JPH09310189A - Descaling method for metallic material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perfectly remove only scale, subjecting the surface of a metallic material having scale to descaling by irradiating it with a laser beam while it is scanned, by prescribing the scanning velocity by a specified inequality. SOLUTION: At the time of subjecting the surface of a metallic material (such as high strength carbon steel, stainless steel) having scale to descaling by irradiating it with a laser beam while it is scanned, the scanning velocity V (m/min) of the laser beam to the surface of the metallic surface is prescribed so as to satisfy the inequality of 200XD<=V<=2520XD [D: is the average energy density (kW/mm<2> ) in the surface of the metallic material]. Moreover, as the laser beam, a carbon dioxide laser or a YAG laser is preferably used. In this way, only scale can perfectly be removed without damaging the base metallic material.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for descaling a surface of a metal material using a laser beam.

[0002]

2. Description of the Related Art When manufacturing a metal material, it is melted and refined at a high temperature, forged or rough-rolled at a high temperature, further subjected to a predetermined finish forming process, and further cooled through a necessary process such as heat treatment. It is common to That is, there is always a high temperature process in the manufacturing process.

Therefore, the metallic material reacts with oxygen and nitrogen in the atmosphere in a high temperature process, and surface substances such as oxides and nitrides are produced and adhered to the surface thereof. These surface substances are generally called scales, and it is said that the use of a metal material having the scales adhered thereto significantly deteriorates the product performance, particularly the corrosion resistance performance. Examples of typical metal materials include high-strength carbon steel, stainless steel, and Ni-containing alloy steel.

As a method for removing the scale, that is, a descale method, a pickling treatment or a shot blasting treatment is generally used.

[0005]

However, the above-mentioned pickling treatment has a problem that the facility cost for wastewater treatment and the like is high and the cost is high. Further, the shot blasting process has a problem in that consumables such as shot particles and nozzles are expensive and costly, and in addition, the surface of the metal material after the treatment becomes uneven and hardness increases.

Therefore, it has been desired to develop a descaling method which replaces the above pickling treatment and shot blasting treatment.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a new descaling method which replaces the pickling treatment and the shot blasting treatment.

[0008]

The inventors of the present invention have heretofore considered that surface modification means such as welding and cutting of metal materials, heat treatment, film forming treatment and overlaying, and the scale and composition of the surface of metal materials have been used. Focusing on lasers used as welding and cutting means for almost the same ceramics, as a result of numerous experiments to achieve the above-mentioned problems, the following things have been found and the present invention has been accomplished.

As is well known, since a laser is light, any substance such as a metallic material can be heated from the surface. On the other hand, scale metal oxides and nitrides are more excellent in laser absorption than metal itself. From this, it is considered very effective to use a laser as a descaling method for metallic materials if only the scale can be melted by heating and removed.

In recent years, the output of carbon dioxide lasers has been increased, and several tens of kW class oscillators have come to be commercially available. Further, for a YAG laser capable of transmitting a beam through an optical fiber, an oscillator of several kW class has come to be commercially available. Therefore, even if a laser is used as a necessary descaling means in a steel manufacturing process that requires high productivity, there has been no problem in terms of efficiency.

However, the technical idea itself of using a laser for the descaling means on the surface of a metal material has never existed in the past. It is presumed that the cause is that the scanning speed of the laser beam required for descaling, which the inventors of the present invention have found by experiments described below, is orders of magnitude higher.

That is, the processing speed (scanning speed) by the above-mentioned conventional laser beam is several to several tens of m / min at the fastest, regardless of welding, cutting and surface modification treatment.

Therefore, if an attempt is made to carry out an experiment at a scanning speed higher than that, a special moving table equipment is required.
It is considered that the experiment at a scanning speed higher than that was not attempted.

Therefore, the present inventors conducted an experiment in which a metal material was processed into a disk shape, which was rotated at high speed by a motor so as to rotate a record disk, and a laser beam was irradiated perpendicularly to the surface thereof. . As a result, when the scanning speed V (m / min) of the laser beam is D (kW / mm ² ) of the average energy density of the laser beam on the surface of the metal material, V = 200 × D or more, V = 2520 × D It was found that only the scale can be melted and removed within the following range. Further, they have found that even if the scale is thick, by repeating the scanning, only the scale can be completely removed without damaging the underlying metal material.

Here, the laser beam is irradiated once or plural times, and at the final point when the scale is completely melted and removed, the metal material itself is also irradiated with the laser beam. However, even at this point in time, only the scale is melted and the underlying metal material is not melted and damaged because, as described above, the scale is superior to the metal material in laser absorption.

That is, in general, the laser absorption capacity of a material is proportional to the square root of the electric resistance of the material if the wavelength of the laser is constant. Therefore, the laser absorption capacity on a scale close to that of an insulator is much higher than that of the metallic material itself which is a conductor. For this reason, although only the scale is heated and melted, the metal material itself is not heated and melted and is not damaged.

The present invention was made based on the above findings, and the gist thereof is the following descaling method for metallic materials.

A descaling method for irradiating a surface of a metal material having a scale with a laser beam while scanning, wherein a scanning speed V (m / min) is applied to the surface of the metal material.
Satisfies the following formula: A method for descaling a metal material.

200 × D ≦ V ≦ 2520 × D Here, D: average energy density (kW / mm ² ) of the laser beam on the surface of the metal material.

In the above-described method of the present invention, as the descalable metal material, any metal material can be used as long as a scale having a laser absorption capacity higher than that of the underlying metal material is formed and formed on the surface thereof. May be The representative metal materials are as follows.
That is, examples include iron-based alloys such as carbon steel, low-alloy steel, high-alloy steel and stainless steel, nickel-based alloys, aluminum and its alloys, titanium and its alloys, and the like.

Although any laser beam may be used as the laser beam, it is preferable to use a carbon dioxide gas laser or a YAG laser. The reason is that, as described above, a high-power oscillator other than the carbon dioxide laser and the YAG laser has not been developed and marketed yet, and its efficiency is extremely low, so that it is not industrial.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION The descaling method of the present invention will be described in detail below.

First, the scanning speed of the laser beam V (m / m
The reason why (in) is limited to the above range will be described.

When the average energy density of the laser beam on the surface of the metal material is D (kW / mm ² ), the scanning speed V of the laser beam on the surface of the metal material is 200 × D.
If it is less than the range, the underlying metal material itself is melt-damaged. On the contrary, when the scanning speed V of the laser beam with respect to the metal material surface exceeds 2520 × D, the scale is not melted and removed. This is clear from the experimental results shown below.

The experiment was carried out with 0.10% C-0.5% by weight.
6% Mn-0.28% Si-Carbon steel with balance Fe and unavoidable impurities, targeting a hot rolled steel sheet with a thickness of 9 mm and a scale of 150 μm mainly composed of Fe ₂ O ₃ attached to the surface. , Was conducted under the following conditions.

From the above hot-rolled steel sheet, a test piece processed into a disk shape having a diameter of 300 mm was taken. Then, this test piece was fixedly placed on a rotary table driven by a rotation speed variable motor and rotated, and a laser beam was irradiated perpendicularly to the surface thereof.

At this time, the output of the laser oscillator is 25 k.
The carbon dioxide laser oscillator of W was used to change its output variously, and the energy density D was changed variously by adjusting the laser beam diameter on the surface of the test piece.

That is, as the energy density D (kW / mm ² ) on the surface of the test piece, 0.20 (laser output 10 kW, beam diameter 8 mm), 0.31 (laser output 20 kW, beam diameter 9 mm), 0.40 (Laser output 5
kW, beam diameter 4 mm), 0.71 (laser output 20 k
W, beam diameter 6 mm, 0.80 (laser output 10 k
W, beam diameter 4 mm, 1.02 (laser output 20 k
W, beam diameter 5 mm, 1.59 (laser output 5 kW,
Beam diameter 2mm) and 2.83 (laser output 20k
W, beam diameter 3 mm) was adjusted in 8 steps.

When the rotation speed of the test piece (scanning speed of the laser beam) and the irradiation time (the number of times of scanning) are variously changed, the laser beam is irradiated and the descaling condition is visually inspected. Was evaluated as "○", and the case where descaling was not possible was evaluated as "●". In order to blow off the melted scale, air with an original pressure of 5 kgf / cm ² was blown toward the irradiation point at a substantially horizontal angle.

The results of the investigation are shown in FIG.

As is apparent from FIG. 1, the energy density D of the laser beam on the surface of the test piece was 0.40 kW / m.
It can be seen that the optimum scanning speed of the descalable laser beam for m ² is in the range of about 80 to 1000 m / min.

Similarly, the energy density D is 0.20 kW.
/ Mm ² about 40-500m / min, 0.31kW
/ Mm ² about 60 to 800 m / min, 0.71 kW
/ Mm ² is about 150 to 1800 m / min, 0.80
At kW / mm ² , it is about 160 to 2000 m / min.
At 02 kW / mm ² , about 200-2500 m / min,
Approximately 320 to 4000 m / mi at 1.59 kW / mm ^2.
n, 2.83 kW / mm ² approximately 560-7000 m /
It can be seen that it is min.

The primary straight line obtained by these lower limit values is V = 200 × D, and the primary straight line obtained by the upper limit value is V = 2520 × D.

The subscripts in FIG. 1 indicate the number of laser beam scans. If the scanning speed V exceeds 2520 × D, the scale is not removed at all even if the number of laser beam scans is increased. I understand. The number of scans of “◯” is the number of times required for complete descaling.

Further, the scanning speed V of the laser beam is set to 20
If it is less than 0 × D, even if the number of scans is once,
It can be seen that the underlying metal material itself is melt-damaged.

The number of times of scanning depends on the scanning speed V. Further, it naturally changes depending on the thickness of the scale and the composition of the scale. However, the number of scans is
About 1 to 10 times is sufficient.

By the way, when the present invention is applied during the actual steel manufacturing process, it may be carried out as follows. For example, when the metal material to be treated is a steel pipe, it is fed in the axial direction while rotating the steel pipe at a high speed around its axis by a roller conveyor capable of skew feeding,
It suffices to irradiate the surface of the steel pipe with a laser beam from a nozzle fixedly arranged at a predetermined position in the moving region.

When the metal material to be treated is a steel plate, a member that reciprocates at a high speed in a direction orthogonal to the conveying direction is provided above the roller conveyor that conveys the steel plate, and the nozzle is attached to this member. It suffices to attach it and irradiate the laser beam perpendicularly to the steel plate surface.

From the viewpoint of adjusting and managing the energy density D of the laser beam on the surface of the metal material, it is preferable to irradiate the laser beam perpendicularly to the surface of the metal material to be treated. However, if the energy density D is within the range that can be adjusted and managed, it is not always necessary to irradiate vertically, and it is possible to irradiate at a certain angle with respect to the metal material surface.

The method of the present invention is basically applied to the descaling of a metallic material at room temperature, but it can also be applied to a metallic material up to about 600 ° C.

[0041]

[Example] The following two types of steel pipes (made of low alloy steel and stainless steel) were subject to descaling by irradiating a laser beam under various conditions shown in Table 1, and the descaling conditions were visually inspected. evaluated.

Low-alloy steel pipe: low-alloy steel with an outer diameter of 50.8 mm, a wall thickness of 4 mm and a length of 500 mm (0.07 wt% C
-1.32 wt% Mn-0.21 wt% Si-0.03
A steel pipe made of wt% Nb-the balance Fe and unavoidable impurities) and having a scale of 100 μm thick mainly composed of Fe ₂ O ₃ attached to the outer surface thereof.

Steel pipe made of stainless steel: outer diameter 101.6 m
m, wall thickness 6 mm, length 500 mm made of austenitic stainless steel (SUS304 specified in JIS),
A steel pipe with a scale of 50 μm mainly composed of Cr ₂ O ₃ attached to its outer surface.

At this time, the laser beam was applied perpendicularly to the outer surface of the steel pipe placed on the roller conveyor capable of skew feed, from directly above. Further, the scanning speed of the laser beam was set so that a predetermined scanning speed was obtained by changing the rotation speed of the steel pipe placed on the roller conveyor. Further, in each case, the steel pipe was moved at a speed of 0.2 m / min in the axial direction by changing the skew angle of the rollers constituting the roller conveyor according to the rotation speed thereof. Furthermore, in order to blow off the molten scale,
Air having an original pressure of 5 kgf / cm ² was blown onto the steel pipe from a direction orthogonal to the axis toward the irradiation point at a substantially horizontal angle.

The evaluation of the descaling condition was "good" when completely descaled, "not descalable" when part of the scale remained, and partial melt damage occurred on the surface of the base metal of the steel pipe. When it did, it was designated as "underlying metal damage".

The results are shown in Table 1 together with the laser beam irradiation conditions.

[0047]

[Table 1]

As is clear from the results shown in Table 1, when the scanning speed V of the laser beam exceeds the upper limit value defined by the present invention, none of them could be completely descaled (No. 5, 10, 15). , 20). Further, when the scanning speed V of the laser beam was less than the lower limit value specified in the present invention, damage due to melting loss occurred on the underlying metal surface (see Nos. 1, 6, 11, 16).

On the other hand, when the scanning speed V of the laser beam was within the range defined by the present invention, descaling could be completed in all cases (Nos. 2 to 4, 7 to 9, 12).
-14, 17-19).

[0050]

EFFECTS OF THE INVENTION According to the method of the present invention, special auxiliary equipment such as waste water equipment necessary for conventional pickling treatment and consumables such as shot particles necessary for shot blasting treatment are not required. Since the cost and running cost are relatively low, descaling can be performed at low cost. Further, unlike the conventional shot blasting treatment, no unevenness is generated on the surface of the metal material, so that a product having excellent surface quality can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the energy density of a laser beam and the scanning speed that affect descaling.

Claims (2)

[Claims] 1. A descale method for irradiating a surface of a metal material having a scale while scanning a laser beam, wherein a scanning speed V (m / min) is applied to the surface of the metal material.
Satisfies the following formula: A method for descaling a metal material. 200 × D ≦ V ≦ 2520 × D where D: Average energy density of laser beam on metal surface (kW / mm ² ). 2. The method of descaling a metal material according to claim 1, wherein the laser beam is a carbon dioxide laser or a YAG laser.