Investigation On Solidification Cracking Susceptibility Of 690 Nickel-based Welding Strip Surfacing Metal

These perieds, as the newest stress-corrosion-resistance material, 690 nickel-based alloy has been more and more used in pressurized water reactor (PWR) nuclear plant. However, as to China, the 690 alloy welding strips used in the corrosion-resistance layer of tube sheet in steam generator are mainly from abroad, the homemade products of which are in urgent need. Solidification cracking is a frequent and serious welding defect during 690 alloy electro-slag surfacing process.In order to solve the solidification cracking problem, trans-varestraint test was applied to 690 alloy welding strip surfacing metal. Solidification cracking susceptibility of different alloy system was compared, and then the effects of Nb and Mn on the solidification cracking susceptibility were investigated. Analytic methods including optical microscope metallography analysis, SEM fracture analysis and TEM metallography analysis were applied to investigate the mechanism and influencing factors of solidification cracking in 690 alloy surfacing metal. The main results are as follows:As to the 690 alloy surfacing metal researched in this thesis, the solidification cracking resistance of Mn&Nb alloy system is better than that of Al&Ti alloy system. When the content of Nb increases, the quantity of low-melting-point eutectic precipitates increases, and the degree of compositional supercooling of welding metal increases, which increases the austenite grain size. As a result, the solidification cracking susceptibility increases. When the content of Mn increases, The adverse effects of Nb, S and O are restrained to some extent by Mn. Thus, the formation tendency of low-melting-point eutectic precipitates decreases. Therefore, the solidification cracking susceptibility decreases. The solidification cracking of 690...