Investigation of hardness behavior in heat affected zone of ASTM A517 steel in single-pass and multi-pass welds

quenched and Tempered ASTM A517 steel belongs to the category of high strength steels, which has a good toughness due to the tempering heat treatment at high temperatures. During fusion welding, the thermal cycle of welding leads to severe microstructural and mechanical changes in the heat affected zone of the base metal. Theformation of an untempered hard martensitic region in the heat-affected zone is one of these changes, which reduces the toughness of this zone and also the possibility of cold hydrogen cracking. In the present study, the hardness behavior in the heat affected zone of ASTM A517 steel was investigated. Therefore single-pass and multi-pass welds with different heat inputs were fabricated. The maximum hardness in the heat affectedzone of single-pass welding specimens with different heat inputs was close to each other, which was due to the transformation of the area adjacent to the fusion boundary to an untempered martensitic structure for both specimens. In multi-pass welds, the hardness of the heat-affected area near the upper surface of the specimens was similar to that in single-pass welds, while this parameter experienced a sharp drop near the middle passes due to the tempering of these regions resulting from the heat generated in the next passes. The results showed that the presence of hard and brittle martensitic structure in the heat affected zone of this type of steel is almost inevitable and for critical applications that require high toughness, post weld heat treatment should be used.

کلیدواژه ها:

ASTM A517 steel ، Vickers Hardness ، Untempered Martensite ، Toughness ، Hardness Prediction.