Austenic Steel Research Articles

Наукоёмкие технологии в материаловедении: высокотемпературное сквозное азотирование жаростойкой стали

The topicality of the research is occasioned by exaggeration of working conditions of products used at high temperatures and made of heat-resistant sheet alloys, including in particular austenitic chromium-nickel steels. When steel parts under load are operated in an oxidizing atmosphere and aggressive environments, besides resistance to electrochemical and gas corrosion, they require increased strength, hardness, and heat resistance. The increase in the characteristics of these proper-ties is achieved by three-dimensional and surface hardening techniques, which include the nitration process. The applica-tion of traditional technologies of furnace gas nitriding for chromium-nickel steels is complicated due to the problems of the low rate of the nitrogen saturation, which significantly increases the process time, and the formation of chromium nitrides, which negatively affects corrosion and heat resistance. The development of new technologies for nitrogen hardening of high-alloyed chromium-containing steels is carried out in the direction of saturation process intensification and regulation of the phase composition of the nitrided layer to minimize the formation of chromium nitrides. The article is aimed at defin-ing rational technological options and modes of gas austenitic nitriding of austenic steel, making it possible to increase strength characteristics at RT and higher temperatures without sacrificing its heat resistance. Thermodynamic modeling of the phase composition based on the CALPHAD technique shows that primary ways for minimizing the release of chromium nitrides on the nitrided surface are to increase the concentration of titanium in steel and to reduce the activity of the saturat-ing gas atmosphere, which is achieved by inert gas dilution of nitrogen. Experimental studies were carried out on sheet samples of 1.5 mm thick austenic steel of the type X18N10T with a standard (0.5%Ti) and increased (1%Ti) titane content. The experiments were carried out on a laboratory installation for high-temperature nitriding (900.1200 °); pure nitrogen and mixtures of nitrogen with argon were used as saturating media. Two-stage processes consisting of nitrogen hardening in nitrogen followed by argon afterburning were also investigated. Metallographic analysis showed that at the same nitrid-ing temperature, the amount of chromium nitrides decreases in experimental steel with an increased titanium content, and dilution of nitrogen with argon reduces the temperature of chromium nitride release. According to the study of saturation process kinetic, the time of through-the-thickness nitriding of a sheet sample under different saturation modes was deter-mined, as well as the duration of de-nitriding annealing, calculated on the basis of the known thickness of the chromium nitride zone. It was found that the dispersion hardening of the zones of internal nitriding with titanium nitrides leads to an increase in the strength characteristics of steels both at RT and higher temperatures compared to the characteristics of base steel 08X18N10T after typical heat treatment, while the greatest hardening effect is achieved due to through-the-thickness nitriding of steel with 1%Ti. Recommended options for the processes of through-the-thickness nitriding of 1.5 mm sheet of experimental steel: tn=1050 ℃, N2, 16 h; tn= 1100 ℃, 50%N2 + 50%Ar, 22 h; tn=1100 ℃, N2, 5 h + tann=1200 ℃, Ar, 9 h. The temporary passive hardness of nitrided steel at RT increases by 45...50%, and when tested at 800 ℃ - by 40... 65%, de-pending on the process mode. Through-the-thickness nitriding makes it possible to raise the working temperature of steels by 100.150 ° with the same long-term strength. The heat resistance at 900 ℃ remains at the level of non-carbonated steel after two-stage processes that ensure maximum chromium nitrides removal from the surface at the annealing stage.

Calculation-experimental evaluation of austenic steel mechanical properties variation in operation

Calculation-experimental evaluation of austenic steel mechanical properties variation in operation

Improvement of wear resistance of austenic steels by applying of carburization and diffusion saturation in liquid metal media solutions

The technology of the increase of wear resistance of austenitic steel products by combining the technologies of carburization and diffusion alloying in the medium of fusible liquid metal solutions has been described. The preliminary and subsequent carburization led to increase of surface layers microhardness of coated material to 5600 MPa. At the same time, the depth of the doped layer can reach 420 microns.

Study of Radiation Properties of Structural Materials for Advanced Nuclear Energy Systems

This paper introduces briefly the development of nuclear energy systems from the GEN I to the advanced GEN IV, the progress of manufacturing radiation resistant materials associated with the development of nuclear energy systems and the new methods of investigating radiation properties of the structural materials for the GEN IV nuclear energy systems at first. Irradiation induced deterioration of materials properties is a bottle neck problem, which must be investigated and solved for the development of the GEN IV nuclear energy systems. Unfortunately, all the currently available neutron sources cannot meet the requirements of investigating radiation properties of structural materials irradiated by high dose neutron irradiation in the GEN IV nuclear energy systems. Therefore, two new methods of the accelerator heavy ion irradiation that simulates the high-dose neutron irradiation and the triple beam irradiation that mimics the real neutron irradiation environment in the GEN IV nuclear energy systems have been developed. These two methods are introduced in this paper. The present status of the study on radiation properties of structural materials for nuclear energy systems of the new generation and the near future development plan at China Institute of Atomic Energy (CIAE) are described also. The accelerator heavy ion irradiation facilities for different applications and the simultaneous triple beam irradiation platform with three separate accelerators or implanters have been established at the HI-13 tandem accelerator of CIAE. A series of structural materials for nuclear energy systems, such as the home-made modified austenic steel, CLAM steel, 1515 steel, Tantalum, Tungsten, etc. have been tested and investigated systematically. A superconducting linear accelerator and a variable energy heavy ion cyclotron have been imported from abroad for a better performance of the study. Combined with the currently existing facilities of 2×13 MeV and 2×1.7 MV tandem accelerators, 30 and 100 MeV proton cyclotrons, China experimental fast reactor, China advance research reactor, Miniature neutron source reactor, etc. a comprehensive and advanced system of experimental irradiation platform for structural materials of nuclear energy systems will be established in the near future for both domestic and foreign users.

НАНОСТРУКТУРИРУЮЩИЕ КОМБИНИРОВАННЫЕ ФРИКЦИОННО-ТЕРМИЧЕСКИЕ ОБРАБОТКИ АУСТЕНИТНОЙ СТАЛИ 12Х18Н10Т

Corrosion-resistant austenitic chromium-nickel steels have low strength properties that cannot be improved using thermal treatment. The application of frictional treatment as the finishing operation allows providing the increased wear resistance, effective strain hardening and high quality of work surface of 2Kh18N10T steel. During operation and processing, the austenic steel parts could be subjected to heating. In this paper, the authors used the methods of transmission electronic microscopy, X-ray diffraction analysis, and microhardness testing to study the influence of heating in the temperature range of 100–750 °С on the structural-phase state and microhardness of 2Kh18N10T steel subjected to frictional treatment and to consider the possibilities of hardening of metastable austenic steel using combined frictional thermal treatment. It is determined, that during frictional treatment, 65 vol. % of strain-induced α'-martensite appears in the steel surface layer and the microhardness increases up to HV 0,025=690. Two-hour annealing at 450 °С ensures the retention of 65 vol. % of α'-phase in the structure and the additional increase of surface hardness up to HV 0,025=900 due to nanoscale Cr 23 C 6 carbides precipitation, and their application for hardening of nano- and sub-microcrystalline martensite-austenic structures formed in surface layer after the frictional treatment. In the result of heating up to 650 °С, the austenic submicro- and nanocrystalline structure with HV 0,025=630 hardness exceeding the initial hardness of austenic steel in hardened condition by about three times appears on the steel surface. Based on the results obtained, the authors proposed two regimes of nanostructuring combined strain-heat treatment, which involve frictional treatment and further annealings at the temperatures of 450 and 650 °С.

Corrosion and Mechanical Properties of Austenic Steel Weld Joints

This paper presents results of experiments on how tungsten, molybdenum and aluminum oxyhydroxide nanopowders, imbedded into the weld pool, affect corrosion resistance and mechanical properties of welded joints. It is shown that nanopowders have a significant effect on the intergranular corrosion of the weld.

МЕХАНИЧЕСКИЕ ХАРАКТЕРИСТИКИ АЗОТИСТОЙ АУСТЕНИТНОЙ СТАЛИ 04Х20Н6Г11М2АФБ ПРИ СТАТИЧЕСКОМ РАСТЯЖЕНИИ В ИНТЕРВАЛЕ ТЕМПЕРАТУР ОТ −70 ДО +140 ºС

The introduction of strong concentrations of nitrogen into the austenic steels of various alloying systems allows achievement of high performance of strength, plasticity, rust-resistance and tribological properties. The use of metal goods and structures under the low temperatures conditions increases the risk of their brittle fracture during various types of volume and contact loading. However, until the present, the mechanical properties (including plasticity, viscosity, crack resistance) of nitrogen steels under the low temperature tests were studied not as carefully as they were studied at room temperature. The paper presents the set of studies on the determination of mechanical properties and the fractographic investigation of special features of the structure destruction and evolution during the tension tests of 04H20N6G11M2AFB rust-resisting nitrogen steel with austenic structure under the temperature from −70 to +140 °С. The authors disclosed a new phenomenon of more intensive growth of strength characteristics of 04H20N6G11M2AFB steel under the static tension tests conditions while lowering test temperature in the interval from +50 to −70 °С in comparison with the strengthening while lowering test temperature within the range of higher temperatures (from +140 to +50 °С) at some simultaneous increase of values of plasticity characteristics under the tension test conditions at the temperature lower than +20 °С compared with tests at higher temperatures. The authors determined the retention of ductile fracture behavior of 04H20N6G11M2AFB steel while lowering tension test temperature up to −70 °С that corresponds to the lower interval limit of the negative climatic temperatures.

Structure and Mechanical Properties of 1.4539 Austenic Steel Joints Made by TIG and Laser-Beam Welding

This paper presents the analysis of structural research, micro-hardness and fatigue properties of the base material which is 1.4539 steel and joints made with CO2laser beam and TIG method. Theoretical and experimental analysis of low cycle fatigue based on deformation criterion was presented. Safe fatigue estimation consistent with the results of experiments was obtained during calculations.

Effect of grain boundary structure on the intercrystalline damaging of austenic steel during brazing

During brazing of austenitic stainless steel with copper based brazing material a common failure occurs, namely that the brazing material solutes along grain boundaries, which looks like cracks. This unfortunate effect occurred when AISI 304 and 310 steels are brazing. To avoid this unwanted effect - since the cracks propagate mainly on high angle grain boundaries - our goal was to enhance the number of special coincident site lattice type grain boundaries with thermomechanical treatment. Experiments were performed for 1, 48 and 72 hour heat treatments on materials cold rolled at different levels. After the thermomechanical treatment significant decrease in the crack size was found in depth and width, respectively.

Relaxation mechanism of rotational type in fracture of weld joints for austenic steels

Studied is the mesoscale behavior of plastic deformation and fracture of weld joints for austenic steels. Large-scale rotational modes of deformation in heat affected zones are identified with the first stage of formation of band structures; it is related to the “traveling neck” phenomenon in the base metal. The second stage is connected with crack generation and the state of affairs in the heart-affected zone.

Identification of cyclic softening and σ-ε hysteresis in austenitic steel with plasticity-induced martensitic transformation

The essential aim of this paper is the description of cyclic properties of metastable austenic steel with martensitic transformation induced by cyclic plastic deformation. The main problem is the model of σ-ε hysteresis loop as well as the phenomenon of cyclic softening. The original model of elasto-plastic body was applied to make a description. The model includes the appearance of cyclic plasticity limit and strain ε 1 corresponding to the inflexion point at CSS curve. This point separates the one phase range (austenite) from the two phase range (austenite + martensite). The plastic deformation ε 1 was accepted as the material constant and named the cyclic limit of martensitic transformation. The experimental fatigue investigations of high nickel alloy steel of the type AISI 304 were carried to identify the model. The experiments were performed for the controlled plastic deformation ampliture value ε p = constant. The results confirmed adequacy of the accepted model.

A STUDY OF He TRAPPING AND RELEASE IN THE HR-1 STAINLESS STEEL

The HR-1 austenic steel have been irradiated with 70 keV 4He ions to the dose of 5×1016—1018cm2 at room temperature. Isochronal post-annealing has been carried out at temperatures up to 1273 K. 2.5 MeV proton elastic scattering,TEM and SEM are used to investigate the trap-ping, migration and release of He.

Vを含むMn-Cr系オーステナイト鋼の析出挙動

The precipitation behaviour of V4C3 and the structural change in Mn-Cr-V type austenitic steel with a chemical composition of 0.44%C, 17.40%Mn, 12.15%Cr and 2.37%V have been studied by measuring the changes in dilatation and hardness and by transmission electron microscope observations. The results obtained are as follows:(1) The precipitated carbide which brings about a remarkable hardening and dilatation change is spherical V4C3 only.(2) The strain field caused by the coherency between V4C3 and the matrix is released when the particle size grows up to a diameter of 150∼160 Å, resulting in contraction and the hardness decrease of the austenic steel. This suggests that the coherency between V4C3 and the matrix plays an important role in the strengthening of austenitic steel in the Mn-Cr-V system.

高マンガン高クロム大洲田鋼の高温特性に及ぼす各種元素の影響に就て

This paper gives the effect of the addition of carbon, tungs en, molybdenum, silicon, aluminium and copper on the mechanical properties at, high temperature up to 900°C, oxidizing resistance at 900°C, creep limit at 600°C and brittleness after long time heating of high manganese high chromium austenic steel of the 18% manganese 10% chromium 0.10% carbon type.