WO2014081779A1 - Procédé de fabrication d'une bande d'acier ferritique laminée à chaud - Google Patents

Procédé de fabrication d'une bande d'acier ferritique laminée à chaud Download PDF

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Publication number
WO2014081779A1
WO2014081779A1 PCT/US2013/070927 US2013070927W WO2014081779A1 WO 2014081779 A1 WO2014081779 A1 WO 2014081779A1 US 2013070927 W US2013070927 W US 2013070927W WO 2014081779 A1 WO2014081779 A1 WO 2014081779A1
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WO
WIPO (PCT)
Prior art keywords
hot rolled
max
strip
temperatures
steel
Prior art date
Application number
PCT/US2013/070927
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English (en)
Inventor
Chris John Paul SAMUEL
Bertram Wilhelm EHRHARDT
Markus Wilhelm FORSCH
Roger Dale BOGGS
Stanley Wayne BEVANS
Original Assignee
Thyssenkrupp Steel Usa, Llc
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Thyssenkrupp Steel Usa, Llc filed Critical Thyssenkrupp Steel Usa, Llc
Publication of WO2014081779A1 publication Critical patent/WO2014081779A1/fr

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Classifications

    • 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
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • 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

Definitions

  • the present invention relates in general to a process for manufacturing ferritic hot rolled steel strip, and in particular to a process for producing ferritic hot rolled carbon steel that can be used for components via deep draw stamping.
  • ultra low carbon (ULC ⁇ 0.005 wt C) and extra low carbon (ELC: ⁇ 0.02 wt C) steels including interstitial free steels with a reduced manganese content ( ⁇ 0.3 wt Mn)
  • ferritic rolling of ULC and ELC steels can produce desirable soft and formable steel grades, however it can also produce a high risk of uncontrolled rolling behavior and cobbling in a finishing train.
  • Heretofore methods have attempted to solve this problem by replacing one of the rolling stands with an additional water cooling step during finish rolling, which requires investment and alteration of a hot strip mill finishing train.
  • a process for manufacturing a ferritic hot rolled steel strip includes providing a steel slab with a chemical composition in weight percent (wt ) within a range of 0.10 maximum (max) carbon (C), 0.15-0.60 manganese (Mn), 0.20 max silicon (Si), 0.04 max titanium (Ti), 0.008 max vanadium (V), 0.006 max molybdenum (Mo), 0.1 max nickel (Ni), 0.05 max chromium (Cr), 0.08 max copper (Cu), 0.015 max sulfur (S), 0.04 max phosphorus (P), 0.01 max nitrogen (N), 0.006 max boron (B), 0.06 max aluminum (Al), balance iron (Fe) and incidental melting impurities known to those skilled in the art.
  • a steel slab having a chemical composition within the above-stated range is soaked at temperatures between 1100-1400°C and then hot rolled using a roughing treatment at temperatures between 900-1400°C in order to produce a transfer bar.
  • the transfer bar is hot rolled using a finishing treatment with finishing treatment entry temperatures between 900-1100°C and finishing treatment exit temperatures between 720-850°C.
  • the finishing treatment produces hot rolled strip which is coiled at a coiling station at temperatures between 580-780°C.
  • the hot rolled steel strip has a yield strength between 130-210 megapascals (MPa), a tensile strength greater than 260 MPa, a uniform elongation greater than 15%, a total elongation to failure greater than 30%, and a strain hardening exponent (n-value) greater than 0.2.
  • the steel slab is hot rolled in the roughing treatment at temperatures between 1200-1300°C. In other instances, the steel slab is hot rolled in the roughing treatment at temperatures between 1220-1280°C. In still other instances, the steel slab is hot rolled in the roughing treatment at temperatures between 1230-1270°C.
  • the finishing treatment has an entry temperature between 1000-1080°C and an exit temperature between 750-825°C. In some instances, the finishing treatment has an entry temperature between 1035-1065°C and an exit temperature between 760-800°C.
  • the hot rolled strip produced from the finishing treatment can be coiled at temperatures between 640-750°C, and in some instances coiled at temperatures between 660-700°C.
  • the hot rolled strip has a thickness between 1.5-6.5 millimeters (mm).
  • the hot rolled strip is subjected to only air cooling while traveling across a run-out table between the finishing treatment and the coiling station. Stated differently, the hot rolled strip is not subjected to water or liquid cooling between the finishing treatment and the coiling station. In some instances, the hot rolled strip is only static air cooled on the run-out table between the finishing treatment and the coiling station, i.e. the hot rolled strip is not subjected to forced air cooling between the finishing treatment and the coiling station.
  • the coiled hot rolled strip can have a uniform elongation of at least 17.5% and a total elongation of at least 35%. In some instances, the coiled hot rolled strip has a uniform elongation of at least 20% and a total elongation of at least 38%.
  • the steel slab can have a carbon content of at least 0.025 wt% C.
  • the steel slab can have between 0.050-0.080 wt% C.
  • the chemical composition of the steel slab can also meet a number of different chemical composition criteria, for example the Mn to S ratio (Mn/S) of the steel slab can be at least 15; the Ti and N content can obey the relationship -0.001 ⁇ (Ti - 3.42N) ⁇ 0.002; the B and N content can obey the relationship -0.001 ⁇ (B - 0.78N) ⁇ 0.002; and the Mn/S ratio can obey the relationship Mn/S > 15.
  • the coiled hot rolled steel strip can be subsequently cold rolled to produce cold rolled sheet, followed by hot dip galvanizing or continuous annealing of the cold rolled sheet without an over-aging step.
  • inventive material and/or process can provide a bake hardenable steel with a yield strength between 180-210 MPa.
  • Figure 1 is a temperature versus time graphical representation illustrating a process according to an embodiment of the present invention
  • Figure 2 is a graphical plot of 0.2% yield strength versus coil thickness for ferritic hot rolled carbon steel produced according to an embodiment of the present invention compared to the 0.2% yield strength of conventional austenitic hot rolled carbon steel;
  • Figure 3 is a graphical plot of tensile strength versus coil thickness for ferritic hot rolled carbon steel produced according to an embodiment of the present invention compared to the tensile strength of conventional austenitic hot rolled carbon steel;
  • Figure 4 is a graphical plot of percent elongation to fracture versus coil thickness for ferritic hot rolled carbon steel produced according to an embodiment of the present invention compared to the percent elongation to fracture of conventional austenitic hot rolled carbon steel;
  • Figure 5 is a graphical plot of strain hardening exponent (n-value) versus coil thickness for ferritic hot rolled carbon steel produced according to an embodiment of the present invention compared to n-values of conventional austenitic hot rolled carbon steel.
  • the present invention provides a process for producing ferritic hot rolled carbon steel that can be used for fabrication of components via deep draw stamping (DDS), cold rolling, and the like. As such, the present invention has use as a process for producing carbon steel sheet.
  • DDS deep draw stamping
  • the inventive process uses or can use steels with a minimum carbon content in order to avoid cobbling of the material in the hot strip mill.
  • the minimum carbon content avoiding cobbling is 0.025 wt in combination with suitable temperatures and set points in the finishing train.
  • carbon contents between 0.050 to 0.080 % can be processed to produce soft bake hardenable (BH) steels with a minimum 0.2% yield strength between 180 to 210 MPa and sufficient shelf time capability after a hot dip galvanizing process or a continuous annealing process without an over-aging section.
  • BH steels are known to those skilled in the art to be steels that exhibit or can exhibit a significant increase in strength, e.g.
  • a 30 MPa increase through a combination of work hardening, e.g. cold forming of steel sheet during production of a fender panel, followed by strain aging via a thermal treatment, e.g. paint baking of the fender panel after it has been painted.
  • work hardening e.g. cold forming of steel sheet during production of a fender panel
  • strain aging via a thermal treatment, e.g. paint baking of the fender panel after it has been painted.
  • the process includes hot rolling a steel slab having a chemical composition (in weight percent) within the range of 0.10 max C, 0.15-0.60 Mn, 0.20 max Si, 0.04 max Ti, 0.008 max V, 0.006 max Mo, 0.1 max Ni, 0.05 max Cr, 0.08 max Cu, 0.015 max S, 0.04 max P, 0.01 max N, 0.006 max B, 0.06 max Al, with a balance Fe and possible melting impurities.
  • the steel slab has a composition of 0.10 C, 0.15-0.60 Mn, 0.06 max Si, 0.009 max Ti, 0.008 max V, 0.006 Mo, 0.1 max Ni, 0.05 max Cr, 0.08 max Cu, 0.015 max S, 0.04 max P, 0.005 max N, 0.0015 max B, 0.03-0.017 Al with the balance Fe.
  • the ratio of manganese to sulfur (Mn/S) is greater than 15, i.e., Mn/S > 15.
  • the steel slab has a chemical composition of 0.10 max C, 0.15-0.60 Mn, 0.04-0.20 Si, 0.01-0.04 Ti, 0.008 max V, 0.006 max Mo, 0.1 max Ni, 0.05 max Cr, 0.08 max Cu, 0.015 max S, 0.04 max P, 0.005 max N, 0.0015-0.0045 B, 0.08-0.5 Al with the balance Fe.
  • the amount of Ti minus 3.42 times the amount of N is equal to a value between -0.001 to 0.002, i.e., -0.001 ⁇ (Ti - 3.42N) ⁇ 0.002.
  • the amount of B minus 0.78 times N is between -0.001 to 0.002, i.e. -0.001 ⁇ (B - 0.78N) ⁇ 0.002.
  • the steel slab can also have a Mn and S content such that Mn/S > 15.
  • the slab thickness can be between 50 and 280 mm and is subjected to a soaking temperature in order to ensure that most if not all of the alloying elements are in solid solution.
  • the steel slab is subjected to a roughing treatment in which the material is hot rolled at a temperature or temperature range between 1100-1400°C.
  • the roughing treatment produces a transfer bar which is subjected to a hot rolling finishing treatment.
  • the entry temperature of the finishing treatment is between 900-1100°C and the exit temperature of the finishing treatment is between 720-850°C.
  • the finishing treatment produces hot rolled strip which is coiled at a temperature between 580-780°C.
  • the hot rolled strip has a thickness between 1.5 and 6.5 mm, a 0.2% yield strength of 130-210 megapascals (MPa), a tensile strength of greater than 260 MPa, and a total elongation of greater than 30%.
  • the uniform elongation is greater than 15% and the strain hardening exponent 'n' is greater than 0.2.
  • the microstructure of the material is ferritic and the steel exhibits excellent weldability.
  • n the greater the value of n for a material, the greater the degree of work hardening the material exhibits upon cold forming and thus the greater the yield strength and tensile strength of the material after being cold formed into a component.
  • Hot rolled strip produced by the inventive process is produced without an aging treatment, and is soft and ductile to the extent that it can be used for DDS. It is appreciated that the hot strip is soft and ductile due to a coarse and homogeneous ferrite grain size.
  • the ferritic hot strip also has low aging sensitivity due to a low solute nitrogen content and/or generally fast aluminum nitride precipitation in the ferrite phase during rolling and coiling.
  • the hot strip is suitable for cold rolling and annealing with a corresponding high performance at the cold rolling mill in terms of productivity, less roll wear and less energy consumption compared to austenitic hot rolled strip.
  • lower reheating temperatures are required during processing of the ferritic hot strip and thus less oxidation and energy consumption occurs in the reheating furnace.
  • the less roll wear is due to reduced rolling temperatures and less intermediate roll changes.
  • no cooling water is needed on the run-out table after the finishing treatment.
  • the process can include rough rolling of the steel in the austenite phase region for the material, finish rolling in the ferrite phase region and stress free recrystallization on the run-out table and during coiling.
  • Such processing provides for a softer and more ductile material that can be used for DDS operations and/or cold rolling and annealing.
  • the chemical composition of the steels is not restrained to the ELC or ULC steels taught by the prior art.
  • a steel slab having a chemical composition of 0.025-0.045 C, 0.32-0.4 Mn, 0.03 max Si, 0.008 max Ti, 0.008 max V, 0.05 Mo, 0.1 Ni, 0.05 Cr, 0.05 Cu, 0.01 S, 0.015 P, 0.005 N, 0.003-0.0045 B, 0.02-0.04 Al with the remainder Fe was soaked at an elevated temperature and subjected to a roughing treatment at temperatures between 1230-1270°C. Thereafter, the transfer bar produced from the roughing treatment was subjected to a finishing treatment that had an entry temperature between 1035-1065°C and an exit temperature between 760-800°C.
  • the finishing treatment produced hot rolled strip with a thickness between 3.0-3.2 mm that was coiled at temperatures ranging from 660-700°C.
  • the material was also subjected to flattening elongation, also known as tension leveling, of between 0.3 and 0.7% at a pickle line. There was no cooling of the material after the finishing treatment and thus no cooling water was provided on the run-out table.
  • flattening elongation refers to stretching the hot rolled strip beyond its yield point and thereby providing a small amount of elongation and flattening of the product.
  • Samples of ferritic hot strip produced by the inventive process had a 0.2% yield strength between 130-210 megapascals, a tensile strength greater than 260 megapascals, and a total elongation of greater than 38%. Uniform elongation was greater than 20% and the strain hardening exponent was greater than 0.20. The microstructure was fully ferritic and the material exhibited excellent weldability.
  • FIG. 1 a graphical representation of the process is shown via a temperature versus time plot. As shown in the figure, the material is soaked, e.g. at 1250°C, followed by a roughing treatment, then a finishing treatment and then coiling of the material.
  • Figures 2, 3 and 4 illustrate yield strength, tensile strength, and total elongation, respectively, for samples of the ferritic hot strip having the above chemical composition range compared to conventional hot strip formed by prior art austenitic hot rolling. As shown by the figures, the ferritic hot strip is generally softer and more ductile than the conventional hot rolled material.
  • Figure 5 provides a comparison of the work hardening exponent 'n' for the two materials, and again, the ferritic hot rolled material disclosed herein exhibits superior work hardening compared to conventional austenitic hot rolled strip.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Sheet Steel (AREA)

Abstract

La présente invention concerne un procédé de fabrication d'une bande d'acier ferritique laminée à chaud. Le procédé comprend la fourniture d'une brame d'acier, le laminage à chaud de la brame pour produire une barre de transfert et le laminage à chaud ferritique de la barre de transfert pour produire des bandes laminées à chaud. La bande laminée à chaud ferritique est enroulée à des températures comprises entre 580 et 780 °C et a une limite d'élasticité comprise entre 130 et 210 MPa, une résistance à la traction supérieure à 260 MPa, un allongement uniforme supérieur à 15 %, un allongement total à la rupture supérieur à 30 %, et une valeur n supérieure à 0,2.
PCT/US2013/070927 2012-11-20 2013-11-20 Procédé de fabrication d'une bande d'acier ferritique laminée à chaud WO2014081779A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US201261728554P 2012-11-20 2012-11-20
US61/728,554 2012-11-20

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WO2014081779A1 true WO2014081779A1 (fr) 2014-05-30

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US (1) US20140137990A1 (fr)
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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN109332379A (zh) * 2018-12-06 2019-02-15 唐山市德龙钢铁有限公司 一种冲压件用热轧窄带钢及其制备方法和应用

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CN109439873B (zh) * 2018-11-28 2020-07-17 北京首钢冷轧薄板有限公司 一种1000MPa级马氏体汽车用钢的工艺控制方法
CN114645132B (zh) * 2020-07-14 2023-11-17 柳州钢铁股份有限公司 性能接近罩退产品的连退spcc钢带
CN112063927A (zh) * 2020-09-17 2020-12-11 南京奇纳金属材料科技有限公司 高成形性超低碳烘烤硬化钢板及其制备方法
CN112695178A (zh) * 2020-12-17 2021-04-23 包头钢铁（集团）有限责任公司 一种提高冷轧低碳钢冲压性能的方法
CN113215373B (zh) * 2021-04-14 2022-11-18 首钢集团有限公司 一种消除含硼钢边部细线缺陷的方法
CN115478231B (zh) * 2021-05-31 2023-10-17 宝山钢铁股份有限公司 极限拉深比≥2.2的压缩机壳体用热轧酸洗板及其制造方法

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JPH02259023A (ja) * 1989-03-31 1990-10-19 Nippon Steel Corp 超深絞り用薄鋼板の製造方法
WO2003018858A1 (fr) * 2001-08-29 2003-03-06 Sidmar N.V. Composition d'acier d'ultra-haute resistance, procede de fabrication d'un produit en acier d'ultra-haute resistance et produit ainsi obtenu
WO2004079022A1 (fr) * 2003-02-05 2004-09-16 Usinor Procede de fabrication d'une bande d'acier dual-phase a structure ferrito-martensitique, laminee a froid et bande obtenue
RU2432404C1 (ru) * 2010-04-05 2011-10-27 Открытое акционерное общество "Магнитогорский металлургический комбинат" Способ производства холоднокатаных полос низколегированной стали класса прочности 260

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CN1169991C (zh) * 2001-10-19 2004-10-06 住友金属工业株式会社 具有优异的可加工性和成型精度的薄钢板及其制造方法
US8157933B2 (en) * 2007-03-27 2012-04-17 Nippon Steel Corporation High-strength hot rolled steel sheet being free from peeling and excellent in surface properties and burring properties, and method for manufacturing the same
JP5326403B2 (ja) * 2007-07-31 2013-10-30 Ｊｆｅスチール株式会社 高強度鋼板

Patent Citations (4)

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Publication number Priority date Publication date Assignee Title
JPH02259023A (ja) * 1989-03-31 1990-10-19 Nippon Steel Corp 超深絞り用薄鋼板の製造方法
WO2003018858A1 (fr) * 2001-08-29 2003-03-06 Sidmar N.V. Composition d'acier d'ultra-haute resistance, procede de fabrication d'un produit en acier d'ultra-haute resistance et produit ainsi obtenu
WO2004079022A1 (fr) * 2003-02-05 2004-09-16 Usinor Procede de fabrication d'une bande d'acier dual-phase a structure ferrito-martensitique, laminee a froid et bande obtenue
RU2432404C1 (ru) * 2010-04-05 2011-10-27 Открытое акционерное общество "Магнитогорский металлургический комбинат" Способ производства холоднокатаных полос низколегированной стали класса прочности 260

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN109332379A (zh) * 2018-12-06 2019-02-15 唐山市德龙钢铁有限公司 一种冲压件用热轧窄带钢及其制备方法和应用

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