As-cast 2.25 Cr1mo0. 25 V Steel Research Of Coarse Grain Refinement

In recent years, with the development of petrochemical technology and theexpansion of the fuel market demand, the requirements for large hydrogenationreactor become bigger and bigger. Because the large volume and weight of largehydrogenation reactor, it is maked by forged welding structure, the steel is the2.25cr-1mo-0.25v low alloy high strength steel with high strength and hightoughness and good ability to resist hydrogen. At present, it is more that thestudy of forging thermal Deformation and microstructure evolution mechanismof2.25cr-1mo-0.25v, but the study of cast thermal Deformation andmicrostructure evolution mechanism of2.25cr-1mo-0.25v is less, This paper isintended for research of the grain refinement in the as-cast2.25cr-1mo-0.25vsteel under compressive deformation, the following conclusions has beenobtained through micro-hardness analysis and analysis of TEM and the secondphase precipitation of analysis, comparative analysis of refinement and grew up:(1) Cast2.25cr-1mo-0.25v steel compressive deformation (variation6%),950grain boundary softening positions is less, it is also elongated grains,1050℃and1150℃grain boundaries soften location is increase. The grainrefinement is obvious. The cast2.25cr-1mo-0.25v steel compressivedeformation of nucleation location is at grain boundaries(2) Cast2.25cr-1mo-0.25v steel after high temperature and precipitation, astemperatures rise, the second phase percentage decline, precipitationtemperature of950C and1050C release of the second phase is suitable fortemperature, thanks to precipitation of1050degrees Centigrade of the secondphase, pinning effect of grain boundary, resulting in the thermal deformation of1050degrees centigrade, grain refinement of the most obvious.(3) In950℃, the grain growth of the beginning is slow, then becomes fast.The grains basically grows up at a certain rate of growth in1050℃and1150℃,the grain size is the smallest at the start in1050℃, grow up fast, and then stablein1250℃. The sample after heated360min substantially have the same grainsize in950℃,1150℃,1250℃. The grain size of the start is the smallest in1050℃, after360min it is the smallest as well, which is the second-phase grain boundary pinning, resulting in small grain size of the final.(4) The average grain size decreases with the compression time in1050℃with Gleeble-1500D, and the dynamic recrystallization grain refinementplays the dominant role, a large number of second-phase separating outprecipitation of grain boundary pinning, so that grain boundary migrates at a lowrate, and the grain are finer; the grains are fine when heat compression starts in1150℃, the average grain size is essentially the same with time, finally slightlyincrease, which make dynamic recrystallization and grain growth remainequilibrium;1250℃, the grain boundary migration rate is large, dynamicrecrystallization of fine grains grow rapidly, resulting in coarse grains.In this paper the cast coarse grain refinement rules and refinementmechanism are obtained, and they provide scientific theoretical support for therealization of large ingots of the "modified" Forged.