Effect of Ferritic Morphology on Yield Strength of CGHAZ in a Low Carbon Mo-V-N-Ti-B Steel

Abstract

For investigating the impact of ferritic morphology on yield strength (YS) of the high-heat-input welding induced coarse-grained heat-affected zone (CGHAZ) of a low carbon Mo-V-N-Ti-B steel, a group of particular welding heat inputs were designed to obtain different ferritic microstructures in CGHAZ. The tensile properties were estimated from typical samples with ferritic microstructures. The mixed microstructures dominated by the intragranular polygonal ferrite (IGPF), the intragranular acicular ferrite (IGAF), and the granular bainite (GB) were obtained at the heat inputs of 35, 65, 85 and 120 kJ/cm, respectively. When the main microstructure changed from IGPF to IGAF and GB, YS increased first and then decreased. The microstructure consisting mainly of IGAF possessed the maximum YS. As the main microstructure changed from IGPF to IGAF and GB, the contribution of grain refinement strengthening to YS was estimated to be elevated remarkably. This means the strength of CGHAZ in a low-carbon steel subjected to the high-heat-input welding could be enhanced by promoting the fine-grained AF and GB formation.

Enhanced Strength-Ductility Synergy of Bimetallic Laminated Steel Structure of 304 Stainless Steel and Low-Carbon Steel Fabricated by Wire and Arc Additive Manufacturing

“…The inverse pole figure (IPF) in Fig. 3b also verifies that in the LCS layer, there are fine grains distributed between the coarse grains, mainly at the coarse grain boundaries [25]. Grain orientations are randomly distributed, with no obvious preferred orientation or strong texture.…”

“…Even within the same layer, the distribution of alloying elements is not completely uniform, such as the presence of an inhomogeneous distribution of fine grains near the grain boundaries in the LCS layer (Fig. 3b), which is closely related to the elemental diffusion [25].…”

Effect of Heat Input on Microstructure and Tensile Properties in Simulated CGHAZ of a V-Ti-N Microalloyed Weathering Steel

“…while the dislocation density decreases (Figures 4 and 5), resulting in a monotonic decrease in YS of CGHAZ. Typically, the LAGBs defined by MTAs ranging from 2° to 15° have the most effective contribution to boundary strengthening [22], the HAGBs (θ ≥ 15°) have the most significant contribution to blocking crack propagation [21,46], and the remaining boundaries (θ < 2°) contribute to dislocation strengthening [47]. YS and grain size can be described by the Hall-Petch equation, as shown in Equation (4).…”

“…Shi et al [21] also obtained similar research conclusions: as the time of T 8/5 is increased from 45 s to 285 s, the CGHAZ toughness of V-Ti-N microalloyed steel significantly improved; however, the YS of CGHAZ decreased from 385 MPa to 335 MPa due to the formation of a large amount of intragranular polygon ferrite (IGPF) with the extension of T 8/5 . Moreover, Wang et al [22] investigated the CGHAZ tensile properties of V-Ti-N microalloyed steel containing 0.28 wt % Mo under varied E j , during the process of increasing E j from 35 kJ/cm to 65 kJ/cm and 120 kJ/cm; the YS of CGHAZ showed a trend of first increasing from 545 MPa to 610 MPa, and then decreasing to 394 MPa, respectively, the main reason being that the CGHAZ main microstructure transformed from GBF to IGAF and IGPF, respectively.…”

Influence of Heat Input on the Microstructure and Impact Toughness in Weld Metal by High-Efficiency Submerged Arc Welding

“…As the E j increased, phase transition temperatures (Ar3) increased, and the C atoms diffused more fully, leading to a significant increase in the PF content. At the same time, the various microstructures also underwent significant coarsening with sufficient diffusion of C atoms [37]. The microstructure of AF is small, and AF has a precise interlocking structure, forming HAGBs between each other.…”