EP4575006A1 - Verfahren zur wärmetechnischen verarbeitung von kohlenstoffarmem bainitischem stahl mit restaustenit, verwendung des nach dem verfahren hergestellten stahls - Google Patents

Verfahren zur wärmetechnischen verarbeitung von kohlenstoffarmem bainitischem stahl mit restaustenit, verwendung des nach dem verfahren hergestellten stahls Download PDF

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Publication number
EP4575006A1
EP4575006A1 EP23020560.1A EP23020560A EP4575006A1 EP 4575006 A1 EP4575006 A1 EP 4575006A1 EP 23020560 A EP23020560 A EP 23020560A EP 4575006 A1 EP4575006 A1 EP 4575006A1
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EP
European Patent Office
Prior art keywords
mass
temperature
less
steel
forging
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP23020560.1A
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English (en)
French (fr)
Inventor
Aleksandra Kozlowska
Anna Wojtacha
Adam Skowronek
Wojciech Borek
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Politechnika Slaska im Wincentego Pstrowskiego
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Politechnika Slaska im Wincentego Pstrowskiego
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Publication date
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Priority to EP23020560.1A priority Critical patent/EP4575006A1/de
Publication of EP4575006A1 publication Critical patent/EP4575006A1/de
Pending legal-status Critical Current

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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/02—Hardening articles or materials formed by forging or rolling, with no further heating beyond that required for the formation
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C21D1/19—Hardening; Quenching with or without subsequent tempering by interrupted quenching
    • C21D1/20—Isothermal quenching, e.g. bainitic hardening
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D7/00—Modifying the physical properties of iron or steel by deformation
    • C21D7/13—Modifying the physical properties of iron or steel by deformation by hot working
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/0075—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for rods of limited length
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/001—Austenite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/002—Bainite

Definitions

  • the subject of the invention is a thermomechanical processing method of low-carbon bainitic steel containing retained austenite, in particular for forgings.
  • High-strength bainitic steel with retained austenite is intended especially for forgings showing increased plasticity and resistance to the development of contact-fatigue defects.
  • the method of obtaining high-strength bainitic steel containing retained austenite was shown for example in the American application US20210047705A1 , in which the range of element content is as follows: C less than 0.4%, Si more than 1%, Mn is in the range of 0.2-1%, Mo is in the range of 0.4-0.8%, Cr is in the range of 0.1-0.9%, expressed in mass %, while the rest of the composition are unavoidable impurities and Fe.
  • High-strength bainitic steel containing retained austenite with increased manganese content has been shown in the Japanese patent JP6765495B2 , in which the element content range is as follows: C from 0.1 to 0.4%, Si from 1 to 2%, Mn from 1 to 2.5 %, Cu from 0.25 to 1%, B from 0.0001 to 0.035%, Ni from 0.1 to 1%, expressed in mass %, while the rest of the composition are unavoidable impurities and Fe.
  • this steel still requires the addition of carbon up to 0.4% and it is also intended for flat products.
  • the subject of the invention is a method of thermomechanical treatment of bainitic steel with retained austenite carried out by austenitization, hot forging and cooling, characterized by the fact that the initial material with the mass content of individual elements: not more than 0.22% mass.
  • C not less than 3% mass.
  • Mn not less than 0.9% mass.
  • Si not more than 0,8 % mass.
  • Al not less than 0.1% mass.
  • Mo not less than 0.03% mass.
  • the B s temperature is above 460 °C for isothermal heat treatment
  • the incubation time of the bainitic transformation is below 10s for the isothermal holding range between 380 and 460°C
  • the bainitic transformation completion time is below 25 min for the isothermal holding range between 380 and 460 °C
  • the M s temperature is below 400°C.
  • the steel has the following structural composition: less than 3% of fresh blocks of martensite, more than 80% of carbide-free bainite, more than 10% of retained austenite in the form of laths with a thickness of not exceeding 0.6 ⁇ m with a weight content of C min. 1.1%.
  • Aluminum and silicon added to steel with a total content of at least 1.5% mass prevent the formation of cementite in steel allowing to enrich the austenite in carbon during the isothermal holding process.
  • the aluminum content must not exceed 0.8% to not reduce the hardness and strength of the steel.
  • the addition of aluminum also shortens the incubation time and accelerates the bainitic transformation, which is economically beneficial.
  • Manganese is used to stabilize the retained austenite and improve the hardenability of steel.
  • Molybdenum is used to increase solid solution strengthening and to improve the hardenability of steel. Increasing the hardenability of steel and, consequently, reducing its sensitivity to the cooling rate due to Mn and Mo is necessary to achieve a uniform bainitic transformation at the surface and in the core after cooling the forging to the isothermal holding temperature.
  • Ti and V a minimum of 0.1% mass allows to obtain fine austenite grains during the hot forging process and ensures the strengthening of the bainitic ferrite matrix with TiC and VC carbide nanoparticles. It has been experimentally established that the refinement of the austenite grain also increases the resistance to wear processes of bainitic steels. However, maintaining the proportions between the content of molybdenum, titanium and vanadium allows you to control the growth of TiC and VC particles in technological processes.
  • the content of alloy additions in the steel according to the invention is set to achieve a specific hardenability and critical temperatures: B s and M s , as well as the kinetics of the bainitic transformation, i.e. the incubation time and the completion time of the bainitic transformation.
  • Designing the steel meeting above requirements allows for carrying out the bainitic transformation at a relatively low temperature, which increases the strength properties of the steel and also allows for a shortened isothermal step, which shortens the technological process and reduces its costs.
  • Cooling the steel which is the subject of the invention, after the forging process to the temperature in a range of 390-410°C allows the formation of fine fine-lath bainite and stabilization of more than 10% of retained austenite in less than 15 min., which allows the reduction or elimination of the presence of blocks of fresh martensite in the microstructure.
  • the key structural constituent of steel is ductile retained austenite with optimal stability, determined by the carbon content of min. 1.1% weight, which prevents the initiation and development of microcracks during cyclic service conditions and/or may be transformed into martensite (TRIP effect), which causes a gradual strengthening of the forging surface.
  • the structure of multiphase steel according to the invention ensures increased durability of high-strength forgings.
  • the chemical composition of the steel according to the invention allows obtaining retained austenite in the structure with the following parameters:
  • An ingot with a chemical composition of 0.17C-3.1Mn-1.0Si-0.55Al-0.22Mo-0.034Ti-0.073V with a cross-section of 100x100mm and a mass of 100 kg was produced using a vacuum furnace in an argon atmosphere. Then, the ingot was initially forged into a rod with a diameter of 80 mm. The forging process was preceded by austenitizing of the ingot in a furnace at 1150°C for 60 min; the same austenitizing parameters were used during the next hot forging cycle. Hot forging was carried out in a press in two deformation steps at the following temperatures: 1100°C (I) and 980°C (II). The forging obtained in this way was cooled in air to the temperature of 400°C and heat treated for 10 minutes. Then, the forging was cooled in air to the room temperature.
  • Table 1 Melt C Mn Si Al. Mo Ti V P max S max S837 0.17 3.1 1.0 0.55 0.22 0.034 0.073 0.015 0.013
  • Fig. 1 shows DCCT and DTTT diagrams for steel according to the invention from the melt named as 5837.
  • the DCCT diagram indicates that cooling after plastic deformation to 390-410°C at a rate in the range of 50 - 2 °C/s allows avoiding phase transformations, which is important in the case of bainitic steels, and the M s temperature is 382 °C.
  • the DTTT diagram shows that for the isothermal holding temperature range between 380 and 460°C, the incubation time of the bainitic transformation is below 5 s and the transformation is completed within 25 min, which results in a hardness higher than 370 HV.
  • Fig. 1 shows DCCT and DTTT diagrams for steel according to the invention from the melt named as 5837.
  • the DCCT diagram indicates that cooling after plastic deformation to 390-410°C at a rate in the range of 50 - 2 °C/s allows avoiding phase transformations, which is important in the case of bainitic steels, and the M s temperature
  • FIG. 2 shows a scheme of thermomechanical processing of a steel forging according to the invention, consisting of hot forging with finishing deformation temperature of 980 °C, cooling at an average rate in the range of 50 - 2 °C/s to a temperature of 400 °C and held the steel at this temperature for 10 min and finally cooled in air to the room temperature.
  • Fig. 3 shows the microstructure of the steel according to the invention obtained using scanning electron microscope at magnification of 10,000 ⁇ .

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Manufacturing & Machinery (AREA)
  • Heat Treatment Of Steel (AREA)
EP23020560.1A 2023-12-19 2023-12-19 Verfahren zur wärmetechnischen verarbeitung von kohlenstoffarmem bainitischem stahl mit restaustenit, verwendung des nach dem verfahren hergestellten stahls Pending EP4575006A1 (de)

Priority Applications (1)

Application Number Priority Date Filing Date Title
EP23020560.1A EP4575006A1 (de) 2023-12-19 2023-12-19 Verfahren zur wärmetechnischen verarbeitung von kohlenstoffarmem bainitischem stahl mit restaustenit, verwendung des nach dem verfahren hergestellten stahls

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Application Number Priority Date Filing Date Title
EP23020560.1A EP4575006A1 (de) 2023-12-19 2023-12-19 Verfahren zur wärmetechnischen verarbeitung von kohlenstoffarmem bainitischem stahl mit restaustenit, verwendung des nach dem verfahren hergestellten stahls

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EP4575006A1 true EP4575006A1 (de) 2025-06-25

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Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2004292876A (ja) * 2003-03-26 2004-10-21 Kobe Steel Ltd 絞り特性に優れた高強度鍛造部品、及びその製造方法
US20160060723A1 (en) * 2013-04-15 2016-03-03 Jfe Steel Corporation High strength hot-rolled steel sheet and method of producing the same
JP6455461B2 (ja) * 2016-02-26 2019-01-23 Ｊｆｅスチール株式会社 曲げ性に優れた高強度鋼板およびその製造方法
JP6765495B2 (ja) 2016-07-06 2020-10-07 ▲馬▼▲鋼▼（集▲団▼）控股有限公司 高強度、高靭性、耐ヒートクラック性鉄道輸送用ベイナイト鋼車輪及びその製造方法
US20210010117A1 (en) * 2018-03-23 2021-01-14 Arcelormittal Forged part of bainitic steel and a method of manufacturing thereof
US20210047705A1 (en) 2018-03-08 2021-02-18 Northwestern University Carbide-free bainite and retained austenite steels, producing method and applications of same

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2004292876A (ja) * 2003-03-26 2004-10-21 Kobe Steel Ltd 絞り特性に優れた高強度鍛造部品、及びその製造方法
US20160060723A1 (en) * 2013-04-15 2016-03-03 Jfe Steel Corporation High strength hot-rolled steel sheet and method of producing the same
JP6455461B2 (ja) * 2016-02-26 2019-01-23 Ｊｆｅスチール株式会社 曲げ性に優れた高強度鋼板およびその製造方法
JP6765495B2 (ja) 2016-07-06 2020-10-07 ▲馬▼▲鋼▼（集▲団▼）控股有限公司 高強度、高靭性、耐ヒートクラック性鉄道輸送用ベイナイト鋼車輪及びその製造方法
US20210047705A1 (en) 2018-03-08 2021-02-18 Northwestern University Carbide-free bainite and retained austenite steels, producing method and applications of same
US20210010117A1 (en) * 2018-03-23 2021-01-14 Arcelormittal Forged part of bainitic steel and a method of manufacturing thereof

Non-Patent Citations (5)

* Cited by examiner, † Cited by third party
Title
KOHICHI SUGIMOTO ET AL: "Hot Forging of Ultra High-Strength TRIP-Aided Steel", MATERIALS SCIENCE FORUM, vol. 638-642, 1 January 2010 (2010-01-01), pages 3074 - 3079, XP055176039, DOI: 10.4028/www.scientific.net/MSF.638-642.3074 *
MORAWIEC MATEUSZ ET AL: "Kinetics of Austenite Phase Transformations in Newly-Developed 0.17C-2Mn-1Si-0.2Mo Forging Steel with Ti and V Microadditions", vol. 14, no. 7, 30 March 2021 (2021-03-30), pages 1698 - 1, XP009554275, ISSN: 1996-1944, Retrieved from the Internet <URL:https://www.ncbi.nlm.nih.gov/pubmed/33808308> DOI: 10.3390/MA14071698 *
OPIELA M.GRAJCAR A.PAKIETA W.: "Effect of hot deformation and isothermal holding temperature on retained austenite characteristics in 3 -5% Mn multiphase steels", BULLETIN OF THE POLISH ACADEMY OF SCIENCES, vol. 71, no. 2, 2023
WIRTHS VERA ET AL: "Bainitic Forging Steels for Cyclic Loading", vol. 922, 7 May 2014 (2014-05-07), pages 813 - 818, XP009554262, ISBN: 978-3-03835-074-3, Retrieved from the Internet <URL:https://www.scientific.net/AMR.922.813> [retrieved on 20140507], DOI: 10.4028/WWW.SCIENTIFIC.NET/AMR.922.813 *
ZMIK J ET AL: "Modification of structure and properties of TRIP steel by forging thermomechanical process", 26 May 2008 (2008-05-26), pages 235 - 241, XP009554273, ISBN: 978-0-87339-729-2, Retrieved from the Internet <URL:https://search.proquest.com/docview/35480141> *

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