Studies on Hot Cracking Susceptibility and Establishment of Welding Procedure of Austenitic Stainless Steel Grade UNS S31035 for Power Plant Application

摘要

Austenitic stainless steel Sandvik Sanicro 25 (UNS S31035) was developed in European Advanced ultra super critical boiler program called Thermie-AD700 project. Compared to all other commercial heat resistant austenitic stainless steels, Sanicro 25 has the highest creep strength. Hence, this material has been identified as one of the candidate materials in reheater and super heater lines of advanced ultra super critical boiler for up to 700 A degrees C temperature usage. In this austenitic stainless steel, along with Fe, Ni and Cr, solid solution hardening element, like W, Co & N and precipitation hardening elements like Nb and Cu are added to enhance the creep and high temperature oxidation resistance. Addition of more alloying elements and full austenitic microstructure may lead to the possibility of solidification cracking susceptibility during welding. Hence, investigation on the weldability of this material becomes inevitable to establish the welding procedure. In this paper, solidification cracking behaviour of UNS S31035 has been studied with varestraint test. From the test results, it is concluded that solidification cracking susceptibility is higher in this steel and similar composition filler cannot be used for welding. Based on this conclusion, Ni based super alloy filler ER NiCrCoMo-1 is used for establishing welding procedure in gas tungsten arc welding process. Test results are presented and discussed in this paper.