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Microstructure forming processes of the 26Mn-3Si-3Al-Nb-Ti steel during hot-working conditions

Dobrzański L. A., Borek W.

Journal of Achievements in Materials and Manufacturing Engineering

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2010

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Vol. 40, nr 1

25-32

EN

Purpose: The influence of hot-working conditions on microstructure evolution of new-developed 26Mn-3Si-3Al-Nb-Ti high-manganese steel was investigated. Design/methodology/approach: The force-energetic parameters of hot-working were determined in continuous and multi-stage compression test performed in temperature range of 850 to 1100°C using the Gleeble 3800 thermomechanical simulator. Evaluation of processes controlling work-hardening were identified by microstructure observations of the specimens compresses to the various amount of deformation (4x0.29, 4x0.23 and 4x0.19). Findings: The investigated steel is characterized by high values of flow stresses from 250 to 430 MPa. Increase of flow stress along with decrease of compression temperature is accompanied by translation of ĺmax strain in the direction of higher deformation. Results of the multi-stage compression proved that applying the true strain 4x0.29 gives the possibility to refine the austenite microstructure as a result of dynamic recrystallization. In case of applying the lower deformations 4x0.23 and 4x0.19, the process controlling work hardening is dynamic recovery and a deciding influence on a gradual microstructure refinement has statical recrystallization. Research limitations/implications: To determine in detail the microstructure evolution during industrial rolling, the hot-working schedule should take into account real number of passes and higher strain rates. Practical implications: The obtained microstructure – hot-working relationships can be useful in the determination of power-force parameters of hot-rolling and to design a rolling schedule for high-manganese steel sheets with fine-grained austenitic structures. Originality/value: The hot-deformation resistance and microstructure evolution in various conditions of hot-working for the new-developed high-manganese 26Mn-3Si-3Al-Nb-Ti austenitic steel were investigated.

2

Surface modification, microstructure and mechanical properties of investment cast superalloy

Zielińska M., Kubiak K., Sieniawski J.

Journal of Achievements in Materials and Manufacturing Engineering

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2009

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Vol. 35, nr 1

55-62

EN

Purpose: The aim of this work is to determine physical and chemical properties of cobalt aluminate (CoAl2O4) modifiers produced by different companies and the influence of different types of modifiers on the grain size, the microstructure and mechanical properties of high temperature creep resisting superalloy René 77. Design/methodology/approach: The first stage of the research work took over the investigations of physical and chemical properties of cobalt aluminate manufactured by three different companies: Remet, Mason Color and Permedia Lublin. There were determined the grain size distribution of cobalt aluminate powder, the average diameter of the powder particles, phase composition, cobalt contamination. In the next step, the ceramic moulds were made with different kind of cobalt aluminate (Mason Color, Remet, Permedia Lublin) and its concentration (0.5%) in the primary slurry. The samples of stepped and cylindrical shape were poured in the ceramic moulds prepared earlier. The average grain size of the . phase, was determined on the stepped samples. The microstructure investigations let to examine the influence of the surface modification on the morphology of . ‘ - phase and carbides precipitations. Samples were turned from cylindrical castings for mechanical properties investigations: creep tests. Findings: Modification of the face coat of ceramic mould results in the reduction of the grains size of . matrix and disintegration of carbide precipitates. It results in the improvement of mechanical properties of the alloy. On the grounds of the obtained results, it was found that the type of used modifier influenced the grain size of the alloy and its mechanical properties. Research limitations/implications: The established physical and chemical properties of modifier let to get better control of grain size of the castings and their quality what will result in decrease of defective products. Originality/value: It was proved that the effectiveness of cobalt aluminate modifier as an inoculant depends not only on its concentration in ceramic slurry but on its chemical composition. The researches allowed to find the optimal concentration of Co in CoAl2O4 to produce casting elements made from superalloy René 77.

3

Evaluation of Al-5Ti-1B and Al-10Sr in LM6 sand castings

Lim Y. P.

Journal of Achievements in Materials and Manufacturing Engineering

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2009

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Vol. 34, nr 1

71-78

EN

Purpose: of this paper is to study the separate effects of grain refiner and modifier on the metallurgical properties of LM6 sand castings. The research aims to determine how grain refiner and modifier will influence the microstructure of LM6 sand casting and the associated mechanical properties of hardness, ultimate tensile strength and engineering strain. Design/methodology/approach: A grain refiner consists of 0.5wt% Al-5Ti-1B and a modifier consists of 0.5wt% Al-10Sr have been introduced separately into the melt of hypoeutectic LM6 Al-Si alloy to produce slab castings by CO2 sand casting process. The geometry of the slab casting is designed to have different section moduli to induce directional solidification. Temperature profile of cooling process is taken to correlate between the section modulus and cooling rate. This enables the effect of cooling rate on microstructure and mechanical properties to be studied for grain refined and modified LM6 sand castings. Findings: The significant finding is that a nearly full eutectic solidification at 540°C is achieved in the Sr-modified casting with faster cooling rates than those of solely grain-refined and original LM6. The hardness and ultimate tensile strength can be improved respectively between 20~40% and 11~18% by Al-10Sr modifier. It is observed that the Al-5Ti-1B grain refiner and Al-10Sr modifier increase the strain at UTS by 11% and 22% respectively. The metallographic observations show that the eutectic phase is finer and in fibrous form in the Sr-modified LM6. Research limitations/implications: Further research can study a wider range of inoculant percentage. Practical implications: This eutectic solidification at 540°C achieved in Sr-modified LM6 is lower than the solidus temperature of LM6 to reduce superheat and save electrical energy consumption while ensuring complete liquid mould filling. Originality/value: This is the original work of slab casting of LM6 and the effects of Sr modifier and TiB grain refiner on its metallurgical properties.