Failure in Stainless Steel Welds Joining Low-Carbon Steel Handles to Type 502 Stainless Steel Covers Because of Martensite Zone in the Welds

Abstract

Handles welded to the top cover plate of a chemical-plant downcomer broke at the welds when the handles were used to lift the cover. The handles were fabricated of low-carbon steel rod; the cover was of type 502 stainless steel plate. The attachment welds were made with type 347 stainless steel filler metal to form a fillet between the handle and the cover. The structure was found to contain a zone of brittle martensite in the portion of the weld adjacent to the low-carbon steel handle; fracture had occurred in this zone. The brittle martensite layer in the weld was the result of using too large a welding rod and too much heat input, melting of the low-carbon steel handle, which diluted the austenitic stainless steel filler metal and formed martensitic steel in the weld zone. Because it was impractical to preheat and postheat the type 502 stainless steel cover plate, the low-carbon steel handle was welded to low-carbon steel plate, using low-carbon steel electrodes. This plate was then welded to the type 502 stainless steel plate with type 310 stainless steel electrodes. This design produced a large weld section over which the load was distributed.