Study of the mechanical properties and the microstructure of welded joints made of structural high-strength steels S690QL of Russian and foreign origin

Steel S690QL is designed for welded heavy-loaded structures: lifting booms, traverses, trailers of heavy trucks, etc. We present the results of studying the mechanical properties and the microstructure of S690QL steel manufactured both in Russia and abroad, as well as the viscous properties of welded samples at different temperatures. The methods of atomic emission spectroscopy, tensile and impact strength tests, and microstructural analysis were used. Hardness was determined by the Vickers method. It is shown that the chemical composition of both grades of steel is almost identical. The values of the impact strength of samples made of domestic S690QL exceed those of foreign ones. This is especially true for metal that has not been subjected to welding processes (the impact strength for Russian steel S690QL in this zone was 200 J/cm 2 at –40°C, which exceeds the impact strength for foreign analogs in the same zone by almost 80%). The temperatures of brittle-viscous transition (BVT) for zones of welded joints made of Russian steel S690QL were determined. In the areas of welded metal deposit and heat affected zones the BVT temperature was –40°C. The microstructures of both steels are similar in all areas of the weld seam of control welded joints. The hardness in the studied samples of welded joints has similar values and similar changes in the zones of welded joints. The results obtained can be used in mechanical engineering for certification and design of welded structures, primarily for the Arctic zone.