Effect Of Hot Deformation Process On Microstructure And Microoritentation Of X80Pipeline

In this paper, X80pipeline steel was taken as an object for the study,systematically studied the changes of microstructure and micro-oriented underdifferent thermal deformation conditions. Gleeble-1500D thermal simulation testingmachine were used to study the variation of X80pipeline steel curves of stressrelaxation under the RPC process. Optical Microscopy (OM) and Scanning ElectronMicroscopy (SEM) were used to study the variation of microstructure and precipitatesof X80pipeline steel in the different deformation temperatures, different relaxationtime and different deformation conditions. By transmission electron microscopy(TEM), it studied the evolution of dislocation under different relaxation timeconditions. The microscopic orientation, micro-orientation and changes of CSL grainboundary of X80pipeline steel, in the different deformation temperatures, werecollected by electron backscatter diffraction (EBSD).The experimental results showed that: the microstructure of X80pipeline steelwhich was deformed and relaxed in the austenite non recrystallization region wasobviously different from which was deformed and not relaxed, and the microstructureof X80pipeline steel through the relaxation process was mainly lath bainite; Indifferent relaxation time, the microstructure of X80pipeline steel showed thecoarsening after refining with the extension of relaxation time, and the microstructurecoarsened in the beginning of relaxation then it showed a trend of refinement as therelaxation time is extended to200seconds, and the microstructure achieved finestwhen it relaxed at200seconds, and the microstructure occurred gradually coarseninguntil the end of the relaxation; Under different deformation conditions, the magnitudeof the deformation has a significant impact on the size of bainite lath and the greaterdeformation,the finer of the size of bainite lath in the same relaxation time. Theresults indicated that the test temperature selected was below the nose temperature, sothe higher deformation temperature under the same deformation and relaxation timeconditions, the finer microstructure we obtained; When it was850℃and thedeformation of35%,there was almost no precipitation of second phase particles at therelaxation time of0second,and the number of precipitated particles was gradually increasing with the extension of the relaxation time, until the relaxation time of200seconds the number of precipitated particles achieved the most and the microstructurewas finest, then precipitated particles grew up obviously, weakening the effect ofgrain refinement, with the continued extension of the relaxation time. Throughout therelaxation process, the evolution of the dislocation presents the following rules:starting scattered disordered state, and gradually evolved into a network ofdislocations, dislocation walls and even formed substructure with a certain orientation;The proportion of small-angle grain boundaries of X80pipeline steel with relaxationincreased at first and then decreased and the proportion achieved the greatest at therelaxation time of200seconds, and the number of the low-energy Σ3grainboundaries showed an increase tendency in the whole relaxation process; Inconclusion that, when X80pipeline steel was deformed at900℃，the amount ofdeformation was35%，and the relaxation time was200seconds，the overallperformance of pipeline steel can be greatly improved。Analysis the Microdomains ofEBSD the results show when hot-rolled X80pipeline steel that will produce muchtexture, After relaxation treatment, A higher proportion of texture will produce, suchas{111}<112>，{111}<110>，{112}<110>. Treatment severely affected aboutmaterial; After relaxation treatment X80pipeline steel mainly contain small-anglegrain boundaries. Increased with relaxation time, the quantity of small-angle grainboundaries increases first and then decreases.with the process of relaxation, thequantity of the Σ3grain boundaries of X80pipeline steel will decreases. Increasedwith relaxation time, the quantity of the interface of CSL will increased until200sachieve maximum. The more of the quantity of the interface of CSL, the better of thefunction of anti-brittle fracture of material. Help to improve the plastic and toughnessof X80pipeline steel.