Microstructural Prediction of Heat Treated Steel Forgings for Severe Applications

An in-house 2D finite volume model, specific for components of simple shape, was developed and applied to predict the thermal and microstructural evolution during heat treatment of steel forgings. The results of the thermal metallurgical modelling, including hardness profiles through the thickness, were compared with the experimental ones. Moreover, the 3D FEM software Deform-HT, able to calculate the thermal and microstructural evolution and the stress field during quenching, was specialized for the cases of interest. Examples of optimal heat treatment to develop the target microstructure and strength and reduce the risk of quenching cracks are discussed.

Influence of sherardizing on working properties of metal parts subjected to prior heat treatment

The article reveals the data concerning the mechanical properties changes of heat-treated steel articles subjected to thermo diffusion pack cementation. The temperature frames of thermo diffusion influence on tensile strength were determined for heat-treaded steel articles. Results of tensile test of high strength bolts treated using thermo diffusion pack cementation at 420 °C show no any effect from the side of pack cementation treatment on working properties of the tested samples. It is shown that in conditions of cyclic fatigue loading thermo diffusion pack cementation of heat treated article may leads to strength loss that can be explained by formation of solid intermetallic phases in a surface area of the article.

SOME STATISTICAL DISTRIBUTIONS, WHICH DESCRIBE THE NANOTOPOGRAPHY OF TECHNICAL SURFACES

Исследована нанотопография технических поверхностей деталей из высоколегированной термообработанной стали и электротехнического серебра после финишной механической обработки. Экспериментально определены функции плотности вероятности параметров нанотопографии - высот выступов и радиусов кривизны их вершин, которые необходимы для теоретического описания процессов контактного взаимодействия технических поверхностей (на примере поверхностей серебра и стали). Установлено, что распределение указанных параметров наношероховатости сильно асимметрично и далеко от нормального. Доказано, что для исследованных поверхностей плотность вероятности указанных параметров наношероховатости адекватно описывается бета-распределением. Достоверность данного заключения подтверждается с помощью критериев согласия Пирсона χ и Романовского. The nanotopography of engineering surfaces of machine parts made of high alloy heat-treated steel and electric silver after finishing mechanical treatment was studied. The probability density functions of the nanotopography parameters - the heights of peaks and the radii of curvature of their vertices - were experimentally determined. These parameters are necessary for theoretical description of processes of the contact interaction of engineering surfaces (exemplifying on surfaces of silver and steel). It is established that the distributions of the above mentioned nanoroughness parameters are essentially asymmetrical and are far from normal ones. It has been proved that for the studied surfaces the probability densities of the above mentioned nanoroughness parameters are adequately described by the beta-distribution. The validity of this conclusion is confirmed by the fitting criteria such as χ (K. Pearson’s criterion) and Romanovsky’s criterion.

Structuroscopy of Heat-Treated Steel Bars by the Speed of Propagation of Rayleigh Waves

В статье обсуждаются вопросы возможности оценки структурного состояния после разных видов и режимов термической обработки прутков из стали 45 по результатам измерения скорости рэлеевской волны с использованием метода многократной тени. Для обеспечения разработанной методики использован дефектоскоп ДЭМА и специальный накладной электромагнитно-акустический (ЭМА) преобразователь с системой подмагничивания. Преобразователь обеспечивает возбуждение и прием рэлеевских волн, распространяющихся по окружности прутка. Исследованы образцы прутков в состояниях поставки, отжига, нормализации, закалки и отпуска. Для качественного измерения скоростей рэлеевских волн измерены диаметры прутков с точностью 0,01 мм. Представлены результаты изменения скорости рэлеевской волны в прутках при всех режимах термической обработки. В состоянии поставки скорость рэлеевской волны в прутке составила 3017 м/с. Скорость рэлеевской волны в прутке после закалки упала до 2995 м/с. После нормализации скорость рэлеевской волны увеличилась до 3049 м/с. Постепенное увеличение температуры отпуска приводит к увеличению скорости волны. Полученные экспериментальные данные показывают, что отпуск при температуре 600 °С и нормализация при 850 °С увеличивают скорость распространения рэлеевской волны в прутке на 55 м/с относительно закалки без отпуска, что свидетельствует о схожих структурных состояниях в поверхностных слоях образцов.

Effect of Intercritical Rolling on Microstructure, Mechanical and Corrosion Properties of the Dual Phase X70 American Petroleum Institute Pipeline Steel

The effect of intercritical annealing heat treatment on mechanical and corrosion properties of fer-rite/martensite dual-phase steels with and without deformation by rolling has been investigated in this study. The X70 steel was rolled at intercritical temperatures (760 and 800 °C) with 30% amount of reductions followed by water quenching in order to produce dual-phase microstructure. The experimental results show that microstructures, mechanical and corrosion properties and were strongly affected by intercritical rolling conditions. It is established that the intercritical rolling provides a fibrous structure, and improves the mechanical and corrosion properties of X70 dual phase steel. It was found that after intercritical rolling (DQR), grain refinement and hardness improved significantly compared to intercritical heat-treated steel without rolling (DQ). A carefully conducted comparison of resistance corrosion of the representative specimens obtained after (DQ) and (DQR) treatments has been studied. (DQR) treatment shows better corrosion resistance than (DQ) treatment. The microstructure, mechanical and corrosion properties of the rolled X70 dual phase steel were investigated by optical microscopy, scanning electron microscopy, hardness tests and electrochemical measurements.

Process optimization of the mechanical properties of AISI 1020 steel quenched using maize-stover ash potash solution

The process parameter optimization of maize-stover ash potash (MSAP) as a quenching medium for heat treatment of AISI-1020 steel was conducted in this study to improve the mechanical properties of steel after carburization and quenching. The optimization process utilized Taguchi L9(32) orthogonal array method to determine the individual Signal to Noise (S/N) ratio and Analysis of Variance (ANOVA). A multi-response weighted analysis technique was applied to derive combined quality responses of the heat treated test pieces. The result shows that the optimal factor level of MSAP solution strength was achieved at AM1BM1, which offered 57.6 HRC hardness, 39 J toughness and 1971 N/mm2 tensile strength as improved mechanical properties for the heat treated steel. Keywords: Optimization, MSAP, quenching, Taguchi, ANOVA

THE TRIBOLOGICAL ASPECT OF THE COOPERATION OF VARIOUS SURFACE-STRENGTHENED STEELS WITH HEAT-TREATED STEEL

The presented work was mainly aimed at assessing the tribological properties of gas nitrided samples subsequently subjected to shot peening. This assessment was carried out using the standard “three rollers – cone” method. In these tests, different materials of roller samples were used, i.e. both structural and tool steels. In addition, the selected material of conical counter-samples, i.e. heat-treated medium carbon steel, was used. The obtained test results allowed us to assess the influence of the use of dissimilar material of nitrided (under different conditions) roller samples, as well as their surface plastic processing, i.e. shot peening.