Enhancing the mechanical properties of the near-weld zone of a 09G2S steel welded joint during friction stir processing

The paper proves the effectiveness of the friction stir processing of the near-weld zone in a 09G2S steel welded joint by a carbide tool with a spherical tip having a radius of 10 mm, a normal force of 3000 N, a rotation speed of 2500 rpm, and feeds of 50, 75, and 100 mm/min. During processing, the mixed structure of the upper bainite, Widmanstӓtten ferrite, and ferrite grains changes to a globular ferrite-pearlite structure when the grains are refined in the stir zone up to 96%. The practical application of friction stir processing by a tool with a spherical tip for the hardening of the near-weld zone of the 09G2S steel welded joint is demonstrated. As a result of the processing, the yield strength and the ultimate strength increased by 15.5% and 23.3%, respectively, the specific elongation increased by 78.6%, and the maximum recorded average increase in microhardness was 171%.