EA027767B1 - Method for production of cold-worked, die-rolled section reinforcement steel for non-tensional reinforced concrete structures with improved ductility properties - Google Patents

Abstract

The invention is related to ferrous metallurgy and can be used for production of reinforcement steel of a three-side die-rolled section for non-tensional reinforced concrete structures of 400-600 MPa class, 4.0-14.0 mm in diameter. For production of cold-worked reinforcement steel of B and C ductility classes, the steel is subjected to induction heating in a drawing bench to a temperature of 350-450°C followed by cooling to a temperature of 100-150°C in a conveyor cooling tank or in a shower device. The lower temperature limit of 350°C is obtained by an empirical method. Heating to higher than 450°C results in a drastic drop of strength characteristics of steel. Cooling to a temperature of 100-150°C is required for provision of operating durability of coiling device assemblies. A rolled bar of the following chemical composition is used for blanks: carbon not more than 0.24%, manganese not more than 1.40%, silicon not more than 0.30%, nitrogen not more than 0.014%, iron and inevitable impurities - the balance. Carbon equivalent does not exceed 0.52. Scale removal from the rolled bar surface is performed in a drawing mill line in roller scale breakers. Section application is performed in non-driven roller stands providing a total reduction of up to 30%. Provision of the required class (conventional yield strength) of reinforcement steel is performed by adjustment of carbon and marganese content in the rolled bar. The required ductility class of reinforcement bars (B or C class) is provided by induction heating of ready reinforcement bars within a range of 350-450°C. According to the research performed, heating in the selected temperature range of 350-450°C makes it possible to ensure the required ductility class of cold-worked reinforcement steel (B or C class) without worsening its strength properties. Holding time does not influence any physical or mechanical properties, so one can use both accelerated quenching and reinforcement bar coiling at the heat treatment temperature.

Description

The invention relates to ferrous metallurgy and can be used for the production of reinforcing steel of a periodic profile for non-tensile reinforced concrete structures of class 400-600 MPa with a diameter of 4.0-14.0 mm

In accordance with European Norm ΕΝ 1992, Eurocode 2 [1] provides for 3 plasticity classes (Table 1). The traditional method of producing cold-deformed reinforcing steel in coils consists in applying a periodic profile (ribs) to a hot-rolled billet in a non-driven rolling stand (rolling cassette, roller draw) with a relative deformation (exhaust) of up to 30%.

Table 1. The main plastic characteristics of reinforcing steel (in the straightened state)

Reinforcing plasticity class BUT IN FROM Minimum Conditional Limit fluidity, under, MPa 400-600 Total elongation, Ag1,% > 2.5 > 5.0 > 7.5 Ratio of temporary tensile strength to conditional yield strength, Ov / Oo, 2 > 1.05 > 1.08 ΑΙ VI

In the manufacture of reinforcing steel by cold deformation of a hot-rolled billet in a rolling stand, the necessary geometric parameters of the ribs are provided (to meet the requirements for the anchoring ability of the reinforcement), the requirements for the conditional yield strength and temporary tensile strength. At the same time, the ductility indicators sharply decrease: the ratio of the temporary tensile strength to the conditional yield strength (σ _Β / σ ₀ , ₂ ), the total elongation at maximum load (Αβί). This technology allows to obtain cold-deformed reinforcing steel, which corresponds to ductility class A.

To increase the ductility of cold-deformed reinforcement, alternating bending devices are used, for example, a method for producing reinforcing wire is known, where a wire rod is used as a billet, from low-carbon steel with a carbon content of 0.060.12%; drawing is carried out with a total deformation of 14-22% and the formation of a profile with several longitudinal rows of ribs inclined to its axis on the workpiece in a fine multi-roller die; deformation by alternating bending is carried out without preheating, with a hood comprising 14-22% along the symmetry planes of the workpiece section passing through the rows of ribs, with the ratio of the working diameter of the rollers to the diameter of the workpiece in a bend section of 7-15, ensuring at least three bends blanks in each plane [2].

This method does not allow to obtain reinforcing steel of plasticity classes B and C.

To date, the main methods for producing reinforcing steel of ductility classes B and C are the LGSZsItd process (hardening of hot-rolled reinforcement in the cold state) and hot rolling [3]. It is not advisable to use the ZI'sTsNtd process in the manufacture of reinforcing bars of thin diameters. Hot rolled reinforcing steel with high ductility has low strength and performance properties (the presence of scale on the surface, low quality of winding in the riot, low corrosion resistance).

The objective of the invention is to obtain cold-deformed reinforcing steel in coils with a diameter of 4.0-14.0 mm plasticity classes B and C.

1. The essence of the proposed method for the production of cold-deformed reinforcing steel of a periodic profile for non-tensile reinforced concrete structures with increased ductility, differs in that in the line of the drawing mill is the induction heating of the finished reinforcing steel to a temperature of 350-450 ° C followed by cooling to a temperature of 100-150 ° C in bathtub or in the shower unit. A wire rod with the following chemical composition is used as a preform: carbon no more than 0.24%, manganese no more than 1.40%, silicon no more than 0.30%, nitrogen no more than 0.014%, iron and unavoidable impurities - the rest. The carbon equivalent is not more than 0.52. Scale removal from the surface of the wire rod is carried out in the line of the drawing mill in roller descalers. The profile is applied in non-driven roller stands with a total compression of up to 30%. The lower temperature limit of 350 ° C was obtained by the empirical method. Heating above 450 ° C leads to a sharp decrease in the strength characteristics of steel. Cooling to a temperature of 100-150 ° C is necessary to ensure the operational stability of the nodes of the winding device.

The invention is characterized by drawings, where in FIG. 1 depicts a drawing mill in accordance with the claimed method with a cooling bath or a shower unit. In FIG. 1 marked: 1 wire rod rip, 2 - unwinding device, 3 - roller descaler, 4 - lubrication unit, 5 - drawing drum, 6 - non-driven roller cassette (rolling stand), 7 - induction heater, 8 - passage cooling bath (choking device), 9 - dual drum, 10 - straightening device 1 027767 shaft device, 11 - bypass roller, 12 - reeling device.

2. It differs from claim 1 in that cooling to a temperature of 100-150 ° C is carried out on an air or water-cooled drawing drum due to the large number of turns of the valve.

In FIG. 2 shows a drawing mill in accordance with the claimed method with an air or water-cooled drawing drum. In FIG. 2 are marked: 1 - wire rod rip, 2 - unwinding device, 3 - roller descaler, 4 - lubrication unit, 5 drawing drum, 6 - non-driven roller cassette (rolling stand), 7 - induction heater, 8 - air or water cooled drawing drum, 9 - leveling device, 10 - bypass roller, 11 - reeling device.

3. It differs from claim 1 in that accelerated cooling is not used. The winding of the reinforcement is carried out on a winding device equipped with automatic linking of coils, which can produce winding of reinforcing steel at a temperature of 350-450 ° С.

In FIG. 3 shows a drawing mill in accordance with the claimed method with a winding device equipped with automatic linking of coils, which can produce winding of reinforcing steel at a temperature of 350-450 ° C. In FIG. 3 are designated: 1 - wire rod rip, 2 - unwinding device, 3 - scale descaler, 4 - lubrication unit, 5 - non-driven roller cassette (rolling stand), 6 - drawing drum, 7 - induction heater, 7 - winding device with automatic coordination of skeins (special design allowing to ensure operation at temperatures up to 450 ° C).

The installation location of the induction heating device and accelerated cooling devices can be changed depending on the specific layout of the drawing line.

Using the above schemes can significantly increase the plastic characteristics of cold-deformed reinforcing steel without reducing its strength characteristics, due to the removal of internal stresses arising during the application of the profile.

Ensuring the required class (conditional yield strength) of reinforcing steel is carried out by regulating the requirements for the content of carbon and manganese in wire rod. The required class of plasticity of reinforcement (class B or C) is provided by induction heating of the finished reinforcement in the range of 350-450 ° C.

The tests according to this invention were carried out in the conditions of BMZ OJSC, a management company of BMK holding on valves with a diameter of 6.0 and 8.0 mm, class 500 MPa. The test results of reinforcing steel are presented in table. 1 and 2.

Table 1. Results of physical and mechanical tests of reinforcement with a diameter of 8.0 mm under various heat treatment modes

Manufacturing Method ¹ Tensile strength, N / mm ² Conventional yield strength, N / mm ² Attitude before, durable. to conv. before, fluid. Total elongation at maximum load A _{8 {>} % ~ x /? 619-620 620 ² 538-556 554 1.12-1.15 1.13 2.9-4.8 3.8 X / d + heating 625-632 535-538 1.17-1.18 3.6-5.1 250 ° C. Without excerpts 628 536 1.17 • 4.2 X / d + heating 631-635 540-545 1.16-1.17 4.8-4.8 250 ° C. 2 hours exposure 633 543 1,166 4.8 X / d + heating 643-648 530-540 1.20-1.21 6.8-7.5 350 ° C. Without excerpts 645 536 1.20 7.2 X / d + heating 641-648 527-542 1.20-1.22 6.4-7.5 350 ° C. 644 534 1.21 6.9

2 hours exposure H / d + Heating 450 ° C. Without excerpts - 624-638 631 505-531 514 1.20-1.25 1.23 5.7-10.4 8.0 H / d + Heating 625-628 501-503 1.25-1.26 450 ° C. 2 hours exposure 626 502 1.25 9.3

- 2 027767

Table 2. The results of physical and mechanical tests of reinforcement with a diameter of 6.0 mm under various heat treatment modes

Preparation method Tensile strength, N / mm ² Conventional yield strength, N / mm ² Attitude before, durable. to conv. before, fluid. Total elongation at maximum load A _e % H / d ³ 604-607 605 ² 512-532 523 1.14-1.17 1.15 4.7-5.3 5.1 X / d + heating 350-450 ° C. Water cooling to 100-150 ° C 628-633 630 527-549 539 1.15-1.19 1.16 3.8-5.6 4.7 X / d + heating 350-450 ° C. Cooling in water to room temperature 633-635 634 543-552 547 1.15-1.16 1,159 3.4-4.9 4.2 X / d + heating 350-450 ° C. Air cooling to room temperature 641-645 643 526-535 535 1.20-1.22 1,210 6.6-7.4. 7D

- The samples were cooled to room temperature in air.

- The denominator indicates the average value.

- Cold deformation.

According to the studies, heating in a selected temperature range of 350-450 ° C allows us to provide the required plasticity class of cold-deformed reinforcing steel (class B or C) without reducing its strength properties. The exposure time does not affect the physicomechanical characteristics, which makes it possible to use both accelerated cooling and winding of the reinforcement at the processing temperature.

The inventive method has signs of novelty and can be implemented in industry. The main element of the novelty is the induction heating of the finished fittings in the line of the drawing mill to a temperature of 350-450 ° C.

Literature:

1. ΕΝ 1992-1-1-2009.

2. Patent 2302916 of the Russian Federation. Method for the production of reinforcing wire / Kireev E.M., Shulyak M.N., Stolyarov A.V., Soloviev S.V. IPC B211C 1/00. Publ. 2007.

3. V.A. Kharitonov, I.M. Petrov. Current state and directions of development of technological processes for the production of steel grades - Production of rolled products - No. 1 -2014 -С.28-32.

Claims (1)

CLAIM A method for the production of cold-deformed reinforcing steel of a periodic profile for non-tensile reinforced concrete structures with increased ductility, including descaling from the surface of the wire rod in the drawing line in roller descalers, applying a profile in non-driven roller stands with a total compression of up to 30% on a hot-rolled billet with the following chemical composition: carbon not more than 0.24%, manganese not more than 1.40%, silicon not more than 0.30%, nitrogen not more than 0.014%, iron and unavoidable impurities - the rest, tlichayuschiysya in that the line drawing machine performed induction heating finished reinforcing steel to a temperature of 350-450 ° C, followed by cooling to a temperature of 100-150 ° C in a continuous bath or dushiruyuschem device.