International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

An experimental study was carried out to develop a technique for manufacturing a high silicon Al-Si-Ni sintered alloy with a coefficient of thermal expansion close to steels. A stage of hot forging was added to overcome porosity and improve silicon inclusions morphology to obtain better mechanical properties. Liquid and solid phase regimes of sintering were studied for the material made of the elemental components powders mixture as well as of a pre-alloyed powder. The impracticality of liquid-phase sintering modes is shown for this type of material primarily because of the tendency to liquid-phase exudation. It was proposed to carry out a solid-state vacuum sintering with subsequent hot deformation. Only the pre-alloyed powder is suitable for the technique; the other way, it leads to the course and sometimes, not equilibrium intermetallic inclusions will form in place of nickel particles because of the insolubility of Ni in solid Al. It is shown the possibility of successful plastic deformation of this material after sintering despite its extremely low ductility, which helps successfully overcome porosity and improve the characteristics of the microstructure of the material.

Using computer modelling with originally developed semi empirical physical grounded models a study was carried out to investigate influence of previous hot deformation on carbonitrides formation from austenite in low-carbon micro-alloyed steel. Studied in the article is an influence of degree and rate of the deformation on processes of nucleation and growth of Nb and Ti carbonitride particles. The model helps to predict not only process of changing in number and average size of the particles but also to estimate their final size distribution. One of additional peculiarities of the developed model is its ability to predict composition of the cabinetries formed in certain conditions. The model takes into account process of recrystallization and returning, which affect carbonitrides precipitation and are influenced by it. Acceleration was shown of both nucleation and growth rates of the particles due to increasing of deformation degree and strain rate. Another result is that previous deformation significantly affects size distribution function of the particles precipitated with rather lesser effect on their average size. Kinetic curves and final size distribution plots are given.

Using computer modelling with originally developed semi empirical physical grounded models study of structure formation when austenite transformation during cooling by certain regime in eutectoid steel was carried out. The model allowed us to predict final structure. Cooling curves leading to fine pearlite (almost without bainite) and lower bainite (with a small part of fine pearlite) structures were find out. The results obtained could be useful for high carbon ordinary instrumental and constructional steels with higher manganese production and processing (rails, cord and rope wire, springs, low stressed instruments). Realization of the fine pearlite obtaining regime needs equipment that could provide cooling rates from 0.04 deg./sec. to 6.6 deg./sec. with average value of 1.1 deg./sec.. For bainitic structure obtaining the range of cooling rates provided shoud be from 0.14 deg./sec. to 14.0 deg./sec. with average value of 2.2 deg./sec. The cooling intensivity must have an ability to arbitrary and controlled changing during process.