Mechanical Properties Of Heat-resistant Steel Research Articles

Application of Schaeffler Diagram for Predicting the Structure and Mechanical Properties of Heat-Resistant Steels with More than 10 wt.% Cr

Application of Schaeffler Diagram for Predicting the Structure and Mechanical Properties of Heat-Resistant Steels with More than 10 wt.% Cr

Developing the optimal chemical composition of heat-resistant Cr-Ni steel for aerospace equipment

The object of research in this work is the processes of forming the microstructure and mechanical properties of heat-resistant steels depending on their chemical composition. The microstructure and high-temperature mechanical properties of austenitic heat-resistant chrome-nickel steels of the proposed chemical composition were investigated in the work. The microstructure study determined the grain size and topography of inclusions in steels. Based on the results of mechanical tests, a multifactorial experiment was planned, which made it possible to establish the relationship between the mechanical properties of steels with alloying elements selected as factors. The obtained regression equations were used to estimate the quantitative influence of each alloying element on the corresponding mechanical properties. Analysis of the results of the experiment made it possible to determine the optimal chemical composition of steel for gas turbine engines used in the aerospace industry, as well as in the metallurgy of titanium production. It is shown that the state of solid solution and heat-resistant niobium and molybdenum carbides (chromium carbides dissolve at a temperature of 950 °C) are an important factor that significantly affects the structure, mechanical, and service properties of heat-resistant steel. The austenite structure is provided by the required amount of nickel. The resulting indicators of heat resistance of steels of different compositions, tested at temperatures of 850 °C, 950 °C, and 1050 °C, proved the superiority of steel with a higher content of carbon and chromium and a lower content of nickel. The mechanism of steel strengthening and the influence of alloying with carbon, chromium, and nickel on it have been determined. The optimal chemical composition of heat-resistant steel on an iron-nickel basis for operation at a temperature of 950 °C has been established

Effect of tempering temperature on the precipitation behavior of B-containing carbides and mechanical properties of heat-resistant steel

The precipitation behavior of B-containing carbides during tempering at 300–700 °C has here been studied. With an increase in the tempering temperature, the variation of mechanical properties of the heat-resistant steel was then revealed. It was found that the BN inclusion, which had been formed during solidification, disappeared and a fine (Nb,V)(C,N) precipitation was observed by SEM analysis after isothermal quenching. The carbides were acicular M7(C,B)3, with a dominant brittle fracture morphology, when the tempering temperature was lower than, or equal to, 550 °C. Also, the carbides were block M23(C,B)6, with a dominant ductile fracture morphology, when the temperature was higher than 550 °C. It was also found that the lath boundaries of the martensite and the phase boundaries of M7(C,B)3 were favorable conditions for a preferential nucleation of M23(C,B)6.

Detection and evaluation of thermal aging brittleness of heat-resistant steel using magneto-acoustic compound techniques

ABSTRACT The service life and structural safety of components are affected by the thermal ageing of materials; therefore, a non-destructive evaluation of materials is extremely essential and crucial. In this work, heat-resistant steel Cr12MoV was selected as a specimen, and the embrittlement period of heat-resistant steel Cr12MoV was obtained by accelerated thermal ageing experiments. The effects of service temperature and service time on the mechanical properties of heat-resistant steel were analysed. The non-destructive testing of heat-resistant steel was carried out by using magneto-acoustic compound detection techniques based on electromagnetic acoustic transducers. In the process, magneto-acoustic compound detection signals were decoupled. The electromagnetic characteristic parameters and ultrasonic characteristic parameters of the detection signals were extracted to evaluate the mechanical properties and thermal ageing of heat-resistant steel. The quantitative evaluation ability of thermal ageing brittleness of heat-resistant steel was improved by using the magneto-acoustic compound detection techniques compared with single eddy current detection method or single ultrasonic detection method.

Damage characterization of belt conveyor made of the 330Nb alloy after service in a carburizing atmosphere in a continuous heat treatment furnace

In this paper, the failure of the belt conveyor made of 330 Nb heat-resistant steel, working in a furnace for continuous heat treatment in a carburizing and oxidizing atmosphere is investigated. On the basis of microscopic tests and X-ray phase analysis, changes in the microstructure in the cross-section of the conveyor wire after 731, 1642 and 2138 cycles carburizing and oxidizing in the temperature range 30–850 °C in 160 min were determined. Moreover, tensile tests were carried out to investigate the effect of the microstructure on the mechanical properties of heat-resistant steel. The failure was due to a cross crack of wires of the conveyor belt mesh. The results show that the on the surface of the alloy, Cr2O3 chromium oxides and FeCr2O4, Mn1.5Cr1.5O4 oxides are formed. On the border of the alloy and chromium oxides, the airtight SiO2 layer is created. As a result of the actions of external forces, transverse and longitudinal cracks are formed in the oxide layer. These cracks are the ways of carbon and oxygen diffusion. In addition, in the oxidation and carburization process, degradation of the SiO2 layer is promoted by the presence of Na, which is applied in washing agents used for cleaning products before placing them on the conveyor. Microstructure of the unused wire of the conveyor belt consisted of G and H phases and NbC in austenitic matrix. Under the operating conditions of the conveyor belt, phase H dissolves in the matrix with the simultaneous increase of the G phase, and also the G phase is formed around the NbC carbides. High temperature carburizing leads to the precipitation of massive carbides M23C6 with simultaneous significant depletion of chromium into an austenitic matrix to about 13%at. Quantitative microstructural analysis showed that the there was an increase in the size and participation, of hard phases M23C6, G, NbC in the alloy microstructure. The volume fraction of precipitation increased from 3 to 24%vol. The resulting structure is characterized by low strength. The ductility of the alloy has decreased significantly.

Influence of the activation of the nicarbing process on mechanical properties of heat-resistant steel

The results of evaluating the microhardness, durability, and back-to-back endurance of heat-resistant VKS-7 and VKS-10 steels after the nicarbing process have been presented. The evaluation consisted of two stages, i.e., prior plastic deformation by the warm sinking strain method and nicarbing. Supplementary reserves for improving serviceability of critical parts made of heat-resistant steel were shown.

Improvement of mechanical properties of heat-resistant steels by activation of the nitriding process

Values of hardness, wear resistance, and contact endurance limits for steels VKS-7 and VKS-10 found experimentally in various test conditions are presented. Characteristics of mechanical properties of heat-resistant steels are improved by the use of the new complex technology of thermal and chemical-thermal treatment based on the formation of a finely dispersed structure during hot deformation and activation of diffusion saturation during ion-plasma nitriding.

Microstructure Evolution and Nitridation in an As-Cast 25Cr-35Ni-1Mo Radiant Tube After Long-Term Service

The microstructure evolution of 25Cr-35Ni-1Mo radiant tubes was investigated after approx- imately two years of service in a continuous annealing furnace. The inner and outer tube walls were exposed to N2-containing combustion environment and protective atmosphere, respec- tively. The decarburization feature analysis indicated that carbon content decreased toward the tube surface. However, precipitates at the inner and outer walls were coarser, their content increased and the microhardness value also increased compared to that in the central area. X-ray diffraction illustrated that M2(C,N) and M6(C,N) were the dominant carbide at the inner and outer walls, and precipitates in the central area were mainly M23C6 and M6(C,N) phases. The results were assumed to be associated with the nitridation phenomenon that occurred in the N2-containing environment at elevated temperatures. IN the manufacturing process for the cold-rolled sheet of steels, steel strips are submitted to an annealing furnace section after cold rolling in order to obtain required mechanical properties. The continuous anneal- ing furnace is now commonly used as reheating equip- ment, in which the annealing process involves passing steel strips continuously through a heating furnace filled with classical N2-H2 protective atmosphere. In the continuous annealing process, radiant tubes are used as indirect heating equipment. Heat is transferred from combustion gas to the radiant tube, and then it radiates energy to the load, without any direct flame or com- bustion exhaust coming in contact with the load. Centrifugally cast Fe-Ni-Cr based heat-resistant steels (1) are widely used in heat treatment applications, such as radiant tubes, for their good exhibition of mechanical property and corrosion resistance at high temperatures. The microstructure of these centrifugally cast tubular materials consists of austenite dendrites delineated by a network of eutectic carbides. (2-4) As a consequence of the high Cr content in this class of steels, various types of those carbides can be precipitated. For example, precipitation of Cr-rich carbide M7C3 and M23C6 is very common, and the addition of stabilizing elements such as Ti, Nb, and V usually results in MC type carbides, (5,6) and so on. Detailed mechanical properties of these heat-resistant steels are dependent on the stability of the microstructure, particularly the formation, coarsening, and transformation of these precipitates. However, precip- itates initially formed in as-cast microstructures undergo morphological and chemical changes under service condi- tions such as high-temperature aging, corrosion, and creep. Then coarsening and phase transformation of these pre- cipitates occur. Those changes, with few exceptions, are undesirable and they can be detrimental to the corrosion resistance and mechanical properties of heat-resistant steels. Precipitation behaviors in austenitic stainless steels were studied extensively, and detailed information of such phases can be followed in the literature of other

Effect of high-force impulse loads on the modification of mechanical properties of heat-resistant steel after service

The main regularities are found in the deformation and failure of heat-resistant steel 25Cr1Mo1V after service under load and complex loading mode static load - additional impulse loading - load, when dynamic unbalanced processes are implemented. The fracto- graphic investigations performed confirmed the revealed regularities in the modification of the mechanical properties of the steel 25Cr1Mo1V under the action of impulse loads of identical intensity at different levels of the preliminary deformation.

Mutual determination of the solutions of problems of the description and analysis of special features of high-temperature creep of metallic materials

The article analyzes the problem of the necessity of systematizing the known data on the mechanical properties of heat-resistant steels and alloys with the object of improving the effectiveness of checking the possibilities of the constructed equations of state. It substantiates one of the variants of describing the regularities of instantaneous and short-term strain, creeps, stress relaxation, and creep limit from the same positions.