We studied the energetic behaviors of interstitial and substitution carbon （C）/nitrogen （N） impurities as well as their interactions with the vacancy in vanadium by first-principles simulations. Both C and N impur...We studied the energetic behaviors of interstitial and substitution carbon （C）/nitrogen （N） impurities as well as their interactions with the vacancy in vanadium by first-principles simulations. Both C and N impurities prefer the octahedral site （O-site）. N exhibits a lower formation energy than C. Due to the hybridization between vanadium-d and N/C-p, the N-p states are located at the energy from -6.00 eV to -5.00 eV, which is much deeper than that from -5.00 eV to -3.00 eV for the C-p states. Two impurities in bulk vanadium, C-C, C-N, and N-N can be paired up at the two neighboring O- sites along the （111） direction and the binding energies of the pairs are 0.227 eV, 0.162 eV, and 0.201 eV, respectively. Further, we find that both C and N do not prefer to stay at the vacancy center and its vicinity, but occupy the O-site off the vacancy in the interstitial lattice in vanadium. The possible physical mechanism is that C/N in the O-site tends to form a carbide/nitride-like structure with its neighboring vanadium atoms, leading to the formation of the strong C/N-vanadium bonding containing a covalent component.展开更多
This paper reports a study of the addition effects of either titanium or titanium and nitrogen of steel grade DIN 56NiCrMoV7 on mechanical properties. Three steel grades were produced in 30 kg-induction furnace, one c...This paper reports a study of the addition effects of either titanium or titanium and nitrogen of steel grade DIN 56NiCrMoV7 on mechanical properties. Three steel grades were produced in 30 kg-induction furnace, one conforms the chemical composition of conventional 56NiCrMoV7 while the other two produced steels were microalloyed by either titanium or titanium and nitrogen. The produced cast steel grades were reheated to 1150°C and hold for 2 hours, followed by forging process. The forging process was carried out in temperature range 950°C - 1100°C. Solution treatment of hot forged steels was conducted at 880°C, 850°C followed by air and oil quenching, respectively. Quenched steel samples of different steel grades were tempered at different temperatures in the range of 300°C to 650°C for 45 min. The hardness variations after tempering of the two modified steels comparing with the conventional 56NiCrMoV7 steel were studied. Microadditions of titanium or titanium and nitrogen were found to produce secondary hardening at 550°C to 575°C (45 min) with a hardness peak higher than that attained in the conventional 56NiCrMoV7 steel. The effect of titanium and nitrogen additions on phases formation was investigated by Thermo-Calc. SEM was used to confirm Thermo-Calc analysis. Interpretation between hardness and formed phases has been illustrated.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11575153 and 11375108)
文摘We studied the energetic behaviors of interstitial and substitution carbon （C）/nitrogen （N） impurities as well as their interactions with the vacancy in vanadium by first-principles simulations. Both C and N impurities prefer the octahedral site （O-site）. N exhibits a lower formation energy than C. Due to the hybridization between vanadium-d and N/C-p, the N-p states are located at the energy from -6.00 eV to -5.00 eV, which is much deeper than that from -5.00 eV to -3.00 eV for the C-p states. Two impurities in bulk vanadium, C-C, C-N, and N-N can be paired up at the two neighboring O- sites along the （111） direction and the binding energies of the pairs are 0.227 eV, 0.162 eV, and 0.201 eV, respectively. Further, we find that both C and N do not prefer to stay at the vacancy center and its vicinity, but occupy the O-site off the vacancy in the interstitial lattice in vanadium. The possible physical mechanism is that C/N in the O-site tends to form a carbide/nitride-like structure with its neighboring vanadium atoms, leading to the formation of the strong C/N-vanadium bonding containing a covalent component.
文摘This paper reports a study of the addition effects of either titanium or titanium and nitrogen of steel grade DIN 56NiCrMoV7 on mechanical properties. Three steel grades were produced in 30 kg-induction furnace, one conforms the chemical composition of conventional 56NiCrMoV7 while the other two produced steels were microalloyed by either titanium or titanium and nitrogen. The produced cast steel grades were reheated to 1150°C and hold for 2 hours, followed by forging process. The forging process was carried out in temperature range 950°C - 1100°C. Solution treatment of hot forged steels was conducted at 880°C, 850°C followed by air and oil quenching, respectively. Quenched steel samples of different steel grades were tempered at different temperatures in the range of 300°C to 650°C for 45 min. The hardness variations after tempering of the two modified steels comparing with the conventional 56NiCrMoV7 steel were studied. Microadditions of titanium or titanium and nitrogen were found to produce secondary hardening at 550°C to 575°C (45 min) with a hardness peak higher than that attained in the conventional 56NiCrMoV7 steel. The effect of titanium and nitrogen additions on phases formation was investigated by Thermo-Calc. SEM was used to confirm Thermo-Calc analysis. Interpretation between hardness and formed phases has been illustrated.
