JP2001107217A - Method for treating cementation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method, with which a cementation can be executed even in the case of heating in the atmosphere, and a large quantity of large materials to be treated can simultaneously be treated and thus, the mass- production can be obtained. SOLUTION: A coating type cementation composition is applied on the surface of a steel plate or a steel strip, and after baking and filming over, these steel plates or steel strips are laminated and heated in the atmosphere to form the cementation layer on the surfaces of the steel plate or the steel strip.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for carburizing a steel plate or a steel strip. More specifically, the present invention relates to a method of applying a coating-type carburizing composition to the surface of a steel sheet or a steel strip, baking it, forming a film, and then heating in an air atmosphere to form a carburized layer.

[0002]

2. Description of the Related Art Carburizing treatment for diffusing and infiltrating carbon into the surface of steel is the most widely used method for hardening steel. Generally, carburizing methods include solid carburizing method, liquid carburizing method and gas carburizing method, all of which are mainly applied to small members and small parts.

That is, in the solid carburizing method, an object to be treated is put in a carburizing box, and a large amount of an individual carburizing agent is filled between the objects to be treated in order to generate a sufficient carburizing gas.
It is performed by heating to about 850 ° C. or more. In the liquid carburizing method, a method of immersing an object to be treated in a salt bath containing a carburizing agent is generally used. further,
In the gas carburizing method, the gas is put into a sealable heating furnace, and methane,
Carburizing gas is introduced by introducing a carburizing gas such as propane or butane and bringing the gas into contact with an object to be treated.

[0004] All of these prior art methods are carried out in a closed system, because it is necessary to bring the surface of the object to be treated into contact with a carburizing gas at a high concentration and a high pressure. Therefore, the size of a carburizing box, a salt bath layer and the like is restricted, and the object to be treated by this method is limited to small parts and small members, and has a drawback that it cannot be applied to large steel materials and the like. In addition, as a method of inserting the workpiece into the carburizing box,
In general, in order to improve the contact with the carburizing gas, a sufficient interval between the objects to be treated is ensured, and a carburizing agent is filled in the interval. Therefore, the amount of the material to be treated at one time is small and mass production is impossible, and a large amount of carburizing agent is required for the amount of the material to be treated at one time. However, there is a disadvantage that it takes a long time to heat the entire closed system and requires a large amount of energy, and is economically expensive.

[0005]

SUMMARY OF THE INVENTION The present invention provides a method for performing carburizing treatment in an air atmosphere on a closed system as a method enabling mass production at low cost, which was difficult with the conventional carburizing method. With the goal.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies in order to achieve the above object, and as a result, after applying the coating type carburizing composition on the surface of a steel sheet or a steel strip, drying and forming a film, The present inventors have found that the above objects can be achieved by laminating the steel sheets and heating the steel strip in an air atmosphere in a wound coil shape, and have completed the present invention.

That is, the first aspect of the present invention is not a method of generating and contacting a carburizing gas in the vicinity of an untreated material as in the prior art, or a method of contacting a carburizing gas introduced from outside the system. The purpose is to generate a carburizing gas directly on the surface of a steel sheet or a steel strip, whereby the carburizing gas can be instantaneously and efficiently sufficiently carburized on the surface of the steel sheet or the steel strip.

The method of generating a carburizing gas directly on the surface of a steel sheet or a steel strip is achieved by applying a coating type carburizing composition to the surface of a steel sheet or a steel strip, baking it, forming a film, and then heating. That is, when the olefin-based polymer resin in the coating-type carburizing composition is baked, it is melted and formed into a film on the surface of the steel sheet or the steel strip, thereby forming an adhered film. Furthermore, it is based on the fact that the carburizing reaction proceeds efficiently by generating carburizing gas directly on the surface of the steel sheet or the steel strip by oxidizing combustion of the charcoal powder blended in the film and thermal decomposition of the carburizing accelerator. .

[0009] The coating type carburizing composition to be used is a water-based paint obtained by dispersing an olefin polymer resin in an aqueous dispersion, as a carburizing agent, 10 to 100 parts by weight of charcoal powder per 100 parts by weight of the resin. a parts and composition obtained by blending 5 to 80 parts by weight of sodium carbonate per the resin 100 parts by weight of carburizing promoter, applying the composition so as to 10g / m ² ~150g / m ² Is preferred.

A second aspect of the present invention is a means for suppressing the emission of the generated carburizing gas. When applied to a steel sheet, two or more single-side coated steel sheets coated with a carburizing composition and baked are used. By laminating and heating, the carburizing gas generated from the film stays between the laminated steel sheets, and is suppressed from radiating from the steel sheet surface. When applying to steel strip, apply and bake on one side of steel strip,
By forming the coil into a winding shape, the carburizing gas generated from the film at the time of heating stays between the steel strips and is prevented from being diffused. The present invention relates to a treatment method in which a steel sheet or a steel strip is subjected to heat treatment in such a manner to enable carburization even in an air atmosphere.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The present invention can be applied to various steel plates or strips for the purpose of improving scratch resistance, wear resistance, and fatigue fracture resistance, and is appropriately selected according to the application purpose. It is preferable to provide a carburized hardened layer having a Vickers hardness of 550 or more. In the present invention, first, the coating type carburizing composition is applied to the surface of the steel sheet or the steel strip. At this time, it is preferable to wash the surface in advance in order to obtain a uniform coating layer. The washing method is not particularly limited as long as a uniform film is formed after applying and baking the coating composition, and then a uniform carburized layer can be formed when carburizing is performed.
For example, alkali degreasing, degreasing with an organic solvent and the like can be mentioned. The coating type carburizing composition is applied to the surface of the pre-cleaned steel sheet or steel strip.

The carburizing composition used in the present invention is a coating type carburizing composition comprising a water-based paint and a carburizing agent and a carburizing accelerator inert to the water-based paint. Here, as a water-based paint in a coating type carburizing composition, a film can be easily formed in a short time by heating at a relatively low temperature, and the formed film has excellent adhesion to the surface of a steel material. It is preferable to use an aqueous coating material in which an olefin-based polymer resin is dispersed in an aqueous medium, from the viewpoint that harmful substances are not released even when heated when forming the carburized layer.

Examples of such olefin polymer resins include resins composed of olefin polymers such as polyethylene and polypropylene, resins composed of olefin copolymers such as ethylene-propylene copolymer, and blend polymers thereof. These can be used alone or as a mixture of two or more. In addition, it is preferable to use a powder having an average particle size of about 1 μm to 3.0 μm in consideration of the properties as a water-based paint, the formation of a film on an untreated material, and the processability. It is preferable that these resins are blended in an amount of about 10 to 40 parts by weight with respect to 100 parts by weight of water. Further, a small amount of an organic solvent, an antifoaming agent or the like for improving wettability may be added.

Examples of the carburizing agent to be blended in the coating type carburizing composition include graphite, carbon black, charcoal powder and the like, and these can be used alone or as a mixture of two or more. The present inventors have conducted a thermal analysis of these carburizing agents in the air. As a result, graphite powder rapidly oxidized and burned at around 750 ° C.
Even after the temperature was raised to 00 ° C. or higher, the fuel remained without burning.
In contrast, carbon black oxidized and burned at 650 ° C, and charcoal powder rapidly oxidized and burned at around 500 ° C. For carbon black or charcoal powder, 100
No residual weight was observed after the temperature was raised to 0 ° C. or higher. From these experimental results, as a carburizing agent for forming a uniform carburized layer in a short heat treatment, carbon black and charcoal powder capable of rapidly oxidizing and burning at a low temperature to increase carburizing gas pressure are preferable, and more preferably charcoal is used. Powder.

A carburizing accelerator is added to the coating type carburizing composition for the purpose of increasing the pressure of CO ₂ or the like when heating to form a carburized layer to promote carburization. The carburizing accelerator is not particularly limited as long as it does not generate a gas such as CO ₂ when added to the base water-based paint, and generates a gas only when heated to the carburizing temperature.
These carburizing accelerators are determined depending on the type of the aqueous medium used and the method of forming the film, but sodium carbonate and its equivalent are preferred. Carburizing accelerator example, when using an aqueous coating paint as a base by dispersing olefin polymer resin in an aqueous medium as base, CO ₂ during dispersion formulation when using barium carbonate (BaCO ₃₎
And potassium permanganate (K ₂ MnO ₄ )
Is not preferred since O ₂ is generated during dispersion blending.

In the coating type carburizing composition used in the present invention, a carburizing agent and a carburizing accelerator inert to the above-mentioned water-based paint are blended in the water-based paint. Is appropriately selected in consideration of the physical properties, paint viscosity, generation time of carburizing gas and the like. For example, using an aqueous paint prepared by dispersing an olefin polymer resin in an aqueous medium, using a charcoal powder as a carburizing agent, and a coating type carburizing composition using sodium carbonate as a carburizing accelerator, on the surface of a steel sheet or a steel strip. The hardness of the carburized hardened layer to be formed is 550
As described above, when the thickness of the carburized layer was set to be 1 μm or more and an appropriate composition was examined, the amount of charcoal powder added as a carburizing agent was in the range of 10 parts by weight to 100 parts by weight with respect to 100 parts by weight of the resin. It is preferably 30 to 80 parts by weight, and the addition amount of sodium carbonate as a carburizing accelerator is preferably 5 to 80 parts by weight, particularly preferably 15 parts by weight, per 100 parts by weight of the resin. Parts to 50 parts by weight.

If the blending amount of the charcoal powder exceeds 100 parts by weight, the adhesion and workability of the film formed due to the lack of the resin to the object to be treated and the viscosity of the coating when applied are extremely high. It is not preferable because it becomes difficult to apply by dipping, brush coating, roll coating, or the like. Conversely, if the compounding amount is less than 10 parts by weight, it takes a long time to generate carburizing gas, and a long time is required for the carburizing heat treatment, which is not preferable. If the compounding amount of the carburizing accelerator is less than 5 parts by weight, the effect as the carburizing accelerator is undesirably reduced. Conversely, if the amount exceeds 80 parts by weight, the liquid properties of the composition are undesirably reduced.

The coating type carburizing composition is coated on the surface of a steel plate or a steel strip, and the coating method at this time is appropriately selected from conventional coating methods. Examples of such a coating method include brush coating, roll coating, spray coating, dipping, and the like. In the case of steel strip, it is continuously applied and baked in a continuous coating facility. The coating amount of the coating type carburizing composition at this time is appropriately selected depending on the purpose of use of the steel sheet or the steel strip. However, when the hardness of the carburized hardened layer is 550 or more and the thickness of the carburized layer is 1 μm or more, the dry film amount is 10 g / m ^{2 to} 150 g /
It is preferable to apply so as to obtain m ² . If the dry film amount is less than 10 g / m ² , the carburizing source is insufficient and it is difficult to secure a carburized hardened layer of 1 μm or more, which is not preferable. Conversely, if the amount of the dried film exceeds 150 g / m ² , the adhesion and processability of the film deteriorate, and it becomes difficult to process the film into a desired shape, which is not preferable. Further, even if the applied amount exceeds 150 g / m ² , the effect corresponding to the increased amount application cannot be obtained.

The coating-type carburizing composition coated in this manner is dried to form a film. In the case of using a dispersion obtained by dispersing a thermoplastic resin such as an olefin polymer resin in an aqueous medium as a base, Heat to a temperature above the boiling point of water and above the melting point of the resin used. For example, when an olefin-based polymer resin is used, a film having excellent adhesion can be formed by heating to 100 ° C to 150 ° C.

The steel sheet 1 having the film formed on one side in this manner is laminated under the steel sheet 2 for the cover in the state shown in FIG. 1 and heated. In the laminating method of FIG. 1, a carburized layer is formed on the surface on which the film is formed and on the surface on which the film is not formed, but on the opposite surface in contact with the film by lamination. That is, a carburized layer is formed on both sides by forming a film on one side of the steel sheet, heating after lamination. When a film is formed on one side of a steel sheet and a carburized layer is formed only on one side of the steel sheet, the lamination method shown in FIG. 2 is used.

When applied to a steel strip, a film is formed on one side of the steel strip, then wound into a coil, and heated in a coil state. In this case, carburized layers are formed on both sides of the steel strip.
Thus, by coating the coating type carburizing composition of the present invention on the surface of a steel plate or a steel strip and heating in a laminated or coiled state, a carburizing gas is directly generated on the surface of the steel plate or the steel strip,
In addition, since the film is in a laminated or coiled state, the emission of the generated carburizing gas is suppressed and the carburizing gas is sufficiently brought into contact with the surface of the object to be treated.

The heating temperature in the carburizing treatment is 900 ° C.-1
When the heating temperature is lower than 900 ° C., it takes time to form the carburized layer, and the heating temperature is lower than 120 ° C.
If the temperature exceeds 0 ° C., the crystal grain size becomes coarse, and not only the toughness of the steel material is reduced, but also it becomes difficult to control the carburizing concentration.

[0023]

EXAMPLES Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to the following examples. (Workpiece) In the examples of the present invention, a low alloy steel having the following composition was used as a workpiece. C 0.23%,
Si 0.23%, Mn% 0.44%, Cr 0.3
0%, P 0.008%, S 0.008%, B 0.
004%, Fe balance (coating type carburizing composition) A coating having the following composition was used as the coating type carburizing composition of the present invention. 100 parts by weight of polyethylene resin 50 parts by weight of charcoal powder 30 parts by weight of sodium carbonate

Example 1 A steel sheet (thickness 1.6 mm, width 80 mm, length 150 mm) composed of the above components was degreased.
The coating was applied to one surface of the coating so as to have a dry film amount of 40 g / m ² and dried at 130 ° C. for 2 minutes to form a film. The steel sheet on which the film was formed in this manner was laminated by the method shown in FIG. 1 and inserted into a muffle furnace heated to 950 ° C.
After 0 minute, it was taken out and allowed to cool. The hardness of the carburized steel sheet was measured, and the cross-sectional structure was separately observed to evaluate the formed carburized layer. Table 1 shows the Vickers hardness measurement results.

[0025]

[Table 1]

As shown in Table 1, Vickers hardness of 202 to 186 at a depth of about 200 μm from the surface layer on the A side coated with the carburizing composition, and a central portion of the thickness of the steel sheet (a part of about 0.8 mm from the surface layer) 173 was higher. In addition, the surface B to which the carburizing composition was not applied (the surface in contact with the coating layer of the lower plate in the laminated state) showed almost the same tendency. Furthermore, it was confirmed from the observation results of the cross-sectional structure that a carburized layer was formed on both surfaces.
From these results, carburizing is performed on both the coated surface and the uncoated surface by heating in the air atmosphere in a state where the coating-type carburizing composition according to the present invention is applied to one surface of the steel plate and the steel plates are laminated, and then heated. I understand.

Example 2 A steel strip (1.6 mm in thickness, 300 mm in width, 30 kg in weight) composed of the above components was degreased.
The coating was applied to one surface of the coating so as to have a dry film amount of 50 g / m 2, and dried at 150 ° C. for 1 minute to form a film. The steel strip on which the film was formed was wound into a coil (the film surface was wound on the inner surface), inserted into a muffle furnace heated to 950 ° C., taken out 15 minutes later, and allowed to cool. The hardness of the carburized steel strip was measured, and the cross-sectional structure was separately observed to evaluate the formed carburized layer. Table 2 shows the Vickers hardness measurement results.

[0028]

[Table 2]

As shown in Table 2, the V side hardness of the steel strip at the depth of about 200 μm from the surface layer is 213 to 188 on the side A coated with the carburizing composition, ) 171). In addition, the surface B on which the carburizing composition was not applied (the surface in contact with the coating layer of the outer plate in the coil state) showed almost the same tendency. Furthermore, it was confirmed from the results of observation of the cross-sectional structure performed separately that a carburized layer was formed on both surfaces.
From these results, the coating type carburizing composition according to the present invention was applied to one surface of a steel strip, and the steel strip was formed into a coil, and then heated in an air atmosphere to cause carburization on both the coated surface and the non-coated surface. It turns out that it is done.

As is clear from the above results, the coating type carburizing composition according to the present invention is applied to one surface of a steel sheet or a steel strip to form a film, and then the steel sheets are laminated, and the steel strip is wound around a coil. After that, it was found that a sufficient carburized layer was formed by heating in an air atmosphere.

[0031]

As described above, the coating type carburizing composition according to the present invention is applied to one surface of a steel plate or a steel strip, dried to form a film, the steel sheets are laminated, and the steel strip is wound around a coil. By heating after taking, a carburized layer can be formed even in an air atmosphere. Further, in the conventional method, since it is carried out in a closed system such as a carburizing box, the method cannot be applied to a large object to be treated. It can also be applied to Furthermore, according to the present invention, since the steel sheets can be laminated and the steel strip can be carburized in a coil state, mass production becomes possible.

[0032]

[Brief description of the drawings]

FIG. 1 is a lamination method in which a carburizing composition is applied to one side of a steel sheet to form a film, and then heated to carburize both sides.

FIG. 2 is a lamination method in which a carburizing composition is applied to one side of a steel sheet to form a film and then heated to carburize the one side.

[Explanation of symbols]

 1: steel sheet with a film formed on one side 2: steel sheet for cover A side: carburized composition coated side B side: carburized composition uncoated side

Continuing from the front page (72) Inventor Kenji Koshiishi 1 at Nisshin Steel Co., Ltd. Technical Research Laboratory Coating / Composite Materials Research Dept.

Claims (3)

[Claims] 1. A carburizing method wherein a carburizing layer is formed on a steel sheet surface by coating and baking a coating type carburizing composition on the surface of the steel sheet to form a film, and then laminating the steel sheets and heating in an air atmosphere. Processing method. 2. A coating-type carburizing composition is continuously applied to the surface of a steel strip to form a film by baking, and then the steel strip is wound and heated in an air atmosphere to form a carburized layer on the surface of the steel strip. A carburizing method comprising: 3. A water-based paint obtained by dispersing an olefin-based polymer resin in an aqueous dispersion, wherein the coating type carburizing composition to be used is a carburizing agent containing 10 parts by weight of charcoal powder per 100 parts by weight of the resin. 100 parts by weight and the carburizing accelerator is a composition obtained by blending a sodium carbonate per the resin 100 parts by weight 5 to 80 parts by weight, so that the composition with 10g / m ² ~150g / m ² The carburizing method according to claim 1 or 2, wherein the method is applied.