JP6972640B2 - Heat treatment method - Google Patents

Description

The present invention relates to a heat treatment method for heat-treating a metal plate.

Conventionally, there is a hot press (diquenching) as a means for processing a steel sheet with high strength. This is a technology that heats a steel plate to a high temperature and presses it in a high temperature range. In particular, the steel plate is pressed at a transformation temperature (about 900 ° C) or higher, and the press pressure is applied by rapidly cooling it with a die. It is a technology to manufacture high-strength stamped products by causing transformation in the state.
As a means for heating a steel sheet to a high temperature, a heating means by irradiation with infrared rays is expected. For example, in Patent Document 1, a large number of straight tube type heating lamps that irradiate one surface of a steel sheet with infrared rays are provided, and the output intensity of each heating lamp is adjusted according to the contour shape of the steel sheet to obtain a desired region. Is disclosed as a means of heating to a high temperature.

Further, in order to improve the productivity and quality of stamped products, a technique for pressing steel sheets having portions having different thicknesses (hereinafter, also referred to as "differential thickness steel sheets") has been proposed (for example, Patent Documents). 2). If the difference thickness steel sheet can be pressed in this way, the welding process becomes unnecessary and the production time can be greatly shortened.

However, in the press working method disclosed in Patent Document 1 and Patent Document 2, when the differential thickness steel sheet is uniformly heat-treated, the heating temperature reached tends to differ depending on the thickness of the steel sheet, and the entire steel sheet is uniformly heat-treated. There is a problem that it is difficult to heat to a desired temperature.
Further, not only when heating a steel sheet having a special contour, but also when heating a steel sheet having a special contour, partial temperature unevenness is likely to occur during uniform heat treatment, and such temperature unevenness is likely to occur during press working. There is also the problem that it affects the quality of the steel sheet.

Japanese Unexamined Patent Publication No. 2014-149133 Japanese Unexamined Patent Publication No. 2005-138112

The present invention has been made based on the above circumstances, and an object thereof is in a heat treatment method for heat-treating a heated object by a heating means that evenly radiates infrared rays in a direction toward the heated object. In order to provide a heat treatment method capable of uniformly heating the entire object to a desired temperature even when the object to be heated has an irregular shape such as a differential thickness steel plate or a steel plate having a special contour. be.

In the heat treatment method of the present invention, an infrared absorber is contained as an infrared absorption treatment in a portion of the irradiated surface of the object to be heated made of metal where the rate of temperature rise due to irradiation of infrared rays is relatively small. Infrared rays in the heated object that form a coating film coated with the paint and are different from the portion of the irradiated surface of the heated object in which the rate of temperature rise due to infrared irradiation in the heated object is relatively small. After applying infrared reflection treatment to the portion where the rate of temperature rise due to irradiation is relatively high , the heating target is heat-treated by evenly irradiating the infrared rays from the heating lamp in the direction toward the heating target. It is a heat treatment method
The coating material is characterized by being a water-based coating material in which the infrared absorber is dispersed in a solvent containing no resin.

In the heat treatment method of the present invention, it is preferable that the infrared absorption treatment is performed on the irradiated surface of the relatively thick portion of the object to be heated.

In the heat treatment method of the present invention, it is preferable that the infrared reflection treatment is performed on the irradiated surface of the relatively small portion of the object to be heated.

In the heat treatment method of the present invention, after applying infrared absorption treatment to a part of the irradiated surface of the object to be heated, heat treatment is performed by a heating means that evenly radiates infrared rays in the direction toward the object to be heated (hereinafter, "the present invention". It is also called "heat treatment"). Therefore, by applying the infrared absorption treatment to the irradiated surface of the heated object where the rate of temperature rise due to the irradiation of infrared rays is relatively small, the amount of infrared rays absorbed in the portion is increased as compared with the untreated region, and the infrared rays are absorbed. The temperature rise rate due to the irradiation of infrared rays is adjusted to be large. As a result, the distribution of the temperature rise rate for the heating object when the infrared rays radiated evenly in the direction from the heating means toward the heating object is irradiated is the thickness and contour of the heating object, and the heating object. Since it can be made substantially uniform regardless of the reflectance of the surface of the surface, the whole can be uniformly heated to a desired temperature.
Further, in another heat treatment method of the present invention, after applying infrared reflection treatment to a part of the irradiated surface of the object to be heated, the present heat treatment is performed by a heating means that evenly radiates infrared rays in the direction toward the object to be heated. It is something to do. Therefore, by applying the infrared reflection treatment to the irradiated surface of the heated object where the rate of temperature rise due to the irradiation of infrared rays is relatively high, the amount of infrared rays absorbed from the heating lamp in the portion is higher than that in the untreated region. It is adjusted so that it is reduced and the rate of temperature rise due to infrared irradiation is reduced. As a result, the distribution of the temperature rise rate for the heating object when the infrared rays radiated evenly in the direction from the heating means toward the heating object is irradiated is the thickness and contour of the heating object, and the heating object. Since it can be made substantially uniform regardless of the reflectance of the surface of the surface, the whole can be uniformly heated to a desired temperature.
In the present invention, "can be uniformly heated to a desired temperature" means that the desired range of the object to be heated is irradiated with infrared rays uniformly emitted from the heating means toward the object to be heated. In addition, it means that the temperature can be raised to the target temperature range of the main heat treatment within a predetermined time, and the main heat treatment can be performed at the main heat treatment temperature within the temperature range.

It is a perspective view which shows an example of the light absorption treatment region in the heating object of the heat treatment method of this invention. It is a perspective view which shows another example of the light absorption treatment region in the heating object of the heat treatment method of this invention. It is a perspective view which shows an example of the light absorption treatment region and the light reflection treatment region in the heating object of the heat treatment method of this invention. It is a top view which shows the specific example of the shape of the object to be heated. It is a perspective view which shows the differential thickness steel plate used in Experimental Example 1. FIG. It is a graph which shows the result of Experimental Example 1.

Hereinafter, embodiments of the present invention will be described.

The heat treatment method of the present invention is a method of heat-treating a work (this heat treatment) by irradiating an object to be heated (hereinafter, also referred to as “work”) with infrared rays from a planar light source using a heating lamp. ..
Then, prior to this heat treatment, an infrared absorption treatment and / or an infrared reflection treatment is performed on a part of the irradiated surface of the work (hereinafter referred to as “compensation area”).
In the present invention, the irradiated surface of the work means the surface irradiated with infrared rays from the heating lamp. Specifically, for example, when infrared rays are radiated in a state where the heating lamp is provided facing the upper surface of the work, it means the upper surface and the side peripheral surface of the work.

Specifically, in the infrared absorption treatment, for example, an infrared absorption film containing an infrared absorber is formed in the compensation region of the irradiated surface of the work, or the work itself is preliminarily heated at a temperature lower than the main heat treatment temperature. This can be done by heating or by blackening the color state of the irradiated surface by an oxidation treatment of applying a chemical, so that the absorption rate of infrared rays is higher than that of the untreated region other than the compensation region.

As the infrared absorber, it is preferable to use a material having an infrared absorption rate of 60% or more, and specifically, a metal alone or a metal such as a metal oxide, a metal nitride, a metal boride and a metal carbide. Compounds can be used.
Examples of the infrared absorbing film include a coating film coated with a paint containing an infrared absorber, a film or a vapor-deposited film plated with an infrared absorber, and a film or tape made of an infrared absorber.
As the coating material containing the infrared absorber, for example, a paint obtained by converting the infrared absorber into nanoparticles and mixing it with a solvent can be used. Specifically, for example, a silicone resin-based paint, an acrylic resin-based paint, a urethane resin-based paint, a fluororesin-based paint, or the like in which an infrared absorber is dispersed can be used. Further, a water-based paint in which an infrared absorber is dispersed in a solvent containing no resin can also be used. Further, depending on the height of the heat treatment temperature, a semi-dry state containing these solutions or solutions or a binder connecting particles may be used as an infrared absorber.
Of these paints, they can be appropriately selected according to the material of the work and the main heat treatment temperature.

Preheating that preheats the work itself to a temperature lower than the main heat treatment temperature is performed, for example, in the atmosphere and varies depending on the material of the work. For example, when the work is a steel plate, it is heated to about 400 ° C. It can be carried out.
The infrared absorption treatment by preheating can be preferably performed, for example, when the work is a differential thickness steel plate. Specifically, for example, in a work (difference thickness steel plate) in which a steel plate having a small area (small area steel plate) is laminated on a steel plate having a large area (large area steel plate), the thicknesses overlap before spot welding to raise the temperature. By preheating only the small-area steel sheet that is difficult to do, the infrared absorption treatment can be performed only on the small-area steel sheet. Alternatively, after spot welding, the infrared absorption treatment can be performed only on the small area steel sheet by lighting only the heating lamp corresponding to the small area steel sheet in the heating means.

By performing the infrared absorption treatment by preheating, it is not necessary to form an infrared absorption film containing an infrared absorber. Further, it is not necessary to consider the reactivity between the material of the infrared absorbing film and the material of the work, and further, if the material of the infrared absorbing film remains on the work after the main heat treatment, it is necessary to remove it. You can get advantages such as no.

Specifically, the infrared reflection treatment includes forming an infrared reflective film having a high infrared reflectance from a metal compound such as a metal, a metal oxide, a metal nitride, a metal boride, or a metal carbide, or performing a plating treatment. It can be applied, or the surface can be mirrored by changing the surface roughness by, for example, polishing.
The infrared reflective film is preferably, for example, a film having an infrared reflectance of 70% or more, and specifically, a film obtained by plating such as aluminum plating or gold plating.

Infrared absorption treatment and / or infrared reflection treatment in the compensation area of the irradiated surface of the work is performed, for example, one minute after the start of the main heat treatment, that is, the start of the infrared irradiation, and the entire work is subjected to the main heat treatment temperature (for example, 1000 ° C. ±). It is preferably applied so as to reach 50 ° C.).

The infrared absorption treatment and / or the infrared reflection treatment on the irradiated surface of the work is performed, for example, according to the thickness and contour of the work. Specifically, the infrared absorption treatment is performed on the irradiated surface in a region where the rate of temperature rise due to the irradiation of infrared rays is relatively small, for example, a portion having a relatively large thickness. Further, the infrared reflection treatment is performed on the irradiated surface in a region where the rate of temperature rise due to the irradiation of infrared rays is relatively high, for example, a portion having a relatively small thickness.
In the present invention, the "heat rising rate due to infrared irradiation" is the temperature rise of the work when the work is irradiated with infrared rays radiated with an even intensity distribution in the direction from the planar light source by the heating lamp toward the work. Refers to the rate of temperature rise related to.
Specifically, as shown in FIG. 1, for example, in a rectangular flat plate-shaped work W1, the central region 15 of the work W1 in the plane direction in which the work W1 extends is the other end region 17. Compared to this, the rate of temperature rise due to infrared irradiation is small. This is because, in the end region 17 of the work W1, infrared rays are irradiated not only to the upper surface of the work W1 but also to the side peripheral surface. Therefore, the irradiated surface related to the central region 15 is subjected to infrared absorption treatment to form a light absorption treatment region (shown with a mesh line in FIG. 1) Ab1.
Further, as shown in FIG. 2, for example, in the work W2, which is a single steel plate and is a differential thickness steel plate having a thick portion 25 and a small thickness portion 27, a portion having a relatively large thickness. Since the heat capacity of the volume per unit area of the upper surface of the work W2 is larger in 25 than in the portion 27 having a small thickness, the rate of temperature rise due to infrared irradiation is small. Therefore, the irradiated surface of the thick portion 25 is subjected to infrared absorption treatment to form a light absorption treatment region (shown with a mesh line in FIG. 2) Ab2.

Further, in one work, both infrared absorption treatment and infrared reflection treatment may be performed depending on the thickness thereof.
Specifically, in the work W3 which is a differential steel plate in which the lower work 10 and the upper work 20 having different shapes are laminated, the temperature of the two laminated portions 30 is higher than that of the single layer portion 40 by irradiation with infrared rays. The speed is low. Therefore, as shown in FIG. 3A, the irradiated surface of the laminated portion 30, that is, the surface of the upper work 20 facing the heating lamp (upper surface in FIG. 3A) is subjected to infrared absorption treatment. A light absorption processing region (shown with a mesh line in FIG. 3A) Ab3 is formed.
On the other hand, in the single layer portion 40, the rate of temperature rise due to the irradiation of infrared rays is higher than that in the laminated portion 30. Therefore, as shown in FIG. 3A, the irradiated surface of the single layer portion 40, that is, the surface of the lower layer work 10 facing the heating lamp (upper surface in FIG. 3A) is subjected to infrared reflection treatment. The light reflection processing region (shown with diagonal lines in FIG. 3A) Re1 is formed.

Further, in the work W3, infrared absorption processing and infrared reflection processing may be performed according to the contour thereof. Specifically, in the central region of the laminated portion 30 of the work W3 in the plane direction in which the work W3 extends, the rate of temperature rise due to infrared irradiation is smaller than that in the end region. Therefore, as shown in FIG. 3B, the infrared absorption treatment is performed on the irradiated surface related to the central region, that is, the central region on the surface of the upper work 20 facing the heating lamp (upper surface in FIG. 3B). (Shown with a mesh line in FIG. 3 (b) 2) Ab4 is formed.
Further, in the work W3 having a triangular protruding portion 41 whose contour extends continuously from the short side of the rectangle and which is entirely pentagonal, the protruding portion 41 has a high rate of temperature rise due to infrared irradiation. This is because the infrared rays from the heating lamp are also irradiated to the side peripheral surface (thick portion), so that the ratio of the heating from the side peripheral surface to the heating from the surface (upper surface) in the protruding portion 41 of the work W3. This is because Therefore, as shown in FIG. 3B, the surface of the irradiated surface related to the single layer portion 40 and facing the heating lamp of the projected portion 41, that is, the surface of the irradiated portion 41 (FIG. 3). Infrared reflection processing is applied to the upper surface of 3 (b) to form a light reflection processing region (indicated by a diagonal line in FIG. 3 (b)) Re2. Further, the temperature rise rate of the lower work 10 in the end region in the plane direction in which the work W3 extends has a higher rate of temperature rise due to infrared irradiation than in the central region. Therefore, as shown in FIG. 3 (b), the side peripheral surface of the lower work 10 is subjected to infrared reflection processing to form a light reflection processing region (shown with diagonal lines in FIG. 3 (b)) Re3. ..

Further, the infrared absorption treatment and / or the infrared reflection treatment in the compensation region of the irradiated surface of the work may be performed according to the reflectance of the surface of the work.
For example, when the surface of the work has a high gloss, the rate of temperature rise due to the irradiation of infrared rays can be increased by applying the infrared absorption treatment to the entire surface of the irradiated surface of the work to form a light absorption treatment region.
Further, in a differential steel plate in which lower work and upper work having different shapes are laminated, for example, when the gloss of the upper work is higher than that of the lower work, the irradiated surface of the upper work is subjected to infrared absorption treatment. Can also be applied to form a light absorption processing region.

〔work〕
In the heat treatment method of the present invention, the work to be heat-treated is made of a substantially flat metal, and is, for example, a steel plate.
In the present invention, the "steel plate" refers to a plate material containing iron as a main component. For example, a steel plate having a carbon content of 2% by mass or less is included as a target.
The detailed shape of the work is not limited, and it may be a flat steel plate having a uniform thickness or a differential thickness steel plate, and even if the contour is rectangular or square, the contour has a special shape. It may be.
Specifically, a work Wa having a rectangular contour (FIG. 4 (a)), a work Wb having a parallelogram contour and having an acute-angled corner 42 (FIG. 4 (b)), and a parallelogram contour. Work Wc having a curved contour with one corner cut out in an arc shape (FIG. 4 (c)), workpieces Wd, We with contours having different side lengths (FIG. 4 (d) and FIG. 4 (FIG. 4)). e)), a work Wf having a hole 45 (FIG. 4 (f)), and a differential thickness steel plate having a portion having a different thickness obtained by laminating two different types thereof.
As the difference thickness steel plate, for example, a work W2 made of one steel plate having a thick portion 25 and a thin portion 27 as shown in FIG. 2 and a work W2 having different shapes as shown in FIG. Examples thereof include work W3, which is a differential steel plate in which a lower work 10 and an upper work 20 are laminated.

[Heat treatment equipment]
As the heating means for performing the heat treatment method of the present invention, for example, light which is a planar light source having a treatment chamber and being provided in the treatment chamber so as to face the irradiated surface of the work supported on the support portion. A heat treatment apparatus provided with an irradiation unit can be used.
This heat treatment apparatus heats the work from the irradiated surface by uniformly radiating infrared rays from the light irradiation unit toward the work in a certain direction to perform the main heat treatment.

[Light irradiation unit]
The light irradiation unit may be composed of, for example, a plurality of point light source type heating lamps (hereinafter, also referred to as “point lamps”) arranged vertically and horizontally along the plane direction in which the work extends.
It is preferable that each of the point lamps is installed so that the distances of the adjacent point lamps are all evenly spaced.
As the point lamp, for example, a single-ended filament lamp can be used.
The single-ended filament lamp is provided with, for example, a spherically chipped bulb, the split plane of the bulb is sealed by a sealing portion, and both ends thereof are provided in the socket via an internal lead. It contains a filament connected to the two electrodes.

The light irradiation unit is, for example, in a state where a plurality of rod-shaped heating lamps (hereinafter, also referred to as “rod-shaped lamps”) are positioned in one plane so that the central axis of each lamp is parallel to the surface on which the work extends. , They may be arranged side by side so as to be separated from each other.
It is preferable that each of the rod-shaped lamps is installed so that the distances of the adjacent rod-shaped lamps are all evenly spaced.
As the rod-shaped lamp, for example, a double-ended filament lamp can be used.
A double-ended filament lamp is provided with, for example, a straight tubular bulb whose both ends are sealed by a sealing portion, and the filament is housed in the bulb in a coaxially extended state, and both ends of the filament are sealed. It is connected to two electrodes via a stop.

In the heat treatment method of the present invention, first, depending on the thickness and contour of the work, the reflectance of the surface of the work, etc., a part of the irradiated surface of the work is subjected to infrared absorption treatment and / or as described above. Alternatively, infrared reflection processing is applied. As a result, the entire work is warmed up within the target temperature range of the main heat treatment within a predetermined time. After that, the entire surface of the irradiated surface of the work is irradiated with infrared rays radiated with an even intensity distribution in a certain direction from the light irradiation part toward the work, and the temperature rises to the target temperature range of the main heat treatment within a predetermined time. Then, the main heat treatment is performed while being maintained at the main heat treatment temperature within the target temperature range of the main heat treatment.
The main heat treatment temperature is, for example, 1000 ° C. ± 50 ° C.
The coating film to which the paint containing the infrared absorber is applied, which is formed in the infrared absorbing treatment, may be heat-decomposed and disappeared by heating at the main heat treatment temperature, although it depends on the type of the paint. ..

In the heat treatment method as described above, a part of the irradiated surface of the work is subjected to infrared absorption treatment and / or infrared reflection treatment, and then the main heat treatment is performed by a heat treatment apparatus that evenly radiates infrared rays in the direction toward the work. It is a thing. Therefore, by applying the infrared absorption treatment to the irradiated surface related to the portion of the work where the temperature rise rate due to infrared irradiation is relatively small, and / or the portion where the temperature rise rate due to infrared irradiation in the work is relatively high. By applying the infrared reflection treatment to the irradiated surface according to the above, the amount of infrared rays absorbed in each portion is controlled and the temperature is raised to the target temperature range of the main heat treatment within a predetermined time. As a result, the distribution of the temperature rising rate of the work due to the irradiation of infrared rays can be made substantially uniform regardless of the thickness and contour of the work, the reflectance of the surface of the work, and the like. In other words, it is possible to correct the non-uniformity of the distribution of the temperature rise rate due to the irradiation of infrared rays. Therefore, the whole can be uniformly heated to a desired temperature.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications can be made.

Hereinafter, experimental examples performed to confirm the effects of the present invention will be described, but the present invention is not limited thereto.

<Experimental Example 1>
As shown in FIG. 5, a rectangular steel plate (small area) having a length of 50 mm, a width of 50 mm, and a thickness of 2 mm is placed on one surface (upper surface) of a rectangular steel plate (large area steel plate (1)) having a length of 100 mm, a width of 200 mm, and a thickness of 2 mm. A differential thickness steel plate (3) was prepared by laminating the steel plates (2)) so that the corners match.
A paint "heat resistant weather resistant marker black" containing a silicone resin on the entire surface (upper surface) of the small area steel plate (2) of the differential thickness steel plate (3) opposite to the surface in contact with the large area steel plate (1). (Manufactured by Okitsumo Co., Ltd.) was applied to form a coating film. This is the object to be heated [A1].
On the other hand, for comparison, a differential thickness steel plate (3) to which the above paint is not applied is prepared, and this itself is used as a heating object [B].

These heating objects [A1] and [B] are arranged vertically and horizontally along the plane direction in which the point light source type filament lamp (rated power 7000W, outer diameter 13mm) has an arrangement pitch between lamps of 18mm and the heating object extends. This heat treatment was performed using the heat treatment equipment provided.
Further, the small area steel sheets (2) are not laminated at positions separated from two adjacent sides on the upper surface of the small area steel sheets (2) on the irradiated surfaces of the objects to be heated [A1] and [B] by 10 mm, respectively. The temperature for each time at a position 10 mm apart from two adjacent sides on the upper surface of the large-area steel sheet (1) was measured by a thermocouple (4, 5), respectively. The results are shown in FIG.
In FIG. 6, the result for the surface of the small area steel plate (2) of the object to be heated [A1] is shown by a thick solid line (A1-2), and the result for the surface of the large area steel plate (1) of the object to be heated [A1] is shown. The result is shown by a thick broken line (A1-1). Further, the results on the surface of the small-area steel plate (2) of the object to be heated [B] are shown by a thin solid line (B-2), and the results on the surface of the large-area steel plate (1) of the object to be heated [B] are shown. It is shown by a thin broken line (B-1).
Table 1 shows the temperature changes during the main heat treatment.

<Experimental Example 2>
A rectangular steel plate (small area steel plate (2)) with a length of 50 mm, a width of 50 mm, and a thickness of 2 mm is used as a point light source type filament lamp (rated power: 7000 W, outer diameter: 13 mm). Preheating was performed to 600 ° C. using heat treatment devices arranged vertically and horizontally along the plane direction. Then, it was laminated on one surface (upper surface) of a rectangular steel plate (large area steel plate (1)) having a length of 100 mm, a width of 200 mm, and a thickness of 2 mm so that one corner coincided. This is the object to be heated [A2].

This heat treatment object [A2] was subjected to the main heat treatment using the above heat treatment apparatus.
Then, the large-area steel plate (1) on which the small-area steel plate (2) is not laminated is located at a position 10 mm apart from the two adjacent sides on the upper surface of the small-area steel plate (2) on the irradiated surface of the object to be heated [A2]. ), The temperature for each time at a position 10 mm apart from the two adjacent sides on the upper surface was measured by a thermocouple (4, 5), respectively. The temperature change during this heat treatment is measured in 0.5 second increments, and the temperatures of "small area steel sheet temperature" and "large area steel sheet temperature" when the small area steel sheet reaches the temperature range of 950 ° C or higher are measured. It is shown in Table 1.

As is clear from the graph of FIG. 6, in the heated object [A1] subjected to the infrared absorption treatment, the temperature of the small area steel plate (2) is compared with that of the small area steel plate (2) in the heated object [B]. It was confirmed that the temperature rose sharply. Further, as is clear from Table 1, in this object to be heated [A1], the difference (temperature) from the temperature of the large area steel sheet (3) when the temperature of the small area steel sheet (2) reaches around 950 ° C. It was confirmed that the difference of 183 ° C.) was smaller than that of the heated object [B] (temperature difference of 224 ° C.) without the infrared absorption treatment.
Further, it was confirmed that the heating time of the heated object [A1] and [A2] until reaching around 950 ° C. was shorter than that of the comparative heated object [B].
The same tendency was confirmed for the heated object [A2] that had been subjected to the infrared absorption treatment by preheating.

1 Large area steel plate 2 Small area steel plate 3 Difference thickness steel plate 4, 5 Thermocouple 10 Lower layer work 15 Central area 17 End area 20 Upper layer work 25 Thick part 27 Thin part 30 Laminated part 40 Single layer part 41 Projection Part 42 Corner 45 Holes Ab1, Ab2, Ab3, Ab4 Light absorption processing area Re1, Re2, Re3 Light reflection processing area W1, W2, W3, Wa, Wb, Wc, Wd, We, Wf Work

Claims (5)

On the irradiated surface of the object to be heated made of metal, a coating film coated with a paint containing an infrared absorber is formed as an infrared absorption treatment on the portion of the object to be heated where the rate of temperature rise due to infrared irradiation is relatively small. However, the rate of temperature rise due to infrared irradiation on the object to be heated is relative to the portion of the irradiated surface of the object to be heated, which is different from the portion where the rate of temperature rise due to infrared irradiation of the object to be heated is relatively small. A heat treatment method for heat-treating a heated object by uniformly irradiating a large portion with infrared rays from a heating lamp in a direction toward the heated object.
A heat treatment method, wherein the paint is a water-based paint in which the infrared absorber is dispersed in a solvent containing no resin. The heat treatment method according to claim 1, wherein the object to be heated is a steel plate. The heat treatment method according to claim 1 or 2, wherein the infrared absorption treatment is performed on an irradiated surface related to a portion of the object to be heated having a relatively large thickness. The heat treatment method according to any one of claims 1 to 3, wherein the infrared reflection treatment is performed on an irradiated surface related to a portion of the object to be heated having a relatively small thickness. The heat treatment method according to any one of claims 1 to 4, wherein the coating film remaining on the object to be heated is removed after the heat treatment.

Images