Effect of forge pressure on the microstructure and mechanical properties of high nitrogen austenitic stainless steel joints by continuous drive friction welding

The high nitrogen austenitic stainless steel joint was fabricated by continuous drive friction welding (CDFW). The aim of this work is to study the effect of forge pressure on the microstructure and mechanical properties of austenitic stainless steel joints. The microstructure, the hardness, and the tensile properties of joint were analyzed using optical microcopy, scanning electron microscopy (SEM), a computerized Buehler hardness tester and universal testing machine. The results showed that the welding process resulted in a remarkable microstructure change across the joint. The band δ-ferrites were found in the weld zone (WZ), and it decreased with increasing the forging pressures. The precipitated phase (Cr2N) was observed in the WZ and thermomechanical affected zone in the joint, and it increased with increasing the forging pressure. The lowest hardness was found in the WZ, and it didn't change significantly at various forging pressure. But the width from the WZ to the heat affected zone (HAZ) increased slightly. With the increase of the forging pressure, the strength increased, the hardening capacity and strain hardening exponent decreased. In addition, all the joints exhibited stage III and IV, unlike the base metal, only stage III appeared. All the tensile specimens failed in the weld center and the fracture surfaces was characterized by a typical dimple at different forge pressure.