G. Yu. Kalinin

Comparative analysis of corrosion cracking of austenitic steels with different contents of nitrogen in chloride- and hydrogen-containing media

The structural state and the resistance to stress-corrosion cracking (SCC) at constant loads have been studied using samples with a grown crack by the method of the cantilever bending on quenched austenitic stainless steels of the 20Cr-6Ni-11Mn-2Mo-N-V-Nb (Kh20N6G11M2AFB) type, with different contents of nitrogen (0.17, 0.34, 0.43, and 0.50 wt % N). The tests were conducted in a 3.5% aqueous solution of NaCl (without providing polarization) and in a similar solution under cathodic polarization, which causes the formation of hydrogen. It has been shown that, in a chloride solution without polarization, the steels do not undergo SCC for 2000 h. In the case of significant cathodic polarization via employment of a magnesium protector, there was revealed a brittle character of fracture upon SCC in all steels. It has been shown that steel with a nitrogen content of 0.43 wt % possesses the maximum absolute values of rupture stresses under the conditions of cathodic polarization.

Structural transformations in hull material clad by nitrogen stainless steel using various methods

Specimens of a 10N3KhDMBF shipbuilding hull steel were clad by a 04Kh20N6G11M2AFB nitrogen austenitic steel using various treatment conditions, which included hot rolling, austenitic facing, and explosive welding followed by hot rolling and heat treatment. Between the base and cladding materials, an intermediate layer with variable concentrations of chromium, manganese, and nickel was found, in which a martensitic structure was formed. In all the cases, the strength of bonding of the cladding layer to the hull steel (determined in tests for shear to fracture) was fairly high (σsh = 437–520 MPa). The only exception was the specimen produced by unidirectional facing without subsequent hot rolling (σsh = 308 MPa), in which nonfusions between the faced beads of stainless steel were detected.

Structure and mechanical properties of the nitrogen-containing austenitic plate steel 04Kh20N6G11AM2BF

Structure and mechanical properties of the nitrogen-containing austenitic plate steel 04Kh20N6G11AM2BF with a thickness of 20 and 40 mm after hot rolling, quenching from different temperatures, and final strengthening by cold or warm deformation have been studied. For these large-section plates, sufficiently high mechanical properties were obtained, namely, the yield stress σ0.2 ≥ 690 MPa, the relative elongation δ ≥ 20%, the relative reduction ϕ ≥ 50%, and the impact toughness KCV+20 ≥ 100 J/cm2. This complex of strength and plastic properties of hot-rolled steel was produced after the quenching of the plates from 1150°C and subsequent strengthening warm (600°C) or cold (20°C) rolling with a reduction of up to 15%. These properties of steel were due to several causes, namely, the presence of nitrogen in the fcc solid solution, an increased density of dislocations (≈ 1010 cm−2), the precipitation of nanocrystalline vanadium nitrides with sizes of 2–4 nm, and the absence of large amounts of coarse near-boundary particles.

Behavior of magnetic characteristics in promising nitrogen-containing steels upon elastoplastic deformation

We report on the studied influence of the applied normal and tangential stresses, as well as their combined effect on the structure, phase composition, and magnetic properties of three high-nitrogen steels (HNS). Two of the studied steels in the initial state had an austenitic structure and were diamagnetic. The third steel, according to the data of the X-ray diffraction and metallographic analysis, contained 7% δ-ferrite in its composition, which specifies its ferromagnetic properties. The nitrogen steels studied in this work have demonstrated the stability of the phase composition, as well as of the magnetic properties at various loading conditions, and, thus, can be used in the production of articles and elements of structures that are required to exhibit low magnetization and high stable magnetic characteristics under an applied force. Parameters that can be used as the informative ones when estimating changes that occur upon the production and exploitation of articles and elements made of HNSs with small contents of δ ferrite have been determined.

Acoustic detection of stress-corrosion cracking of nitrogen austenitic steels

Structural changes and resistance to the stress-corrosion cracking of the nitrogen-bearing austenitic steels 04Kh20N6G11M2AFB and 09Kh20N6G11M2AFB (with 0.04 and 0.09 wt % C, respectively) after different treatments, including thermomechanical action, quenching from 1200°C, and aging at 700°C for 2 and 10 h, have been studied. It has been shown that aging at 700°C of the air-melted austenitic steel 09Kh20N6G11M2AFB leads to a decrease in the strength of samples with an induced crack upon the cantilever bending in air and in a 3.5% aqueous solution of NaCl as compared to the strength of the steel 04Kh20N6G11M2AFB-EShP with a smaller carbon content after high-temperature mechanical treatment or quenching from 1200°C. The smallest resistance to stress-corrosion cracking is observed in the samples of 09Kh20N6G11M2AFB steel after 10 h of aging, which is accompanied by the most intense acoustic emission and by brittle intergranular fracture. This is explained by the high rate of the anodic dissolution of the metal near chromium-depleted grain boundaries due to the formation of continuous chains of grain-boundary chromium-containing precipitates of carbides and nitrides.

High-strength austenitic welded steel for shipbuilding

The paper depicts long-term research resulting in creation of high-nitrogen austenitic steels for shipbuilding. It shows the influence of the chemical composition and technology on the crystal lattice and steel structure, mechanical and corrosion properties, weldability, and other characteristics. The paper studies the fine structure of nitrogen austenitic steels and shows the important role of nitrogen, which impacts the strength and corrosion resistance more effectively than carbon while maintaining a high level of plastic properties and resistance to cyclic and dynamic loading. Magnetic and vibrodamping characteristics are evaluated. High-strength nitrogen austenitic steel with the yield strength of 650 MPa has been successfully adopted by the domestic industry. Its implementation for heavy duty structures is in the final stage. A prognostic evaluation for further development of nitrogen austenitic steels for various industries is given.

Physical simulation of thermomechanical treatment of a high-strength nitrogen-bearing austenitic steel and its effect on the microstructure and properties of the steel

The effect of the thermomechanical treatment parameters on the structure and properties of a high-strength nitrogen-bearing austenitic Cr-Ni-Mn steel is studied using a Gleeble 3800 plastometer. An increase in the interdeformation pause time during multipass deformation of the steel is shown to decrease the temperature of formation of carbonitride hardening phases in its structure. A shift in the temperature range of deformation toward low temperatures is found to increase the strength properties of the steel, and its plasticity decreases.

Investigation of the structure and properties of the material of various zones of the welded joint of the austenitic nitrogen-containing steel upon elastoplastic deformation

The structural, mechanical, and magnetic properties of metal cut out from the welded joint and from the near-weld zone of the welded joint of high-strength nitrogen-containing 04Kh20N6G11M2AFB austenitic steel have been investigated. The behavior of the magnetic parameters of materials under study subjected to various schemes of loading, such as tension, torsion, internal pressure, and combination of tension and torsion have been investigated. It has been established that the metal of the welded joint and near-weld zone of the welded joint, just as the base metal, has a stable phase composition and magnetic properties under various loading conditions. It has been concluded that 04Kh20N6G11M2AFB steel can be used in the fabrication of welded parts and elements of welded constructions that require low magnetization and high stability of magnetic characteristics under the force action.

The effect of temperature on the mechanical characteristics of the nitrogen-containing 04Kh20N6G11M2AFB steel under static tension

The paper describes a complex of research on the study of the mechanical properties, fractographic features of the fracture and evolution of the structure of the nitrogen-containing stainless steel 04Kh20N6G11M2AFB (0.47 wt. % N) with an austenitic structure under static tension at temperatures ranging between −70 and +140 °C. A new effect has been revealed, namely, a more intensive growth of the strength characteristics with a simultaneous increase in the plasticity characteristics of the 04Kh20N6G11M2AFB steel under static tension at temperature decreasing in the range between +50 and −70 °C as compared with strengthening rate and plasticity characteristics at temperature decreasing in the range between +140 and +50 °C. It has been found that the ductile nature of fracture still prevails for the steel 04Kh20N6G11M2AFB at tensile testing temperatures decreasing to −70 °C, and this corresponds to the lower boundary of the range of negative climatic temperatures.

Corrosion resistance problems of low-magnetic shipbuilding steels

The paper presents results of comparative studies of corrosion resistance and corrosion-mechanical strength for low-magnetic shipbuilding steels of alloying systems Mn–C, C–Mn–Ni, Cr–Ni, Cr–Ni–Mo, and Cr–Ni–Mn–N, produced using various hardening mechanisms. It is shown that nitrogen-containing steels developed by CRISM Prometey constitute new constructional material superior in resistance to corrosion cracking in seawater compared with low-magnetic steels used in shipbuilding nowadays.