Optimization of mechanical properties of rotary friction welding parameters of low alloy steel tubes using design of experiments concept

The main objective of this study is to join SA 213 T11 and SA 213 F12 low alloy steel (LAS) tubes using rotary friction welding (RFW) procedure and to optimise welding parameters (rotating speed, forging pressure and friction pressure). Response surface methodology (RSM) was used to maximise the tensile strength (TS) and fully deformed zone hardness (FDZH) of LAS joints by optimizing the RFW parameters. The mathematical models (MMs) were developed to predict TS and FDZH of LAS joints. The 3D response surfaces were generated using MMs, which show the optimum RFW model parameters for increasing the TS and FDZH of LAS joints. The direct effect of RFW parameters on performance characteristics of LAS joints was analyzed from response surfaces. The microstructural characteristics of LAS joints developed using optimized parameters were analyzed using optical microscopy. Results showed that the LAS joints developed using rotating speed (N) of 60 rps, friction pressure (FF) of 0.851 MPa/s, and forging pressure (FOF) of 0.851 MPa/s exhibited greater TS and WIH of 650 MPa and 515 HV0.5 respectively. The greater TS and FDZH of LAS joints is attributed to the evolution of widmanstatten ferrite and lower bainite structures in interface and narrower TMAZ.