R. Chotěborský

Effect of active rubber powder on structural two-component epoxy resin and its mechanical properties

Abstract The aim of the research was to investigate a possibility to use active rubber powder (ARP) from a process of tyres recyclation in an area of a filler into a reactoplastics matrix applied in structural adhesive bonds. This study focuses on an analysis of a tensile strength, a shear impact strength and a hardness of the composite mixture itself and further on the interaction with an adhesive bonded material, i.e. it evaluates an influence of different ratio of ARP on the adhesive bond strength. Effects of the cyclic degradation environment combining the decreased temperature −40 °C and the increased temperature 90 °C at the simultaneous acting of the increased moisture up 90% is a part of the research. The tensile strength and the hardness were decreased by adding ARP. The experiment results proved a positive effect of ARP in the area of adhesive bonds exposed to the cyclic degradation at increased and decreased temperatures. Elastic ARP is able to absorb an inner tension in the layer of the adhesive bond.

Modelling of the Anisothermal Phase Transformation of Austenite by Electromagnetic Sensor

The characterization of steel microstructures is an important tool for metallurgists as mechanical properties are controlled by microstructural parameters such as grain size, phase balance and precipitates. This paper describes a model of the phase transformation of tool steel CSN 41 9436. Each of the experimental data was observed by electromagnetic sensor. The mathematic model was developed for an optimizing of tool steel heat treatment. The model was developed from one experiment and next experiments were for an evaluation of the model. A model can be satisfactory used for graphical form of the austenite phase transformation.

Using the FEM model for design the heat treatment of an agricultural tools

Agricultural tools need mechanical properties such as abrasive wear, hardness and toughness. These mechanical properties are achieved by choosing a suitable steel and subsequent heat treatment of the steel. Phases of the microstructure affects the final steel properties. The phase composition in the steel is influenced with the designing of the heat treatment. 25CrMo4 steel was investigated for the production of agricultural tools. The heat treatments ware designed for different cooling conditions. The salt bath was used to cooling as a medium with subsequent cooling on the water or in the air. The FEM method was used to designing the heat treatment conditions. The Johnson-Mehl-Avrami-Kolmogorov equation and the Koistinen-Marburger equations were used to prediction the microstructure phases. The microstructures were verified with experimental measurements. The ASTM G65 method was using for abrasion resistance tests. The results show that this procedure can be used to designing parameters of heat treatment of agricultural tools.

Utilization of FEM model for steel microstructure determination

Agricultural tools which are used in soil processing, they are worn by abrasive wear mechanism cases by hard minerals particles in the soil. The wear rate is influenced by mechanical characterization of tools material and wear rate is influenced also by soil mineral particle contents. Mechanical properties of steel can be affected by a technology of heat treatment that it leads to a different microstructures. Experimental work how to do it is very expensive and thanks to numerical methods like FEM we can assumed microstructure at low cost but each of numerical model is necessary to be verified. The aim of this work has shown a procedure of prediction microstructure of steel for agricultural tools. The material characterizations of 51CrV4 grade steel were used for numerical simulation like TTT diagram, heat capacity, heat conduction and other physical properties of material. A relationship between predicted microstructure by FEM and real microstructure after heat treatment shows a good correlation.

Microstructure Changes of Steel Materials under Isothermal Heat Treatment in Salt Bath

Abstract To improve the mechanical properties of steel materials such as Vanadis 4extra, Vanadis 10, Vancron 40, and Böhler S600, the isothermal heat treatment procedure using salt bath was used. Samples of the steels were processed at different time of austempering at various temperatures and compared to the samples processed by heat treatment (i.e. quenching in air or quenching in oil and tempering in air) which is most widely used in practice. Hardness properties are determined by the steel microstructure, the size and number of carbide particles in this microstructure. The suitability of heat treatment for improving mechanical properties of different steel materials is assessed.

Prediction Of Mechanical Properties Of Quench Hardening Steel

Abstract The present study investigated the application of finite element method for prediction of mechanical properties of quench hardening steel. Based on the experimental results obtained, a numerical model for simulation of continuous cooling of quench hardening steel was developed. For the simulation of the kinetics of diffusion phase transformations, the Avrami equation and additive rule were applied. A new model was also developed for martensitic transformation which was validated using metallographic analysis and hardness tests. Experimental and simulation results indicated a good agreement. The developed model information provided here could be used for simulation of continuous cooling and kinetics phase transformation as well as for prediction of final distribution of microstructures and hardness of alloy steels.

Local Mechanical Properties of Borides in Fe-B Steels

One of the ways to increase service life of the abrasive wear parts are new developed as-cast steels with ceramic phase. Expensive wear resistant high chromium cast iron can be exchanged by Fe – B alloys. The mechanical properties of the borides in the Fe – B cast iron depend on alloying elements like chromium or nickel. A set of sample with different content of carbon, chromium, nickel and boron has been prepared. Chemical composition (GDOES) and microstructure of the as-cast alloys have been investigated as well as the hardness and Young modulus of the borides. Our results shown that mechanical properties of borides depends both on chromium and carbon content.