HOT DEFORMATION CHARACTERISTICS AND MICROSTRUCTURE DEVELOPMENT OF Ti-6AI-4V BAR UNDER FORGING CONDITIONS

The uniformity of microstructure distribution across the transverse section of a Ti-6AI-4 V bar afler stepwise radial forging process is a relevant index to the quality of the foaled bar. In this work, hot deformation chamcteristics of Ti-6Al-4 V bar in the stepwise radial forging process were investigated in the or+p and g range 6etween 940℃ and 1000℃. Various flow curves and microstructures were obtained by using Gleeble simulation. The deformation process of a bar from initial diameter to a desired reduction in cross section was simulated by using a FEM code ABAQUS combined with the constitutive models obtained from physical simulation. Heat onduction model was coupled to the computation. The principal stresses and final strain istribution of the bar after forging were predicted by the contours obtained from FEM analysis. Together with the results obtained from Gleeble simulation, a map of microstructure distribu- tion on the cross section of the forged bar was constructed. According to the map,recrystallized zone in the center region of the bar was predicted to be approximately 50 to 65% of the total cross section area.

Analysis on SH-CCT curves of HD15Ni1MnMoNbCu steel for nuclear power station

The microstructural evolution and Vickers hardness measurement in the welding heat-affected zone （HAZ） of HD15 Nil MnMoNbCu steel for nuclear power station were investigated by Gleeble-3180 thermal mechanical simulator, and the simulated HAZ continuous cooling transformation curves （SH-CCT） were measured simultaneously. With ts/5 inereasing from 3.75 s to 15 000 s, the product was obtained martensite, bainite, ferrite and pearlite, successively. The result of microstructure and Vickers hardness in the heat-affected zone was in good agreement with those measured by SH-CCT diagram with the heat input 16. 2 kJ/cm as an example to weld the HD15Ni1MnMoNbCu steel pipe using TIG/SMAW/SAW welding methods.

Chemistry and Process Optimization of V-Microalloyed N80-Class Seamless Casing Tube

The complex effects of different nitrogen （N） contents and thermal routines on the microstructure and mechanical properties of 33Mn2V steels for N80-Class seamless casing tube application were investigated using Gleeble simulation technique. The results showed that the N additions of 0. 014 %- 0. 021 % in the steels for the in-line normalization process （ILNP） increased the strength while the toughngss remained at a high level as compared with the steel with N content of 0. 005 %. It was also revealed that the N addition of 0. 021%could enhance the performance combination of strength and toughness in the steels by using 700 ℃ as the cooling interrupted temperature （CIT） for the non in-line normalizing process （NILNP）. It was further evidenced that the toughness was improved at expense of strength to some degree in all the steels by decreasing reheating temperature for the ILNP, while an increase of CIT for NILNP severely impaired the toughness and slightly improve the strength in the high-N steel with N content of 0. 021%. This can be attributed to the dissolution and precipitation behavior of V（C,N）. The optimization of V （C,N） precipitation could be achieved by enhancing N. The precipitation of V（C, N） in austenite was promoted by cooling to a certain temperature lower than the A,1 for the ILNP. The V（C,N） particles formed in austenite contrib- uted to grain refinement by the VN-induced nucleation of intragranular ferrite, but as a result the effect of precipitation on strengthening would become weaker due to a decrease of the precipitation of V in ferrite.