KR20200043175A - Treating method of steel sheet and antioxidant for high-manganese steel - Google Patents

Abstract

Disclosed is a method for treating a steel sheet, comprising: a step of preparing a steel sheet containing manganese; a step of applying an antioxidant to a surface of the steel sheet; and a step of heat-treating the steel sheet coated with the antioxidant. The antioxidant comprises 10 to 40 wt% of nickel oxide with respect to the total 100 wt%. According to the present invention, the productivity of high manganese steel can be improved.

Description

Method of processing steel sheet 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, the present invention relates to a method of treating a steel sheet and an antioxidant for high manganese steel that can prevent surface defects occurring in a rolling process by suppressing an oxidation reaction by oxygen in a heating furnace to suppress internal oxidation and grain boundary oxidation. .

The steel plate manufacturing process consists of a steelmaking-steel-performing-hot-rolling process, and after undergoing surface correction for surface scaffolding and grinding of the cast steel produced in the performance, it undergoes heat treatment in a heating furnace and finally rolls. do. At this time, the heat treatment in the heating furnace uses CO-CO ₂ mixed gas or the like, but the oxidation reaction of the cast steel is unavoidable as oxygen is blown together for combustion of the mixed gas.

Therefore, in order to remove the oxidized surface layer in the heating furnace, in the rolling process, after the surface oxidation is removed by spraying high-pressure water through a descaler, rolling is performed.

At this time, if the surface oxide layer is not completely removed through the descaler, it is one of the operating goals of the descaler to uniformly remove the oxide layer through uniform spraying because it causes linear and scale-like scalability defects. On the other hand, the oxidation reaction in the heating furnace, as shown in Figure 1, the surface oxidation occurring on the surface of the cast iron and the oxygen atom diffuses below the surface oxidation layer is formed an internal oxidation layer. The surface oxide layer can be almost completely removed through a descaler, but the internal oxide layer is dispersed in the Fe base layer, so it cannot be removed even through high-pressure sprinkling. Therefore, the thicker the thickness of the inner oxide layer, the more likely the surface defects to occur in the rolling process.

In order to suppress the internal oxidation, the oxidation is suppressed by applying an antioxidant to the cast steel in the step before the heating furnace is added. In general, the antioxidant contains an SiO ₂ -Al ₂ O ₃ -based oxide and a flux for application. It is possible to reduce surface oxidation and internal oxidation by preventing contact between the cast steel and oxygen.

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

On the other hand, an internal oxidation layer is formed inside the base material by aluminum (Al) and silicon (Si), etc., which are added to improve the mechanical properties of the steel. For the formation of the internal oxidation layer, oxygen in the atmosphere passes through the surface oxidation layer and diffuses into the base material. Since it must enter, a relatively thin oxide layer is formed compared to the thickness of the surface oxide layer.

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

In the case of high-manganese steel containing silicon, MnO · SiO ₂ composite oxide is formed together with MnO. In the case of the MnO · SiO ₂ composite oxide, as shown in the binary state diagram of FIG. 2, since it forms a liquid oxide at a level of 1200 ° C., it forms a liquid in the heating furnace and invades the grain boundaries of the cast, and FIG. 3. As shown, grain boundary oxidation occurs. The grain boundary oxidation by the liquid oxide occurs locally, and is a major cause of product surface defects 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.

Atmosphere gas control in the furnace is a method of controlling the input ratio of CO-CO ₂ mixed gas and oxygen to prevent oxidation by controlling the ratio of CO gas and CO ₂ gas after the combustion reaction, which is additional compared to the method of applying an antioxidant. It is relatively easy in that the process is omitted, but when 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 heating furnace is not secured to the target temperature level. , There is a problem that it is not possible to prevent internal oxidation due to selective oxidation due to the addition of alloy elements such as Al and Si, which have a higher oxygen affinity than the base material.

As the method of applying the antioxidant, an oxidation reaction is performed because an antioxidant containing oxides such as Al ₂ O ₃ , MgO, and SiO ₂ can be applied to the cast piece before heating to form a barrier film that prevents contact with oxygen during heating. It can be suppressed to some extent, but it cannot effectively prevent oxidation of alloy elements having high oxygen affinity, as in the case of controlling the atmosphere gas of a heating furnace.

In order to compensate for this, a method has been proposed to suppress oxygen from the atmosphere through a preferential oxidation reaction of SiC, Al, and FeSi using antioxidants including SiC, Al, FeSi, and MgO, 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 that of the existing antioxidant, which is insufficient to suppress the formation of the internal oxide layer.

In addition, in order to block the supply of oxygen itself, a method of spraying a coating agent containing a metal powder containing Cr, Ni, and Fe to a level of 1600 ° C. and spraying the surface of the cast iron has been proposed. Although the blocking is more effective, it is effective in suppressing internal oxidation, but the process cost is greatly increased in that the coating agent is sprayed at a higher temperature than the method of applying a room temperature antioxidant to the cast steel, and there is also a risk of operation.

Provided is a method for treating a steel sheet and an antioxidant for high-manganese steel, which is capable of preventing surface defects occurring in a rolling process by suppressing an oxidation reaction by oxygen in a heating furnace to suppress internal oxidation and grain boundary oxidation.

Method of processing a steel sheet according to an embodiment of the present invention comprises the steps of providing 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. The antioxidant includes 10 to 40% by weight of nickel oxide with respect to 100% by weight.

In the step of preparing the steel sheet, the steel sheet, 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 unavoidable impurities.

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

In the step of heat-treating the steel sheet, the steel sheet is heat-treated in a mixed gas of CO-CO ₂ and an air atmosphere, and a 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 positioned under the Ni-Fe alloy layer, and an internal oxide layer positioned under the surface oxide layer.

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

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

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 include 10 to 40% by weight of nickel oxide with respect to 100% by weight.

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

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

In addition, the formation of the alloy layer through the high-temperature thermal spray coating can achieve an effect similar to that of the internal oxidation and intergranular oxidation through room temperature application, which is advantageous in terms of process cost and operation ease, and blocking of oxygen through the formation of the alloy layer It can be more efficient.

1 is a view showing a schematic view of a cast oxide layer in a heating furnace.
2 is a view showing the MnO-SiO _{2 2} ternary phase diagram.
3 is a view showing a crystal grain boundary oxidation optical microscope observation photograph of high manganese steel.
4 is a view showing a Fe-Ni binary system state diagram.
5 is a view showing a Fe-Sn binary state diagram.
6 is a view showing the results of the analysis of the distribution of the components of the oxide layer of high manganese steel according to the application of the conventional material.
7 is a view showing the results of analyzing the distribution of the components of the oxide layer of high manganese steel according to the application of the invention according to an embodiment of the present invention.
8 is a view showing the surface state of the product according to the application of the high-manganese steel antioxidant of the comparative example and the embodiment of 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 portion, component, region, layer or section described below may be referred to as a second portion, component, region, layer or section without departing from the scope of the present invention.

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

When a part is said to be "on" or "on" another part, it may be directly on or on the other part, or another part may be involved therebetween. In contrast, if one part is referred to as being “just above” another part, no other part is interposed therebetween.

Although not defined differently, all terms including technical terms and scientific terms used herein have the same meaning as those generally understood by those skilled in the art to which the present invention pertains. Commonly used dictionary-defined terms are additionally interpreted as having meanings consistent with related technical documents and currently disclosed contents, 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 skilled in the art to which the present invention pertains can easily practice. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein.

Method of processing steel sheet

The 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 coated with the antioxidant, and the antioxidant. Contains 10 to 40% by weight of nickel oxide, based on 100% by weight.

First, in the step of preparing a steel sheet containing manganese, a steel sheet serving 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, the antioxidant is applied to the surface of the steel sheet, and with respect to 100% by weight, an antioxidant containing 10 to 40% by weight of nickel oxide is applied. Specifically, 10 to 40% by weight of nickel oxide, 10 to 50% by weight of a caking agent, 40 to 80% by weight of a solvent and 5% by weight or less of an antifoaming agent may be included with respect to 100% by weight of the total antioxidant.

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

Whether the oxidation and reduction is possible through the reaction between the antioxidant and the base steel sheet and whether the alloy produced by the reaction of the antioxidant and the base material forms a stable solid phase in the furnace temperature condition may be important in selecting the antioxidant. have.

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

In addition, if the alloy is present in the liquid phase at the temperature of the furnace, the liquid alloy may penetrate between the grain boundaries of the base material and cause another surface defect.

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

Table 1 below shows the changes in Gibbs free energy when nickel oxide (NiO) and tin oxide (SnO) undergo oxidation-reduction reactions with iron (Fe) and manganese (Mn), respectively, at a heating temperature of 1200 ° C during heat treatment. Indicates.

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, an antioxidant containing nickel oxide (NiO) and an antioxidant containing tin oxide (SnO) react with iron (Fe) and manganese (Mn) to react with nickel (Ni) metal and tin ( Sn), respectively, when Gibbs free energy changes, nickel oxide (NiO) and tin oxide (SnO) are more stable to react with manganese (Mn) than to react with iron (Fe). It can be expected to form Ni-Fe and Sn-Fe alloys as a result.

Whether the alloy formed by the above reaction forms a stable solid phase in the temperature condition of the heating furnace can be confirmed through the binary state diagrams 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, while in the Fe-Sn alloy as shown in Fig. 5, when tin (Sn) is 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 according to solid phase formation, but the Sn-Fe alloy layer may have a problem that the Sn liquid phase is formed and penetrates the grain boundaries of the cast.

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 less than 10% by weight, a problem that an appropriate level of the alloy layer is not formed may occur, and when it is included in excess of 40% by weight, oxidation in the antioxidant Since the content of nickel is too high, uniform mixing with the residual coating flux is not possible, and uneven coating may be a problem.

Next, in the step of heat-treating the steel sheet, the steel sheet coated with the antioxidant is put into a heating furnace and heat-treated. Specifically, the steel sheet is heat-treated in a mixed gas and air atmosphere of CO-CO ₂ , and 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 furnace may be 1100 to 1300 ° C, and the heat treatment time may be 1 to 7 hours.

After heat-treating the steel sheet, the heat-treated steel sheet may include a Ni-Fe alloy layer, a surface oxide layer positioned under the Ni-Fe alloy layer, and an internal oxide layer positioned under the surface oxide layer.

The surface oxide layer and the internal 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 internal oxide layer may be 30 μm or less. In the case of nickel oxide, it is very difficult to form a complex oxide such as MnO · SiO _{2 because} oxygen affinity is very low, and thus it may be effective in reducing grain boundary oxidation.

Ni-Fe alloy layer is formed by the formation of nickel metal by the reaction of nickel oxide in the antioxidant with manganese contained in the steel sheet, and the surface oxide layer and internal oxide layer including manganese oxide can be formed by oxygen of nickel oxide.

Due to the oxygen diffusion suppression 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 with respect to 100% by weight. Specifically, with respect to 100% by weight of the total antioxidant, it may include 10 to 40% by weight of nickel oxide and the residual coating flux.

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

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

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, in order to confirm the effect of an antioxidant for inhibiting internal oxidation and intergranular oxidation of high-manganese steel, it has a high content of 0.4% by weight carbon (C), 22% by weight manganese (Mn), and 0.2% by weight silicon (Si). After applying the antioxidant according to the comparative example, which is a conventional material, and the antioxidant according to the inventive example, to a manganese steel specimen, an oxidation layer formation test was conducted through a heating furnace simulation.

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 residual coating flux, and the antioxidant according to the inventive example was 30% by weight Nickel oxide and residual coating flux were included.

The gas atmosphere of the furnace simulating apparatus was maintained such that the volume ratio of CO-CO ₂ mixed gas: air was 1: 4 in the same manner as the actual 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 were performed through an electron microscopic analyzer (EPMA), and the results are shown in FIGS. 6 (conventional materials) and 7 (invention materials).

As a result of conducting a test for forming a high-manganese steel oxide layer using a heating furnace imitation device, it was confirmed that in the case of a high-manganese steel to which a conventional material was applied, the internal oxide layer was formed to a level of 50 μm, and the grain boundary oxide layer by MnO-SiO ₂ -based oxide was internal. From the end of the oxide layer, it was confirmed that it was produced at a level of 50 μm.

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

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

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

In order to confirm the effect of an antioxidant for suppressing internal oxidation and intergranular oxidation of high-manganese steel in a real process, a rolling test using an invention material and a conventional material was performed. The high-manganese steel used in the above test is the same as the high-manganese steel component system used in the test using the heater-shape.

In the test, each antioxidant was applied to two cast pieces, followed by heat treatment in a heating furnace at 1150 ° C. for 240 minutes, followed by a rolling process, and hand surface grinding was performed to facilitate defect observation of 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 no surface defect was observed in the product applied with the invention material.

Therefore, it was confirmed that the production of excellent quality products without surface defects is possible through the suppression of internal oxidation and intergranular oxidation of cast iron in the heating furnace according to the application of the invention material.

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

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,
A method of treating a steel sheet containing 10 to 40% by weight of nickel oxide with respect to 100% by weight of the total. According to claim 1,
In the step of preparing the steel sheet,
The steel sheet,
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 method of treating a steel sheet containing residual Fe and unavoidable impurities. According to claim 1,
In the step of applying the antioxidant,
The nickel oxide has an average particle size of 0.1 to 1 mm. According to claim 1,
In the step of heat-treating the steel sheet,
Heat treatment of the steel sheet in a mixed gas and air atmosphere of CO-CO ₂ , wherein the volume ratio of the mixed gas and the air (mixed gas: air) is 1: 3.5 to 1: 4.5. According to claim 1,
In the step of heat-treating the steel sheet,
The heat treatment temperature is 1100 to 1300 ° C. According to claim 1,
In the step of heat-treating the steel sheet,
The heat treatment time is 1 to 7 hours. According to 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 under the Ni-Fe alloy layer, and an internal oxide layer located under the surface oxide layer. The method of claim 7,
The surface oxide layer and the inner oxide layer is a method of treating a steel sheet containing MnO. The method of claim 7,
The average thickness of the surface oxide layer is 20 to 40㎛ processing method of the steel sheet. The method of claim 7,
The method of treating a steel sheet having an average thickness of the internal oxide layer of 30 μm or less. As an antioxidant applied to high manganese steel,
Antioxidant for high manganese steel containing 10 to 40% by weight of nickel oxide, based on 100% by weight. The method of claim 11,
The average particle size of the nickel oxide is 0.1 to 1mm antioxidant for high manganese steel.

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