Non-destructive Characterization of Dissimilar Friction Stir Welded Plate of AISI 304 and AISI 409 M Stainless Steel
摘要
Welding of dissimilar metals is a challenging task with conventional methods, while Friction Stir Welding (FSW) offers a superior weld joint with high quality. In this study, two different grades of stainless steel, i.e., AISI304 (austenitic) and AISI409M (ferritic), were welded using a 3-tonne CNC-controlled FSW machine using a tungsten carbide tool at a rotation and travel speed of 650 rpm and 100 mm/min. However, little work has addressed non-destructive magnetic evaluation of such welds. The welded region is characterized with non-destructive evaluation using Barkhausen noise (BN) analysis and magnetic hysteresis loop (HL) measurements, correlated with microstructure, microhardness, and phase distribution in the weld and base region of both grades. The BN peak and RMS values for AISI409M increased from 1.431 mV/0.162 mV at 13 Hz to 2.075 mV/0.256 mV at 52 Hz, driven by its ferrite content and grain coarsening that facilitate domain wall movement. Conversely, AISI304 remained below 0.063 mV/0.009 mV, reflecting its non-magnetic austenitic matrix. The weld region shows intermediate values (0.58 mV/0.061 mV to 0.78 mV/0.098 mV), due to grain refinement, phase distribution, and mixing, which introduce additional domain wall pinning sites. HL analysis at MF = 0.05 Hz and MFI = 620 Oe revealed average permeability declining from ~ 25 × 103 (AISI409M) to ~ 0.5 × 103 (AISI304), with the weld at ~ 9 × 103; coercivity rose from ~ 70 Oe to ~ 110 Oe in (AISI409M) and from ~ 40 Oe to ~ 80 Oe in the weld due to eddy current damping and increased domain wall pinning at phase boundaries; remanence followed a similar trend. Microhardness peaked in the stir zone (~336 HV), exceeding both base metals (AISI409M: ~ 168 HV; AISI304: ~ 248 HV) due to dynamic recrystallization. XRD confirmed α ferrite in AISI409M and γ austenite in AISI304 and bimodal phases in the stir zone.