Papers by Keyword: Non-Quenched Steel

Abstract: Refinement and uniform austenite grains are essential to obtain excellent and homogenous properties for non-quenched and tempered steel, which is mainly affected by static recrystallization of the rolling process. Using the Gleeble-3500 thermal simulation test machine, 20% compression test was carried out for two passes at 850~1050 °C (interval of 50 °C) and different pass interval time conditions to study the static softening and recrystallization behavior of 38MnSiVS non-quenched and tempered steel during deformation process. The effects of strain rate, deformation temperature and interval time on static softening rate and austenite recrystallization fraction were analyzed. The results showed that the increase of deformation temperature and the increase of pass interval time had more significant impact on the static recrystallization volume fraction of 38MnSiVS steel, while the influence of strain rate was relatively smaller. When the deformation temperature was 950 °C or higher, the non-conditioning steel 38MnSiVS could undergo complete recrystallization, and partial recrystallization occurred in the temperature range of 850-950 °C. A static recrystallization volume fraction model of non-regulatory steel 38MnSiVS was established. The static recrystallization activation energy was 296.7 kJ·mol^-1, and the static recrystallization volume fraction model had a relative error of 2%.

Abstract: The thermal strength properties of a non-quenched and tempered steel, MFT8 were investigated by stress rupture tests at 450°C. High-temperature tensile tests were also carried out to determine the stress range for the accelerated creep experiments. Optical microscope (OM) and scanning electron microscope (SEM) were used to analyze the fractography and microstructure evolution. The results showed that MFT8 steels exhibited transgranular fracture and high ductility in the stress rupture tests. Although the creep cavities were observed, the critical reason of creep rupture was the wedge cracks caused by stress concentration in the area of carbide fragments. The rupture life of MFT8 at 450°C/ 100000 hours was calculated to be 184.4MPa by linear extrapolation. The data of this study inferred that MFT8 had the potential to substitute for the quenched and tempered steels of the same class in power industry.

Abstract: Mechanical properties of non-quenched prehardened (NQP) steel air cooled and sand cooled after forged were tested and their microstructure was investigated by optical microscopy and transmission electronic microscopy(TEM). The results show that mechanical properties of the NQP steel are similar at both cooling conditions, and their microstructure is bainite, whose fine structure is main bainite ferrite laths, retained austenite films, retained austenite islands and their transformation products. Bainite ferrite laths of the NQP steel air cooled are narrower than that sand cooled, while more retained austenite islands exist in latter.

Abstract: The effect of morphology and distribution of sulfides on tensile, impact and bending fatigue properties of non-quenched and tempered steel 49MnVS3 has been investigated in this paper. Microscopic structure and morphology of sulfides are observed, and impact fracture and fatigue fracture have been analyzed by SEM. The results show that the morphology of sulfides is mostly strip and distributes in ferrite, which affects mechanical properties and fatigue life. The length direction of sulfide strip is parallel to the rolling direction of steel. When the length of sulfide is short relatively and is approximate to the shape of particles. The impact properties and bending fatigue performance of 49MnVS3 are higher. Under those conditions, there are more ductile characteristics in their impact fracture and the fatigue fracture. The reasons for the effect of sulfide morphology on the mechanical and fatigue properties are explained.

Abstract: This paper studies the grinding temperature field of non-quenched and tempered steels grind-hardening technology using experiments and finite simulation. A mathematical model of grind-hardening temperature field is established to investigate steel 48MnV which is used for making crankshaft. The grinding temperature field is simulated and the hardened depth is forecasted by finite-element method with the triangular shape of the heat source model based on the ANSYS software. The experimental results show that the simulative temperature and estimating hardened depth are comparatively close to the measuring ones. The model could be utilized to forecast the distribution and variation characteristics of the grinding temperature field and the hardened layer depth.