热处理和环境对GC-4钢CF及SCC裂纹扩展的影响

EFFECT OF HEAT TREATMENT ON CRACK PROPAGATING RATE OF GC-4 STEEL FROM CORROSION FATIGUE OR STRESS CORROSION IN VARIOUS MEDIA

本文对热处理制度、介质成分及 pH值三种影响因素对GC-4(40CrMnSiMoVA)钢的腐蚀疲劳(CF)裂纹扩展速率(da/dN)_(CF)与应力腐蚀开裂(SCC)裂纹扩展速率(da/dt)_(SCC)的影响进行了对比研究。结果表明,这些因素对(da/dN)_(CF) 和(da/dt)_(SCC)有着不同的影响规律.(da/dN)_(CF)和(da/dt)_(SCC)均随σ_s的提高而提高,但(da/dN)_(CF)提高的幅度远小于(da/dt)_(SCC)提高的幅度.蒸馏水中的(da/dt)_(SCC)略大于3.5％NaCl溶液中的(da/dt)_(SCC),但蒸馏水中的(da/dN)_(CF)却远小于3.5％NaCl溶液中的(da/dN)_(CF).在 3.5%NaClI溶液中,随pH值增加,(da/dN)_(CF)下降,(da/dt)_(SCC)却增加.本文分别从裂尖材料的循环软化与硬化、裂纹闭合及闭塞电池效应等方面对上述现象进行了解释。

Comparative investigations were ca1ricd cut of tLe efItct of Leat 1reatment regimes for GC--4 steel, 40CrMnSiMoVA, on its c1ack p1opagating ratcs, from corrosion fatigue, (da/dN)..' or stress cor1osion crackirg, (do/dt),.,', in mcdia with various constituents and VH va1ues. Both (da/dN).. 8'r d (do/dt),.. acce!cra1e wi1h tbe increase of yieId stress of the steel, yet the fOraner js far 1ess tLan 1Le l8tcr. ]n ccmparison with mcdia, tLe (do/dt),,. in distil1td water is sligLt1y grca1cr 1Lan tbat in 3.5% NaCl solution, and tLe (dQ/dN)., in distil1cd water is far less ttan tkat in 3.5% NaCl solution. With the pH value increasing in 3.5% NLCl ao1ution, 1le (do/dN). F lQwerS down and the (da/dt),.. specds up. An xplahation was a1Eo r1oroltd witb concept of the cyclic bardening and softeniDg at crack tip, as we1l as the crack c1osure and occluded ceU effect.