JPH06212282A - Production of heating wire - Google Patents

Abstract

PURPOSE:To stably produce a heating wire in which disconnection is prevented in a wire drawing stage by subjecting a ferrochrome alloy having a specified compsn. essentially consisting of Cr and Al, and the balance Fe to specified wire rod rolling, coiling, annealing, cooling and heat treatment. CONSTITUTION:A ferrochrome alloy contg. <=0.10% C, <=1.50% Si, <=1.0% Mn, 17.0 to 26.0% Cr and 2.0 to 6.0% Al and contg. <=0.04% P and <=0.03% S, and the balance substantially Fe is heated to 950 to 1100 deg.C, is subjected to wire rod rolling and is coiled round a coil at 750 to 1000 deg.C. In this way, the refining of the alloy structure and the prevention of the coarsening of the crystals after being recrystallized are attained. This rolled wire rod is annealed at 650 to 830 deg.C and is thereafter rapidly cooled at 65 to 250 deg.C/sec. In this way, the elongation and drawing of the wire rod are improved, and its workability in ductility is improved. Next, this wire rod is furthermore subjected to heat treatment of heating to 250 to 500 deg.C to increase its wire drawability and scalping properties, and after that, it is subjected to wire drawing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improved method for producing a heating wire of ferrochrome alloy.

[0002]

As a ferrochrome alloy for heating wire,
Currently, the following three types are in practical use: Cr% Al% Fe volume resistance value μΩm FCHW1 17-21 2-4 balance 1.23 ± 0.06 Medium Cr high Al alloy 20-25 4-6 balance 1.37 ± 0.02 FCHW2 23-26 4-6 Remainder 1.42 ± 0.07 Selected and used according to the volume resistance value required according to the application.

The process for producing a heating wire from a ferrochrome alloy is slab rolling-wire rod rolling (hot) -wire drawing (cold), but since these alloys are difficult to work and are brittle at room temperature, they are wire-drawn. It was difficult to keep a stable operation because a wire breakage was likely to occur in the process and a skin removing process performed before or during the wire drawing.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems relating to the production of heating wires of ferrochrome alloys and to provide a production method in which the occurrence of wire breakage during the wire drawing process is significantly reduced.

[0005]

The method for producing a heating wire according to the present invention is as follows: C: 0.10% or less, Si: 1.50% or less, M
n: 1.0% or less, Cr: 17.0 to 26.0% and Al: 2.0 to 6.0% contained, P: 0.04% or less, S: 0.03% or less. And ferrochrome alloy with the balance being essentially Fe, at a heating temperature of 950 to 1100 ° C.
The wire rod is rolled at 750 to 1000 ° C., the coil of this wire is annealed at a temperature of 650 to 830 ° C., then rapidly cooled at a cooling rate of 65 to 260 ° C./sec, and further heated to a temperature of 250 to 500 ° C. It is characterized in that it is subjected to a heat treatment of heating and then directed to the wire drawing step.

The cooling rate after annealing the wire-rolled coil can be obtained by forced air cooling or water cooling with a blower.

The subsequent heat treatment at 250 to 500 ° C. is carried out in a short heating time. The lower limit of 250 ° C. is less than 1 hour, and the upper limit of 500 ° C. is less than 10 minutes. When pickling the coil prior to wire drawing, it is often immersed in a salt bath at about 440 ° C. for several minutes, and this salt bath immersion can replace the heat treatment.

[0008]

The function of the ferrochrome alloy defined in the present invention is
Regarding Cr and Al, the specifications of the above-mentioned grades for ordinary heating wire are put together. C, Si
Although the amounts of Mn and Mn, and the impurities P and S are not specified in the standard, they are the limits of the products that are actually commercially available.

Heating temperature for rolling the wire rod 950 to 110
0 ° C. is in a region lower than the temperature around 1200 ° C. which is usually adopted in this operation. In the present invention, an attempt is made to make the crystal fine by inducing dynamic recrystallization in the alloy structure, and a heating temperature of 950 ° C. or higher is selected, while preventing the crystal after the recrystallization from becoming coarse. Therefore, the upper limit of 1100 ° C. is set.

The practical basis for choosing this temperature is shown in FIG.
It is in. The graph of FIG. 1 shows the results of examining the presence or absence of recrystallization by heating steel billets of FCHDD alloy to various temperatures and rolling at a rolling reduction of 40% or 80%.

If the temperature at the time of coiling, that is, at the end of rolling of the wire rod is lower than 750 ° C., the workability is deteriorated. On the other hand, if the temperature is higher than 1000 ° C., the crystal grains become coarse. , Within this range.

The annealing temperature of 650 to 830.degree. C. is essentially the same as the temperature used for normal strain relief annealing.

The rapid cooling after annealing is an important step, and the lower limit of the cooling rate of 65 ° C./sec or more is necessary to avoid the occurrence of so-called 475 ° C. brittleness. The upper limit was set as a limit that can usually be achieved by water cooling, which is a quenching operation that can be easily performed.

The rationale for a high cooling rate is shown in FIG. FIG. 2 is a graph showing the results of measuring the tensile strength, elongation, and drawing of a sample obtained by rolling an FCH1 alloy into a wire having a diameter of 6 mm, heated at 750 ° C. for 10 minutes, and cooled at various cooling rates. From this data, it can be seen that quenching improves elongation and drawing and enables ductility processing.

The final heat treatment, together with the processing and heat treatment operations up to that point, is a step necessary for improving the wire drawability and peeling property of the wire. The effect is obtained by heating at 250 ° C. or higher, and is effective at a temperature up to about 700 ° C. However, high temperature causes coarsening of crystal grains and must be avoided. The upper limit of 500 ° C. is determined mainly based on the balance between effect and energy consumption.

[Test Example] C: 0.02%, Si: 0.49%, Mn: 0.26
%, Cr: 20.8%, Al: 5.0%, P: 0.02
%, S: 0.001%, the balance Fe was a medium Cr high Al ferrochrome alloy and was cast, cast into a steel ingot, and slab-rolled.

This steel piece was rolled into a wire at a heating temperature of 1000 ° C. and wound into a coil at a temperature of 780 ° C. Coil 7
It was annealed at 50 ° C., cooled at various cooling rates, and subsequently subjected to heat treatment of heating to various temperatures.

The aperture value of each sample was measured, and a drawing wire machine was used to draw a heating wire having a diameter of 3.8 mm.
The results are shown in the table below.

Table No. Cooling rate after annealing Heat treatment after cooling Drawing of wire rod Drawing ℃ / sec ℃ % disconnection 1 25 100 12 frequent 2 25 350 350 18 frequent 3 45 100 13 frequent 4 45 350 350 24 scattered 5 70 100 8 high 6 670 250 63 no 7 7 70 450 74 no 8 No. 240 150 18 Many 9 240 240 71 No 10 240 450 76 No No. 6, 7 and 9, 10 are examples of the invention, and others are comparative examples.

[0020]

[Example] The wire coil of the test example was annealed at 750 ° C and rapidly cooled at a cooling rate of 240 ° C / sec. This was subjected to a pickling step according to the procedure of actual operation, and was immersed in a salt bath at 440 ° C. for about 5 minutes to perform heat treatment and wire drawing.

The drawing value of the material before wire drawing was 74%, and heat insulation did not occur during the wire drawing process.

[0022]

According to Table 1 of the present invention, when manufacturing the heating wire of the ferrochromium alloy, it is possible to prevent the disconnection which is likely to occur in the wire drawing step and to carry out the stable manufacturing.

[Brief description of drawings]

FIG. 1 is a graph showing the presence or absence of recrystallization when a steel piece of a ferrochrome alloy is heated and rolled in relation to the rolling reduction and the temperature.

FIG. 2 is a graph showing the results of measuring the tensile strength, elongation, and drawing of the FCHW1 alloy wire heated and annealed and cooled at various cooling rates.

Claims (2)

[Claims] 1. C: 0.10% or less, Si: 1.50%
Hereinafter, Mn: 1.0% or less, Cr: 17.0 to 26.0
% And Al: 2.0 to 6.0%, P: 0.0
4% or less, S: 0.03% or less, and the balance is substantially F
The ferrochrome alloy consisting of e is heated at a heating temperature of 950 to 11
The wire rod is rolled at 00 ° C. and wound around a coil at 750 to 1000 ° C., and the coil of this wire rod is heated at a temperature of 650 to 830.
A method for producing a heating wire, which comprises annealing at 60 ° C., quenching at a cooling rate of 65 to 260 ° C./second, and further performing a heat treatment of heating at a temperature of 250 to 500 ° C. before directing to a wire drawing step. 2. The method for producing a heating wire according to claim 1, wherein the coil is pickled after the annealing step, and the heat treatment is replaced by immersion in a salt bath at 400 to 500 ° C. in the pickling step.