Key Engineering Materials Vol. 635

Abstract: The proposed paper deals about the heat treatment of two types of chromium tool steels that are assigned to work in specific conditions of abrasion wear. The materials are heat treated to achieve high hardness for higher abrasion wear resistance. An additional increase of the materials abrasion wear resistance can be achieved by applying nitridation with diffusion annealing of the material surface. The paper deals about the influence of the material purity, his chemical composition on the process of diffusion, the quality of the nitrided layer of a vacuum smelted steel Bӧhler W400 VMR and a chromium steel X210Cr12.

Abstract: During pressing using high speed, the material is stressed to the limit of its mechanical properties. And this generates problems during production. For this reason, opens debate on the factors previously neglected, such as the strain rate. For determining the effect of strain rate on the pressing process has been designed to CTU, Faculty of Mechanical Engineering, Institute of Manufacturing Technology, equipment for monitoring the behaviour of the material at different strain rates. The article describes the creation of testing methodologies material behaviour using this device.

Abstract: The paper analyses the influence of the strain rate on the behaviour of unalloyed steels with R_e 210 – 550 MPa in the deformation process. It presents and analyses the results of the influence of the strain rate ranging from 10^-3 to 2.5.10² s^-1 on the yield point, the tensile strength, the elongation and the reduction of area. It analyses the non-homogeneity of development of plastic deformation from both the macroscopic and microscopic points of view, as well as the influence of the strain rate on the development of plastic deformation. Since the intensity of the influence of the strain rate on the properties of materials depends on their internal structure, the tested steels are divided into three groups based on their yield point and yield point to tensile strength ratio.

Abstract: The article summarizes the results obtained within a project PRAMEK. The project is focused on corrosion behavior of structural materials in water environment with supercritical parameters. Ferritic - martensitic materials P91 and P92 was evaluated. Multi-layered oxide was created on materials sample surface after 1000 hours long exposures in Supercritical Water Loop (SCWL) and Supercritical Water Autoclave (SCWAc) under SCWR operational parameters (600 °C, 25 MPa). The outer layer consisted of magnetite was porous and may tend to exfoliate. The inner layer is formed by spinel with Cr and Fe oxides. Microstructure of materials P91 and P92 and surface oxidic scales were evaluated by means of light and scanning electron microscopy equipped with wave and energy spectroscopy.

Abstract: Quality of machine production is very close-knit with quality of metallurgical semi-products and with improvement their working properties. It can be achieved first of all by decrease of sulphur and non-metallic inclusions content in metal. Improvement of working properties provide remelted processes above an electro slag remelting (ESR). The slags play very important role by ESR process. By experiments steel with next chemical composition was used: C (0,9 – 1,1%), Mn (0,30 – 0,50%), Si (0,15 – 0,35%), Cr (1,30 – 1,65%), Ni (max.0,30%), Cu (max.0,25%), P (max.0,027%), S (max.0,030%). The steel was remelted under 8 types of slags on the base of CaO, Al₂O₃, CaF₂ and SiO₂ in different ratios. The contribution deals with influence of chemical composition of slag on mechanical properties and cleannes of metal after electro slag remelting. Variation of slag chemical composition enables to change chemical composition of remelted steel, to reduce the non-metallic inclusions and sulphur content and to improve the mechanical properties of steel.

Abstract: Strain rate is a significant external factor and its influence on material behaviour in forming process is a function of its internal structure. In this contribution the influence of loading on the deformation IF steel is investigated using rotate hammer. To study the influence of rate deformation from 8.33 x 10^-3 s^-1 to 4000 s ^-1 to changes in the fracture of steel sheet used for bodywork components in cars. Experiments were performed on samples taken from interstitial free (IF) grade strips produced by cold rolling and hot dip galvanizing. Material strength properties were compared based on measured values, and changes to fracture surface character were observed.

Abstract: Worldwide laboratory research proves that replacement of coke breeze by solid biomass in the process of agglomeration is possible [1,2,3]. One possibility of solid biomass use is the charcoal. Literature indicates that coke breeze can be replaced by charcoal up to 40% based on calorific value [4]. This paper deals with the poblems of coke breeze substitution by charcoal in laboratory conditions sintering and the impact of such substitution on the resulting agglomerate properties, i.e. microstructure. Agglomerate microstructure consists of mineralogical phases; hematite, magnetite, calcium and aluminum silico-ferrites, and silicates. Substituting coke breeze for charcoal up to 40% in the process of agglomeration, slight changes occur in the volume fractions of individual phases of the agglomerates. Volume fractions of agglomerate phases change significantly above 40% substitution by charcoal. Phase composition has an effect on the quality characteristics of the produced agglomerate. The amount of calcium and aluminum silico-ferrites influences the strength of the agglomerate [5].

Abstract: Nowadays, more and more scientific studies deal with the formation of electroplating alloy coatings due to the possibility of combination and share content type metal – forming alloy. To produce coatings that fulfil pre-defined specific requirements is possible by a suitable combination of process conditions. The paper deals with the study of tribological properties of Ni-Co coatings that were prepared by electrodeposition technique from sulphate electrolyte on the copper substrate. Effect of current density on the properties of electroplated coatings was determined via a morphology characteristics and micro-hardness of coating′surface. The tribological behaviour of Ni – Co coatings was described by friction coefficient using the pin-on-disc method.

Abstract: The paper deals with the analysis of the crack detected in the Kaplan turbine blade. In order to keep the blade integrity the sample was removed by using small sample method. Fractographic and metallographic analyses were used to determine the cause of a detected crack appearance and propagation. The material of the turbine blade was made in 1937 and its structure containing numerous eutectic sulphide inclusions corresponded to the steelmaking technology of that time. Numerous occurrences of sulphide inclusions and sulphide eutectics were identified as the main cause of material failure. Regardless of these non-metallic inclusions the blade was repaired by welding and nowadays the repaired blade has been under safe operation for more than 9 years.

Abstract: In the cellular extrusion process, the extrusion head gives the extrudate the desired cross-section shape and dimensions, taking into account the Barus effect and the shrinkage effect. However, if strict requirements are imposed with regard to cross-section shape and dimensions, it is necessary to fix the shape and dimensions by calibrating the extrudate obtained. The aim of this study is to present methods and constructional solutions of calibration tooling (calibrators) and to present the new calibrator that constitutes a significant element of the adapted and modernized technological extrusion line.