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利用光滑拉伸试样以及带有应力梯度的弯曲试样和预裂纹试样(Ⅰ型、Ⅲ型以及Ⅰ—Ⅲ复合型),研究了氢对产生局部宏观塑性变形所需外应力(称为表观屈服应力)的影响。结果表明,氢对低合金钢的屈服强度影响不大,但如试样中存在拉应力梯度,则当钢的强度和进入试样的氢浓度超过临界值后,氢能使表观屈服应力明显下降,这就是氢致滞后塑性变形的原因。氢致表观屈服应力的下降是由氢的扩散所控制的。它明显依赖加载速度和试验温度。但它随试验温度的变化不是单调的,在室温附近存在一个极值。对仅存在剪应力梯度的Ⅲ型裂纹试样,充氢后表观扭转屈服应力并不降低,沿原裂纹面也不产生滞后裂纹,即K_(ⅢH)=K_(ⅢC),但在和原裂纹面成-45°的平面上却能产生氢致滞后塑性变形和裂纹。对Ⅰ—Ⅲ复合型试样,只有当恒定的K_Ⅰ大到足以单独就能产生滞后塑性变形时才能使表观扭转屈服应力开始下降。提出了一个氢使表观屈服应力下降的机构。
Using the samples with smooth tensile strength and the specimens with the stress gradient and the pre-cracked specimens (type I, type III and type I-III complex), the external stress of hydrogen on the local macroscopic plastic deformation Apparent yield stress). The results show that hydrogen has little effect on the yield strength of low-alloy steels. However, if there is tensile stress gradient in the sample, the apparent yield stress of hydrogen can be obviously enhanced when the strength of steel and the hydrogen concentration of sample entering exceed the critical value Drop, which is the reason that hydrogen causes hysteresis plastic deformation. Hydrogen induced degradation of apparent yield stress is controlled by the diffusion of hydrogen. It obviously depends on the loading speed and the test temperature. But it is not monotonous with the change of test temperature, and there is an extreme value near room temperature. For Type III cracked specimens with shear stress gradient only, the apparent torsional yield stress did not decrease after hydrogen charging, and no hysteresis crack was produced along the original cracked surface, ie K Ⅲ H = K Ⅲ C, Cracked surface into a -45 ° plane can produce hydrogen induced hysteresis plastic deformation and cracks. For I-III composite samples, the apparent torsional yield stress begins to decline only when constant K_I is large enough to produce hysteresis plastic deformation alone. A mechanism has been proposed to reduce the apparent yield stress of hydrogen.