KR20180027534A - Hot-rolled steel sheet excellent in corrosion resistance of sulfuric acid and hydrochloric acid complex and method for manufacturing the same - Google Patents

Abstract

A hot-rolled steel sheet excellent in sulfuric acid and hydrochloric acid combined corrosion resistance and a method for producing the same. An aspect of the present invention relates to a steel sheet comprising 0.05 to 0.1% of C, 0.5 to 1.5% of Mn, 0.02% or less of P, 0.02% or less of S, 0.01 to 0.1% of Al, 0.2 to 0.6% , 0.05 to 0.1% of Sb, and the balance of Fe and unavoidable impurities. Cu and Sb are concentrated within 500 nm in the thickness direction from the surface, and the corrosion loss of 2.0 mg / cm < ² > / hr and excellent corrosion resistance against hydrochloric acid.

Description

Hot-rolled steel sheet excellent in corrosion resistance of sulfuric acid and hydrochloric acid complex and method for manufacturing the same

The present invention relates to a hot-rolled steel sheet excellent in complex corrosion resistance against sulfuric acid and hydrochloric acid, which can be preferably applied as a material for desulfurization of a thermal power plant, a denitration facility, a preheater, and parts thereof, and a method for manufacturing the same.

Sulfuric acid or sulfuric acid-hydrochloric acid composite corrosion resistant steel reacts with moisture in exhaust gas containing sulfurous acid gas and chlorine gas generated by burning fossil fuel such as coal or petroleum to generate sulfuric acid and hydrochloric acid, and sulfuric acid or sulfuric acid- It is used as a heat element material which requires the use of a relatively thick steel sheet of a pipe and GGH (Gas Gas Heater) of a severe thermal power plant desulfurization and denitrification facility or a combined power plant.

In general, sulfuric acid - hydrochloric acid composite corrosion resistant steel has been known to add a large amount of copper (Cu) to the steel in order to delay the corrosion rate in a mixed atmosphere of sulfuric acid and hydrochloric acid.

Copper (Cu) has an effect of significantly retarding the sulfuric acid corrosion rate compared to other additive elements, but when added in large amounts, it causes cracks in the steel sheet during hot rolling. (Japanese Laid-Open Patent Publication No. 1997-025536, Japanese Laid-Open Patent Publication No. 1998-110237, Laid-Open Patent Publication No. 2009-0070249, etc.) have been developed.

As described above, the higher the content of copper (Cu) in the sulfuric acid-hydrochloric acid combined corrosion resistant steel, the better the corrosion resistance. On the other hand, the copper (Cu) is an expensive element, ) Is segregated or cracked due to slight deformation at a high concentration region, cracks are generated in the corner of the slab which is subjected to a lot of processing in the continuous casting process, and the surface defect is left after the hot rolling, .

Therefore, there is a demand for a method for securing high complex corrosion resistance while minimizing the content of copper (Cu) in sulfuric acid-hydrochloric acid combined corrosion resistant steel.

An aspect of the present invention is to provide a hot-rolled steel sheet having excellent corrosion resistance in a corrosive environment in which sulfuric acid and hydrochloric acid are mixed and a method of manufacturing the same.

An aspect of the present invention provides a steel sheet comprising, by weight%, 0.05-0.1% of C, 0.5-1.5% of Mn, 0.02% of P or less, 0.02% or less of S, 0.01 to 0.1% Cu, and Sb are concentrated within 500 nm in the thickness direction from the surface, and the corrosion loss of 2.0 mg / m < 2 > for a solution of sulfuric acid of 16.9 vol% + hydrochloric acid of 0.35 vol% / cm < ² > / hr, which is superior in corrosion resistance to sulfuric acid and hydrochloric acid.

Another aspect of the present invention is to provide a method of manufacturing a semiconductor device, comprising: 0.05 to 0.1% of C, 0.5 to 1.5% of Mn, 0.02% or less of P, 0.02% or less of S, 0.6%, Sb: 0.05-0.1%, the remainder Fe and other unavoidable impurities at 1100-1300 캜; Hot-rolling the reheated steel slab and finishing hot-rolling at 850 to 950 ° C to obtain a hot-rolled steel sheet; Rapidly cooling the hot-rolled steel sheet at a rate of 120 to 150 ° C / s; Winding the cooled hot-rolled steel sheet at 650 to 750 ° C; And slowly cooling the rolled hot-rolled steel sheet to a cooling stop temperature of 350 to 400 ° C at a rate of 30 to 40 ° C / h. The present invention also provides a method of manufacturing a hot-rolled steel sheet excellent in sulfuric acid and hydrochloric acid composite corrosion resistance.

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.

According to the present invention, it is possible to provide a hot-rolled steel sheet having a low corrosion resistance and excellent corrosion resistance compared with conventional sulfuric acid-hydrochloric acid combined corrosion resistant steel. In addition, the hot-rolled steel sheet of the present invention can be suitably applied to materials requiring relatively thick thicknesses of denitrification plants, desulfurization facilities, flue gas piping of boilers, and preheaters where complex corrosion of sulfuric acid and hydrochloric acid occurs, It is possible to greatly extend the life of the battery.

Best Mode for Carrying Out the Invention

The inventors of the present invention have conducted studies on the composition and manufacturing method of steel sheet for a method capable of ensuring high complex corrosion resistance while minimizing the content of copper (Cu) in sulfuric acid-hydrochloric acid composite corrosion resistant steel. As a result, When Sb is added as a composition and the cooling conditions after hot rolling and the cooling conditions after winding are controlled appropriately, Cu and Sb concentrated layers are formed on the surface of the steel sheet in the sulfuric acid and hydrochloric acid corrosion environment to have excellent composite corrosion resistance The present invention has been accomplished on the basis of these findings.

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

First, the alloy composition of the hot-rolled steel sheet of the present invention will be described in detail.

Carbon (C): 0.05 to 0.1 wt%

Carbon (C) is an element favorable in securing strength of a steel sheet. When the content is less than 0.05% by weight, it is difficult to secure a desired strength and there is a problem that wear resistance characteristics are deteriorated. On the other hand, if the content exceeds 0.1% by weight, the weldability is greatly deteriorated in the case of welding the steel sheet, so that the possibility of occurrence of defects is high, and the corrosion resistance is greatly deteriorated. Therefore, in the present invention, the carbon content is preferably limited to 0.05 to 0.1 wt%.

Manganese (Mn): 0.5 to 1.5 wt%

Manganese (Mn) is an element that acts to prevent hot shortness caused by the solid solution sulfur by precipitating sulfur dissolved in the steel into manganese sulfide, and exhibiting the solid solution strengthening effect. When the content of manganese is less than 0.5% by weight, manganese sulfide can not be sufficiently precipitated, and there is a fear that a hot brittleness due to solid sulfur is generated, and it is difficult to secure a target strength. On the other hand, when the content exceeds 1.5% by weight, the above-mentioned effect is saturated and the production cost increases sharply. Therefore, in the present invention, the content of manganese is preferably limited to 0.5 to 1.5% by weight.

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

Phosphorus (P) is an element which is inevitably added in the steel, and when the content exceeds 0.02% by weight, there is a problem that the intended composite corrosion resistance is largely lowered. Therefore, it is preferable to control the P content to 0.02 wt% or less.

Sulfur (S): 0.02 wt% or less

Sulfur (S) is an element which is dissolved in the steel and causes red embrittlement. Therefore, it is desirable to control the content as low as possible. When the content exceeds 0.02% by weight, there is a problem that the possibility of occurrence of defects due to the heat-induced brittleness is increased. Therefore, it is preferable to control the S content to 0.02% by weight or less.

Aluminum (Al): 0.01 to 0.1 wt%

Aluminum (Al) is an element which is inevitably added in the production of aluminum killed steel (Al-killed steel), and is preferably added in an amount of 0.01 wt% or more for deoxidizing effect. However, when the content of aluminum exceeds 0.1% by weight, there is a problem that not only the possibility of causing surface defects of the steel sheet increases but also the weldability is deteriorated. Therefore, in the present invention, the content of Al is preferably limited to 0.01 to 0.1% by weight.

Copper (Cu): 0.2 to 0.6 wt%

Copper (Cu) is an element to be added in consideration of the complex corrosion property of sulfuric acid and hydrochloric acid. When the content is too low, it is difficult to ensure the desired complex corrosion resistance. Therefore, % Or more. The complex corrosion resistance increases as the content of Cu increases. However, when the content is too high, the increase in corrosion resistance greatly decreases, the manufacturing cost increases sharply, and surface cracks such as star cracks are caused. Therefore, in the present invention, the upper limit of the content of Cu is preferably 0.6% by weight, more preferably 0.5% by weight.

Antimony (Sb): 0.05 to 0.1 wt%

Antimony (Sb) is an element added as an indispensable element for improving the composite corrosion resistance together with the Cu. Especially, it is an element that can effectively improve the composite corrosion resistance by forming a Cu-Sb composite oxide in a corrosive environment. If the content of antimony is less than 0.05% by weight, it is difficult to obtain the above-mentioned effect. On the other hand, if it exceeds 0.1% by weight, the above-mentioned effect is saturated and the production cost increases sharply. .

In addition to the above composition, the remainder is composed of Fe and unavoidable impurities. On the other hand, it is not excluded that other compositions other than the above composition can not be included, but it is more preferable to control the sum of the contents of W, Mo, Co and Ni to be less than 10 ppm. This is because these elements may deteriorate the material properties of the hot-rolled steel sheet, such as ductility.

On the other hand, in the hot-rolled steel sheet of the present invention, it is preferable that Cu and Sb are concentrated within 500 nm in the thickness direction from the surface. These elements are present in a concentrated state on the surface during the production of the steel sheet, and when exposed to the corrosive environment by sulfuric acid and hydrochloric acid, they change to the form of Cu-Sb composite oxide, thereby improving the corrosion resistance of the hot-rolled steel sheet to a very good level.

At this time, the content of concentrated Cu and Sb is not particularly limited, and it may be enough to form an oxide layer having a thickness of 400 nm or more from the surface of the hot-rolled steel sheet in a corrosive environment by sulfuric acid and hydrochloric acid, as described below . When the thickness of the oxide layer is less than 400 nm, it is difficult to secure the intended corrosion resistance of the present invention. On the other hand, since the corrosion resistance is improved as the thickness of the oxide layer is increased, the upper limit of the thickness of the oxide layer is not particularly limited in the present invention. However, when it is more than 500 nm, there is a problem that the effect of improving the corrosion resistance as compared with the addition of a large amount of alloy is low, and the manufacturing cost is excessively increased. Therefore, the thickness of the oxide layer is more preferably 400 to 500 nm.

The hot-rolled steel sheet of the present invention has a corrosion resistance loss of 2.0 mg / cm 2 / hr or less with respect to 16.9% by volume sulfuric acid + 0.35% by volume hydrochloric acid solution, and has excellent excellent corrosion resistance.

Hereinafter, a method of manufacturing a hot-rolled steel sheet having excellent corrosion resistance to sulfuric acid and hydrochloric acid, which is another aspect of the present invention, will be described in detail.

First, a steel slab satisfying the above composition is prepared and reheated at 1100 to 1300 ° C. When the reheating temperature is less than 1100 ° C, there is a problem that it is difficult to secure the temperature during subsequent hot rolling. On the other hand, when the reheating temperature exceeds 1300 ° C, Cu having a low melting point elutes and cracks There is a problem that the possibility of occurrence is high.

Thereafter, the reheated steel slab is hot-rolled and finishing hot-rolled at 850 to 950 ° C to obtain a hot-rolled steel sheet. When the final hot rolling temperature is lower than 850 ° C, there is a problem that the elongation rate is greatly lowered due to the formation of the elongated crystal grains and the material deviation is uneven in each direction. On the other hand, when it exceeds 950 ° C, the austenite grains become coarse, There is an increasing problem.

Thereafter, the hot-rolled steel sheet is rapidly cooled to 120 to 150 ° C / s based on the surface temperature of the steel sheet. By the quenching as described above, it is possible to provide the driving force necessary for the alloying element which is advantageous in corrosion resistance after winding to move to the surface of the steel sheet. If the cooling rate is less than 120 ° C / s, the surface temperature of the hot-rolled steel sheet is too high, so that the driving force of the oxide forming elements existing in the steel is low, and when the steel sheet is exposed to a complex corrosive environment, There is a problem that is difficult to be done. On the other hand, when the cooling rate exceeds 150 ° C / s, the temperature inside the steel sheet becomes too low, so that there is a problem that the alloying element which is advantageous for the formation of the oxide layer is not smoothly moved. Therefore, the cooling rate is preferably 120 to 150 DEG C / s.

Thereafter, the cooled hot-rolled steel sheet is rolled at 650 to 750 ° C. When the coiling temperature is less than 650 캜, the movement of atoms is not easy in the winding step, so that formation of a dense layer is difficult, and an oxide layer is not formed in a corrosive environment, so that it is difficult to secure sufficient corrosion resistance. If the coiling temperature exceeds 750 캜, the coiling temperature may be too high to cause defects such as warping of the wound steel plate. Therefore, the coiling temperature preferably ranges from 650 to 750 캜.

On the other hand, at the time of winding, it is preferable that the surface of the steel sheet is made 720 to 750 ° C due to a double heat phenomenon. The surface of the steel sheet has a temperature lower than the temperature range by quenching even if the temperature inside the steel sheet is in the range of 650 to 750 ° C through the cooling process. Therefore, by moving the alloying element favorable for the formation of the oxide layer through the repetition process, the concentrated layer can be formed to have a sufficient thickness. In order to sufficiently obtain the above effect, the surface temperature of the steel sheet subjected to the double heat treatment is preferably 720 DEG C or more. However, it is difficult for the surface temperature of the steel sheet to exceed 750 ° C even after sufficient repetition.

The wound steel sheet is slowly cooled to a cooling stop temperature of 350 to 400 DEG C at a rate of 30 to 40 DEG C / hr. In the case where the cooling rate is excessively high, the movement of Cu, which is an element forming the concentrated layer, is insufficient and it may be difficult to form a thick layer having a sufficient thickness. Therefore, the cooling rate is preferably 40 占 폚 / hr or less . On the other hand, when the cooling rate is less than 30 ° C / hr, the grain size excessively increases and the strength may be lowered. Therefore, the cooling rate is preferably in the range of 30 to 40 ° C / hr. On the other hand, when the cooling-stop temperature is lower than 350 ° C, there is a problem that the material properties of the hot-rolled steel sheet, such as ductility, deteriorate and productivity deteriorates. On the other hand, when it exceeds 400 ° C, There may be a problem of dwarfism. Therefore, the cooling stop temperature is preferably in the range of 350 to 400 ° C.

DETAILED DESCRIPTION OF THE INVENTION

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)

A steel ingot prepared by dissolving in a composition as shown in Table 1 was held in a heating furnace at 1200 占 폚 for 1 hour and then hot-rolled. At this time, finishing hot rolling was performed at 900 캜, and a hot-rolled steel sheet having a final thickness of 4.5 mm was produced. Thereafter, it was cooled and wound up under the conditions shown in Table 2, and then held. Then, the steel sheet was slowly cooled to a cooling termination temperature of 380 ° C at a rate of 35 ° C / h to prepare a final hot-rolled steel sheet.

In order to observe the corrosion characteristics of the hot-rolled steel sheet manufactured according to the above, the specimens were immersed in a solution of 16.9 vol% sulfuric acid at 60 ° C and 0.35 vol% hydrochloric acid for 6 hours, and then the corrosion loss of each specimen was measured. Are shown in Table 2 below.

Further, the thickness of the oxide layer (corrosion resistant layer) formed on the surface of the steel sheet after completion of the deposition under the sulfuric acid-hydrochloric acid complex corrosion condition was measured and shown in Table 2.

Steel grade Component composition (% by weight) C Mn P S Al Cu Sb Inventive Steel 1 0.075 0.69 0.012 0.009 0.033 0.32 0.08 Invention river 2 0.068 0.67 0.011 0.009 0.029 0.39 0.06 Invention steel 3 0.074 0.75 0.009 0.01 0.029 0.44 0.05 Comparative River 1 0.069 0.74 0.012 0.011 0.035 0.28 -

Steel grade Cooling rate (° C / s) Coiling temperature (캜) Corrosion loss (mg / cm ² / hr) Oxide layer thickness (nm) division Inventive Steel 1 130 700 1.8 420 Inventory 1 130 500 4.5 57 Comparative Example 1 10 700 3.8 63 Comparative Example 2 Invention river 2 130 700 1.6 440 Inventory 2 10 700 3.6 69 Comparative Example 3 Invention steel 3 130 700 1.4 460 Inventory 3 10 700 3.2 75 Comparative Example 4 Comparative River 1 130 700 8.8 220 Comparative Example 5

As can be seen from Tables 1 and 2, in the case of Inventive Examples 1 to 3 satisfying the alloy composition and manufacturing conditions proposed by the present invention, an oxide layer of 400 nm or more is formed, and the corrosion loss is 2.0 mg / ㎠ / Hr or less.

The comparative example 1 satisfies the alloy composition of the present invention, but the oxide layer is not sufficiently formed because the coiling temperature is as low as 500 占 폚, so that the corrosion loss is 4.5 mg / cm2 / hr and the corrosion resistance is very low.

Comparative Examples 2 to 4 satisfied the alloy composition of the present invention but the cooling rate was as low as 10 占 폚 / s, so that the oxide layer was not sufficiently formed, and the corrosion loss was 3.2 mg / It can be seen that it is very low.

In the case of Comparative Example 5, the production conditions of the present invention are satisfied, but Sb is not added, and the corrosion resistance is 8.8 mg / cm ² / hr in the corrosive environment by sulfuric acid and hydrochloric acid. This is because there is no Cu-Sb composite oxide having excellent corrosion resistance in the oxide layer.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims. .

Claims (6)

0.05 to 0.1% of C, 0.5 to 1.5% of Mn, 0.02% or less of P, 0.02% or less of S, 0.01 to 0.1% of Al, 0.2 to 0.6% of Cu, 0.05 to 0.1% of Sb, , The remainder Fe and inevitable impurities, Cu and Sb are concentrated within 500 nm in the thickness direction from the surface, sulfuric acid having a corrosion loss of 2.0 mg / cm ² / hr or less to 16.9% by volume of sulfuric acid + 0.35% Hydrochloric acid composite Hot-rolled steel with excellent corrosion resistance. The method according to claim 1,
The inevitable impurities include W, Mo, Co and Ni, and the sum of these contents is less than 10 ppm. The method according to claim 1,
Wherein the concentrated Cu and Sb form an oxide layer containing a Cu-Sb composite oxide in a sulfuric acid and hydrochloric acid corrosion environment. The method of claim 3,
Wherein the oxide layer is formed to a thickness of 400 to 500 nm in a thickness direction from a surface of the hot-rolled steel sheet. 0.05 to 0.1% of C, 0.5 to 1.5% of Mn, 0.02% or less of P, 0.02% or less of S, 0.01 to 0.1% of Al, 0.2 to 0.6% of Cu, 0.05 to 0.1% of Sb, , Remainder Fe and other unavoidable impurities at 1100-1300 캜;
Hot-rolling the reheated steel slab and finishing hot-rolling at 850 to 950 ° C to obtain a hot-rolled steel sheet;
Rapidly cooling the hot-rolled steel sheet at a rate of 120 to 150 ° C / s;
Winding the cooled hot-rolled steel sheet at 650 to 750 ° C; And
And cooling the rolled hot-rolled steel sheet at a cooling rate of 30 to 40 占 폚 / h to a cooling-stop temperature of 350 to 400 占 폚. 6. The method of claim 5,
Wherein the surface of the steel sheet is 720 to 750 占 폚 due to a double thermal phenomenon during the winding, wherein the steel sheet has excellent corrosion resistance to sulfuric acid and hydrochloric acid.