Effects of cooling rate and Al on MnS formation in medium-carbon non-quenched and tempered steels

The effect of Al on the morphology of MnS in medium-carbon non-quenched and tempered steel was investigated at three different cooling rates of 0.24, 0.43, and 200°C·s^-1. The formation mechanisms of three types of MnS were elucidated based on phase diagram information combined with crystal growth models. The morphology of MnS is governed by the precipitation mode and the growth conditions. A monotectic reaction and subsequent fast solidification lead to globular Type I MnS. Type II MnS inclusions with different morphological characteristics form as a result of a eutectic reaction followed by the growth in the Fe matrix. Type III MnS presents a divorced eutectic morphology. At the cooling rate of 0.24°C·s^-1, the precipitation of dispersed Type III MnS is significantly enhanced by the addition of 0.044wt% acid-soluble Al（Als）, while Type II MnS clusters prefer to form in steels with either 0.034wt% or 0.052wt% Als. At the relatively higher cooling rates of 200°C·s^-1 and 0.43°C·s^-1, the formation of Type I and Type II MnS inclusions is promoted, and the influence of Al is negligible. The results of this work are expected to be employed in practice to improve the mechanical properties of non-quenched and tempered steels.

Influence of soaking time in deep cryogenic treatment on the microstructure and mechanical properties of low-alloy medium-carbon HY-TUF steel

The influence of soaking time in deep cryogenic treatment on the tensile and impact properties of low-alloy medium-carbon HY-TUF steel was investigated in this study. Microstructural studies based on phase distribution mapping by electron backscatter diffraction show that the deep cryogenic process causes a decrease in the content of retained austenite and an increase in the volume fraction of η-carbide with increasing soaking time up to 48 h. The decrease in the content of retained austenite from ~1.23vol% to 0.48vol% suggests an isothermal martensitic transformation at 77 K. The η-type precipitates formed in deep cryogenic-treated martensite over 48 h have the Hirotsu and Nagakura orientation relation with the martensitic matrix. Furthermore, a high coherency between η-carbide and the martensitic matrix is observed by high-resolution transmission electron microscopy. The variations in macrohardness, yield strength, ultimate tensile strength, and ductility with soaking time in the deep cryogenic process show a peak/plateau trend.

The Stochastic Stability of a Viscoelastic Cable with Small Sag

In this paper, the almost sure stability of a viscoelastic cable subjected to an initial stress on the uniform cross section is studied. The constitutive of the cable material is assumed to be the hereditary integral type, the relaxation kernels of which are represented by the sums of exponents. The initial stress and the damping coefficientto the environment and also relaxation kernel coefficients are a random wide band stationary process. The partial differential integral equation of motion is derived first. Then by applying Galerkins method, the governing equation is reduced to a set of second order differential integral equations. Based on the Liapunovs direct method, sufficient conditions for almost sure stability of viscoelstic cable are obtained.

Recent progress in medium-Mn steels made with new designing strategies, a review

After summarizing the relevant researches on the medium Mn steels in references, two new targets on the tensile properties have been defined. One is that both transformation-induced（TRIP） and twinninginduced plasticity（TWIP） could be realized for the steel with a relatively low Mn content, which exhibits the similar tensile properties to the classical TWIP steels with higher Mn content. The other is to achieve ultrahigh ultimate tensile strength（〉1.5 GPa） without sacrificing formability. To achieve these goals,new designing strategies was put forward for compositions and the processing route. In particular, warm rolling was employed instead of the usual hot/cold rolling process because the former can produce a mixture of retained austenite grains with different morphologies and sizes via the partial recrystallization. Consequently, the retained austenite grains have a wide range of mechanic stability so that they can transform to martensite gradually during deformation, leading to enhanced TRIP effect and then improved mechanic properties. Finally, it is succeeded in manufacturing these targeted medium Mn steels in laboratory, some of them even exhibit better tensile properties than our expectation.

Microstructures and properties of CuZrAl and CuZrAlTi medium entropy alloys prepared by mechanical alloying and spark plasma sintering

Equiatomic CuZrAl and CuZrAlTi medium entropy alloys were designed and synthesized by mechanical alloying and spark plasma sintering technique.The alloying behavior,phase evolutions,microstructures and properties of samples were investigated by X-ray diffraction,differential scanning calorimetry,field emission scanning electron microscopy,microscopy/Vickers hardness testing and electrochemical polarization measurement.The results indicate that the final products of as-milled alloys consist of amorphous phases.Ti addition improves the glass forming ability of as-milled alloys.The as-sintered CuZrAl alloy contains face-centered cubic（fcc）solid solution,Al_（1.05）Cu_（0.95） Zr and AlZr_2 phases at different sintering temperatures.With Ti addition,the as-sintered sample is only composed of intermetallics at 690°C,while fcc1,fcc2 and CuTi3phases are formed at 1100°C.CuZrAlTi-1100°C alloy exhibits the highest hardness value of 1173HV0.2owing to the high sintering density,solid solution strengthening and homogeneous precipitation of nano-size crystalline phase.CuZrAlTi-690°C alloy presents a similar corrosion resistance with304 Lstainless steel in seawater solution and further possesses the lower corrosion rate.

Microstructure and Tensile Properties of a Nb–Mo Microalloyed 6.5Mn Alloy Processed by Intercritical Annealing and Quenching and Partitioning

The transformation behavior, microstructural evolution and mechanical properties were compared in a coldrolled Nb–Mo microalloyed 6.5Mn alloy after intercritical annealing（IA） and quenching and partitioning（Q ＆ P）,respectively. The thermodynamic calculation and theoretical analysis were used to determine the optimal heat treatment parameters. The Q ＆ P samples exhibited relatively higher strength with relatively low ductility, mainly due to the hard martensite matrix, which resulted in continuous yielding behavior upon loading, whereas the IA samples showed the significantly improved ductility, which benefited from the more sufficient transformation-induced plasticity（TRIP） effects and the softer ultrafine ferrite matrix. The dependence of yield point elongation（YPE） of IA samples on grain size demonstrated that the YPE value was in the reverse proportional relationship to the average grain size, which agreed well with theoretical analysis.