen, the hydrogen induced delayed cracking can occur on the plane inclined at an angle of 135°（or -45°） to the original crack plane when a large enough torque is sustained for a long time. This delayed failure is a typical intergranular fracture. The plane shear fracture can be obtained on the original crack if the charged type Ⅲ specimen is twisted to fracture immediately. For uncharged or outgassing type Ⅲ specimen, no delayed cracking and failure occurs even if a maximum torque is sustained for a long time. The interactive energy between the stress field of type Ⅲ crack and the strain field of hydrogen atom is calculated. The result shows that the interactive energy has a minimum value on the plane inclined at an angle of 135° （or-45°） to the original crack plane. Therefore, atomic hydrogen will diffuse to and enrich into these planes. The hydrogen induced delayed cracking and fracture will occur on the plane inclined at an angle of 135° to the original crack plane when the hydrogen concentration on the plane reaches a critical value.更多还原