JPS6096726A - Direct heat treatment of steel wire material - Google Patents

Abstract

PURPOSE:To enhance strength and wire drawing processability, by applying control cooling to a high temp. steel wire material by using an air-water mixing phase fluid containing a large amount of oxidative air bubbles in a strongly agitated state and held to a predetermined temp. CONSTITUTION:The cooling medium 5 in a heat treatment tank 4 is held at 95 deg.C or less and a large amount of oxidative air bubbles 6 are contained in said cooling medium 5 to form an air-water mixing phase fluid under a strongly agitated state. A ring shaped coil comprising a high temp. steel wire material, of which the metal structure shows austenite, is continuously transferred through the cooling medium 5 under this state in a horizontally developed state to perform control cooling. By this method, the strength and wire drawing processability are enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical alter ego) The present invention provides a method for producing hot-rolled steel wires used in springs, PC (pre-nutrest, concrete) steel wires, PC steel wires, etc. steel wire under high temperature,
Alternatively, the present invention relates to an improvement in a so-called direct heat treatment method in which a steel wire heated to a high temperature at a size in the middle of being wire-drawn is controlled and cooled with a refrigerant to obtain a wire with excellent wire-drawability.

(Background Art) The conditions for the direct heat treatment method are, for example, to cool the steel wire (hereinafter simply referred to as wire rod) immediately after hot rolling at an appropriate cooling rate and almost uniformly over the entire length of the coil, and to finely refine the metal structure. The method is to make the wire mainly composed of pearlite, and to make the strength and wire drawability similar to that of patenting treatment. By using this wire, the patenting process can be omitted depending on the wire diameter and product quality specifications. However, with the conventional direct heat treatment method, for example, when the wire diameter is large and high strength is required, such as for PC, the tensile strength is lower than that of lead patenting. Currently, lead patenting cannot be omitted because the lead patenting is also inferior.

Conventionally, various methods have been proposed as direct heat treatment methods for wire rods, but each method has the following losses.

The Nutilmer method (Japanese Patent Publication No. 15463/1973), in which a ring-shaped coil is spread out on a horizontal conveyor and forcedly air-cooled, has no localized quenching sections and can produce a uniform wire rod, but the cooling power is weak and It is not strong enough.

Although the strength increases depending on the strength of strong winds, the overlapping edges of the rings are ineffective and therefore induce non-uniformity.

Alternatively, the wire rod is formed into a ring-shaped coil and wound up in hot water (Special Publication No. 45-8536), or immersed in hot water while being transferred on a horizontal conveyor (Special Publication No. 46-8089). With the cooling method, a homogeneous line can be obtained in skin dehydration cooling, but the strength is insufficient (the tensile force is lower than that of ship patenting), and even if air is blown in and strongly disturbed, it will not work. The tensile force is 5-71+/in lower.

In addition, the strength increases with hot water boiling cooling (water temperature, below 95""C), but film boiling is unstable, nucleate boiling is induced even at high temperatures, localized rapid cooling occurs, and the martenzite structure deteriorates. occurs and becomes defective.

(Disclosure of the Invention) The present invention has been made to solve the above-mentioned problems, and does not induce nucleate boiling even in water-cooled boiling cooling, and achieves a necessary and sufficient cooling rate only by film boiling rotation. , the strength is equivalent to that of lead patenting, less variation, homogeneous,
The present invention also aims to provide a direct heat treatment method that can produce a steel wire rod with good wire drawability.

The present invention is a method in which a steel wire ring-shaped coil at a high temperature with an austenitic metallographic structure is controlled and directly heat-treated by being continuously transferred in a horizontally expanded form. The steel wire rod is immersed and passed through a refrigerant consisting of an air-water multiphase fluid maintained at a temperature of 95° C. or lower, which is in a disturbed state and contains a large amount of oxidizing bubbles. This is a direct heat treatment method for wire rods.

In the present invention, the steel wire at high temperature refers to carbon steel or alloy steel to which a small amount of alloying elements such as Ni, Cr, V, Mo, and W are added, and is hot-rolled in a high-temperature state. It means a wire rod or a wire rod heated to a high temperature during wire drawing, and the metal structure exhibits austenite.

Hereinafter, a hot-rolled wire rail will be explained as an example, but the present invention is not limited thereto.

The present inventors obtained a predetermined cooling rate to obtain a strength comparable to that of lead patenting, and prevented the induction of nucleation flow.
In order to provide uniform cooling, we investigated various surface treatment conditions and refrigerant conditions, and found that the surface of wire GJ was oxidized,
It has been discovered that the intended purpose can be achieved by immersing the material in a refrigerant consisting of a multiphase fluid of air and water at 95°C or less containing oxidizing bubbles, that is, by performing surface chemical treatment and cooling treatment simultaneously. It is something.

Hereinafter, the present invention will be explained by examples using the drawings.

1 and 2 are diagrams showing an example of a direct heat treatment apparatus used in an embodiment of the method of the present invention, with FIG. 1 being a longitudinal cross-sectional view and FIG. 2 being a cross-sectional view. In the figure, 1 is a ring-shaped coil (hereinafter referred to as a coil) formed from high-temperature rolled steel wire to a predetermined ring diameter using a laying head (not shown).
Then, it is transferred to the conveyor 2 in a non-concentric continuous ring,
It is left to cool in the air.

On this conveyor 2, the surface of the carp/l/l is air oxidized. This is to prevent the induction of nucleate boiling due to the surface oxide film during the next immersion in the refrigerant, and to improve the cooling rate at the film boiling stage, and is preferably 3 to 20 seconds as described below.

After preliminary air cooling, the carp/l/,1 falls onto the horizontal conveyor 3 in the heat treatment tank 4 and is transported in a horizontally developed form. The heat treatment tank 4 accommodates a refrigerant 5 made of air-water multiphase fluid,
The coil 1 on the conveyor 3 is immersed in this for a predetermined time.

The refrigerant 5 is a mixture of air and water by strongly stirring reeds and containing a large amount of oxidizing bubbles 6 in hot water, and is maintained at a temperature of 95° C. or lower. As the oxidizing bubbles 6, for example, a gas containing oxygen such as oxygen, oxygen-enriched air, or air is used.

In order to contain a large amount of oxidizing bubbles 6 in the hot water, for example, air 8 is blown into the hot water from above using a gas supply system 7 as shown in the figure to form bubbles.

Note that this gas may be blown in from the bottom or side of the hot water. Alternatively, an air/water mixed fluid containing a large amount of oxidizing bubbles may be prepared outside the heat treatment tank 4, and this may be supplied into (a) 1 from the top, side, or bottom of the tank 4.

Such a refrigerant 5 is circulated throughout the tank by a plurality of anti-stirring machines 9 and is strongly stirred, and the coils 4 and 1 are strongly stirred.
By being cooled with a mixed air-water fluid in an agitated state, it receives a predetermined controlled cooling. The refrigerant and disturbance conditions in this case will be described later.

In addition, the horizontally deployed coil 1 has dense overlapping on both sides in the direction perpendicular to the running direction, and in order to equalize the cooling rate, priority is given to cooling in this part. Measures will be taken to strengthen the situation. For example, increase the agitation in this area or increase the amount of air bubbles.

The carp (carp) v] that has been cooled for a predetermined period of time is pulled up into the refrigerant 5 by, for example, an inclined conveyor 10 for carrying out, and is collected into a collection machine (not shown).

Next, the following experiments were conducted under various conditions in the method of the present invention.

(Experiment example) As a steel wire sample] 1. Ommφ CO, 8%, Si0
．． 2%.

Using a wire density of 5WRH82B (JIS standard) with Mn 0.7%, it was heated to 950°C in a non-oxidizing atmosphere, left to cool in the air for various times to be air oxidized, and then immersed in various refrigerants. , conducted a controlled cooling experiment.

(1) As a refrigerant, (a) hot water (conventional method) and (b)
Air-water multiphase fluid (if the refrigerant temperature is 95°C or lower, the method of the present invention is used; air is blown into hot water. However, if the refrigerant temperature is 1
No blowing at 00°C. ) Air oxidation time before refrigerant immersion: 05 seconds or less, 3 to 5 seconds, 1
It was immersed for 100 seconds in a refrigerant maintained at 70 to 100°C, and then pulled out.

The relationship between the refrigerant temperature and the tensile strength immediately after treatment is shown in FIG. 3 for each air oxidation time.

Figure 3 shows the 9th order.

(a) The air-water mixture of the present invention (2) The strength of the fluid is greater than that of hot water.

(b) For air-water multiphase fluids, when the air oxidation time is 5 seconds or less, nucleate boiling does not occur before the dust is completed at temperatures above 75°C, stable one-boiling rotation can be obtained, and a wire rod with high strength can be obtained. 80
A tensile strength of I 25 kq/mtA is obtained at temperatures around 0.degree. C., and the strength increases as the humidity decreases, and the rate of increase is greater than that of hot water cooling. On the other hand, with hot water cooling, if the air oxidation time is 3 seconds or more, the
Transformation is completed below 1) 1) Nucleic boiling is induced at 11, martensitic l-structure is generated due to local rapid cooling, and the strength is deteriorated.
Even at °C, martensi I tissue does not occur.

(c) In air-water multiphase fluids, the longer the period of immersion (before air oxidation 11δ), the greater the increase in strength.

According to these results, the refrigerant temperature is 70 to 95"C, preferably 75 to 90 degrees Celsius. Below 70 degrees Celsius, nucleate boiling tends to occur, forming a martensitic structure and reducing strength. However, if the temperature exceeds 95°C, the strength will be insufficient.If the temperature is lower than 75°C, there is a risk of nucleate boiling, and if the temperature exceeds 90°C, the strength comparable to that of lead patenting cannot be obtained.

The appropriate time for air oxidation before immersion in the refrigerant is 3 to 20 seconds. Note that this cooling in the air is normally performed after exiting the rolling mill until coil forming and refrigerant immersion, so it is not necessarily necessary to provide a cooling device (such as a conveyor).

When the time exceeds 20 seconds, the strength increase reaches saturation and
It's time consuming and unfortunate.

(2) A sample with air oxidation time of 4 seconds was held at 80°C using the same refrigerant as in the +I+ term (a) hot water (conventional method) and (b)
The cooling rate was investigated by immersing it in an air-water multiphase fluid (method of the present invention). The temperature of the sample before immersion was 950°C.

The relationship between the elapsed immersion time and the temperature of the wire is shown in FIG.

As shown in Figure 4, cooling is extremely stable in air-water multiphase fluids.
It can be seen that there is no problem because the desired cooling rate can be obtained and nucleate boiling always occurs below 500°C.

In contrast, with hot water cooling, the cooling rate varies greatly from test to test, and reproducibility is low. It is observed that nucleate boiling is likely to occur, and the temperature at which it occurs is not constant.

(3) The characteristic feature of the air-water multiphase fluid in the present invention is that the air bubbles escape from the multi-fluid every moment due to buoyancy.
Since chemical properties are affected by superficial velocity (volume of gas passing through unit time and unit area), we investigated the influence of superficial velocity on the strength of the wire.

As a refrigerant, (b) e-formable gas-containing fluid (method of the present invention,
(same as (b) in section (1)) and (c) using a nitrogen gas-containing fluid (nitrogen gas blown into hot water) (no gas blown at superficial velocity 0) and heated to 82℃. held. A sample with an air oxidation time of 4 seconds was subjected to a superficial velocity of 0 to 10σ.
/ immersed in each refrigerant for 100 seconds and treated.

The relationship between the superficial velocity and the tensile strength of the wire is shown in FIG.

From FIG. 5, it can be seen that (b) the fluid-based method of the present invention is (c)
It can be seen that the tensile strength is much higher than that using fluid, and that the tensile strength increases as the superficial velocity increases. This is because although the superficial velocity increases, the disturbance increases, the heat transfer coefficient decreases, and the cooling rate increases. That is,
When the superficial velocity is sufficiently high, the water temperature around the wire is always maintained at the set temperature, and a wire with high tensile strength corresponding to the set temperature can be obtained. On the other hand, when the superficial velocity decreases, the circulation of hot water around the wire worsens and stagnation occurs, and the water temperature increases due to the heat flux supplied from the wire.

It is thought that for this reason, the cooling rate of the wire rod decreases, and the tensile strength of the obtained wire rod also decreases.

On the other hand, the one using (c) fluid has extremely low tensile strength. This tends to cause nucleate boiling, and the cooling rate becomes abnormally high, resulting in the formation of a martensitic structure.

According to these results, the superficial velocity of the air-water multiphase fluid is 3 to 20.
1/sec is appropriate. If it is less than 3 to 7 seconds, the strength-improving effect will be insufficient, and if it exceeds 2oα/second, "blow-through" (single phase formation due to bubble coalescence) will occur, which is not good.

(4) Using a refrigerant consisting of air-water multiphase fluid (b) (same as (b) in item 1j), The relationship between the cylinder velocity, gas hold, up (gas mixed phase ratio), and approximate disturbance intensity with and without stirring foot is shown in FIG.

As shown in FIG. 6, at the above-mentioned required superficial velocity of 3 to 20 cm and 7 seconds, the gas mixed phase ratio is 01 to 0.35, and the approximate disturbance intensity is 5 to 7 X I O3 erg layer.

Below these ranges, the strength-improving effect is insufficient, and above these ranges, "blow-through" occurs.

! 51 Using a refrigerant consisting of a gas-water multiphase fluid (b) (same as (b) in section (1)), the results of investigating the oxygen concentration and bubble expansion coefficient at a refrigerant temperature of 70 to IOO''C are shown in Section 7.
The rules are shown in the table.

According to FIG. 7, a suitable oxygen concentration in the oxidizing bubbles is 10% or more at a refrigerant temperature of 75°C, and 5% or more at a refrigerant temperature of 90'C. Expressing the relationship between these in a formula, the oxygen concentration is y
%, and if the refrigerant temperature is x''c, it is approximated as y-x+353.

When air is mixed into hot water to produce a refrigerant such as a gas-water multiphase fluid, water vapor immediately evaporates into unsaturated water vapor bubbles and becomes saturated. As a result, the effective superficial velocity, ie, the disturbance force, increases, while the oxygen concentration is diluted. Although this is advantageous for stirring power and bubble mixing ratio, it is disadvantageous for oxidizing power. According to the experimental results, a predetermined boiling temperature was stably obtained within the above range.

Next, the cooling rate of the wire rod is determined by the above experimental examples (1) and (3).
By appropriately combining the necessary conditions obtained in (6) to ~
b If the temperature is less than 15°C/sec in the range of 650°C, the transformation temperature will shift to a high temperature and the strength will be insufficient. Partial martinsite metamorphosis occurs, which is not good. Also 630~5
If the temperature is less than 0°C/sec in the range of 00°C, untransformed autenite will transform into a non-rutted pearlite structure, resulting in insufficient strength; if the temperature exceeds 20°C/sec, there will usually be no problem, but the material will be segregated. In this case, a martensitic structure is likely to occur, which is not good.In addition, in the case of a wire rod to which an alloying element is added, the hardenability of the steel increases, and the above-mentioned conditions shift to the lower cooling rate side.

Also, pearlite transformation begins at around 600°C, at which point 2
Must be cooled at a rate of ~3 u/#see.

If it is less than 2u/kg sec, the transformation temperature will rise to a high temperature, resulting in insufficient strength, and if it exceeds 3θ/kg sec, the transformation temperature will shift to a low temperature, easily inducing martensitic transformation.

The preferred conditions for the method of the present invention obtained from the above experimental examples depend on the steel type of the wire, size, coil size, wire speed, refrigerant capacity, type of oxidizing gas, tank length, etc. , are selected accordingly.

(Example) Hot rolled 11. C0,82% of o+xmφ, Mn
5WRH82B (J
IS standard) steel wire (A) was directly heat-treated by the method of the present invention using the apparatus shown in FIGS. 1 and 2.

The rolling speed of the wire rod is 9 m/s, and the wire rod temperature immediately after rolling is 92
It was molded into a coil with a ring diameter of 1050 tnm at 0°C.

A gas-water multiphase fluid in which air was blown into hot water was used as a refrigerant, and the temperature was maintained at 82° C., the superficial velocity was 10 cm/sec, and the gas mixing ratio was about 0.02 cm/sec.

The wire was pulled up to a temperature of 920°C to 850'C through a water-cooled nozzle and directly heat treated.

For comparison, the same hot-rolled wire rod was cooled by immersion in hot water maintained at 98° C., and then directly heat-treated using a conventional method. The obtained coil was sampled continuously at intervals of 40 cm, and the tensile strength was measured.

The distribution of tensile strength according to the method of the present invention and the conventional method is as shown in FIG.

As shown in FIG. 8, the product according to the present invention has an average of +i1! which is comparable to that of lead patenting. It can be seen that a tensile strength of 5.9 kyA- is obtained and shows a normal distribution.

In contrast, the conventional method has a tensile strength force i of approximately 11k.
g/-low.

(Effects of the Invention) The method for direct heat treatment of steel wire of the present invention configured as described above has the following effects.

(a) Adjusted cooling is performed at temperatures below 95°C with strong stirring and a large amount of oxidizing bubbles. 1'' steel in a refrigerant consisting of a gas-water multiphase fluid maintained at 1 degree,
Because the process is carried out by immersing the wire for the previous month, the surface of the wire is oxidized by exposure to the air or cooling in the air immediately after rolling, and oxidizing bubbles in the refrigerant, forming an oxide film.
Air/water mixture containing oxidizing bubbles 1] Because it is immersed in a fluid,
Is it nuclear even in hot water, cooling, boiling, and cooling? Since the desired cooling rate is achieved without inducing A', lW&,
It is possible to produce a steel wire rod with strength comparable to that of lead patenting, less variation, and excellent wire drawability.

(b) By using a gas-water multiphase fluid containing a large amount of oxidizing bubbles, if a large amount of gas unsaturated with water vapor is mixed in,
A large amount of water vapor evaporates into bubbles toward the equilibrium 'vapor pressure,
As a result, the temperature of the refrigerant decreases, so that the refrigerant has white cooling properties, which can be effectively used to control the refrigerant temperature, so that the temperature of the refrigerant can be maintained economically. Note that this cooling capacity can be easily calculated from the ratio of the processing capacity of the wire (CT/hour) and the temperature and amount of the refrigerant.

[Brief explanation of the drawing]

1 and 2 are diagrams illustrating an example of a direct heat treatment apparatus that uses water in an embodiment of the method of the present invention, in which FIG. 1 is a longitudinal cross-sectional view and FIG. 2 is a cross-sectional view. Figures 3 to 7 are diagrams showing the results obtained in experimental examples of the present invention, and Figure 3 shows the relationship between the refrigerant temperature and the tensile strength of the wire after treatment for each air oxidation time. Figure 4 shows the cooling curves for various refrigerants, Figure 5 shows the relationship between the superficial velocity of various refrigerants and the tensile strength of the wire, Figure 6 shows the relationship between the superficial velocity of the refrigerant and the gas mixture ratio, and Figure 6 shows the relationship between the superficial velocity of the refrigerant and the gas mixture ratio. Figure 7 shows refrigerant temperature 70 to 100°C
The oxygen concentration and bubble expansion rate are shown. FIG. 8 is a diagram showing the tensile strength distribution of steel wire rods manufactured by an example of the method of the present invention and a conventional method. l... Link-shaped coil, 2.3.10... Conveyor,
4...natural treatment right, 5...refrigerant, 6...oxidizing bubbles,
7... Gas supply system, 8... Air, 9... Stirrer. Prayer 1 Figure Yoshi 2 Figure 3 Refrigerant temperature (0C) Piece 4 Figure 5ir-LIL (C''/5eC) Mushroom 6 Figure School traces (Cm/5ee) Hole 7 Figure 4 thirst (0c)

Claims (1)

[Claims] (]) A method in which a ring-shaped coil of steel wire at a high temperature with an autenite metal structure is continuously transferred in a horizontally expanded form, controlled cooling and direct heat treatment. This is carried out by immersing and passing the steel wire through a refrigerant consisting of an air-water multiphase fluid maintained at a temperature of 95° C. or lower and containing a large amount of oxidizing bubbles and in a strongly disturbed state. Features: Direct heat treatment method for steel wire. (2) The method for direct heat treatment of a steel wire rod according to claim 1, wherein the steel wire rod is opened in air for 3 to 20 seconds to oxidize the cold surface thereof before being immersed in a refrigerant consisting of a gas-water multiphase fluid. (3) The oxidizing bubbles are formed using oxygen, oxygen-enriched air, or air, and the oxygen concentration y in the bubbles is
(%), when the refrigerant temperature is x℃, y≦−−x +
35. The method for direct heat treatment of a steel wire according to claim 1 or 2. (4) The gas-water multiphase fluid has a gas multiphase ratio of O1 to 035. A direct heat treatment method for steel wire according to claim 1, 2 or 3, wherein the superficial velocity is from 3 to 20 am/sec. (6) The method for direct heat treatment of steel wire according to claim 1, 2, 3, or 4, wherein the refrigerant has a disturbance intensity of 5 to 7 XIOerg/i. (6) The temperature of the refrigerant is 70 to 95°C, preferably 75 to 95°C.
Claims 1, 2, and 3 that the temperature is 90°C;
W! described in paragraph 4 or 5! Direct heat treatment method for wire rods. (7) Controlled cooling increases the cooling rate of the steel wire from 900 to 65
15-b in the range of 0°C 10-b in the range of 630-500°C Method.