Zbigniew Grzesik

Thermal Shock Corrosion of Valve Steels Utilized in Automobile Industry

The high-temperature corrosion behavior of four valve steels (X33CrNiMn23-8, X50CrMnNiNbN21-9, X53CrMnNiN20-8 and X55CrMnNiN20-8) in combustion gases of fuel oil, containing different concentrations of bio-components (5 and 10xa0wt%) has been studied under thermal shock conditions. It was found that the addition of bio-components decreased the corrosion resistance of steels investigated. It was also found that the X33CrNiMn23-8 steel containing the highest chromium concentration, behaved in the investigated atmospheres much better than three remaining steels due to the formation of highly protective chromia scale.

The Influence of Hybrid Coatings on Scaling-Resistant Properties of X33CrNiMn23-8 Steel

The influence of two-layer hybrid coatings on the oxidation behavior of X33CrNiMn23-8 steel, utilized in valves of Diesel engines, have been studied as a function of temperature (873 1273 K) and oxygen pressure (1-10 Pa), using modern microthermogravimetric techniques. Phase composition of the oxidation products (scale) was investigated by X-ray diffraction (XRD), and the morphology and chemical composition of reaction products by electron probe micro analysis (ΕΡΜΑ) and scanning electron microscopy (SEM) with energy disperse X-ray analyzer (EDX). It has been found that uncoated material shows very good oxidation resistance under isothermal conditions, comparable with that of chromia formers, due to the formation on its surface of Cr203 scale. However, beneath the scale, steel undergoes rapid degradation, as a result of crack formation; the deeper the penetration, the longer is the oxidation time. On the other hand, no cracks were observed in the coated steel and the oxidation rate was even slightly lower than that of uncoated material.

The Behavior of Valve Materials Utilized in Diesel Engines Under Thermal Shock Conditions

The oxidation resistance of two X33CrNiMn23-8 and X50CrMnNiNbN21-9 steels, utilized for the production of valves in Diesel engines has been studied under thermal shock conditions. It has been found that X50CrMnNiNbN21-9 steel undergoes under such sever conditions dramatic degradation, due to extensive cracking and scale spallation. The second X33CrNiMn23-8 steel, with higher chromium concentration behaved much better, due to the formation of the protective chromia scale. It has been found also that both steels under investigation, covered with metalceramic hybrid coating, show excellent oxidation resistance.

Oxidation Kinetics of Steels Utilized in the Production of Valves in Automobile Industry

Abstract The oxidation kinetics of four Fe-Cr-Mn-Ni based steels, utilized in automobile industry, have been studied as a function of temperature (973–1273 K) and oxygen partial pressure (5–105 Pa). It has been shown that the rate of corrosion of these steels under isothermal conditions is determined by diffusion of reagents through the scale, which phase composition and morphology depend first of all on chromium and to some extend also on nickel and manganese contents. The highest oxidation resistance at high temperatures is observed in the case of the X33CrNiMn23-8 steel, containing highest chromium concentration, equal 23.4 wt.% and nickel equal 7.8 wt.%. The remaining three steels with virtually the same chromium content (≈20 wt.%), but lower than that in the first one, show comparable oxidation resistance. Small differences in the oxidation rates of these three steels may be related to different nickel and manganese contents. It has been found also that the rate of corrosion of all steels under investigation does not depend under steady state conditions on oxygen partial pressure.

The Interpretation of Marker Experiment Conducted during Formation of Higher Oxide on the Surface of Lower Oxide

The marker method in studying the formation mechanism and defect structure of higher oxide during oxidation of lower oxide has been discussed. The approach to this problem needs specific treatment, both in experimental procedure and in the interpretation of results. It has been shown that the correct results of marker experiments in the case of highly defected substrates can be obtained, if these substrates before the marker deposition process are submitted to homogenization under highest oxidant activity, at which they remain stable at a given temperature. In addition, the nonstoichiometry must be considered in formulating appropriate chemical reactions, being the basis for foreseeing the location of markers in the interior of reaction product. The other very important problem consists in the possibility of the formation of reaction product not only on the surface of oxidized substrate but also inside of this substrate. In such a situation, the formulation of final conclusions concerning the crystalline lattice disorder from marker position should be combined with considerations of chemical reactions and transport processes occurring in a given substrate.

Oxidation Resistance of Austenitic Steels under Thermal Shock Conditions in an Environment Containing Water Vapor

Abstract The oxidation behavior of Super 304 H, Sanicro 25, HR3C and HR6W steels, which are recommended for use in ultra-supercritical power plants, as well as corrosion resistant X2CrNiMo17-12-2 steel was studied in this work. Oxidation tests were carried out under thermal shock conditions in an oxygen-rich environment (containing 50 vol. % water vapor) at a temperature equal to 750u2006°C. The investigated steels (excluding X2CrNiMo17-12-2 steel) are characterized by good oxidation resistance under thermal shock conditions. A highly protective Cr2O3 layer was formed in the internal part of scales growing on the surfaces of investigated steels. The X2CrNiMo17-12-2 steel has worse oxidation resistant properties than the other grades of steels.

Marker Method in Studying the Defect Structure in Products of the Oxidation of Highly Disordered Substrates

Abstract The interpretation of marker experiments in studying the formation mechanism and defect structure of higher oxides during oxidation of lower oxides, showing rather high deviations from stoichiometry, has been discussed. It has been shown that correct results can be obtained only if the concentration of point defects in the substrate is taken into account. Theoretical considerations presented in this paper have been illustrated by the experimental results obtained during sulphidation of highly disordered Co1-yS to form CoS2, as well as Ni1-yS to form NiS2.