US20110146850A1 - Method for Producing A Steel Strip Having A Dual-Phase Microstructure - Google Patents
Method for Producing A Steel Strip Having A Dual-Phase Microstructure Download PDFInfo
- Publication number
- US20110146850A1 US20110146850A1 US13/058,085 US200913058085A US2011146850A1 US 20110146850 A1 US20110146850 A1 US 20110146850A1 US 200913058085 A US200913058085 A US 200913058085A US 2011146850 A1 US2011146850 A1 US 2011146850A1
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- United States
- Prior art keywords
- microstructure
- strip
- temperature
- heat treatment
- elements
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- 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.)
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Classifications
-
- 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
- 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
Definitions
- the invention is directed to a method for producing semi-finished product, particularly steel strip, having a dual-phase microstructure (DP steel strip) and a tensile strength between 500 and 1000 MPa.
- DP steel strip dual-phase microstructure
- High-strength steel sheet with good formability, stability of microstructures, and mechanical characteristics up to approximately 600° C. is required in many fields.
- the sheets should also be suitable for hot-dip galvanization.
- steels with a dual-phase microstructure that has already been adjusted have the disadvantage that an unwanted, pronounced yield strength generally results when heated above 200° C. as occurs during or in connection with hot-dip galvanization.
- a method for producing semi-finished product, particularly steel strip, having a dual-phase microstructure and a tensile strength between 500 and 1000 MPa is disclosed.
- Elements such as carbon and nitrogen which are interstitially dissolved in the ferritic matrix are bound by alloying elements such as Al, Mo, Nb, Ti and V which form carbide, nitride or carbonitride in order to adjust a microstructure of hard components such as martensite, bainite, carbide with low fractions of residual austenite in a ferritic matrix which is substantially free from interstitially dissolved elements (IF character).
- the alloy content of the alloying elements is adapted stoichiometrically to the ferrite content and to the solubility of carbon and nitrogen at the temperature of a subsequent heating or heat treatment of the DP microstructure.
- the semi-finished product or a structural component part manufactured therefrom acquires the properties characteristic of a DP steel with respect to microstructure, strength, minimum elongation, yield strength ratio, and strain hardening exponent also after a subsequent heat treatment or heating, particularly hot-dip galvanization and possibly subsequent dressing.
- the hot strip is cooled in the two-phase region after exiting the finishing mill train in order to adjust a suitable amount of residual austenite and is subsequently cooled in an accelerated manner to a temperature below the martensite start and finish temperature.
- the cold strip is heated in the two-phase region to adjust a suitable amount of residual austenite and is subsequently cooled in an accelerated manner to a temperature below the martensite start and finish temperature.
- This heat treatment is preferably carried out in a continuous annealing installation.
- N content should be fixated as low as possible and by adding Al and possibly Ti.
- a correspondingly increased V content can also be used for nitrogen fixation.
- Table 1 contains some possible chemical compositions:
- FIG. 1 is a cooling curve of steel sheet after hot rolling for adjusting a dual-phase microstructure
- FIG. 2 is a typical stress-strain diagram for a DP steel with low yield strength ratio ( ⁇ 75%) and without a pronounced yield strength.
- the austenite fraction is plotted over the time axis on the left-hand side and the core temperature is plotted over the time axis on the right-hand side.
- the cooling curve of a steel sheet after hot rolling for adjusting a dual-phase microstructure is shown by way of example.
- the ferrite region is cooled initially, and most of the austenite is transformed to ferrite within a very short time period.
- This first cooling stage can be followed by a holding period, or further cooling to temperatures below the martensite start temperature is carried out directly. In so doing, any remaining residual austenite transforms to martensite and generates the second, hard phase.
- a coiling temperature of about 200° C. is aimed for.
- the solid line shows the austenite dissociation as cooling time increases.
- the curve in dashes shows the lowering of the core temperature, also over the cooling time. It can be seen that cooling is accelerated between approximately 600° C. and the holding temperature of 200° C.
- the method provides a semi-finished product, particularly steel strip, having a dual-phase microstructure and a tensile strength between 500 and 1000 MPa elements such as carbon and nitrogen that are interstitially dissolved in the ferritic matrix are bound by alloying elements such as Al, Mo, Nb, Ti and V which form carbide, nitride or carbonitride in order to adjust a microstructure of hard components such as martensite, bainite, carbide with low fractions of residual austenite in a ferritic matrix which is substantially free from interstitially dissolved elements (IF character).
- alloying elements such as Al, Mo, Nb, Ti and V which form carbide, nitride or carbonitride in order to adjust a microstructure of hard components such as martensite, bainite, carbide with low fractions of residual austenite in a ferritic matrix which is substantially free from interstitially dissolved elements (IF character).
- the alloy content of the aforesaid alloying elements is adapted stoichiometrically to the ferrite content and to the solubility of carbon and nitrogen in the ferrite at the temperature of a subsequent heat treatment or heating, particularly hot-dip galvanization.
- the production of hot strip with a DP microstructure the hot strip is cooled in the two-phase region after exiting the finishing mill train of the rolling mill in order to adjust a suitable amount of residual austenite for achieving the desired strength class, and is subsequently cooled in an accelerated manner to a temperature below the martensite start and finish temperature.
- the cold strip is heated in the two-phase region to adjust a suitable amount of residual austenite and is subsequently cooled in an accelerated manner to a temperature below the martensite start and finish temperature.
- Heat treatment for adjusting the DP microstructure in cold strip is preferably carried out in a continuous annealing installation. The heat treatment is carried out between 400° C. and A 3 .
- the A3 point is the temperature at which grains of ferrite start to form.
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- Heat Treatment Of Sheet Steel (AREA)
Abstract
A method for producing semi-finished product, particularly steel strip, having a dual-phase microstructure and a tensile strength between 500 and 1000 MPa. Elements such as carbon and nitrogen which are interstitially dissolved in a ferritic matrix are bound by alloying elements such as Al, Mo, Nb, Ti and V which form carbide, nitride or carbonitride in order to adjust a microstructure of hard components such as martensite, bainite, carbide with low fractions of residual austenite in a ferritic matrix, which is substantially free from interstitially dissolved elements (IF character).
Description
- This is a U.S. national stage of Application No. PCT/DE2009/001136, filed on Aug. 7, 2009, which claims priority to German Application No: 10 2008 038 865.3, filed: Aug. 8, 2008, the contents of which are incorporated herein by reference.
- 1. Field of the Invention
- The invention is directed to a method for producing semi-finished product, particularly steel strip, having a dual-phase microstructure (DP steel strip) and a tensile strength between 500 and 1000 MPa.
- 2. Related Art
- High-strength steel sheet with good formability, stability of microstructures, and mechanical characteristics up to approximately 600° C. is required in many fields.
- One such field is the automotive industry, for example, in which efforts are made to reduce emissions by reducing the weight of structural chassis parts because the consumption of fuel can be reduced by reducing weight. On the other hand, there is also a demand for achieving a greater strength of the sheets that are used.
- Finally, the sheets should also be suitable for hot-dip galvanization.
- However, steels with a dual-phase microstructure that has already been adjusted have the disadvantage that an unwanted, pronounced yield strength generally results when heated above 200° C. as occurs during or in connection with hot-dip galvanization.
- Owing to this absence of temperature stability in the materials above approximately 200° C., semi-finished products such as strip, sheet, pipe and other structural components or workpieces comprising DP steel are not suitable for hot-dip galvanization.
- Therefore, it is the object of the invention to provide a method for the production of a semi-finished product, particularly DP steel strip, which is economical and by which a DP steel strip can be produced which not only has optimal formability properties but also has a temperature stability up to 600° C. and is therefore also suitable for hot-dip galvanization.
- According to one embodiment of the invention, a method for producing semi-finished product, particularly steel strip, having a dual-phase microstructure and a tensile strength between 500 and 1000 MPa, is disclosed. Elements such as carbon and nitrogen which are interstitially dissolved in the ferritic matrix are bound by alloying elements such as Al, Mo, Nb, Ti and V which form carbide, nitride or carbonitride in order to adjust a microstructure of hard components such as martensite, bainite, carbide with low fractions of residual austenite in a ferritic matrix which is substantially free from interstitially dissolved elements (IF character).
- The alloy content of the alloying elements is adapted stoichiometrically to the ferrite content and to the solubility of carbon and nitrogen at the temperature of a subsequent heating or heat treatment of the DP microstructure.
- In this way, the semi-finished product or a structural component part manufactured therefrom acquires the properties characteristic of a DP steel with respect to microstructure, strength, minimum elongation, yield strength ratio, and strain hardening exponent also after a subsequent heat treatment or heating, particularly hot-dip galvanization and possibly subsequent dressing.
- For the production of hot strip with a DP microstructure, the hot strip is cooled in the two-phase region after exiting the finishing mill train in order to adjust a suitable amount of residual austenite and is subsequently cooled in an accelerated manner to a temperature below the martensite start and finish temperature.
- Conversely, for producing cold strip with a DP microstructure, the cold strip is heated in the two-phase region to adjust a suitable amount of residual austenite and is subsequently cooled in an accelerated manner to a temperature below the martensite start and finish temperature. This heat treatment is preferably carried out in a continuous annealing installation.
- In order to exclude the influence of dissolved N on the aging behavior, the N content should be fixated as low as possible and by adding Al and possibly Ti. A correspondingly increased V content can also be used for nitrogen fixation. Table 1 contains some possible chemical compositions:
-
TABLE 1 Chemical composition concept IF-DP in percent by mass No. Concept C Si Mn P S Al Mo Ti Nb V Cr N 1 reference 0.06 0.35 1.1 0.02 0.004 0.025 — — — — 0.65 min. 2 Mo 0.2 — 3 MoV 0.06 0.35 1.1 0.02 0.004 0.025 0.1 — — 0.05 0.65 min. 4 V — 0.1 - In the accompanying diagrams:
-
FIG. 1 is a cooling curve of steel sheet after hot rolling for adjusting a dual-phase microstructure; and -
FIG. 2 is a typical stress-strain diagram for a DP steel with low yield strength ratio (≦75%) and without a pronounced yield strength. - In
FIG. 1 , the austenite fraction is plotted over the time axis on the left-hand side and the core temperature is plotted over the time axis on the right-hand side. - The cooling curve of a steel sheet after hot rolling for adjusting a dual-phase microstructure is shown by way of example.
- In so doing, the ferrite region is cooled initially, and most of the austenite is transformed to ferrite within a very short time period. This first cooling stage can be followed by a holding period, or further cooling to temperatures below the martensite start temperature is carried out directly. In so doing, any remaining residual austenite transforms to martensite and generates the second, hard phase. A coiling temperature of about 200° C. is aimed for.
- The solid line shows the austenite dissociation as cooling time increases. The curve in dashes shows the lowering of the core temperature, also over the cooling time. It can be seen that cooling is accelerated between approximately 600° C. and the holding temperature of 200° C.
- The method provides a semi-finished product, particularly steel strip, having a dual-phase microstructure and a tensile strength between 500 and 1000 MPa elements such as carbon and nitrogen that are interstitially dissolved in the ferritic matrix are bound by alloying elements such as Al, Mo, Nb, Ti and V which form carbide, nitride or carbonitride in order to adjust a microstructure of hard components such as martensite, bainite, carbide with low fractions of residual austenite in a ferritic matrix which is substantially free from interstitially dissolved elements (IF character). The alloy content of the aforesaid alloying elements is adapted stoichiometrically to the ferrite content and to the solubility of carbon and nitrogen in the ferrite at the temperature of a subsequent heat treatment or heating, particularly hot-dip galvanization. The production of hot strip with a DP microstructure, the hot strip is cooled in the two-phase region after exiting the finishing mill train of the rolling mill in order to adjust a suitable amount of residual austenite for achieving the desired strength class, and is subsequently cooled in an accelerated manner to a temperature below the martensite start and finish temperature.
- For producing cold strip with a DP microstructure, the cold strip is heated in the two-phase region to adjust a suitable amount of residual austenite and is subsequently cooled in an accelerated manner to a temperature below the martensite start and finish temperature. Heat treatment for adjusting the DP microstructure in cold strip is preferably carried out in a continuous annealing installation. The heat treatment is carried out between 400° C. and A3. The A3 point is the temperature at which grains of ferrite start to form.
- Thus, while there have shown and described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.
Claims (8)
1.-6. (canceled)
7. A method for producing semi-finished product having a dual-phase microstructure and a tensile strength between 500 and 1000 MPa, comprising:
interstitially dissolving elements including one or more of carbon and nitrogen in a ferritic matrix;
binding the interstitially dissolved elements by alloying elements including one or more of Al, Mo, Nb, Ti and V, which form carbide, nitride, or carbonitride to adjust a microstructure of hard components including one or more of martensite, bainite, carbide having low fractions of residual austenite in a ferritic matrix that is substantially free from interstitially dissolved elements; and
adapting an alloy content of the alloying elements stoichiometrically to a ferrite content and to a solubility of the carbon and the nitrogen in the ferrite at a temperature of at least one of a subsequent heat treatment and heating.
8. The method according to claim 7 , wherein for production of a hot strip with a DP microstructure, the hot strip is cooled in a two-phase region after exiting a finishing mill train of a rolling mill to adjust a suitable amount of residual austenite to achieving a desired strength class, and
the hot strip is subsequently cooled in an accelerated manner to a temperature below a martensite start and finish temperature.
9. The method according to claim 7 , wherein for producing a cold strip with a DP microstructure, the cold strip is heated in a two-phase region to adjust a suitable amount of residual austenite and the cold strip is subsequently cooled in an accelerated manner to a temperature below a martensite start and finish temperature.
10. The method according to claim 9 , wherein the heat treatment for adjusting the DP microstructure in the cold strip is performed in a continuous annealing installation.
11. The method according to claim 7 , wherein the heat treatment is performed between 400° C. and A3, where A3 is the temperature at which grains of ferrite start to form.
12. The method according to claim 7 , wherein the semi-finished product is steel strip.
13. The method according to claim 7 , wherein the at least one of the subsequent heat treatment and the heating is a hot-dip galvanization.
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
DE102008038865.3 | 2008-08-08 | ||
DE102008038865A DE102008038865A1 (en) | 2008-08-08 | 2008-08-08 | Process for the production of semi-finished products, in particular steel strip, with dual-phase structure |
PCT/DE2009/001136 WO2010015251A2 (en) | 2008-08-08 | 2009-08-07 | Method for producing a semi-finished product, especially steel strip, having a dual-phase microstructure |
Publications (1)
Publication Number | Publication Date |
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US20110146850A1 true US20110146850A1 (en) | 2011-06-23 |
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ID=41353805
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US13/058,085 Abandoned US20110146850A1 (en) | 2008-08-08 | 2009-08-07 | Method for Producing A Steel Strip Having A Dual-Phase Microstructure |
Country Status (10)
Country | Link |
---|---|
US (1) | US20110146850A1 (en) |
EP (1) | EP2318556A2 (en) |
JP (1) | JP2011530649A (en) |
KR (1) | KR20110036928A (en) |
CN (1) | CN102105605B (en) |
BR (1) | BRPI0917007A2 (en) |
CA (1) | CA2732495C (en) |
DE (1) | DE102008038865A1 (en) |
RU (1) | RU2475545C2 (en) |
WO (1) | WO2010015251A2 (en) |
Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US20040035500A1 (en) * | 2002-08-20 | 2004-02-26 | Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd) | Dual phase steel sheet with good bake-hardening properties |
US20080178972A1 (en) * | 2006-10-18 | 2008-07-31 | Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd) | High strength steel sheet and method for producing the same |
US20100304174A1 (en) * | 2007-07-19 | 2010-12-02 | Corus Staal Bv | Strip of steel having a variable thickness in length direction |
Family Cites Families (9)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPS5839736A (en) * | 1981-09-01 | 1983-03-08 | Kobe Steel Ltd | Manufacture of composite structure type high tensile cold rolled steel plate |
US5545270A (en) * | 1994-12-06 | 1996-08-13 | Exxon Research And Engineering Company | Method of producing high strength dual phase steel plate with superior toughness and weldability |
DE19936151A1 (en) * | 1999-07-31 | 2001-02-08 | Thyssenkrupp Stahl Ag | High-strength steel strip or sheet and process for its manufacture |
JP4010131B2 (en) * | 2000-11-28 | 2007-11-21 | Jfeスチール株式会社 | Composite structure type high-tensile cold-rolled steel sheet excellent in deep drawability and manufacturing method thereof |
JP4062118B2 (en) * | 2002-03-22 | 2008-03-19 | Jfeスチール株式会社 | High-tensile hot-rolled steel sheet with excellent stretch characteristics and stretch flange characteristics and manufacturing method thereof |
US6811624B2 (en) * | 2002-11-26 | 2004-11-02 | United States Steel Corporation | Method for production of dual phase sheet steel |
JP4214006B2 (en) * | 2003-06-19 | 2009-01-28 | 新日本製鐵株式会社 | High strength steel sheet with excellent formability and method for producing the same |
CN100507053C (en) * | 2004-11-29 | 2009-07-01 | 宝山钢铁股份有限公司 | 800MPa cold rolled and hot zinc plated double phase steel and its producing method |
JP4725973B2 (en) * | 2006-10-18 | 2011-07-13 | 株式会社神戸製鋼所 | High strength steel plate with excellent stretch flangeability and method for producing the same |
-
2008
- 2008-08-08 DE DE102008038865A patent/DE102008038865A1/en not_active Withdrawn
-
2009
- 2009-08-07 US US13/058,085 patent/US20110146850A1/en not_active Abandoned
- 2009-08-07 JP JP2011521437A patent/JP2011530649A/en active Pending
- 2009-08-07 BR BRPI0917007A patent/BRPI0917007A2/en not_active Application Discontinuation
- 2009-08-07 CA CA2732495A patent/CA2732495C/en not_active Expired - Fee Related
- 2009-08-07 KR KR1020117002936A patent/KR20110036928A/en active Search and Examination
- 2009-08-07 EP EP09736097A patent/EP2318556A2/en not_active Ceased
- 2009-08-07 CN CN200980129258.9A patent/CN102105605B/en not_active Expired - Fee Related
- 2009-08-07 RU RU2011108570/02A patent/RU2475545C2/en active
- 2009-08-07 WO PCT/DE2009/001136 patent/WO2010015251A2/en active Application Filing
Patent Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US20040035500A1 (en) * | 2002-08-20 | 2004-02-26 | Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd) | Dual phase steel sheet with good bake-hardening properties |
US20090242085A1 (en) * | 2002-08-20 | 2009-10-01 | Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd) | Dual phase steel sheet with good bake-hardening properties |
US20080178972A1 (en) * | 2006-10-18 | 2008-07-31 | Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd) | High strength steel sheet and method for producing the same |
US20100304174A1 (en) * | 2007-07-19 | 2010-12-02 | Corus Staal Bv | Strip of steel having a variable thickness in length direction |
Also Published As
Publication number | Publication date |
---|---|
CA2732495C (en) | 2015-01-20 |
CN102105605A (en) | 2011-06-22 |
WO2010015251A2 (en) | 2010-02-11 |
EP2318556A2 (en) | 2011-05-11 |
CA2732495A1 (en) | 2010-02-11 |
JP2011530649A (en) | 2011-12-22 |
DE102008038865A1 (en) | 2010-02-11 |
WO2010015251A3 (en) | 2010-07-01 |
KR20110036928A (en) | 2011-04-12 |
CN102105605B (en) | 2015-04-15 |
RU2011108570A (en) | 2012-09-20 |
RU2475545C2 (en) | 2013-02-20 |
BRPI0917007A2 (en) | 2016-02-16 |
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