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用抛光的恒位移试样对不同强度(σ_b=900—1800MPa)的四种低合金钢在各种致氢环境(电解充氢、氢气、H_2S气体、水介质、H_2S水溶液、缓蚀剂水溶液、丙酮、酒精等有机溶液)下跟踪观察了氢致裂纹的产生和扩展过程.与此同时也测量了在这些致氢环境中的K_(ISCC)(或K_(IH))和da/dt,并研究了它们随强度变化的规律。结果表明,当加载裂纹前端的K_I>K_(ISCC)(K_(IH))后,在上面所说的任何一种致氢环境都能产生氢致滞后塑性变形,并由此导致裂纹的产生和扩展。即随着氢的扩散进入,原裂纹前端塑性区及其变形量逐渐增大。对超高强度钢,在滞后塑性区端点形成不连续的氢致裂纹,它们随滞后塑性变形的发展逐渐长大以致互相连接。当强度降低时,氢致裂纹沿滞后塑性区边界连续地向前扩展。这就表明,在Ⅰ型裂纹条件下,氢致滞后塑性是产生氢致滞后裂纹的必要和充分条件。在所有的致氢环境中,止裂的K_(ISCC)(K_(IH))均随钢的强度下降而升高,da/dt均随钢的强度下降而降低。强度相同时,水中加缓蚀剂和阳极极化使K_(ISCC)升高,da/dt下降,与此相反,阴极极化使K_(ISCC)下降,da/dt升高。而在饱和H_2S溶液以及加载下电解充氢时K_(ISCC)(K_(IH))最低,da/dt最高。实验也表明,在电解充氢条件下还能以另一种机构形成裂纹。它们的产生和展不依赖外载荷,且不伴随有宏观塑性变形,因此,是通过氢压机构形成和扩展的。
Four kinds of low alloyed steels with different strength (σ_b = 900-1800MPa) were treated with polishing constant displacement specimen in a variety of hydrogen-evolving environments (Electrolytic hydrogen charging, hydrogen gas, H 2 S gas, aqueous medium, H 2 S aqueous solution, Acetone, alcohol and other organic solvents), the formation and propagation of hydrogen induced cracks were observed and K_ (ISCC) (or K_ (IH)) and da / dt were also measured in these hydrogen- The law of their changes with the intensity was studied. The results show that hydrogen induced hysteresis plastic deformation can be produced in any of the hydrogen-generating environments mentioned above after K_I> K_ (ISCC) (K_ (IH)) at the tip of the crack is loaded, Expand. That is to say, as the diffusion of hydrogen enters, the plastic zone at the front of the original crack and its deformation gradually increase. For ultra-high strength steels, discontinuous hydrogen-induced cracks are formed at the end of the hysteresis plastic zone. They gradually grow up with the development of the plastic deformation of the hysteresis and thus connect with each other. As the strength decreases, the hydrogen-induced crack propagates continuously along the boundary of the hysteretic plastic zone. This shows that hydrogen-induced hysteresis plasticity is the necessary and sufficient condition to produce hydrogen-induced hysteresis cracks under type I crack conditions. In all hydrogen-producing environments, the cracked K_ (ISCC) (K_ (IH)) increases with the decrease of steel strength, and da / dt decreases with the decrease of steel strength. At the same intensity, K_ (ISCC) increased and da / dt decreased with the addition of corrosion inhibitor and anodic polarization in water. In contrast, cathodic polarization decreased K_ (ISCC) and da / dt increased. However, the K_ (ISCC) (K_ (IH)) was the lowest and the da / dt was the highest under the saturated H_2S solution and under the charge. Experiments also show that cracks can be formed by another mechanism under the condition of electrolysis and hydrogen charging. Their production and development do not rely on external loads, and are not accompanied by macroscopic plastic deformation, therefore, is formed and expanded by the hydrogen pressure mechanism.