JPS61257417A - Production of wire having excellent cold workability - Google Patents

Abstract

PURPOSE:To produce a wire having excellent cold workability with high productivity by rolling a steel having the large ideal critical diameter calculated from the component compsn. by using the specific equation and high hardenability to the wire then coiling the wire in a holding furnace or slow cooling furnace. CONSTITUTION:The steel having >=100mm, more preferably about >=130mm ideal critical diameter calculated by the equation; DI(mm)=7.95C0.5(1+0.64Si)X(1+4.10Mn)X(1+2.87P)X(1-0.69S)X(1+2.33Cr)X(1 +0.52Ni)X(1+3.14Mo)X(1+0.27Cu)X{1+1.5(0.9-C)}, (where DImm; ideal critical diameter, {1+1.5(0.9-C)} is applied only when <=0.9% C and B is added) and the hardenability is heated to the Ac1 point or above and is then rolled to the wire. The wire is worked at >=10% reduction of area in the temp. region of Ae1 point - Ar1 point in the final stage of rolling and is then coiled in the holding furnace or slow cooling furnace.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for manufacturing wire rods with excellent cold workability, and particularly to wire rods having an ideal critical diameter (DI) of 100 or more and high hardenability. The present invention relates to a method of directly heat-treating a wire to obtain a wire coil with excellent cold workability.

Conventional technology and its problems In the production of wire rods, if the rolled wire rod is large in diameter, it is wound up on a polling reel and left to cool in a coil, but if it is small in diameter, it is wound up in a laying cone. Conveyor L
It is expanded and cooled either by air cooling or by blowing air. Therefore, the cooling rate of the small diameter coil is 2°C/SeC ~ 1
0℃/see, 10 at the contact part with reel and conveyor
The cooling rate may be higher than °C/sec. Therefore,
When manufacturing wire rods with high hardenability and an ideal critical diameter (DI) of 100 degrees or more, a bainite or martensite structure is generated, and if as-rolled, peeling,
Processing such as wire drawing, profile processing, forging, cutting, and drilling becomes difficult. For this reason, the following methods are conventionally known for steel having high hardenability.

■A method of annealing a rolled wire rod coil in a heat treatment furnace with separate fins for 10 to 100 hours, ■A method of forging, annealing, cutting, etc. from a steel ingot while abandoning wire rods that require a high cooling rate, ■Rolling A method of softening the wire by slowly cooling or heat-retaining it immediately after rolling using the head heat of the wire (Japanese Patent Application Laid-open No. 56-133445, Japanese Patent Application Laid-Open No. 58-27926)
．． JP 58-58235° JP 58-107416
．． JP-A-59-13024, etc.).

However, in all of these methods, the temperature is reduced only on the surface of the coil because it is wound outside the furnace after rolling, and only the part where the coil contacts the winding device is locally cooled. The disadvantage is that the temperature distribution inside the coil becomes uneven and the quality of the coil fluctuates widely. Furthermore, since the transformation rate varies widely depending on the W4 type, continuous processing of different steel types is difficult.

Purpose of the Invention The present invention has been made in view of the above-mentioned conventional tessellation point, and is a wire rod having high hardenability with an ideal critical diameter (DI') of 100 m or more, which is directly heat-treated to improve cold workability. The purpose of this book is to suggest a method for obtaining excellent wire coils.

Composition of the Invention The method for manufacturing a wire rod with excellent cold workability according to the present invention involves rolling a steel having high hardenability with an ideal critical diameter (DI) of 100 mm or more into a wire rod, and then holding the wire rod. It is characterized by being rolled up in a heat furnace or a slow cooling furnace, and after heating steel with the same high hardenability to a point of Ac1 or higher,
c. It is characterized in that it is rolled into a wire rod with a working degree of 1096 or more in a temperature range of 1096 or higher, and then wound in a heat retention furnace or a slow cooling furnace, and also has the same high hardenability. After heating the steel to Ac 2 point or higher, As 1 point or less 500
It is characterized in that it is rolled into a wire rod with a working degree of 1096 or higher in a temperature range of .degree. C. or higher, and then wound in a heat retention furnace or a slow cooling furnace.

Here, the ideal critical diameter (DI) is a value calculated from the chemical composition values of steel using the following formula.

DI (x)-r, 95J5.96xt 1+0.64
rst% month X (1+4.10 [Mn%])X mouth+
2.87 [P%]}×{1-0,69(8%)}×{1
+2.33 [Cr%]}×{1+0.52 (N1%)}
×{1+3.14 [Mo%]}×{1+0.27(Cu
%) lx(1+1.5 (0,9-CG system) However, [
1+1.5 (0,9-CC%])) is 0.9% for C child.
Applicable only to the following steels to which B is added.

That is, this invention has an ideal critical diameter (DI) of 10
Targeting steel wire rods of 0 m or more, preferably 130 m or more, As1 to Ar! at the final stage of rolling. , preferably 70
A degree of workability of 10% or more, preferably 20% or more is imparted to the untransformed state in a temperature range of 0°C to 500°C, and after rolling, it is rolled in a heat retention furnace or a slow cooling furnace installed close to the rolling fins. This is the way to take it.

In this invention, the reason why a pearlite structure wire rod made of steel with an ideal field 1f diameter (DI) of 100 mm or more, preferably 130 m or more is targeted is as follows.

For steel wire rods with high hardenability, there is no problem if they are reheated with separate fins after rolling or treated with lead patenting. A wire rod with a structure that does not contain bainite or martensite can be obtained, but if the wire diameter is less than 9 φ, martensite will be mixed and cannot be drawn or processed, and DI≧
This is because when the wire rod becomes 130+W, bainite and martensite coexist in all wire diameters in a coiled wire, making it impossible to draw the wire.

Furthermore, the reason why the pre-rolling mi degree of the steel is set to be Ac, or higher is due to the following reasons. In order to make the structure after rolling into a pearlite structure, it is necessary to once decompose pearlite into a solid solution and eliminate it before rolling. For this reason, it is necessary to raise the heating temperature to above the Ac point, and below the Ac H point, cementite remains undecomposed in the structure and is rolled, resulting in a pearlite structure with excellent green workability. This is because it becomes impossible to do so.

In addition, setting the finish-E rolling start temperature to 1 point or more of Ar below the As point, preferably 500°C or more below the Ae H point is as follows:
This is due to the reasons shown below. Since austenite is metastable at an Ae of 1 or less, barfit transformation can be induced by applying working strain, and a pearlite structure can be easily obtained even in highly hardenable steel. However, in the temperature range above the AeI point, austenite is in a stable range, so the above effect becomes very small. Further, when the temperature is below the Ar point, austenite precipitates ferrite and cementite, so even if rolling is performed after such a structure appears, the desired pearlite structure cannot be obtained. In addition, with the target high hardenability steel, it takes a long time to reach the Ar1 point, and on a continuous rolling line, it takes a long time to reach the Ar1 point.
It is often difficult to perform rolling below a point. In order to obtain the desired pearlite structure, it is desirable that the transformation temperature of austenite is 500° C. or higher. This is because bainite is mixed at temperatures below 500°C. Therefore, the finish rolling start temperature is set at AsH to Ar1, preferably AsH point to 5.
The temperature was limited to 00°C.

The As1 point is determined by the steel type composition, and for low alloy steel it is 73
It is widely distributed from around 0°C to around 850°C in some tool steels.

Note that when the rolling speed is high, the wire temperature may rise or fall due to processing heat generated by rolling, and the rolling end temperature may be higher than the finish rolling start temperature.

There are many factors that affect this rolling end temperature, and precise control is extremely difficult. Therefore, in the present invention, the finish rolling start temperature is limited as described above. However, when the rolling end temperature exceeds AC1 point, the wire returns to the austenitic structure, and the rolling end temperature is AC8.
It is necessary to keep it below the point.

In addition, in this invention, 10% or more, preferably 20%
The reason for applying the above processing is that when processing in the above temperature range, the higher the processing degree, the greater the effect of promoting pearlite transformation, and when the degree of processing is less than 10%, this effect is not fully exhibited.
This is because 20% or more is practically desirable.

Further, the present invention is characterized in that after rolling, the coil is wound in a heat retention furnace or a slow cooling furnace, and this is to ensure uniformity of temperature in the height direction and radial direction of the coil, thereby stabilizing quality. That is, since the wire remains in the heat retention furnace or the slow cooling furnace from the start to the end of winding, there is no difference in temperature from the start to the end of winding. Therefore, the temperature in the height direction of the coil is made uniform, and temperature buffing in the coil radial direction due to heat dissipation from the coil surface is also eliminated. Furthermore, Ar
Since the 1g state occurs, extremely stable quality can be obtained. Here, slow cooling means cooling at a cooling rate of 2° C./8 eC or less, and heat retention means isothermal maintenance.

Specific example 1s1 figure, figure 2, figure 3, figure 4 and w! FIG. 15 shows an example of a direct softening heat treatment apparatus for carrying out the method of this invention. That is, the ts1 diagram shows a wire rod (M) hot or warm rolled by a rolling mill (1) in a pot furnace (
2) shows the method of heat treatment in I-9, rolling mill (1)
The wire rod (M') that has come out is formed into a spiral shape by a laying head 3), and immediately wound up in a bobbin (21) installed in the vicinity of the laying head.

The pot furnace (2) is maintained at a predetermined temperature in advance by a heating element (4) provided inside. When the wire (M) is wound up in the pot furnace (2) and becomes a coil, it is immediately sealed with a furnace lid (5).The coil stored in the pot furnace is transported on a conveyor (6). Then, during transportation, a predetermined slow cooling or heat retention is performed, and when the direct softening treatment is completed after reaching a predetermined temperature or a predetermined time, the furnace lid (5) is removed.
taken out. The emptied pot furnace passes through another fin, returns to a predetermined temperature near the laying head (3), and is again directly used for softening heat treatment.

Figure 2 shows a method of directly performing softening heat treatment in a continuous furnace.
After the wire rod (M'l) is hot or warm rolled by the rolling mill (1), it is wound up in the continuous furnace mouth by the laying head (3). )
However, in the case of a continuous furnace, a conveyor (1ω) is installed inside the furnace, and a door (1ω) is installed on the exit side to take out the coil.
2) is provided.

The wire rod (M) that comes out of the rolling mill (1) is sent to the laying head (3)
A continuous furnace (rolled in the mouth, carp tv (J
), the furnace ffi (15) is closed immediately. When the preceding coil (φ) in the continuous furnace moves and can be carried into the furnace, the entrance door Oη opens and the conveyor (16) passes through the entrance door (1η) and is transported sequentially, and is heated or slowed during transportation. The coil products that have been subjected to the prescribed heat treatment are taken out through the exit door and the carry-out door (13), and the direct softening heat treatment is completed.

Figure 3 shows an example of a method for winding wire without using a laying head.The winding device is driven by a motor (8) in a pot furnace equipped with a heating element. J--fv
(2) is installed, and the wire rod (M) coming out of the rolling mill (1) is sequentially wound onto a take-up reel (support). When winding is completed to form a coil (M), the furnace cover (E) is closed and the coil (M) is conveyed one cycle by the conveyor (1).

FIGS. 4 and 5 show examples of apparatuses in which the laying head is of a horizontal type and an ink fin type, respectively. In this case, since the laying head is open in the direction of movement of the wire, the wire formed into a loop is transferred to the furnace after moving on the heat retention or slow cooling conveyor (6-) ()16-1. It is wound up inside.

In addition, in order to prevent oxidation and decarburization from occurring on the surface layer of the wire during heat treatment, the pot furnace (2) (support) or the continuous furnace (12) is equipped with equipment that can seal inert gas or reducing gas. Therefore, in this case, in a continuous furnace, in order to prevent the furnace atmosphere from being disturbed when the coil is brought in and taken out, the inlet and outlet should be provided with an inlet door α'7) and an outlet door (shown by broken lines). 181 must be provided.

In addition, as a means for raising the temperature of the furnace atmosphere and retaining heat, we have shown here a case in which a heating element installed inside the furnace is used, but the heat source does not necessarily have to be inside the furnace. It's okay.

Furthermore, if a predetermined heat retention or slow cooling can be carried out, a heat source is not necessarily required.

Example 1 Smelting in electric furnace in vacuum and forming into 2 ton steel ingot 130■X
After hot forging into a steel billet with a cross section of 130 m, the components and ideal critical diameter (
Among the nine types of test steels with DI), steel types A, B,
Wire rods were manufactured using two pieces of each steel pieces E, F, and G under the manufacturing conditions shown in Table 2. At that time, the heat pattern for slow cooling was such that the furnace temperature was set at 750° C. during coil winding, and after winding was completed, slow cooling was carried out to 650° C. over 1 hour, and the coil was taken out.

The wire rod was beered by the reverse die method and then cold drawn to 2.5 φ using a continuous wire drawing machine to investigate its workability.

Also, for comparison, steel types A and B shown in Table 1, which is the same as above.
, E, F, and G steel billets were manufactured using the conventional method shown in Table 2, and the workability was investigated using the same method as above.

The results of this example are shown in Table 3.

(Left below) From the results in Tables 2 and 3, it can be seen that in conventional steel type A, bainite is mixed in the structure, and pearlite structure or softened #I
It is not organized and does not achieve its purpose. Also steel type B
However, it had a mixed structure of bainite and martensite, and could not be processed. Similarly, in steel types E, F, and G, bainite and martensite were partially generated in the cross section and longitudinal direction of the wire rod, and the structure was nonuniform. Although peeling processing was possible, wire drawing processing was not possible.

On the other hand, in the examples of the present invention, there was no tissue defect at all.
The hardness was also lower, and bealling and wire drawing became extremely easy and there were no troubles.

Example 2 Steel types C, D, H, and I shown in Table 1 were used, and after rolling, they were wound up in a pot furnace shown in FIG. 1 and kept at a constant temperature of 730° C. for 3 hours. The finishing rolling temperature was 490° C. to 950° C., the finishing rolling degree was 9% to 64%, and the manufacturing conditions were as shown in Table 4. In addition, to prevent oxidation and decarburization, the atmosphere inside the pot furnace was injected with Toganu. After keeping the temperature constant, it was allowed to cool inside the furnace. The results of this example are shown in Table @5.

From the results in Tables 4 and 5, it is clear that w4 type C, which becomes a bainite and martensitic structure using conventional manufacturing methods and cannot be processed raw,
Regarding D, H, and I, it was found that according to the method of the present invention, they can be manufactured as wire rods that can be processed raw. Looking at the effect of finish rolling temperature on steel type I among the four types of steel, test No. 6, in which finish rolling was applied at 490°C, had a bainite structure, and some wire breakage occurred during wire drawing. However, it is clear that raw processing is possible. However, the die wears out a lot during peeling, making it difficult to use. In addition, the finishing degree shown as a comparative example is 9%, 16
．． In the case of the 5φ wire rod, a bainite structure was present, and wire breakage was observed during wire drawing. Therefore, it can be seen that when the degree of working is less than 10%, both the structure and properties become somewhat unstable.

Effects of the Invention As explained above, according to the method of this invention, it has high hardenability with an ideal critical diameter (DI) of 100 mm or more, and it has a high hardenability of 100 mm or more. High-alloy steel wire rods can be easily processed, and since the wire rods are rolled and rolled in a furnace, the quality fluctuations within the cari μ are extremely small. Furthermore, as is clear from the above examples,
According to the method of this invention, even steels with greatly different hardenability can undergo Arl deformation after being kept at constant temperature for about 3 hours, making it possible to continuously produce these steels under the same manufacturing conditions.
Productivity will also be extremely high.

[Brief explanation of the drawing]

FIGS. 1, 2, 3, 4, and 5 are schematic diagrams showing an example of a direct softening heat treatment apparatus for carrying out the method of the present invention. 1...Rolling mill, 2,22...Pot furnace, 3...
... Laying head, 4, 14, 24... Heating element, 5, 15, 25... Furnace lid, 6, 16, 26...
...conveyor, 17...inlet door, 18...outlet door, 27...motor, 28...take-up reel,
M...Wire rod, M...Coil.

Claims (1)

[Claims] 1. A steel having hardenability with an ideal critical diameter calculated by the following formula of 100 mm or more is rolled into a wire rod, and then the wire rod is wound in a heat retention furnace or a slow cooling furnace. A method for producing wire rods with excellent cold workability. 2 After heating a hardenable steel with an ideal critical diameter of 100 mm or more calculated by the following formula to a temperature of Ac_1 or higher, it is rolled into a wire rod with a working degree of 10% or more in a temperature range of Ac_1 or Ar_1 or higher. A method for producing a wire rod with excellent cold workability, characterized in that the wire rod is wound in a heat retention furnace or a slow cooling furnace. 3 After heating the hardenable steel with an ideal critical diameter of 100 mm or more calculated by the following formula to the Ac_1 point or higher, it is rolled into a wire rod with a working degree of 10% or more in a temperature range of 500°C or higher below the Ae_1 point. A method for producing a wire rod with excellent cold workability, characterized in that the wire rod is wound in a heat retention furnace or a slow cooling furnace. DI (mm)=7.95√C%×{1+0.64[Si
%]}×{1+4.10[Mn%]}×{1+2.87
[P%]}×(1-0.69[S%])×{1+2.3
3 [Cr%]}×{1+0.52[Ni%]}×{1+
3.14 [Mo%]}×{1+0.27[Cu%]}×
{1+1.5(0.9-[C%])}DI (mm): Ideal critical diameter However, {1+1.5(0.9-[C%])} means that the C content is 0.9% or less. Applicable only to steel with B added.