JPS5846534B2 - Direct current annealing method for steel wire - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of annealing a steel wire by direct current application.

Steel wire rods that undergo secondary processing such as cold forging and rolling after wire drawing (
Wire rods (hereinafter abbreviated as wire rods) are usually subjected to an annealing treatment in order to restore the ductility and adjust the strength of materials that have been work-hardened by wire drawing.

The annealing treatment is generally carried out in a heating furnace called a pot furnace or a bell-shaped furnace.In the annealing treatment in these heating furnaces, several coils of wire are placed in a container with an appropriate atmosphere, and the wire is heated indirectly or directly using a burner, etc. This method involves heating and cooling in the atmosphere after heating, and therefore has the following problems.

(1) Thermal efficiency is very poor (usually around 60%) and heating costs are high.

(2) Processing time is long (0.1 to 0.5 /1
1. ) (3) Product lacks uniformity due to unrestricted temperature distribution in the furnace and non-uniform cooling during cooling.

The present invention eliminates the above-mentioned drawbacks, improves thermal efficiency and processing capacity, and at the same time satisfies various mechanical properties (tensile strength, reduction of area, twist value, cold workability, etc.) of the wire rod after processing. The amount of C should be 0.55 to keep it within the desired set point.
While feeding out the steel wire containing less than 700% of
After heating the wire to a temperature of ~800°C, the winding start temperature is set to 350°C or higher, and the wire is kept warm and gradually cooled using the heat of the wire itself while being wound on a heat-insulating winding Lisbourg. The present invention relates to a direct current annealing method for wire rods.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained in detail below based on an illustrated embodiment.

FIG. 1a shows an example of an apparatus for actually testing the method of the present invention.
FIG. 2 is a front view schematically showing a direct current annealing line for wire rods using a heat-insulating winding Lisbourg for heat-retaining winding.

The wire material 2 to be annealed stored on the payoff reel 1 passes through a guide roller 3 and is straightened by a straightening roller row 4,
The input side of the delivery roller passes through the idle roller 5 and is wound up on the delivery roller 6 which rotates via a motor and a transmission (not shown).

In order to avoid excessive tension from being applied to a series of wire rods on the complete annealing line from the payoff reel 1 through the electrode roller 9 to the insulated winding spool 15, the number of turns of the wire rod 2 on the above-mentioned delivery roller 6 is normally set. It will be set in 2 to 3 volumes.

Feeding out from the feeding roller 6, roller exit side guide roller 7
The wire rod 2 sent out through the electrode roller inlet guide roller 8 is sent to three electrode rollers 9.

In the electrode roller 9, the wire to be annealed 2 is directly energized from its contact point, and the temperature of the wire to be annealed 2 rises to 700°C to 800°C on the exit side of the electrode roller 9 at the last stage due to Joule heat due to the electrical resistance of the wire to be annealed 2 itself. The current and voltage are adjusted so that the temperature is ℃.

In this actual estimation, the electrode roller 9 is driven by a drive motor.

Wire rod to be annealed 1 after heating heated to 7000-800°C
1 is an electrode roller exit side guide roller 10 while being air-cooled;
Through the take-up spool guide roller 12, the take-up guide roller 13 of the take-up guide device 14 takes up the winding in an aligned manner onto an adiabatic take-up lisbourg 15 which rotates via a drive motor and a transmission (not shown).

FIG. 1 is a plan view of the winding guide device 14 and the heat insulating winding spool 15 in FIG. A winding guide roller 13 provided in a winding guide device 14 that reciprocates in the direction of arrow B on a track 16 in accordance with the rotation of the take-up spool 15 causes the windings to be wound on the heat-insulating winding Lisbourg 15 in alignment.

The temperature of the annealed wire material 11 after heating at the start of winding is:
In the present invention, the temperature is 350° C. or higher, and the higher the winding temperature is, the shorter the air cooling section from the electrode roller 9 to the winding spool 15 can be, and the overall length of the line can be made more compact.

Furthermore, if the temperature at the start of winding does not need to be high, the air cooling time can be shortened, which means that the speed of the line can be increased.

Of course, there are cases where the line length from the electrode roller 9 to the insulated winding spool 15 cannot be set freely, or there is a limit to how fast the line can be run due to the electric capacity of the electrical heating machine, and the winding start temperature cannot be adjusted to the required value. If it is not possible to reduce the temperature, the objective can also be achieved by applying slow cooling or forced cooling by an appropriate method between the electrode roller 9 and the adiabatic take-up spool 15.

The structure of the insulated take-up spool 15 is shown in FIG. 1C.

The contact portion of the heat-insulating take-up spool 15 with the wire material 11 to be annealed is covered with a heat-insulating material 17 to prevent the wire material 11 from being rapidly cooled.
and is further protected by a heat insulating material protection material 18 to prevent the heat insulating material 17 from being worn out.

In addition, good results can be expected by surrounding the take-up spool 15 itself with a cover made of a heat insulating material in order to enhance the effect of slow cooling.

When the annealing of a predetermined amount of wire rod is completed, the insulating winding spool 15 is taken out from the line, and the wire rod is gradually cooled to a temperature of 200° C. or less, and then air cooled to complete the annealing.

The results of investigating the influence of electrical annealing conditions on the steel wire rods listed in Table 1 using such an apparatus are shown below.

Figures 2 and 3 are graphs showing the results of investigating the relationship between the wire rods, heating temperature, and mechanical properties of the wires imparted by the direct current heating method of the present invention for steel A and steel D; The axis shows the heating temperature, and the vertical axis shows the mechanical properties, ie, tensile strength, reduction of area, and torsion value, respectively.

Here, the temperature at the start of adiabatic winding (hereinafter referred to as winding temperature) was set at 620°C.

From this temperature, 9 windings of approximately 500 mm are wound on the insulated winding spool 15, and then left to cool slowly. When the wire temperature drops to 200°C or less, the wire is removed from the insulated winding Lisbourg 15, and the temperature is lowered to room temperature by air cooling. After that, the mechanical properties were tested.

As is clear from the graph, when the heating temperature exceeds 700°C, the tensile strength of steel A and steel D decreases, respectively.
53 kg/1art and 42 to 9/yn? is approximately constant around 700℃, the aperture is 65% or more and 70% or more, and the twist value is 90 or more and 100 or more times, maintaining favorable conditions in which these properties are balanced compared to temperatures below 700℃. do.

Therefore, the lower limit of the heating temperature was set at 700°C.

Furthermore, the reason why the upper limit of the heating temperature was set at 800°C is that at temperatures above 800°C, the twist value decreases and at the same time the power consumption used for heating increases compared to the range of 700° to 800°C. It's for a reason.

FIGS. 4 and 5 are graphs showing the influence of the winding temperature after direct current heating on the mechanical properties, with the horizontal axis representing the winding temperature and the vertical axis representing the mechanical properties.

The wire rods to be annealed subjected to the test were A steel and D steel as in the case of Figs. 2 and 3, and the heating temperature in this case was
In Fig. 3, the temperature was set at 740°C, which gave the best mechanical properties.

As is clear from the graphs in Figures 4 and 5,
When the winding temperature is 350'C or higher, the mechanical properties stabilize on the high quality side, or improve slightly as the winding temperature increases.

Therefore, the lower limit of the winding temperature was set at 350°C.

The upper limit of the winding temperature is theoretically considered to be the heating temperature.

Next, the reason why the amount of C was limited to 0.55% or less will be described.

FIG. 6 shows the drawing of wire rods annealed under current annealing conditions (heating temperature 740° C., coiling temperature 620° C.) considered to be the best for six steel types up to A and D-H steels.

For comparison, the same figure also shows the results of pot annealing the same wire.

The reduction of area of the annealed wire rod according to the method of the present invention is very close to that of the pot annealed wire rod.

In either case, the reduction of area decreases as the amount of C increases, but when the amount of C exceeds 0.55%, the area of area of the annealed wire rod according to the method of the present invention decreases rapidly.

From this, it can be seen that the effect of annealing according to the method of the present invention is
It is noticeable in steels with a content of 5% or less.

As an example showing the effect of the annealing method of the present invention, a wire rod according to the present invention, a wire rod annealed in a conventional pot furnace, and a wire rod treated by rapid heating by energization, air cooling, and water cooling by a comparative method conducted experimentally. The torsion value is shown in Table 2, the drawing value is shown in Table 3, and the limit compression ratio is shown in Table 4.
Table 5 shows a comparison of the thread formability when rolled in 25).

As is clear from these results, the direct current annealing method of the present invention is far superior to the comparative current annealing method tested, and is superior to the conventional pot furnace annealing method that is commonly used. However, it is almost comparable, and in fact, it is a far superior treatment method when compared including heat treatment cost and processing capacity, and its industrial value is extremely high.

Although FIG. 1 shows an example in which a take-up spool is used for winding the wire, the same effect can be obtained by using a polling reel or a laying reel.

Table 1 shows the chemical composition and fine diameter of the sample materials, and Tables 2, 3, 4, and 5 show the torsion values after annealing, respectively.
The present invention is compared with a conventional method and a comparative method in terms of reduction of area, critical compression ratio, and tapping thread rolling property.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an example of an apparatus for carrying out the method of the present invention, in which a is an overall front view, b is a plan view of a as viewed from arrow A, and C is a
2 is a cross-sectional plan view of the take-up spool 15. FIG. FIGS. 2, 3, and 3 are graphs showing the influence of the heating temperature on the mechanical properties of the wire in the present invention, and FIGS. 4, 5, and 5 are graphs showing the influence of the winding temperature on the mechanical properties of the wire. FIG. 6 is a graph showing the relationship between the C content of the steel wire rod and the reduction of area after annealing in the present invention and the conventional method (pot annealing method). The following is a brief explanation of the drawings: 1... Payoff reel, 2... Wire to be annealed, 3... Guide roller, 4... Straightening roller row, 5・・・・・・Guide roller on the input side of the feeding roller, 6・・・・・・Feeding roller, 7・・・・・・The exit side of the feeding roller is the idle roller,
8... Electrode roller entry side guide roller, 9...
... Electrode roller, 10 ... Electrode roller exit side is idle roller, 11 ... Wire material to be annealed after heating, 1
2... Winding spool guide roller, 13...
... Winding guide roller, 14... Winding guide device, 15... Heat insulation winding Lisbourg, 16.
... Winding guide device track, 17 ... Heat insulation material, 18 ... Heat insulation material protection material.

Claims (1)

[Claims] 700 to 800 by direct energization with an electrode roller while feeding out a steel wire containing 0.55% or less of C content.
Direct energization of a steel wire, which is characterized in that after being continuously heated to a temperature of 350°C or higher, the wire is kept warm and slowly cooled using the wire's own heat while being wound on a heat-insulating coiled Lisbourg at a temperature of 350°C or higher. Annealing method.