JPS59153842A - Production of steel wire rod having excellent scale detachability after annealing - Google Patents

Abstract

PURPOSE:To obtain a titled steel wire rod and to prevent a decarburization phenomenon generated during welding in the stage of annealing continuously a wire rod on which scale sticks or after primary drawing by using a nitrogen atmosphere contg. a specific amt. of O2 for the atmosphere in an annealing furnace. CONSTITUTION:A hot-rolled wire rod coil on the surface of which scales stick or a wire rod after primary drawing is annealed in a continuous annealing furnace. Fuel is burned at a required air mixing ratio in a gas generator and gaseous N2 contg. 0.5-0.9vol% O2 is produced. Such gas is introduced into the furnace through an introducing port (a) provided in the point in a heating zone where the wire rod is at <=570 deg.C. The atmospheric air is passed through a gas refiner to remove H2O and is then introduced through another introduction port (b) at the point of the above-mentioned wire rod temp. into the furnace. The feed rates of these introducing gases are adjusted to maintain N2+0.002-0.3vol% O2 in the astmosphere in a soaking zone. The atmosphere in the furnace is then removed through a discharging port (c) on the inlet side of the furnace and is fed again to a cooling zone through an introducing port (d) on the outlet side. Part of the atmosphere in the furnace is extracted through a discharging port (e) in the cooling zone and is introduced in the furnace after CO2 and H2O are removed with the refiner.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for annealing uncut hot-rolled steel wire rods or primary wire-drawn wire rods with scale attached thereto.
The present invention relates to an annealing method that allows annealing to produce a product with excellent scale releasability after annealing.

Conventionally, in the process of manufacturing steel wire rods for welding, the wire rods usually go through an annealing process, but when annealing wire rods with scale attached and remaining on the surface, if treated in a reducing atmosphere, the scales are dense and hard. Since Fe3O4 is difficult to crack, the mechanical descaling properties of the wire are poor. On the other hand, in an oxidizing atmosphere such as the air, Fe2O3 is generated, and since this has poor acid solubility, strong pickling with HCl or the like is required. In addition, the yield of steel material (pickling loss) also decreases due to pickling. Furthermore, in the case of an oxidizing atmosphere, 02 reacts with 0 in the wire, causing a decarburization phenomenon in the wire. However, N2
Even in inert atmospheres such as gases, trace amounts of CO2 and N
The existence of 20 cannot be prevented. In other words, air and moisture are brought in when the wire coils are brought in, and trace amounts of 02 and N2 contained in the supplied gas cause CO2 and l]
20 occurs.

These CO2 and N20 react with C in the wire, causing decarburization of the wire.

On the other hand, in order to anneal steel wire without scale adhering, it is necessary to pickle it before annealing, but pickling in this case is complicated and has low efficiency. . Furthermore, during annealing, CO in the atmosphere is used to prevent carburization and decarburization.

It is necessary to control CO2 concentration. However, since the atmospheric concentration changes due to CO9CO2 generated from the wire during annealing, it is difficult to control the concentration, and in addition, the amount of gas introduced from the gas generator must be increased in response to the concentration change to maintain the concentration at a predetermined value. Since the concentration is controlled so that the amount of gas used is increased, the amount of introduced gas must also be increased.

The object of the present invention is to provide a method for annealing a hot-rolled 14 wire rod with scale attached or a wire rod after primary wire drawing.
It is an object of the present invention to provide a method for annealing steel wire rods, which eliminates the above-mentioned drawbacks of the conventional methods and allows annealing of the steel wire material with excellent scale removability after annealing. An object of the present invention is to provide a method for annealing a steel wire rod, which makes it possible to prevent the decarburization phenomenon that occurs when annealing the steel wire rod.

That is, the gist of the present invention is as follows.

Hot-rolled wire coil or 1 with scale attached to the surface
Next, when the wire rod after wire drawing is annealed in a continuous annealing furnace, 02 is placed in the heating zone of the annealing furnace where the steel wire rod is heated to 570°C or less, toward the inlet side of the annealing furnace. Sail 5~
0.9vo7. At the same time, atmospheric gas is extracted from the inlet side of the annealing furnace, and this gas is again introduced into the annealing furnace mouth from the outlet side of the annealing furnace, and from the outlet side of the annealing furnace. After extracting a part of the atmospheric gas and passing this exhaust gas along with the atmosphere through a gas purifier to remove CO2 and N20'i from these gases, these purified gases are introduced into the above-mentioned part of the annealing furnace during heating, and the above The annealing furnace atmosphere'cO20O2~0.3 vot
A method for annealing @4 wire with excellent scale removal properties after annealing, characterized by maintaining an N atmosphere containing 02% and 02%, and performing annealing in this atmosphere.

Hereinafter, the scale layer of the steel material in which the present invention will be explained in detail includes F eo ,
Iron oxides of the form F C3C4 and F C2C3 exist. Among these, the Fe3O4 layer is dense and has a much lower breaking strength than the other layers, so it has the worst mechanical descaling properties. On the other hand, since Fe2O3 has a relatively low fracture strength, if it has good mechanical descaling properties, it is likely to cause cracks, so it also has good pickling properties.

The present inventor conducted various studies on annealing conditions that can improve the peelability of scale after annealing regarding a method of annealing hot rolled steel wire rods with scale remaining on the surface, and found that 0.0. It was found that by annealing in a N2 gas atmosphere containing 02 with a coefficient of 3vom or less, Fe3O4 in the inner layer of the scale becomes FC203 and becomes an iron oxide with good descalability by mechanical descaling method. It was.

The present invention is based on this knowledge. In the present invention, a coil of hot-rolled steel wire with scale remaining on its surface is annealed in a continuous annealing furnace in an N2 atmosphere containing O, O'02~Q, 3 vot, and 02%. The reason for limiting the 02 concentration in the N2 atmosphere in this way is as follows.

By adding a small amount of 02 to the N2 gas in the atmosphere, Fe304fi in the scale can be changed to Fe2O3 with good mechanical descaling properties as described above. If the amount is too low, Fe of 71Jtsuku will be generated in the scale and the mechanical descaling effect will be small.On the other hand, if the amount of 02 exceeds 3 voj!, the amount of 02 will be too large and the amount of C in the wire will Reacts and decarburization occurs.Or F
I(2S
O4 pickling produces insoluble scale, or even HOA pickling requires a longer pickling time. Furthermore, the amount of scale increases due to excess 02, resulting in poor pickling yield.

FIG. 1 is a chart showing the influence of the 02 concentration (VAT, %) in the N atmosphere on the rate of increase (ratio) of the scale amount after annealing with respect to the scale amount of the steel wire rod before annealing. 1st
As is clear from the figure, the smaller the 02 concentration, the less the scale increases. However, in such a case, it is difficult to manage the furnace operation, and as mentioned above, metallic Fe is generated in the scale, causing mechanical problems.・Descalability deteriorates. On the other hand, as the concentration of 02 increases, poorly soluble scale (F
e203) increases, resulting in a decrease in pickling efficiency and pickling yield.

Next, the adjustment of the atmosphere inside the annealing furnace in the present invention will be described.

As specified in the present invention, the atmosphere inside the furnace was set to 0.02 to 0.00.
As a means of maintaining an atmosphere of N2 gas containing 0.02 to 0.3 vOt, %, fuel and air are combusted at the required mixing ratio using a gas generator, and the generated gas (0.2, N20.
It is conceivable that it would be sufficient to remove the N2 gas (containing Co and the remainder being N2) using a N20° co2'1 adsorbent and supplying this to the annealing furnace as N2 gas with the above 02 concentration.
When the concentration falls below the 5th coefficient (voL), a small amount of CO2I-I2 is generated even though the combustion is complete. This N2 reacts with a trace amount of 02 in the furnace to become N20, raising the dew point in the furnace and causing grain boundary oxidation and decarburization.
(The presence of 2 must be absolutely suppressed. Therefore, in the present invention, the gas from the gas generator has a high 02 concentration to N2 + 0.5 to 0.9102. When this gas is introduced into the furnace, Since the 02 reacts with the wire, the 02 in the furnace atmosphere gradually decreases and eventually reaches 0%.

Therefore, in order to adjust the 02 of the atmosphere in the furnace to 002 or more and less than 000, the internal adsorbent is used to pass through the purifier outside the furnace. The atmosphere from which 1lI (20) has been removed is supplied into the furnace.Since the 02 concentration of the gases introduced into the furnace from both the generator and the purifier is higher than the atmosphere gas in the furnace, these gases are When introduced into a place with a temperature of 600℃ or higher,
The scale of the wire rod contains a lot of Fe2O3, and it is stuck into the iron base, so it cannot be removed by mechanical descaling and cannot be dissolved by H2SO4.

If you try to dissolve it at +-107, it will take more time than usual.

Therefore, when the gas was introduced at a place where the temperature of the wire was low during the entire heating zone, that is, below 570°C, it was found that there was little Fe2O3 formed on the wire scale, and therefore pickling could be performed without any problems. .

In addition, instead of adjusting the atmosphere in the furnace with air from the atmosphere as described above, the combustion gas is converted into N2+0 in the gas generator.
=5~0.9CH Increase the amount of 02 than 02, for example, N2
Although it is possible to manage the 02 in the furnace by introducing it as a 02 of 10.9 to 1.3, it is possible to control the 02 in the furnace due to fluctuations in the calorie of the fuel, e.g.
Even if gas around %02 is introduced into the zone below 570°C as mentioned above, the scale will contain a lot of Fe2O3, so the 02 concentration from the generator will be low, that is, N2+0-5 to 0.9.
It is more effective to use Chi o2.

However, the wire coils that are continuously fed into the furnace are
As it progresses and becomes high temperature, it reacts with 02 in the atmosphere and c
O2'1 is generated, but as this CO2 gradually increases, decarburization of the wire is promoted, so the annealing gas containing this CO2 must be discharged to the outside of the furnace. However, in this case N
2 gas will also be released, leading to an increase in the cost of producing inert gas.

Therefore, in the present invention, after all of the gas to be released is released, it is sucked into a gas purifier and the COz is removed by a built-in adsorbent, and the remaining Nzk is sent into the furnace again. In this way, gas costs can be reduced and energy can be saved.

Note that the purifier has the ability to remove N20 that has been brought into the furnace by adhering to the wire coil, and at the same time removes the CO2 in the waste gas, it also removes 1 (□0) in the furnace. Therefore, the effect of lowering the dew point of the atmosphere in the furnace and preventing the occurrence of grain boundary oxidation can also be obtained.

Figure 2 shows the atmospheric gas circulation system of the continuous annealing furnace according to the present invention, and Figure 3 shows the temperature of the wire as it moves in the annealing furnace. .

To explain Fig. 2, fuel is combusted with air in a gas generator at the required mixing ratio to produce N2 gas containing 5 to 0.9% 02, and the wire temperature in the heating zone is 570°C.
The gas is introduced from the gas inlet port (a) provided at the location below, and the atmosphere is passed through the gas purifier to produce N20
(After removing il-, the wire is introduced into the furnace through an inlet (b) separately provided at the point where the wire temperature is the same.The supply amount of these introduced gases is adjusted to maintain an atmosphere in the soaking zone of kN2+0.002 to 0.
．． Then, the air inside the furnace is extracted from the furnace through the exhaust port (C) provided on the furnace inlet side, and is passed through the fan through the inlet port Cd provided at the furnace outlet 1IllIIIK as shown in the flow. ) to the furnace cooling zone. As described above, the atmospheric gas is circulated in the direction shown in the figure. In addition, a part of the gas generated during annealing is extracted from the exhaust port (e) provided in the cooling zone and guided to a gas purifier to remove N20, 002'e from the exhaust gas, and then the gas generated by the annealing is removed from the exhaust port (b). Re-introduce from.

With the above atmospheric gas circulation system, the N2 gas with a relatively high O2 concentration comes into contact with the wire rod at a low temperature, and the N2 gas with a reduced O2 concentration comes into contact with the wire rod at a high temperature. Therefore, decarburization of the wire can be prevented and descaling can be carried out completely effectively. Furthermore, the furnace inner walls and wire rods are not contaminated by the gas used.

Examples of the present invention will be described below.

Table 1 It is. Let's talk about the annealing furnace atmosphere gas.

The position (a) of the gas inlet from the gas generator is at the furnace temperature 2.
At a position of 00 to 300℃, the gas input amount is 70 to 140℃.
Ntr? /Hr, gas composition is 020.5-0.9V
oA staff, CO□0.2~0.4■ot%, CO Otoho IV
ot'Z, the remaining N2 (C no., the amount of gas flowing into the furnace from the gas outlet in the furnace is 70
Since it is Nm/Hr, the gas inflow ratio is 70/70~1
40=1~2, the gas composition at the gas outlet in the p1 furnace is 020.002~0, 3V o is 0.
2-0.4 VojJ, 0040. IVoLl, residual N2, and the same as the average gas composition in the furnace.

Six examples of wire rod A made of steel with the components shown in Table 1,
Five examples of B were annealed in an atmosphere of 02-containing N2 gas under the annealing conditions shown in Table 2. The 02% inside the furnace in Table 2 was obtained by the atmosphere gas circulation method explained in connection with FIG. 2 on each side.

Next, after measuring the increase in scale for each annealed wire rod obtained from each side, a descaling test was performed for all mechanical descaling and pickling,
All descaling properties were evaluated.

The above test results are shown in Table 2.

Medium Wire diameter 4.5φ Compared to the amount of scale (wt.) before umbrella annealing ○ Good ◎ Very good As is clear from Table 2, the comparative example 7.8.9, which exceeds the upper limit of the 02 concentration in the annealing atmosphere specified in the present invention, has a large increase in scale. , the pickling yield is low and the pickling property is poor.
The comparative example of 10911vC, which has a concentration lower than the lower limit, has poor mechanical descaling properties.

On the other hand, all of the samples according to the examples of the present invention have better descaling properties and higher pickling yields. Therefore, according to the present invention, it is clear that an annealed material with excellent scale peeling can be obtained from a hot-rolled @wire rod with scale still attached.

[Brief explanation of the drawing]

FIG. 1 is a chart showing the relationship between 02a degree (VO7-%) in the N2 annealing atmosphere and the scale increase rate (Wt, %) after annealing, and FIG. FIG. 3 is a chart showing the temperature of the wire in the annealing furnace. a... Gas inlet from the gas generator, b... Gas inlet from the gas purifier, C... Furnace gas outlet, d...
・Exhaust gas inlet, e...Furnace gas outlet, F...Fan agent Koji Suzuki "Figure 1 022 agricultural degree CVo ox 1% in N2 atmosphere) Procedure correction @c
System) Kazuo Wakasugi, Commissioner of the Japan Patent Office, May 1, 1982 1 Indication of the case 1988 Patent Application No. 25515 2 Name of the invention Method for manufacturing steel wire rod with excellent scale removal properties after annealing 3
Relationship with the case by the person making the amendment Patent applicant President Takayoshi Takahashi 4th generation Masato 105 Telephone: 03-434-0832 Address: 4-22-7-7, Shinbashi, Minato-ku, Tokyo Statement of contents of amendment 12 Pages 1 and 15 are revised by adding separate sheets. to the cooling zone of the furnace. As described above, the atmospheric gas is circulated in the direction shown in the figure. In addition, a part of the gas generated in the dawn bell is extracted from the exhaust port (e) provided in the cooling zone and guided to the gas purifier to remove H2O and Co from the exhaust gas, and then the gas generated by the dawn bell is removed from the exhaust port (b). Re-introduce from. With the above atmospheric gas circulation method, the N2 gas with a relatively high 02 concentration comes into contact with the wire rod at a low temperature (4 degrees Celsius), and the N2 gas with a low 02 concentration comes into contact with the wire rod in a high temperature state. Therefore, decarburization of the wire rod can be prevented and descaling can be carried out effectively.Furthermore, the inner wall of the furnace and the wire rod are not contaminated by the first refill gas.Examples of the present invention will be described below.First This is a table. Regarding the annealing furnace atmosphere gas, - ○ Good (0 Very good) with respect to the scale It (wt, Chi) before annealing

Claims (1)

[Claims] Hot-rolled steel wire coil or 1 with scale attached to the surface
Next, when annealing the drawn wire in a continuous annealing furnace,
A sail 5 of 02 is placed in the heating zone of the annealing furnace where the steel wire rod is heated to 570°C or less, with the sail 5 pointing toward the inlet of the annealing furnace.
Introducing N2 gas containing ~0.9 voL, extracting atmospheric gas from the annealing furnace inlet side, and introducing this gas into the annealing furnace again from the annealing furnace outlet side, and A part of the furnace atmosphere gas is extracted from the side, and this exhaust gas is passed through a gas purifier together with the atmosphere to remove CO2 and 1120 from these gases, and then these purified gases are passed through the above-mentioned i in the heating zone of the annealing furnace. The scale removability after annealing is improved by maintaining the annealing atmosphere in a N2 atmosphere containing 02 of sail 002 to Q, 3 vom attack by the above operations, and annealing is performed in this atmosphere. Excellent steel wire annealing method.