KR20130143374A - Hot-rolled steel sheet having excellent multi-corrosion resistant and weldability and method for manufacturing thereof - Google Patents

Abstract

The present invention relates to a hot-rolled steel sheet having excellent multi-corrosion resistant in comparison with steels containing copper and sulfuric acid in which defective surface caused by copper is not generated or sulfuric acid-hydrochloric acid multi-corrosion resistant and weldability and a manufacturing method thereof. The hot-rolled steel sheet contains 0.01-0.1 wt% of C, 0.5-1.5 wt% of Si, 0.5-1.5 wt% of Mn, 0.1-0.2 wt% of Al, 0.2-1.0 wt% of Cu, 0.1-0.5 wt% of Ni, 0.03-0.1 wt% of Co, 0.05-0.15 wt% of Sb, less than 0.02 wt% of S, less than 0.02 wt% of P, the remainder of Fe, and impurities. The ratio of Ni and Cu exceeds 0.4 and less than 0.7. In a multi-corrosion process, an oxide layer containing the oxide of CuO and Al2O3 is formed.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot-rolled steel sheet having excellent corrosion resistance and corrosion resistance,

The present invention relates to a hot-rolled steel sheet having excellent corrosion resistance and weldability, and a method of manufacturing the same.

Sulfuric acid-hydrochloric acid composite corrosion resistant steel reacts with moisture in exhaust gas containing sulfurous acid gas and chlorine gas produced by burning fossil fuels such as coal or petroleum to generate sulfuric acid and hydrochloric acid and desulfurization of thermal power plant And a heat element material in which a relatively thick steel sheet of a denitration facility or piping of a combined power plant and a GGH (Gas Gas Heater) is used.

Generally, sulfuric acid - hydrochloric acid corrosion resistant steel has been known to add a large amount of Cu in steel to delay the corrosion rate than ordinary steel in sulfuric acid and hydrochloric acid atmosphere. In Patent Documents 1 to 3, it can be seen that as a steel containing a large amount of Cu, the effect of significantly delaying the sulfuric acid corrosion rate is superior to that of a steel to which a large amount of other elements are added.

However, in the Cu-added steel, cracks are liable to occur even when Cu having a relatively low melting point is segregated or a portion having a high concentration of Cu is slightly deformed. Further, cracks are generated in the corners of the slabs, which are subjected to a lot of machining in the continuous casting process, so that they remain as surface defects after hot rolling and corrode earlier than other parts.

In addition, since the actual sulfuric acid-hydrochloric acid corrosion resistant steel is mostly used by welding, if the welding quality is not ensured, the stress is concentrated on the welding defect portion, causing breakage or corrosion. There is a problem in that the Cu-added steel does not consider the welding quality and thus it is very difficult to work because defects are generated in the welding part or the welding workability is poor.

Therefore, there is a demand for the development of a steel having excellent properties even when an appropriate amount of Cu is added.

(Patent Document 1) Japanese Laid-Open Publication No. 1997-025536

(Patent Document 2) Japanese Laid-Open Patent No. 1998-110237

(Patent Document 3) Korean Published Patent Application No. 2007-0138183

An object of the present invention is to provide a hot-rolled steel sheet excellent in corrosion resistance and excellent in corrosion resistance and weldability, which is superior in corrosion resistance to a conventional Cu-added steel and does not cause surface defects due to Cu, or sulfuric acid or hydrochloric acid-hydrochloric acid composite.

The hot-rolled steel sheet having excellent corrosion resistance and weldability, which is one aspect of the present invention, comprises 0.01 to 0.1% of C, 0.5 to 1.5% of Si, 0.5 to 1.5% of Mn, 0.1 to 0.2% of Al, The balance of Fe and other unavoidable impurities, and Ni / Cu (Cu / Ni) of 0.1 to 1.0%, Ni of 0.1 to 0.5%, Co of 0.03 to 0.1%, Sb of 0.05 to 0.15%, S of 0.02% Is less than 0.7 and less than 0.7, and an oxide layer containing oxides of CuO and Al ₂ O ₃ is formed in the course of the complex corrosion.

A method of manufacturing a hot-rolled steel sheet having excellent corrosion resistance and weldability according to another aspect of the present invention is characterized by comprising 0.01 to 0.1% of C, 0.5 to 1.5% of Si, 0.5 to 1.5% of Mn, 0.1 to 0.2% of Al, 0.1 to 0.5% of Cu, 0.03 to 0.1% of Co, 0.05 to 0.15% of Sb, 0.02% or less of S and 0.02% or less of P and the balance Fe and other unavoidable impurities , Reheating the slab having a Ni / Cu ratio of more than 0.4 and less than 0.7 at 1200 to 1300 캜, finishing hot rolling the reheated slab at 850 to 950 캜, heating the finished hot- And cooling the rolled steel sheet to 300 to 100 DEG C at a cooling rate of 20 to 50 DEG C / hour.

In addition, the solution of the above-mentioned problems does not list all the features of the present invention. The various features of the present invention and the advantages and effects thereof will be more fully understood by reference to the following specific embodiments.

The hot-rolled steel sheet of the present invention is excellent in sulfuric acid-hydrochloric acid composite corrosion resistance, and is suitable for materials requiring relatively thick thickness such as sulfuric acid dew point corrosion or sulfuric acid-hydrochloric acid composite corrosion in a power plant preheater, denitrification equipment, desulfurization equipment, boiler pipe and peripheral equipment It is possible to reduce the manufacturing cost by lowering the addition amount of the alloy element compared with the conventional Cu-added steel.

The inventors of the present invention have conducted studies to derive a hot-rolled steel sheet excellent in the corrosion resistance and weldability of a sulfuric acid / hydrochloric acid composite used as a thermal element of a thermal power plant preheater or an incinerator exhaust system. As a result, It is possible to produce a hot-rolled steel sheet having improved corrosion resistance and weldability compared to the conventional steel sheet.

Hereinafter, a hot rolled steel sheet having excellent corrosion resistance and weldability, which is one aspect of the present invention, will be described in detail.

The hot-rolled steel sheet having excellent corrosion resistance and weldability, which is one aspect of the present invention, comprises 0.01 to 0.1% of C, 0.5 to 1.5% of Si, 0.5 to 1.5% of Mn, 0.1 to 0.2% of Al, The balance of Fe and other unavoidable impurities, and Ni / Cu (Cu / Ni) of 0.1 to 1.0%, Ni of 0.1 to 0.5%, Co of 0.03 to 0.1%, Sb of 0.05 to 0.15%, S of 0.02% and the ratio is over 0.4 but less than 0.7, to form the oxide layer including an oxide of CuO and Al ₂ O ₃ in the composite corrosion process.

Carbon (C): 0.01 to 0.1 wt%

Carbon is the most effective element for strengthening the steel, but it degrades the weldability when added in large amounts. When the content of carbon is less than 0.01% by weight, it is difficult to realize the target strength intended in the present invention, and it is not economical because a large amount of expensive alloying elements such as Mo and Ni should be added in order to increase the strength. On the other hand, when the content of carbon is more than 0.1% by weight, the weldability is deteriorated. Therefore, the carbon content is preferably 0.01 to 0.1 wt%.

Silicon (Si): 0.5 to 1.5 wt%

Silicon, like carbon, is an element added to improve strength. When the amount of silicon is less than 0.5% by weight, internal defects occur during welding and the welded portion is not sound. When the amount of silicon exceeds 1.5% by weight, the rate of occurrence of surface defects increases due to the formation of silicon oxide. Therefore, it is preferable that the silicon content is included in the range of 0.5 to 1.5 wt%.

Manganese (Mn): 0.5 to 1.5 wt%

It is mainly added to precipitate sulfur in manganese sulfide in the steel to prevent hot-shortness due to sulfur. In addition, the present invention is added for the purpose of preventing red-hot brittleness and improving weldability. When the content of manganese is less than 0.5 wt%, defects occur after welding and the welds are not sound. On the other hand, when it exceeds 1.5% by weight, there is no probability of further occurrence of the fused brittleness. Accordingly, the content of manganese is preferably 0.5 to 1.5% by weight.

Aluminum (Al): 0.1 to 0.2 wt%

It is added when making Al-killed steel. In the present invention, 0.1% by weight or more is added to improve the composite corrosion resistance property. The upper limit of aluminum was limited to 0.2 wt% in order to prevent the weldability from being significantly lowered when the content of aluminum was large. Therefore, the content of aluminum is preferably 0.1 to 0.2% by weight.

Copper (Cu): 0.2 to 1.0 wt%

Copper is an element added to improve the sulfuric acid-hydrochloric acid composite corrosion resistance. In order to exhibit such an effect in the present invention, it is preferable to include at least 0.2 wt%. As the content of Cu increases, the complex corrosion resistance is improved. However, since the complex corrosion resistance does not increase proportionally with the increase of the additive amount, the upper limit is preferably limited to 1.0 wt%. Therefore, the copper is preferably contained in an amount of 0.2 to 1.0% by weight.

Nickel (Ni): 0.1 to 0.5 wt%

Nickel is an element added to improve both strength and toughness. When the amount of nickel is less than 0.1% by weight, surface defects due to Cu crystallization are generated, thereby causing surface defects. As the content of nickel increases, the strength and toughness are improved. However, since the strength and toughness do not increase proportionally as the amount of nickel is increased, the upper limit is preferably limited to 0.5 wt%. Accordingly, it is preferable that the nickel content is 0.1 to 0.5 wt%.

Cobalt (Co): 0.03 to 0.1 wt%

Cobalt is an element added to activate Cu in a corrosive environment to easily deposit on the surface to improve corrosion resistance. When the amount of the cobalt is less than 0.03% by weight, the intended corrosion resistance of the present invention can not be secured. On the other hand, when the content of cobalt exceeds 0.1% by weight, the effect is not further increased. Therefore, cobalt is preferably contained in an amount of 0.03 to 0.1% by weight.

Antimony (Sb): 0.05 to 0.15 wt%

Antimony, like cobalt, is an element added to improve corrosion resistance. If the amount of antimony is less than 0.05 wt%, the intended corrosion resistance of the present invention can not be secured. On the other hand, when the content of antimony exceeds 0.15% by weight, the effect does not increase any more. Therefore, antimony is preferably contained in an amount of 0.05 to 0.15% by weight.

The remainder of the present invention is iron (Fe). However, in the ordinary manufacturing process, impurities which are not intended from the raw material or the surrounding environment may be inevitably incorporated, so that it can not be excluded. These impurities are not specifically mentioned in this specification, as they are known to any person skilled in the art of manufacturing.

However, since phosphorus and sulfur are generally referred to as impurities, a brief description thereof is as follows.

Phosphorus (P): not more than 0.02% by weight

The phosphorus is inevitably contained as an impurity and is preferably controlled as low as possible. Theoretically, it is preferable to limit the phosphorus content to 0%, but it is inevitably contained inevitably in the manufacturing process. Therefore, it is important to manage the upper limit, and in the present invention, the upper limit of the phosphorus content is preferably limited to 0.02% by weight.

Sulfur (S): 0.02 wt% or less

The sulfur is inevitably contained and is preferably controlled as low as possible. Theoretically, it is advantageous to limit the content of sulfur to 0%, but it is inevitably contained inevitably in the manufacturing process. Therefore, it is important to manage the upper limit, and in the present invention, the upper limit of the sulfur content is preferably limited to 0.02 wt%.

In the above composition, Cu and Ni preferably satisfy 0.4 < Ni / Cu < 0.7.

The above relational expression is for securing the welding quality which is not obtained in the conventional Cu-added steel and securing the corrosion resistance. If the value is 0.4 or less, there is a problem that surface defects occur and the corrosion resistance of the defect occurrence site is greatly lowered and cracks occur during processing. On the other hand, when it is 0.7 or more, there is a problem that the amount of Ni to be added increases and the manufacturing cost increases.

Further, it is preferable to form an oxide layer on the surface of the hot-rolled steel sheet.

By forming the oxide layer on the surface of the hot-rolled steel sheet during the complex corrosion process, the corrosion resistance of the steel sheet is greatly improved, thereby prolonging the life of the steel sheet and reducing the manufacturing cost. The complex corrosion process as referred to in the present invention means a process of corroding in a sulfuric acid-hydrochloric acid complex corrosion environment.

It is preferable that the oxide layer includes at least one of Cu, Ni, Sb and Al. The Cu formed in the oxide layer may be present as CuO, Al ₂ O ₃ .

In addition, the oxide layer is preferably formed to a thickness of 100 to 500 nm. When the thickness of the oxide is less than 100 nm, it is difficult to expect the effect as an oxide. When the thickness exceeds 500 nm, the effect is excellent, but the economical efficiency with respect to the cost decreases.

The corrosion loss of the hot-rolled steel sheet is preferably 2.0 to 3.0 mg / cm 2 per hour in order to maintain a life of more than 20 years in a complex corrosion atmosphere.

Hereinafter, a method for manufacturing a hot-rolled steel sheet having excellent corrosion resistance and weldability, which is one aspect of the present invention, will be described in detail.

A method of manufacturing a hot-rolled steel sheet having excellent corrosion resistance and weldability according to another aspect of the present invention is characterized by comprising 0.01 to 0.1% of C, 0.5 to 1.5% of Si, 0.5 to 1.5% of Mn, 0.1 to 0.2% of Al, 0.1 to 0.5% of Cu, 0.03 to 0.1% of Co, 0.05 to 0.15% of Sb, 0.02% or less of S and 0.02% or less of P, the balance Fe and other unavoidable impurities Reheating the slab at 1200 to 1300 占 폚, finishing hot-rolling the reheated slab at 850 to 950 占 폚, winding the finished hot-rolled steel sheet at 650 to 700 占 폚, And cooling to 300 to 100 占 폚 at a cooling rate of 50 占 폚 / hour.

Reheat step

It is preferable to reheat the slab satisfying the above-mentioned component system at 1200 to 1300 占 폚. The reason for heating at 1200 ° C or more is to secure the hot rolling temperature as described above. The upper limit of the reheating temperature is not particularly limited, but is preferably 1300 占 폚 or less in consideration of the economical efficiency of the process.

Hot rolling step

Preferably, the reheated slab is hot-rolled and the finish rolling temperature is 850 to 950 ° C. If the finish rolling temperature is lower than 850 占 폚, transformation occurs before rolling, and the workability is greatly lowered. On the other hand, when the finish rolling temperature is 950 DEG C , The crystal grains have a lower coarsening strength.

Winding stage

The hot rolling is followed by winding. At this time, the coiling temperature is preferably 650 to 700 占 폚. If the coiling temperature is less than 650 ° C, the size of the carbide becomes very small and the workability is extremely low. On the other hand, when it exceeds 700 ° C, there is a problem that the strength of the crystal grains is lowered.

Cooling stage

After the winding, cooling is performed. At this time, the cooling rate is preferably cooled to 300 to 100 占 폚 at a cooling rate of 20 to 50 占 폚 / hour. When the cooling rate is less than 20 ° C / hour, the cooling rate is too low to increase the crystal grain size, resulting in a problem of lowering the strength. On the other hand, when the cooling rate exceeds 50 ° C / hour, Cu and Al are deposited during the sulfuric acid / hydrochloric acid complex corrosion, so that the CuO and Al ₂ O ₃ oxides can not be easily formed and the sulfuric acid / hydrochloric acid composite corrosion resistance can not be secured. Further, by cooling to 100 deg. C, Cu and Al sufficiently diffuse sufficiently to the surface. On the other hand, when the cooling is terminated at a temperature exceeding 300 ° C, Cu and Al are not sufficiently diffused to the surface, and CuO and Al ₂ O ₃ are not easily produced at the time of complex corrosion.

Hereinafter, the present invention will be described more specifically by way of examples. It should be noted, however, that the following examples are intended to illustrate the invention in more detail and not to limit the scope of the invention. The scope of the present invention is determined by the matters set forth in the claims and the matters reasonably inferred therefrom.

(Example)

The steel slab having the composition shown in Table 1 was maintained in a heating furnace at 1250 캜 for 1 hour and then subjected to hot rolling. At this time, the hot finish rolling temperature was 900 ° C, the coiling temperature was 650 ° C, and the cooling rate was 40 ° C / hour to 200 ° C to obtain Inventive Examples 1 to 4 and Comparative Examples 1 to 4 having a final thickness of 4.5 mm. Comparative Example 5 is the same as Examples 1 to 4 and Comparative Examples 1 to 4 except that the cooling was performed at a cooling rate of 150 占 폚 / hour.

In order to examine the corrosion resistance of the inventive and comparative examples, the corrosion loss of each specimen was measured by immersing in a sulfuric acid 16.9 vol% + 0.35 vol% solution of hydrochloric acid at 60 DEG C for 6 hours and is shown in Table 2 below. In order to examine the weldability of the inventive and comparative examples, whether or not surface flaws occurred after welding and whether or not cracks occurred after bending at 180 ° after welding were visually confirmed, are shown in Table 2 below.

As can be seen from the results of Tables 1 and 2, Inventive Examples 1 to 4 satisfying the composition and manufacturing conditions of the present invention have corrosion loss values of 3.0 mg / cm 2 or less per hour, It was confirmed that cracks did not occur even after 180 ° bending after welding.

On the other hand, Comparative Examples 1 to 4 did not satisfy the composition range proposed by the present invention, and it was confirmed that the corrosion loss was higher than the value of 3.0 mg / cm 2 or less per hour proposed by the present invention. And it was confirmed that a crack occurred at 180 ° bending. In Comparative Example 5, the composition range proposed by the present invention is satisfied, but the cooling rate is 150 ° C / hour, which is outside the range proposed by the present invention, so that CuO and Al ₂ O ₃ oxides are not well formed during the corrosion process It was confirmed that the corrosion loss was very high.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined in the appended claims. It will be possible.

Claims (6)

By weight%, C: 0.01-0.1%, Si: 0.5-1.5%, Mn: 0.5-1.5%, Al: 0.1-0.2%, Cu: 0.2-1.0%, Ni: 0.1-0.5%, Co: 0.03- 0.1%, Sb: 0.05 ~ 0.15%, S: 0.02% or less, P: 0.02% or less, balance Fe and other unavoidable impurities, Ni / Cu ratio is more than 0.4 and less than 0.7, CuO and Al in complex corrosion process Hot-rolled steel sheet excellent in composite corrosion resistance and weldability in which an oxide layer containing an oxide of ₂ O ₃ is formed.
The method of claim 1,
Wherein the oxide includes at least one of Ni and Sb, and has excellent corrosion resistance and weldability.
3. The method of claim 2,
Wherein the oxide layer has a thickness of 100 to 500 nm and is excellent in corrosion resistance and weldability.
The method of claim 1,
Corrosion loss of the hot rolled steel sheet is 2.0 ~ 3.0mg / ㎠ per hour composite corrosion resistance and weldability excellent hot rolled steel sheet.
The steel sheet according to any one of claims 1 to 3, wherein the steel sheet contains 0.01 to 0.1% of C, 0.5 to 1.5% of Si, 0.5 to 1.5% of Mn, 0.1 to 0.2% of Al, 0.2 to 1.0% of Cu, 0.1 to 0.5% of Ni, The slab having a Ni / Cu ratio of more than 0.4 and less than 0.7, which contains 0.1% of Sb, 0.05 to 0.15% of S, 0.02% or less of S, 0.02% or less of P and the balance of Fe and other unavoidable impurities is reheated at 1200 to 1300 ° C step;
Subjecting the reheated slab to finish hot rolling at 850 to 950 占 폚;
Rolling the finished hot-rolled steel sheet at 650 to 700 ° C; And
And cooling the rolled steel sheet at a cooling rate of 20 to 50 占 폚 / hour to 100 to 300 占 폚.
6. The method of claim 5,
Wherein the hot-rolled steel sheet forms an oxide layer containing oxides of CuO and Al ₂ O ₃ in a complex corrosion process, and has excellent corrosion resistance and weldability.