EP0179952B1 - Verfahren zur Herstellung von hochfestem und duktilem Stahl - Google Patents

Verfahren zur Herstellung von hochfestem und duktilem Stahl Download PDF

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Publication number
EP0179952B1
EP0179952B1 EP84201584A EP84201584A EP0179952B1 EP 0179952 B1 EP0179952 B1 EP 0179952B1 EP 84201584 A EP84201584 A EP 84201584A EP 84201584 A EP84201584 A EP 84201584A EP 0179952 B1 EP0179952 B1 EP 0179952B1
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EP
European Patent Office
Prior art keywords
steel
sequence
rolling
temperature
range
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.)
Expired
Application number
EP84201584A
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English (en)
French (fr)
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EP0179952A1 (de
Inventor
Erik Anders Ake Josefsson
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.)
SSAB AB
Original Assignee
SSAB Svenskt Stal AB
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Filing date
Publication date
Application filed by SSAB Svenskt Stal AB filed Critical SSAB Svenskt Stal AB
Priority to EP84201584A priority Critical patent/EP0179952B1/de
Priority to DE8484201584T priority patent/DE3474042D1/de
Priority to AT84201584T priority patent/ATE37202T1/de
Publication of EP0179952A1 publication Critical patent/EP0179952A1/de
Application granted granted Critical
Publication of EP0179952B1 publication Critical patent/EP0179952B1/de
Expired 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
    • 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 of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling

Definitions

  • the present invention relates generally to a method for fabricating structural steel which has high strength and good ductility. '
  • the former structure is obtained by making the finishing rolling passes with a high degree of reduction, the latter structure by effecting the finishing rolling passes at a low temperature i.e., at a temperature lower than about 900°C. It is the fine grain of the recrystallized austenite, and in the alternative, the high degree of reduction of the non-recrystallized austenite that provide the basis for forming a fine-grained polygonal ferrite during the subsequent cooling, and thus a basis for the combination of the high strength and good ductility characteristics of the finished steel.
  • the present invention provides a method for producing hot rolled steel products having high strength and ductility.
  • the method consists in a process for manufacturing hot rolled steel products having high strength and good ductility as hot rolled, the method comprising heating and low-alloy steel having a C content within the range of about 0.02 to 0.15 wt% a Nb content within the range of about 0.015 to 0.100 wt% and a titanium content within the range of about 0.005 to 0.040 wt% to a temperature in the range of about 1150 to 1250°C, hot rolling the steel in one or more passes during a first rolling sequence such that the average austenite grain size is reduced to below 50 J.lm at the end of the first sequence, the first sequence being completed with, the steel at a temperature in the range of about 950 to 1100°C, directly thereafter hot rolling the steel at about 9000 to 1100°C in a second rolling sequence of one or more passes, the reduction in each pass being below about 15%, and cooling the steel to ambient temperature.
  • the steel should contain a certain amount of Nb, e.g., about 0.015 to about 0.100%, the lower amount applicable to higher carbon contents, e.g., about .15% C and the higher amount applicable to a carbon content of about 0.05% and lower.
  • the steels particularly suitable for the method contain minor amounts, e.g., less than about 2%, of one or more of Si, Mn, Cr and Mo.
  • the rolling of the steel is divided into two sequences.
  • the first sequence is conducted such that the steel has a uniform, relatively fine grained recrystallized austenite (average less than 50 J.lm measured on a sample section which has been cut out and water quenched) at the end of the sequence.
  • the area reduction oftentimes exceeds about 25%, preferably about 30%.
  • the second rolling sequence includes one or more light passes, each pass producing less than about 15% in area reduction. This second sequence can immediately following the first sequence without any time waiting for the steel to cool if the temperature of the heat at the end of the first sequence is below about 1100°C, and for lower amounts of Nb, below about 1070°C.
  • the procedure of the invention is well adapted to be combined with accelerated cooling by water spraying and the like as an extra strength increasing step performed after the second rolling sequence.
  • the steel produced by the method of the invention is compared to steel produced by methods outside the scope of the invention in the following example.
  • a number of steel blooms with the approximate analysis of 0.09% C, 0.33% Si, 1.41% Mn, 0.013% P, 0.011 % S, 0.010% N, 0.027% Al, 0.007% Ti and 0.027% Nb were heated to about 1200°C and hot rolled from a thickness of about 120 mm to a thickness of about 20 mm as per the different pass schedules set forth in the following table.
  • the temperature of the plate bar was determinsd and sample sections were cut and cooled in water. In each of the sample sections, the austenite grain size existing before the cooling was determined.
  • the plates were allowed to cool in air. The mechanical properties of the plates were determined from test bars that were cut normal to the rolling direction. The test results are set forth in the upper portion of the Table.
  • the plates with low reductions in the second rolling sequence show a better combination of yield point and transition temperature characteristics than the plates produced with high reductions, such as 35% in the finishing pass. It should also be noted that, with a reduction of 17% in the finishing pass (plate 0), a lower ductility is obtained than in the plates where finishing reductions are limited to below about 15%. A lower ductility is also obtained after the normal rolling with high finishing reduction of 35% (plates D and K).

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

Claims (6)

1. Verfahren zur Herstellung warmgewalzter Stahlprodukte mit hoher Festigkeit und guter Streckbarkeit beim Warmwalzen, wobei beim Verfahren ein niedrig ligierter Stahl mit einem C-Gehalt im Bereich von etwa 0,02 bis 0,15 Gew.%, einem Nb-Gehalt im Bereich von etwa 0,015 bis 0,100 Gew.% und einem Ti-Gehalt im Bereich von etwa 0,005 bis 0,040 Gew.% auf eine Temperatur im Bereich von etwa 1150 bis 1250°C erwärmt wird, der Stahl in einem oder mehreren Durchgängen während einer ersten Walzreihe warmgewalzt wird, so daß die mittlere Austenitkorngröße auf kleiner 50 um am Ende der ersten Reihe verringert wird, nach Beendigung der ersten Reihe der Stahl bei einer Temperatur im Bereich von etwa 950 bis 1100°C ist, worauf unmittelbar danach der Stahl bei etwa 900 bis 1100°C in einer zweiten Walzreihe von einem oder mehreren Durchgängen warmgewalzt wird und die Verringerung bei jedem Durchgang unter etwa 15% liegt und der Stahl bei Raumtemperatur gekühlt wird.
2. Verfahren nach Anspruch 1, bei dem die Verringerung beim letzten Durchgang der ersten Walzreihe etwa 25% überschreitet.
3. Verfahren nach Anspruch 1, bei dem die Verringerung beim letzten Durchgäng der ersten Walzreihe etwa 30% überschreitet.
4. Verfahren nach Anspruch 1, bei dem während wenigstens einem Durchgang der zweiten Walzreihe die Temperatur des Stahles im Bereich von etwa 1100 bis 950°C ist.
5. Verfahren nach Anspruch 1 oder 4, bei dem das Kühlen nach der zweiten Walzreihe durch Wassersprühung beschleunigt wird.
6. Verfahren nach Anspruch 1, bei dem der Stahl weniger als 2 Gew.% einer oder mehrerer der Substanzen Si, Mn, Cr und Mo enthält.
EP84201584A 1984-10-30 1984-10-30 Verfahren zur Herstellung von hochfestem und duktilem Stahl Expired EP0179952B1 (de)

Priority Applications (3)

Application Number Priority Date Filing Date Title
EP84201584A EP0179952B1 (de) 1984-10-30 1984-10-30 Verfahren zur Herstellung von hochfestem und duktilem Stahl
DE8484201584T DE3474042D1 (en) 1984-10-30 1984-10-30 Method for producing high strength steel with good ductility
AT84201584T ATE37202T1 (de) 1984-10-30 1984-10-30 Verfahren zur herstellung von hochfestem und duktilem stahl.

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
EP84201584A EP0179952B1 (de) 1984-10-30 1984-10-30 Verfahren zur Herstellung von hochfestem und duktilem Stahl

Publications (2)

Publication Number Publication Date
EP0179952A1 EP0179952A1 (de) 1986-05-07
EP0179952B1 true EP0179952B1 (de) 1988-09-14

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Family Applications (1)

Application Number Title Priority Date Filing Date
EP84201584A Expired EP0179952B1 (de) 1984-10-30 1984-10-30 Verfahren zur Herstellung von hochfestem und duktilem Stahl

Country Status (3)

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EP (1) EP0179952B1 (de)
AT (1) ATE37202T1 (de)
DE (1) DE3474042D1 (de)

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
ZA705046B (en) * 1969-07-30 1971-04-28 Armco Steel Corp Process for production of high strength low alloy steel
US3849209A (en) * 1972-02-01 1974-11-19 Nippon Steel Corp Manufacturing method of high tension, high toughness steel
US4400223A (en) * 1981-08-21 1983-08-23 Inland Steel Company Hot rolled steel product and method for producing same
CS330783A2 (en) * 1982-07-09 1984-06-18 Mannesmann Ag Zpusob vyroby plechu s jemnozrnnou strukturou z nizce legovane oceli pro vyrobu trub velkeho prumeru

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Publication number Publication date
DE3474042D1 (en) 1988-10-20
ATE37202T1 (de) 1988-09-15
EP0179952A1 (de) 1986-05-07

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