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Hot forming of boron steel has become increasingly popular due to the demand of both weight reduction of body parts and enhanced safety for passengers. The most commonly used boron steel grade for hot forming is 22MnB5, with an ultimate tensile strength of ~1,500MPa and quite low total elongation of ~6% in the martensitic state. Recent research mainly focused on improving the ductility of hot formed steels by either introducing a post-hot forming tempering treatment for 22MnB5 or developing an alternative class of hot formed steels such as a medium Mn steel. However, the dimensional variability of the cold-stamped TRIP parts is too high due to the high instantaneous plastic modulus at all strains; whereas hot forming provides a new opportunity for these types of steel grades. This present work will focus on the microstructure characteristics and mechanical behavior of the warm-rolled 0.17C-6.5Mn-1.1Al-0.22Mo-0.05Nb steel, and compared with the commercial hot formed 22MnB5 steel and the conventional multi-stage thermo-mechanical process including hot rolling, cold rolling and intercritical annealing. It can be concluded that the microstructure and mechanical characteristics strongly depended on the warm rolling temperature. The best combination of UTS and TE (~32.0GPa%) was achieved in the 660°C-warm rolled specimen, which is much higher than 12.3GPa% for the hot formed 22MnB5 steel, and is also comparable to 38.3GPa% for the annealed CR specimen.

Large-size electronic-grade polycrystalline silicon is an important material in the semiconductor industry with broad application prospects. However, electronic-grade polycrystalline silicon has extremely high requirements for production technology and currently faces challenges such as carbon impurity breakdown, microstructure and composition nonuniformity and a lack of methods for preparing large-size mirror-like polycrystalline silicon samples. This paper innovatively uses physical methods such as wire cutting, mechanical grinding and ion thinning polishing to prepare large-size polycrystalline silicon samples that are clean, smooth, free from wear and have clear crystal defects. The material was characterized at both macroscopic and microscopic levels using metallographic microscopy, scanning electron microscopy (SEM) with backscattered electron diffraction (EBSD) techniques and scanning transmission electron microscopy (STEM). The crystal structure changes from single crystal silicon core to the surface of the bulk in the large-size polycrystalline silicon samples were revealed, providing a technical basis for optimizing and improving production processes.

Electron backscatter diffraction (EBSD) was used to study the microstructure and formation mechanism of tailor welded sheet of dissimilar steel. The microstructure of weld zone mainly was matensite, the microstructure of heat affected zone (HAZ) were matensite, bainite and ferrite. The analysis of EBSD showed that the microstructure of weld zone was coarser and it had obvious texture. The microstructure in HAZ consisted of equiaxed grains principally. And there was no obvious preferred orientation. A lot of grain boundary and dislocation improved hardness and reduced plasticity for weld and HAZ. The grains of two kind steels had no significant preferred orientation. A large number of high-angle boundaries made the base metal show good strength and plasticity.

Shot peening is a mechanical surface modification technology, which can extend the fatigue life of materials by introducing work hardening, compressive stress, and/or some additional microstructural change in surface layer resulting in a restraint of crack initiation and propagation on the surface. In this study, SUS304, which has high formability and corrosion resistance, was shot peened and fatigued for the determination of their effect on the evolution of microstructures. The fatigue of the specimens were carried out at three different cycles, followed by second shot peening and finish fatigue of 10⁶ cycles. The microstructures of the specimens were investigated using OM, EBSD, SED and EDS. The resulting mechanical property such as microhardness and residual stress was also investigated. Deformed layer of ~100μm and mechanical twins were observed after fatigue and shot peening test. The top surface layer of shot peened specimen showed the highest twin density and microhardness. The increase of the fatigue before shot peening caused increase and deepening of the compressive residual stress. However, the finish fatigue of 10⁶ cycles decreased overall compressive residual stress.