18—8钢制换热器U形管失效分析

Analysis on the Failure of the 18-8 Steel Heat Enchanger with U-Shaped Pipes

通过宏观与微观测定分析，提出临氢环境下１８—８钢制Ｕ形换热器Ｕ形区局部开裂失效的根本原因如下：粗糙的冷加工产生过大的残余应力，从而使钝化膜严重损伤，材料表面活性增大，硫腐蚀加速；使表面吸附环境中的Ｃｌ－量增大，氯腐蚀加速；冷加工和氢渗入量增大，使马氏体相变倾向增强，马氏体相变量增大．综上所述，在给定的工况介质中腐蚀被加速，脆性迅速增大，过早地发生开裂失效．

By the analysis of macroscopic and microscopic detection the paper put forword the basic reasons that U model heat enchanger of 18-8 steel has presented cracks at U area under hydroforming environment as follows: rough cold machining may produces residual over stress that causes serious damage of the inactivation film, aggravated surface activity of the materials, and the speed-up of the sulphur corrosion. Because rough surface could result in the increase of great amount of Cl- in the surface adsorb environment, it may speed up chlorine corrosion, cold machining and great hydrogen doping could reinforce the tendency of martensitive transformation and the value of phase transformation.As stated above, due to the speed up corrosion in the given performance medium, the brittleness increases rapidly resulting in too early crack failure.