CA1201960A - Method of manufacturing steel reinforcements for concrete, having improved properties - Google Patents
Method of manufacturing steel reinforcements for concrete, having improved propertiesInfo
- Publication number
- CA1201960A CA1201960A CA000406914A CA406914A CA1201960A CA 1201960 A CA1201960 A CA 1201960A CA 000406914 A CA000406914 A CA 000406914A CA 406914 A CA406914 A CA 406914A CA 1201960 A CA1201960 A CA 1201960A
- Authority
- CA
- Canada
- Prior art keywords
- yield strength
- concrete
- log
- elongation
- mpa
- 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
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
- C21D1/02—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
-
- 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
- C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
- C21D9/525—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length for wire, for rods
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Thermal Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- Mechanical Engineering (AREA)
- Physics & Mathematics (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Manufacturing & Machinery (AREA)
- Heat Treatment Of Steel (AREA)
- Metal Rolling (AREA)
- Heat Treatment Of Strip Materials And Filament Materials (AREA)
- Manufacturing Of Tubular Articles Or Embedded Moulded Articles (AREA)
- Reinforcement Elements For Buildings (AREA)
Abstract
ABSTRACT
In order to achieve a yield strength of between 400 and 600 MPa and an elongation of at least 14%, steel reinforcing bars are rapidly cooled during or immediately after rolling.
The mean calorific flux density, ? (MW/m2), between 800 and 600°C and the duration of cooling, t (seconds), satisfy the following conditions:
0.45 d - 0.4<? . t<0.82 d + 0.6 log?? ,- 0964 log d + 2.098 in which d (mm) is the bar diameter.
In order to achieve a yield strength of between 400 and 600 MPa and an elongation of at least 14%, steel reinforcing bars are rapidly cooled during or immediately after rolling.
The mean calorific flux density, ? (MW/m2), between 800 and 600°C and the duration of cooling, t (seconds), satisfy the following conditions:
0.45 d - 0.4<? . t<0.82 d + 0.6 log?? ,- 0964 log d + 2.098 in which d (mm) is the bar diameter.
Description
6~3 The present invention relates to a method for the economical manufac~ure of steel reinforcements for concrete, haviny both a high yield strength and a high ductility as well as, if required, good weldability. Manufacture is carried out by a rapid cooling treatment applied dur;ng or immediately after rolling.
It is known ~hat the rolling mill operator who wishes to solve the problem stated above must take into account several constraints which are imposed on him. In th2 first instance, the outpu~ speed and ~emperature of rolled bars are in practice fixed by his rolling mill. In addition, the rolling mill operator has limited space for the possible installa~ion of a cooling plant.
There are already several solutions enabling a compromise between mechanical properties, on one hand~ and cost price, on ~he other hand. A first solution is to produce "naturally hard" steel bars whose yield strength is obtained by the addition oF carbon (for example 0.35%) and manganese (for example 1.370). These steels have an acceptable yield strength (at least 420 MPa), but the~r elongation and bendability are comparatively low and their weldability is not good at all.
In order to improve weldability it is necessary to decrease the carbon content, which causes a decrease in the yield strength.
. , ., ~'~
o There are two known ways of offsetting this decrease in the yield strength. The first is to incorporate microalloying elements, such as niobium or vanad;um, in ~he steel. Th~s technique is costly, however, as a result of the price of the 2110ying elements. The second way is to increase the yie1d strength of the steel by cold deformation of the bar, for e~ample by torsion. In adclition to the costs which this operation involves, the yield strength increase is provided to the detriment of the elongation.
The method of the present invention is based on the recent technique which consists in applying rapid cooling (which is limited in time~ to the hot rolled concrete reinforcements in order to produce a surface layer of martensite or bainite in the bar. This quenching is followed by cool;ng during which the core of the bar, i.e. the portion which has not been reached by the rapid cooling3 is converted into ferrite and carbides. By suitably limitlng the duration of the rapid cooling it is also possible to preserve heat in the core of the bar and to create a temperature gradient in the cross-section of the bar such that, during the sald further cooling9 tempering of the martensitlc or bainitic surface layer takes place. A suitable limitation of the duration of the rapid cooling may be ensured by aiming for a given temperature of the core at the end of the rapid cooling state~ In practlce, an operation of this type may be carried out by observing the temperature of the surface at the location of the bar where re-heating is observed as a result of the heat coming from the core.
A method of this type, commonly kno~n as "quenching and self-tempering" may therefore be applied - in a given plant with known specifications for manufacturing given reinforcements - on the basis of the characteristic constituted by the core temperature at the end of the rapid cooling phase.
It has been claimed in addition thal this temperature should be approximately 850C in order to proYide a combination, considered to be optimum, of the yield strength and elongation of the reinforcemen~.
The use of this combination obviously leads to the production of reinforcements of improved quality. As the operator has available this operating condition, he is able to select the means to be used to obtain the said required temperature.
The method of the present invention is designed to specify the parameters for each product which are characteristic o~ a rapid cooling plant and which confer the reinforcements the desired properties. It is known that these parameters are, on one hand, the intensity o~ the rapid cooling, i.e.
the mean densi~y of calor~fic flux, given here at between 800 and 600C, commonly designated by ~ and expressed in MW/m2 and, on the other hand, the duration of the rapid cooling designated by t and expressed in seconds.
This method may in partioular be applied to the production of steel reinforcements having mechanical properties satisfying quality standards9 for example a yield strength of between 400 and 600 MPa and an elongation of at least 14%.
~2~ i0 In the method of manufacture of steel reinforcements to which the present invenkion relates, in which khe bars are rapidly cooled during or immediately after rooling, the parameters ~ and k for regulating the rapid cooling simultaneously satisfy the following conditions:
0~45 d - 0~4 ' ~ . t ~ 0.82. d + 0.6 log~ ~ - 0.~64 . log d ~ 2.098 in which d represents the diameter of the treated bar in mm.
The method of the invention enables the achievement of 1~ the most advantageous product with respect to the combination of the mechanical properties. On one hand the volume of the martensit~c/bainitic area as well as its degree of softening by self-tempering are such that they lead to a high yield strength On the o~her hand~ the elongation still remains within the deslred limits.
A first example of applicat~on o~ the method oF the invention relates to the manufacture of bars having a diameter of 20 mm which are discharged from the rolling mill at a speed of 12 m/s and at a temperature of 1050C. For reasons of weldability and economy, the chemical composition of the steel is contained within a given range, for example 0.10 - 0 20b C, n.s 1 3% Mn. In the case in question, the stee1 contained 0.13% C and 1.2% Mn. In the as~rolled condition it had a yield strength of approximately 365 MPa and an elongation of 22 to 24%.
In order to obtain steel reinforcements, for concrete, having an improved yield strength and ductility, the rolling mill operator selects, in accordance with the equipment and space a~ailable, a plant whose rapid cooling intensity and length (therefore duration of ~reatment) correspond to the above conditions, i.e.
~ ~ 7 MW/m2 8.6 ~ ~ .t ~ 17.
The selection of a plant whose average calorific flux density between 800 and 600C is 10 MW/m and whose length, L, is 12 m, leads to a yield strength of 500 MPa and an elongation of 20.6%. The s~lection of a plant whose characteristics are ~ = 8.4 MW/m2 and L = 20.5 m would provide a steel reinforcement having a yield strength of 550 MPa and an elonga$ion of 18.5%. In thls case, the duration of treatment would be 1.7 seconds and the product ~ ould be 14.350 A second example relates to the manufacture of bars of 8 mm in diameter which are discharged from ~he rolling mill at a speed of 18 m/s and at a temperature of approximately 1000C. The steel contains 0.18% and 0.8% Mn. In the as-rolled condition, it has a yield strength of 325 MPa and an elongation of approximately 30%.
In this case, the limits imposed by the method of the invention are:
/
~Z~1~60 ~ ~r/ 17 MW/m2 3.2 ~ ~ . t < 7.16.
If a plant is selected having ~ = 17 MW/mm2 with a length of treatment L ~ 4.5 m9 bars are obtained having a yield strength of 500 MPa and an elongation of 18%. In this case, the duration of treatment would be 0.25 s and ~he product ~ . t would be 4.25. The same properties were obtained with ~ = 25 MW/m2 and a duration of treatmen~
of 0.17 seconds, i.e. a rapid coo1ing 1ength of 3 m.
It is known ~hat the rolling mill operator who wishes to solve the problem stated above must take into account several constraints which are imposed on him. In th2 first instance, the outpu~ speed and ~emperature of rolled bars are in practice fixed by his rolling mill. In addition, the rolling mill operator has limited space for the possible installa~ion of a cooling plant.
There are already several solutions enabling a compromise between mechanical properties, on one hand~ and cost price, on ~he other hand. A first solution is to produce "naturally hard" steel bars whose yield strength is obtained by the addition oF carbon (for example 0.35%) and manganese (for example 1.370). These steels have an acceptable yield strength (at least 420 MPa), but the~r elongation and bendability are comparatively low and their weldability is not good at all.
In order to improve weldability it is necessary to decrease the carbon content, which causes a decrease in the yield strength.
. , ., ~'~
o There are two known ways of offsetting this decrease in the yield strength. The first is to incorporate microalloying elements, such as niobium or vanad;um, in ~he steel. Th~s technique is costly, however, as a result of the price of the 2110ying elements. The second way is to increase the yie1d strength of the steel by cold deformation of the bar, for e~ample by torsion. In adclition to the costs which this operation involves, the yield strength increase is provided to the detriment of the elongation.
The method of the present invention is based on the recent technique which consists in applying rapid cooling (which is limited in time~ to the hot rolled concrete reinforcements in order to produce a surface layer of martensite or bainite in the bar. This quenching is followed by cool;ng during which the core of the bar, i.e. the portion which has not been reached by the rapid cooling3 is converted into ferrite and carbides. By suitably limitlng the duration of the rapid cooling it is also possible to preserve heat in the core of the bar and to create a temperature gradient in the cross-section of the bar such that, during the sald further cooling9 tempering of the martensitlc or bainitic surface layer takes place. A suitable limitation of the duration of the rapid cooling may be ensured by aiming for a given temperature of the core at the end of the rapid cooling state~ In practlce, an operation of this type may be carried out by observing the temperature of the surface at the location of the bar where re-heating is observed as a result of the heat coming from the core.
A method of this type, commonly kno~n as "quenching and self-tempering" may therefore be applied - in a given plant with known specifications for manufacturing given reinforcements - on the basis of the characteristic constituted by the core temperature at the end of the rapid cooling phase.
It has been claimed in addition thal this temperature should be approximately 850C in order to proYide a combination, considered to be optimum, of the yield strength and elongation of the reinforcemen~.
The use of this combination obviously leads to the production of reinforcements of improved quality. As the operator has available this operating condition, he is able to select the means to be used to obtain the said required temperature.
The method of the present invention is designed to specify the parameters for each product which are characteristic o~ a rapid cooling plant and which confer the reinforcements the desired properties. It is known that these parameters are, on one hand, the intensity o~ the rapid cooling, i.e.
the mean densi~y of calor~fic flux, given here at between 800 and 600C, commonly designated by ~ and expressed in MW/m2 and, on the other hand, the duration of the rapid cooling designated by t and expressed in seconds.
This method may in partioular be applied to the production of steel reinforcements having mechanical properties satisfying quality standards9 for example a yield strength of between 400 and 600 MPa and an elongation of at least 14%.
~2~ i0 In the method of manufacture of steel reinforcements to which the present invenkion relates, in which khe bars are rapidly cooled during or immediately after rooling, the parameters ~ and k for regulating the rapid cooling simultaneously satisfy the following conditions:
0~45 d - 0~4 ' ~ . t ~ 0.82. d + 0.6 log~ ~ - 0.~64 . log d ~ 2.098 in which d represents the diameter of the treated bar in mm.
The method of the invention enables the achievement of 1~ the most advantageous product with respect to the combination of the mechanical properties. On one hand the volume of the martensit~c/bainitic area as well as its degree of softening by self-tempering are such that they lead to a high yield strength On the o~her hand~ the elongation still remains within the deslred limits.
A first example of applicat~on o~ the method oF the invention relates to the manufacture of bars having a diameter of 20 mm which are discharged from the rolling mill at a speed of 12 m/s and at a temperature of 1050C. For reasons of weldability and economy, the chemical composition of the steel is contained within a given range, for example 0.10 - 0 20b C, n.s 1 3% Mn. In the case in question, the stee1 contained 0.13% C and 1.2% Mn. In the as~rolled condition it had a yield strength of approximately 365 MPa and an elongation of 22 to 24%.
In order to obtain steel reinforcements, for concrete, having an improved yield strength and ductility, the rolling mill operator selects, in accordance with the equipment and space a~ailable, a plant whose rapid cooling intensity and length (therefore duration of ~reatment) correspond to the above conditions, i.e.
~ ~ 7 MW/m2 8.6 ~ ~ .t ~ 17.
The selection of a plant whose average calorific flux density between 800 and 600C is 10 MW/m and whose length, L, is 12 m, leads to a yield strength of 500 MPa and an elongation of 20.6%. The s~lection of a plant whose characteristics are ~ = 8.4 MW/m2 and L = 20.5 m would provide a steel reinforcement having a yield strength of 550 MPa and an elonga$ion of 18.5%. In thls case, the duration of treatment would be 1.7 seconds and the product ~ ould be 14.350 A second example relates to the manufacture of bars of 8 mm in diameter which are discharged from ~he rolling mill at a speed of 18 m/s and at a temperature of approximately 1000C. The steel contains 0.18% and 0.8% Mn. In the as-rolled condition, it has a yield strength of 325 MPa and an elongation of approximately 30%.
In this case, the limits imposed by the method of the invention are:
/
~Z~1~60 ~ ~r/ 17 MW/m2 3.2 ~ ~ . t < 7.16.
If a plant is selected having ~ = 17 MW/mm2 with a length of treatment L ~ 4.5 m9 bars are obtained having a yield strength of 500 MPa and an elongation of 18%. In this case, the duration of treatment would be 0.25 s and ~he product ~ . t would be 4.25. The same properties were obtained with ~ = 25 MW/m2 and a duration of treatmen~
of 0.17 seconds, i.e. a rapid coo1ing 1ength of 3 m.
Claims
1. A method of manufacturing a steel reinforcement for concrete, having a yield strength of between 400 and 600 MPa and an elongation at least equal to 14%, in which steel reinforcing bars are rapidly cooled during or immediately after rolling, the mean calorific flux density between 800 and 600°C, designated by ? and expressed in MW/m2, and the duration of cooling, designated by t and expressed in seconds, simultaneously satisfying the Following conditions:
0.45 d - 0.4 < ? . t 0.82 d + 0.6 log? ? - 0.964 log d + 2.098 in which d represents the diameter of the bar expressed in mm.
0.45 d - 0.4 < ? . t 0.82 d + 0.6 log? ? - 0.964 log d + 2.098 in which d represents the diameter of the bar expressed in mm.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| BE889575 | 1981-07-09 | ||
| BE6/47492A BE889575A (en) | 1981-07-09 | 1981-07-09 | PROCESS FOR THE MANUFACTURE OF STEEL CONCRETE REINFORCEMENTS WITH IMPROVED PROPERTIES. |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1201960A true CA1201960A (en) | 1986-03-18 |
Family
ID=3874897
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000406914A Expired CA1201960A (en) | 1981-07-09 | 1982-07-08 | Method of manufacturing steel reinforcements for concrete, having improved properties |
Country Status (21)
| Country | Link |
|---|---|
| JP (1) | JPS589920A (en) |
| KR (1) | KR870001090B1 (en) |
| AT (1) | AT375401B (en) |
| AU (1) | AU536703B2 (en) |
| BE (1) | BE889575A (en) |
| BR (1) | BR8108179A (en) |
| CA (1) | CA1201960A (en) |
| CH (1) | CH639137A5 (en) |
| DD (1) | DD202309A5 (en) |
| DK (1) | DK152691C (en) |
| ES (1) | ES513811A0 (en) |
| FI (1) | FI72748C (en) |
| GR (1) | GR77249B (en) |
| IE (1) | IE53019B1 (en) |
| IN (1) | IN154221B (en) |
| LU (1) | LU84263A1 (en) |
| MX (1) | MX159859A (en) |
| NO (1) | NO156903C (en) |
| SE (1) | SE462853B (en) |
| YU (1) | YU42779B (en) |
| ZA (1) | ZA818244B (en) |
Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS6066099A (en) * | 1983-09-21 | 1985-04-16 | Hitachi Ltd | Temperature balance control of multistage heat exchanger |
| CH681603A5 (en) * | 1984-05-30 | 1993-04-30 | Von Roll Ag | |
| JPS61110897A (en) * | 1984-11-06 | 1986-05-29 | Toshiba Corp | Flow rate control method of heat exchanger |
| DD234281B1 (en) * | 1984-12-21 | 1989-06-21 | Florin Stahl Walzwerk | METHOD FOR PRESSURE WATER TREATMENT OF ROLLING STEEL PRODUCTS |
| KR101225251B1 (en) * | 2010-09-29 | 2013-01-22 | 현대제철 주식회사 | Apparatus for manufacturing high-strength steel bars in adjusting metallugical transformation and the method thereof |
| RU2583554C1 (en) * | 2015-01-22 | 2016-05-10 | Акционерное общество "Научно-исследовательский центр "Строительство" (АО "НИЦ "Строительство") | Method for production of hardened reinforcing bar of periodic profile |
-
1981
- 1981-07-09 BE BE6/47492A patent/BE889575A/en not_active IP Right Cessation
- 1981-08-21 IN IN934/CAL/81A patent/IN154221B/en unknown
- 1981-08-31 CH CH559081A patent/CH639137A5/en not_active IP Right Cessation
- 1981-10-14 DK DK455481A patent/DK152691C/en active
- 1981-11-13 JP JP56182941A patent/JPS589920A/en active Granted
- 1981-11-27 ZA ZA818244A patent/ZA818244B/en unknown
- 1981-12-16 BR BR8108179A patent/BR8108179A/en unknown
- 1981-12-18 AU AU78624/81A patent/AU536703B2/en not_active Ceased
-
1982
- 1982-07-07 SE SE8204207A patent/SE462853B/en not_active IP Right Cessation
- 1982-07-07 GR GR68675A patent/GR77249B/el unknown
- 1982-07-08 AT AT0265382A patent/AT375401B/en not_active IP Right Cessation
- 1982-07-08 CA CA000406914A patent/CA1201960A/en not_active Expired
- 1982-07-08 NO NO822384A patent/NO156903C/en unknown
- 1982-07-08 YU YU1497/82A patent/YU42779B/en unknown
- 1982-07-08 IE IE1651/82A patent/IE53019B1/en not_active IP Right Cessation
- 1982-07-08 FI FI822426A patent/FI72748C/en not_active IP Right Cessation
- 1982-07-08 ES ES513811A patent/ES513811A0/en active Granted
- 1982-07-08 LU LU84263A patent/LU84263A1/en unknown
- 1982-07-09 MX MX193521A patent/MX159859A/en unknown
- 1982-07-09 KR KR8203079A patent/KR870001090B1/en active
- 1982-07-09 DD DD82241555A patent/DD202309A5/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| ES8401530A1 (en) | 1983-12-01 |
| DK152691B (en) | 1988-04-18 |
| FI822426A0 (en) | 1982-07-08 |
| IE821651L (en) | 1983-01-09 |
| NO156903B (en) | 1987-09-07 |
| JPS589920A (en) | 1983-01-20 |
| CH639137A5 (en) | 1983-10-31 |
| IN154221B (en) | 1984-10-06 |
| GR77249B (en) | 1984-09-11 |
| MX159859A (en) | 1989-09-21 |
| ZA818244B (en) | 1983-04-27 |
| NO156903C (en) | 1987-12-16 |
| DD202309A5 (en) | 1983-09-07 |
| AT375401B (en) | 1984-08-10 |
| BE889575A (en) | 1982-01-11 |
| AU7862481A (en) | 1983-01-13 |
| SE8204207L (en) | 1983-01-10 |
| DK455481A (en) | 1983-01-10 |
| FI822426L (en) | 1983-01-10 |
| YU42779B (en) | 1988-12-31 |
| ES513811A0 (en) | 1983-12-01 |
| NO822384L (en) | 1983-01-10 |
| BR8108179A (en) | 1983-04-12 |
| YU149782A (en) | 1985-04-30 |
| LU84263A1 (en) | 1983-02-07 |
| KR840000653A (en) | 1984-02-25 |
| FI72748C (en) | 1987-07-10 |
| DK152691C (en) | 1988-08-29 |
| SE462853B (en) | 1990-09-10 |
| IE53019B1 (en) | 1988-05-11 |
| KR870001090B1 (en) | 1987-06-04 |
| AU536703B2 (en) | 1984-05-17 |
| SE8204207D0 (en) | 1982-07-07 |
| FI72748B (en) | 1987-03-31 |
| JPS6219488B2 (en) | 1987-04-28 |
| ATA265382A (en) | 1983-12-15 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |