Peculiarities of the formation of high-coercivity structure of (Sm,Zr)(Со,Cu,Fe)z alloys in varying the (4f-,4d-)/(3d-) element relationship

Processes of the formation of high-coercivity state of Sm0.85Zr0.15(Co0.702Cu0.088Fe0.210)z alloys with different z = 6.0, 6.5 and 6.8, which is the value characterized the relationship of (4f-,4d-)/(3d-) elements in these alloys, are studied. It is shown the interrelation of the chemical composition of samples and their microstructure with the coercive force formed in the course of isothermal tempering and tempering during slow cooling (or stepped tempering). The interrelation of the high-coercivity state of the alloys and quantitative ratio (volume fractions) of the main structural components based on the 2:17R and 1:5H phases is discussed. It is shown that the cellular morphology of the alloy, which corresponds to the high-coercivity state, forms during isothermal tempering, whereas the final phase compositions of the main structural components form in the temperature range from the isothermal aging temperature to 400 °С during stepped (slow) cooling or upon quenching. The magnetic properties of sample in the high-coercivity state are determined by the degree of completeness of phase transformations of the main structural components; this directly depends on their quantitative relationships and the relationship of the (4f-,4d-)/(3d-) elements, i.e., on the z value in the alloy formula (Sm,Zr)(Со,Cu,Fe)z.

Effect of Carbide Precipitation on the Evolution of Residual Stress during Tempering

The evolution of microstructure and residual stress during the tempering of 700 L low-carbon micro-alloyed steel was studied using a crack compliance method for measuring residual stress. Additionally, a non-isothermal tempering dilatation test, Vickers micro-hardness test, and transmission electron microscopy were used. The evolution of residual stress during tempering consists of two stages. The first stage coincided with cementite precipitation. Under the initial residual stress, the transformation plasticity due to cementite precipitation leads to partial relaxation of the micro-stress evoked by the austenite-to-ferrite transformation during quenching. It also caused the material surface and the core to exhibit different residual stress evolution trends. After tempering at 300 ∘ C for 30 min, the residual stress was reduced from 487 MPa to 200 MPa; however, the elastic strain energy remained unchanged. The second stage coincided with alloy carbide precipitation and Mn partitioning, but the precipitation of the alloy carbide only reduced the elastic strain energy by 8.7%. Thus, the change in activation energy was the main reason for the relaxation of residual stress at this stage. After tempering at 600 ∘ C for 30 min, the residual stress was reduced to 174 MPa, the elastic strain energy was reduced by 72.72%, and the residual stress was controlled.

Influence of Starting Microstructure on Dilatation Behavior during Tempering of a High Strength Steel

The aim of this study was to determine the effect of non-isothermal tempering on microstructure evolution in large-size slabs. Using high-resolution dilatometry, three different cooling rates (from 0.08 to 3°C/s) representative of different regions from the surface to the core of the slab were experimentally simulated, and then tempering was carried out for each starting microstructure. A combination of light and electron microscopy and X-ray diffraction analyses were employed to accurately analyze different phenomena occurring during the tempering process, specially, the identification of different microstructures (bainite, martensite and retained austenite), and the determination of the percentage of retained austenite for each experimental condition were considered. Experimental results revealed that the microstructure after the cooling rate of 0.08°C/s consisted of bainite and some retained austenite. For the cooling rate of 0.3°C/s, martensite plus bainite was detected, and when the cooling rate was increased to 3°C/s, a martensitic microstructure was obtained. Analysis of dilatometry curves indicated that tempering behavior varied significantly with the starting microstructure. Martensite tempering was accompanied with a length decrease due to the decomposition of medium-carbon martensite to low-carbon martensite plus carbides. Tempering of bainite and retained austenite resulted in a remarkable length increase.

Retained Austenite Decomposition and Carbide Precipitation during Isothermal Tempering of a Medium-Carbon Low-Alloy Bainitic Steel

The effect of isothermal tempering on retained austenite decomposition and carbide precipitation were investigated in a medium-carbon low-alloy bainitic steel. High-resolution dilatometry was used to perform isothermal tempering at 350 °C, 550 °C and 600 °C for different holding times up to 16 h. The decomposition of retained austenite, morphology and composition of carbides were investigated by analyzing the dilatometric curves and were confirmed through scanning and transmission electron microscopy observations. The decomposition behavior of retained austenite varied significantly as a function of the tempering temperature with a full decomposition observed at 600 °C. It was also found that by increasing the tempering temperature from 550 °C to 600 °C, carbides precipitate approximately twice as fast, and evolve from M3C type to Cr7C3 and Cr23C6 after 16 h of tempering at 600 °C.

Impact of sintering method on certain properties of titanium dioxide nanopowder materials

Titanium dioxide nanopowder samples consolidated by method of cold uniaxial compaction at 200 MPa and conventionally sintered in air at 1300?? with isothermal tempering during 60 minutes or spark-plasma sintering at 1300?? and 30 MP? were studied using the method of light combination scattering spectroscopy (Raman spectroscopy) and scanning electron microscopy. The samples were found to differ significantly in terms of color, density, phase composition and microstructure.