Use Of Austenitic Steels Research Articles

Research of Properties of Cast Austenitic Steels for Low-temperature Equipment

This paper considers the possibility of using Cr-Ni, Cr-Ni-Mn and Cr-Mn cast metastable austenitic steels with alloying systems of the grades 12Cr18Ni10TiL, 10Cr14Mn14Ni4TiL and 10Cr14NMn20L for the manufacture of complex-shaped parts for use in equipment operated at low temperatures. The results of tests to assess the characteristics of strength, ductility and toughness of austenitic steels in the cast state in the temperature range from plus 20 to minus 196 ° C are presented. The obtained data allow us to estimate the change in the values of the mechanical properties of cast asutenite steels with decreasing test temperature. Based on the analysis of the results obtained, recommendations were given on the use of austenitic steels in a cast state for low-temperature equipment at various operating temperatures. It is shown that metastable austenitic steel 10Cr14NMn20, in comparison with other studied steels, despite relatively low values of plasticity, has higher values of strength and toughness at mines 196 ° C and can be recommended for the manufacture of cast parts of low-temperature equipment.

Long‐term exposure of austenitic steels and nickel‐based alloys in lignite‐biomass cofiring

AbstractThe aim of this study was to assess the long‐term impact that the addition of biomass provokes on superheater materials exposed to fireside corrosion environments. Alloys covering a broad range of commercially available materials were investigated. Their corrosion kinetics under different corrosive deposits and atmospheres was evaluated, and their corrosion products analyzed to deepen understanding of the underlying corrosion mechanisms. Therefore, three nickel‐based alloys and three austenitic steels containing 20–24 wt.% Cr were tested at 650°C for 7,000 hr. The long‐term exposure shows new mechanistic aspects of Type II hot corrosion that were revealed by accelerated material depletion. The formation of Ni–NiS eutectic and the formation of a Cr depleted zone close to the substrate corrosion product interface are indicative of the breakaway occurrence. Differences in the corrosion behavior are related to the balance of Ni, Mo, Co, and Cr and can serve as the material selection argument. The evaluation concluded with the finding that alloys presenting Mo and Ni might be preferentially used in fireside corrosion in the presence of biomass, whereas the use of austenitic steels suffer less corrosion if no biomass is present in the corrosive atmosphere.

Perspectives of Materials for Fin Tubes

Modern design solutions of power boiler using the welded fin tubes for heat exchangers. Depending on thermal parameters (pressure and temperature), the heat transfer fluid and flue gas these constructions can be preheater, economizers or superheaters. Their use can significantly increase the energy efficiency of boilers. For the manufacture of welded fin tubes are used non-alloy steels and low-alloy C-Mo, C-Cr-Mo. Analysis of project assumptions supercritical blocks indicates that the range of conventional steel for power and martensitic steels has been depleted. Designing higher performance outlet of steam to 720C and 35MPa requires the use of austenitic steels and nickel alloys. These materials are not easily available and not fully recognized, both technologically and in terms of materials, especially in the area of their weldability. In this work, performed the review of probably directions of development of materials for the finned tubes, with a particular focus on laser welding technology.

Energy absorption by the steel structure of ships in the event of collisions

Even though in recent years safety has been increased as a result of technical, administrative and nautical measures taken, collisions and groundings constitute maritime accidents which still occur relatively frequently. The damages resulting from accidents may be drastically reduced by an appropriate hull structure, which will ensure tightness of the cargo tanks and floatability of the ship in damaged condition. The results of large–scale collision experiment were used to validate numerical calculations of the collision process. By means of the results obtained in respect of the breaking strains to be used in the calculations and other parameters numerical calculations were performed of a double–skin structure with austenitic inside wall and/or austenitic shell and inside wall. It was shown that, with identical structure and identical mass of construction, the use of austenitic steel offers considerably greater resistance to collisions.

Synthèse des observations d'érosion-corrosion recueillies en centrale sur des circuits en vapeur humide

From the HP turbine up to and including the separator feed heaters, there has been considerable erosion-corrosion of carbon steels in the PWR stations under observation; it has affected about 35 % of surfaces with losses of thickness locally attaining 2.7 mm/10,000 h. This erosion-corrosion has been stopped at Chooz by morpholine treatment of the secondary circuit together with the use of finned elbow pieces. At Tihange, treatment with morpholine has caused a spectacular reduction in erosion-corrosion. Compared with ammonia treatment, total content of iron in the drain water from the separators has been reduced by a factor of 11 ; this value is strongly representative of erosion-corrosion phenomena. At Doel, despite the use of ammonia treatment, erosion-corrosion has been limited by the total demineralization unit and the use of finned elbow joints. At Fessenheim, one unit has been treated with ammonia and the other with morpholine. The former showed extensive destruction by erosion-corrosion, while in the latter there was repassivation after the adoption of morpholine as the treatment reagent. Samples of different grades of steel were placed under severe exposure conditions facing a flow of damp steam in various PWR stations. Useful information was obtained after 40,000 hours of test: - steels with low chromium content (Cr = 1 %) appear to be on the threshold of the appearance of erosion-corrosion phenomena, though these steels stand up well when used for elbow joints ; - steels containing about 2 % chromium are unaffected by erosion-corrosion and make it possible to avoid the use of austenitic steels, which are subject to corrosion under tension. While finned elbow joints improve the flow, the experiment with laminar elbows, of circular or elliptic section, divergent convergent, did not give the expected results. An attempt was made to reduce the humidity of the steam at the HP output by preseparation of the liquid phase using experimental equipment of the water-trap type. While 30 % of the water is recovered with this equipment, the slight reduction in the liquid film cannot prevent the electrochemical process of erosion-corrosion in a unsuppressed electrolytic environment. High-speed driers seem to be a solution to the problems of erosion-corrosion for the future in PWR stations; they would result in total elimination of humidity in the HP exhaust, and consequently remove ail problems of erosion-corrosion, whatever steels or treatments are used. The Studies and Research Division of Electricite de France has developed such devices : they are a special type of centifugal separator, consisting of separation cells placed in parallel in the linkage piping immediately after the HP turbine. Two experimental units have been installed since 1980 in the Le Bugey station. The humidities attained at the output from them are less than 0.1 %, thus bringing us back to the classical conditions in the steam turbines of fossil-fuel power stations, and eliminating all erosion-corrosion problems. If the test results were confirmed, the very substantial reduction in the size of the separators should make it possible to lower the cost of the drier-feed heaters, and in general that of the machine room.

Neutron energy-dependent damage function for analysis of austenitic steel creep data

Proper correlation and subsequent application of irradiation-effects data for materials exposed in different reactor environments depend upon a knownledge of the energy dependence of neutron damage. A theoretical model of neutron damage in austenitic steel was adjusted with available creep-strain data for austenitic steel irradiated at temperatures below ∼ 400°C. This procedure yielded a damage function for the neutron-energy dependence of irradiation-induced creep-strain. Although the derived damage function correlates available creep data, it is only roughly defined and is presented to meet immediate demands for such correlation. Additional and more accurate flux-spectral, fluence and property-change data for more test reactor environments are required to confirm the adequacy of the damage function. As a means of interpreting and correlating available test-reactor data for application to different environments, the present damage function will help establish proper engineering design requirements for use of austenitic steels in fast test, thermal test, and power reactors. The damage function is now being used to analyze irradiation conditions in the Fast Test Reactor (FTR) among others.

Experience With Austenitic Steels in High-Temperature Service in Petroleum Industry

Abstract Experience in the petroleum industry shows there are other factors besides tensile, creep, and stress rupture to consider in the use of austenitic steels in high-temperature service. There is no advantage in using stabilized grades in many applications. A spheroidizing heat-treatment is generally effective where stabilized steel is required. The coefficient of expansion and the thermal conductivity have been important factors in thermal-shock and thermal-fatigue failures in austenitic steels.