JPH0215603B2 - - Google Patents

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to an apparatus for directly heat-treating steel bars and wires by effectively utilizing the heat held during rolling. The present invention relates to an apparatus suitable for manufacturing rods and wires for low temperature use.

(Prior technology) In direct surface hardening of steel rods, the surface layer of the wire rod is heated to Ar ₁ by water jet cooling following hot rolling.
A method of rapidly cooling from above the transformation temperature to below the bainite transformation temperature is known. That is, in the cooling device, the rod and wire are cooled so that the heat transfer coefficient on the surface thereof becomes larger than the radial heat transfer coefficient of the rod and wire. After quenching, high-pressure air is blown onto the bar and wire to drain it, and the surface layer is reheated by heat conduction from the high-temperature core while being transported in the atmosphere between the cooling device and winder or cooling bed. It is. As such a means, for example, Japanese Patent Publication No. 56-48566 is known.

Typically, a cooling system consists of several cooling units (cooling boxes) arranged in tandem. Each cooling box is equipped with an annular forward injection nozzle or reverse injection nozzle, and the cooling water is injected from the nozzle to the rods and wires at high pressure. In some cases, the draining device is disposed in the middle of a row of cooling boxes.

FIG. 1 is an explanatory diagram showing the configuration of a typical cooling device. The cooling device 3 is formed from a plurality of cooling boxes 7, cooling water constituting a draining device 11, and a reverse injection device 12, and is provided following the finishing mill 1. 2
1 indicates a winder, but it may be installed instead of a cooling bed.

FIG. 2 is a chart showing the temperature history of the surface and center of a steel bar when surface hardening is performed using the direct heat treatment apparatus after rolling as shown in FIG.

The cooling device 3 consists of a plurality of cooling boxes 7, each of which is connected to a cooling water supply main pipe via a water flow control valve. Each cooling box 7 is equipped with an annular forward injection nozzle or a reverse injection nozzle (none of which is shown). The rods and wires M running through the cooling box 7 are cooled by jetting cooling water from around them through nozzles. Reference numeral 12 denotes a cooling water reverse injection device, in which the shape of the cooling box at the rear end is configured to allow cooling water to be reversely jetted, thereby adding water draining properties. Reference numeral 13 denotes an air blowing device provided next, which completely removes water from the surface of the wire rod.
Reference numeral 11 shows a draining device consisting of a combination of two such devices, which is connected to the quenching zone 4 together with the cooling device 3.
form. The subsequent aerial cooling line up to the winder is defined as a recuperation zone 5 here. The effective cooling line length L for cooling is represented by the length including the cooling device 3 and the cooling water reverse injection device 12.

The rod wire M that has been cooled by the cooling device 3 and entered the draining device 11 is first subjected to a cooling water reverse injection device 12 in which cooling water attached to the rod wire M and entrained therein is blown off by reverse injection. Subsequently, the residual adhering water is blown off with high-pressure air in the air blowing device 13, and the surface of the wire rod is dried.

Finishing temperature detectors 1 are installed on the exit side of the finishing rolling mill 1, the exit side of the draining device 11, and the entry side of the winding machine 21, respectively.
4. A quenching end temperature detector 15 and a recuperation temperature detector 17 are arranged. Temperature detector 14,1
5 and 17 are non-contact thermometers, such as radiation thermometers.

In the figure, a indicates a temperature measurement point on the exit side of the finishing rolling mill 1, b indicates a temperature measurement point on the exit side of the drainer 11, and c indicates a temperature measurement point on the entry side of the winder (or cooling bed). It shows.

Using such equipment, we can apply the desired heat treatment to the rod and wire rod after rolling, and in order to give the product the required mechanical properties, we adjust the quenching length through simulation and experience, and adjust the surface temperature of the rod and wire immediately after draining. At the same time, the rod and wire rod temperatures were also measured at positions sufficiently far away from the outlet side of the cooling device, and the cooling rate was controlled by adjusting the amount of cooling water so that the target temperature was reached at each position.

(Problems to be solved by the invention) In rolling steel bars and wire rods, individual rolling conditions,
For example, it is inevitable that the diameter of the rod and wire rod, the rolling speed, the speed at which the steel passes through the cooling device, etc. will be changed, and it is important to have the optimal cooling device according to these individual conditions in order to obtain good rolled steel products. This is necessary for this purpose. In particular, in the production of low-temperature rods and wires with excellent low-temperature toughness, which the present invention advocates, extremely strict control is required, and the temperatures at points a, b, and c mentioned above must be controlled to optimal values. It is necessary.

For example, if the cooling length is longer than necessary, the cooling time will be longer, and if the recuperation temperature at point c is within the target range, the temperature at point b immediately after draining will be higher and out of the target range, and vice versa. If the temperature at point C falls within the target range, the temperature at point c will drop too much, making it impossible to manufacture the target product. Furthermore, if the cooling length is shorter than necessary, the opposite result will occur, and the target temperature range at points b and c cannot be satisfied by controlling only the amount of cooling water and water pressure. In such a case, it is possible to increase or decrease the rolling speed or adjust the cooling length. However, increasing or decreasing the rolling speed cannot be freely selected due to restrictions on mill load, etc., but it is possible to adjust the cooling length appropriately. The selection is relatively easy to implement. Conventionally, there was no appropriate means to deal with the rolling conditions at the time, so the only option was to determine the cooling length based on past experience. If the rolling speed is not constant due to a problem, it is not possible to take prompt and appropriate measures, making it difficult to build in stable quality.

(Means for Solving the Problems) The present invention involves cooling the surface layer of the rod and wire material by water injection cooling following hot rolling, from above the Ar ₁ transformation temperature to below the bainite transformation temperature, and then transporting the rod in the atmosphere. In a device that recuperates the surface layer by heat conduction from a high-temperature part near the center of the wire, the length L of the cooling line that performs water jet cooling is calculated from the diameter d of the wire rod, rolling speed V, and amount of cooling water Q using the following conditional expression. This is an apparatus that directly cools and recuperates rolled rods and wires, which is characterized by being set and configured to a required length.

Conditional expression L=0.9・^d2・V(9.80−0.97・lnQ)+K …(1) 0.5≧Q/πdL・10 ³ ≧0.2 …(2) However, L: Length of cooling line (mm) d: Diameter of rod and wire (mm) V: Rolling speed (m/sec) Q: Cooling water amount (m ³ /hr) K: Correction coefficient determined in the range of -4000 to +2000 The bar surface temperature before the quenching line is determined by the temperature of the heating furnace. The extraction temperature is controlled and usually maintained at 820±20℃. b, which is the temperature measurement point in the production of low-temperature rods and wires;
The total length L of the water injection quenching line required to obtain the target steel bar temperature at point c is determined from the above equations (1) and (2), which were obtained using theoretical calculations and actual results. (1)
In the equation, ^d2・V is a term representing the volumetric velocity (production amount), and as the production amount increases, the quenching line length L increases, and if the amount of cooling water used in the quenching line Q increases, the cooling length increases. This means that L becomes shorter.

The correction coefficient K is within a range that satisfies the mechanical strength of a steel bar for low-temperature use, and also reflects changes in finishing temperature, for example, if the bar and wire temperature before the cooling line is higher or lower than the standard temperature of 820°C. Therefore, it corrects the cooling length, and is usually selected in the range of -4000 to +2000.

In addition, equation (2) determines the upper and lower limits of the amount of water used in the cooling line, and defines the amount of cooling water injected per unit heat transfer area, that is, the water amount density, and prevents uneven cooling of the rod and wire in the circumferential direction. This provides an appropriate value to prevent quality variations and to perform heat treatment efficiently with a reasonable amount of water.

(Function) Next, a method for surface hardening a rod or wire rod using the apparatus configured as described above will be described.

When cooling water is injected onto the wire rod, the wire rod is cooled so that the heat conductivity from the wire rod to the cooling water is greater than the heat transfer coefficient to the inside of the wire rod in the radial direction. Therefore, as shown in FIG. 2, the surface temperature drops rapidly from the start of cooling. In the example shown in Figures 1 and 2, the draining device 11 is installed at the rear of the cooling device 3, and the quenching start position is changed depending on the diameter of the steel bar so that the quenching end position is always immediately before the draining device. This is the case with cooling lines.

The quenching end temperature of the surface-hardened rod and wire rod is measured at point b. Note that point a is the temperature measurement point of the rod and wire before entering the cooling line, and is usually approximately the same as the finishing temperature. In addition, the recuperation temperature is measured at point c, which is located sufficiently away from the cooling line.

Each temperature at point a, point b, and point c has a predetermined desired target value, and is adjusted so as to satisfy each of the target values. In this case, according to the present invention, the length (L) of the cooling line is set to an appropriate value derived from the diameter (d) of the rod and wire rod, the rolling speed (V), and the amount of cooling water (Q). It is extremely easy to satisfy these temperature conditions for heat treatment of rods and wires for use, and products of excellent quality with little variation can be manufactured.

(Example) In the device arranged as shown in Fig. 1, 3.5
An example of processing %Ni steel is shown below. Steel bar temperature at finishing temperature point a is 820℃, size d: 38mmφ,
Finishing speed V: 2.2m/s, cooling water amount Q: 380m ³ /hr
The quenching length L was calculated from equation (1). here
The correction coefficient K in equation (1) was -1545, with the main focus on improving elongation, so that the quenching depth could be made shallower, and the length of the cooling line would be shorter. As a result, it was calculated that L=10m. As a result of measuring the bar temperature with thermometers 15 and 17, the temperature at point b, which is approximately 1.6 m away from the rear end of the cooling water reverse injection device 12, was approximately 250°C, which was within the predetermined target temperature range of 230 to 280°C. In addition to being fully satisfied, the recuperation temperature at point c, which is approximately 58 m away, was 500°C, exceeding the predetermined target value of 500.
We were able to fully satisfy the temperature of ±50℃.

As a result, the mechanical properties required for low-temperature reinforcing bars made of 3.5% Ni steel, yield strength σy≧410N/mm ² , elongation E1≧
20%, impact value vE _-120 ≧100Joule, we were able to stably manufacture a product that satisfies all of the following.

(Effects of the Invention) According to the present invention, even if the size is changed frequently or the rolling speed is changed, the necessary cooling line length can be set appropriately in relation to the rolling speed and the amount of cooling water after the change. (L), it is possible to stably clear the target temperature range at points b and c even with changes in rolling conditions, etc., making it possible to build in excellent quality. In addition, there is no need to make adjustments each time through experience, which was conventionally done, and variations among operators are also eliminated.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the configuration of an apparatus according to the present invention, and FIG. 2 is a chart showing an example of a cooling curve of a rod or wire rod. 1... Finishing rolling mill, 3... Cooling device, 7... Cooling box, 11... Draining device, 12... Cooling water reverse injection device, 13... Air blowing device, 14, 15,
17... Temperature detector, 21... Winder, L... Cooling line length.

Claims (1)

[Claims] 1. Following hot rolling, the surface layer of the bar and wire is cooled by water jet cooling from above the Ar ₁ transformation temperature to below the bainite transformation temperature, and then transported in the atmosphere to reduce the high temperature area near the center of the bar and wire. In a device that regenerates heat in the surface layer by heat conduction, the length L of the cooling line that performs water jet cooling is set to the length determined by the following conditional expression from the diameter d of the rod and wire, the rolling speed V, and the amount of cooling water Q. An apparatus for directly cooling and recuperating rolled rods and wires. Conditional expression L=0.9・^d2・V(9.80−0.97・lnQ)+K …(1) 0.5≧Q/πdL・10 ³ ≧0.2 …(2) However, L: Length of cooling line (mm) d: Diameter of wire rod (mm) V: Rolling speed (m/sec) Q: Cooling water amount (m ³ /hr) K: Correction coefficient determined in the range of -4000 to +2000