| This thesis is based on the 10 # steel, by adding FeV and carbon to change vanadium, carbon content. The author wants to prove with the help of the experiment that there exist five experimental steels after such treatement. They are the vanadium 0.1%, carbon content of 0.1%, 0.15% and 0.2%; and carbon content of 0.1%, vanadium content of 0.2% and 0.3% respectively.Five series of tested steels are firstly designed, and then subsequently investigated systematically, considering significant aspects of mechanical properties, microstructure characterization and microstructure evolution after tempering. By high temperature treatment, thermal simulation and temper experiment; using tension and impact tests incorporated with various analytical techniques such as optical microscopy (OM), transmission electron microscopy (TEM). It is expected that the effect of the alloy elements, such as C and V, on the microstructure and properties of microalloy steels are all completely analyzed; and then discussMicro-alloy steel, precipitation of second phase how to control composition and process.The paper's main conclusions are as follow: (1) the strength of test steel can be increased by increasing in vanadium content, but little effect on its toughness. (2)Test steel at 1100℃for 30min with the furnace heat and then cooled to 700℃for 30min followed by air cooling, Ferrite grains are coarsened, size to about 50μm. Therefore, the vanadium is completed solid solution in austenite at the austenite range, no apparent role in preventing austenite grain growth. (3)To 0.1% C-0.3% V steel as the research object, in Gleeble 1500 hot simulation test machine is not deformed austenite, single pass compression deformation of 20% of the continuous cooling transformation experiments, the microstructure are observed under 860℃the conditions of not deformation and deformation. The results show that increase of cooling rate, ferrite, pearlite content reduction and grain size is diminished, bainite content with the increase of cooling rate and increasing; hot deformation promotes the phase transformation, so organization was refined; Deformation of the critical cooling rate of bainite increased, inhibited the formation of bainite.(4)To 0.1% C-0.3% V steel as the research object, using Gleeble 1500 hot simulation test machine, by compression deformation test of deformation temperature and deformation passes the test of steel microstructure and secondary phase. The results show that multi-pass hotdeformation, recrystallization and recrystallized grain has grown up, TEM has very little precipitate on of second phase particle. There is a certain refinement of the grain n the low temperature deformation of single-pass. In TEM there is no second phase precipitation, deformation increases dislocation density.(5)To 0.1% C-0.3% V steel as the research object, the original sample, the 850,1100℃for 30min heat treatment with the furnace cooled to 700℃for 30min followed by air cooling and then holding the sample and 700℃single pass compression of the specimen tempered at 600℃,TEM samples have found that after tempering the precipitation of second phase VC, The VC and the matrix there are four orientation relationship, but do not completely satisfy the phase precipitation B-N orientation relationship(.6)Theoretical calculation, 0.1% C-0.3% V test steel, the entire solution temperature is about 1100℃,in 738 ~ 1100℃, the carbon is completely dissolved in the austenite, the second-phase VC can not precipitate at the way of phase precipitation. Dislocation nucleation is the main nucleation mode about VC, nucleation of the dislocation line, so that it can significantly reduce the critical form of nuclear energy. However, little effect on the PPT curves. Strain energy storage can effectively promote the precipitation of VC.VC precipitates in ferrite the PPT curve in the monotonic curve, there is no nasal temperature. |
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