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
  • C21D8/06—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
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P10/00—Technologies related to metal processing
  • Y02P10/20—Recycling

Definitions

• the balance consisting essentially of iron by cooling it in quiet air from the hot-rolled state with the formation of bainite structure and, thereafter, either cold deforming it plastically without essential increase of tensile strength and tempering the same at a temperature in the range of 100 to 400 C. or tempering it in the temperature range between 150 and 550 C.
• This invention is directed to providing a steel composition particularly useful as a bar steel for prestressed concrete to lend support to such concrete. More particularly, this invention is directed to an unannealed reinforcing b ar steel to reinforce prestressed concrete provided by a process involving the selection of a suitable particular steel composition and treating the same either by cold-deforming the same plastically and subjecting it to a tempering operation carried out at a temperature between 100 and 400 C. or by tempering the same (without preceding cold-deforming) at a temperature between 150 and 550 C.
• Bar steels of greater strength would permit higher prestressing forces with the same steel cross section, or for a given prestressing force they would permit a reduction in the number of bars needed. This would not only permit a reduction in material costs but also it would reduce the manufacturing costs and make possible more slender constructions.
• the invention is aimed at accomplishing this objective, and its purpose was to manufacture an unannealed, plain or deformed reinforcing steel with a high tensile strength and a high notch ductility for prestressed concrete, in a dimensional range of from 15 to 60 millimeters diameter, with a minimum tensile strength of 120 ltg/mm. and a minimum reduction of area at failure of 25%.
• this invention contemplates a process for manufacturing an unannealed reinforcing bar steel for prestressed concrete which comprises providing a steel having a composition of:
• the steel of the present inveniton may contain an amount of molybdenum up to 0.40 Wt.-percent and/or a quantity of vanadium up to 0.40 wt.-percent and/or a quantity of boron up to 0.01 wt.-percent.
• molybdenum up to 0.40 Wt.-percent and/or a quantity of vanadium up to 0.40 wt.-percent and/or a quantity of boron up to 0.01 wt.-percent.
• the steel of the present invention can be prepared in essentially two different manners starting from the initial steel composition having the required contents of carbon, silicon, manganese, chromium, iron and the required relationship between the manganese and chromium.
• the steel is cooled from a temperature at or near the hot-roll end temperature in quiet air and thereafter cold-deforming the same after the steel has been cooled from the hot-rolled state and thereafter tempering at a temperature between 100 and 400 C.
• Another embodiment of the present invention involves tempering the steel cooled from the hot-rolling state without cold-deforming at a temperature between and 550 C.
• such steel is referred to as a plain steel in contrast to one which has been deformed.
• a tempering temperature between 300 and 500 C.
• time and temperature are inversely proportional to one another.
• temperatures at the lower portion of the range are employed, it is generally desirable to temper for a longer period of time than would be employed had the temperature been towards the upper limit of the range.
• the cold-deforming operation for the plain bars and the deformed bars is preferably carried out at a room temperature.
• the deformation of the steel generally by means of a cold stretching in a range from 0.1 to 1.0%, preferably in the range from 0.2 to 0.5%.
• the forces depend on the cross section and the yield point after cooling the steel in quiet air (as rolled condition).
• steels of the present invention have minimum tensile strengths of 120 kg./mm.
• such steels generally have a tensile strength between 120 and 180 kg./mm. preferably between 135 and 160 kg./ mmf They also have a minimum reduction of area at failure of at least 25%, generally at least 40%.
• the plastic deformation is done by stretching the bar so that it is elongated or extended in an amount between 0.1 and 1.0%.
• the deforming or stretching operation should be carried out over a period of time between 5 sec. and 3 min.
• the process of the present invention employs a tempering in the stated temperature ranges depending upon whether an as rolled or a cold-deformed steel is desired.
• the tempering operation should be carried out for a period of time between 1 min. and 12 hours, depending on whether it is done by continuous annealing or by batch annealing in a furnace.
• the strength of a 30 mm. bar for example can be estimated on the basis of the formula and a suitable composition can be selected accordingly.
• the tensile strength can be found in kg./mm. if the percentages of the alloying components are given in percentages by weight.
• the reinforcing steel has a content of 0.02 to 0.40 wt.-percent Mo and/ or 0.02 to 0.40 wt.-percent V and/or 0.001 to 0.01 wt.-percent B.
• the reinforcing bar made by the process of the invention attains considerably better strength values for equal toughness characteristics.
• the desired mechanical characteristics can be achieved either by a tempering operation e.g., one half hour at 400 C. bar steel with 26.4 mm. diameter or by stretching followed by tempering.
• the yield point can be adjusted to the desired value by varying the stretch percentage.
• the tempering operation that follows may be performed at 270 C. over a period of between 5 and -60 minutes, although its effect does not vary appreciably from that achieved by a tempering time of 5 minutes. In the case of tempering below 200 C. the tempering time would, in a known manner, have to be extended; if the tempering were performed at temperatures above 300 C. the time could be less than 5 minutes.
• the notch was made by machining; the notch depth was 0.5 mm., the notch radius was 0.25 mm. and the angle of the flanks was 45 TABLE II Steel used at the New steel, 30 mm. present time,
• the steel of the invention in spite of the sparing use of alloying elements and its uncomplicated and inexpensive method of manufacture, offers an outstanding and improved combination of properties, especially in regard to tensile strength and reduction of area at rupture. Furthermore, it is characterized by a very good creep resistance, which is especially important for use in prestressed concrete construction in which it is subject to long-term high tensile stress.
• the simple, inexpensive process of the present invention provides steels having a minimum tensile strength of 120 kg./mm. and a minimum reduction of area at failure of 25% and upwardly of about 43%. Additionally, the properties with respect to the notched steel are compared favorably with steels prepared by prior art processes. Note that such notched steels have substantially better elongation at rupture and compare quite favorably to prior art steels which 'have not been notched. The reduction of area at rupture for a notched steel is 17%, whereas the same value for the notched steel of the prior art is too small to measure. Thus, it is seen that the inexpensive process of the present invention provides steels which are substantially superior in elongation, tensile strength and reduction of rupture to those heretofore provided. Such has been provided with such steels even though the diameter is slightly less.
• unannealed steel in this description means that the steel is not subjected to a heat treatment consisting of hardening the steel by quenching it from hardening temperatures and subsequently tempering of the quenched (hardened) steel.
• a kg./mm. yield strength at a yield stress in kg./mrn.- at which the steel exhibits a deviation of 0.2% from proportionality of stress and strain;
• kg./mm. tensile strength in l g./mm. the maximum stress at fracture (breaking) in tensile test;
• Reduction of area at failure the difference, expressed as a percentage of the original cross-sectional area, between the original cross-sectional area of a tensile test specimen and the minimum cross-sectional area after complete separation;
• Plain bar means a bar with a smooth surface
• deformed bar means a bar equipped with ribs or the like on its surface.
• the balance consisting essentially of iron and hot rolling it followed by immediate cooling from a temperature at or near the hot roll temperature in quiet air, thereafter, either cold-deforming the same plastically without substantial strength increase and thereafter tempering it at temperatures between and 400 C. or tempering the same at a temperature between and 550 C.
• a process according to claim 1 wherein the steel composition is selected to satisfy the formula 9.
• a process according to claim 1 wherein the tempering is carried out over a period of time between one minute and twelve hours, wherein the shorter times belong to continuous annealing and the longer time batch annealing.

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

Applications Claiming Priority (1)

Publications (1)

Family

ID=5811654

Family Applications (1)

Country Status (17)

Cited By (35)

Families Citing this family (2)

• 1971
  • 1971-06-24 DE DE2131318A patent/DE2131318C3/de not_active Expired
• 1972
  • 1972-05-18 IT IT50341/72A patent/IT965788B/it active
  • 1972-05-24 LU LU65413D patent/LU65413A1/xx unknown
  • 1972-05-29 BE BE784097A patent/BE784097A/xx not_active IP Right Cessation
  • 1972-06-01 ZA ZA723765A patent/ZA723765B/xx unknown
  • 1972-06-16 ES ES403952A patent/ES403952A1/es not_active Expired
  • 1972-06-20 US US00264669A patent/US3810793A/en not_active Expired - Lifetime
  • 1972-06-20 TR TR17213A patent/TR17213A/xx unknown
  • 1972-06-20 SE SE7208115A patent/SE382076B/xx unknown
  • 1972-06-21 GB GB2904072A patent/GB1334349A/en not_active Expired
  • 1972-06-22 BR BR4065/72A patent/BR7204065D0/pt unknown
  • 1972-06-22 CH CH938972A patent/CH586751A5/xx not_active IP Right Cessation
  • 1972-06-22 AT AT538772A patent/AT327977B/de not_active IP Right Cessation
  • 1972-06-23 NL NL7208702.A patent/NL156446B/xx not_active IP Right Cessation
  • 1972-06-23 FR FR7222791A patent/FR2143382B1/fr not_active Expired
  • 1972-06-24 JP JP47063630A patent/JPS52446B1/ja active Pending
  • 1972-06-26 CA CA144,079A patent/CA958311A/en not_active Expired

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