The Research On The Cooling Technology Of Low Alloyed And High Strength H-beam After Rolling

It is of great importance to produce high value-added and recycled steel products byeffective composition design and reduction of the production process due to Resources shortageand environment deterioration. Base on combining production capacity of ultra fast coolingequipment in H-beam factory of Ma steel and the effect of the microalloy and referencing toultra fast cooling technology developed and used in the domestic and foreign plate and mediumplate, the hot-rolled H-beam that performance is more superior and resources more economicalwas produced by used the ultra fast cooling technology as the core of the controlled rolling andcontrolled cooling technology in article.Thermal simulation experiments in lab were carried out to study the effect of the coolingrate on transformation behavior and microstructure of undercooled austenite. Temperature fieldof controlled cooling after rolling of H-beam was simulated by nonlinear finite elementsoftware MSC/MARC. Based on the above, the microstructure and mechanical property of Hbeam in the different of controlled cooling process were studied by hot rolling. The mainconclusions were obtained as follows:(1) To VN micro-alloyed steel，it occurs that supercooling austenite transforms to ferritewhen the cooling rate is0.1～70℃/s, and ferrite grain size decreases with the increase ofcooling rate; it happens that supercooling austenite transforms to pearlite when the cooling rateis0.1～7℃/s; it happens that supercooling austenite transforms to bainite at3～70℃/s; ithappens that supercooling austenite transforms to martensite when the cooling rate is more than15℃/s.(2) The ideal microstructure (acicular ferrite+bainite or a little pearlite) with higherstrength and toughness can be obtained when controled cooling speed is10～13℃/s and finalcooling temperature is below587℃.(3) In the case of the water pressure is1.3MPa, for the purpose of avoiding martensitetransformation occurred in the controlled cooling process and minimizing the cross-sectiontemperature, the temperature field of Ultra-Fast cooling after rolling of different thickness of H-beam is simulated by FEM to determine water spray cooling time, and the result shows that: it is3.1seconds for the15mm thick H-beam,3.5seconds for the20mm thick H-beam and4.3seconds for the30mm thick H-beam.(4) In the case of basically same contents of C and Si, ordinary low-alloy steel with1.4%Mn of the yield strength reached420MPa level, ordinary low-alloy steel with0.02%V of theyield strength reached460MPa level, ordinary low-alloy steel with0.07%V of the yield strength reached500MPa level, the reasonable range of alloy composition about levels(420MPa,460MPa,500MPa) of H-beam with the ultra fast cooling technology weredetermined by using ultra fast cooling technology of hot rolling test.(5) The simulation of temperature field, rolling test and the actual rolling parametersdetermined controlled cooling process in the different specifications of H-beam.