WO2022096656A1 - Austenitic stainless steel - Google Patents

Austenitic stainless steel Download PDF

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Publication number
WO2022096656A1
WO2022096656A1 PCT/EP2021/080791 EP2021080791W WO2022096656A1 WO 2022096656 A1 WO2022096656 A1 WO 2022096656A1 EP 2021080791 W EP2021080791 W EP 2021080791W WO 2022096656 A1 WO2022096656 A1 WO 2022096656A1
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Prior art keywords
stainless steel
austenitic stainless
steel according
trace amounts
content
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PCT/EP2021/080791
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English (en)
French (fr)
Inventor
Rui WU
Marie Louise Falkland
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Outokumpu Oyj
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Priority to CN202180080895.2A priority Critical patent/CN116601324A/zh
Priority to AU2021374827A priority patent/AU2021374827A1/en
Priority to MX2023005403A priority patent/MX2023005403A/es
Priority to KR1020237018520A priority patent/KR20230100735A/ko
Priority to US18/035,878 priority patent/US20230416889A1/en
Priority to JP2023527394A priority patent/JP2023553258A/ja
Publication of WO2022096656A1 publication Critical patent/WO2022096656A1/en

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    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
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    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/001—Austenite

Definitions

  • the present invention relates to an austenitic heat and creep resistant stainless steel. It also relates to the use of this austenitic stainless steel, especially in oxidizing and carburizing environments. Further, the present invention relates to products made of this austenitic heat and creep resistant stainless steel.
  • S31008 is the most commonly used high temperature stainless steel for applications in the temperature range of 800 - 1050°C. It is however outperformed by S30815 both in regards to creep resistance and oxidation resistance in cyclic temperatures. It is however so that S31008 performs better in reducing or carburizing environments.
  • the present invention relates to an austenitic heat resistant stainless steel, intended to replace the existing heat resistant stainless grades S30815 and S31008 for special high temperature applications like muffle and heat treatment furnaces where both oxidizing and reducing environments exist.
  • an austenitic heat resistance stainles steel is provided having even better high temperature corrosion resistance and creep properties, being cost effective and easy to produce.
  • the austenitic stainless steel according to embodiments provides high temperature corrosion resistance and creep properties and is particularly suitable for high temperature applications in aggressive environments such as heat treatment equipment e.g. muffle furnaces.
  • the austenitic stainless steel according to embodiments can be economically manufactured in a practical and environmentally sound manner.
  • an austenitic stainless steel has a composition utilizing the benefits of several alloying elements in order to combine good oxidation resistance through the formation of a tight and adhesive oxide layer and to, at the same time, be alloyed in a way to resist carburizing. Furthermore, it is designed in a way to have excellent creep resistance.
  • a well-defined and balanced alloying with carbon and nitrogen increases the creep strength through the formation of intra- and to some extent intergranular carbides and nitrides; so-called precipitation strengthening.
  • Chromium and silicon are added in order to have a high oxidation resistance.
  • the amount is carefully balanced in order to not have a negative influence on the structure stability, since both these elements promote the formation of intermetallic and brittle phases such as sigma phases.
  • Rare earth metals e.g. cerium has in earlier micro alloyed (MA) grades shown to have an excellent effect on the cyclic oxidation resistance.
  • MA micro alloyed
  • rare earth metals are added in an amount optimized to get the benefits of a more elastic and adhesive oxide layer. The amount, however, is limited since it has been shown that a surplus amount of rare earth metals is no longer beneficial for oxidation resistance and that it might cause clusters of oxide inclusions having a negative effect on mechanical properties and formability.
  • the nickel content is at a level known from other well-known commercially- available high temperature stainless steels but different from other high temperature grades micro alloyed with rare earth metals. Thus, the combination of the elements is utilized in a novel way.
  • the nickel in combination with silicon promotes resistance to carburization.
  • the melts 1-8 are produced using a Mullite crucible and heated up to melt in an Ar protection atmosphere using a high frequency coil. The melt process takes about 10 to 15 min. Each melt is weighed about 600 grams. The melts are forged by using the hydraulic press Interlaken. An in-house software program has been developed that presses the ingot in short bursts to the desired thickness over a predetermined number of steps. The melt is heated to about 1250°C between each step. The thickness of the final piece is 8 mm.
  • the test melts 9-15 are produced using a Leybold-Heraeus vacuum induction furnace having minimum pressure of 4 x 10-4 bar. The melts are tapped to metal mound in vacuum for producing 65 kg ingots. Heating up to 1250°C, the Frdhling rolling mill with furnaces on both sides is used to hot roll 38 mm thick slab to 10 and 6 mm thick plates, respectively. The rolling speed is 45 m/min. The rolling passes are 7 and 9 for 10 mm thick plate and for 6 mm thick plate, respectively. Annealing temperature and holding time have been chosen to bring about a fully recrystallized austenite, proper hardness and grain size. Annealing temperature and holding time cover from 1100°C to 1200°C and from 0 min to 30 min, respectively. Table 1: Chemical composition of austenitic stainless heats (wt%).
  • melts listed in Table 1 fulfill the basic idea behind this austenitic stainless steel to chemically combine main elements like chromium, nickel, silicon, nitrogen and REM of S31008 and S30815. Therefore, the chemical compositions obtained in above test melts result in a target and preferred chemical composition as described below in Table 2.
  • the microstructure investigation, oxidation and carburisation tests, as well as creep test are performed in the most cases using the melts 7, 8, 14 and 15.
  • the austenitic stainless heat resistant steel as defined hereinabove and herinafter is intended to be used for manufacturing of objects such as semis, plate, sheet, coil, strip, par, pipe, tube and/or wire.
  • the methods used for manufacturing these products include conventional manufacturing processes such as, but not limited to, melting, refining, casting, hot rolling, cold rolling, forging, extrusion and drawing.
  • FIG. 1 shows microstructure of the austenitic stainless steel (ASS).
  • Figure 2 Figure 3, Figure 4, Figure 5 and Figure 6 show grain growth behavior for the austenitic stainless steel (ASS) in comparison to commercial grades like S31008, S30815 and S31400 at given times at 1000°C, at 1050°C, at 1100°C, at 1150°C and at 1200°C, respectively.
  • ASS austenitic stainless steel
  • Figure 7 and Figure 8 exhibit cyclic oxidation test in dry air at 1150°C/90 h and at 1175C/50 h, respectively, for the austenitic stainless steel (ASS) in comparison to commercial grades like S31008, S30815 and S31400.
  • ASS austenitic stainless steel
  • Figure 9 Figure 9 display isothermal oxidation test in dry air at 1000°C/250 h, at 1100°C/250 h and at 1150C/250 h, respectively, for the austenitic stainless steel (ASS) in comparison to commercial grades like S31008, S30815 and S31400.
  • ASS austenitic stainless steel
  • FIG 12 shows carburization test result for the austenitic stainless steel (ASS), S31008, S30815 and S31400.and S31400. Mechanical testing
  • Figure 13, Figure 14, Figure 15 and Figure 16 show creep properties for the austenitic stainless steel (ASS) at 900°C comparing to those for S30815 and S31008.
  • Microstructure for the as-produced austenitic stainless steel has been melting, metallurgical treatment, casting and hot rolling followed by optimized annealing process.
  • the microstructure consists of austenite and few oxide inclusions. This is common for MA grade.
  • the grain size is approximately 70 pm (ASTM 5 - 5.5) and the hardness is 170 (HV5).
  • the grain growth study includes heat treatment, metallographic sample preparation and grain size measurement.
  • the size of the test samples is approximately 15x25x6 mm.
  • the heat treatment is conducted in a chamber furnace in open air. After heat treatment, the samples are cooled in water.
  • the grain size is measured on the etched samples according to the standard ASTM E112. The mean grain size is determined by three to five measurements. The positions for the grain size measurements are randomly selected to cover entire cross section.
  • the austenitic stainless steel shows superior microstructure stability in terms of grain growth to other commercial grades.
  • the austenitic stainless steel has more stable microstructure than S31008, S30815 and S31400. Finer grain size improves oxidation and corrosion resistance, as well as ductility.
  • Figure 3 illustrates
  • the austenitic stainless steel shows superior microstructure stability in terms of grain growth to other commercial grades.
  • the austenitic stainless steel shows superior microstructure stability in terms of grain growth to other commercial grades.
  • the austenitic stainless steel shows superior or similar microstructure stability in terms of grain growth to other commercial grades.
  • the austenitic stainless steel shows superior or similar microstructure stability in terms of grain growth to other commercial grades.
  • the test has been performed using Setaram TGA 96 thermogravimetry set-up.
  • a single cycle includes 1 ) heating up to target temperature, 2) holding two hours at target temperature, and 3) cooling down to room temperature and holding for 10 min.
  • the samples are prepared is in accordance with the standard ISO 21608:2012. Cuboid sample is used. The sample size is approximately 20x20x2.5 - 6 mm. Prior to the test, the total surface area and weight are carefully measured and recorded.
  • the chamber is first heated up to target temperature. Then, the sample is put into the chamber and the temperature is allowed to be harmonized and stabilized.
  • the mass change is the sum of mass gain due to oxide formation and mass loss due to evaporation of volatile species plus spallation.
  • the breakaway time accounts actually for the time when mass loss is larger than mass gain, or spallation. Generally speaking, the longer the breakaway time and the lower the maximum value of mass change, the better the cyclic oxidation resistance.
  • the weight (mass) change is monitored and measured continuously using a Setaram TG 96 microbalance during testing. In total, there are approximately 4900 measurements for each test.
  • Austenitic stainless steel has an adherent oxide layer with high oxide spallation resistance resulting in a cyclic oxidation resistance superior to S31008, S30815 and S31400.
  • Austenitic stainless steel has an adherent oxide layer with high oxide spallation resistance resulting in a cyclic oxidation resistance superior to S31008, S30815 and S31400.
  • Figure 9 illustrates
  • the sample preparation, test equipment and test methodology for isothermal oxidation test are the same as those for cyclic oxidation test, except that there is no temperature variation.
  • the test is constantly kept at target temperature for 250 hours.
  • Austenitic stainless steel has an adherent oxide layer with high oxide spallation resistance resulting in an isothermal oxidation resistance equivalent or superior to S31008, S30815 and S31400.
  • Austenitic stainless steel has an adherent oxide layer with high oxide spallation resistance resulting in an isothermal oxidation resistance superior to S31008, S30815 and S31400.
  • Austenitic stainless steel has an adherent oxide layer with high oxide spallation resistance resulting in an isothermal oxidation resistance superior to S31008, S30815 and S31400.
  • Cuboid sample is used.
  • the sample size is approximately 20x20x6 mm. Before the test the samples are ground to 1200.
  • Austenitic stainless steel shows hardly any intra- or intergranular carbides, while other commercial grades show both intra- and intergranular carbides and carbide penetration from surface (left hand side) deep inside the matrix.
  • the austenitic stainless steel shows superior carburization resistance to S31400, S31008 and S30815. Mechanical testing
  • the rupture time of the austenitic stainless steel is similar to that of S30815.
  • the austenitic stainless steel has utilized the advantages of elements of C, Cr, Ni, Si, N as well as rare earth elements.
  • the austenitic stainless steel has combined the above mentioned elements and optimized them to a preferred range.
  • the austenitic stainless steel has received appropriate hot rolling process and annealing treatment to provide fully recrystallized austenite, favorable grain size and hardness.
  • the austenitic stainless steel has more stable microstructure than S31008, S30815 and S31400. Finer grain size improves oxidation and corrosion resistance, as well as ductility.
  • the austenitic stainless steel shows superior cyclic oxidation resistance to S31400, S31008 and S30815.
  • the austenitic stainless steel shows superior isothermal oxidation resistance to S31400, S31008 and S30815.
  • the austenitic stainless steel shows superior carburization resistance to S31400, S31008 and S30815.
  • the austenitic stainless steel shows a creep resistance on par with S30815 and superior to S31400 and S31008. According to embodiments the austenitic stainless steel is provided with improved heat resistance and corrosion resistance. According to an embodiment the austenitic stainless steel has finer grain size which improves oxidation and corrosion resistance as well as ductiliy. In a preferred embodiment the austenitic stainless steel has superior cyclic oxidation reistance. In a particular embodiment the steel has superior isothermal oxidation reistance. In a suitable embodiment the steel has superior carburization resistance. In a particularly preferred embodiment the steel has a creep resistance comparable with commercial grades.
  • the steel contains in weight % carbon ⁇ 0.20, chromium 20.00 - 26.00, nickel 10.00 - 22.00, silicon 0.50 - 2.50, manganese ⁇ 2.00, nitrogen 0.10 - 0.40, sulphur ⁇ 0.015, phosphous ⁇ 0.040, rare earth metals 0.00 - 0.10, and the rest being iron (Fe) and inevitable impurities.
  • the austenitic stainless steel contains ⁇ 0.20 carbon in weight %. Keeping the carbon content ⁇ 0.20%, preferably at least 0.05% but not more than 0.10% provides an optimization between austenite, mechnical strength and intergranullar corrosion resistance.
  • Chromium is the most important alloying element for the stainless steels. Chromium gives stainless steels their fundmental oxidation and corrosion resistance. All stainless steels have a Cr-content of at least 10.5% and the oxidation and corrosion resistance increases with increasing chromium content. In addition, chromium carbide and nitride improve mechanical strength. On the other hand, chromium promotes a ferritic microstructure. High chromium also contributes to intermetallic sigma phase formation. In a preferred embodiment the chromium content is at least 24.0 but not more than 26.0% for the austenitic stainless steel.
  • Nickel is present in all of the austenitic stainless steels since nickel promotes an austenitic microstructure. When added to a mix of iron and chromium, nickel increases ductility, high temperature strength, and resistance to both carburization and nitriding because nickel decreases the solubility of both carbon and nitrogen in austenite. On the other hand, high nickel is bad for sulphidation resistance.
  • the chromium content is at least 19.0 but not more than 22.0 w-% for the austenitic stainless steel.
  • Silicon improves both carburization and oxidation resistance, as well as resistance to absorbing nitrogen at high temperature. On the other hand, silicon tends to make the alloy ferritic, and promotes to intermetallic sigma phase formation.
  • the amount of silicon in the austenitic stainless steel is further controlled so that the silicon content is at least 1 .20 but not more than 2.50 w-%.
  • Manganese is usually considered an austenitizing element and can also replace some of the nickel in the stainless steel. Manganese improves hot workability, weldability, and increases solubility for nitrogen to permit a substantial nitrogen addition. On the other hand, manganese is mildly detrimental to oxidation resistance, so it is limited to 2 w-% maximum in most heat resistant alloys. In a preferred embodiment the amount of manganese in the austenitic stainless steel is at least 0.50 but not more than 2.00 w-%.
  • Nitrogen is a very strong austenite former that also significantly increases the mechanical strength. Nitrogen tends to retard or prevent ferrite and sigma formation. On the other hand, high content nitrigen impairs toughness and causes embrittlement.
  • the amount of nitrogen in the austenitic stainless steel is at least 0.12 but not more than 0.20 w-%. Sulphur and phosphorus are normally regarded as impurities. Sulphur is commonly below 0.010 w-%, while phosphorus is usually not specified. In a preferred embodiment the sulphur and phosphorus content in the austenitic stainless steel is not more than 0.010 w-% and 0.040 w-%, respectively.
  • the rare earth elements are used singly or in combination to increase oxidation resistance by forming a thinner, tighter and more protective oxide scale in austenitic stainless alloys. Residual REM oxides in the metal may also contribute to creep-rupture strength. On the other hand, a surplus amount of rare earth metals might cause clusters of oxide inclusions having a negative effect on mechanical properties and formability.
  • the REM content in the austenitic stainless steel, maninly cerium and lanthanum is at least 0.03 w-% but not more than 0.08 w-%. In a particularly preferred embodiment the REM is cerium and is present in the range of 0.03% to 0.08 w-%
  • the N, C and rare earth metal (REM) contents in the austenitic stainless steel satisfy the relationship: 0.40% ⁇ N + 3xC + 3xREM ⁇ 0.60% (2)
  • the austenitic stainless steel comprises one or more of the inevitable impurities contains in weight %: trace amounts V ⁇ 0.20% trace amounts Co ⁇ 0.60% trace amounts Sn ⁇ 0.05% trace amounts As ⁇ 0.05% trace amounts W ⁇ 0.40% trace amounts B ⁇ 0.0050% trace amounts Nb ⁇ 0.060% trace amounts Cu ⁇ 0.50% trace amounts Zr ⁇ 0.1 %. Further embodiments relate to objects formed from the stainless steel according to embodiments of the present invetion. In one embodiment is provided an object comprising the stainless steel according to any of the embodiments described herein.
  • the stainless steel according to embodiments of the present invention has a diverse range of uses.
  • the object formed and/or used according to embodiments is selected from the group consisting of plate, sheet, strip, tube, pipe, bar and wire.
  • Further embodiments relates to uses of objects formed in heat treatment applications. Such object are apt for use in difficult environments.
  • the object may be used in aggressive high temperature environments, which have oxidazing and reducing carburizing atomspheres, like in muffle funace and in metal manufacturing process applications.

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PCT/EP2021/080791 2020-11-06 2021-11-05 Austenitic stainless steel WO2022096656A1 (en)

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CN202180080895.2A CN116601324A (zh) 2020-11-06 2021-11-05 奥氏体不锈钢
AU2021374827A AU2021374827A1 (en) 2020-11-06 2021-11-05 Austenitic stainless steel
MX2023005403A MX2023005403A (es) 2020-11-06 2021-11-05 Acero inoxidable austenitico.
KR1020237018520A KR20230100735A (ko) 2020-11-06 2021-11-05 오스테나이트계 스테인리스 강
US18/035,878 US20230416889A1 (en) 2020-11-06 2021-11-05 Austenitic Stainless Steel
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JPH09209035A (ja) * 1996-01-31 1997-08-12 Sumitomo Metal Ind Ltd 高温用オーステナイト系ステンレス鋼の製造方法
US5824264A (en) * 1994-10-25 1998-10-20 Sumitomo Metal Industries, Ltd. High-temperature stainless steel and method for its production
JP2003129192A (ja) * 2001-10-24 2003-05-08 Nisshin Steel Co Ltd 耐水蒸気酸化性，耐浸炭性及び耐σ脆化性に優れたオーステナイト系ステンレス鋼
JP2004083976A (ja) * 2002-08-26 2004-03-18 Sumitomo Metal Ind Ltd 耐高温酸化性オーステナイト系ステンレス鋼板
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US20180274055A1 (en) * 2015-10-06 2018-09-27 Nippon Steel & Sumitomo Metal Corporation Austenitic stainless steel sheet
US20200131595A1 (en) * 2016-03-23 2020-04-30 Nippon Steel & Sumikin Stainless Steel Corporation Austenitic stainless steel sheet for exhaust component having excellent heat resistance and workability, turbocharger component, and method for producing austenitic stainless steel sheet for exhaust component

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US5126107A (en) * 1988-11-18 1992-06-30 Avesta Aktiebolag Iron-, nickel-, chromium base alloy
US5824264A (en) * 1994-10-25 1998-10-20 Sumitomo Metal Industries, Ltd. High-temperature stainless steel and method for its production
JPH08239737A (ja) * 1995-02-28 1996-09-17 Nisshin Steel Co Ltd 熱間加工性および耐σ脆化性に優れた耐熱用オーステナイト系ステンレス鋼
JPH09209035A (ja) * 1996-01-31 1997-08-12 Sumitomo Metal Ind Ltd 高温用オーステナイト系ステンレス鋼の製造方法
JP2003129192A (ja) * 2001-10-24 2003-05-08 Nisshin Steel Co Ltd 耐水蒸気酸化性，耐浸炭性及び耐σ脆化性に優れたオーステナイト系ステンレス鋼
JP2004083976A (ja) * 2002-08-26 2004-03-18 Sumitomo Metal Ind Ltd 耐高温酸化性オーステナイト系ステンレス鋼板
US20080107559A1 (en) * 2005-04-11 2008-05-08 Yoshitaka Nishiyama Austenitic stainless steel
CN101691630A (zh) * 2009-09-17 2010-04-07 苏州贝思特金属制品有限公司 无缝钢管的制造方法
US20180274055A1 (en) * 2015-10-06 2018-09-27 Nippon Steel & Sumitomo Metal Corporation Austenitic stainless steel sheet
US20200131595A1 (en) * 2016-03-23 2020-04-30 Nippon Steel & Sumikin Stainless Steel Corporation Austenitic stainless steel sheet for exhaust component having excellent heat resistance and workability, turbocharger component, and method for producing austenitic stainless steel sheet for exhaust component

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KR20230100735A (ko) 2023-07-05
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