Thermodynamic Analysis for the Magnetic-Field-Induced Precipitation Behaviours in Steels

Alloy carbide M23C6 plays a significant role in the creep strength of reduced activation steels. Experiments have proven that a magnetic field accelerates the precipitation of M23C6 at intermediate temperature. A scheme that combines first-principle calculations, Weiss molecular field theory and equilibrium software MTDATA is proposed to investigate the thermodynamic features of magnetic-field-induced precipitation. The calculated results reveal that the origin of the magnetic moment is the NaCl-like crystal structure. The magnetic field enhances the exchange coupling and stabilizes the ferromagnetic phase region. The external field influences the Curie temperature, thereby changing the magnitude and position of the maximum magnetic heat capacity, magnetic entropy and enthalpy. The strong magnetic field improves the stability of M23C6, and the theoretical results agree well with the previous experiment. The study provides a theoretical basis for the magnetic-field-induced precipitation behaviours in steels.

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.

ELECTRO-CHEMICAL PRODUCTION OF TUNGSTEN OXIDE FROM PSEUDO-ALLOY CARBIDE TYPE WC-Co

Widespread use of specialized tools, the component part of which is tungsten, leads to the accumulation of its secondary raw materials (worked tools, cutters, drills, etc.). That is why there is a need to create technologies for recycling of the demanded metals, in particular tungsten. The purpose of this work is to study the anode behavior of carbide pseudoalloy type WC-Co in solutions of nitric acid with the addition of fluoride acid to obtain, as a target product, higher tungsten oxide in one stage. The corrosion behavior of carbide type pseudoalloy in acid solutions has been studied, and it has been found that the highest oxidation rate occurs in a concentrated solution of nitric acid. In order to accelerate the process and to increase the yield on the substance, adding to the fluoride acid working electrolyte has been proposed. As a result of the researches, it has been found that the behavior of the dissolution of pseudoalloys of the carbide type is characterized by the properties of the main component — tungsten. An electrolyte for obtaining higher tungsten oxide in one stage has been proposed. Bibl. 10, Fig. 1, Tab. 1.

Atom Probe Compositional Analysis of Interphase Precipitated Nano-Sized Alloy Carbide in Multiple Microalloyed Low-Carbon Steels

The composition of nano-sized alloy carbides formed by interphase precipitation in V–Nb and V–Ti multiple microalloyed low-carbon steels is analyzed by using three-dimensional atom probe. Carbide-forming alloying elements including V, Nb, and Ti, are simultaneously precipitated from the early stage of isothermal treatment, whose atoms are uniformly distributed in the carbide particles, even after prolonged holding. Cluster analysis by the maximum separation method, with parameters optimized using different methods, is carried out to extract alloy carbides from matrix. The composition of alloy carbides evaluated by site fraction of substitutional carbide-forming alloying elements indicates that at the early stage of their formation, Nb and Ti are more strongly enriched than V.

Structure Stability of Ni-Base and Co-Base Alloys

This article summarises results of structure stability investigation of cast Ni-base and Co-base alloys after prolonged high temperature exposure at 900-1100 °C. Cast Ni (Co)-Cr-W-C alloys are resistant to high-temperature corrosion, due to high chromium content. Their heat resistance is caused by presence of carbides, which are stable at very high temperatures. Carbides precipitate in shape of large plate-like particles or carbide eutectics at casting cell boundaries, thus forming carbide skeleton of the alloy. Carbide morphology and temperature stability depends on chemical composition of the alloy, e.g. carbide content, type and content of carbide-forming elements. Microstructure changes were evaluated by stereological analysis and X ray-spectral microanalysis.