High Temperature Stainless SteelsOutokumpu MA grades
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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
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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 1100°C. 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 doesn’t everyone add these elements? The answer is simple; it is extremely difficult to get it right. Most stain-less steel producers don’t 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:•Ashchutecovers•Bellfurnaces•Castingmouldsforglass•CFBCBoilers•Combustionchambers•Componentsfor rotary kilns•Conveyerbelts•Cyclones•Cyclonediptubes•Dryingchambers•Fans•Flametubes•Flexibletubes (e.g. bellows and inner sleeves)
•Furnacelinings•Heatexchangers•Heattreatmenttrays•Incinerators•Impactseparators•Muffles•Radianttubes•Recuperators•Refractoryanchors•Roasters•Tubehangers•Tubeseparators•Tubeshields•Valves•VehicleexhaustmanifoldsAnd many more…
“The expert's voice
Timo Piitulainen,Outokumpu Research & Development
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Outokumpu 153 MA™The chemical composition of Outokumpu 153 MA™ is balanced to provide optimum properties in the intermediate temperature range 600–950°C, where most other stainless steels become brittle during service.
Outokumpu 153 MA™•Excellentoxidationresistance•Excellentresistancetoembrittlement•Excellentstrengthathightemperatures•Excellentweldability
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 MA®
Outokumpu 253 MA® is an excellent choice for high to very high temperatures (700–1100°C), 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®
•Excellentoxidationresistance•Goodresistancetoembrittlement•Superiorstrengthathightemperatures•Excellentweldability
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 850°C.
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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 1000°C, 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 50–150°C, 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 and tough oxide layer with good protection against carbon and nitrogen pickup. In reducing conditions, 314 and 310S could be better alterna-tives.
Erosion-corrosion Erosion, including abrasive wear, can enhance or retard corrosion rates. Outokumpu 253 MA® has shown excellent resistance due to the very adherent oxide layer.
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Mechanical propertiesCreep strength The design stress for a material determines the load to which it can be subjected without failing or being significantly deformed during service. At 550–600°C and higher temperatures, creep strength will determine the design stress values. As a rule, creep strength is expressed as the creep rupture strength, i.e. the stress that causes rupture after 10 000 or 100 000 hours (Rkm, 10 000 and Rkm, 100 000).
Figure 3 shows the relative creep strength for rupture after 100 000 hours as a function of temperature, compared to the reference grade Outokumpu 253 MA®. The higher creep strength of the Outokumpu MA grades is primarily a result of the higher nitrogen content. The higher strength means that the component can carry a higher load, have a longer service life or need less material as the example in Figure 4 shows.
Figure 3.100 000 hours creep rupture strength, relative to Outokumpu 253 MA®.
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1.2
Relative creep rupture strength
Temperature (˚C)
0.8
0.6
0.4
0.2
0500 600 700 800 900 1000 1100
153 MA™
4828/309S310S
253 MA®
304H
321H
253 MA®
601 H
314
310S
Creep deformation test:310S and 314 rings collapsed due to own weight. 1000°C, 35 h, 1 mm thickness.
250
200
150
100
Rela
tive
wal
l thi
ckne
ss
Design temperature (°C)
50
0
300
600 700 800 900
4828/309S 310S
Figure 4.Wall thickness required to achieve the same strength as 253 MA® when designing a cylinder with an internal pressure.
253 MA®
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Fatigue strengthService conditions at elevated temperatures are rarely constant. In most cases a component will be subjected to varying loads and temperatures which can eventually lead to fatigue failure.
Fatigue typically occurs in two regimes:
•HighCycleFatigue,HCF,whichisstresscontrolledwithlow amplitudes•LowCycleFatigue,LCF,straincontrolledwithgreatamplitudes and a correspondingly shorter life
HCF occurs mainly in rotating and/or vibrating components, such as automotiveexhaustsystems.LCFisprimarilyduetolargetransientsduring start-ups, shutdowns, and major changes in service conditions.
Pure thermal fatigue in a component is caused by thermal gradients and the corresponding differences in thermal expansion. The most complex situation is when temperature and load vary simultaneously.
The superior mechanical properties of Outokumpu MA grades make them exceptionally cost-effective for a wide range of high temperature environments. The advantages, for example the creep strength and resistance to fatigue can lead to up to 60% weight savings in some cases.
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Chromium and silicon are the principal alloying elements that increase the oxidation resistance, i.e. they raise the maximum service temper-ature. Although these elements improve the corrosion resistance, they also increase the propensity for precipitation of embrittling phases, such as sigma phase. Nickel improves the creep strength and the resistance to oxide spallation caused by rapid temperature fluctuations and increases the corrosion resistance in certain environments.
Carbon and nitrogen raise the creep strength at intermediate temper-atures by forming chromium carbides and nitrides. At higher temper-atures, solution hardening is the most important mechanism to main-tain strength.
Steel designation Typical composition, %Max. service temp. (°C) in dry airOutokumpu EN
Ferr
itics
4713 1.4713 – 0.06 – 6.5 – 0.8 0.8Al 800
4724 1.4724 – 0.07 – 12.5 – 1.0 0.9Al 850
4736 1.4736 – 0.02 – 17.5 – 1.0 1.8Al 1000
4742 1.4742 – 0.07 – 17.5 – 1.0 1.0Al 1000
4762 1.4762 – 0.08 – 23.5 – 1.0 1.5Al 1150
Aust
eniti
cs
4948 1.4948 304H 0.05 – 18.1 8.3 – – 800
4878 1.4878 321H 0.05 – 17.3 9.1 – Ti 800
,Ti
153 MATM 1.4818 S30415 0.05 0.15 18.5 9.5 1.3 Ce 1000
4833 1.4833 309S 0.06 – 22.3 12.6 – – 1000
4828 1.4828 – 0.04 – 20 12 2.0 – 1000
253 MA® 1.4835 S30815 0.09 0.17 21 11 1.6 Ce 1100
4845 1.4845 310S 0.05 – 25 20 – – 1100
4841 1.4841 314 0.07 – 24.5 19.5 2.0 – 1125
ASTM C N Cr Ni Si Others
Chemical composition of Outokumpu high temperature steels
Table 1.
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For most high temperature alloys, the composition is optimized with regard to strength and/or resistance to corrosion at elevated temper-atures. Diffusion-controlled transformations will occur in the material at sufficiently elevated operating temperatures, typically in the range 650°C to 850°C. The most common type of reaction is the precipita-tion of secondary phases, which, besides lowering the corrosion resist-ance by consuming beneficial alloying elements (above all chromium), leads to a reduced toughness and ductility of the material – espe-cially at room temperature. Such embrittlement of the material is illus-trated in Figure 5. In Outokumpu 153 MA™ and 253 MA® grades, the formation of sigma phase is counteracted by the relatively high content
of nitrogen in the steels (and carbon in 253 MA®). Some precipita-tion of carbides and nitrides can occur in the same temperature range andalsodecreasetheimpacttoughnessatroomtemperature.Graingrowth, occurring at high temperatures, will also reduce the ductility/toughness.
The best steels with regard to embrittlement are Outokumpu grades 4878, 4948 and 153 MA™.
Microstructure stability
Figure 5. Outokumpu 153 MA™ shows no embrittlement compared to 309S, which deteriorates early as a result of secondary phase precipitation at 800°C. Bending performance at room temperature.
180
200
Angle (˚)
Time at temperature (h)
160
140
120
100
800 1000 2000 3000 4000 5000 6000
153 MA™
309S
Courtesy of Kvaerner Pulping AB, Sweden
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FabricationCold formingLikeotherausteniticsteels,heatresistantsteelscanbecoldformed.However, as a result of their relatively high nitrogen content, the mech-anical strength of MA grades is higher and consequently greater forces during forming will be required and the springback will be slightly larger. Additions of REM, Si and Ti improve the high temperature performance, but they also reduce formability. Still, the formability is much better thanforferriticgrades.Generally,theminimuminnerbendingradiuscan be taken as “the thickness”.
Hot formingHot forming should be carried out within the temperature ranges given in Table 2.
MachiningThe relatively high hardness of MA grades and their ability to strain harden must be taken into consideration when machining. For more detailed data on machining, please contact Outokumpu’s Avesta Research Centre. Separate guidelines are available for MA grades and 310S.
WeldingOutokumpu high temperature steels have good or very good weldabilityand can be welded using the following methods:•Shieldedmetalarc(SMA)weldingwithcoveredelectrodes.When welding 253 MA® steel, Avesta welding ‘253 MA-NF’ electrodes are suggested for applications at 650°C to 950°C. The absence of ferrite provides a stable, ductile microstructure in the weld metal A ‘253 MA’ electrode can be used for applications involving tempera- ures over 950°C•Gasshieldedwelding,e.g.,GTA(TIG),plasmaarcandGMA(MIG). PureargonisnormallyusedastheshieldinggasforTIG,while Ar+0.03% NO or Ar+30% He+2-2.5% CO2isrecommendedforMIG welding.TIG/MIGweldjointshavebeenfoundtogivethebestcreep resistance compared to other weld processes
•Submergedarc(SA)welding.Theriskofhotcrackingislesswhen welding 253 MA® compared to 310S. Basic fluxes are preferred
Some general recommendations for the welding of high temperature steels:1. The oxide layer on a component already exposed to high temper- ature must be removed through brushing or grinding before welding2. The penetration into base material is less for high temperature steels compared to standard grades such as 304/316. Fluidity of the molten filler materials is also less. This necessitates somewhat greater bevel angles (60 -70°) and slightly increased root gap (2-3 mm) compared to standard austenitic grades
More detailed information concerning welding procedures can be obtainedfromtheOutokumpuWeldingHandbook,availablefromoursales offices. Specialist support is available on request.
Heat treatmentHeat treatment after hot or cold forming or welding will often not be necessary because the material will be exposed to high temperatures during service. However, if that is not sufficient, the best option would be a proper solution annealing, with the second best choice being a stress relief annealing. Suitable temperature ranges for both treat-ments are given in Table 2. Components in which the material has become embrittled during service will benefit from solution annealing before any maintenance work, e.g. straightening or repair welding, is carried out.
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Oxidation resistance
Rela
tive
cree
p st
reng
th
304H321H
309S4828 310S
314
153 MATM
253 MA®
Table 2.Heat treatment temperatures of high-temperature grades.
4984 1150-850 1050-1110 840-900
4878 1150-850 1020-1120 840-900
153 MA™ 1150-900 1020-1120 900
4828 1150-950 1050-1150 1010-1040
4833 1150-950 1050-1150 1010-1040
253 MA® 1150-900 1020-1120 900
4845 1150-980 1050-1150 1040-1070
4841 1150-980 1050-1150 1040-1070
Outokumpu grade Hot forming °C Annealing °C Stress relief annealing (min 0.5 h) °C
Comparison of creep strength and oxidation resistance of common austenitic heat resistant grades show that the MA grades has an excellent combination of both properties.
Figure 6.Comparison of creep strength and oxidation resistance for common austenitic heat resistant grades.
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The Outokumpu MA Family – the cost-effective solution for your high temperature application
Outokumpu MA product range•Hotrolledquartoplate•Hotandcoldrolledcoil, sheet and plate (up to 2 m wide)•Precisionstrip•Weldedpipe•Billet,rodcoilandbar•Slabs,blooms
A full dimension program can be found on outokumpu.com
Figure 7.Relative creep strengths and costs for different high temperature grades.
153 MATM
253 MA® 1.4959(800HT)
2.4851(601HT)
321H304H
309S4828
310S314
Low
er c
reep
str
engt
hH
ighe
r cr
eep
stre
ngth
Lower relative cost Higher relative cost
1529EN
-GB
:1. D
ecember 2013
Working towards forever.
Information given in this brochure may be subject to alterations without notice. Care has been taken to ensure that the contents of this publication are accurate but Outokumpu and its affiliated companies do not accept responsibility for errors or for information which is found to be misleading. Suggestions for or descriptions of the end use or application of products or methods of working are for information only and Outokumpu and its affiliated companies accept no liability in respect thereof. Before using products supplied or manufactured by the company the customer should satisfy himself of their suitability.
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