Papers by Keyword: Chromium

Abstract: The technology of diffusion saturation of austenitic steels by chromium and nickel in the medium of low-melting liquid metal melts is shown. The saturation temperature was up to 1050°C, and the duration was up to 8 hours. It was found that it is the most effective to apply coatings according to the technological scheme: pre-carburization-diffusion metallization – final carburization. It was found that the coating consists of 4 layers. The surface layer has a thickness of up to 5 mkm and a microtuberance of up to 19500 MPa. The second layer, up to 12 mkm thick, has a microhardness of up to 7500 MPa. The third, up to 50 mkm thick, has a microhardness of 2300 MPa. In the fourth layer, up to 150 mkm thick, the microhardness gradually decreases from 2300 MPa to the microhardness of the base. At the same time, the total thickness of the coatings is up to 200 mkm.

Abstract: The use of hydrogen peroxide and hydrazine sulfate for the treatment of chrome-containing rinsing waters of galvanic production of machine-building enterprises is proposed. The process of reducing chromium (6+) to (3+) from rinsing waters with a concentration of 8.55 mg/dm³ was studied. These reagents allow reducing more than 99% of chromium (6+) to chromium (3+) and maintaining a low salt content of treated wastewater. The consumption of hydrogen peroxide is 1.5 mg/dm³, and the consumption of hydrazine sulfate is 10 mg/dm³. The current situation in the treatment of galvanic wastewater leads to pollution of the environment with dangerous substances (CN^-, Cr⁶⁺, F^-, Cd²⁺), irrational use of raw materials and significant economic losses. The possibility of extracting valuable components from wastewater, in order to recycle them and return the treated water to production, is considered. Hydrogen peroxide is effective for treating acidic wastewater, and hydrazine sulfate can be used for both acidic and alkaline wastewater. Removal of excess hydrogen peroxide from the solution after reduction of chromium (6+) before precipitation of chromium (3+) hydroxide is required. The toxicity of hydrazine compounds must be taken into account.

Abstract: A high strength austenitic steel is expected as a structural material for cryogenic use because fcc material does not cause a cleavage fracture despite high strength. High manganese steel which is a strong candidate material of the cryogenic high strength austenitic steel was originally famous for the Hadfield steel and widely applicable in actual use. In general, an excellent cryogenic toughness of the high manganese steels is achieved by obtaining stable fcc microstructure with an adequate amount manganese which is a typical austenite former alloy. However, as addition of manganese is not effective for increasing strength, other strengthening alloying elements like carbon and chromium need to be added. In this study, an effect of alloying elements on strength and cryogenic toughness of the high manganese austenitic steel is studied.

Abstract: Press-hardening is an intensively developing forming technology which is mainly used for the production of car body parts. Because it is a hot forming technology, small forming forces can be utilized and, due to the lower spring-back effect, more accurate products are achieved. In car bodies, materials with high energy absorption and a sufficient hardening coefficient are mainly used in impacted parts. One of these materials is TRIP multiphase steels with different chemical composition. In these steels, it is possible to achieve an ultimate strength up to 1000 MPa with the ductility of 20-30%. In order to achieve the desired properties, it is necessary to select a suitable heat treatment that allows to achieve a multiphase structure. Phase transformations and mechanical properties are influenced by the use of suitable alloying elements. Three low-alloy, multiphase TRIP steels with different chemical compositions with a carbon content of 0.2% were chosen for the experimental program. The first steel was alloyed only with manganese and silicon, in the second niobium was added, and in the third the influence of chromium on increase of hardenability and strength was investigated. Press-hardening was performed in a heated forming tool. To describe the effect of the cooling rate, the forming was carried out in a tool at room temperature and after preheating to 425°C. The influence of holding time in the tool at 425°C to support the formation of bainite and retained austenite stabilization was also investigated. Mixed ferritic-bainitic-martensitic structures with some retained austenite content were obtained.

Abstract: Conventionally, chromium is deposited from hexavalent chromium baths containing extremely toxic compounds of Cr (VI). Due to serious health and environmental concerns of Cr (VI), trivalent chromium bath is proposed as a counter approach towards greener and safer chromium plating. In the present work, chromium coatings were electrodeposited onto copper substrate using a modified trivalent chromium electroplating bath with addition of polyethylene glycol (PEG 1500). The effects of PEG on the Cr coating were investigated. The crystalline structure, composition and surface morphology of the deposits were studied by X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX) and scanning electron microscopy (SEM). The surface roughness of the coatings were characterized by atomic force microscopy (AFM). With addition of PEG, the surface roughness of Cr coating decreased by 44.5 % and the corrosion rate decreased by 23.3 % compared to that of without PEG. Meanwhile, the hardness increased by 22.7 %.

Abstract: Chromium absorption using modified zeolites in the form of mono-cation (H-Zeolite) was carried out. Modifications are intended to increase the ability of ion exchange. Modifications made were chemical activation by adding ammonium chloride solution and physically by calcination. Zeolite used came from Kasongan, while as an activity test liquid waste from the electro plating industry PT. Mega Andalan Electro Plating. The parameter used for this study is the comparison of zeolite mass with waste samples. Comparisons used are 1: 5, 1: 7, 1:10, 1:20 and 1:50. From the results of the study it can be seen that there is an increase in the ability of ion exchange in the modified zeolite and produces an optimum ratio of 1: 7 with an absorption efficiency of 13.44%..

Abstract: Short-range order in Fe–Cr alloys is investigated by Monte Carlo method. The modelling was performed by Metropolis algorithm using the LAMMPS software package. Modelling results were analyzed by the visualization and data analysis package Ovito. The model of the alloys supposed that the lattice structure was fixed and interaction exists between the first and the second neighbours. The Fe–Cr interaction was established with the use of interatomic interaction potential Abell–Brenner–Tersoff (ABOP). Different concentrations of substitutional impurity of chromium in iron were investigated, viz. 5–50 at. %. The energy of mixing in the Fe–Cr system was calculated for various concentrations of substitutional impurity. Calculation showed that the chosen interaction potential reproduces correctly the changes of the sign of the energy of mixing as a function of Cr concentration. When applied in Monte Carlo kinetic modelling the potential predicts correctly the immiscibility of initially chaotic Fe–Cr alloys as a function of Cr content. The Cowley short-range order parameter is determined that is used for quantitative estimation of the degree of ordering. A strong tendency towards ordering in Cr distribution is observed at low concentrations which is exhibited by negative values of short-range order parameters, in accordance with the experiment.

Abstract: The present study has been undertaken to replace W by Cr in as-cast HSSs using B as alloying element. For this reason, a special alloying system was suggested. The basic steel containing approximately 12 wt. % of Cr was alloyed with B, V, V and Mo in different proportions. The microstructure of the steels was studied using electron microscopy, X-ray diffraction, and energy dispersive X-ray analysis. It was shown that the matrix structure, as well as the origin and morphology of the carbides or carboborides formed during solidification greatly depended on the alloy chemical composition.

Abstract: The possibility of reduction of chromium and iron from complex oxides by gaseous carbon monoxide and solid carbon was investigated. The chromium ore concentrates of Kempirsai and Aganozero deposits used in present study had different ratio of iron and chromium content. The Reduction in CO gas atmosphere did not result in reduction of chromium and iron from spinels; however, it resulted in reduction of fines from the drying apparatus, where the particles of coke presented along with the particles of the Kempersai chromite. At the same time, iron and nickel were reduced from the silicates of the gangue minerals. In the samples mixed with solid carbon a continuous layer of carbides formed on the surface of the spinel grains. The formation of a continuous shell retarded and practically stopped the reduction process. The further development of reduction was possible after destruction of the shell that occurred as a result of smelting of the carbides and silicides mixture that constitute the shell.

Abstract: In this work, the wear resistance of hardened simultaneous diffusion saturation on S235J0, C45, 55NiCrMoV6, C80W1 and X162CrMoV12 steels with boron, chromium and titanium and rigidly fixed abrasive Al2O3 particles were investigated. Wear was determined by measuring the loss of mass every 30 seconds of the test. Full wear of the layer occurred in 10 minutes with a load on the sample of 9.5 MPa. According to the test results, it is found that the wear resistance of alloyed steels increases as the content of alloying elements and carbon increases, but this increase is not unambiguous because of a decrease in the thickness of the diffusion layer as the degree amplification of alloying steels. Taking into account the economic parameters, such as the cost of steel, the cost of manufacturing products, we can conclude that the greatest economic effect shape can be achieved when using the hardening steels with a carbon content of 0.5 mass percent and the total content of alloying elements up to 5 - 7 mass percent.