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High-strength martensitic steels with low Ms temperature

Bublikova D., Masek B., Jirkova H., Jenicek S., Ibrahim K., Cubrova J.

Archives of Materials Science and Engineering

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2014

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Vol. 65, nr 2

53--57

EN

Purpose: Various novel heat treatments and thermomechanical treatment procedures have been developed recently in order to enhance mechanical properties of high-strength steels. Design/methodology/approach: The new heat treatment process was tested on newly designed low alloy AHSS steels alloyed with manganese, silicon, chromium and alternatively molybdenum and nickel. Two different cooling rates of 16°C/s and 1°C/s showed that over a wide interval of cooling rates a hardened structure based on martensite and retained austenite can be achieved with an average hardness from 538 to 716 HV10 and ultimate strength in the range between 1837 and 2354 MPa. Findings: The main aim of these steels was to decrease the temperature Mf to below 100°C by quenching in a water or oil bath and use common industrial techniques. Manganese alloying was used for the required decrease of temperatures Ms and Mf. Silicon and chromium were used to increase the ultimate strength, silicon was used to eliminate the carbide formation and to support sufficient oversaturation of martensite. Practical implications: The industrial application of this process is complicated by the need for quenching in the range between Ms and Mf. The Ms temperature normally lies in the 200-250 °C interval. This is why new steels with low Ms temperature were selected for the experimental programme. Thanks to this feature, the steels could be quenched in water or polymer-based baths. The primary alloying elements of these four selected steels were manganese, silicon, molybdenum and chromium. Originality/value: The experimental heat treatment led to microstructures of martensite with retained austenite in all steels. Their strengths were in the range of 1750-2400 MPa and their A5 mm elongation levels were up to 10%. The morphology and distribution of retained austenite dictate the resulting mechanical properties of the material.

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Optimization of recycling process of white bronze chips

Skalova L., Luka J., Masek B.

Archives of Materials Science

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2007

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Vol. 28, nr 1-4

143-148

EN

This work focuses on optimization of recycling process of white bronze chips which come from the manufacturing of slide elements. Present recycling technology was applied on the chips with unsatisfactory results. The aim of this work is to increase the efficiency of recycling process and to obtain maximal amount of recycled metal with optimized recycling method which would use forming of the chips and their remelting with suitable anti-oxidation addition. Their first part of experimental program will be evaluated and a new direction of work will be proposed for further experiments.

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Influence of thixoforming on structure development of the tool steel

Stankova H., Klauberova D., Ronesovs A., Masek B.

Archives of Materials Science

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2007

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Vol. 28, nr 1-4

149-154

EN

Forming in the thixotropic state is one of the alternative forming methods, which allows producing semi-products with relatively complicated shape. The process is based on semi-product forming in the region between solid and liquid, where the material exhibits the thixotropic behaviour. This technology applies especially to higheralloyed steels, which are otherwise processed by pressure casting. Thixoforming runs in the die cavity. Among the advantages of this technology belongs the possibility to produce components with complicated shape in one step and to utilize lower forming forces. On the other hand, high forming temperatures and the narrow forming temperature interval can be considered as disadvantages. To reach the thixotropic behaviour necessary for obtaining the required component shape, the parameters of semi-solid state play an important role. These include, for example, the fraction of the liquid phase, the shape of solid particles and the location of the liquid phase in the structure. The tool steel was used for the development of an alternative forming process. The structures were observed using light and laser confocal microscopy. The fraction of liquid phase and the size of solid particles were evaluated via image analysis.