RU2245928C1 - Method for heat strengthening of reinforcement, plant for performing the method and cooling apparatus - Google Patents

Abstract

FIELD: ferrous metallurgy, namely heat strengthening of reinforcement of carbon and low-alloy steel, mainly of reinforced-concrete sleepers.

SUBSTANCE: method comprises steps of heating moving reinforcement at least in one inductor until temperature exceeding austenization temperature by value up to 300 C; heating reinforcement until termination of austenite conversion before introducing it in flow of cooling fluid; intensified cooling successively in air flow, water flow, water-steam mixture flow for super-cooling reinforcement until temperature of beginning martensite conversion and preferably lower than 100 C. Plant for performing the method includes two inductors for heating before quenching; pairs of drive rollers arranged in front of first inductor, between inductors and after last inductor; apparatus for intensified successive cooling of reinforcement by means of air, water and water-steam mixture in nozzle unit placed inside quenching reservoir; inductor for tempering and straightening apparatus.

EFFECT: enhanced efficiency of heat strengthening process, significantly improved mechanical properties of reinforcement.

10 cl, 3 dwg, 3 tbl

Description

The invention relates to ferrous metallurgy, and in particular to thermal hardening of reinforcing bars of carbon and low alloy steel, and can be used for thermal hardening of rolled products.

A known method of continuous heat treatment of a wire of carbon and low alloy steels, in which a wire moving at a speed of 5 m / min, is heated in a continuous muffle furnace to an austenization temperature, is cooled in a bath with molten salts at a temperature of 250-300 ° C for 15- 25 s, then cooled with a stream of air to 140-160 ° C, then with water to a temperature of no higher than 80 ° C, after which they spend a vacation at 400-540 ° C for 1-3 minutes [1].

The disadvantage of this method is the low productivity due to the exposure time both when cooling in the bath at a temperature of 250-300 ° C, and when tempering at a temperature of 400-500 ° C.

There is also known a method of heat treatment of hot rolled bars or wires having the following content of components in wt.%: Carbon 0.30-0.80; silicon 0.20-0.50; manganese 0.30-0.80; chrome 0-0.80; copper 0-0.50; vanadium 0-0.15; niobium 0-0.06; titanium and boron or nickel no more than 0.80 individually or in combination, iron and impurities - the rest, including quenching when cooled by water from a temperature of 860-1060 ° C, at which the peripheral zone of the rod is martensitic, and then tempered at 300 -500 ° C for a period of time from 1 to 6 s depending on the diameter of the bar [2].

The disadvantage of this method is that the ultimate tensile strength is reached, not exceeding 1300 MPa, and the specific energy consumption is not more than 123.6 MJ / m ³ . The closest set of essential features is the method of thermal hardening of the bar during its movement, including heating in the inductor to the temperature of austenization and holding, intensive cooling first with a water-air mixture, and then with water in a quick cooling chamber, then heating in a second inductor for the final thermal processing [3]. The disadvantage of this method is the low productivity due to its versatility, which provides for not only hardening and tempering, but also drawing and annealing at a low speed of the bar.

The closest analogue of the invention to the installation for implementing the method of thermal hardening of reinforcement is an installation for processing calibrated steel [3], including the correct and feeding device (U), pushing U, a heating inductor for austenitizing steel, cooling U, a heating inductor for tempering and receiving U.

A disadvantage of the known installation is that it does not provide high performance, since the required exposure at the austenitizing temperature is provided due to the low speed of the rod. The installation is not suitable for the thermal hardening of measuring rods, since it does not provide for the limitation of the sagging of the rod due to elongation during heating in the inductor and distortion during cooling. The description of the installation did not disclose the design of the cooling device, the design features of which would allow intensive cooling of the valve without significant leakage of coolant or water.

A device is known for cooling valves with water under pressure during its thermal hardening, consisting of a housing with a central hole for a moving and cooled rod and with an annular cavity extending to the central hole and with a water supply pipe connected to the annular cavity [4] .

A disadvantage of the known device is that in it the cooling of a rod heated to 1000 ° C with water under pressure occurs at a high speed, reaching 300 ° C / s. A reinforcement bar heated in an induction furnace to a temperature significantly higher than the austenitization temperature can cause cracks to form a martensitic structure in the surface layer at such a high cooling rate, which is unacceptable.

There is also known a cooling device for cooling a moving rod of reinforcement heated to 950-1050 ° C with a water-air mixture. The device consists of a housing with a central hole for a moving rod and with a first annular cavity filled with water passing into a conical cavity into which air is supplied under pressure from the second annular cavity [5].

The first drawback of this device is the lack of a tank for collecting water and protecting it from flowing out along the armature. The second disadvantage is the possibility of cracks during cooling of the surface of the rod heated in the inductor to a temperature of 1150 ° C.

Closest to the proposed invention is a device for heat treatment of long products, consisting of a quenching tank, in the opposite side walls of which are openings for passing bars of reinforcement with a cooling unit in the form of a collector located inside the quenching tank [6].

The disadvantage of this device is that the cooling speed of a moving rod depends on the temperature of the cooling medium, the heat from which is removed slowly using its cooling collector. With this design, the cooling rate can be changed in a very narrow range, in addition, rapid heat removal and intensive cooling are difficult due to vaporization around the rod and the lack of means for rapid removal of steam.

The invention has the technical task of creating a method of thermal hardening of reinforcement, an installation for implementing the method and cooling device, providing high process performance for reinforcement of carbon and low alloy steel, high tensile strength of steel, elongation and specific energy consumption.

The first task is solved by a method in which during the movement of the reinforcing bar, at least one inductor is heated to a temperature exceeding the austenization temperature (A _c3 ) by up to 300 ° C, heating to complete the austenitic transformation before entering the cooling medium flow, sequential cooling in air, water and air-air mixture flows to a temperature below 100 ° C, and final heat treatment - tempering when heated in an inductor to a temperature of 390-600 ° C. High performance at high Mexico City strength properties of reinforcement achieved when the length of its heating in an inductor above austenitizing temperature (A _c3) with 1,2-6,0 depending on the diameter of the rod and its velocity and at a ratio of durations of heating, warming, cooling and intensive heating in an inductor for leave as (1-4): 2: 3: 1.

One of the distinguishing features of the proposed method is that reinforce the reinforcement made of steel in the following ratio of components in wt.%: Carbon 0.4-0.8; silicon 0.17-2.8; manganese 0.5-1.0; chrome 0.2-1.2; nickel up to 1.7; copper up to 0.3; tungsten up to 1.2; vanadium up to 0.2; aluminum up to 0.05; calcium up to 0.005; boron up to 0.005, iron and impurities - the rest.

When hardening reinforcing bars from these steels by the proposed method, a bainitic-martensitic structure is obtained with a tensile strength of at least 1500 MPa with a relative elongation to break of at least 0.06 and a specific energy consumption equal to

σ _in · δ ₅ = 90-180 MJ / m ³

where σ _in - tensile strength, MPa, σ _in = 500-1600 MPa;

δ _{5 is the} elongation to break, δ ₅ = 0.06-0.12.

Intensive cooling speeds are controlled by changing the air and water supply and the speed of the rods.

Distinctive features of the method according to the invention are: heating in the inductor to the surface temperature of the bar, exceeding the temperature of the end of austenization (A _c3 ) by an amount reaching 300 ° C in a time of 1.2-6 s (with known methods [1, 2] heating by 40 -180 ° C, exceeding temperature A _s3 ); sectional heating of the bar until it enters the flow of the cooling medium, due to the high temperature difference in the surface and central parts of the bar. (With known methods, heating may not be provided, since with a small temperature difference along the cross section of the rod, it may cool down over the entire cross section after exiting the inductor); intensive sequential cooling in streams of air, water, water-air mixture, providing the formation of bainitic-martensitic structure of the rod and high values of mechanical properties at high performance.

The second technical task is to create an installation for implementing the proposed method of thermal hardening, providing a high speed of the rods through heat-treating devices, intensive heating to a temperature exceeding the austenitic transformation temperature (A _c3 ) by a value reaching 300 ° C, intensive cooling to form a martensitic steel structure with a minimum of residual austenite and intense heating to a tempering temperature of 390-600 ° C, providing a bainitic-martensitic steel structure consisting of tempering martensite and a ferrite-carbide mixture. The distinguishing features of the proposed installation are as follows: the induction heating device consists of at least two inductors with pairs of drive rollers located in front of the first inductor, between the inductors and after the last in-line inductor rod, before and after the tempering inductor; an intensive cooling device for the reinforcement bar with air, water and a water-air mixture located between the induction heating device and the tempering inductor.

The third technical task is to create, as part of the installation, an intensive cooling device for a moving rod from the heating temperature in the inductor to a temperature below the onset of the martensitic transformation of carbon and low alloy reinforcing steel containing 0.4-0.8 wt.% Carbon.

The problem is solved in the invention of a device for sequential intensive cooling with air, water and a water-air mixture, consisting of a quenching tank with holes in the side walls to promote the fittings and the nozzle block located along an axis connecting the centers of the holes in the side walls, consisting of a first air nozzle located near the left side wall of at least one water nozzle located behind the air nozzle, and a water-air nozzle located behind the water nozzle. To exclude the ejection of water from the water-air nozzle through the hole in the right side wall of the quenching vessel, an additional air nozzle may be located near the right wall.

A distinctive feature of the proposed device for cooling valves is the presence of a block of air, water and water-air nozzles arranged in series along the axis connecting the centers of the holes in the side walls of the quenching tank.

The causal relationship between performance and the hallmarks of the proposed inventions is as follows. The performance of thermal hardening of reinforcing bars depends on the speed of their movement in the installation

P≈ υ, m / s,

where P is the performance

υ - rod speed, m / s,

where L is the installation length, m,

t is the duration of the processing of the bar in the installation, s.

At a high speed of movement of the rod, to reduce the length of heating and cooling devices, it is necessary to accelerate the processes of austenization during heating of the martensitic transformation during cooling, the transformation of the unstable martensitic structure of steel and residual austenite into a more stable bainitic-martensitic structure while maintaining the elastic properties of steel. This is achieved by intensive induction heating of the bar for 1.2-6 s to a temperature exceeding the temperature A _c3 by an amount reaching 300 ° C, rapid cooling in 2.3-10 with air, water and a water-air mixture and tempering at a temperature of 390-600 ° C for 1.2-6 s, which ensures high quality fittings with high installation performance.

Figure 1 shows the general layout of the installation for implementing the method of thermal hardening of valves, figure 2 - the design of a device for cooling valves, figure 3 - the design of the nozzle.

The installation consists of sequentially located (Fig. 1): roller table 1, pusher device 2, induction heating device 3 with inductors 4 and pairs of drive rollers 5 placed in front of the first heating inductor, between the inductors and the last inductor, significantly limiting the sagging of the heated rod; a cooling device 6, a holiday inductor 7 with two pairs of drive rollers, a leveling device 8, scissors 9 and a storage device 10. The cooling device 6 consists (Fig. 2) of a quenching tank 11 with openings 12 in the left and right side walls 13 and 14; block 15 nozzles located along an axis passing through the centers of the holes 12, consisting of air nozzles 16 and 17, one of which is located near the left wall 13, and the other is near the right wall 14, water nozzles 18 and air-water nozzle 19, composed of water pipes 20 and air nozzles attached to its ends. Each nozzle (Fig. 3) consists of a housing 21 with a central hole 22 for a rod 23 moving and cooled in the nozzle, a sleeve 24 with a central hole 25, coaxial with the opening 22. The housing 21 of each nozzle is fixed in the quenching tank and has a nozzle 26 with a supply hose 27. The regulation of the flow rate of the cooling medium is carried out by rotation of the sleeve 24 in the housing 21.

The installation works as follows (figure 1). From the roller table 1, the rod is fed into the pushing device 2, captured by the drive rollers 5 of the induction heating device 3 and enters the first inductor 4, where it is heated intensively when moving at a speed selected from the range of 0.1-0.5 m / s and infinitely adjustable, and in the following inductors, the entire cross section of the rod is heated to a temperature exceeding the austenization temperature (A _c3 ). Depending on the speed of the bar and its diameter include 1, 2 or 3 inductors. The greater the speed and diameter of the bar, the greater the number of inductors included. At the entrance to the block 15 of the nozzles of the cooling device 6 (Fig. 2), the bar is first cooled by air in the nozzle 16 at a low speed necessary to cool the finned surface without excessive stresses, then in the water nozzles 18 it is cooled at a high speed to a surface temperature of the rod less than 100 ° C, necessary for supercooling of austenite. After exiting the water nozzles, an intense martensitic transformation takes place, which is completed upon cooling with the water-air mixture in the nozzle 19. Cooling with the water-air mixture avoids excessive internal stresses in the martensitic steel structure. In the inductor 7, the steel is tempered when the bar is heated to 390-600 ° C with the formation of a bainitic-martensitic structure with tempering martensite. When exiting the inductor 7, the bar is cooled in air for 2-10 s to a temperature of no higher than 200 ° C and is corrected in the correct device 8, then, if necessary, it is cut with scissors 9 into measured billets that enter the storage device for forming packages for shipment .

The creation and testing of a plant for the thermal hardening of reinforcing bars with the cooling device described above, in which the proposed method is implemented, confirmed its high productivity and quality of reinforcement for reinforced concrete products, including railway sleepers. The technical characteristics of the created and tested installation are shown in table 1. The test results of fittings made from carbon and low alloy steels (table 2) are shown in table 3.

From the test results it follows that the reinforcement thermally hardened by the proposed method exceeds in terms of the achieved tensile strength and specific energy intensity the reinforcement manufactured in a known manner [2], and in terms of the achieved specific energy intensity exceeds the high-strength reinforcement made in known ways [1, 7]. The performance of the method implemented on the installation according to the invention exceeds 2-3 times achieved in a known manner [1].

In comparison with the reinforcement thermally hardened from rolling heating [4], the reinforcement manufactured by the proposed method is characterized by high stability of mechanical properties both along the length of the bar and on various bars in the batch.

Sources of information

1. A.S. No. 1296610, 05.27.85.

2. EP 0260717 B1, 09/19/86.

3. RU 2070582 C1, 11.25.92.

4. RU 2149906 C1, 01/27/99.

5. EP 0132249 B1, 07/18/83.

6. RU 2009216 C1, 04/14/92.

7. EP 0761825 A2, 08.24.95.

Table 1 Installation Specifications №№ p.p. Name of the parameters of hardened rods and installation Parameter value unit of measurement 1 Bar material - structural carbon and low alloy steels 2 Sizes of heated rods of round, square or hexagonal sections: length 2-4 m round diameter 10-20 mm square (side of the square) 9-18 mm hexagon (diameter of the circumscribed circle) 3 Heating temperature (max.) 1250 ° C 4 The speed of the rods through the heater 0.1-0.5 m / s 5 Number of Inductors: for heating under quenching 3 PCS. for vacation 1 PCS. 6 Current frequency 8000 Hz 7 Transformer substation power: over network 8000 Hz 1000 kw over the network 50 Hz 1600 kw 8 Water consumption for cooling the unit 122 m ³ / hour nine Water pressure 200-300 kPa 10 Compressed air consumption 2,5 m ³ / hour eleven Air pressure 400-600 kPa 12 Installation Dimensions: Length 11.34 m width 5.2 m height 1.4 m

table 2 Chemical composition of tested steels No. Mark Content in wt.% FROM Mn Si Cr Ni Cu W V Al Ca B P S 1 - 0.40 0.5 2,8 1,2 1.7 0.3 - 0.2 0.05 0.005 0.005 0.014 0,022 2 55С2А 0.55 0.61 1.72 0.20 0.09 0.1 - - - - - 0.015 0,021 3 60S2A 0.58 0.83 1,50 0.22 0.14 0.18 - - - - - 0.024 0,025 4 60С2ХФА 0.59 0.60 1,6 1,2 0.2 0.2 - 0.2 - - - 0,021 0.024 5 60С2Н2А 0.58 0.70 1.8 0.9 1.7 0.18 - - - - - 0,021 0,023 6 65S2VA 0.63 0.90 2.0 0.2 0.25 - 1,2 - - - - 0.017 0,022 7 70SZA 0.72 0.80 2,4 0.3 0.25 0.2 - - - - - 0.018 0,021 8 - 0.80 0.80 0.3 0.25 0.24 0.18 0.8 - - - - 0,023 0.024 Carbon content outside declared nine 85 0.84 0.8 0.36 0.25 0.23 0.19 - - - - - 0.015 0,025 Prototype method: cooling with water-air mixture and water 10 55С2А 0.54 0.70 1,66 0.19 0.13 0.14 - - - - - 0.018 0.024

Table 3 Mechanical properties of tested steels No. Mechanical properties σ _in , MPa σ _t , MPa δ ₁₀ % HRC 1 1850 1620 9.0 44 2 1520 1450 8.0 45 3 1538 1446 8.0 45 4 1597 1508 8.5 46 5 The values are given for 3 samples cut from different sections of the bar along the length 1515 1450 8.0 42 1522 1443 7.0 43 1516 1452 7.0 43 6 1588 1290 12.0 42 7 1569 1495 7.5 46 8 1620 1544 6.0 47 nine Cracks on the surface of the reinforcing bar 10 Cracks on the surface of the reinforcing bar

Claims (8)

1. The method of thermal hardening of reinforcement made of carbon and low alloy steel, including continuous movement of the reinforcement, heating at least one inductor to a temperature above the austenitizing temperature, heating until the austenitic transformation is completed, cooling in the cooler stream, tempering with heating in the inductor and cooling after tempering , characterized in that the heating is carried out to a temperature exceeding the temperature of completion of austenization by an amount reaching 300 ° C, heating is carried out with continuous movement of the valve ry before entering the flow of coolant, cooling is then carried out sequentially in an air flow, water, water-air mixture to a temperature below 100 ° C, and the rental is carried out at a temperature of 390-600 ° C. 2. The method according to claim 1, characterized in that the duration of heating of the reinforcement above the austenitization temperature is in the range of 1.2-6 s depending on the cross-sectional area of the reinforcement, while the duration of heating is higher than the temperature of austenization, heating, intensive cooling and heating at vacations are correlated as (1-4): 2: 3: 1. 3. The method according to claim 1, characterized in that the reinforcement is reinforced from steel containing the following components in wt.%: Carbon 0.4-0.8; silicon 0.17-2.8; manganese 0.5-1.0; chrome 0.2-1.2; nickel up to 1.7; copper up to 0.3; tungsten up to 1.2; vanadium up to 0.2; aluminum up to 0.05; calcium up to 0.005; boron up to 0.005, iron and impurities - the rest. 4. The method according to claim 3, characterized in that the structure of thermally hardened steel is bainitic-martensitic. 5. The method according to claim 4, characterized in that the thermally hardened steel has a tensile strength of at least 1500 MPa. 6. The method according to any one of claims 1 to 5, characterized in that the thermally hardened steel has a relative elongation of at least 0.06 and a specific energy consumption σ _in · δ ₅ = 90-180 MJ / m ³ where σ _in - tensile strength of the reinforcement, MPa; δ ₅ - elongation after rupture. 7. Installation for thermal hardening of carbon steel and low alloy steel reinforcement, consisting of a correct device, a pushing device with pairs of rollers with drives, an induction heating unit, a device for cooling valves, a tempering inductor and a receiving and storage device, characterized in that the induction heating unit has at least one additional inductor with additional pairs of drive rollers located in front of each inductor, the tempering inductor has two pairs of rollers, located s in front of and behind the inductor, and the correct device is located between the inductor and the receiving and release stored device. 8. A device for cooling the reinforcement, consisting of a quenching tank, in the opposite side walls of which there are openings for advancing the reinforcement, and a cooling block located in the quenching tank, characterized in that the cooling block consists of air, water and air nozzles located in the quenching containers sequentially and coaxially with holes in the side walls.

Images