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

Definitions

• the present invention relates to a reinforcing steel or concrete bar having high mechanical strength, easily souda- bl e to a predetermined content of carbon, which is resistant to corrosion by the air, which satisfies optimally the requirements of modern construction.
• This steel is particularly useful in the construction of concrete elements with complex properties, which must have good bearing properties and be able to be used under high temperature conditions as well as in the preparation of formwork constructions using these concrete elements.
• Concrete is one of the most used building materials, which has a high compressive strength, but a low tensile strength.
• This drawback of concrete has been resolved in construction by introducing concrete construction elements, steel bars or steel reinforcements into the traction zone which absorb the tensile stresses and relieve the concrete of such stresses. These steel reinforcements are what are called reinforcing bars.
• Concrete rods can be divided into two groups according to their way of introduction or the constraints to which they are intended to be subjected. The method of use at the same time determines the requirements for such steels.
• the concrete reinforcing bars are intended to absorb or eliminate after their introduction, the tensile and shear stresses of the construction.
• These reinforcing steels are hot rolled, they are most often round unalloyed or low alloyed steels provided with ribs and of a quality which can be welded or not.
• the hot-rolled concrete rods must have an apparent limit of elasticity guaranteed, appropriate flexibility, ribs increasing the adhesion necessary for the transfer of forces and, if necessary, they must be able to be welded.
• the tensile stresses of the construction are eliminated by the rounds at concrete, by prestressing concrete elements.
• This method of use significantly reduces the weight of the construction.
• the reinforcing steels or reinforcing bars are drawn with a tensile force corresponding to the elastic limit, are prestressed and embedded in this state in the concrete.
• the concrete element is therefore prestressed in compression by the reinforcing steel embedded in it after solidification of the concrete; the prestress corresponding to the tension used during the prestressing of steel.
• the tension resulting from the stresses of the construction which are exerted in the element of concrete is lowered to a minimum acceptable value for the concrete.
• Pre-stressed reinforcing steel must therefore function as a tension spring, which determines the requirements for such steel.
• prestressed concrete rods are already different from the requirements for hot-rolled reinforcing steel because their function is not the same.
• Their apparent elastic limit must reach at least 80% of their tensile strength and in addition, the elasticity must exhibit minimum bending, appropriate relaxation and sensitivity to corrosion under low stress.
• the high tensile strength of reinforcing steels is also an essential industrial requirement.
• the greater the strength of the steel the greater in general the allowable working stress. This increases the value of use of prestressed concrete rods, and the loss of tensile force which is inevitable following the shrinking and slow deformation of the concrete thereby loses its importance.
• the embedded non-prestressed reinforcing steel which must be used in concrete, must have a plasticity which tolerates a crack in the concrete as a result of the bending stresses of the construction before the steel breaks, but which nevertheless prevents the reinforcing steel from being subjected due to this crack to the action of environmental corrosion .
• Reinforcing steels suitable for prestressing must still have favorable rheological properties and good resistance to corrosion under stress.
• Reinforcing steels which can be used under stress or not and which have appropriate mechanical strengths are currently known.
• the chemical composition of the reinforcing steels which are not used for prestressing is characterized in that the carbon content is most often not more than 0.60% by weight and that their manganese content is between 0.50 and 1.60% by weight.
• Some steels additionally contain 0.20 - 0.60% by weight of silicon and 0.03% by weight of niobium or vanadium.
• Steels which are used in hot-rolled form and which are not suitable for prestressing are generally weldable up to a carbon content of at most 0.20%.
• Their tensile strength is generally between 350 and 6 00 N / mm 2 and can be used in 40 to 60% of constructions.
• the tensile strength of the non-weldable range is between 600 and 800 Nlmm2, but only 30 to 40% can be used for the transmission of a bending which does not require a modification of final shape.
• the reinforcing steels used for prestressing are manufactured by deformation and cold and hot treatment processes, which are expensive and complicated, or by a combination of these treatments.
• Their chemical composition can be characterized by the fact that their carbon content is generally between 0.50 and 0.80% by weight and that their silicon content is between 1.00 - 2.00%, in manganese between 0.70 - 1.20% and some other elements and even 0.50 - 1.50% chromium and 0.30 - 0.80% molybdenum.
• a characteristic of their mechanical properties is a tensile strength between 1300 and 185 0 N / mm 2 and by a traction which requires a deformation of 0.05% which remains from 800 to 1200N / mm. The relaxation of these steels presents for a loaded to 70% of tensile strength good relaxation.
• the known and used reinforcing steels have a relatively low resistance. They can only be welded in very narrow areas of resistance and produced by complicated technological processes requiring a large workforce to obtain the spring effect necessary in modern uses and construction.
• the object of the invention is the preparation of a reinforcing steel which has a high mechanical resistance even in the hot rolled state and which can be welded up to a determined carbon content, which can be used as steel of prestressed reinforcement after a simple heat treatment for a higher carbon content than that previously possible, which exhibits excellent relaxation and stability to stress corrosion and which is suitable for the production of concrete or structural elements formwork which optimally meets the requirements of the construction but which can also be used at higher temperatures.
• the reinforcing steel according to the invention comprises, in addition to iron, at most 1.20% of carbon, at most 3.5% by weight of manganese, at most 2.80% by weight of silicon, at most 1.00% by weight of molybdenum, at most 3.00% by weight of copper and / or nickel, at most 0.15% by weight of zirconium and / or cerium, 0.04 to 0.30% by weight of niobium and / or vanadium, 0.008 to 0.035% by weight of nitrogen, 0.0005 to 0.025% by weight of calcium, 0.02 - 0.15% by weight of aluminum and 0.001 at 0.05% by weight of boron and / or beryllium.
• Steels more particularly preferred according to the invention comprise, in addition to iron and the usual residual elements, the following elements in the proportions indicated below.
• the properties of the constituents and their appropriate proportions in the alloy system according to the invention create physicochemical, kinetic as well as germination conditions such, during their dissolution, solidification, recrystallization and hot deformation that the availability of the constituents to enter interstitially into solution, the quantity of these constituents as well as the number and the degree of stress, of the networks prestressed in this way are markedly increased. Thanks to the increase in the number of networks with interstitial prestressing and their degree of stress, the number of metallurgical dislocations which promote or determine the formation, of metallic precipitates and the density of their disposition, is appreciably increased, which has the effect of increasing the effectiveness of the anchoring function precipitation during the frontal displacement of the dislocations caused by the charges.
• the speed of diffusion or the number of neighboring metal atoms is reduced, thereby also reducing the formation of inconsistent seeds.
• This avoids the formation of an inhomogeneous zone along the grain boundaries, by alloying elements or precipitation and that their mechanical resistance or their creep resistance decreases.
• the bursting which previously occurred at the grain boundaries as a result of the loads is therefore delayed and their elongation and contraction is increased during rupture by creep.
• the elements according to the invention, and their proportion make it possible to automatically obtain a remarkable metallurgical quality of the reinforcing steel during its production.
• the mechanical resistance as well as the endurance limit of the steel is increased by several times without cold treatment or deformation but by an effective combination of the consolidation mechanism.
• the non-weldable field it is possible to obtain in a very simple manner and with lower expenses mechanical strengths in particular higher as well as rheological properties more favorable than for known reinforcing steels.
• the reinforcing steel according to the invention contains in its chemical composition also alloying compounds which concentrate if necessary on the surface of the steel during the hot deformation process, and which form over time, at following atmospheric action on this surface a protective layer. This layer protects the steel from corrosion of the air and markedly reduces the corrosion rate in comparison with known non-alloy reinforcing steels.
• the reinforcing steel according to the invention is well weldable up to a determined carbon content and its properties are similar in the zone of thermal influence during welding, to the properties of the starting product.
• the reinforcing steel according to the invention can be prepared and worked with the same installations as the known reinforcing steels, which means that it does not require new installations and investments to be prepared in large quantities. It has remarkable mechanical properties and guarantees stability to air corrosion if necessary and widens the resistance range in which a welded joint can be used.
• the manufacturing costs of the products prepared from the steel according to the invention do not exceed the average level currently reached due to the improved mechanical strength.
• Three charges of a steel according to the invention are prepared.
• the charges bearing the references 1 and 2 which belong to the weldable area were prepared in a 70-ton arc furnace and then poured into 3.5-ton molds quadratic profile.
• the resulting cast ingots were then rolled under normal conditions into square blocks having a section of 180 mm, they were then rolled into concrete rods with grooves and a diameter of 16 mm and allowed to cool to air on a cooler.
• the load bearing the reference 3 which does not belong to the weldable field, was prepared in a 20-ton arc furnace and poured into an ingot mold of 6 tonnes with a quadratic profile. This charge was rolled in a similar manner to that of charges 1 and 2, and was prepared in the form of a grooved concrete rod with a diameter of 8 mm in rolled form and air-cooled.
• the results of the material tests are as follows:

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Reinforcement Elements For Buildings (AREA)
• Heat Treatment Of Steel (AREA)
• Manufacture Of Alloys Or Alloy Compounds (AREA)

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• 1979
  • 1979-06-08 DE DE7979101819T patent/DE2967517D1/de not_active Expired
  • 1979-06-08 AT AT79101819T patent/ATE15816T1/de not_active IP Right Cessation
  • 1979-06-08 EP EP79101819A patent/EP0022134B1/de not_active Expired

Patent Citations (6)

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