High Temperature Stainless Steels - Outokumpu ? Â· 4 MA grades, alloyed to last longer in extreme environments Outokumpu MA grades have been specifically designed for excellent creep and oxidation

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  • High Temperature Stainless SteelsOutokumpu MA grades

  • 2

    ContentsIntroduction............................................................................................................4

    The expert's voice.................................................................................................5

    Product positioning...............................................................................................6

    High-temperature oxidation and corrosion...................................................8

    Mechanical properties.......................................................................................9

    Chemical composition......................................................................................11

    Microstructure stability.....................................................................................12

    Fabrication...........................................................................................................13

    Product assortment..........................................................................................15

  • 3

    The world needs and deserves innovations that pass the test of time and are able to be recycled and used again at the end of their lifecycle. Outokumpu stainless steel is durable in the most chal-lenging of conditions delivering ever longer project life-cycles. The recycled content of Outokumpu advanced materials varies between 70% and 90% depending on the grade and Outokumpu stainless steel is also fully recyclable. The properties of Outokumpu advanced materials, also make them an economically sustain-able solution. Our vision of a world that lasts forever not only reflects these properties but also our ongoing commitment to innovation and the development of lasting customer relationships.

    We believe in a world that lasts forever

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    MA grades, alloyed to last longer in extreme environmentsOutokumpu MA grades have been specifically designed for excellent creep and oxidation properties at temperatures up to 1100C. This has been achieved by the addition of a number of important alloying elements in the steel ensuring superior performance across a wide spectrum of high-temperature applications.

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    Just a tiny portion of nitrogen, rare earth metals and silicon makes a good heat resistant stainless steel outstanding. Nitrogen increases the strength and rare earth metals, in combination with silicon, provide the protective oxide with exceptional properties. So, the obvious question is; why doesnt everyone add these elements? The answer is simple; it is extremely difficult to get it right. Most stain-less steel producers dont bother trying. But at Outokumpu, many years of hard work have made us the unquestioned expert in producing MA grades.

    Outokumpu 153 MA and 253 MA are suitable in many high-tem-perature conditions and there they provide substantial savings. Direct savings can be achieved as less material is necessary when using 253 MA, compared to e.g. 310S, thanks to the superior strength of 253 MA and indirect savings are realised through improved service life of components. Price stability is also achieved as 253 MA is lean in nickel compared to 310S.

    Many high-temperature applications are very harsh. The service life for a high-temperature component is often relatively short compared to applications at normal temperatures. Replacement of high-tem-perature components is thus often necessary during costly planned maintenance breaks. Even more costly are the unplanned mainten-ance breaks that are required when a component failure occurs. Our MA grades can increase the service life of many components thanks to the addition of nitrogen and rare earth metals. The increased strength decreases the risk of failures caused by deformation and creep rupture. The addition of rare earth metals results in a slower growing oxide that is more ductile and adherent. The ductility and adherence of the oxide make our MA grades more erosion and corrosion resistant. All in all, the service life of an MA grade can be significantly longer compared to other stainless steel grades, e.g. 310S.

    Examples of MA applications:AshchutecoversBellfurnacesCastingmouldsforglassCFBCBoilersCombustionchambersComponentsfor rotary kilnsConveyerbeltsCyclonesCyclonediptubesDryingchambersFansFlametubesFlexibletubes (e.g. bellows and inner sleeves)

    FurnaceliningsHeatexchangersHeattreatmenttraysIncineratorsImpactseparatorsMufflesRadianttubesRecuperatorsRefractoryanchorsRoastersTubehangersTubeseparatorsTubeshieldsValvesVehicleexhaustmanifoldsAnd many more

    The expert's voice

    Timo Piitulainen,Outokumpu Research & Development

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    Outokumpu 153 MAThe chemical composition of Outokumpu 153 MA is balanced to provide optimum properties in the intermediate temperature range 600950C, where most other stainless steels become brittle during service.

    Outokumpu 153 MAExcellentoxidationresistanceExcellentresistancetoembrittlementExcellentstrengthathightemperaturesExcellentweldability

    153 MA is suitable for all kind of applications where good microstruc-tural stability, in combination with high creep strength is essential. Use of this grade allows reduced section thickness or higher load capacity in comparison with other high-temperature steel grades. 153 MA also has excellent oxidation resistance.

    High creep strength and an adherent oxide layer are MA features. These are qualities that are important and beneficial for many applica-tions.

    Outokumpu 253 MAOutokumpu 253 MA is an excellent choice for high to very high temperatures (7001100C), particularly for conditions involving erosion-corrosion in oxidizing and neutral environments, as well as sulfur attack. The excellent mechanical strength at high temperatures allows higher loads or thinner wall thickness than common high-temperature steels e.g. 309S (EN 1.4833) and 310S (EN 1.4845).

    Outokumpu 253 MA

    ExcellentoxidationresistanceGoodresistancetoembrittlementSuperiorstrengthathightemperaturesExcellentweldability

    253 MA provides better oxidation/corrosion resistance than Outokumpu 153 MA. However 153 MA has better microstructural stability than 253 MA, especially at temperatures below 850C.

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    MA stands for Micro AlloyedOutokumpu 153 MA and 253 MA have additions of nitrogen, silicon and Rare Earth Metals (REM) which include cerium. MA in the designa-tion stands for Micro Alloyed. Cerium combined with silicon improves the oxidation resistance, erosion corrosion resistance and oxide spal-lation resistance, whereas nitrogen raises the strength and delays the precipitation of sigma phase, Figure 1. The 153 MA and 253 MA steels have proved to have better properties than steels without these alloying elements.

    Figure 1.The oxidation/corrosion resistance of Outokumpu MA grades is like most high-temperature steels primarily based on a protective Cr2O3 (chromia) layer, but the difference is that the properties of the scale are further improved by adding silicon and REM.

    Micro Alloying (MA) A way to improve the oxide scale

    Outokumpu 153 MA used to cast 23 ton mirrors with a diameter of 8.2 m for a telescope located in Atacama Desert, Chile.

    Cr oxide

    Base metalFe, Cr, Ni

    Thinner oxide

    Adherent oxide

    + silicon

    Si oxide

    + cerium

    Si oxide

    Improvedresistance against

    Oxidation/Corrosion

    Thermal cycling

    Erosion/Abrasion

    A thinner, tougher and more adherent oxide

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    High-temperature oxidation and corrosion

    Figure 2. Oxide growth in air at 1000C, 165 hour cycles for austenitic high temperature steels.

    309S

    153 MA

    4828

    310S

    253 MA

    0

    100

    200

    300

    400

    500

    Weight gain (g/m2)

    0 500 1000 1500 2000 2500 3000

    Time (h)

    All stainless steels rely on the formation of a protective oxide layer. Thus the environment must be oxidizing for the formation of a protective layer. Even so, all oxide scales will eventually experience breakdown due to growth stresses in the scale, hence a slow growing oxide is very beneficial.

    Cyclic conditionsThe MA-concept affects the growth rate so that the formed oxide will be thinner, tougher, more adherent and thus more protective. Figure 2 shows that, in spite of its lower chromium content, Outokumpu 253 MA shows better oxidation resistance than 310S under cyclic conditions.

    Water vapourThe presence of water vapour in the atmosphere reduces the resist-ance to oxidation and thus the maximum recommended service temperature. The reduction can be 50150C, depending on steam content and flow rate.

    SulfidationDifferent sulfur compounds are often present as contaminants in flue gases and some process gases. If formed, sulfide scales are gener-ally less protective than the corresponding oxide scales, leading to a faster corrosion rate, especially in nickel-sulfur compounds. This results in rapid deterioration of the material. In environments with sufficient oxygen to form an oxide scale, that scale determines the resistance to the corrosion. The adherent oxide of Outokumpu 153 MA and 253 MA makes them more suitable to those environments than materials with similar or higher nickel contents. In sulfidizing conditions where it is difficult to form an oxide, steels with high chromium content and little or no nickel are superior, for example ferritic grades Outokumpu 4742 and 4762.

    Carburization and nitridationExcessive uptake of carbon or nitrogen has a detrimental effect on material properties. The resistance against this is improved by increased nickel content. However, only traces of oxygen in the environ-ment can be suffient for the lean alloy 253 MA to produce a thin an

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