Showing papers by "S. Sankaran published in 2003"
25 Mar 2003-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, a multiphase microstructure was developed in a V-bearing medium carbon microalloyed steel using a two-step cooling and annealing (TSCA) treatment following finish forging.
Abstract: In an attempt to improve fatigue and fracture resistance, a multiphase (ferrite–bainite–martensite) microstructure was developed in a V-bearing medium carbon microalloyed steel using a two-step cooling and annealing (TSCA) treatment following finish forging. The monotonic, cyclic stress–strain and low cycle fatigue behavior of this steel are reported. These results are compared with those of ferrite–pearlite and tempered martensite microstructures obtained by air cooling (AC) and quenching and tempering (Q&T), respectively. The tensile properties of the multiphase microstructure are superior to those of the ferrite–pearlite and the Q&T microstructures. Under cyclic loading, the ferrite–pearlite microstructure showed hardening at higher total strain amplitudes (≥0.7%) and softening at lower total strain amplitudes (<0.7%). The quenched and tempered and the ferrite–bainite–martensite (TSCA) microstructures displayed cyclic softening at all total strain amplitudes employed. Despite the cyclic softening, the ferrite–bainite–martensite structure was cyclically stronger than the ferrite–pearlite and the Q&T microstructures. Bilinearity in the Coffin–Manson plots was observed in Q&T and the multiphase TSCA conditions. An analysis of fracture surface provided evidence for predominantly ductile crack growth (microvoid coalescence and growth) in the ferrite–pearlite microstructure and mixed mode (ductile and brittle) crack growth in Q&T and the multiphase TSCA microstructures.
77 citations
05 Dec 2003-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, a mutiphase microstructure was developed in a V-bearing medium carbon microalloyed (MA) steel through a two-step cooling process that was followed by an annealing treatment.
Abstract: To improve toughness and fatigue strength, a mutiphase (ferrite (F)–bainite (B)–martensite (M)) microstructure was developed in a V-bearing medium carbon microalloyed (MA) steel through a two-step cooling process that was followed by an annealing (two-step cooling and annealing (TSCA)) treatment In the present paper, the high cycle fatigue (HCF) response determined in terms of the endurance limit, long crack fatigue threshold (ΔKth), crack closure and fatigue crack growth rate (FCGR) in a material that has a multiphase microstructure is presented and compared with those of the same material with a ferrite–pearlite (F–P) and a tempered martensite (T–M) microstructure obtained by air-cooling (AC) and quenching and tempering (Q&T), respectively Long crack fatigue threshold (ΔKth) and crack closure were evaluated using a dynamic compliance (DYNACOMP) measurement technique The fatigue limit of the F–B–M and the T–M microstructures (∼400 MPa) was greater than that of the F–P microstructure (∼340 MPa) At load ratios less than 05, the threshold for long crack growth was lower for the F–B–M microstructure compared with that of the F–P microstructure This is attributed to the reduced roughness-induced crack closure (RICC) contribution to the threshold in the former multiphase microstructure A quantitative analysis of the near-threshold fracture surfaces validated the above conclusion Fatigue crack growth rate in the Paris regime was found to be independent of the microstructure but dependent on the load ratio
51 citations
TL;DR: In this paper, a vanadium-bearing medium carbon MA steel was subjected to the above processing but finish forged at two different temperatures, and the resulting multi-phase microstructures and mechanical properties were evaluated by optical and transmission electron microscopy, hardness and tensile property measurements.
23 citations
TL;DR: In this article, a multiphase (ferrite-bainite-martensite) microstructure was developed in an automotive grade medium carbon microalloyed steel 38MnSiVS5 through a two-step cooling and annealing process following controlled rolling.
20 citations