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Hot compression tests are carried out on low carbon steel with carbon content of 0.037 wt% over a temperature range of 900–700 °C. Stress–strain curves show that deformation resistance decreases from 870 to 820 °C and then increases. The temperatures of Ar3 and Ar1 are 873.8 and 796.4 °C, respectively, and the phase transformation speed reaches a maximum at 840 °C. The volume fractions of recrystallized grain, subgrain, and deformed grain are analyzed using optical microscope and electron back‐scattering diffraction. The distributions and the proportions of misorientation angles are also calculated. Textures are described using the inverse pole figure (IPF) colored orientation maps and orientation distribution functions (ODF). The results show that dynamic recrystallization (DRX) of austenite occurs to varying degrees during deformation in the austenite and double‐phase region. Dynamic recovery (DRV) of ferrite leads to the growth of ferrite grains in the double‐phase region. DRX of ferrite by the subgrain coalescence occurs at 700 °C. The main deformation textures in most of the double‐phase and single ferrite region are both cube texture. However, {112}<110> component has the highest texture intensity at 750 °C, reaching 5. The evolution mechanism of microstructure and texture is also discussed. [ABSTRACT FROM AUTHOR]

The effect of Nb on the dissolution and precipitation behaviours of the network carbide in bearing steel, including the precipitation and dissolution temperature and the thickness of network carbide has been investigated in this paper. The precipitation and dissolution processes were carefully compared and analysed in bearing steels with different contents of Nb. The results showed that the presence of Nb has significantly reduced precipitation and dissolution temperatures of network carbide. The precipitation temperatures of Nb free, 0.018%Nb and 0.040%Nb steel are found to be 753°C, 723°C and 719°C, and the dissolution temperatures are 845°C, 785°C and 780°C, respectively. The average thicknesses of network carbide in 0.018%Nb steel and the 0.040%Nb steel are reduced by 21% and 27% compared with Nb-free steel, respectively. [ABSTRACT FROM AUTHOR]

This paper studies the formation of intragranular ferrite in a V-Ti-N medium-carbon steel containing MnS inclusions. The (Ti, V)(C, N) particles precipitating on MnS inclusions are confirmed to be the main nucleation sites of intragranular ferrite. Because of the small lattice mismatch and low-energy ferrite/V(C, N) interphase boundary, the vanadium-rich edge of (Ti, V)(C, N) particles increases the nucleation potency of intragranular ferrite. The interphase of MnS inclusions and austenite provides suitable sites for (Ti, V)(C, N) particles to grow big enough to reach the critical size for intragranular ferrite nucleation. Furthermore, the efficiency of the formation of intragranular ferrite starts to increase rapidly when the length of MnS inclusions decreases to less than 10 µm. The shape of intragranular ferrite is also significantly influenced by the length of MnS inclusions. In addition, the intragranular ferrite is confirmed to have a new type of orientation relationship with the particles precipitating in liquid phase, which indicates that the orientation relationship between the intragranular ferrite and (Ti, V)(C, N) particles is not sole, but diversified. [ABSTRACT FROM AUTHOR]

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]