KR102174156B1 - Treating method of steel sheet and antioxidant for high-manganese steel - Google Patents

Abstract

Preparing a steel sheet containing manganese; Applying an antioxidant to the surface of the steel sheet; And heat-treating the steel sheet coated with the antioxidant, wherein the antioxidant includes 10 to 40% by weight of nickel oxide based on 100% by weight of the total amount of nickel oxide.

Description

Treatment method of steel plate and antioxidant for high manganese steel {TREATING METHOD OF STEEL SHEET AND ANTIOXIDANT FOR HIGH-MANGANESE STEEL}

The present invention relates to a method for treating a steel sheet and an antioxidant for high manganese steel. More specifically, it relates to a method of treating a steel sheet capable of preventing surface defects occurring in the rolling process by inhibiting oxidation reactions due to oxygen in a heating furnace and suppressing internal oxidation and grain boundary oxidation, and an antioxidant for high manganese steel. .

The manufacturing process of the thick plate at the steel mill consists of iron making-steel making-casting-hot rolling, and the cast steel produced in the casting is subjected to surface correction by surface scarfing and grinding, followed by heat treatment in a heating furnace, and finally rolling. do. At this time, the heat treatment in the heating furnace is heated using a CO-CO ₂ mixed gas, etc., but as oxygen is injected together for combustion of the mixed gas, the oxidation reaction of the cast steel cannot be avoided.

Therefore, in the rolling process in order to remove the oxidized surface layer in the heating furnace, high-pressure water is sprayed through a descaler to remove surface oxidation, and then rolling is performed.

At this time, if the surface oxide layer is not completely removed through the descaler, it causes scalability defects in the form of linear and scales, so it is one of the operating goals of the descaler to evenly remove the oxide layer through uniform spraying. Meanwhile, in the oxidation reaction in the heating furnace, as shown in FIG. 1, surface oxidation occurring on the surface of the cast iron and an internal oxide layer generated by diffusion of oxygen atoms under the surface oxide layer are formed. The surface oxide layer can be removed almost completely through the descaler, but the internal oxide layer is dispersed in the Fe base material layer, so it cannot be removed even through high pressure watering. Therefore, as the thickness of the inner oxide layer increases, the likelihood of surface defects occurring in the rolling process increases.

In order to suppress such internal oxidation, oxidation is suppressed by applying an antioxidant to the cast steel in the step prior to the input of the heating furnace.In general, the antioxidant contains an oxide of SiO ₂ -Al ₂ O ₃ and a flux for coating. It is possible to reduce surface oxidation and internal oxidation by preventing the contact of oxygen with the cast iron.

In general, in the hot rolling process, heat treatment is performed for several hours using a heating furnace to perform hot rolling, and then rolling is performed. Oxidation occurs in the order of elements having strong bonding strength with oxygen during the heat treatment time, but in general carbon steels, most of the FeO _x- based surface oxide layer is formed, and the thickness of the surface oxide layer is 1 to 5 mm due to the increase in the rate of oxidation reaction at high temperature Level.

Meanwhile, an internal oxide layer is formed inside the base material by aluminum (Al) and silicon (Si), etc., which are introduced to improve the mechanical properties of the steel, and oxygen in the atmosphere is diffused into the base material through the surface oxide layer to form an internal oxide layer. Because it has to enter, an oxide layer that is relatively thinner than the thickness of the surface oxide layer is formed.

As shown in FIG. 1, in high manganese steel having 10% by weight or more of manganese (Mn), the oxidation reaction in a heating furnace exhibits a different behavior from that of general carbon steel. Since manganese has a higher oxygen affinity than iron, FeO _x oxide is formed in general carbon steel, whereas MnO-based oxide is formed in high manganese steel.

In the case of high manganese steel containing silicon, MnO·SiO ₂ complex oxide is formed with MnO. In the case of the MnO·SiO ₂ composite oxide, as shown in the binary phase diagram of Fig. 2, since the liquid oxide is formed at the level of 1200°C, it forms a liquid in the heating furnace and enters the grain boundaries of the cast steel. As shown, grain boundary oxidation occurs. The grain boundary oxidation by the liquid oxide occurs locally, and is a major cause of defects on the product surface along with internal oxidation caused by diffusion of oxygen.

As a method for suppressing the oxidation reaction in the heating furnace, there are a method of controlling the atmospheric gas in the heating furnace and a method of applying a coating agent to prevent oxidation.

The atmospheric gas control in the heating furnace is a method of preventing oxidation by controlling the ratio of CO gas and CO ₂ gas after the combustion reaction by controlling the input ratio of the CO-CO ₂ mixed gas and oxygen. It is an additional method compared to the method of applying an antioxidant. It is relatively easy in that the process is omitted, but if the input amount of oxygen is reduced by adjusting the input ratio of fuel gas and oxygen, the combustion efficiency of the mixed gas decreases, and the temperature inside the furnace cannot be secured to the target temperature level. , There is a problem in that internal oxidation due to selective oxidation due to the addition of alloy elements such as Al and Si, which has higher oxygen affinity than the base material, cannot be prevented.

The method of applying an antioxidant is to apply an antioxidant containing oxides such as Al ₂ O ₃ , MgO, SiO ₂ etc. to the cast steel before putting it into the furnace to form a barrier film that prevents the contact of oxygen during heating. Although it can be suppressed to some extent, it cannot effectively prevent oxidation of the alloy element having high oxygen affinity as in the case of controlling the atmosphere gas of the heating furnace.

To compensate for this, a method of suppressing oxygen from the atmosphere through preferential oxidation reaction of SiC, Al, and FeSi using an antioxidant including SiC, Al, FeSi, and MgO was proposed, and Al ₂ O ₃ , SiO ₂ , MgO Since the oxide layer is formed, surface oxidation can be suppressed, but the final product is made of an oxide similar to the existing antioxidant, and there is a lack of suppressing the formation of the internal oxide layer.

In addition, in order to block the supply of oxygen itself, a method of heating a coating agent containing Cr, Ni, and Fe metal powders to a level of 1600°C and spraying the coating on the surface of the cast has been proposed. Since the blocking is more effective, it is effective in inhibiting internal oxidation, but the process cost is greatly increased in that the coating agent is sprayed at a high temperature compared to the method of applying an antioxidant at room temperature to the cast steel, while there is also a risk of operation.

It provides a method for treating a steel sheet and an antioxidant for high manganese steel capable of preventing surface defects occurring in a rolling process by inhibiting oxidation reactions caused by oxygen in a heating furnace to suppress internal oxidation and grain boundary oxidation.

A method of treating a steel sheet according to an embodiment of the present invention includes the steps of preparing a steel sheet containing manganese; Applying an antioxidant to the surface of the steel sheet; And heat-treating the steel sheet to which the antioxidant is applied, wherein the antioxidant includes 10 to 40% by weight of nickel oxide based on 100% by weight of the total.

In the step of preparing the steel sheet, the steel sheet is, C: 1.0% by weight or less (excluding 0%), Mn: 10 to 30% by weight, Si: 1.0% by weight or less (excluding 0%), the balance Fe And inevitable impurities.

In the step of applying the antioxidant, the average particle size of the nickel oxide may be 0.1 to 1 mm.

In the heat treatment of the steel sheet, the steel sheet is heat-treated in an atmosphere of CO-CO ₂ mixed gas and air, and the volume ratio of the mixed gas and the air (mixed gas: air) may be 1:3.5 to 1:4.5. .

In the step of heat treating the steel sheet, the heat treatment temperature may be 1100 to 1300°C.

In the step of heat treating the steel sheet, the heat treatment time may be 1 to 7 hours.

After the step of heat-treating the steel sheet, the heat-treated steel sheet may include a Ni-Fe alloy layer, a surface oxide layer located below the Ni-Fe alloy layer, and an internal oxide layer located below the surface oxide layer.

The surface oxide layer and the inner oxide layer may include MnO-SiO ₂ .

The average thickness of the surface oxide layer may be 20 to 40 μm.

The average thickness of the internal oxide layer may be 30 μm or less.

As an antioxidant applied to high manganese steel according to an embodiment of the present invention, the antioxidant for high manganese steel may contain 10 to 40% by weight of nickel oxide based on 100% by weight of the total.

The average particle size of the nickel oxide may be 0.1 to 1 mm.

According to the method of treating a steel sheet according to an embodiment of the present invention, it is possible to reduce surface defects occurring in the rolling process after heat treatment by suppressing internal oxidation and grain boundary oxidation. Accordingly, it is possible to improve the productivity and increase the error rate of high manganese steel.

In addition, since the alloy layer formation through high-temperature thermal spray coating can obtain an effect similar to that of preventing internal oxidation and grain boundary oxidation through room temperature coating, it is advantageous in terms of process cost and ease of operation. It can be more efficient.

1 is a diagram showing a schematic diagram of an oxide layer of a cast iron in a heating furnace.
2 is a view showing the MnO-SiO _{2 2} ternary phase diagram.
3 is a view showing an observation photograph of a high manganese steel grain boundary oxidation optical microscope.
4 is a view showing a state diagram of the Fe-Ni binary system.
5 is a diagram showing a state diagram of the Fe-Sn binary system.
6 is a view showing the result of analysis of the oxide layer component distribution of high manganese steel according to the application of a conventional material.
7 is a view showing the result of analysis of the oxide layer component distribution of high manganese steel according to the application of the inventive material according to an embodiment of the present invention.
8 is a view showing a surface state of a product according to the application of the high manganese steel antioxidant of Comparative Example and Example according to the present invention.

Terms such as first, second and third are used to describe various parts, components, regions, layers, and/or sections, but are not limited thereto. These terms are only used to distinguish one part, component, region, layer or section from another part, component, region, layer or section. Accordingly, a first part, component, region, layer or section described below may be referred to as a second part, component, region, layer or section without departing from the scope of the present invention.

The terminology used herein is for referring only to specific embodiments and is not intended to limit the present invention. Singular forms as used herein also include plural forms unless the phrases clearly indicate the opposite. As used in the specification, the meaning of “comprising” specifies a specific characteristic, region, integer, step, action, element and/or component, and the presence of another characteristic, region, integer, step, action, element and/or component It does not exclude additions.

When a part is referred to as being "on" or "on" another part, it may be directly on or on another part, or other parts may be involved in between. In contrast, when a part is referred to as being “directly above” another part, no other part is intervened.

Although not defined differently, all terms including technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. Terms defined in a commonly used dictionary are additionally interpreted as having a meaning consistent with the related technical literature and the presently disclosed content, and are not interpreted in an ideal or very formal meaning unless defined.

Hereinafter, embodiments of the present invention will be described in detail so that those of ordinary skill in the art can easily implement the present invention. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

Steel plate treatment method

A method of treating a steel sheet according to an embodiment of the present invention includes preparing a steel sheet containing manganese, applying an antioxidant to the surface of the steel sheet, and heat-treating the steel sheet coated with the antioxidant. Contains 10 to 40% by weight of nickel oxide based on the total 100% by weight.

First, in the step of preparing a steel plate containing manganese, a steel plate as a base material is prepared. Specifically, a high manganese steel sheet can be prepared, and the steel sheet is 1.0% by weight or less of carbon (C), 10 to 30% by weight of manganese (Mn), and 1.0% by weight or less of silicon (Si ), balance Fe and unavoidable impurities.

Next, in the step of applying the antioxidant, an antioxidant is applied to the surface of the steel sheet, but an antioxidant containing 10 to 40% by weight of nickel oxide is applied based on 100% by weight of the total. Specifically, based on 100% by weight of the total antioxidant, 10 to 40% by weight of nickel oxide, 10 to 50% by weight of a binder, 40 to 80% by weight of a solvent, and 5% by weight or less of an antifoaming agent may be included.

Antioxidant can be evenly applied over the surface of the steel plate. To this end, the average particle size of nickel oxide can be controlled to 0.1 to 1 mm.

Whether oxidation or reduction is possible through the reaction between the antioxidant and the base steel sheet, and whether the alloy formed by the reaction of the antioxidant and the base material forms a stable solid phase under the heating furnace temperature conditions, it may be important to select an antioxidant. have.

This is because if the oxide contained in the antioxidant does not form an alloy layer by reaction with the base material in the first place, it may not be effective as an antioxidant.

In addition, when the alloy is present in a liquid state under a heating furnace temperature condition, the liquid alloy may penetrate between the grain boundaries of the base material and cause another surface defect.

Considering the above aspects, the oxygen affinity is low compared to iron (Fe) and manganese (Mn), so it can be reduced on the surface of the cast iron to form a metal. Nickel oxide (NiO) and tin oxide (SnO) may be selected.

Table 1 below shows the change in Gibbs free energy when nickel oxide (NiO) and tin oxide (SnO) reacted with iron (Fe) and manganese (Mn) for oxidation-reduction reaction at 1200°C, which is a heating furnace temperature condition, during heat treatment. Represents.

reaction Gibbs free energy change (KJ/mol) NiO + Fe = Ni + FeO -60 NiO + Mn = Ni + MnO -167 SnO + Fe = Sn + FeO -35 SnO + Mn = Sn + MnO -143

As shown in Table 1 above, the antioxidant containing nickel oxide (NiO) and the antioxidant containing tin oxide (SnO) react with iron (Fe) and manganese (Mn) to react with nickel (Ni) metal and tin ( It is reduced to Sn), but when the Gibbs free energy change is seen, it can be seen that nickel oxide (NiO) and tin oxide (SnO) react with manganese (Mn) more stable than react with iron (Fe). The results can be expected to form Ni-Fe and Sn-Fe alloys.

Whether the alloy formed by the above reaction forms a stable solid phase under the heating furnace temperature condition can be confirmed through the binary phase diagram of FIGS. 4 and 5.

As shown in FIG. 4, the Ni-Fe alloy forms an austenite solid phase in the entire concentration range of 1200° C., whereas, as in FIG. 5, when the Fe-Sn alloy has a tin (Sn) of 20% by weight or more at 1200° C. It can be seen that a liquid phase is formed. Based on these results, the Ni-Fe alloy layer does not have a problem due to the solid phase formation, but the Sn-Fe alloy layer has a problem of penetrating the grain boundaries of the cast steel due to the formation of a Sn liquid phase.

Therefore, it is possible to use an antioxidant containing nickel oxide. In the case of nickel oxide, 10 to 40% by weight is included. If nickel oxide is included in less than 10% by weight, there may be a problem that an appropriate level of alloy layer is not formed. If it is included in more than 40% by weight, oxidation in the inhibitor Since the nickel content is too high, it is not uniformly mixed with the remaining coating flux, which may cause non-uniform coating.

Next, in the step of heat-treating the steel sheet, the steel sheet coated with an antioxidant is added to a heating furnace to heat treatment. Specifically, the steel sheet is heat-treated in an atmosphere of CO-CO ₂ mixed gas and air, but the volume ratio of the mixed gas and air (mixed gas: air) may be 1:3.5 to 1:4.5. The heat treatment temperature in the heating furnace may be 1100 to 1300°C, and the heat treatment time may be 1 to 7 hours.

After the heat treatment of the steel sheet, the heat-treated steel sheet may include a Ni-Fe alloy layer, a surface oxide layer located below the Ni-Fe alloy layer, and an internal oxide layer located below the surface oxide layer.

The surface oxide layer and the inner oxide layer may include MnO, the average thickness of the surface oxide layer may be 20 to 40 μm, and the average thickness of the inner oxide layer may be 30 μm or less. In the case of nickel oxide, since the oxygen affinity is very low, it is very difficult to form a complex oxide such as MnO·SiO ₂ , which may be effective in reducing grain boundary oxidation.

Nickel oxide in the antioxidant and manganese contained in the steel sheet react to form nickel metal, thereby forming a Ni-Fe alloy layer, and a surface oxide layer and an internal oxide layer including manganese oxide may be formed by oxygen of the nickel oxide.

Due to the oxygen diffusion suppressing effect due to the formation of the Ni-Fe alloy layer, the average thickness of the internal oxide layer is suppressed to 30 μm or less, and grain boundary oxidation can be prevented.

Antioxidant

The antioxidant for high manganese steel according to an embodiment of the present invention is an antioxidant applied to high manganese steel and contains 10 to 40% by weight of nickel oxide based on 100% by weight of the total. Specifically, it may include 10 to 40% by weight of nickel oxide and the balance coating flux based on 100% by weight of the total antioxidant.

As mentioned above, it is based on whether oxidation and reduction is possible through the reaction between the antioxidant and the high manganese steel as the base material, and whether the alloy produced by the reaction of the antioxidant and the base material forms a stable solid phase under the heating furnace temperature conditions. Nickel oxide was applied as, and other reasons for the selection and content limitation of nickel oxide will be replaced by the above explanation.

On the other hand, in order to evenly apply the antioxidant over the surface of the high manganese steel, the average particle size of nickel oxide can be controlled to 0.1 to 1 mm.

Hereinafter, specific examples of the present invention will be described. However, the following examples are only specific examples of the present invention, and the present invention is not limited to the following examples.

Example

First of all, in order to check the effect of antioxidants for inhibiting internal oxidation and grain boundary oxidation of high manganese steel, a high-grade material containing 0.4% by weight of carbon (C), 22% by weight of manganese (Mn) and 0.2% by weight of silicon (Si). After applying the antioxidant according to the conventional comparative example and the antioxidant according to the inventive example, respectively, to the manganese steel specimen, an oxide layer formation test was performed through a heating furnace simulation device.

The antioxidant according to the comparative example, which is a conventional material, included 40% by weight of silicon oxide, 10% by weight of aluminum oxide, 5% by weight of magnesium oxide, and the balance coating flux, and the antioxidant according to the inventive example was 30% by weight. Nickel oxide and balance applied flux were included.

The gas atmosphere of the heating furnace simulation apparatus was maintained so that the volume ratio of CO-CO ₂ mixed gas:air was 1:4 as the actual heating furnace gas input conditions, and the heat treatment conditions were performed at 1200°C for 4 hours.

After the test, the shape and component distribution of the cross section of the specimen surface was performed through an electron microscope analyzer (EPMA), and the results are shown in FIGS. 6 (conventional materials) and 7 (inventive materials).

When the high manganese steel by applying the exemplary high-manganese steel oxide layers formed utilizing a simulated test device with the heating result, the conventional material, the inner oxide layer is formed, the paper shows the 50㎛ level, the grain boundary oxidation by the oxide of the system MnO-SiO ₂ inside It was confirmed that it was generated at a level of 50 μm from the end of the oxide layer.

On the other hand, in the case of high manganese steel to which the invention material is applied, a Ni-Fe alloy layer is found on the top, and some surface oxide layers are formed at a level of 30 μm, and an internal oxide layer at a level of 20 μm is formed below the surface oxide layer. Became.

It was confirmed that no grain boundary oxidation occurred. According to the application of the invention, nickel oxide (NiO) and manganese (Mn) react to form a nickel (Ni) metal to form a Ni-Fe alloy layer, while a MnO layer is formed by oxygen from nickel oxide (NiO). I could see that.

It was found that the diffusion of oxygen was suppressed by the formation of the Ni-Fe alloy layer, so that the internal oxide layer decreased to less than half compared to the conventional material at the level of 20 μm. On the other hand, it can be seen that the formation of a grain boundary oxide layer is prevented by suppressing oxygen diffusion by the Ni-Fe alloy layer. From these results, it was confirmed that the antioxidant containing nickel oxide (NiO) was effective in inhibiting internal oxidation and grain boundary oxidation of high manganese steel.

In order to confirm the effect of the antioxidant for suppressing internal oxidation and grain boundary oxidation of high manganese steel in the actual process, a rolling test was conducted using the invention and conventional materials. The high manganese steel used in the above test is the same as the high manganese steel component system used in the test using a heating furnace simulation device.

The test was carried out by applying an antioxidant to each of the two slabs, heat-treating in a heating furnace at 1150° C. for 240 minutes, then rolling, and hand grinding the surface to facilitate observation of defects on the product surface. As a result, as shown in FIG. 8, it was confirmed that a defect was observed on the surface in the product applied with the conventional material, whereas the surface defect was not observed in the product applied with the invention material.

Therefore, according to the application of the invention material, it was confirmed that the production of excellent quality products without surface defects was possible through the inhibition of internal oxidation and grain boundary oxidation of the cast steel in the heating furnace.

The present invention is not limited to the above embodiments and/or embodiments, but may be manufactured in various different forms, and those of ordinary skill in the art to which the present invention pertains change the technical spirit or essential features of the present invention. It will be appreciated that it can be implemented in other specific forms without doing so. Therefore, it should be understood that the embodiments and/or embodiments described above are illustrative and non-limiting in all respects.

Claims (12)

Preparing a steel sheet containing manganese;
Applying an antioxidant to the surface of the steel sheet; And
Including; heat-treating the steel sheet coated with the antioxidant,
The antioxidant,
Contains 10 to 40% by weight of nickel oxide, based on the total 100% by weight,
In the step of heat-treating the steel sheet, the steel sheet is heat-treated in an atmosphere of CO-CO ₂ mixed gas and air, and the volume ratio of the mixed gas and the air (mixed gas: air) is 1:3.5 to 1:4.5, steel sheet Treatment method. The method of claim 1,
In the step of preparing the steel plate,
The steel plate,
C: 1.0% by weight or less (excluding 0%), Mn: 10 to 30% by weight, Si: 1.0% by weight or less (excluding 0%), a method for treating a steel sheet containing the balance Fe and inevitable impurities. The method of claim 1,
In the step of applying the antioxidant,
A method of treating a steel sheet having an average particle size of 0.1 to 1 mm of the nickel oxide. delete The method of claim 1,
In the step of heat treating the steel sheet,
The heat treatment temperature is 1100 to 1300 ℃ processing method of the steel sheet. The method of claim 1,
In the step of heat treating the steel sheet,
The heat treatment time is 1 to 7 hours in the treatment method of steel sheet. The method of claim 1,
After the step of heat treating the steel sheet,
The heat-treated steel sheet,
A method of treating a steel sheet comprising a Ni-Fe alloy layer, a surface oxide layer located below the Ni-Fe alloy layer, and an internal oxide layer located below the surface oxide layer. The method of claim 7,
The surface oxide layer and the inner oxide layer are a method of treating a steel sheet containing MnO. The method of claim 7,
The method of treating a steel sheet having an average thickness of the surface oxide layer of 20 to 40 μm. The method of claim 7,
The method of treating a steel sheet having an average thickness of the inner oxide layer of 30 μm or less. delete delete

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