MICROSTRUCTURE AND PROPERTIES OF LASER-WELDED BUTT JOINTS OF X2CRTINB18 STEEL

Abstract

The process of autogenous laser welding of stainless steel X2CrTiNb18 was investigated. The Yb:YAG disk laser was used in the study for welding of 1.5mm thick butt joins. The influence of basic laser welding parameters on the joint quality, fusion zone geometry, microhardness distribution across the butt joint, structure and microstructure of fusion zone (FZ) and heat affected zone (HAZ) was studied and determined. The quality level of the test joints was determined according to the PN-EN ISO 13919-1 standard. The chemical composition of the base metal was determined by spark emission spectroscopy. Results of the study have shown that laser welding parameters have a significant influence on the quality of butt joints. However, it is possible to produce joints that meet the high requirements and criteria of quality. The width of HAZ of the butt joints welded in the investigated range of parameters was narrow and did not exceed 0.2 mm. It was found that the most common imperfections of the analysed joints are concavity of the weld face and insufficient penetration. The HAZ region of joints is characterized by mainly ferritic microstructure with complex carbides precipitates. In turn, the fusion zone is dominated by a ferritic microstructure but also precipitates were observed, which were identified as fine dispersion carbides. Hardness of the base metal is round 160÷170HV0.3. A tendency to increase in hardness in the HAZ and FZ was observed. The maximum hardness measured in HAZ was approx. 220HV0.3, while in the FZ 190HV0.3.