Crack growth study of dissimilar steels (Stainless - Structural) butt-welded unions under cyclic loads

Abstract

The research shows the study of the mechanisms of emergence and propagation of fatigue cracks caused by mechanical tension stress fluctuations in dissimilar steels butt-welded joints; structural steel ASTM A537 (I), austenitic stainless steel ASTM A240 (304L), through GMAW with argon as protecting gas and ASTM A240 (E308L) as supplier material, without pre and post welding thermal treatment. Samples were evaluated through optical and scanning electron microscopy and inspected by not destructive test with penetrating liquids and ultrasound, to discard surface and internal defects. The following mechanical tests were completed; Vickers microhardness profile, tension, impact Charpy, bending guided, axial fatigue, and speed of propagation of fatigue cracks. The phenomenon of initiation and crack growth was characterized from pre-cracked specimens, using the curve of the crack size vs. the number of fatigue cycles, and the curve of crack growth rate, vs. the variation of stress intensity factor. Results showed a proper mechanical steel behavior under cyclic loads, in spite of showed high values of microhardness, mainly in the fusion line between the welding and 304L stainless steel, as well inclusions between the structural and the stainless one. Pre-cracked test evidence a faster growth of crack in the fusion line between structural steel and stainless steel.