Investagations Of Mechanical Properties And Mcro-Structure During Strain Strengthening For Pressure Vessel Steel

As a part of project (No.2006BAK02B02) funded by National Eleventh-five-year Science and Technology Surporting Plan, this study designed two methods to investigate the effect of plastic deformation on performances and structures of Pressure Vessel Steels Q235 and 16MnR. One method is prestrain experimentation which is used to examine the effect of plastic deformation on the mechanical behaviours of these two materials, and the other one is quasi in situ tensile EBSD experiment which is to reseach the effect of plastic deformation on material microstructure, espacially crystal structure.There was no significant change between the original material and the prestrained one at their mechanical performance when prestain were smaller than 5%. The strength is inhanced due to the strain strengthing effect. Meanwhile, the thoughness is still between the range of the national standard though it decreases a little. It is indicated that the orientations of the grains don't have obvious change when strain is smaller than 5%. The strain which can lead to slip in different materials are distinct, it is 2.5% for rolled Q235, 1.5% for anealed Q235, 5% for rolled 16MnR, and 2.5% for anealed 16MnR respectively. The statistical disciplines of the grain boundries and misorientation of the two materials were studied. Both materials have their own regularities and characteristic strain points. The characteristic strain point of Q235 is 1.0%, and the one of 16MnR is 1.8%.When the prestrain is bigger than 5%, the peel effect of the deformed matterial became distinct. And the yield ratios increased, impact toughnesses decrease. Some grains rotated, most grains didn't change their orientations but formed some subgrains inside.Seven grains were chosen to research their rotation and Taylor factor's change during the deformation process. Six grains rotated large angles during the process from no strain to 0.2% strain. And the rotating angle decreased 46.4% averagely from 0.2% strain to 1.0% strain. When the strain was bigger than 1.0%, the rotating angle of each grain increased continuously, untill the strain became very big, even the necking stage. There had not significant change from 1.0% strain to 1.5% strain, and from 2.6% strain to 5% strain. It notes that the deformation work that the materials need to overcome change a little during the two period.The expected slip systems were calculated from the orientations of the crystallites obtained by OIM maps. The starting and changing of slip system during deformation process were studied according to the schmid law.