某超临界机组二级屏式过热器异种钢焊口开裂泄漏，通过宏观观察、金相检验、硬度测试、扫描电镜分析及能谱分析等方法，对异种钢焊口开裂的原因进行了分析。结果表明：该二级屏式过热器同屏内钢管间膨胀变形不协调导致异种钢焊口发生低周疲劳开裂。在分析焊口开裂原因的基础上，提出了金属磁记忆检测焊口应力集中水平的方法，该方法可有效预防异种钢焊口开裂。

Dissimilar steel welding seam of the secondary platen superheater of a supercritical unit cracked and leaked. The cracking reasons of the dissimilar steel welding seam were analyzed by using macroscopic observation, metallographic examination, hardness test, scanning electron microscope analysis and energy spectrum analysis and so on. The results show that the disharmony between the expansion and deformation of the two platen superheater on the same screen leads to the low-cycle fatigue cracking of the dissimilar steel welding seam. On the basis of the analysis of the causes of the cracking of the welding seam, the method of measuring the stress concentration level of the metal magnetic memory was put forward, which can effectively prevent the crack of the dissimilar steel welding seam.