Advanced Materials Research Vols. 97-101

Abstract: High-strength IF steel sheet has increasingly attracted more attention of steelmakers in recent years as it has the potential to lighten the weight of automobiles and save energy and lower the production cost. In this paper, the effect of processing parameters on microstructures and mechanical properties especially deep drawability of ferritic-rolled P-added high strength Ti-stabilized IF steels were investigated and the precipitates in the steels were also analyzed. The results show that lubricant condition has great influence on the r-value and deep drawability of high-strength IF steels. And with the decrease of rolling temperature in ferrite region, the deep drawability of steels is improved.

Abstract: The method for establishing the forming limit diagram (FLD) of multi-gauge high strength steel laser tailor-welded blanks (LTWB) is introduced based on analyzing the failure mechanism of multi-gauge LTWB. The Nakazima test is performed to generate the limit strain of multi-gauge high strength steel LTWB. By means of the ARGUS strain measuring system, the limit strain is measured and the FLD of LTWB is plotted subsequently. The FLD established by the Nakazima test is introduced into the FEA forming process as the failure criteria. Compared with the predicted result of the FLD of thinner metal, better correlation between the simulation and experimental results is indicated by adopting the FLD of LTWB as the necking criteria, which also reveals the validity and practicability of the FLD research method for multi-gauge high strength steel LTWB.

Abstract: After heat treatment, the structures and properties of ZL101A alloy with different La and La+Sr contents were studied. The results show that a significant modifying effect can be achieved in ZL101A in metal mould casting. The Si phase in the alloy becomes finer and the average alloy grain size is reduced from 3 mm to 1 mm with La addition 0.6%, which is mainly attributed to the enrichment of La at the eutectic front. The tensile strength and elongation increased with the increasing of La addition. However, excessive amount of La will have negative effects on the tensile strength and elongation. Mixed 0.2% La and 0.015% Sr results in further refined average grain down to 0.5mm, exhibiting improved strength and elongation properties.

Abstract: Effects of shot-peening on Cr-Rare earth-boronizing at 650°C for 4 – 8h for medium carbon steel are investigated in this paper. The value difference in boron diffusion activation energy between shot-peening and undeformation is calculated. The layer depth, microhardness and brittleness are also analyzed. The results show that the activation energy has a decrease of 5647.78 J/mol after shot-peening for 1.5h, and the layer depth increases with prolonged shot-peening time. The layer can also retain its high hardness with low brittleness. The analysis indicates that shot-peening can provide a large number of crystal lattice defects that facilitates boron diffusion in the steel, and the low temperature is apt to remain high dislocation density.

Abstract: The problem of bifurcation and chaos in a 4-side simply supported rectangular thin electro-magneto-elastic plate in electro-magnetic, mechanical and temperature fields is studied. Based on the basic nonlinear electro-magneto-elastic motion equations for a rectangular thin plate and expressions of electromagnetic forces, vibration equations are derived for the mechanical loading in a nonlinear temperature field and a steady transverse magnetic field. By using Melnikov function method, the criteria are obtained for chaos motion to exist as demonstrated by the Smale horseshoe mapping. The vibration equations are solved numerically by using a fourth-order Runge-Kutta method. Its bifurcation diagram, Lyapunov exponents diagram, displacement wave diagram, phase diagram and Poincare section diagram are obtained for some examples. The characteristics of the vibration system are analyzed, and the roles of parameters on the systems are discussed separately as well, such as electromagnetic field intensity, temperature and mechanical force.

Abstract: A low cycle fatigue life (LCF) prediction model for nickel-based single crystal (SC) is presented based on the LCF experiments of notched specimens. Fatigue notch factor is adopted to reflect the influence of notch shape on LCF. Orientation function is adopted to modify total strain range and eliminate the influence of orientation on LCF. Cycle stress ratio is adopted to reflect the influence of mean stress and cycle character on LCF. The predicted results shows that all the data are in the factor of 2.1 scatter band, which means that the model proposed in this work is reasonable.

Abstract: The effect of reactive-Al2O3 addition on the pore size distribution and thermal conductivity of carbon blocks for blast furnace was investigated by using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray, mercury porosimetry, and a laser thermal conductivity meter. The results showed that the pore size distribution and the thermal conductivity of carbon block were mainly influenced by SiC whiskers and reactive-Al2O3. With increasing addition of reactive-Al2O3, the mean pore diameter reduced and < 1μm pore volume increased of open pores owing to the more efficient filling of pores by SiC and reactive-Al2O3, and the thermal conductivities of samples increased due to the facts that the higher thermal conductivity of reactive-Al2O3 than that of brown corundum and the more formation amount of high thermal conductivity of SiC.

Abstract: The Deep Cryogenic Treatment(DCT) process of W4Mo3Cr4VSi HSS was studied by orthogonal experiment method. The paper analysed the effect of various DCT process parameters on mechanical properties and observed microstructure before and after DCT treatment by the SEM. The results show that the effect of soaking temperature on the properties of drill is the first factor, the soaking time is second and the cooling rate is third. DCT enhances the transformation of austenite to martensite, and distributable carbide particles are precipitated from martensite. Therefore DCT increase hardness and enhance wear resistance of twist drill.

Abstract: Bi4Ti3-xNbxO12+x/2 (BNT) ceramics were prepared by a solid-state reaction method. Effects of Nb doping on dielectric and ferroelectric properties of BNT were investigated. XRD patterns show that Nb5+ substitutions do not change the phase structure. With the increase of Nb doping, dielectric constant and Curie temperature decrease gradually. At the same time, dielectric loss peaks become flatter and dielectric losses become smaller due to the decrease of oxygen vacancies derived from the introduction of Nb5+ at Ti4+ site in BNT. Remanent polarization Pr and coercive field EC of BNT ceramics are both larger than those of BIT without Nb doping. With the increase of Nb doping from 0 to 0.045, Pr increases to the largest value of 17 μC/cm2 and EC decreases to the lowest value of 87 kV/cm, but Pr will decrease when Nb doping content is over 0.045.

Abstract: Vanadic-titanomagnetite-coal mixed pellets with minor addition of Na2CO3 were reduced isothermally at 900°C, 945°C, 1100°C, 1255.4°C and 1300°C. The variables parameters studied are temperature, the amount of carbon and the amount of Na2CO3 as additive. The experiment was designed with the technique of orthogonal regression in order to quantitatively assess the effect of each variable and the interactional effect of different variables. It is found that temperature, the amount of carbon and the amount of Na2CO3 as additive substantially influence the degree of reduction and metallization, and the presence of Na2CO3 can increase the reducibility of the pellets. The interaction of temperature and the amount of Na2CO3 have negative influences on the degree of reduction and metallization.