STUDY OF HOT CRACKING BEHAVIOUR OF 14Cr-15Ni-2.5Mo Ti-MODIFIED FULLY AUSTENITIC STAINLESS STEELS USING VARESTRAINT AND HOT DUCTILITY TESTS

摘要

Studying the hot cracking behaviour of 14Cr-15Ni-2.5Mo Ti-modified austenitic stainless steel is an important weld-ability consideration because this material solidifies in the prior austenitic mode without any residual delta ferrite and also contains titanium. Hot cracking in this material is attributed to the formation of low melting phases in the solidifying weld metal and in the heat-affected zone that lead to cracking due to shrinkage stresses and restraint imposed on the weld joint. Different heats of this fully austenitic alloy, containing 0.022-0.025% P, 0.75-1.00% Si and 0.21-0.42% Ti, as well as 316L stainless steel (SS) were investigated. Both Varestraint and hot ductility tests were used to evaluate the hot cracking susceptibility of these alloys. Longitudinal Varestraint tests were carried out at four strain levels of 0.5, 1.0, 2.0 and 4.0%, and the brittleness temperature range (BTR) was evaluated during testing. The Varestraint test results indicated that this material has a very high hot cracking susceptibility during autogenous welding, as the total crack length and maximum crack length in both the weld and heat-affected zone as also the BTR values were very high compared to that of SS 316L. Hot ductility tests were also conducted on using a Gleeble thermo-mechanical simulator to determine the nil ductility temperature (NDT). The NDT of this material is lower than SS316L, with the material containing higher titanium and silicon. This paper discusses the results of the hot cracking behaviour of this fully austenitic SS material using the longitudinal Varestraint and hot ductility tests.