Advanced Materials Research Vols. 535-537

Abstract: In order to obtain the optimal rolling and cooling processes-parameters for producing C-Mn-Si dual phase steel on CSP line, computer-aid modeling austenite decomposition during laminar cooling is carried out in present paper. Effects of chemical compositions, finishing rolling temperature (FT7), isothermal holing temperature (HT) and isothermal holding time (t) on austenite decomposition are investigated. The optimal steel chemistry and rolling and cooling processing-parameters are obtained through the modeling. According to the modeling results, 580MPa grade C-Mn-Si DP steel is successfully produced on CSP line with 0.05~0.07mass%C,1.20~1.50mass%Mn, 0.50~0.70mass%Si, FT=820~840°C, HT=680~720°C,t=8~11s. Comparison of modeling results and industrial trials show that current modeling structure is able to model and optimize processing parameters for C-Mn-Si DP steel production on CSP line.

Abstract: Effect of annealing time on the microstructure and texture of IF steel sheets was investigated. Average grain size, grain boundary character and recrystallization texture were measured by X-ray diffraction (XRD) and electron backscatter diffraction (EBSD) in order to clarify the effect of annealing time on microstructure of recrystallization process. The average grain size increased with increasing annealing time. With rising annealing time, the number of low angle boundary (0～15o) decreased due to the mergence of grain with sub-boundary. The //ND (-fiber) pole intensity had a highest value annealed at 60s. The annealing time played an important role in recrystallization process which affected the mechanical properties and microstructure of IF steels.

Abstract: Pure 410L powder is used to mix with an additive to prepare a powder mixed paste. 410L honeycombs are fabricated by extruding the powder mixed paste, then dried and sintered. With sintering temperature increasing from 1120°C to1150°C, the density of sintered honeycombs increasing, powder particles bind together and become grains. The structure parameters and properties of sintered honeycombs were obtained by measuring and calculating. Results show that wall thickness 0.13~0.18mm, cell number (1/in2) 350~385, clear cross section (%) 73~80, specific surface Sv(sq m/cu dm）2.68~2.85； specific heat capacity Cp(J/g.K) 0.50~0.56, heat conductivity κ(W/m.K) 11.2~12.5. SEM/EDS analysis shows that the structure of sintered honeycombs consists of matrix phase α-Fe(Cr) and small particles which are complex compounds of silicon, iron and inclusion elements distributed in matrix. Chromium oxide is formed on surface of sintered honeycombs.

Abstract: The influence of tempering temperature on the microstructure and mechanical properties of low carbon low alloy steel was investigated. The results show that tempering temperature has considerable influence on both yield strength and tensile strength. With the increase in tempering temperature, the yield strength increases first and then decreases after it reaches the highest point at 600°C with a strength of 843MPa, while the tensile strength decreases fastly from 550°C to 650°C and keeps stable after increasing drastically at 720°C. The yield ratio is about 0.60 except at 600°C and 650°C with a high yield ratio of 0.90, while the total elongation has little change. It is concluded that the major change of mechanical properties after tempering has a connection with the decomposition of M/A(martensite/austenite) islands, the recovery of dislocations and the precipitation of alloy elements.

Abstract: The influence of prior austenite grain size on the crystallography of allotriomorphic ferrite is investigated in a low carbon steel. The results show that as the prior austenite grain size decreasing, the fraction of allotriomorphic ferrites that do not keep K-S orientation relationship with any surrounding prior austenite grains is increased. It is observed that such ferrites usually form at the grain edges or grain corners. It is known that with the grain size decreasing, the fraction of grain edges and corners increases. It is suggested that the free energy of the defects at such nucleation sites is higher than that at grain faces, and the nucleation barrier of ferrite is lower. As a result, the possibility for the ferrite to form that does not have orientation relationship with all surrounding austenite grains is increased at such sites.

Abstract: Cleanliness of steels is one of the major factors influencing the final product quality. This paper introduced industrial practice of producing clean steel by EAF-LF-VD-Billet casting process. The cleanliness of 55SiMnMo steel during the whole producing process was analyzed by methods of sampling systematically and comprehensive analysis including total oxygen and nitrogen content analysis, optical microscope observation and SEM+EDS. The factors affecting the steel cleanliness were discussed. Some measures to improve steel cleanliness were proposed.

Abstract: The 4.2wt.%Si non-oriented electrical steel thin sheets with the thickness of 0.30mm were produced by the conventional procedure including hot rolling, cold rolling and annealing. The recrystallization texture was analyzed with emphasis on the effect of normalizing annealing. The results show that the  fiber with peak at {111} is weaker and η fiber is stronger in the sheets with normalizing annealing than those without normalizing annealing, either under the cold rolled reduction of 77% or 86%. Effects of normalizing annealing on the recrystallization texture can be explained in terms of the characteristic of the shear bands formed during cold rolling process.

Abstract: High temperature confocal laser microscope, FE-SEM-EDS and EPMA were utilized to study the Ti-Mn-Al-Si-O-S complex inclusion inducing IAF in Ti deoxidized steel. FactStage was also used to calculate the thermodynamics of inclusion formation. It was demonstrated that when the cooling rate is fixed to 5°C/s, IAF can be induced by complex inclusions which act as the core of IAF at 609°C. Microstructure of the complex inclusions is complicated. These inclusions are consisted of the TiOx-MnO core which is surrounded by MnO-Al2O3-SiO2 complex inclusions and small amount of MnS. The reason that Ti-Mn-Al-Si-O-S complex inclusions can induce IAF is that a Mn-depleted zone is formed by the core TiOx-MnO and the MnS around it. Meanwhile, the difference between MnO-Al2O3-SiO2 and austenite thermal expansion coefficients is tremendous is another principle element for the IAF formation.

Abstract: Considering the specialities of high strength normalized steel, the main roles of vanadium in normalized steel were investigated. The results show that adding vanadium can improve the strength and deteriorate the impact energy, but for vanadium steel, the strengths increase and the impact energies have no changing regulation with increasing vanadium. The microstructures of experimental steels are composed of polygonal ferrite and pearlite, vanadium can not refine ferrite grain size, most of them dissolve into the matrix, and the forms of precipitation in vanadium steel are complex carbonitrides. Grain refinement plays a greater role in improving the low temperature toughness of high strength normalized steels, the strength index is firstly considered in designing this kind of steels.

Abstract: It was analyzed by strain-induced precipitation model that Nb(C,N) precipitation in micro alloy steel slab was effected by strain rate during continuous casting process. The results are as follows: The changing of casting speed could effect the time for 5%precipitation of Nb(C,N), which was decreasing with increasing casting speed at certain temperature and strain rate. Slab strain and strain rate were too small in bending zone and leveling zone. The effect of slab strain rate on Nb(C,N) precipitation could be ignore when Nb(C,N) precipitation in continuous casting process was studied.