RU2768064C1 - Method for production of cold-deformed steel reinforcement of periodic profile with increased plastic properties - Google Patents

Abstract

FIELD: reinforcing steel production.SUBSTANCE: invention relates to the production of cold-deformed steel reinforcement of a periodic profile with increased plastic properties. The wire rod is fed from the unwinding device to the scale breaker and transferred to a roller cage, in which the wire rod is deformed to obtain a periodic profile reinforcement. At the same time, a wire rod with a carbon content of up to 0.24% is used, the total compression in the roller cage is adjusted to 40% with a minus tolerance field for the diameter of cold-deformed reinforcing steel. Stepwise heat treatment of the finished reinforcement is carried out in coils with heating to t = 300-600°C and exposure at a given temperature for austenitization and alignment of the steel structure, followed by uniform cooling together with the furnace and then in air to obtain a relative elongation of Agt≥5.9% and a ratio of σв/σ0.2≥1.09.EFFECT: as a result, the plastic properties of cold-formed reinforcing steel increase without reducing its strength properties.1 cl, 1 dwg, 2 tbl, 1 ex

Description

The invention relates to the technology of forming metals and can be used in the manufacture of fittings from low-carbon steels.

A known method for the production of cold-formed reinforcing steel of a periodic profile for non-stressed reinforced concrete structures, with increased ductility (see the number of the Eurasian application No. 201401338, IPC B21 C 1/00; C21 D 8/08; C 22 C 38/04, the published patent search is completed May 28, 2015).

The essence of the proposed method for the production of cold-formed reinforcing steel of a periodic profile, with increased ductility. Reinforcing steel is inductively heated directly in the production line to a temperature of 350-45CGS, followed by cooling to a temperature of 100-150°C in a continuous bath or in a suffocating device. The removal of scale from the surface of the wire rod is carried out in non-driven roller stands, with a total reduction of up to 30%. Heating reinforcing steel above 450°C leads to a sharp decrease in the strength characteristics of the steel. To ensure the operability of the nodes of the winding device, the steel reinforcement is cooled to a temperature of T=100-150°C, through the use of air or a water-cooled drawing drum. Reeling of steel reinforcement can be carried out at a temperature of T=450°C.

The patent also notes that accelerated cooling is not applied. At the same time, further in the patent materials it is noted that after the installation of induction heating, an accelerated cooling device was mounted. The above layout of the units of the installation allows you to increase the plastic characteristics of cold-formed reinforcement, without reducing its strength characteristics, by relieving internal stresses that arise during the application of the profile

The required plasticity class of reinforcement (class "B") is provided by induction heating of finished reinforcement in the production line in the temperature range T=350-450°C.

The installation location of the inductor and accelerated cooling devices depends on the specific line layout.

The disadvantages of the method include:

- the method is implemented on a specific steel grade and does not take into account the heterogeneity of the metal;

- the use of induction heating of fittings affects the feed rate, and as a result reduces the productivity of the installation;

- induction heating does not take into account the hood obtained between the block and the winding device at T=350-450°C and, as a result, the instability of the diameter and the index of geometric parameters Fr;

- when using air and a water-cooled drum at standard speeds of the production line, the finished fittings with a temperature of 350-450 ° C after the inductor will not have time to cool down to the required temperature, which ensures the normal operation of the winding device and its components;

- when cooling with water in a suffocating device or a continuous bath (accelerated cooling) after induction heating, the surface hardening of the finished reinforcement, the formation of scale and its effect on further processing by consumers are not taken into account;

- with induction heating, the properties on the finished fittings when stopping and starting the production line, the holding time at these stops, the acceleration time and the stop time of the production line to the specified speed parameters are not taken into account, and as a result, setting the inductor in the same parameters. The characteristics of the stable operation of the production line are given.

A known method for the production of rebar of a periodic profile (see RF patent No. 2.333.059, class B21C 1/00, published 10.09.2008, bull. No. 25).

The method is aimed at obtaining a reinforcing profile from ordinary steel grades, with cold working by pressure, while maintaining plastic and strength properties at a predictable level. This is achieved by selecting the parameters of the original workpiece and the degree of deformation.

The deformation of the blank is carried out at a ratio of the yield strength of the blank to the yield strength of the finished profile of 0.68-0.76.

The invention under consideration is aimed at providing the minimum required reduction of the workpiece during hardening of steel and applying a periodic profile due to the selection of the steel grade, mechanical properties and diameter of the wire rod.

The rollers for compressing the wire rod deform the latter at a ratio of the yield strength σ tr. to the yield strength of the finished profile σ g.p., constituting K1=0.68-0.76. The total degree of deformation is set in accordance with the ratio:

K1 / K2 \u003d 3.84-5.43

where:

where:

d _c - the diameter of the original workpiece;

d _p - nominal diameter of the finished reinforcing profile.

The disadvantages of the method include:

- a limited range of steels and the exact chemical composition of steels from which finished fittings can be made;

- it is known that the mechanical properties within the same smelting and steel grade vary within fairly large limits. This has a significant impact on the characteristics of the finished product, including plastic properties;

- the need to determine the cross-sectional area of the billet-wire rod, as well as the reinforcing profile, after rolling, in order to evaluate the plastic and mechanical properties of the resulting reinforcement, taking into account the requirements for the area of the ribs Fr;

- if the obtained indicators do not correspond to the required ones, the finished reinforcement can be considered as a marriage;

- ensuring the necessary properties of reinforcement with minimal deformation limits the range of steel grades.

A known method for the production of fittings of small diameter wire (see US Pat. RF No. 2.302.916, IPC V21S 1/00, publ. 20.07.2007), taken as a prototype. The method includes cold drawing of a workpiece with its subsequent deformation by alternating bending in a multi-plane roller device, with winding of the finished product. A low-carbon steel rod is used as a blank. When drawing, the total deformation is carried out in the range of 14-22%, with the formation of a profile in the form of longitudinal rows of ribs inclined to its axis on the workpiece in the finishing multi-roller drawing die. Deformation by alternating bending is carried out without forced heating with an elongation of 1.03-1.1 along the planes of symmetry of the section of the workpiece passing through the rows of ribs, providing at least three bends of the workpiece in each plane. The lower strain limit, about 14%, is due to the fact that lower strain values do not allow obtaining a reinforcement profile with given geometric parameters. The upper value of the deformation, about 22%, during cold drawing of low-carbon steel wire rod, does not make it possible to obtain a product with desired plastic properties, which requires a change in the deformation scheme, namely: the cold deformation of drawing is replaced by cold deformation in the form of alternating bending.

The deformation of the wire by alternating bending is carried out in an unheated state.

The disadvantages of the method include the following:

- the method allows to obtain single values of the required ductility in the reinforcement at a low carbon content, without taking into account the effect on the ductility of the steel composition, including impurities in the form of phosphorus, sulfur and copper;

- heterogeneity of the metal and, as a consequence, the spread of the obtained properties; triple bending on the rollers affects the wire rod feed rate and reduces the productivity of the installation;

- the range of maintaining the total deformation within 14-22% also affects the performance in the direction of reducing the final length of the reinforcement per unit weight.

A patent search has shown that there is a known method for continuous heat treatment of wire rod with heating in a continuous muffle furnace to austenitization temperature, within T=250-300°C, with air cooling to T=140-160°C, followed by tempering at T= 400-540°C for 1-3 minutes

A known method of heat treatment of steel wire having a set of alloying components. Hardening is carried out at a heating temperature of up to T=860-1060°C, using water, with tempering at a temperature of T=300-500°C, for a period of time from 1 to 6 seconds (see EP 0260717 B1, dated 19.08.1986 .).

There is also known a method of thermal hardening of the wire during its movement, including heating in the inductor to the austenitization temperature and exposure, for a certain period of time, with intensive cooling with an air-water mixture, with the transition to water, in a rapid cooling chamber, with reheating in the second inductor for final heat treatment (see Pat. RU No. 2070 582. C1, dated 11/25/1992). The installation for implementing the method of thermal hardening of reinforcement consists of a straightening and feeding device, a pusher, a heating inductor for steel austenization, a cooling device, a heating inductor for tempering and a receiving device.

There is a known method for increasing the plastic properties of cold-formed reinforcement (e-mail: zamk.stpc3@bmz.gomel.by), which discusses the use of devices for relieving stress in reinforcement and improving plastic characteristics.

The ratio of tensile strength to yield strength (σ _in /σ _0.2 ) and total relative elongation at maximum load (Agt) are presented as characteristics of steel ductility.

The technical result that can be obtained by implementing this invention is the possibility of obtaining cold-formed steel reinforcement with a diameter of 6.0 mm -14.0 mm, with increased strength and plastic properties, from low-carbon steel C = 0.24% in the presence of chemical elements.

-increasing the yield of reinforcement due to the comprehensive total reduction of wire rod up to 40%;

- increase in the minimum elongation to Agt>5.9%;

- the actual deviation from the nominal diameter of the finished product is -3.9%, which allows to increase the number of meters of cold-formed steel reinforcement in one ton.

With stepwise thermal heating and cooling in a bell-type furnace of cold-formed steel reinforcement, the metal structure is leveled, which corresponds to the plasticity level "B", with a yield strength σ _0.2 > 500 N/mm ² ; and tensile strength σ _in > 550 N / mm ² at full relative elongation Agt > 5.9%

- the practical absence of aging of finished rolled products, even in the presence of harmful impurities;

- minimal loss of plastic properties when leveling on straightening and cutting machines (mechanical straightening, Appendix No. 3).

The technical result is achieved by the fact that a method for the production of cold-formed steel reinforcement of a periodic profile, including the supply of wire rod from an unwinder to a scale breaker, with the removal of scale and transfer to a roller stand, with wire rod deformation and obtaining a periodic profile in the form of several longitudinal rows of ribs inclined to the axis. In this case, wire rod with a carbon content of up to 0.24% is used. The total reduction in the roller stand is adjusted to 40%, with a minus tolerance field for the diameter of cold-formed steel reinforcement up to -3.9%, stepwise heat treatment of the finished reinforcement in coils is carried out, heating it to t = 300-600 ° C, holding at given temperature, for austenization and alignment of the steel structure, for 8-14 hours, followed by uniform cooling together with the furnace to t = 80-150 ° C, in a nitrogen atmosphere, with the end of cooling in air, to obtain a relative elongation Agt> 5.9% and ratios σ _to /σ _0.2 > 1.09.

The implementation of the method for producing cold-formed steel reinforcement can be carried out on the line shown schematically in the figure, where:

- position 1 - unwinding device;

- position 2 - scale breaker;

- position 3 - roller stand;

- position 4 - drum;

-position 5 - rebellion;

- position 6 - bell-type furnace;

- position 7 - soap dish.

The method for producing cold-formed steel reinforcement includes the supply of wire rod from the coil to the decoiler (1), through the scale breaker (2) to the roller stand (3), with the impact of smooth and profiling rollers on the surface of the wire rod, with deformation and the formation of a profile in the roller stand (3) protrusions, in the form of several longitudinal rows, directed at an angle to the axis of the wire rod. The application of protrusions (or ribs) in the roller stand (3) on the surface of the wire rod occurs at a deformation of up to 40%. After the armature leaves the roller stand (3), it is wound onto the winding drum (4), with the formation of a coil (5) weighing Q=5,000 kg.

To obtain the required indicators of plasticity and strength of steel reinforcement, the riot is fed into a bell-type furnace (6), preheated to a temperature of T=350-700°C (see Appendix No. 1).

The temperature range is selected for each brand of finished products, taking into account the presence of harmful impurities, and the required plastic properties of the finished product, in accordance with the requirements of product standards.

The coil (5) is heated to the required temperature, about T=500°C, with holding time t=12-14 hours. The heating of the furnace (6) is stopped and cooling is carried out to a temperature of T=80-150°C, with austenization of the steel structure in the buntearmatura.

Example

Wire rod is made of low-carbon steel containing:

The resulting rebar with a periodic profile was investigated in order to evaluate the plasticity and strength indicators. Average values: yield strength σ _0.2 \u003d 535 N / mm ² , tensile strength σ _in \u003d 612 N / mm ² , maximum reduction in the diameter of the finished reinforcement by -3.9% of the nominal value.

Stepwise heating of the reinforcement in coil (5), with a delay in time, with a continuous supply of nitrogen, makes it possible to obtain a product corresponding to the B500V grade, reducing the diameter of the reinforcement to minus 3.9% will allow obtaining an additional number of meters of finished rolled products per 1 ton of products.

The use of the proposed method for the manufacture of reinforcement can significantly improve its plastic characteristics, without reducing its strength properties, by relieving internal stresses that arise in the process of applying the profile and leveling the metal structure.

Reinforcement studies have shown the possibility of manufacturing cold-formed rebar from wire rod with a sufficiently high content of harmful impurities and a certain carbon equivalent. The composition of impurities is shown earlier.

Tests of reinforcement according to this invention are displayed in tables (see Appendix No. 2, Appendix No. 3)

The resulting reinforcement does not have such a parameter as the aging of the finished material (even if there is a content of harmful impurities and minimizing the loss of plastic properties after mechanical straightening). Setting the profile "Fr" at linear density, in a minus diameter tolerance field, is simple and depends on the obtained plastic properties in cold-formed reinforcement.

Claims (1)

A method for the production of cold-formed steel reinforcement of a periodic profile with increased plastic properties, including the supply of wire rod from an unwinder to a scale breaker with the removal of scale and its transfer to a roller stand, in which the wire rod is deformed to obtain a reinforcement of a periodic profile, having several longitudinal rows of ribs inclined to it axis, characterized in that they use wire rod with a carbon content of up to 0.24%, the total reduction in the roller stand is adjusted to 40% with a minus tolerance field for the diameter of cold-formed reinforcing steel up to -3.9%, stepwise heat treatment of finished reinforcement in riots is carried out with heating to t=300-600°C and holding at this temperature for 8-14 hours for austenization and leveling of the steel structure, followed by uniform cooling together with the furnace to t=80-150°C in a nitrogen atmosphere with the end of cooling in air obtaining a relative elongation Agt≥5.9% and a ratio of σ _in /σ _0.2 ≥1.09.

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