冷加工对304不锈钢孔蚀敏感性的影响

EFFECT OF COLD WORKING ON PITTING SUSCEPTIBILITY OF 304 STAINLESS STEEL

对 30 4不锈钢设备由于冷加工产生的马氏体相变进行现场测试 .结果表明 ,室温下经不同方式、不同程度冷加工后 ,相关部位的马氏体相变量约在 0 5 %～ 10 % .用电化学动电位极化法、恒电流电位—时间曲线测定法和模拟闭塞电池法研究经 70℃不同程度拉伸变形的 30 4不锈钢在 3 5 %NaCl水溶液 (5 0℃± 1℃ )中的孔蚀击穿电位(Eb)、稳态孔蚀成核电位 (Enp)和自腐蚀电位 (Ecorr)与马氏体相变量的关系 .在马氏体含量为 0 1% (材料未经冷变形 )至 11 5 % (材料冷拉伸形变量为 10 % )范围内 ,随马氏体含量增大 ,Eb、Enp、Ecorr值变负 (马氏体含量为 5 %时最负 ) ,闭塞区内pH值降低 ,阳极腐蚀电流密度变大 ,表明冷加工变形不仅诱发 30 4不锈钢孔蚀 。

Cold working induced martensite content on type 304 stainless steel equipment was examined on-site.With different modes and different degree of cold working at room temperature,the martensite content was about 0.5%～10%.By potentiodynamic polarization,galvanostatic polarization and simulated occluded corrosion cell methods,the relationship between pitting potential(E b),pitting initiation potential(E np),corrosion potential(E corr) and martensite content on 304 stainless steel which had been prepared by low temperature(-70℃) tensile deformation was investigated in 3.5%NaCl solution.Experimental result showed that when the martensite content was between 0.1%(the material without low temperature tensile deformation) and 11.5%(the material with 10% low temperature tensile deformation),with the increasing of martensite content the potential of E b,E np and E corr changed negative(when then martensite content is 5%,the potentials were the most negative),the pH value in occluded cell dropped and the current density increased.It meant that cold working not only accelerated pitting initiation,but also accelerated pitting propagation of 304 stainless steel.