JPS6237384A - Method for descaling coil of steel wire rod - Google Patents

Abstract

PURPOSE:To improve the suitability of a coil of a steel wire rod to pickling and to shorten the time necessary for finish pickling by air-cooling the coil to a specified surface temp. after softening and by putting the coil in a cooling tank, where it is rapidly cooled under applied ultrasonic waves. CONSTITUTION:A coil 6 of a hot rolled steel wire rod is placed on a tray 4, softened in an annealing furnace 2, sent out of the furnace 2 with rollers 8 and air-cooled to <=650 deg.C surface temp. The coil 6 is then put in a cooling tank 12 contg. a refrigerant 14 with a crane 10. In the tank 12, the coil 6 is rapidly cooled under ultrasonic waves applied from magnetostriction oscillators 16, 16A. Scale on the coil 6 is innumerably cracked over the full length and part of the scale is stripped, so descaling can easily be carried out in the following finish pickling stage.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for descaling TLL wire rod coils, and in particular to an effective method for descaling oxide scale that adheres during softening and sintering. Widely used in the field.

[Conventional technology]

Hot rolled #1 wire rods are often made into products through processes such as wire drawing and cold forging, but wire rods made of high carbon steel, alloy steel, stainless steel, etc. are hard when hot rolled. Since cold working is difficult, in many cases softening annealing is used to soften the material and improve workability.

When cold working xi material, the oxidized scale that adheres to the wire surface during softening and annealing is removed in order to reduce the frictional resistance with the processing tool and extend the tool life, and then treatments such as surface film formation are performed. The above-mentioned descaling methods can be roughly divided into mechanical methods and pickling methods, but both conventional methods reduce productivity during wire manufacturing and increase manufacturing costs. When surface quality is required, pickling is generally carried out in a coiled form to improve productivity.

Sulfuric acid, hydrochloric acid, nitric acid, hydrofluoric acid, etc. are used singly or in a mixed acid state for pickling steel wire rods, but all of these acids dissolve scale and base metal with the acid and mechanically peel off with the generated gas. It is interpreted that the scale is descaled by the action. Therefore, since the pickling properties of steel wire rods largely depend on the dissolution of scale and the rate of acid penetration into the steel base, measures have been taken to improve pretreatment to improve the pickling properties before pickling. For example, by controlling the composition of the softening annealing atmosphere, pickling properties can be improved, and by passing through a roll bending line and introducing cracks into the scale, the dissolution of scale and the rate of acid penetration into the base iron can be increased. In addition to methods such as changing the scale composition of stainless steel wire rods, methods such as changing the scale composition through melting treatment are also used. Although these methods have somewhat shortened the pickling time and reduced the amount of acid consumed, they not only result in a decrease in productivity and do not serve as a measure to reduce the final manufacturing cost, but also the roll bending method. There are many quality problems such as occurrence of surface flaws and changes in material quality. For this reason, in order to improve production even at the expense of increasing acid consumption and lengthening the pickling time, pickling is often performed in a coiled form.

In order to effectively carry out the above-mentioned coiled pickling treatment, various improvements have been proposed, such as optimizing the type and temperature of the acid used, and adding vibration to the pickling equipment, but none of these conventional techniques This method was concerned with improving the pickling equipment, but there was nothing related to the steel wire itself, and the effectiveness was not necessarily constant depending on the steel type and processing conditions, and it was still extremely unsatisfactory as a stable descaling method. . Furthermore, in molten salt processing, etc., there are many problems in terms of environmental protection, such as the mixing of harmful substances into the processing tank or cleaning tank.

[Problem that the invention seeks to solve]

The purpose of the present invention is to solve the problems of the prior art described above in the descaling treatment of oxide scale that adheres during softening annealing of steel wire coils, to significantly improve the peelability of the oxide scale, and to improve the subsequent descaling treatment. An object of the present invention is to provide a method for descaling a steel wire coil, which can be greatly simplified.

[Means and operations for solving the problems] The gist of the present invention is as follows.

That is, hot rolled fl! 1. In a method for descaling oxide scale that adheres during softening annealing of a steel wire coil, when the surface temperature of the softening annealing temperature coil of the steel wire coil reaches 650'c, lu or less, ultrasonic waves are applied to the cooling bath. A method for descaling a steel wire coil, comprising the steps of immersing and quenching the coil, and finishing pickling the coil after the quenching step.

The details of the present invention will be explained below. First, in the present invention, during cooling during softening annealing, the surface temperature of the steel wire coil is 6.
The coil is rapidly cooled when the temperature drops below 50℃. Generally, cooling of steel wire rod after softening annealing is performed by gradual cooling or air cooling. However, in the case of such conventional methods, a strong scale is generated on the surface of the manufactured steel wire coil during the heat treatment and the cooling process, and it does not peel off even in the subsequent pickling process, making descaling extremely difficult. This is because when the cooling rate is slow, less stress is generated due to the difference in coefficient of thermal expansion between the adhered scale and the base steel, and the adhesion of the scale is high. Furthermore, even if cracks occur in the scale and the base metal is exposed, it will be reoxidized and become scale again.

In the present invention, it is softened and baked! During cooling after 4I, when the surface temperature of the coil reaches 650° C. or lower, the coil is rapidly cooled. The reason why the quenching point was limited to the point when the surface temperature of the coil became 650° C. or less is as follows. That is, the material of the steel wire depends on the softening annealing temperature, holding time, and cooling pattern up to 650°C during cooling, and the cooling process below 650°C has little effect on softening. On the contrary, slow cooling below 650°C may cause the material to deteriorate, such as the 475°C brittleness of stainless steel.

Therefore! The upper limit that does not affect the softening of the wire is 650℃
When the temperature reaches 650°C or lower, it is rapidly cooled.

When the coil is rapidly cooled, a large temperature difference is generated between the scale attached to the surface and the steel base, and the difference in thermal expansion coefficients generates large stress, resulting in the introduction of many cracks in the scale. At this time, boiling and convection effects of the refrigerant occur, but the mechanical stirring action of these refrigerants promotes the introduction of cracks into the scale and peeling off of the scale, and the reoxidation of the exfoliated base metal is prevented by the refrigerant. There are secondary effects.

Next, the present invention uses a cooling tank in which ultrasonic waves are applied to a refrigerant that rapidly cools the coil. Ultrasonic waves have the effect of significantly increasing mechanical effects such as boiling of the refrigerant that occurs during rapid cooling of the coil, introduction of cracks due to convection, and exfoliation of scale, and is particularly effective against exfoliation of cracked scale. I found that. Ultrasonic waves have been conventionally used for ultrasonic cleaning, and it is well known that they are effective in causing so-called cavitation of a solution and removing foreign matter from minute parts. It has been found from the present invention L9 that by simultaneously applying ultrasonic waves to the refrigerant that rapidly cools the coil, the frequency of scale cracking and peeling increases significantly synergistically compared to when each is treated separately.

Although the detailed reason for this phenomenon is not clear, it is generally believed that when ultrasonic waves are applied to a liquid in which bubbles are present, the ultrasonic waves are scattered and absorbed by the bubbles, reducing the effect. The effect of the present invention is also relatively small during boiling of the refrigerant, and by accelerating the transition from film boiling to nuclear SS at high temperatures, the number of cracks introduced due to an increase in thermal stress increases, and convection with these cracks as the nucleus increases. This is thought to be due to crack extension and increase in the cooling region. In the present invention, the effect of the ultrasonic waves described above is also effective in a portion where the wires inside the coil are in close contact with each other due to the characteristics of ultrasonic waves.

After the coil is immersed in a refrigerant to which such ultrasonic waves have been applied and rapidly cooled, the core coil is subjected to finishing pickling. In other words, when a coil is pickled according to the present invention with many cracks occurring in the scale along the entire length of the coil and some of the scale has peeled off, the penetration of the pickling progresses extremely quickly, resulting in poor finish. Pickling time is significantly reduced.

〔Example〕

Example 1 Ferritic stainless steel N4 wire S U as a test material
Using S430, it was hot rolled into a 10 mm diameter of 55 mm.
After forming the coil into a 00 kg coil, it was subjected to softening annealing at 780° C. for 6 hours in the air.

As shown in Table 1, the coils that have undergone the softening annealing process are cooled by the method of the present invention as well as by various conditions other than the method of the present invention, and then immersed in a 10% sulfuric acid bath at a liquid temperature of 7oC to descale. After that, 5% of
Minute 1 [immersion and final pickling were performed. The pickling property was evaluated by changing the immersion time in a sulfuric acid bath and measuring the time required until almost complete descaling was achieved visually. The results are shown in Table 1. In the present invention method of applying ultrasonic waves, ultrasonic waves were applied using a 50 KHz oscillator, but please refer to Fig. 1 for the ultrasonic device used in carrying out the present invention method and the work procedure using the same. and explain.

The sample material S IJ S 430 was heated at 780°C for 6 hours while being loaded on the tray 4 in the annealing furnace 2. %@material 6 is
After being sent out of the furnace by rollers 8 and air-cooled until the surface temperature defined by the method of the present invention becomes 650° C. or lower, the coil is placed in a cooling tank 12 by a coil conveying crane 10 and rapidly cooled. The cooling tank 12 contains a refrigerant 14 such as water, and ultrasonic waves are applied by magnetostrictive vibrators 16 for applying ultrasound waves attached to the bottom and sides of the cooling tank 12 . In addition,
In this experiment, a vibrator 16A with a lifting device was inserted inside the coil 6 placed in the cooling tank 12 so that sufficient ultrasonic waves were applied to the inside of the coil 6.

In this experiment, 50 Kl (z
Although an AI strain transducer was used, there are no particular restrictions on the type of ultrasonic transducer used in the present invention;
From the viewpoint of economy, a frequency of about 10 to 1000 KHz is preferable.

The contents of the above comparative test are as shown in Table 1.
1 to 4 are comparative examples in which the samples were air cooled to the softening annealing process temperature, and among these, No. 2 and No. 3 were cooled to room temperature and then placed in the same cooling bath 12 as in the method of the present invention and ultrasonic waves were applied. This is an example in which only the time is changed to 10 minutes and 30 minutes.

In addition, sample material No. 4 is an example in which the stainless steel wire coil was not subjected to pickling in one step, but was subjected to molten salt treatment, and in this case, it was treated with (NaOH + N
aN0) salt path was used. In this case, the finishing pickling time was extremely short at 10 minutes, whereas the sample material No.
, 1 takes an extremely long time, 50 minutes. Sample material No.
Although the effect of applying ultrasonic waves is recognized in No. 2.3, it is not as good as No. 4, which is a special conventional method.

Next, the cooling method for sample materials Nos. 5 to 9 is water cooling, only No. 5 uses a comparative method in which no ultrasonic waves are applied, and the other Nos. 6.7 and 8.9 use a cooling method that does not apply ultrasonic waves. Although it is different,
All of these are examples of the present invention that satisfy the processing requirements regulated by the present invention law.

As is clear from the evaluation of the finish pickling time shown in Table 1 (
For sample material No. 5, the water cooling conditions were the same as in the present invention, but
In contrast, the effect of improving pickling properties was small because no ultrasonic waves were applied, whereas N of the present invention example.

6.7,8,9. It was found that regardless of the difference in application time, the final pickling time was approximately the same in all cases, approximately 10 minutes, indicating that the pickling properties were significantly improved.

In addition, the results of Nos. 6.7 and 8.9 of the above-mentioned invention examples are almost the same, and the application time was 5 minutes or more, preferably 10 minutes.
It is sufficient to apply the voltage for more than 10 minutes, and the molten salt treated N015
It was found that it has pickling properties equivalent to that of Therefore, according to the present invention, there is a possibility that the conventional molten salt treatment step can be omitted.

As is clear from the above comparative test results, it has become clear that the descaling treatment method according to the present invention significantly improves the pickling properties compared to any other comparative method or conventional method.

Example 2 Carbon steel wire 345C was used as a test material, and after hot rolling it into a 1800kg coil with a diameter of 911111φ,
After performing softening annealing in an atmospheric gas at 80°C for 6 hours, it was taken out of the furnace and air cooled to 600°C.

Thereafter, it was immersed in a cooling tank 12 shown in FIG. 1 to be rapidly cooled.

Thereafter, it was immersed in a 15% hydrochloric acid bath at 50°C to descale it.

In this test, as in Example 1, in addition to cases in which ultrasonic waves are applied according to the present invention in the cooling tank 12 and cases in which they are not applied, the purpose of this test is to further investigate the effect of the frequency when applying ultrasonic waves. The results were divided into cases where a 50 KHz g1 strain oscillator was used and cases where a 700 kHz barium titanate oscillator was used. Regarding the evaluation of pickling properties, a comparative test was conducted in which the immersion time in a 15% hydrochloric acid bath was varied and the evaluation was performed based on the time required for almost complete descaling by visual observation. The results are shown in Table 2.

As is clear from Table 2, sample material No. 10 is a comparative example in which only water cooling was performed and no ultrasonic waves were applied, and in this case, the pickling time was as long as 25 minutes, and the effect of improving pickling properties was small.

Sample materials No. 11 to 14 and No. 15.16 are all examples of the present invention, and No. 11 to 14 are 50
This is an example in which a KHz ultrasonic wave was applied and the application time was varied from 5 minutes to 60 minutes, and No. 15.16 was an example in which a 700 KHz ultrasonic wave was applied and the application time was changed from 5 minutes to 20 minutes. This is an example.

As is clear from the evaluation of the pickling time, the results of the above comparative test revealed that the pickling time according to the present invention was significantly shorter than that of Comparative Example No. 10. In addition, the effect is hardly affected by changes in the applied frequency, and the effect is almost the same even when the application time is extended.
It has been found that very good pickling can be imparted by application for more than a minute, preferably 10 minutes.

〔Effect of the invention〕

As is clear from the above embodiments, the method for descaling a steel wire coil according to the present invention involves softening and annealing a #4 rolled steel wire coil and then cooling it in air so that the coil surface temperature reaches 650°C.
When the following effect was reached, the material was immersed in a cooling bath to which ultrasonic waves were applied to rapidly cool it, and then the material was finished with pickling, so that the following effects could be overcome.

(a) According to the present invention, since rapid cooling and ultrasonic wave application are simultaneously applied to the W4 wire coil, it is possible to prevent the introduction of cracks due to stress generation against oxide scale attached during softening annealing, boiling of the refrigerant, mechanical effects such as convection, etc. On the other hand, the agitation cleaning action by ultrasonic waves was added9, and its synergistic effect made it easier to remove the scale, making it possible to significantly improve the pickling performance in the subsequent finishing pickling process.

(b) Due to the characteristics of the ultrasonic waves applied in the present invention, the effect can be achieved evenly even in the parts where the steel wire coils are in close contact with each other, so that the productivity of the 11-wire coil can be significantly improved. This greatly contributed to reducing manufacturing costs.

(c) In addition to making it possible to improve the quality of steel wire rods due to the remarkable improvement in pickling properties, the purpose of softening and sintering is not obstructed because the process is rapidly cooled at a temperature of 650° C. or lower.

(d) The method of the present invention can be effectively applied to any type of steel wire or material, and is particularly applicable to high-grade MS materials such as high carbon steel, alloy steel, and stainless steel.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing the process of quenching a #l wire coil according to the present invention by immersing it in a cooling tank to which ultrasonic waves are applied.

Claims (1)

[Claims] (1) In a sharp scale treatment method for oxide scale that adheres during softening annealing of a hot rolled steel wire coil, the surface temperature of the steel wire coil after softening annealing is 650°C.
A steel wire coil characterized by comprising the steps of immersing the coil in a cooling bath to which ultrasonic waves have been applied to rapidly cool the coil when the temperature reaches ℃ or below, and finishing pickling the coil after the rapid cooling step. Descaling method.