| Strengthening is the only one way which not only increases strength, but also improves plasticity and toughness. As a new core technology of steel materials,study the ultrafine-grained steel materials has great significance.The author used "Kungang micro-alloy element iron powder",the Superfine crystal of bulk materials was prepared by high-energy ball-milling and spark plasma sintering (SPS) in this paper.Research was focused on the following content:First of all, the "Kungang micro-alloy Fe powder" was used to prepare nanocrystalline powders by high-energy ball milling. During the ball-milling process, with the increasing of milling time, the iron powders changed from original flakes powders to tiny spheroid, then easy to reunite. At the same time, the longer duration of ball mill, its, and decreases the particle size, particle size distribution curve of the expansion degree of narrow, high peak, powder particle size distribution more uniform, and its grain size has been reduced. Metallograph analysis shows that, ball milled for 40h, grain size has reached nanometer level. When using the ball material than those days, the ball mill speed of 350 r/min under the conditions of ball mill of 70 h microalloy iron powder, grain size is about 0.6um.In addition, the ball mill speed is also a important factor during the process. Experimental results show that within a certain range, the ball mill efficiency of powder with the increase of ball mill speed, namely powder rapid refinement. By increasing the ball speed grinding ball mill can shorten the time. But the ball mill of high speed will make powder morphology were severely stretched, deformation, is flat, particles grew up to 70 microns.Powder under the high speed due to the large internal energy when the ball mill, easy adhesion, causes the flour extraction rate is low, easy to mix impurities and pollution to the samples.The discharge plasma sintering (SPS) technology will be the ball material than those days, the ball mill speed of 350 r/min under different time of ball mill, ball mill powder for sintering. Studied the sintering temperature, holding time and so on degree of sintering process parameters on the densification of sintered sample, the influence of the microstructure and mechanical properties are studied. The results show that the relative density of sintered specimens, microhardness, compress yield strength and rupture strength are increased with the rising of sintering temperature. When the sintering temperature is 900℃, rate of temperature is 100℃/min, heat preservation after 7 min, sintered sample the relative density of 95% or higher, close to the density, its are equiaxed grain, nanoscale average grain size, grain size grow up to be effectively suppressed, preparation with the optimal mechanical properties of ultrafine crystalline Fe sintered sample, the fracture strength of sintered specimens of 2765 Mpa, elongation is 10%. The fracture morphology in the intergranular fracture characteristics. When the sintering temperature to 1000℃,the sintered specimens of grains growing up dramatically, fracture morphology for tiny toughening of ductile fracture characteristics. Holding time on the relative density of sintered samples, microhardness, microstructure and mechanical properties of impact is not obvious. With the extension of heat preservation time, the relative density of sintered samples slightly ascending, the slow rise trend the compressive yield strength, heat preservation time is too long, grain grew up slightly, but the plastic strain is also improved. |
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