304酸洗板表面发黑原因分析

对304酸洗板表面发黑现象进行了研究，通过金相组织分析发现夹杂物以A、C类夹杂物为主.经退火、酸洗后发黑的304板出现严重的晶间腐蚀现象.固溶处理和酸洗实验后，组织内铁素体数量明显减少，晶界上几乎没有碳化物析出，且经固溶处理后的酸洗板板面较白.分析认为304酸洗板表面发黑的主要原因是：退火不当，在晶界上富集大量的碳化物，使材料处于严重的敏化状态，导致酸洗时出现了板面晶间腐蚀，进而造成酸洗板表面发黑.

Analysis of causes for surface tarnishing of 304 pickling plate

The surface tarnishing phenomenon was analyzed. The main inclusions are type A and type C determined by metallographic analysis. Serious intergranular corrosion was found in surface tarnishing 304 plate after annealing and pickling. After solution treatment and pickling test,the amount of ferrite decreases significantly,little carbide precipitation happens,and surface tarnishing phenomenon decreases. The result shows that the improper annealing results in carbide enrichment on the grain boundary and sensitization of material,which lead to intergranular corrosion when pickling,and then surface tarnishing of 304 pickling plate.