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用抛光的恒位移试样对不同钢种、不同强度的高强钢在水介质中应力腐蚀裂纹的产生和扩展进行了金相跟踪观察。结果表明:超高强钢(σ_b≥160公斤/毫米~2的30CrMnSiNi_2A,ZG-18铸钢)应力腐蚀时,裂纹前端塑性区逐渐扩大,闭合后形成不连续裂纹,以后随塑性区中变形量增大主裂纹扩展並与新裂纹相连。当强度降低时,(σ_b≤138公斤/毫米~2的30CrMnSiNi_2A,40CrNiMoA,30CrMnSiA)塑性区随时间增大,但不闭合,随其变形量增大,原裂纹沿弹塑性边界向前扩展。强度更低(σ_b<110公斤/毫米~2的30CrKnSiNi_2A,σ_b≤120公斤/毫米~2的40CrNiMoA)塑性区不增大,裂纹也不扩展。 同样试样在电解充氢条件或干氢条件下,加载裂纹前端同样能产生滞后塑性变形,而且裂纹产生和扩展的情况完全和水介质中类似。由此可知,裂纹前端滞后塑性变形是由氢引起的。 高强钢或超高强钢在水介质中应力腐蚀的机构如下:阴极放氢,它进入裂纹前端引起滞后塑性变形,从而导致裂纹的产生和扩展。
Polished constant displacement specimens were used to observe the generation and propagation of stress corrosion cracking of high strength steel with different steel grades and different strengths in aqueous media. The results show that when the stress corrosion of ultra-high strength steel (30CrMnSiNi_2A, ZG-18 cast steel with σ_b≥160kg / mm ~ 2), the plastic zone at the front of the crack gradually enlarges and forms a discontinuous crack after closure, The main crack expands and connects with the new crack. As the strength decreases, the plastic zone (30CrMnSiNi_2A, 40CrNiMoA, 30CrMnSiA) with σ_b≤138 kg / mm 2 increases with time but does not close. As the deformation increases, the original crack propagates along the elastic-plastic boundary. Lower strength (30CrKnSiNi2A with σ_b <110 kg / mm2 and 40CrNiMoA with σ_b≤120 kg / mm2) does not increase the plastic zone nor does the crack develop. The same samples in the electrolysis hydrogenation conditions or dry hydrogen conditions, loading crack front can also produce hysteresis plastic deformation, and the crack generation and expansion of the situation completely and aqueous medium similar. It can be seen that the crack front lag plastic deformation caused by hydrogen. High-strength steel or ultra-high strength steel in aqueous medium stress corrosion mechanism is as follows: the cathode discharge hydrogen, it enters the crack front caused by delayed plastic deformation, resulting in the generation and expansion of cracks.