Research On Ultra Fast Cooling Process Of H-Beam Used For Offshore Oil Platform

H-beam is a new kind of economic cross-section steel and has been widely used, which has the advantages of single light weight, energy saving, simple construction, high anti bending ability, etc. Ultra fast cooling technology is a high cooling rate method, which has gradually developed in recent years. It is mainly used in thermal processing of steel in the process of intermediate billet rapid cooling or rapid cooling after rolling. Ultra fast cooling technology has been widely applied to the wide and heavy plate and some hot rolled strip production line, and it has gradually formed a mature technology, while it does not form a mature cooling theory and technology in the H-beam production line now.The thesis takes H-beam used for offshore oil platform(SM490YB) as the research object,with ultra fast cooling technology. Firstly, the thermal expansion test was conducted to plot SM490 YB curve and analyze the influence of cooling rate on transformation behavior, and it provided the theoretical basis for developing the controlled cooling process. Secondly, the temperature field of H-beam in ultra fast cooling process was simulated and analyzed by nonlinear finite element software MSC.Marc, and studied by different specifications H-beam.Finally, the variation between the surface temperature and cooling time was analyzed to establish the ultra fast cooling process model and determine the optimization of ultra fast cooling process, and it provided the theoretical basis for improving the microstructure and performance. The main conclusions are obtained as follows:(1) It occurs that supercooling austenite transforms to ferrite when the cooling rate of SM490 YB steel is 1~50oC/s, the transition temperature at the start of ferrite decreases with the increase of cooling rate; and the critical cooling rate at the end of pearlite transformation is30oC/s, the critical cooling rates at the start of bainite and martensitic transformation are 3oC/s and 15 o C/s respectively.(2) The ideal microstructure(ferrite + bainite or ferrite + bainite + a little pearlite) with higher strength and toughness and the corrosion resistance can be obtained when cooling rate is controlled between25oC/s and 30oC/s, and final cooling temperature is controlled above 453 oC.(3) The temperature field of ultra fast cooling process for H-beam is simulated to determine water-cooling time, the results show that: it is 3 s for HW300×300×10×15, 3.28 s for HM588×300×12×20 and 3.55 s for B305×305×223.(4) The temperature variation of cross-section in H-beam is simulated and analyzed to respectively determine the equilibrium temperature and the average cooling rate. The equilibrium temperature and the average cooling rate are as follows: it is 622 o C and 42.8o C/s for HW300×300×10×15; it is 722 o C and 12.7o C/s for HM588×300×12×20; it is 756 o C and11.1oC/s for B305×305×223.(5) The index variation between surface temperature and cooling time is analyzed,controlled cooling process model is established by Origin exponential fitting, and the test results and the calculation results are basically same.