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Abstract Microalloying behavior in medium carbon non-quenched and tempered steel was investigated in this paper. The mechanical properties and microstructures in steels with different V, Ti, Nb and V contents were carefully compared and analyzed. The results showed that V and N largely reduced the average size of network ferrite and increased the volume fraction of intragranular ferrite (IGF) and ferrite. Ti, and Nb had the same effect as V and N while the effect was weaker. Ti and Nb could further increase the IGF content by increasing the size of the IGF nuclei (V, Ti)(C, N) and (V, Ti, Nb)(C, N). The precipitation strengthening of V-N steel was the highest. The precipitation strengthening of other steels was weaker due to the larger size of the particles. The highest elongation of the microalloying elements free steel can be attributed to the lack of precipitation strengthening in the steel. The relatively lower elongation of V-N steel can be ascribed to the larger grain size of steel. The V(C, N) and (V, Ti)(C, N) particles decreased the impact energy of V-N steel and V-Ti-N steel. The highest impact energy of V-Ti-Nb-N steel resulted from the refinement of the grain size. The comprehensive mechanical properties can be obtained in V-Ti-Nb-N steel as: the yield strength was 509.7 MPa, the elongation was 19.2% and the impact energy AkU was 55.4 J. [ABSTRACT FROM AUTHOR]

The microstructural characteristics of three medium carbon steels, namely MnCrB, NiCrSi and NiCrMoV containing steels, have been investigated when the steels were hardened by quenching in water or oil from different austenitisation temperatures (i.e. 850, 900 and 950 °C). The microstructure was characterised using optical microscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy, and X-Ray diffraction technique, whereas the mechanical properties were measured by Vickers hardness testing, V-notched Charpy impact testing and tensile testing. The microscopy observations suggested a fully martensitic microstructure, whereas martensite was considerably finer in NiCrSi and NiCrMoV steels compared to MnCrB steel. Moreover, the NiCrSi and NiCrMoV steels showed significantly higher strengths and lower ductility than MnCrB steel. The results suggested that the small additions of alloying elements and different prior austenite grain sizes were mainly responsible for the observed microstructural and mechanical properties variations. [ABSTRACT FROM AUTHOR]

The dynamic recrystallization (DRX) behavior of a medium carbon Cr-Ni-Mo alloyed steel 34CrNiMo was studied in the wide temperature range of 900–1150 °C and the strain rate of 0.002–5 s −1 . Based on relations between the strain hardening rate and stress, the characteristic points, including critical strain ( ε c ), critical stress ( σ c ), peak strain ( ε p ), peak stress ( σ p ), were determined from the strain rate hardening versus stress curves. The Avrami equation was developed to model the kinetics of DRX, whereas the characteristic points can be expressed as a function of Zener-Hollomon parameter. Then the austenite grain size of DRX was measured by metallography and found to be a power law function of Zener-Hollomon parameter with an exponent of −0.2013. Besides, a mesoscopic cellular automaton model has been established to simulate the austenite DRX for the tested steel. This model was verified by means of the kinetics and topology of DRX. [ABSTRACT FROM AUTHOR]

This study provides an effective surface processing technology to increase the local mechanical properties of medium carbon steel castings. Ultrafine dual-phase structure of the ferrite and the martensite was obtained in the processed zone with a depth of 1 mm via submerged friction stir processing (FSP). Significantly enhanced yield strength (YS) of 2070 MPa was achieved in the FSP steel compared to that of the base material (BM) with a relatively low YS of 590 MPa, but a low uniform elongation (UE) of 3.0% was achieved compared to that of the BM (9.4%). After annealing, obvious carbide precipitation was observed in the original quenched martensite phases. Therefore, good strength-ductility synergies with high YS of 1020 MPa and 925 MPa, and acceptable UE of 5.9% and 9.3% were achieved in the FSP steel after annealed for 2 h at 500 °C and 600 °C, respectively. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, extremely high strength was obtained in medium carbon steel having a carbon content of 0.35% by weight through cold drawing. Experimental results showed that the tensile strength of the steel increased by nearly three folds from the original value ~615MPa to 1810MPa corresponding to drawing strain of 3.0. To reveal the mechanisms that govern the strengthen increase, the microstructural evolution was analyzed during cold drawing, with respect to the change of the deformation resistance (measured by micro-hardness) of micro-constituents (i.e., primary or proeutectoid ferrite and pearlite) in the material. The proeutectoid ferrite became elongated and, at the same time, increasingly hardened while the pearlite maintained equiaxed shape after initial drawing. With the increase of the drawing strain, the pearlite was stretched parallel to drawing direction, accompanied by an increase in the 〈110〉 texture intensity and dislocation density in the ferrite phase. Under heavy drawing, a laminate structure formed, consisting of alternating pro-eutectoid ferrite and pearlite both parallel to the drawing direction. The 〈110〉 texture intensity in the ferrite phase became saturated as ε>1.2. High density dislocation zones further spread in the ferrite phase. The interlamellar spacing between ferrite and cementite phases in the pearlite decreased. Based upon these observations, mechanistic models were constructed to provide insight into the deformation and strengthening mechanisms of this steel. [Copyright &y& Elsevier]

Abstract: The warm deformation behavior of quenched 0.45C steel was investigated, and the constitutive equation of the warm deformation was established. The effect of warm deformation on the microstructure and mechanical properties was analyzed. Results show that the ultrafine grain microstructure composed of submicron ferrite grains and nanoscale cementite particles can be created in the steel by quenching and warm deformation under moderate conditions. Compared to conventional quenching and high-temperature tempering, quenching and subsequently warm deformation at 600°C can result in much higher tensile strength (861MPa), nearly double the yield strength (777MPa), and about the same total elongation (19.1%) and uniform elongation (9.3%). [Copyright &y& Elsevier]

Abstract: A compressive type split-Hopkinson pressure bar is utilized to compare the impact plastic behaviour of three steels with different levels of carbon content. S15C low carbon steel, S50C medium alloy heat treatable steel (abbreviated hereafter to medium carbon steel) and SKS93 tool steel with a high carbon and low alloy content (abbreviated hereafter to high carbon steel) are tested under strain rates ranging from 1.1×103 s−1 to 5.5×103 s−1 and temperatures ranging from 25 to 800°C. The effects of the carbon content, strain rate and temperature on the mechanical responses of the three steels are evaluated. The microstructures of the impacted specimens are studied using a transmission electron microscope (TEM). It is found that an increased carbon content enhances the dynamic flow resistance of the three steels. Additionally, the flow stress increases with strain and strain rate in every case. A thermal softening effect is identified in the plastic behaviour of the three steels. The activation energy, ΔG *, varies as a function of the strain rate and temperature, but is apparently insensitive to the carbon content level. The present study identifies maximum ΔG * values of 58kJ/mol for the S15C low carbon steel, 54.9kJ/mol for the S50C medium carbon steel, and 56.4kJ/mol for the SKS93 high carbon steel. A Zerilli–Armstrong BCC constitutive model with appropriate coefficients is applied to describe the high strain rate plastic behaviours of the S15C, S50C and SKS93 steels. The errors between the calculated stress and the measured stress are found to be less than 5%. The microstructural observations reveal that the dislocation density and the degree of dislocation tangling increase with increasing strain rate in all three steels. Additionally, the TEM observations indicate that a higher strain rate reduces the size of the dislocation cells. The annihilation of dislocations occurs more readily at elevated temperatures. The square root of the dislocation density increases linearly with the work hardening stress. The current results provide a valuable reference for the application of S15C low carbon steel, S50C medium carbon steel, and SKS93 high carbon steel in high-speed plastic forming processes. [Copyright &y& Elsevier]

Tempered medium carbon steel with poor low-temperature toughness always limits its practical applications, while temper forming process can realize the strengthening-toughening aim by changing the microstructure. In this work, a grade 45 medium carbon steel was deformed with different rolling reduction ratios of 28%, 52%, 78%, and 82% by caliber rolling at the temperature of 500oC, respectively. The texture intensity, high angle boundaries density, and elongated fibrous grains are gradually increased, as well as the tensile strength, fracture elongation, and low-temperature impact toughness are also improved with the increase of caliber rolling reduction ratio, and strengthening-toughening aim of 45-grade steel has been realized at high caliber rolling reduction ratio. Fibrous grains, <110>//RD texture, grain boundaries type, and carbides bimodal distribution resulted in the formation of crack bifurcation and delamination cracks during the tensile testing and impact testing, which can obviously decrease the ductile-brittle transition temperature and improve the low-temperature impact toughness. The caliber rolled 45 steel at the rolling reduction ratio of 82% obtains superior mechanical properties with the tensile strength of 964MPa, uniform elongation of 0.18, and low-temperature impact toughness of 176J at −40oC, which can effectively extend the practical low-temperature service range of 45-grade steel. [ABSTRACT FROM AUTHOR]