Abstract:To better understand the tensile deformation and fracture behavior of 35CrMo steel during hot processing, uniaxial tensile tests at elevated temperatures and strain rates were performed. Effects of deformation condition on the flow behavior, strain rate sensitivity, microstructure transformation, and fracture characteristic were characterized and discussed. The results indicated that the flow stress was sensitive to the deformation condition, and fracture occurs immediately after the peak stress level is reached, especially when the temperature is low or the strain rate is high. The strain rate sensitivity increases with the deformation temperature, which indicates that formability could improve at high temperatures. Photographs showing both the fracture surfaces and the matrix near the fracture section indicated the ductile nature of the material. However, the fracture mechanisms varied according to the deformation condition, which influences the dynamic recrystallization (DRX) condition, and the DRX was accompanied by the formation of voids. For samples deformed at high temperatures or low strain rates, coalescence of numerous voids formed in the recrystallized grains is responsible for fracture, while at high strain rates or low temperatures, the grains rupture mainly by splitting because of cracks formed around the inclusions.

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Adsorption of hydrogen on Al(111), Cu(111), Mg(0001), and Ti(0001) surfaces have been investigated by means of first principles calculation. The calculation of surface energy indicates that Mg(0001) is the most stable surface, while Ti(0001) is the most unstable surface among all the four calculated surfaces. The obtained adsorption energy shows that the interaction between Al and H atoms should be energetically unfavorable, and the adsorption of hydrogen on Mg(0001) surface was found to be energetically preferred. Besides, the stability of hydrogen adsorption on studied surfaces increased in the order of Al (111), Ti(0001), Cu(111), Mg(0001). Calculation results also reveal that hydrogen adsorption on fcc and hcp sites are energetically stable compared with top and bridge sites for Ti(0001), Cu(111), and Mg(0001), while hydrogen adsorbing at the top site of Al (111)

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Abstract:The compression deformation behaviors of 35CrMo steel at different conditions was studied by using Gleeble-3810 thermo-simulation machine under large strain. The results indicate that the flow stress curves of 35CrMo steel is affected by strain rate and deformation temperature, showing the characteristics of dynamic recovery (DRV) and dynamic recrystallization (DRX), which is the main softening mechanism of 35CrMo steel. The activation energy (Q) and Zener-Hollomon parameter (Z parameter) expression for thermal deformation of this steel was calculated by linear regression. The inflection point on the curve of strain hardening rate and flow stress (θ-σ curve) corresponds to the beginning of DRX, and the critical strain of DRX increases with the decrease of deformation temperature and the increase of strain rate. Based on the inflection point criterion, the constitutive equation of the critical strain of DRX of 35CrMo steel was established: ε c = 0.000232Z 0.1673 , which reflects the variation of the critical strain of DRX with the Z parameter. In addition, through metallographic observation, the rationality of the inflection point criterion in determining the critical strain of DRX of 35CrMo steel was verified, and the DRX state diagram was established.