O. N. Baklanova

Effect of Carbon Steel Structural Inhomogeneity on Corrosion Resistance in Chlorine-Containing Media

It is established that structural inhomogeneity of 20-KSKh steel rolled product produced in the casting and rolling complex at OMK-Stal is caused by presence of bainitic areas within a ferrite-pearlite matrix. Differences in this inhomogeneity are shown due to banding of the ferrite-pearlite structure, determined according to GOST 5640. A method is proposed for evaluating the degree of structural inhomogeneity (banding number) containing bainitic areas. Comprehensive corrosion tests are performed for specimens with “bainitic” and ferrite-pearlite banding. It is established that specimens with “bainitic” banding exhibit better corrosion resistance.

Microstructure and Property Formation for High-Strength Low-Carbon Steels Microalloyed with Titanium and Molybdenum

Features of microstructure formation for hot-rolled product of low-carbon steels microalloyed with titanium and molybdenum are studied. The possibility is demonstrated of achieving a high level of mechanical properties due to forming a volumetric system of nanosize complex (Ti, Mo)C carbide precipitates during cooling after hot rolling, including during cooling of a wound coil with γ → α transformation, and also as a result of forming a finely dispersed ferrite structure with increased dislocation density. Conformity of the temperature for the end of rolling and strip winding on a coil with a cooling regime in this temperature range, and also an increase in free titanium content in this steel, are desirable.

Development of a New Generation of High-Strength Low-Carbon Microalloyed Steels for the Main Layer of Clad Rolled Product

The importance is demonstrated of developing new low-carbon high-strength steels for a marked improvement in both mechanical and service properties of a main metal layer, strength and continuity of joined layers, and also quality characteristics of corrosion-resistant clad rolled product as a whole. In order to resolve this problem on the basis of original methods of physicochemical prediction a new low-carbon high-strength steel is created of weldable economically alloyed steel, and its main production technology is developed. It is shown that in order to achieve simultaneously high strength indices (yield strength more than 700 MPa, strength more than 850 MPa), ductility (relative elongation more than 17%), and other steel service properties, nanostructuring is of prime importance, realized with relatively slow metal cooling rates typical for preparing clad rolled product.

Preparation of Two-Phase Ferritic-Martensitic Steels of Different Alloy Systems in Continuous Annealing Units

Features of structure and property formation, processing aspects for preparation of cold-rolled, including hot-dip galvanized, product of two-phase ferritic-martensitic steels with the most typical alloying system (silicon, manganese, and chromium), and also additional alloying with molybdenum, are studied with heat treatment in continuous annealing units (CAU). Cold-rolled product of different thickness is heat treated (HT) in the intercritical temperature range established from results of dilatometric measurements. It is established that there is formation in the test steels of a ferritic-martensitic structure with some proportion of bainite and residual austenite in the form of an MA-component (region with a size of several microns consisting of martensite and residual austenite). With modeling of the HT regime typical for CAU steel alloyed with molybdenum has strength 100–150 MPa higher than steel of the typical alloy system, and this is connected with a higher proportion of strengthening phase within the structure.

Effect of Treatment Temperature Regimes in a Continuous Annealing Unit on Two-Phase Ferritic-Martensitic Steel Mechanical Properties

Features of structure and property formation are studied for cold-rolled product in two-phase ferriticmartensitic steels by modeling heat treatment in a continuous annealing unit (CAU) of six laboratory melts of different chemical composition intended for preparing steels of different strength classes according to EN10338:2013. Steel of some melts, apart from alloying with elements currently used extensively, are additionally alloyed with aluminum. Hot- and cold-rolling processing regimes simulate those used under production conditions. Results of modeling heat treatment in a CAU by different regimes show an increase in strength and a reduction in ductility properties with a reduction in overageing temperature. Rolled product of steel alloyed with aluminum has lower strength properties, ratio of yield to ultimate strengths, but better relative elongation values.

Nonmetallic Inclusions and Promising Principles for Improving the Set of Properties and Quality Characteristics of Steel

Results of a detailed study of continuously-cast low-alloy pipe steel metal demonstrate a significant difference in micro- and macrostructural states, including the presence and extent of equiaxed and columnar crystal areas in relation to the later stages of ladle treatment. A marked difference is also recorded in impact strength indices, hydrogen corrosion cracking resistance, and other service properties obtained for different rolled billets. It is established that as a result of adding large amounts of silicon- and manganese-containing ferroalloys in the later stages of ladle treatment or in the process of steel continuous casting there is formation of liquid silicate inclusions. Due to a high silica content during steel crystallization these inclusions are converted into a supercooled liquid or glassy condition and acquire irregular shape, filling the space between growing crystals. As a result of this they effectively reduce the intensity of mass- and heat-transfer during steel crystallization, block development of liquation processes, and facilitate an increase in the degree of metal structural and chemical inhomogeneity. As a consequence there is an increase by a factor of 2–2.5 in impact strength to extremely high values (KCV–40 more than 400–420 J/cm2), and rolled product hydrogen cracking resistance.

Study of Principles for Creating Steel in Order to Prepare High-Strength Reliable Objects by Hot Stamping

Principles for creating a new generation of steels for preparation of objects by hot stamping with an improvement of strength properties (ultimate strength up to 2200 MPa) by a factor of three are analyzed. It is shown that first of all they should be aimed at simultaneous provision of good steel hot ductility indices, quenchability, and hardenability. It is established that boron-containing steels, and also steels of the alloy and microalloy systems Mn–Cr, Mn–Mo–Nb, Mn–Cr–Ni–(Mo–Nb–V) with an attempt to reduce carbon content are most promising for this purpose. With the aim of verifying results obtained experiments are performed for the effect of cooling rate on steel strength properties of the alloy systems selected. Adequacy of the main conclusions and the promise of using boron for alloying, and also alloying and microalloying additions C–Mn–Cr–Ni–Nb–V systems in order to create new low-alloy weldable steels for preparation of objects by hot stamping are confirmed.

Structural Factors Governing Main Gas Pipeline Steel Stress Corrosion Cracking Resistance

Work is devoted to fractographic study of steel specimens from main pipelines previously in operation and steel of current production with the aim of studying the capacity of various structural components to accumulate hydrogen during pipeline operation.

Effect of Chemical Composition and Microstructure Parameters on Carbon and Low-Alloy Steel Corrosion Resistance

An improvement in resistance to overall and local corrosion in neutral aqueous media with hydrogen index pH 6–8 is important for numerous structures operating under atmospheric conditions, in sea water, for heating network pipelines, oil industry pipelines (oil pipelines and water conduits), and many other forms of structure and equipment. Under these conditions, corrosion proceeds by a classical electrochemical mechanism. Today, there is no single point of view for the optimum chemical composition and microstructure for steels for simultaneous provision of good corrosion resistance in aqueous media and satisfactory mechanical properties. In this work, the effect of chemical composition and microstructure parameters on corrosion resistance of carbon and low-alloy steels of strength classes K52–K60 in aqueous media is studied with the aim of developing specifications for these properties in order to increase the operating life of steel equipment, in particular oil industry pipelines.

Effect of Hot Rolling and Strip Tension on Mechanical Properties of Cold-Rolled Two-Phase Ferritic-Martensitic Steels

Results are given for a study of the effect of hot rolling parameters on the mechanical properties of heat-treated cold-rolled product of two-phase ferritic-martensitic steel (TFMS) of grade HCT980X (EN10336:2007). Temperatures for the end of rolling and coiling are varied during hot rolling of a metal laboratory melt. Hot-rolled product obtained by different versions is heat treated by regimes modeling annealing in a continuous hot galvanizing unit (CHGU). Morphological features of structural components and excess phase precipitates in different treatment stages are studied. The effect of strip tension in a CGHU on a set of mechanical properties with a change in temperature is analyzed. Mechanical test results are used to determine the optimum heat treatment temperature range providing the required level of cold-rolled steel strength properties.