某余热锅炉20钢过热管开裂原因分析

某余热锅炉20钢过热管使用不足1月即发生开裂泄漏，通过宏观分析、化学成分测试、力学性能试验、显微组织观察、微观分析和断口分析确定开裂原因。结果表明：过热管为脆性开裂，显微组织中存在沿铁素体晶界析出的三次渗碳体和弥散分布的氧化物夹杂，导致晶界脆化，材料韧性不足。经冷弯加工，弯头表面萌生裂纹。带有裂纹缺陷的过热管服役后，在炉膛高温和蒸汽内压作用下，随着时间的推移，裂纹不断扩展，造成过热管开裂泄漏。

Cause analysis on cracking of 20 steel superheater tube in waste heat boiler

Cracking and leakage of 20 steel superheat tube in a waste heat boiler occurred after service for less than one month. The reason for cracking was determined by macroscopic analysis, chemical composition test, mechanical property test, microstructure observation, microscopic analysis, and fracture analysis. The results show that the cracking of superheat tube belongs to brittle fracture. There are precipitated tertiary cementite and dispersed oxide inclusions along ferrite the grain boundaries of ferrite in microstructure, leading to grain boundary embrittlement and insufficient toughness of the material. During the process of cold bending, some cracks were initiated on the elbow surface. When the superheat tube with crack defects was used, the cracks expanded gradually with time under the action of high temperature and internal pressure of steam in the furnace, which finally resulted in cracking and leakage of the superheat tube.