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In the present study, double-sided gas shield welding (GSW), in a single pass, was applied to Fe-21Cr-15Ni-6Mn-Nb nonmagnetic stainless steel plate. The microstructure and performance of the welded joint were investigated via microstructural and phase analysis, mechanical testing and magnetic analysis. The results showed a satisfactory micrographic appearance with full penetration, and no solidification defects observed in the welded joint, which showed typical epitaxial growth characteristics in the welding solidification. Slight grain growth, with an average size of ~ 18.9 μm, occurred in the heat-affected zone (HAZ). The primary dendrite arms, on both sides of welding joint, grew along the direction of the temperature gradient and met at the centerline of the weld with no parting microstructure in evidence. The secondary dendrite arm spacing was stable in all parts of the weld zone (WZ). The hardness of the weld zone was higher than that of the HAZ and the base metal (BM), with the lowest hardness occurring in the HAZ. The results of tensile testing showed a higher strength of the welded metal (WM) compared to the BM, and a good strength-ductility balance of the welded joint. The impact energy of the HAZ was higher than that of the WZ, corresponding to 60.5 J at room temperature and 52.7 J at − 196 °C. Microvoid coalescence, concurrent with crack propagation along the direction of the long axis of the dendritic sub-grains, was observed during plastic deformation in the WZ. Additionally, the excellent paramagnetic characteristics of the welded specimens were revealed.

The effect of aging on the precipitates, mechanical and magnetic properties of Fe-21Cr-15Ni-6Mn-Nb low magnetic stainless steel were investigated. The steel was aged at 550–750 °C for 2 h after solution heat treatment at 1100 °C for 1 h. During the aging treatment, the (Nb, V)(C, N) particles gradually precipitated in the grain, which were coherent or semi-coherent with the matrix. When the aging temperature was beyond 650 °C, the coarsening rate of (Nb, V)(C, N) particles increase rapidly and the coherent orientation between (Nb, V)(C, N) particles and the matrix was lost gradually. Meanwhile, coarse M23C6 was distributed at the grain boundary with chain shape, which was non-coherent with the matrix. The coarsening behavior of (Nb, V)(C, N) precipitates in the grain was analyzed, and the size of the particles precipitated after aging treatment at 650°C for different time was calculated and studied. After aging treatment at 650 °C for 2 h, the yield strength and tensile strength of the stainless steel was 705.6 MPa and 1002.3 MPa, the elongation and the relative magnetic permeability was 37.8% and 1.0035, respectively.

The microstructural transition and mechanical properties of Fe-Cr-2Ni-Mo-V steel were investigated in a carburizing process with carburizing at 935 °C, oil quenched, re-quenched at 880 °C,and low-temperature tempered at 180 °C. X-ray diffraction was employed for phase analysis and Ir Carbon-sulfur Spectrometer was used for carbon content detection. The morphologies of martensite were observed by scanning electron microscopy. The Vickers hardness was measured and the impact toughness was measured by means of Charpy’s V-notch tests. The results show that the carbon concentration and hardness gradients are established after carburizing process as a function of distance from the case to core. The carbon content gradient results in a gradient of martensitic microstructures, ranging from plate martensitic morphologies with large amounts of retained austenite in case to lath martensitic microstructures with essentially no retained austenite in core. The mechanical properties are significantly improved with adding re-quenching and low-temperature tempering. The case hardness, core hardness, tensile strength and impact energy are 851 HV, 402 HV, 1310 MPa and 92 J, respectively.

Micro-textures and mechanical properties of Fe–21Cr–15Ni–6Mn–Mo–Nb austenitic stainless steel during asymmetric hot rolling were studied. The results show that the shear texture is the dominant texture on the upper surface of steel sheet when the specific velocity ratio is 1.1, and the orientation of γ-Fiber was beneficial to recrystallization and nucleation. The texture strength of the central layer of the steel plate was concentrated in the Cube orientation. When the velocity ratio increases to 1.2, the complete recrystallization of the upper and central layers of the plate was more likely to occur under the condition of high deformation energy, and the structure of the steel sheet had tended to homogenize. Under the conditions of low reduction (20%) or low finishing temperature (860 °C), the steel sheet was partially recrystallized or non-recrystallized, and there were a lot of deformation textures during rolling. In the process of asymmetric hot rolling, the crystal rotates around the direction of TD, and the initial texture of weak γ-Fiber and Copper deviates from the ideal position and gradually approaches to the direction of γ-Fiber. Based on the research, the tested austenitic stainless steel had high strength and toughness (the yield strength, the tensile strength and the elongation is 710.1 MPa, 1010.2 MPa and 46.7%) under the rolling process with specific speed ratio 1.2, the initial rolling temperature 1100 °C and the reduction 60%.

The high heat problem caused by the ferromagnetic effect of traditional large transformer is urgently needed to be solved. Therefore, we need to develop new material large transformers to solve this problem. In the experiment, we measured hysteresis curve and temperature rise rate of the cement base manganese zinc composite materials. In addition, the application performance and transformer ratio of the composite transformer are studied experimentally, and the output voltage of the composite transformer is calculated. By analyzing the experimental data, the manganese zinc soft magnetic concrete composite material can be used in the transformer completely, and can effectively improve the transformer high temperature problem, which extends the new ideas for development of new type transformer.

The present work investigates the annealing twins of Fe-20Mn-4Al-0.3C austenitic steels in symmetric hot rolling (SHR) and asymmetric hot rolling (ASHR). The average grain size is 26 (&plusmn, 9.6) &mu, m and 11 (&plusmn, 7.0) &mu, m for the tested steel in SHR and ASHR processes. The density of high angle grain boundary (HAGB) and annealing twin boundary increase with the decrease of grain size. The annealing twin is obviously higher in ASHR than in SHR. The linear relation model between the logarithm of twin boundary density and the logarithm of the grain size is established. The grain boundary migration is continuously generated during recrystallization in SHR process. The coincident site lattice (CSL) boundary proportion increases with local grain boundary continuing bugling and the migration direction of bugling grain boundary constantly changes. The tensile property of the tested steel is improved due to the effective grain refinement and high density of annealing twins caused by the severe strain in the ASHR process. The purpose of high density HAGB for austenitic steels is helpful to an improvement in mechanical properties.