Surface Nanocrystallization And Alloying Of The Low Carbon Steel

Low carbon steel because of its mature production technology, low cost,arewidely used as the basic material in the industrial production.Due to the rapiddevelopment of modern production technology, the existing material can’t meetthe production demand for materials, scholars have made the metal nanocrystalsto improve its performance, or use alloy method to manufacture new materialsdifferent from base material.This paper selected the industrial pure iron and Q235of low carbon steel asexperimental object, the nanostructured surface layer are made by means ofsurface mechanical attrition treatment (SMAT) of the two materials, and thenanalyzed the influence of the nano to its performance.Siliconizing the industrialpure iron in molten salt, and then analyzed the influence of the nano to itsperformance. Main results are given as follows:1. Both SMAT35min and45min can be able to get industrial pure ironnanocrystals. The variation trend of relevant performance is:With the increase ofthe SMAT time, nanocrystalline grain size became smaller,corrosion resistantin the fluid of the corrosion is poorer, the surface roughness is larger, themicrohardness is higher.Nanocrystalline placed in air for10months，seriouscorrosion happened and corrosion occurs mainly in the dense regions of surface crack, extends to the inside material layer along the rheological curve, corrosiondepthcan be up to150μm.2. The nanosizedcrystalline microstructure on the surface of Q235steel wasinduced by a surface mechanical attrition treatment (SMAT) at high frequency(20KHZ）with smaller balls（4mm in diameter） and low frequency (50HZ）with bigger balls (8mm in diameter）,the grain size is29.70nm and30.44nm.The roughness is respectively30.9times and8.3times compared to the originalsample. The sample’s roughness is bigger at high-frequency experimentalconditions. The corrosion resistances in the corrosive liquid are quite different.The corrosion resistance of the former specimen gets worse, while the latter’corrosion resistance is improved.Under this experimental condition, the changeof corrosion resistance related to the surface roughness. The surface hardness oftwo kinds of material has been greatly improved, respectively reached2.4timesand2.3times of matrix, hardness is larger at low frequency condition.After thenano materials placed in the air for ten months, the corrosion occurred, mainlyis pitting corrosion.3. Using molten salt method can realize the coarse grain, SMATed35minand SMATed45min of pure iron siliconizing, generate Fe3Si.For the samesample, the longer siliconizing’s, the siliconizing depth is the deeper. Along thedirection of siliconizing, the hardness presents the tendency of increase at beginand then reduce, the saturation magnetization is bigger. For the samples ofdifferent grain size siliconizing for the same time, the grain size is the smaller, the siliconizing depth is the deeper, the microhardness is the greater, thesaturation magnetization is also bigger. The greater the coarse grain. Coarsegrain siliconizing for0.5h cannot achieve siliconizing.The siliconizing depth ofpure iron SMATed45min siliconizing for9h depth up to150μm.Siliconizing cannot influence HCand MRobviously.the saturation magnetization of SMATed45min siliconizing for9h is biggest,is235emu/g.