Materials Science Forum Vols. 561-565

Abstract: The microstructure of oxide scale formed in the early stage of oxidation of cold-rolled sheets of 17%Cr-Mn-Ni austenitic stainless steel was examined using SEM and TEM. Samples were oxidized at 973 to1373K for 1 to 15min. Nodules were observed on the surfaces of specimens oxidized at 1173K. The nodules were composed of two layers, which comprised Fe oxides and Cr-rich Fe-Cr-Mn oxides, respectively. The other scale was composed of two layers of Fe-Cr-Mn oxides with different compositions. Nodules were not observed on the surfaces of the specimens oxidized at 973 and 1373K. After oxidation at 1373K for 1min, the scale was composed of three layers. The first layer consisted of Fe-Mn oxides with a spinel structure, the second consisted mainly of Cr oxides, and the third consisted of Cr-Mn oxides containing a small amount of Fe.

Abstract: Susceptibility of hydrogen embrittlement of a super grade AISI 420 tool steel was studied. Tensile samples were cathodically charged to different hydrogen level. Hydrogen induced mechanical property degradation was measured by tensile tests at a low strain rate. Fractography of broken surfaces was observed using SEM. Relationship between hydrogen content and tensile strength and elongation were studied. Critical hydrogen contents were obtained for different heat treatment states. It was found that for annealed materials could stand for a 3.5ppm hydrogen for keeping 80% of original ductility, and the effect of hydrogen on strength was unobvious. However, for material quenched and tempered at 250°C, only 0.3ppm hydrogen could lead the ductility drop to 80% of original. The material quenched and tempered at 500°C was more sensitive on hydrogen, less than 1ppm hydrogen could lead the strength drop to 80% of original.

Abstract: Tensile properties of twinning induced plasticity (TWIP) steels (31%Mn-3%Al-3%Si-Fe) with various mean grain sizes ranging from ultrafine grain size (1.1μm) to conventional one (35.5μm) at a wide range of strain rates from 10-3sec-1 to 103sec-1 were studied. The ultrafine grained TWIP steel exhibits a large work hardening and keeps an adequate elongation at any strain rate. The strength held to the Hall-Petch relationship at each strain rate and the Hall-Petch slopes do not change largely.

Abstract: The precipitation of copper during aging at 650oC within ferrite in high-purity Fe-1.03wt%Cu steel was examined by transmission electron microscopy, and the influence of precipitation particles on property of experimental steel was investigated. The microstructure and the corresponding diffraction patterns of different zone axis were analyzed. Nano-scale copper-rich clusters with B2-like structure and high density dislocation around precipitate was observed during either solution treatment or aging. Nano-scale metastable precipitates and high density around them were found to play the most important role for increasing steel strength.

Abstract: Asymmetric rolling of thin strip has become important due to a significant decrease of rolling force, which contributes to obtain the extremely thin strip, to reduce the rolling passes, and to save the energy by a decrease of anneal treatment. In asymmetric rolling of thin strip, edges of work rolls may contact and deform when no or small work roll bending force is applied. Work roll edge contact forms a new deformation feature. In this paper, the effects of initial thickness of strip and friction coefficient on the rolling pressure, roll edge contact length and strip crown during asymmetric rolling of thin strip with work roll edge contact effect has been discussed, and the calculated rolling force with work roll edge contact is compared with the measured value.

Abstract: Normally, deformation twinning is a process that occurs at rates approaching the speed of sound in bulk metals once a critical stress has been reached. However, recently it has been shown that twins grow at speeds many orders of magnitude lower than the speed of sound during room temperature creep of titanium alloys. The net result is that this twinning process can contribute to the low-temperature (less than 0.25*Tm) creep behavior of α, α−β, and β−titanium alloys. For example, α-Ti alloys with small grain size do not extensively deform by twinning and hence show little overall creep strain. These recent developments are reviewed in this paper. This work is funded by the National Science Foundation under Grant Number DMR-0517351.

Abstract: A new surface treatment technology for the aluminum alloys that exhibits not only high corrosion and weather resistance but also good mirror luster has been developed. By performing electrolytic permeation, the improved corrosion resistance and weather resistance while maintaining a high mirror luster was achieved for an aluminum alloy A2014-T6. The high strength aluminum alloys featuring high corrosion and weather resistance have been available for industrial products. Then the claim number of the products by A2014 T6 aluminum alloy has been reduced sharply to almost zero level in comparison with a past. A few applications and the development of the processing in industrial scale in A2014 T6 aluminum alloy will be presented.

Abstract: In this paper, the effects of Sb and RE on the solutionized microstructure and microhardness of Mg-6A1-1Zn-0.7Si magnesium alloy are investigated. The research results indicate that the solid solution treatment can result to the modification of Chinese script shaped Mg2Si phases in the microstructure of experimental alloy, and adding small amounts of RE and Sb can strengthen the modification efficiency. In addition, after the solid solution treatment at 420°C, the Mg-6A1-1Zn-0.7Si alloy added 0.4%Sb and 0.25%RE exhibits higher microhardness, but the effect of Sb and RE additions on the changing law between microhardness and solutionized time, is not obvious.

Abstract: The effect of RRA treatment with using low retrogression temperatures between 170°C to 190°C on the strength and electrical conductivity (as an indicator of corrosion resistance) of 7B04 aluminum alloy thick plates was investigated. The research results showed that the low-temperature RRA heat treatment provides a means for improving electrical conductivity of the aluminum alloy 7B04 pre-stretched thick plates without sacrificing the mechanical strength. The RRA temper with retrogression at 180°C for 60 min improved electrical conductivity remarkably (reached 21.0MS/m), with only a 3% reduction in strength below T6 temper. Furthermore, TEM observations showed that the microstructure of RRA treated alloy was a very fine distribution of η′ MgZn2 precipitates in the aluminum matrix, similar to T6 condition and η MgZn2 precipitates on grain boundaries distributed similarly to T73 temper.