KR20110000992A - Process for nitriding of reinforce materials for construction and nitrided reinforce materials for construction thereof - Google Patents

Abstract

PURPOSE: A nitration treating method of a reinforcing steel plate for construction and a reinforcing steel plate for construction nitration-treated by the same are provided to prevent the generation of toxic gas during fire. CONSTITUTION: A nitration treating method of a reinforcing steel plate for construction comprises following steps. The contaminant on the surface of a hot rolled steel sheet or cold rolled steel sheet is washed and removed(S1). The washed hot rolled steel sheet or cold rolled steel sheet is injected into a furnace and pre-heated(S2). The preheated hot rolled steel sheet or cold rolled steel sheet is nitrided at low temperature under the mixed gas of ammonia, nitrogen, and carbon dioxide(S3). The gas inside the furnace is discharged to the outside(S4). An oxide film is formed on the steel sheet(S5).

Description

Nitriding method of steel plate for building reinforcement and steel plate for building reinforcement nitrided by this method {Process for nitriding of reinforce materials for construction and nitrided reinforce materials for construction Technical}

The present invention is pre-treated hot rolled steel sheet or cold rolled steel sheet using a cleaning solution and ultrasonic waves, and by adding a small amount of ammonia, nitrogen and carbon dioxide from the preheating step, the surface of the steel sheet has a fine structure, followed by a nitriding treatment step and an oxide film forming step By improving the tensile strength, yield point, etc. of the nitrided steel sheet, it is excellent in elasticity and resilience, so it is suitable for the use of building reinforcement steel sheet, and by using a low weight steel sheet thinner than the conventional steel sheet for reinforcing bars The present invention relates to a nitriding treatment method for a building reinforcement steel sheet and a building reinforcing steel sheet nitrided by this method, characterized by excellent workability and low manufacturing cost.

At present, reinforcement used for building materials is mainly used as reinforcement by forming galvanized steel sheet. In the past, stiffeners were not considered important, but due to the typhoon, the damage of windows and the like became serious, and the role of the stiffeners became important. However, the use of such a conventional reinforcing material is thick, the workability is lowered, the cost is increased, the problem is difficult to use as a real building material.

In general, the building reinforcement material is shown in FIGS. 1 and 2 to reinforce the chassis so that the aluminum chassis or the synthetic resin chassis may withstand external strong wind pressure such as a typhoon or the chassis is not separated from the window frame even under an external strong impact. As shown in the figure, the hollow part 11 of the chassis flame 1 is inserted into the reinforcing bar 2 of various shapes to reinforce the strength. The reinforcing bar has a high tensile strength so that the chassis can be sufficiently endured even by a strong external pressure. And physical properties of hardness are required, and as shown in FIG. 1, it may be used in various forms such as a circle or a rectangle (b) as shown in FIG. 2.

As such, the conventional reinforcement for a building, such as a chassis reinforcing rod is required because the high tensile strength and hardness is mainly used galvanized steel sheet having a thickness of 3 mm or more, and in the case of such a galvanized steel sheet tensile strength properties of about 350 N / ㎜. In particular, when the chassis is constructed in a high-rise building, it is required to have high tensile strength that the chassis can withstand strong wind pressure or impact from outside, and the thickness of the steel plate for chassis reinforcement is thickened to have such tensile strength. In this case, the weight of the chassis is heavy, the workability is very low, and there is a concern that raw material prices increase.

In addition, galvanized steel sheet is post-treated with chromium film to protect the galvanized layer with a dehydrated condensation reaction by trivalent chromium compound and a hydrogenated bond to improve the galvanization layer. Chromium is a carcinogen and is regulated as an environmental regulatory substance in countries such as Europe.

On the other hand, the present inventor has applied for a nitriding treatment method of the steel plate for the chassis reinforcement to Patent Application No. 10-2009-0034763 (April 21, 2009) to solve the above problems, further improved nitriding By improving the physical properties of the reinforcing material after the treatment, it was possible to use as a building reinforcement to complete the present invention.

The present invention for solving the above problems is different from the nitriding treatment of the steel sheet during the nitriding treatment of the hot rolled steel sheet or cold rolled steel sheet through a washing step using a cleaning solution and ultrasonic waves, from the preheating step to a trace amount of ammonia, nitrogen, carbon dioxide The metal structure of the hot rolled steel sheet or cold rolled steel sheet is made very dense, and the temperature of the nitriding treatment is carried out in three stages, and then an oxide film is formed to have excellent tensile strength, yield point, elongation, bending test, and elastic modulus. Nitriding treatment method of building reinforcement steel plate characterized by nitriding to be applicable to reinforcement materials for various building materials such as reinforcement and general structural steel plate (square pipe, C-shaped steel, round pipe, Engle, etc.) and nitriding treatment by this method The object is to provide a steel sheet for reinforcement for construction.

In addition, the present invention improves the tensile strength, yield point, elongation, bending test and modulus of elasticity, and thus exhibits excellent physical properties even when using a thin steel plate material. It has excellent properties, can lower the price of raw materials, and it is an environmentally friendly method that does not generate harmful gases in case of fire by nitriding hot-rolled steel or cold-rolled steel without plating. It is a problem to provide a nitriding treatment method of a general structural steel sheet and a general structural steel sheet nitrided by this method.

The present invention for solving the above problems is a washing step (S1) for cleaning and removing contaminants on the surface of the hot-rolled steel sheet or cold rolled steel sheet;

A preheating step (S2) of adding the washed hot rolled steel sheet or cold rolled steel sheet to a furnace;

A nitriding treatment step (S3) of nitriding the pre-heated hot rolled steel sheet or cold rolled steel sheet in a mixed gas atmosphere of ammonia, nitrogen, and carbon dioxide;

A purging step of discharging the gas in the furnace to the outside of the furnace after the nitriding treatment;

An oxide film forming step (S5) of forming an oxide film on the nitrided steel sheet by injecting steam into the furnace;

Spray-quenching step (S6) of drawing out the steel sheet on which the oxide film is formed and then quenching and treating the steel sheet;

The nitriding treatment method of the reinforcing steel sheet for building, characterized in that the treatment through the as a problem solving means.

The nitriding treated reinforcing steel sheet characterized in that the nitriding treatment is carried out by the above method as another problem solving means.

In the nitriding treatment method of the general structural steel sheet, the washing step (S1) is performed by cleaning a contaminant using ultrasonic waves at 50 to 70 ° C. for 30 to 60 minutes,

The preheating step (S2) is to preheat the furnace to put hot rolled steel sheet or cold rolled steel sheet at 540 ~ 550 ℃, nitrogen into the hot rolled steel sheet or cold rolled steel sheet introduced into the furnace at a rate of 4 ~ 6㎥ N ₂ / ㎥ · hr The temperature lowered by the temperature rises again until the temperature reaches 490 to 520 ° C, followed by ammonia to 4 to 6 ㎥ NH ₃ / ㎥, hr, nitrogen to 2 to 4㎥ N ₂ / ㎥, hr, and carbon dioxide 0.3 Preheating to 560 ~ 580 ℃ while discharging gas by opening only 1/3 of the gas outlet while inputting it at ~ 0.7㎥ CO ₂ / ㎥

The nitriding treatment step (S3) is while supplying ammonia (NH ₃ ) -nitrogen (N ₂ ) -carbon dioxide (CO ₂ ) mixed gas supply amount into the furnace at a rate of 20 to 25 m ³ mixed gas / m ³ · hr 2.5 to 3.5 hours at a temperature of 560 ~ 580 ℃, the temperature is lowered again 30 ~ 80 minutes at a temperature of 530 ~ 550 ℃, the temperature is raised again and nitriding treatment for 20 to 40 minutes at a temperature of 560 ~ 580 ℃,

The oxide film forming step (S5) is that the steam is oxidized for 40 ± 2 minutes at a temperature of 560 ~ 580 ℃ while supplying steam into the furnace at a rate of 2 ~ 4 ㎥ steam / ㎥ to hr as steam of 240 ~ 260 ℃ desirable.

According to the present invention by means of the above-mentioned means to solve the problem, the structure of the steel sheet metal becomes very dense and improves the tensile strength, yield point, elongation, bending test and modulus of elasticity, chassis reinforcement and steel pipes for general building structures (square pipe, C-shaped steel, It is not only applicable to the reinforcement materials for various building materials such as round pipes and anglers), but it also shows excellent physical properties even when using a thin steel plate material. The advantage is that the price of raw materials can be lowered.

The present invention for achieving the above effect relates to the nitriding treatment method of the building reinforcing steel sheet for improving the structural strength of the reinforcing steel sheet used as a reinforcing material of the building material, and the reinforcing steel sheet for building reinforcement nitrided by this method, the present invention It should be noted that only the parts necessary to understand the description will be omitted, and the description of other parts will be omitted within the scope of not disturbing the gist of the present invention.

3 is a process chart showing a nitriding treatment method of a building reinforcing steel sheet according to the present invention,

The present invention washing step (S1) for washing by removing the oil on the surface of the hot-rolled steel sheet or cold rolled steel sheet;

A preheating step (S2) of adding the washed hot rolled steel sheet or cold rolled steel sheet to a furnace;

A nitriding treatment step (S3) of nitriding the pre-heated hot rolled steel sheet or cold rolled steel sheet in a mixed gas atmosphere of ammonia, nitrogen, and carbon dioxide;

A purging step of discharging the gas in the furnace to the outside of the furnace after the nitriding treatment;

An oxide film forming step (S5) of forming an oxide film on the nitrided steel sheet by injecting steam into the furnace;

Spray-quenching step (S6) of drawing out the steel sheet on which the oxide film is formed and then quenching and treating the steel sheet;

It relates to a nitriding treatment method of a steel sheet for building reinforcement, characterized in that the treatment through.

Conventionally, the reinforcing steel sheet for construction used in the present invention uses a galvanized steel sheet or a cold rolled steel sheet, compared to using a galvanized steel sheet.

Hereinafter, each of the above process steps in the present invention will be described in detail.

In the washing step (S1), it is preferable to wash the contaminants by using ultrasonic waves for 30 to 60 minutes at 50 ~ 70 ℃ by adding a cleaning agent.

In general, hot-rolled steel sheets or cold-rolled steel sheets are surface-treated without being washed, and contaminants are attached to hot rolled steel sheets and cold-rolled steel sheets, which are materials for reinforcing materials. This is buried a lot. Since the oil component is not able to efficiently nitriding, which causes a problem of deterioration in the improvement of physical properties after nitriding, the cleaning step is performed to improve the physical properties after nitriding.

If the temperature for cleaning the hot rolled steel sheet or cold rolled steel sheet is less than 50 ℃, or the ultrasonic use time is less than 30 minutes, contaminants attached to the surface of the hot rolled steel sheet or cold rolled steel sheet is not washed well, so that the improvement of physical properties after nitriding is poorly performed. If the cleaning temperature exceeds 70 ℃ or the ultrasonic use time exceeds 60 minutes, the cleaning of the contaminants on the surface of the hot-rolled steel sheet is completed, the effect is insignificant.

And the cleaning agent is not particularly limited, it is preferable to use a contaminant attached to the surface of the hot-rolled steel sheet or cold-rolled steel sheet, in particular, that can wash the oil.

And the preheating step (S2) of the present invention is a preliminary step of the nitriding treatment, preheating the empty furnace to inject hot rolled steel sheet or cold rolled steel sheet at 540 ~ 550 ℃, nitrogen to 4 ~ 6㎥ N ₂ to prevent oxidation of the product Into the furnace at a rate of / m3 / hr. At this time, nitrogen was added again until the temperature lowered by the injected hot rolled steel sheet or cold rolled steel sheet reached the point where the temperature in the furnace reached 490 ~ 520 ° C, and then ammonia was added to 4 ~ 6㎥ NH ₃ / ㎥ Preheating to 560 ~ 580 ℃ while discharging the gas by opening only 1/3 of the gas outlet while inputting ~ 4㎥ N ₂ / ㎥ at hr and carbon dioxide at 0.3 ~ 0.7㎥ CO ₂ / ㎥ at hr Do.

When the hot rolled steel sheet or cold rolled steel sheet in the furnace when the temperature of the furnace is less than 540 ℃, the cold hot rolled steel sheet or cold rolled steel sheet is introduced into the furnace takes a long time to reach the nitriding treatment step 560 ~ 580 ℃, If the temperature exceeds 550 ℃, the hot rolled steel sheet or cold rolled steel sheet due to the too high heat scales in the product not only deteriorate hardness and corrosion resistance, but also aesthetic appearance may occur.

And in the above nitrogen injection rate "4 ~ 6㎥ N ₂ / ㎥ to hr" means that the nitrogen of 4 ~ 6㎥ N ₂ per hour is supplied into the furnace of 1㎥. If the amount of nitrogen supplied in the above is insufficient, the hot steel sheet or cold rolled steel sheet is oxidized due to the lack of nitrogen, the scale is formed during the nitriding treatment, if the amount of nitrogen supplied is excessive by the amount of excess nitrogen There is a fear that the oxide layer is thick and the corrosion resistance is poor.

And the temperature to at the 4 ~ 6㎥ ammonia from the time the 490 ~ 520 ℃ NH ₃ / ㎥ in · hr, the nitrogen to ₂ ~ 4㎥ N 2 / a ㎥ · hr, carbon dioxide 0.3 ~ 0.7㎥ CO ₂ / M 3 / hr, and the gas outlet is opened only 1/3 to discharge the gas so that the gas in the furnace is not quickly discharged to the outside of the furnace, so that it can be in contact with the hot rolled steel sheet or cold rolled steel sheet in the furnace for a long time, In addition, even when the gas is injected, the surface structure of the hot rolled or cold rolled sheet can be made very dense to improve the tensile strength, yield point, elongation and bending test results.

When the preheating temperature of the hot rolled steel sheet or cold rolled steel sheet is less than 560 ° C., the hot rolled steel sheet or cold rolled steel sheet may not be sufficiently preheated, and thus, the nitriding layer may not be formed properly during the nitriding treatment, and the preheating temperature exceeds 580 ° C. In this case, due to overheating of the hot steel sheet or cold rolled steel sheet, the nitride layer may not be densely formed during the nitriding treatment, and thus the numerical values such as tensile strength, yield point, elongation, and elastic modulus may be low.

And the nitriding treatment step (S3) of the present invention is 20 to 25 m ³ mixed gas supply amount of ammonia (NH ₃ ) -nitrogen (N ₂ ) -carbon dioxide (CO ₂ ) mixed gas, unlike the conventional conventional nitriding treatment method 2.5-3.5 hours at a temperature of 560-580 ° C. while lowering the temperature while supplying it into the furnace at a rate of m / min. ³ / hr. Nitriding for 40 minutes is preferred.

 As described above, the nitriding treatment of the hot rolled steel sheet or the cold rolled steel sheet is carried out at a temperature lower than the normal nitriding treatment temperature of 580 to 600 ° C., and the temperature is 530 to 550 ° C. after the nitriding treatment at a temperature of 560 to 580 ° C. By lowering and nitriding, raising to 560 ~ 580 ℃ again and nitriding, ammonia is decomposed by the high temperature in the furnace during purging, red stains do not occur and clean steel surface is obtained. The tensile strength is sharply improved by the treatment.

In the case of nitriding a hot rolled steel sheet or a cold rolled steel sheet at a normal nitriding treatment temperature of 580 to 600 ° C, the nitride compound layer is well formed but the density of the nitrided steel sheet is poor, so that the physical properties of the tensile strength are not improved. do. In addition, when the nitriding treatment is generally performed at a temperature of 560 to 580 ° C. and then lowered to a temperature of 530 to 550 ° C., the ammonia decomposition does not occur completely, resulting in staining of steel sheet products, and red color, not rust, is visible to the naked eye. Suffer from such problems.

When the amount of mixed gas injected into the furnace is insufficient, when the nitriding treatment time is short or when the nitriding temperature is low, less activated nitrogen (NO) is generated or the gas nitriding time is short, so that a sufficient nitride layer cannot be formed. If the tensile strength of the hot rolled steel sheet or cold rolled steel sheet is not improved, and the amount of mixed gas is excessive, the gas nitriding time is long, or the temperature is high, the activated nitrogen (NO) is higher than that of the hot rolled steel sheet or the cold rolled steel sheet. Too much generation or nitriding time is too long, the thickness of the nitride layer is formed too thick, there is a fear that nitride stains are formed on the nitride surface of the hot-rolled steel sheet or cold rolled steel sheet.

In addition, the composition ratio of the mixed gas is preferably 70 ± 2% by volume, 20 ± 1% by volume of nitrogen, 10 ± 1% by volume of carbon dioxide.

When the mixed amount of ammonia is less than 68% by volume, the amount of activated nitrogen is less than the mixed amount of nitrogen and carbon dioxide, so that the nitride layer may not be formed properly. When the mixed amount of ammonia exceeds 72% by volume, Since there is a relatively large amount compared to the mixed amount of nitrogen and carbon dioxide, the nitride layer is formed to an excessive thickness, there is a fear that nitride staining occurs.

And the purging step (S4) of the present invention is a step of discharging the remaining amount of gas, such as ammonia in the furnace to the outside of the furnace, by discharging the gas in the furnace at a temperature of 560 ~ 580 ℃ the same as the nitriding treatment step Since the residual amount of ammonia is decomposed and discharged to the outside, the surface of the steel sheet due to ammonia has a clean surface without the phenomenon of red color.

If purging at the usual purge temperature of 530 ~ 550 ℃ undecomposed in the furnace and remaining ammonia reacts with the steam introduced in the oxide film forming step, the surface of the steel sheet exhibits a red color to reduce the productability and corrosion resistance.

And the oxide film forming step (S5) of the present invention is a step of forming an oxide film (Fe ₃ O ₄ ) on the outer surface by oxidizing the surface of the nitride layer of the nitrided steel sheet by introducing steam into the furnace, The steam to be introduced is preferably steamed at 240 to 260 ° C. and oxidized at a temperature of 560 to 580 ° C. for 40 ± 2 minutes while being supplied into the furnace at a rate of 2 to 4 m 3 steam / m 3. At this time, if the amount of steam supplied into the furnace is small, and the oxidation time is short or the oxidation temperature is low, there is a possibility that a sufficient oxide film is not formed on the outside of the nitride layer, and the amount of steam supplied into the furnace is large and oxidized. If the time is long or the oxidation temperature is high, an excessive oxide film is formed on the outside of the nitride layer, which may cause severe deformation of the appearance of the steel sheet. Such an oxide film enhances the surface color of the steel sheet and improves product quality.

At this time, the thickness of the iron oxide film layer formed on the outer side of the nitride layer is preferably 1 ~ 2㎛.

And in the quenching step (S6) of the present invention, unlike the conventional quenching method of water cooling or air cooling, it is preferable to spray spray quenching, which is a method of slowly spraying with water and quenching on the nitrided steel sheet from the furnace.

When the nitrided steel sheet is slowly cooled, such as the quenching method according to the present invention, not only the tensile strength is improved but also there is no deformation of the nitrided steel sheet.

If the nitrided steel sheet is rapidly quenched by a conventional water cooling method, the nitrided steel sheet may be deformed and various problems may occur. In addition, when the nitrided steel sheet is quenched by a conventional air cooling method, the tensile strength is increased. It will come out low, and its use as a building reinforcement will have no significance.

And the present invention may further include a coating step (S7) for coating by coating the antirust oil on the steel sheet subjected to the quenching step (S6).

The steel sheet subjected to the quenching step (S6) is coated by coating a rust-preventive oil with a thickness of 1 to 2 microns, and the surface of the steel sheet subjected to the quenching step forms an oxide film (Fe ₃ O ₄ ), and this oxide film Since it has a silver sponge phenomenon, the rust preventive oil applied is absorbed and coated on the oxide film.

In addition, the steel sheet coated with the rust preventive oil through the coating step (S7) has a slight blue color with the white through the quenching step to have a gloss while having a black color that the weight is reduced to provide a beautiful steel sheet product. You can do it.

Therefore, the steel sheet nitrided by the nitriding treatment method has a very dense metal structure, improved tensile strength, yield point, elongation, bending test, and modulus of elastic modulus. Even when a steel sheet material having a thickness is used, excellent physical properties can be obtained, so that the thickness of the material can be reduced, so that the weight can be reduced, the handling is easy, the workability is excellent, and the manufacturing cost can be lowered.

Hereinafter, the configuration of the present invention will be described in more detail based on the following examples, but the present invention is not necessarily limited only to the following examples.

1. Nitriding of hot rolled steel and cold rolled steel

(Example 1)

A hot rolled steel sheet (SS330) having a thickness of 2 mm was added to a soapy water detergent and washed with ultrasonic waves at 50 ° C. for 30 minutes. And preheat the furnace to hot-rolled steel sheet at a temperature of 550 ℃ (The temperature in the furnace is estimated to be 380 ℃ immediately after the hot rolled steel is added), nitrogen is introduced into the furnace up to 510 ℃ at a rate of 5 m ³ N ₂ / m ³ , hr, and then ammonia 5 m ³ NH ₃ / m ³ hr · hr, nitrogen was 3 m ³ N ₂ / m ³ hr · hr and carbon dioxide was preheated to 570 ° C. at 0.5 m ³ CO ₂ / m ³ hr. At this time, only 1/3 of the gas outlets were opened to discharge the gas.

Then, the pre-heated hot rolled steel sheet was adjusted to a feed rate of 20 m ³ mixed gas / m ³ furnace / hr in a mixed gas atmosphere of ammonia-nitrogen-carbon dioxide and fed into the furnace for 3 hours at 570 ° C. for 3 hours at 540 ° C. It lowered to the temperature of 50 minutes, and further nitrided for 30 minutes at the temperature of 570 degreeC. At this time, the mixed gas was a mixed gas consisting of 70% by volume of ammonia, 20% by volume of nitrogen, 10% by volume of carbon dioxide.

After nitriding, the gas in the furnace was discharged at a temperature of 570 ° C. in the furnace, followed by oxidizing steam at 250 ° C. for 40 minutes at a temperature of 570 ° C. while supplying steam, which is 250 ° C., with steam of 3 m ³ / m ³ . After forming an oxide film layer having a thickness of 1 μm, spray quenching was performed to treat the steel sheet.

 In this embodiment, the coating process is omitted.

(Comparative Example 1)

A galvanized steel sheet having a thickness of 3 mm was used as a control of Example 1.

2. Physical Experiment Evaluation

Tensile strength, yield point, elongation and modulus of elasticity, and KSB 0804 (2001) based on KS B 0802 (2003) -5 test piece using the hot rolled steel sheet and cold rolled steel sheet of Example 1 and the galvanized steel sheet of Comparative Example 1 Based on the results of the bending test measured by the Korea Testing Institute, they are shown in [Table 1] below.

Test Items unit Example 1 Comparative Example 1 Test Methods The tensile strength N / mm2 585 275 KS B 0802: 2003
(Five test pieces) yield point N / mm2 510 203 Elongation % 26 53 Bending test - clear clear KS B 0804: 2001
(4.0, r = 1.5t) Modulus of elasticity N / mm2 2.26 × 10 ⁵ 1.81 × 10 ⁵ KS B 0802: 2003
(Five test pieces)

As shown in Table 1, in the case of Example 1 (thickness 2 mm test piece), although the steel sheet is thinner than Comparative Example 1 (thickness 3 mm test piece), tensile strength, yield point, elongation, bending test and modulus of elasticity It was confirmed that the physical properties of about 2 times better.

Therefore, in the case of Example 1, the tensile strength, yield point, elongation, bending test, and the modulus of elastic modulus are twice as good as those of Comparative Example 1, and thus, when used as a steel sheet for building reinforcement, a steel sheet thinner than the steel sheet thickness of the galvanized steel sheet is used. It can exhibit tensile strength performance over galvanized steel sheet, and can be easily constructed by reducing the weight of building materials using reinforcement material. Also, it has better elastic modulus than that of galvanized steel sheet. It has been confirmed that it can withstand wind pressure or external shock.

3. Example 1 Hazard Test Evaluation of Samples

The results of conducting the detection test for the harmful compound of the sample of Example 1 in the Chemical Testing Institute are as shown in Table 2 below.

Test Items unit Results Test Methods Pb mg / kg Not detected ASTM E 350: 1995 (Properties, AAS) CD mg / kg Not detected ASTM E 350: 1995 (Properties, AAS) Hg mg / kg Not detected JIS H 1066: 1993 (Junyong, AAS) Cr ⁶⁺ mg / piece Not detected ISO 3613: 2000 (E)

As shown in Table 2, in the case of the sample of Example 1 subjected to nitriding according to the present invention, by nitriding the unplated hot rolled steel sheet, harmful heavy metals such as lead, cadmium, mercury, and hexavalent chromium were detected. It wasn't.

Therefore, the sample of Example 1 according to the present invention is excellent in mechanical properties such as tensile strength, yield point, elongation, bending test and modulus of elasticity, and can be confirmed that it is suitable for building reinforcement materials as an eco-friendly material in which no harmful heavy metals are detected. there was.

As described above, although described with reference to a preferred embodiment of the present invention, those skilled in the art will be able to variously modify and change the present invention without departing from the spirit and scope of the invention described in the claims below. It will be appreciated.

1 is an exploded perspective view of a conventional chassis having a structure in which a circular reinforcement is inserted;

2 is a cross-sectional view of a square reinforcement and channel type reinforcement inserted into the hollow portion of the chassis flame in a conventional chassis;

Figure 3 is a process chart showing the nitriding treatment method of the building reinforcing steel sheet according to the present invention.

Explanation of symbols on the main parts of the drawings

1: chassis flame 2: reinforcement

11: hollow part

Claims (10)

A washing step (S1) of washing and removing contaminants on the surface of the hot rolled steel sheet or the cold rolled steel sheet; A preheating step (S2) of adding the washed hot rolled steel sheet or cold rolled steel sheet to a furnace; A nitriding treatment step (S3) of nitriding the pre-heated hot rolled steel sheet or cold rolled steel sheet in a mixed gas atmosphere of ammonia, nitrogen, and carbon dioxide; A purging step of discharging the gas in the furnace to the outside of the furnace after the nitriding treatment; An oxide film forming step (S5) of forming an oxide film on the nitrided steel sheet by injecting steam into the furnace; A quenching step (S6) of drawing out the steel sheet on which the oxide film is formed and then quenching and treating the steel sheet; Nitriding treatment method of the reinforcing steel sheet for building, characterized in that processing through. The method of claim 1, The cleaning step (S1) is a nitriding treatment method of the steel plate for building reinforcement, characterized in that to clean the contaminants using ultrasonic waves for 30 to 60 minutes at 50 ~ 70 ℃ by adding a cleaning agent. The method of claim 1, The preheating step (S2) is to preheat the furnace to put hot rolled steel sheet and cold rolled steel sheet at 540 ~ 550 ℃, nitrogen into the hot rolled steel sheet and cold rolled steel sheet introduced into the furnace at a rate of 4 ~ 6㎥ N ₂ / ㎥ · hr The temperature lowered by the temperature rises again until the temperature reaches 490 to 520 ° C, followed by ammonia to 4 to 6 ㎥ NH ₃ / ㎥, hr, nitrogen to 2 to 4㎥ N ₂ / ㎥, hr, and carbon dioxide 0.3 Nitriding treatment method for reinforcing steel sheet for building, characterized in that preheating treatment to 560 ~ 580 ℃ while discharging gas by opening only 1/3 of the gas outlet while injecting in ~ 0.7 ㎥ CO ₂ / ㎥. The method of claim 1, The nitriding treatment step (S3) is supplied while supplying the ammonia (NH ₃ ) -nitrogen (N ₂ ) -carbon dioxide (CO ₂ ) mixed gas into the furnace at a rate of 20 to 25 m ³ mixed gas / m ³ . 2.5 to 3.5 hours at a temperature of 560 ~ 580 ℃, lower the temperature again 30 ~ 80 minutes at a temperature of 530 ~ 550 ℃, the temperature is raised again, characterized in that the nitriding treatment for 20 to 40 minutes at a temperature of 560 ~ 580 ℃. Nitriding treatment method of reinforcing steel sheet for building. The method according to claim 1 or 4, The composition ratio of the mixed gas is 70 ± 2% by volume of ammonia, 20 ± 1% by volume of nitrogen, and 10 ± 1% by volume of carbon dioxide. The method of claim 1, The purging step (S4) is a nitriding treatment method of a steel sheet for building reinforcement, characterized in that for discharging the gas in the furnace at a temperature of 560 ~ 580 ℃. The method of claim 1, The oxide film forming step (S5) is that steam is oxidized for 40 ± 2 minutes at a temperature of 560 ~ 580 ℃ while supplying steam into the furnace at a rate of 2 ~ 4 ㎥ steam / ㎥ to hr as steam of 240 ~ 260 ℃ Nitriding treatment method of a steel sheet for reinforcement for construction The method of claim 1, The quenching step (S6) is a nitriding treatment method of the building reinforcing steel sheet, characterized in that the spray quenching. The method of claim 1, Nitriding treatment method of the reinforcing steel sheet for building, characterized in that the treatment further comprises a coating step (S7) to apply a coating to the steel sheet subjected to the quenching step (S6). A nitriding treated building reinforcing steel sheet characterized in that the nitriding treatment by the method of any one of the nitriding treatment method of the building reinforcing steel sheet of claim 1 to claim 10.

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