Thermodynamic Development of Austenite-Martensite Class Corrosion-Resistant Steels Intended for a Bimetal Cladding Layer

Abstract

Thermodynamic modeling is performed for regions of phase existence in economically alloyed corrosionresistant steels with the aim of determining the possibility of their use as a bimetal wear-resistant cladding layer. Quantitative evaluation is obtained for the form of nitrogen and oxygen present. It is demonstrated that for steels of the type in question introduction of niobium is only effective at the microalloying level. Keywords: corrosion-resistant steels, hot rolling, alloying with nitrogen, alloying with niobium, niobium carbonitride, austenite stabilization, thermodynamic analysis.Rapid development of high-speed railway transport in Russia requires the creation of reliable transport systems based on using fundamentally new materials with a breakthrough in wear and corrosion resistance indices, operating reliability, endurance, mechanical, and other service properties. In particular, these materials should guarantee accident-free and repair-free operation of superstructures in current railway bridges, whose construction provides a deadweight "trough." Layered materials are most promising for use in its manufacture with a main layer of high-strength structural steels and a cladding layer of multifunctional steel, which apart from high strength and corrosion resistance should exhibit good wear resistance and toughness. These specifi cations are satisfi ed by chromium steels of the transitional austenite-martensite class, which surpass other corrosion-resistant steels both with respect to reliability properties due to the presence of austenite within the structure, exhibiting improved toughness, and with respect to wear resistance due to the fact that residual metastable austenite is capable of undergoing deformation-dynamic martensitic transformation, absorbing mechanical energy and strengthening stressed parts. According to GOST 5632−72, the chromium and nickel contents in corrosion-resistant steels of the austenite-martensite class are within the limits 12-18% and 3.7-8%, respectively, and the content of manganese and silicon is not more than 0.8%. This level of alloying determines the quite high cost of these materials, and therefore for the bimetal cladding layer it is important to develop new economically alloyed austenite-martensite steels. In these steels with a reduced nickel content, the required austenite stability is provided by increasing manganese and nitrogen contents. Use of nitrogen as an alloying element has developed comparatively recently and has made it possible to create a number of new metallic materials with a nitrogen content of more than 0.1% [1][2][3][4].A possible version of the solution presented above may be composites containing 0.05-0.1% carbon, 14-15% chromium, 1.0-2.5% nickel, 2.5-4% manganese, about 0.5% silicon, and 0.1-0.2% nitrogen, with additional alloying by niobium. As seen from Fig. 1, the equivalent content of chromium and nickel for these composites is located in a Schaeffl er structure diagram [5] close to the boundary of structures: austenite + martensite/austenit...

Evolution of the Structural State and Properties of 32CrB4 Steel during the Production of High-Strength Fasteners

“…To study the effect of the annealing mode on the intensity of the pearlite spheroidization process, various temperature and time parameters were selected (Table 2). The temperatures Ac1 and Ac3 for the investigated steel were found by thermodynamic calculation using our own software (Bardin TsNIIChermet, Moscow, Russia) [20]. Their values were 740 and 794 • C, respectively.…”

Effect of Nanosized Precipitates on Corrosion Resistance of Nb-Microalloyed Steels

“…The temperature of the onset of niobium carbide precipitation was determined using a thermodynamic computer model [26], implemented on the basis of proprietary software (Bardin TsNIIChermet, Moscow, Russia), by finding the conditions of thermodynamic equilibrium in multicomponent, multiphase systems at specified external and internal parameters (temperature, pressure, chemical composition). As a result, the types of equilibrium phases, their quantities and compositions were determined by an analysis of the complete possible set for the alloying system of steels under consideration.…”

Hot Ductility, Homogeneity of the Composition, Structure, and Properties of High-Strength Microalloyed Steels: A Critical Review

“…Such a division can be clearly explained from a thermodynamic analysis of the regions of existence of phases in the steels under consideration [48]. Figure 3 shows the results of the thermodynamic calculation for the steel of a model composition microalloyed with niobium.…”

“…Therefore, when analyzing the influence of microalloying elements, we use the results of a thermodynamic calculation of the regions of existence of the corresponding excess phases conducted in this work and earlier studies. This was performed using a thermodynamic computer model [48], implemented on the basis of proprietary software, by finding the conditions of thermodynamic equilibrium in multicomponent multiphase systems with specified external and internal parameters (temperature, pressure, and composition). The basis of resolving this problem is a search for the nonlinear Gibbs energy functional for a multicomponent multiphase system with linear balanced limitations, i.e., the sum of fractions of the coexisting phases equals one, the sum of molar components in each of these phases also equals one, and, finally, each sum of the products of phase fractions in a molar fraction within the composition of the ith component equals the total molar fraction of this component within a system.…”

“…Indeed, as studies show, at higher temperatures, a more nitrogen-saturated carbonitride is formed [5]. Figure 4 shows the results of the thermodynamic calculation of the temperature of formation of niobium carbonitride precipitates at various Nb and N contents conducted using a computer program [48] for steel of basic composition, wt.%: 0.08 C-0.60 Mn-0.10 Si-0.045 Al-0.005 S-0.005 P. It can be seen that, with an in- easier precipitation of Nb(CN) compared to NbC in the higher temperature region where the straightening operation occurs.…”