EP0737254A1 - Steel bars and rods and manufacturing process - Google Patents

Steel bars and rods and manufacturing process

Info

Publication number
EP0737254A1
EP0737254A1 EP94915667A EP94915667A EP0737254A1 EP 0737254 A1 EP0737254 A1 EP 0737254A1 EP 94915667 A EP94915667 A EP 94915667A EP 94915667 A EP94915667 A EP 94915667A EP 0737254 A1 EP0737254 A1 EP 0737254A1
Authority
EP
European Patent Office
Prior art keywords
steel
bar
levels
yield stress
rolling mill
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.)
Withdrawn
Application number
EP94915667A
Other languages
German (de)
French (fr)
Inventor
Antony Robert Franks
William Allen
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.)
ASW Ltd
Original Assignee
ASW Ltd
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 ASW Ltd filed Critical ASW Ltd
Publication of EP0737254A1 publication Critical patent/EP0737254A1/en
Withdrawn legal-status Critical Current

Links

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
    • 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
    • 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
    • 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
    • C21D8/08—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires for concrete reinforcement

Definitions

  • the invention relates to a process for the manufacture of high strength steel bars, particularly prestressing steel bars and bars for applications requiring similar strength levels.
  • Prestressing steels used in building construction in the UK are required to conform to BS4486 which requires a minimum yield stress of 835 N/mm 2 and a minimum ultimate tensile stress (UTS) of 1030 N/mm 2 .
  • UTS ultimate tensile stress
  • Standards or working practices in most countries require similar strength levels for prestressing steel bars.
  • Some high strength steel bars for other applications such as for shuttering ties require similar strength properties but requirements for stress relaxation and corrosion resistance may be less onerous.
  • MACALLOY has a typical analysis of 0.50% C, 0.80% Mn and 0.80% Cr. Bars from this steel are hot rolled to diameters from 16 to 40 mm and after cooling are cold worked by stretching. Subsequently a thread can be rolled on them. This is an expensive manufacturing process, partly because it can only be applied to limited lengths of bar.
  • One known technique for increasing the strength while achieving good workability for hot rolled steel products is a process known as the QST (Quench-and-Self-Tempering) process.
  • QST Quadench-and-Self-Tempering
  • Tempcore One well known example of this process.
  • the process is described in GB A 1,392269.
  • the quench transforms the surface layer of the bar to martensite and after quenching, heat remaining in the core of the bar tempers the martensite to a more ductile microstructure. . Meanwhile the core transforms on cooling to ferrite and pearlite.
  • a typical steel of 0.15 to 0.22% C, 0.10 to 0.35% Si and 0.60 to 1% Mn can achieve the standards of strength required for reinforcement purposes. These standards can be for a 460/550 steel (yield stress/UTS in N/mm 2 ) or as high as 500/600. The relatively low C results in a steel which is readily weldable.
  • High Carbon steels of the order of 0.7 to 0.8% C can give rise to various difficulties which can be overcome with care but which would be better avoided if a medium Carbon steel could meet the required specification. Possible difficulties include segregation of Carbon on solidification and cracking of billets.
  • a method of producing a high tensile steel bar or rod having a yield stress of at least 830 N/mm 2 and a UTS of at least 1030 N/mm 2 wherein a steel having from 0.35 to 0.65% C, from 0.30 to 1.50% Mn and from 0.05 to 0.30% V is water quenched immediately on exiting the last stand in a rolling mill to such an extent that an outer martensitic layer is formed and remaining heat from the core subsequently tempers the martensitic layer.
  • the C content is from 0.35% to 0.60% and the V content is from 0.10% to 0.30%.
  • V With insufficient V, satisfactory levels of UTS can be achieved but the yield stress may not meet requirements. Typical values for V would be between 0.15 and 0.25%. High cost deters the use of more V than is necessary while lower levels of V make it difficult or impossible to achieve the required yield stress levels. With lower levels of V below about 0.15%, cold working by stretching may be necessary to achieve the required yield stress.
  • Mn is normally present as a result of typical steel manufacture. Typical values are from about 0.3 to about 0.8%. Higher levels of Mn are preferred with the invention because this permits the level of C to be kept in the lower part of the range.
  • a further advantage of a relatively low C content is that it results in a higher martensite start transformation temperature M a , thereby making the quench conditions less onerous to achieve a substantial depth of martensite as required to achieve the desired strength.
  • the steel has from 0.35 to 0.60% C, from 0.80 to 1.50% Mn and from 0.15 to 0.25% V.
  • a particularly preferred steel incorporates 0.45 to 0.55% C, 0.80 to 1.30 % Mn and 0.18 to 0.24% V.
  • a screw thread is cold rolled onto at least end portions of the bar.
  • a semi-continuous thread may be rolled onto the bar in the last stand of the rolling mill immediately prior to quenching.
  • Results achieved from a series of examples are shown in the Table.
  • the table shows some examples marked with an asterisk which do not comply with the requirements of the invention. These examples are provided with a view to illustrating the boundaries of the invention.
  • the table gives essential material composition and mechanical properties for a range of bars which have been treated by the QST process with normal rates of quenching. In the tests, the yield stress was measured as the 0.1% proof stress. An indication of ductility is also given in the column headed A5. This is the elongation in % at fracture over a gauge length of five times diameter.
  • a steel may be used with 0.60 to 0.65% C, with as little as about 0.07% or possibly even less of V and preferably with 0.5%to 1% Mn.
  • the quench and self temper process may in some situations be used in conjunction with cold stretching of the bar after it has cooled.
  • This stretching operation raises the yield strength substantially but has little effect on the tensile strength or tensile ductility. Stretching also improves stress relaxation properties of the steel.
  • Cold stretching may be used in situations where the yield stress has not reached the required level after the QST process itself. This may for example be because a relatively low level of V has been chosen. It may also be used in some bars of larger cross section where achieving the required quench rate to meet the required yield stress can be difficult. A yield stress below the minimum requirement can deliberately be aimed at in the QST process when cold stretching is required to achieve good stress relaxation because the cold stretching will then additionally increase the yield stress.

Landscapes

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

Abstract

High tensile steel bar or rod having a yield stress of at least 835 N/mm2 and a UTS of at least 1030 N/mm2 is produced as follows. A steel having from 0.35 to 0.65 % C, from 0.30 to 1.50 % Mn and from 0.05 to 0.30 % V is water quenched immediately on exiting the last stand in a rolling mill to such an extent that an outer martensitic layer is formed and remaining heat from the core subsequently tempers the martensitic layer.

Description

STEEL BARS AND RODS AND MANUFACTURING PROCESS
The invention relates to a process for the manufacture of high strength steel bars, particularly prestressing steel bars and bars for applications requiring similar strength levels.
Prestressing steels used in building construction in the UK are required to conform to BS4486 which requires a minimum yield stress of 835 N/mm2 and a minimum ultimate tensile stress (UTS) of 1030 N/mm2. Broadly similar Standards or working practices in most countries require similar strength levels for prestressing steel bars. Some high strength steel bars for other applications such as for shuttering ties require similar strength properties but requirements for stress relaxation and corrosion resistance may be less onerous.
Traditional ways of achieving these strength requirements have been to start with a high grade alloy steel and then to either (a) cold stretch or (b) cold stretch and stress relieve or (c) quench and subsequently temper separate bars. One example, known by the registered trade mark
MACALLOY has a typical analysis of 0.50% C, 0.80% Mn and 0.80% Cr. Bars from this steel are hot rolled to diameters from 16 to 40 mm and after cooling are cold worked by stretching. Subsequently a thread can be rolled on them. This is an expensive manufacturing process, partly because it can only be applied to limited lengths of bar.
One known technique for increasing the strength while achieving good workability for hot rolled steel products is a process known as the QST (Quench-and-Self-Tempering) process. One well known example of this process is known as the Tempcore process. The process is described in GB A 1,392269. In carrying out the QST or Tempcore process, bars are subject to a surface quench from the rolling temperature after leaving the finishing stand of a rolling mill. The quench transforms the surface layer of the bar to martensite and after quenching, heat remaining in the core of the bar tempers the martensite to a more ductile microstructure. . Meanwhile the core transforms on cooling to ferrite and pearlite. Using the QST process, a typical steel of 0.15 to 0.22% C, 0.10 to 0.35% Si and 0.60 to 1% Mn can achieve the standards of strength required for reinforcement purposes. These standards can be for a 460/550 steel (yield stress/UTS in N/mm2) or as high as 500/600. The relatively low C results in a steel which is readily weldable.
Attempts have been made to apply the QST process to higher carbon steels with a view to achieving higher strength, for example as required in prestressing steels. For example, in US 4,284,438, QST cooling of 0.65% C and 0.76% C bars produces UTS values of the order required for prestressing and yield stresses which are improved but not to prestressing levels.
It has also been proposed in EP 172,544 Bl that application of the QST process to steels having 0.5 to 0.8% C and 0.3 to 0.8% Mn may be able to produce a high strength bar. This document shows specifically that prestressing requirements can be met by applying the process to steel having 0.74 to 0.76% C and Mn in the range 0.34 to 0.45%.
High Carbon steels of the order of 0.7 to 0.8% C can give rise to various difficulties which can be overcome with care but which would be better avoided if a medium Carbon steel could meet the required specification. Possible difficulties include segregation of Carbon on solidification and cracking of billets.
It is an object of the invention to provide an inexpensive process for the manufacture of high strength steels which can be used in prestressing and similar applications.
According to the invention there is provided a method of producing a high tensile steel bar or rod having a yield stress of at least 830 N/mm2 and a UTS of at least 1030 N/mm2 wherein a steel having from 0.35 to 0.65% C, from 0.30 to 1.50% Mn and from 0.05 to 0.30% V is water quenched immediately on exiting the last stand in a rolling mill to such an extent that an outer martensitic layer is formed and remaining heat from the core subsequently tempers the martensitic layer. Preferably the C content is from 0.35% to 0.60% and the V content is from 0.10% to 0.30%.
The required levels of C, Mn and V are to a certain extent interdependent. Choosing simultaneously the upper levels or the lower levels of all three constituents is unlikely to achieve successful results. Steels with about 0.45% C, 1.2% Mn and 0.20% V have produced satisfactory yield stress of the order of 900 N/mm2 and UTS of about 1100 N/mm2.
With insufficient V, satisfactory levels of UTS can be achieved but the yield stress may not meet requirements. Typical values for V would be between 0.15 and 0.25%. High cost deters the use of more V than is necessary while lower levels of V make it difficult or impossible to achieve the required yield stress levels. With lower levels of V below about 0.15%, cold working by stretching may be necessary to achieve the required yield stress.
A significant level of Mn is normally present as a result of typical steel manufacture. Typical values are from about 0.3 to about 0.8%. Higher levels of Mn are preferred with the invention because this permits the level of C to be kept in the lower part of the range.
A further advantage of a relatively low C content is that it results in a higher martensite start transformation temperature Ma, thereby making the quench conditions less onerous to achieve a substantial depth of martensite as required to achieve the desired strength.
Preferably the steel has from 0.35 to 0.60% C, from 0.80 to 1.50% Mn and from 0.15 to 0.25% V. A particularly preferred steel incorporates 0.45 to 0.55% C, 0.80 to 1.30 % Mn and 0.18 to 0.24% V.
In one application of the bar, a screw thread is cold rolled onto at least end portions of the bar.
Alternatively a semi-continuous thread may be rolled onto the bar in the last stand of the rolling mill immediately prior to quenching.
Results achieved from a series of examples are shown in the Table. The table shows some examples marked with an asterisk which do not comply with the requirements of the invention. These examples are provided with a view to illustrating the boundaries of the invention.
The table gives essential material composition and mechanical properties for a range of bars which have been treated by the QST process with normal rates of quenching. In the tests, the yield stress was measured as the 0.1% proof stress. An indication of ductility is also given in the column headed A5. This is the elongation in % at fracture over a gauge length of five times diameter.
All of these tests were conducted on silicon killed billets rolled at typical temperatures resulting in a temperature at the beginning of the quench of about 1050°C. Quenching was conducted in accordance with normal parameters for the QST process. The degree of quench can best be judged by the recovery temperature, that is the highest surface temperature reached during the tempering stage. For smaller diameter bars of about 16 mm a typical recovery temperature is 640βC and for a larger diameter bar of 40 mm a typical recovery temperature is 590βC. Intermediate temperatures are typical for intermediate sizes.
With a further alternative material composition a steel may be used with 0.60 to 0.65% C, with as little as about 0.07% or possibly even less of V and preferably with 0.5%to 1% Mn.
The quench and self temper process may in some situations be used in conjunction with cold stretching of the bar after it has cooled. This stretching operation raises the yield strength substantially but has little effect on the tensile strength or tensile ductility. Stretching also improves stress relaxation properties of the steel.
Cold stretching may be used in situations where the yield stress has not reached the required level after the QST process itself. This may for example be because a relatively low level of V has been chosen. It may also be used in some bars of larger cross section where achieving the required quench rate to meet the required yield stress can be difficult. A yield stress below the minimum requirement can deliberately be aimed at in the QST process when cold stretching is required to achieve good stress relaxation because the cold stretching will then additionally increase the yield stress.

Claims

1. A method of producing a high tensile steel bar or rod having a yield stress of at least 835 N/mm2 and a UTS of at least 1030 N/mm2 wherein a steel having from 0.35 to 0.65% C, from 0.30 to 1.50% Mn and from 0.05 to 0.30% V is water quenched immediately on exiting the last stand in a rolling mill to such an extent that an outer martensitic layer is formed and remaining heat from the core subsequently tempers the martensitic layer.
2. A method as claimed in claim 1 wherein the C content is from 0.35 to 0.65% and the V content is from 0.10 to 0.30%.
3. A method as claimed in Claim 2 wherein the steel has from 0.35 to 0.60% C.
4. A method as claimed in any one of the preceding claims wherein the steel has from 0.80 to 1.50% Mn.
5. A method as claimed in any one of the preceding claims wherein the steel incorporates from 0.15 to 0.25% V.
6. A method as claimed in Claim 1 wherein the steel incorporates 0.45 to 0.55% C, 0.80 to 1.30% Mn and 0.18 to 0.24% V.
7. A method as claimed in any one of the preceding claims wherein the levels of C, Mn and V and the quench rate are selected to provide the required stress levels in the as-rolled condition.
8. A method as claimed in any one of claims 1 to 6 wherein the bar or rod is subsequently cold stretched .
9. A method as claimed in any one of the preceding claims wherein a screw thread is cold rolled onto at least end portions of the bar.
10. A method as claimed in any one of Claims 1 to 7 wherein a semi-continuous thread is rolled onto the bar in the last stand of the rolling mill immediately prior to quenching.
11. High tensile steel bar produced by a method as claimed in any one of the preceding claims.
EP94915667A 1993-05-26 1994-05-23 Steel bars and rods and manufacturing process Withdrawn EP0737254A1 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
GB9310854 1993-05-26
GB939310854A GB9310854D0 (en) 1993-05-26 1993-05-26 Steel bars and rods and manufacturing process
PCT/GB1994/001122 WO1994028182A1 (en) 1993-05-26 1994-05-23 Steel bars and rods and manufacturing process

Publications (1)

Publication Number Publication Date
EP0737254A1 true EP0737254A1 (en) 1996-10-16

Family

ID=10736156

Family Applications (1)

Application Number Title Priority Date Filing Date
EP94915667A Withdrawn EP0737254A1 (en) 1993-05-26 1994-05-23 Steel bars and rods and manufacturing process

Country Status (3)

Country Link
EP (1) EP0737254A1 (en)
GB (1) GB9310854D0 (en)
WO (1) WO1994028182A1 (en)

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN1044826C (en) 1994-11-15 1999-08-25 新日本制铁株式会社 Perlite rail of high abrasion resistance and method of mfg. the same
US6224693B1 (en) 1999-12-10 2001-05-01 Tenedora Nemak, S.A. De C.V. Method and apparatus for simplified production of heat treatable aluminum alloy castings with artificial self-aging

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE925175C (en) * 1953-02-25 1955-03-14 Gertrud Hofmann Process for producing steel work pieces with zones of different hardnesses
BE854647A (en) * 1977-05-13 1977-09-01 Centre Rech Metallurgique PROCESS FOR THE PRODUCTION OF IMPROVED QUALITY STEEL PROFILES
BE874535A (en) * 1979-02-28 1979-06-18 Centre Rech Metallurgique PROCESS FOR MANUFACTURING HIGH ELASTIC LIMIT STEEL LAMINATED PRODUCTS
DE3431008C2 (en) * 1984-08-23 1986-10-16 Dyckerhoff & Widmann AG, 8000 München Heat treatment of hot rolled bars or wires
DE3631928C2 (en) * 1986-09-19 1994-06-09 Aicher Max Process for the production of rolled steel products

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO9428182A1 *

Also Published As

Publication number Publication date
WO1994028182A1 (en) 1994-12-08
GB9310854D0 (en) 1993-07-14

Similar Documents

Publication Publication Date Title
US3810793A (en) Process of manufacturing a reinforcing bar steel for prestressed concrete
AU590212B2 (en) Controlled rolling process for dual phase steels and application to rod, wire, sheet and other shapes
EP0058016B1 (en) Process for producing steel wire or rods of high ductility and strength
NO321331B1 (en) Stalls and Methods for Manufacturing a Stall Component, Cold Shaped Stall Component, and Hot-Rolled Ferrometallurgical Product
JPH0730394B2 (en) Method for manufacturing steel wire
US4877463A (en) Method for producing rolled steel products, particularly threaded steel tension members
WO1996002676A2 (en) Cold formed high-strength steel structural members
US5453139A (en) Method of making cold formed high-strength steel parts
JPS6119734A (en) Martensite stainless steel bar of wire rod and manufacture
AU676707B2 (en) Cold formed high-strength steel parts
KR20170106973A (en) High tensile strength steel wire
CA1317859C (en) Method for producing roll steel products
WO1994028182A1 (en) Steel bars and rods and manufacturing process
JPH0995735A (en) Production of steel for reinforcing bar excellent in earthquake resistance
JPH0759738B2 (en) Ultra-high-strength PC steel wire or steel bar excellent in uniform elongation and method for producing the same
UA80009C2 (en) Process for production of high-test, high-plastic alloyed carbonaceous steel
JPH0328351A (en) High ductility pc steel stock and its production
FI83045C (en) Process for producing cylinder pipes intended for use in temperatures of -40 ° C and use of steel in cylinder pipes
JPH0678571B2 (en) Stainless steel seamless pipe manufacturing method
KR940007365B1 (en) Method of manufacturing steel rod
JPH0565567B2 (en)
JPS62263924A (en) Production of tough steel pipe
CA2166713C (en) Warm forming high strength steel parts
BR112021001259A2 (en) method to manufacture railway tracks
JPS6043892B2 (en) High tensile strength wire manufacturing method

Legal Events

Date Code Title Description
PUAI Public reference made under article 153(3) epc to a published international application that has entered the european phase

Free format text: ORIGINAL CODE: 0009012

17P Request for examination filed

Effective date: 19951208

AK Designated contracting states

Kind code of ref document: A1

Designated state(s): AT BE CH DE ES FR GB IT LI LU

17Q First examination report despatched

Effective date: 19980519

STAA Information on the status of an ep patent application or granted ep patent

Free format text: STATUS: THE APPLICATION IS DEEMED TO BE WITHDRAWN

18D Application deemed to be withdrawn

Effective date: 19981201