Laser Beam Welding of Quenched and Tempered ASTM A 517 Gr.B Steel

Quenched and tempered steels are required to combine high yield and tensile strengths with good notch toughness, ductility and weldability. However, toughness and soundness of these steels can be affected by welding operations, in particular Heat Affected Zone (HAZ) may undergo embrittlement and cracks through the heating cycles. In this paper, a preliminary investigation is done on welds of steel ASTM A 517 Gr.B, carried out by utilizing LBW process without any filler metal. Experimental work included metallographic examination and microhardness survey. The results show the formation of a mixed bainitic-martensitic structures in the Heat Affected Zone (HAZ), due the relatively high cooling rate of the re-austenitized region close to the melted zone. If compared to Shielded Metal Arc (SMAW) process, LBW technique gives rise to an advantageous reduction of areas of both fusion and heat affected zones, less distortion and residual stresses. The measured HAZ was about 0.40 mm wide, instead of about 1.50 mm as obtained with SMAW process. In spite of higher cooling rates typical of LBW process, hardness values are of the same order as with SMAW process.