Balanced solubility product and enthalpies of formation of Nb compounds in 0.09 % oriented silicon steel

Balance solubility products and enthalpy of for- mation for NbC0.75, NbC0.85, NbC0.88, NbC and NbN in oriented silicon steels were calculated and compared quali- tatively. Meanwhile, the mixing enthalpies of these five Nb compounds were calculated based on Miedema Model. The results show that the solubility products of Nb compounds in ferrite and austenite meet the following relationship, NbC0.75 〉 NbC0.85 〉 NbC0.88 〉 NbC 〉 NbN and NbN has the minimum enthalpy of formation. It indicates that NbN easily precipitate out, but it is more difficult for NbC0.75.

Tension-Compression Yield Asymmetry Influenced by the Variable Deformation Modes in Gradient Structure Mg Alloys

Surface mechanical attrition treatment(SMAT) was carried out on hot-rolled AZ31 Mg samples along two orthogonal directions;as a result,two types of gradient structures with different grain sizes and texture components in different layers were produced.The tension-compression yield asymmetry(YA) was studied using samples with different thicknesses,in order to elucidate the effect of combinations of variable deformation modes operating in different layers of the two oriented SMAT samples.The 0° oriented SMAT sample containing layers with strong basal texture displayed significant YA,because of either dislocation slip or extension twinning domination during tension or compression.By contrast,the 90° oriented SMAT sample containing layers with coexisting orthogonal texture components had an obviously weakened YA,which was attributed to the multi-deformation modes cooperating during tension or compression,i.e.,extension twinning or detwinning in conjunction with dislocation slips,leading to close yield stresses compared between tension and compression.

Microstructure transformation of X70 pipeline steel welding heat-affected zone

The continuous cooling transformation curve of heat-affected zone （HAZ） of X70 pipeline steel was mea- sured by Gleeble-3500 thermal mechanical simulator, optical microscope （OM） and hardness analysis. The microstructure transformation rule at different cooling rates and solution behaviors of microalloy carbonitride during heating process of simulated specimens were investigated. When the cooling rate changes from 10 to 20 ℃.s-l, microstructures at HAZ are identified as granular bainite, lathy bainite, and quasi-polygonal ferrite. This micro- structure is featured with fine ferrite grains, martensite/ austenite islands dispersed, high-density dislocations, and fine carbonitride particles, resulting in improving the strength and toughness of HAZ. With the cooling rate increasing to above 40 ℃.s-1, the microstructure is pre- dominantly coarse lathy bainite with clear primary aus- tenite grain boundary. While the cooling rate decreases to below 1 ℃.s-1, a fairly small amount of pearlite can be observed at the boundaries. The strength and toughness of HAZ are deteriorated because of coarse grains among these microstructures. Most of microalloy carbonitrides in HAZ could be dissolved in the matrix during heating process. A few of TiN particles existing as residues in the matrix can prevent austenite grain from growing, and then improve the strength and toughness of HAZ.

Dependence of tensile properties on microstructural features of bimodal-sized ferrite/cementite steels

A medium-carbon steel was processed through different warm rolling techniques,and the microstructural features with bimodal grain size distribution were found to be different.The combination of strength and ductility was ameliorated in the steel processed through warm rolling characterized by biaxial reduction.The enhanced strength is attributed to the densely distributed fine intragranular cementite particles and the small grain size in the coarse grain regions.The enhanced uniform elongation is due to the improved work hardening behavior at the large-strain stage.This work hardening behavior is predominantly ascribed to the finely dispersed intragranular particles.The relatively small grain size with nearly equiaxed shape in the coarse grain regions helps stabilize the uniform deformation to a large strain.

Deformation resistance of Fe-Mn-V-N alloy under different deformation processes

The deformation resistance of Fe-Mn-V-N alloy under different deformation conditions was investigated by hot compression method on thermal simulator. Effects of deformation degree, deformation temperature, and strain rate on deformation resistance were analyzed. The results show that when other conditions are constant, the deformation resistance increases with the increase in deformation degree and strain rate and decreases with the increase in deformation temperature. At the same time, the mathematical model of deformation resistance for Fe-Mn- V-N alloy was established by lstOpt software using the Levenberg-Marquardt optimization algorithm carried out on the fitting of regression coefficients, which has higher fitting precision.

Constitutive Model of Warm Deformation Behavior of Medium Carbon Steel

The compressive behaviors of medium carbon steel specimens were investigated over a wide range of tem- peratures and strain rates using a Gleeble-3500 thermo-simulation machine. The results show that the flow stress in- creased with strain at first, and then gradually decreased after reaching a peak value. The flow stress softening rate at a high strain rate was larger than that at a low strain rate. The effects of deformation heating and friction on flow stress were analyzed. A new friction correction method, wherein the effect of strain on frictional coefficient was con- sidered, was established here. The stresses revised by the new method deviated from the measured stresses with in- creasing strain. Meanwhile, the apparent frictional coefficient variation law with strain was obtained. The frictional coefficient increased as the strain increased and then slightly decreased after maintaining a constant value. The stress was corrected by considering deformation heating. The accuracy of the temperature correction method was verified using a special experiment. The results of the verification experiment show that the temperature correction method exhibited a good accuracy in calculating the variation of stress caused by deformation heating. A constitutive model considering strain was proposed here to describe the deformation behaviors. Compared with experimental data, the modified constitutive model exhibited a good accuracy as to constitutive correlation.

Nanoscratching and mechanical behaviors of high-entropy alloys with different phase constituents

High-entropy alloys(HEAs)exhibit unique microstructural features and properties in nanoscale and atomic scale because of their multi-element alloy system.The nanoscratching behaviors of three HEAs with different phase constituents,relative to the microstructure and mechanical properties of the HEAs,were investigated.Three typical phase constituents were selected:face-centered cubic(FCC)structure,body-centered cubic(BCC)structure,and a dual-phase structure containing both FCC and BCC phases.Despite the fact that the FCC alloy has the highest ductility and strain hardening capability,it exhibited inferior scratch resistance due to the over-softening of hardness.Due to the brittle failure mode,the BCC alloy hardly exhibited desirable scratch resistance despite its highest hardness.By contrast,the nanostructured dual-phase alloy exhibited the best scratch resistance because of its good combination of strength and ductility,as well as the ductile failure mode.This research suggests that the HEA with structure comprising nanoscale hard and soft phases is desirable for nanoscratch resistance,and possesses appropriate hardness for industrial applications.