A comparative evaluation of welding consumables for dissimilar welds between 316LN austenitic stainless steel and Alloy 800

Transition joints in power plants between ferritic steels and austenitic st ainless steels suffer from a mismatch in coefficients of thermal expansion (CTE) and the migration of carbon during service from the ferritic to the a ustenitic steel. To overcome these, nickel-based consumables are commonly u sed. The use of a trimetallic combination with an insert piece of intermedi ate CTE provides for a more effective lowering of thermal stresses. The cur rent work envisages a trimetallic joint involving modified 9Cr-1Mo steel an d 316LN austenitic stainless steel as the base materials and Alloy 800 as t he intermediate piece. Of the two joints involved, this paper describes the choice of welding consumables for the joint between Alloy 800 and 316LN. F our consumables were examined: 316, 16-8-2, Inconel 82 and Inconel 182. The comparative evaluation was based on hot cracking tests and estimation of m echanical properties and coefficient of thermal expansion. While 16-8-2 exh ibited highest resistance to solidification cracking, the Inconel filler ma terials also showed adequate resistance; additionally, the latter were supe rior from the mechanical property and coefficient of thermal expansion view -points. It is therefore concluded that for the joint between Alloy 800 and 316LN the Inconel filler materials offer the best compromise. (C) 2000 Pub lished by Elsevier Science B.V. All rights reserved.