Grain Structure Of Steel Research Articles

Deoxidation and modification of steels with reduced silicon content

The object of research is the processes that affect the mechanical characteristics of steels after the treatment of melts with silicon-free complex master alloys according to existing technologies. One of the most problematic places is the negative effect of silicon on the weldability of low-alloy steel, sharply increasing the heterogeneity of welds in sulfur and phosphorus and increasing their susceptibility to hot cracks. The cyclic strength of welded joints decreases markedly with an increase in the silicon concentration of steel. Also in this case, there is a threat of the formation of silicon monoxide, which significantly increases the fragility of the finished steel products. Also, steels processed with alloys containing silicon are prone to decarburization, the formation of surface defects during hot working and graphite formation, which reduces their endurance limit. In the research it was possible to prove that the use of silicon-free complex ligatures (SFCL) in smelting made it possible to obtain an increase (2–3 times) in the entire complex of mechanical and operational properties, especially ductility, impact strength at normal and negative test temperatures (cold resistance) , fatigue strength. In some cases, the level of properties of cast metal reaches the deformed version of its manufacture, for example, rolled products and even metal obtained by electroslag remelting. Processing of the melt of various BKL steels when tapping from the furnace into a pouring ladle instead of aluminum master alloys, silicocalcium and ferrocerium (according to the current technology) provided the required level and high stability of the mechanical properties of 20GML steel. Also, thanks to the use of BCL, it was possible to reduce the consumption of ligatures and deoxidizers by 4.2 kg per ton of liquid metal and increase the yield of rejection of casting defects by 6–10 %. It has been established in the work that BCL treatment leads to stabilization of the chemical composition, refinement of the grain structure of steels, as well as an increase in its dispersion and the level of mechanical characteristics.

Overview Impacts of Heat Treatment Techniques on Grain Structures of a Steel

In this study, various techniques used in the modification of the grain structure of steel were considered. It was found that different heat treatment techniques cause changes in the grain structure of steel and subsequent improvement in the mechanical properties of the material. More so, the bimodal grain size, as well as the lamellar structure in steel, will lead to work hardening effect and improved ductility of the steel. The carburization technique also improves the mechanical properties such as hardenability, compressibility, tensile strength, and toughness. While nitriding effects will lead to excellent tribocorrosion performance. More importantly, these heat treatment techniques help to improve the resistance against cyclic load in different application environments. Thus, failures resulting from crack propagation and other failure modes are prevented. In this regard, structural failures are prevented by grain structure modification using heat techniques.

The influence of the heating rate of cemented constructional steels on the growth of austenitic grain in the process of high-temperature holding

The influence of the heating mode of samples of constructional cemented steels 20ХН3А, 20ХГНР and 15ХГН2ТА on the value of austenite grain after high-temperature isothermal aging at 1000 °С is studied. It is shown that the heating of steels at a rate of 1.2–3.0 °C / min in the phase-transformation interval stabilizes the grain structure of the steels and leads to a slowing down of the kinetics of the growth of austenite grains during prolonged high-temperature aging, which makes it possible to increase the temperature of the chemical-thermal treatment of steels. It is concluded that the stabilization of the grain structure of steels is associated with the formation of segregation of impurity atoms and particles at grain boundaries with high-angle disorientation during slow heating, which prevents migration of grain boundaries in the process of prolonged high-temperature aging. A high-temperature chemical-thermal treatment of a batch of billets from steel 20ХН3А under experimental conditions with stepwise heating in the phase-transformation interval provided a qualitative fine-grained structure of the cemented layer.

Effect of Hot-Rolled Microstructure on the Recrystallization Texture of Cold-Rolled Non-Oriented Electrical Steel

With the help of orientation distribution function (ODF) analysis, experiments of different hot band grain microstructure 0.33% silicon steel were cold-rolled and annealed in the laboratory，to study the effect of the microstructure hot-rolled steel strip for cold rolled non-oriented silicon steel microstructure and texture of recrystallization annealing. The results show that hot rolled microstructure on cold rolled Non-Oriented Electrical Steel cold-rolled sheet evolution of texture and recrystallization have important influence, the quiaxed grain structure of steel by cold rolling and recrystallization annealing, the recrystallization speed than the fiber grain-based mixed crystals recrystallization fast , With the equiaxed grains made of cold rolled silicon steel after annealing the {110}<UVW> texture components was enhanced and {100}<uwv> texture components weakened. Different microstructure condition prior to cold rolling in the recrystallization annealing process the texture evolution has the obvious difference, the equiaxial grain steel belt cold rolling and annealing, has the strong crystal orientation. This shows that the equiaxed grain when hot microstructure is detrimental to the magnetic properties of cold-rolled non-oriented silicon steel to improve and increase.

EXPERIMENTAL EVALUATION OF STEREOLOGICAL METHODS FOR DETERMINING 3D GRAIN SIZE AND TOPOLOGICAL DISTRIBUTIONS

The conventional serial sectioning analysis and a set of modern stereological methods, including disector, selector, point-sampled intercepts, point-sampled area, and their combinations, have been used in this paper to measure the grain size, grain size distribution, topological parameters and their distributions in a spacefilling single-phase grain structure of steel. The results from different methods are compared and used to evaluate the methods quantitatively, based on which some suggestions will be given for selection of experimental methods in materials stereology research.

Modeling elasto-plastic behavior of polycrystalline grain structure of steels at mesoscopic level

The multiscale model is proposed to explicitly account for the inhomogeneous structure of polycrystalline materials. Grains and grain boundaries are modeled explicitly using Voronoi tessellation. The constitutive model of crystal grains utilizes anisotropic elasticity and crystal plasticity. Commercially available finite element code is applied to solve the boundary value problem defined at the macroscopic scale. No assumption regarding the distribution of the mesoscopic strain and stress fields is used, apart the finite element discretization. The proposed model is then used to estimate the minimum size of polycrystalline aggregate of selected reactor pressure vessel steel (22 NiMoCr 3 7), above which it can be considered macroscopically homogeneous. Elastic and rate-independent plastic deformation modes are considered. The results are validated by the experimental and simulation results from the literature.

Nucleation of Intragranular Accicular Ferrite in a Ti-Containing Low Carbon Steel of High N Content

Formation of acicular ferrite grains by dispersing non-metallic inclusions which can act as intragranular nucleation sites within austenite grain is proposed as a method to obtain refined grain structure in steels. The microstructure of acicular ferrite steel consists of fine interlocking ferrite plates nucleated on dispersed non-metallic inclusions. This acicular ferrite structure provides a desirable combination of high strength and good toughness because of its small plate thickness and interlocking microstruture. in Ti-containing low carbon steels, researchers proposed that Ti2O3 or MnS, among inclusions, is the most effective nucleant for intragranular ferrite because of the formation of Mn depleted zone(MDZ) around Ti2O3 or MnS particles. TiN is also reported as a nucleation site owing to the coherency between ferrite and TiN crystals. But It has not been a simple task to identify which inclusions and what mechanisms are really effective in the formation of intragranular acicular ferrite.