Papers by Keyword: Tempered Steel

Abstract: In this study, the 38MnSiVS medium carbon non-quenched and tempered steel bar was investigated by optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM) and quantitative metallography. The microstructures were mainly composed of ferrite and pearlite. The phase transition-microstructure prediction models were established to calculate ferrite volume fraction f_α, ferrite grain size d_α and pearlite interlamellar spacing S_o. The volume fraction of the second phase V (C, N) was calculated by thermodynamics. The morphology of the second phase V (C, N) was observed by TEM, and the distribution of particle size of the second phase was determined. And the mechanical properties were measured. Considering the microstructural parameters (f_α,d_α and S_o), the modified coefficient of solid solution elements, and the effect of precipitates, combining with some reference models, prediction model of mechanical properties including yield strength, tensile strength and impact toughness were finally established.

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 effects of final rolling temperature, cooling rate and deformation on phase transition point, the duration of the phase transition and the pearlite laminar layer of non-quenched and tempered steel 45MnSiV were studied by simulating the process of rolling and post-rolling cooling on Gleeble-3500 thermal simulator and thermal expansion tester. The results show that: the ferrite and pearlite transformation temperature ranges from 510 °C to 700 °C, and the bainite transformation temperature ranges from 400 °C to 500 °C when the steel is continuously cooled at a final rolling temperature of 950 °C, and the martensite transforming temperature is 300 °C under high cooling rate (> 10 °C/s); The pearlite laminar spacing decreases with the decrease of final rolling temperature. It can be seen that the rolling deformation increases the temperature at which the test steel undergoes a phase change at each cooling rate by comparing the results of deformation and no-deformation test at 950 °C. The effect of time advance on the phase transition zone of ferrite and pearlite is particularly obvious, but the effect on the phase transition temperature and time of the bainite and martensite phase transition is not obvious. When the final rolling temperature remains constant, the Rockwell hardness value of the test steel gradually increases, and the pearlite layer spacing decreases with the decrease of ferrite transformation temperature gradually and the increase of the cooling rate.

Abstract: The objective of this article is to present the newest results of our research work related to the high cycle fatigue resistance of advanced high strength steels. In order to determine and compare the fatigue resistance, high cycle fatigue (HCF) tests were performed on two strength categories (S690 and S960) of high strength steels including quenched and tempered (Q+T) and thermomechanical (TM) types. During the HCF tests base materials and their welded joints were investigated at different mismatch conditions (matching, undermatching, overmatching). Measured and analysed data about base materials and welded joints were compared and discussed. Statistical approach was applied during the preparation and the evaluation of the investigations, which increased their reliability. The parameters of the HCF design curves were calculated based on the Japanese testing method (JSME S 002-1981) which uses 14 specimens. During the evaluation the results were compared with each other and with literary data. According to the presented examinations the HCF resistance of the base materials is more advantageous than the welded joints. The TM steel indicated better fatigue resistance than the quenched and tempered one of the same category. The matching problem had influence on the HCF resistance of high strength steels, depending on the strength category and the steel type.

Abstract: The objective of this article is to present the newest results of our research work. In order to determination and comparison of the fatigue resistance, high cycle fatigue tests (HCF) were performed both on SSAB WELDOX 700E (S690QL) quenched and tempered and VOESTALPINE ALFORM 960M (S960TM) thermomechanical high strength steels. Welded joints were made from these base materials, using gas metal arc welding (GMAW, MIG/MAG) with matching filler material. In the article, the performance of the welding experiments will be presented, especially with the difficulties of the filler material selection; along with the results of the HCF tests executed on the base material and its welded joints. Furthermore, our results will be compared with different literary data.

Abstract: This paper studies the influence of a laser thermal effect on the material. It presents the research of the steel structure under laser irradiation. It explains and demonstrates the structure of steel 5140 after laser treatment. The research method, preparation for the research and material selection are described.

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: The effect of forging process on microstructure and performance of V-Ti, V-Nb-Ti non-quenched and tempered microalloying steel was investigated in this study. By comparing the characteristics between V-Ti and V-Nb-Ti microalloyed non-quenched and tempered steels by the forging process,the machinsm of micro-alloy technology and forging process for dynamic recrystallization and microstructure refinement was investigated. It revealed that addition of Nb in micro-alloying steel can increase significantly non-recrystallization temperature during forging process, and enhance the V (C, N) precipitation strengthening effect of V-Ti microalloyed non-quenched and tempered steels. V-Nb-Ti microalloying technology and controlling forging temperature in non-recrystallization region, can refine grain size, promote proeutectoid ferrite emerging and pearlite morphology alienating. By controlling final forging temperature in non-recrystallization region, the strength and toughness of V-Nb-Ti micro-alloy non-quenched and tempered steels can be improved.

Abstract: Welding of low carbon martensitic steels with yield strengths above 690 MPa requires careful attention to the welding procedure to avoid hydrogen assisted cold cracking (HACC) and to minimise degradation of the mechanical properties of the weldment. Investigations of the microstructural and hardness gradients in the heat affected zone (HAZ) of these types of steels revealed that the peak hardness does not occur in the grain coarsened heat affected zone (GCHAZ) adjacent to the fusion boundary, as normally observed for ferritic steels, but is displaced towards the grain refined region (GRHAZ). This phenomenon, referred to as the displaced hardness peak (DHP) effect, is considered to arise when the hardenability of the steel is sufficiently high to produce the same microstructure in the both the GC and GR heat affected zones, but the enhanced structural refinement of the GRHAZ increases the hardness and strength above that of the GCHAZ. Implications relative to the susceptibility of the weldments to HACC are discussed.

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.