Abstract: The elbow of a 15CrMoG steel high-pressure boiler tube cracked. The causes of elbow cracking were analyzed by means of macroscopic observation, chemical composition analysis, mechanical property test, metallographic examination, scanning electron microscope and energy spectrum analysis. The results show that the induction coil collided with the steel tube during the elbow, and some coil materials were embedded in the steel tube matrix. The temperature was high during medium frequency heating, which melted the low melting point copper-zinc alloy, resulting in the weakening of the grain boundary of the matrix structure. Under the action of tensile stress, the elbow finally cracked.