Structural steel of strength class s350…s490 and weldability

Goal. Structure and mechanical properties of the steel can vary, sometimes significantly, by thermal welding cycles. As it happens in a metal heat-affected zone of welded joints of some of the most common low-alloy and micro-alloyed structural steels of strength classes from C350 to S490, it was necessary to explore. Methods. Investigations were carried out with respect to the treated by thermal cycle of welding samples and specimens, which were made of naplavlavok on the plate. Effect of welding thermal cycles on the metal structure of the heat affected zone was studied by dilatometric studies and optical microscopy. Mechanical tests on static tensile and impact tests were carried out using standard samples: type II according to GOST 6996-66 and type IX according to GOST 9454-78. Results. It is found that the effect of the thermal cycles of the welding metal structure of the HAZ most alloy steels ranges from ferrite-pearlite to martensite-bainite and martensite. Due to this static parameters the strength and toughness of the metal grow and its plastic properties decrease. In contrast to low-alloyed steel HAZ of welded joints of most micro-alloyed steels with strength class area of the metal structure of the C350 to S490 except 09G2SYuch steel, in a wide range of cooling rates remained stable, and the mechanical properties do not change significantly. Scientific novelty. Expanded view on the influence of thermal cycles of welding on the structure and mechanical properties of the metal heat-affected zone of welds low-alloy and microalloyed structural steels. Practical significance. The research results can be used in the development of welding technology for the manufacture and repair of metal structures made from steel of strength classes from C350 to S490.