JPH07118759A - Heat treatment for wire rod - Google Patents

Abstract

PURPOSE:To shorten the length of a molten salt bath tank part and to miniaturize heat treatment equipment by forming a high temp. steel wire rod directly after hot rolling into a loose coil in unconcentric state and previously performing rapid cooling by means of molten salt spraying at the time of applying heat treatment by a molten bath salt. CONSTITUTION:A steel wire rod 1 directly after hot rolling, having a temp. as high as Ar3 transformation point or above, is formed into a coil by means of a laying head 2 and introduced, in a state of unconcentric loose coil, onto a roller conveyer 3 in the fore half part of a molten salt bath 4 and conveyed. In the course of this conveyance, a molten salt in the molten salt bath 4 is sucked by a pump 5 and cooled by a cooler 9. Subsequently, the molten salt is sprayed as jets 8a, 8b onto the loosely coiled steel wire rod on the roller conveyer 3, through nozzles 7a, 7b of nozzle headers 6a, 6b provided on the upper and lower sides of the roller conveyer 3a to cool the steel wire rod rapidly. Then, the steel wire rod is transferred onto a roller conveyer 3b in the molten salt bath and held in the molten salt bath for a prescribed time, by which heat treatment is finished. At this time, by regulating V2/V1 to 1/1 to 1/4 when the speeds of the roller conveyers 3a, 3b are represented by V1 and V2(m/min), respectively, the whole length of the molten salt bath heat treatment equipment can be shortened and this equipment can be miniaturized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat treatment method for steel wire rods,
In particular, the present invention relates to a heat treatment method for heat treating a wire rod immediately after rolling as a non-concentric loose coil.

[0002]

2. Description of the Related Art A hard steel wire produced by hot rolling needs to be heat-treated in order to maintain good strength and toughness. Conventionally, lead patenting is generally used as this heat treatment method, but a direct heat treatment method has been developed for the purpose of realizing a heat treatment equivalent to that using the sensible heat of the rolling of the wire rod. A method of directly immersing a rolled wire rod in a molten salt is disclosed in JP-A-56-38426.
Japanese Patent Laid-Open Publication No. Sho 56-102524.

For example, in JP-A-56-38426, a low temperature molten salt bath 9 is used as a molten salt bath as shown in FIG.
Using two baths of the high temperature molten salt bath 10 and the wire rod 1 which is dropped onto the roller conveyor 3a in a coil shape by the laying head 2 of the winder through the rolling process, is conveyed in a non-concentric manner.
First, the solvite structure is obtained by immersion cooling in the low temperature molten salt bath 9 and then immersion cooling in the high temperature molten salt bath 10 to complete the solvite transformation of the untransformed austenite. In each of these conventional heat treatment methods, a steel wire rod immediately after rolling is formed into a non-concentric loose coil by a winder, and is continuously cooled while being continuously conveyed and then temperature-retained.

[0004]

In the above-mentioned conventional heat treatment method, the purpose is a quenching-holding type so-called constant temperature transformation heat treatment, so that the time required for temperature holding is usually 10 times or more the time required for rapid cooling. There are many. In particular, the segregated portion at the center of the wire cross section takes a long time to complete the transformation, which is one of the causes for increasing the length of the temperature retaining portion.

On the other hand, in the above-mentioned conventional heat treatment method, although the conveying speed of the wire rod coil is not specified at all, normally, when the winding coil is used to form a loose coil having a non-concentric shape, the rolling amount and the wire rod are conveyed. Due to the speed relationship, the distance between the non-concentric rings is determined, and the wire rod coil is continuously transported at a constant transport speed. The inter-ring distance is substantially proportional to the transport speed, and it is necessary to lengthen the inter-ring distance to a certain extent in order to perform uniform heat treatment even in a portion where the rings overlap each other.

From the above description, the length of the temperature retaining section governs the required length of the entire heat treatment section, and the transport speed is increased to some extent for uniform heat treatment. , Relatively large. The present invention is a heat treatment method for a wire rod, which enables a treatment in which the length of the entire heat treatment portion is significantly shortened by shortening the length of the temperature retaining portion.

[0007]

The gist of the present invention is that a steel wire rod having a temperature of Ar ₃ point or more immediately after rolling is supplied as a non-concentric loose coil on a conveyor by a winder. Prior to placing and immersing in a molten salt bath to heat-treat, after quenching by injecting molten salt from above or below the coil above the bath surface immediately before introducing the wire rod coil into the molten salt bath, upon continued temperature retaining heat treated in a molten salt bath, a ratio of the conveying speed V ₂ of the wire coil of wire conveying speed V ₁ of the coil (m / min) and the molten salt bath during said rapid cooling (m / min) V ₂ / V ₁ is 1/1 to 1/4,
Desirably, the heat treatment method for the wire is characterized in that the treatment is performed while being conveyed at 1/2 to 1/3.

According to the present invention, a steel wire rod immediately after rolling is formed into a non-concentric loose coil by a winder, and after being rapidly cooled while being continuously conveyed, when the temperature is kept constant, the distance between the rings required during the temperature keeping is equal to the distance between the rings required during the rapid cooling. It is based on the idea that it can be shorter than the distance. The reason for this is that the purpose of cooling during quenching is to transform the wire to a constant temperature until it reaches the vicinity of the holding temperature (the temperature at which the constant temperature transformation is desired) before the transformation starts. Since it is to cool as much as possible and requires a large amount of heat removal over the entire ring, it is necessary to reduce the overlap of the rings as much as possible, whereas the purpose of cooling during temperature retention is to remove heat of transformation heat generation, If there is a portion that does not reach the holding temperature, it is heat removal, and the amount of heat removal during temperature holding may be small, so it is assumed that the overlapping of rings is relatively tolerable during quenching. It should be noted that the cooling method at the time of rapid cooling is advantageous in this estimation by reducing the portion that does not reach the above-mentioned holding temperature and reducing the required heat removal amount. An experiment was conducted based on the idea described above, and an optimum ratio of the transport speed during the rapid cooling and the transport speed during the temperature retention was found thereby, and the present invention was achieved.

[0009]

Embodiments of the present invention will now be described in detail with reference to the drawings along with the operation thereof. FIG. 1 is a schematic side sectional view of an embodiment of the present invention, in which 1 is a wire rod, 2 is a laying head, 3a is a roller conveyor, 3b is an in-bath roller conveyor, and 4 is a molten salt bath in which the wire rod 1 is immersed. Is. In this example, the upper half of the molten salt bath 4, that is, the upper surface of the roller conveyor 3a is located above the bath surface over a certain range from the entrance side of the tank, and the wire rod 1 on the roller conveyor 3a moves vertically in this range ( A means for injecting a jet of molten salt is provided from above (in some cases only in the upward direction) to perform forced cooling.

As the molten salt injecting means, an upper nozzle 7a and a lower nozzle 7b opposed to the upper nozzle 7a, which are arranged in a plurality along the wire advancing direction shown in the figure, are employed. 5, an upper nozzle header 6a and a lower nozzle header 6b are provided. 9 is
A molten salt cooler arranged between the pump 5 and the bath 4 for sucking the heated molten salt in the bath 4, cooling it to a predetermined bath temperature and supplying it again to the nozzle header. Is. In the bath, an in-bath roller conveyor 3b for transferring the wire 1 through the bath is provided, and can be driven separately from the roller conveyor 3a. The transport speed V ₂ (m / min) of the in-bath roller conveyor 3b is V ₂ / V with respect to the transport speed V ₁ (m / min) of the roller conveyor 3a.
₁ is 1/1 to 1/4, preferably 1/2 to 1/4
It can be transported as.

The operation of this embodiment will be described below. Figure 1
In the above, the wire rod 1 immediately after rolling is coiled by the laying head 2 of the winder and dropped onto the roller conveyor 3a and conveyed as a non-concentric loose coil. In the present invention, the transportation speed is usually applied in the range of 10 m / min to 40 m / min. Next, the wire rod on the roller conveyer 3a enters the region of the molten salt bath 4, but before being immersed in the molten salt bath, it is melted by the nozzles 7a, 7b from the vertical direction of the wire rod coil over a certain range from the inlet side of the bath. Salt jet 8a,
8b is taken directly and it is cooled rapidly. After that, it is continuously immersed in the molten salt in the molten salt bath 4 and held for a certain period of time. The distance between the rings at this time is shorter than that during the rapid cooling, and the overlapping of the rings is large, but the heat removal amount is small. Therefore, the desired cooling is sufficiently performed. Therefore, the length required for the processing of the temperature retaining unit can be shortened.

At this time, the transport speed ratio V ₂ / V ₁ of the roller conveyor 3a and the in-bath roller conveyor 3b is 1/1 to 1 /
The reason why it is set to 4, preferably 1/2 to 1/3 will be described. In the present invention, the wire diameter is usually 5.0 mm to 15.0 mm
It is applied in the range of. The transport speed ratio V ₂ / V ₁
Is less than 1/4, the overlapping degree of loose coils advancing in the bathtub increases, and part of the ring has a temperature higher than the temperature to be retained due to insufficient heat removal for transformation heat generation. Variation occurs, and the significance of heat treatment as in the present invention is lost. Further, when the transport speed ratio V ₂ / V ₁ is 1/3 to 1/4, the variation in material is slightly inferior to the case where V ₂ / V ₁ = 1/1, but it can be put to practical use. In range. Further, when the transport speed ratio V ₂ / V ₁ is 1/2 to 1/3, the variation of the material is almost the same as the case of V ₂ / V ₁ = 1/1, and the bath is not damaged. The conveying speed of the inner roller conveyor 3b can be reduced. In this case, V ₂ / V ₁ tends to be smaller when the wire diameter is larger. When the transport speed ratio V ₂ / V ₁ is 1/1 to 1/2, it goes without saying that there is no problem in the variation of the material, but in order to shorten the length of the retaining portion, the diameter of the wire is relatively small. When it is small, it is applied to, for example, less than 5.5 mm.

The results of heat treatment using the method of the present invention will be described below. Table 2 shows the results obtained based on the apparatus sequence shown in FIG. The chemical composition of the test material is as shown in Table 1. Table 2 shows the roller conveyor 3 for each wire diameter.
The conveyance speed V ₁ of a is kept constant, and the conveyance speed V ₂ of the in-bath roller conveyor 3b is changed, that is, the distance between the rings in the bath is changed.
This is a comparison of the range of variation in the average of the average cross-section cooling rates during cooling during cooling to ℃. In Table 2,
Even if V ₂ / V ₁ is 1/2 to 1/3, V ₂ / V ₁ is 1/1
Compared with, the range of the cold speed variation is about the same, and from this result, the length of the temperature retaining part can be greatly shortened.

[Table 1]

[0014]

[Table 2]

[0015]

As described above, according to the present invention,
Since it is possible to provide a heat treatment method that makes it possible to significantly reduce the length of the heat treatment part without damaging the material obtained by heat treatment, the construction cost of the heat treatment facility and the amount of molten salt used can be changed according to the length. It is possible to reduce the operating cost, etc., and to expect a great contribution in the relevant industrial field.

[Brief description of drawings]

FIG. 1 is a schematic side sectional view of an embodiment of the present invention.

FIG. 2 is a schematic side sectional view showing an example of a conventional technique.

[Explanation of symbols]

 1 Wire Rod 2 Raying Head 3a Roller Conveyor 3b Bath Roller Conveyor 4 Molten Salt Bath 5 Molten Salt Pump 6a Upper Nozzle Header 6b Lower Nozzle Header 7a Upper Nozzle 7b Lower Nozzle 8a Upper Molten Salt Jet 8b Lower Molten Salt Jet 9 Low Temperature Molten Salt Bath 10 High temperature molten salt bath

Claims (1)

[Claims] 1. A steel wire rod having a temperature of at least the Ar ₃ point immediately after rolling is supplied and placed as a non-concentric loose coil on a conveyor by a winder and immersed in a molten salt bath for heat treatment. Prior to introducing the wire coil into the molten salt bath, immediately above the bath surface, the molten salt was sprayed from above or below the coil to quench the molten salt, and then the temperature was held in the molten salt tank for heat treatment. , The ratio V ₂ / V ₁ of the transport speed V ₁ (m / min) of the wire coil during the rapid cooling and the transport speed V ₂ (m / min) of the wire coil in the molten salt tank is 1/1 to 1 / 4. A heat treatment method for a wire rod, wherein the wire rod is treated while being conveyed.