Microelectrochemical Aspects of Interstitial Carbon in Type 304 Stainless Steel: Improving Pitting Resistance at MnS Inclusion
Microelectrochemical Aspects of Interstitial Carbon in Type 304 Stainless Steel: Improving Pitting Resistance at MnS Inclusion
复制标题
DOI：
10.1149/2.0851506jes
复制
发表时间：
2015
影响因子：
3.9
通讯作者：
A. Chiba;S. Shibukawa;I. Muto;T. Doi;K. Kawano;Y. Sugawara;N. Hara
中科院分区：
文献类型：
--
作者：
A. Chiba;S. Shibukawa;I. Muto;T. Doi;K. Kawano;Y. Sugawara;N. Hara
对304型不锈钢进行低温渗碳处理，以在其表面添加过量的间隙碳。渗碳层中的平均碳浓度约为100%。2.6质量%，并且晶格参数扩展了ca. 2.5%，无任何碳化物沉淀。在0.1M NaCl中，渗碳不锈钢上没有产生点蚀。微观极化测量的一个小区域的MnS夹杂物进行在NaCl和Na 2SO 4溶液中，以澄清提高抗点蚀的机制。在0.1 M NaCl和0.1 M Na 2SO 4中的阳极极化表明，渗碳处理对MnS夹杂物的电化学溶解行为影响很小或没有影响。然而，从模拟含氯化物环境中溶解的MnS夹杂物附近的溶液中钢的阳极极化可以看出，渗碳处理将钢基体的主动溶解速率抑制到百分之一左右。看起来间隙碳抑制钢的溶解速率，导致MnS/钢边界处沟槽的溶解深度减小。这是可能的，渗碳导致的抑制由于Cr 3+的水解反应的酸化和由于在沟槽中的IR下降的电位降低的程度，沟槽内的腐蚀性是不足以从被动到主动状态的局部过渡。因此，在含氯化物的环境中，渗碳不锈钢上的MnS夹杂物不会发生点蚀。
Type 304 stainless steel was subjected to low-temperature carburizing treatment to add excess interstitial carbon to its surface. The average carbon concentration in the carburized layer was ca. 2.6 mass%, and the lattice parameter was expanded by ca. 2.5% without any carbide precipitation. No pitting was initiated on the carburized stainless steel in 0.1 M NaCl. Microscopic polarization measurements of a small area with a MnS inclusion were performed in NaCl and Na2SO4 solutions to clarify the mechanism of the improved resistance against pitting corrosion. The anodic polarization in 0.1 M NaCl and 0.1 M Na2SO4 demonstrated that the carburizing treatment has little or no effect on the electrochemical dissolution behavior of the MnS inclusions. However, from the anodic polarization of the steel in the solution that simulates the vicinity of the dissolved MnS inclusions in chloride-containing environments, it was clarified that the carburizing treatment inhibits the active dissolution rate of the steel matrix to about one hundredth. It would appear that interstitial carbon inhibits the dissolution rate of the steel, resulting in a reduction in the dissolution depth of the trenches at the MnS/steel boundaries. It is likely that the carburization resulted in a suppression of both the acidification due to the hydrolysis reaction of Cr 3+ and the potential decrease due to IR-drop in the trenches to the extent that the corrosivity inside the trenches is insufficient for the localized transition from the passive to active state. Therefore, pit initiation does not occur at the MnS inclusions on the carburized stainless steel in chloride-containing environments.