Studies on fracture toughness and fatigue behaviour of welded dual phase steel for structural application

Abstract

Structural and automobile industries are always in need of light weight and high strength newlinematerials. The researches focusing on the development of novel materials and novel newlineprocessing routes always gain the importance. Dual phase (DP) steels are of the recent newlinematerials which have proven their capability in automobile industry with its distinguished newlinecharacteristics in the recent years. Whereas still researches are going on to adopt DP steels newlineinto structural industry due to their various limitations. newlineIn this regard, the present research work focuses on evaluation of mechanical, fracture and newlinefatigue properties of DP steels produced by intermediate quenching (IQ) technique for both newlinebase metal and welded conditions. To obtain the Ferrite-Martensite dual phase newlinemicrostructure, a hot rolled low carbon micro alloyed steel was austenised above Ac3 newlinetemperature followed by short intercritical annealing and intermediate quenching at newlineselected intercritical temperatures 740, 760,780,800 and 820o C which lies between Ac1 newlineand Ac3 of the untreated steel. The heat treatment process was carried out using a newlinelaboratory thermocouple controlled Muffle furnace of 1200o C capacity. Thus converted newlinelow carbon steel into DP steels. The produced DP steels were examined under optical and newlinescanning electron microscopy and confirmed the presence of the desired ferrite and newlinemartensite phases in varied volume fractions. The DP steel samples were named as A740, newlineA760, A780, A800 and A820 for identification of their IQ temperature. All the mechanical newlinetesting samples were prepared according to ASTM standards and subjected to mechanical newlinetests to evaluate their hardness, tensile properties, impact strength, fracture toughness and newlinefatigue strength. Further, Butt weld joints of all the DP steels were prepared using shielded newlinemanual metal arc welding (SMAW) to evaluate the mechanical, fracture and fatigue newlineproperties of the welded DP steels using AWS prescribed standards and to compare with newlinethe base metal DP steels. newlineFrom the tests outcomes i