Narrow Results

Microstructure evolution and texture formation in low carbon CSP steel were observed by means of metallgraphic, TEM, and SEM equipped with electron back scattered diffraction (EBSD) system. The influence of large particles and fine carbonitrides precipitates on recrystallization and texture formation during the annealing procedure was analyzed with Small Angle X-ray Scattering (SAXS) technique in the steel. It was found that the fine precipitates present in the steel have shown ability to stimulate recrystallization nucleation and transformation during deformation, but hard to accelerate recrystallization growth because of grain boundary pinning effects in the steel. Compared with the conventional low carbon steel, the recrystallization texture and microstructure of the CSP steel show distinct character, and thus modify the mechanical behaviour of the final products.

By means of finite element method, the effect of velocity of balls on the strain and stress of low carbon steel surface layer during the course of surface mechanical attrition treatment (SMAT) are investigated. The effect of different impact velocity on strain rate and grain refinement mechanism is also analyzed. Calculation results confirm that there exists severe plastic deformation in the surface layer: strain, strain rate and stress gradually decrease along the depth of the treated sample during SMAT, which is in agreement with the microstructures observed in corresponding locations. Strain and strain rate play an important role in the grain refinement process and the resultant grain sizes upon plastic deformation.

Selective carburization of steel components is often used to case harden specific areas without altering the properties. The present work is concerned with Selective carburization treatment on low carbon steel by fluidized-bed furnaces. Selective carburizing was achieved by the use of a water-based ceramic stop-off slurry painted on the surface which formed an effective barrier to carbon diffusion. After carburising the Specimens were quenched. The microstructure of carburization area is martensite, and the hardness can reach 750~950 HV0.05. The microstructure of non-carburization area is still ferrite, the hardness under 160 HV0.05 This type of microstructure is potentially used for the manufacture of tailored properties blanks by hot stamping in the automotive industry.