JP6549254B2 - Hot rolled steel sheet excellent in sulfuric acid and hydrochloric acid composite corrosion resistance and method for manufacturing the same - Google Patents

Description

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

  Sulfuric acid or sulfuric acid-hydrochloric acid composite corrosion resistant steel is a sulfuric acid or sulfuric acid or sulfuric acid or hydrochloric acid, because the exhaust gas containing sulfur dioxide gas and chlorine gas generated in the combustion process of fossil fuel such as coal or petroleum reacts with moisture to form sulfuric acid and hydrochloric acid. For desulfurization and denitrification equipment of thermal power plant where complex corrosion of sulfuric acid and hydrochloric acid is severe, or piping of complex power plant and heat element material using relatively thick steel plate such as GGH (Gas Gas Heater) Used.

  In general, a 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 more than general steel in a mixed atmosphere of sulfuric acid and hydrochloric acid.

  Copper (Cu) is excellent in the effect of greatly retarding the sulfuric acid corrosion rate compared to other additive elements, but if added in large amounts, it causes cracking of the steel sheet during hot rolling, etc. A steel has been developed in which other elements are added in combination while adding copper (Cu) (Patent Document 1, Patent Document 2, Patent Document 3 etc.).

  Thus, the higher the content of copper (Cu) in the sulfuric acid-hydrochloric acid composite corrosion resistant steel, the better the corrosion resistance can be, while copper (Cu) is an expensive element, and the manufacturing cost increases as the content increases. Not only the high temperature, but also copper (Cu) having a low melting point is segregated, cracks are likely to occur even in a portion where the concentration is high even by a slight strain, and cracks occur in the corners of slabs etc. After hot rolling, there is a problem that it remains as a surface defect and corrodes earlier than other parts.

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

Japanese Unexamined Patent Publication No. 1997-025536 Japanese Patent Laid-Open Publication No. 1998-110237 Korean Published Patent 2009-0070249

  The present invention provides a hot-rolled steel sheet having excellent corrosion resistance in a corrosive environment in which sulfuric acid and hydrochloric acid exist in combination, and a method of manufacturing the same.

One aspect of the present invention is C: 0.05% to 0.1%, Mn: 0.5% to 1.5%, P: 0.02% or less, S: 0.02% or less, Al by weight. : 0.01% to 0.1%, Cu: 0.2 to 0.6%, Sb: 0.05 to 0.1%, balance Fe and unavoidable impurities, and within 500 nm in the thickness direction from the surface Hot rolled steel sheet excellent in sulfuric acid and hydrochloric acid combined corrosion resistance, wherein Cu and Sb are concentrated and the corrosion loss is 2.0 mg / cm ² / hr or less for 16.9 vol% sulfuric acid + 0.35 vol% hydrochloric acid solution I will provide a.

  Another aspect of the present invention is C: 0.05% to 0.1%, Mn: 0.5% to 1.5%, P: 0.02% or less, S: 0.02% or less by weight , Al: 0.01% to 0.1%, Cu: 0.2 to 0.6%, Sb: 0.05 to 0.1%, balance Fe and other unavoidable impurities at 1100 to 1300 ° C. Reheating the steel slab by hot rolling, finishing hot rolling at 850 to 950 ° C. to obtain a hot rolled steel sheet, and 120 to 150 ° C./s the hot rolled steel plate Quenching at a speed of 350 ° C, winding the cooled hot rolled steel sheet at 650 to 750 ° C., and 350 to 400 ° C. at a speed of 30 to 40 ° C./h And a step of gradually cooling to a cooling stop temperature, to provide a method of producing a hot rolled steel sheet excellent in sulfuric acid and hydrochloric acid combined corrosion resistance.

  The means for solving the above-mentioned problems do not enumerate all the features of the present invention. The various features of the present invention and the advantages and benefits thereof may be more fully understood with reference to the following specific embodiments.

  According to the present invention, it is possible to provide a hot-rolled steel sheet which has excellent composite corrosion resistance while being a low alloy system as compared to conventional sulfuric acid-hydrochloric acid composite corrosion resistant steel. In addition, the heat-rolled steel plate of the present invention is suitable for a material requiring relatively thick thickness such as NOx removal / desulfurization equipment of a power plant where complex corrosion to sulfuric acid and hydrochloric acid occurs, boiler exhaust gas piping and preheater. In addition, they have the effect of significantly extending their lifetime.

  The present inventors conducted studies from both sides of the steel sheet composition and manufacturing method as to a method capable of securing high composite corrosion resistance while minimizing the content of copper (Cu) in sulfuric acid-hydrochloric acid composite corrosion resistant steel. As a result of stacking, the surface of the steel plate is added in a corrosive environment of sulfuric acid and hydrochloric acid by appropriately controlling the cooling condition after hot rolling and further the cooling condition after winding while adding Sb as one composition of the steel plate. It has been found that the Cu and Sb enriched layers are formed to a suitable thickness, and excellent combined corrosion resistance can be secured, and the present invention has been completed.

  Hereinafter, the heat-rolled steel plate excellent in sulfuric acid and hydrochloric acid combined corrosion resistance which is one mode of the present invention is explained in detail.

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

Carbon (C): 0.05 to 0.1% by weight
Carbon (C) is an element advantageous for securing the strength of the steel plate, and when the content is less than 0.05% by weight, it is difficult to secure the target strength and there is a problem that the wear resistance is deteriorated. On the other hand, if the content exceeds 0.1% by weight, the weldability is greatly deteriorated at the time of welding of the steel plate, the possibility of occurrence of defects becomes high, and there is a problem that the corrosion resistance is also significantly reduced. Therefore, in the present invention, the content of carbon is preferably limited to 0.05 to 0.1% by weight.

Manganese (Mn): 0.5 to 1.5% by weight
Manganese (Mn) plays the role of preventing hot shortness due to the above-mentioned solid solution sulfur by precipitating the solid solution sulfur in the steel as manganese sulfide, and expresses the effect of solid solution strengthening Is an element that If the content of manganese is less than 0.5% by weight, manganese sulfide may not be sufficiently precipitated, and red hot embrittlement may occur due to solid solution sulfur, making it difficult to secure the target strength. On the other hand, when the content exceeds 1.5% by weight, the above-mentioned effects are saturated, and there is a problem that the manufacturing cost rises sharply. Therefore, in the present invention, the content of manganese is preferably limited to 0.5 to 1.5% by weight.

Phosphorus (P): 0.02% by weight or less Phosphorus (P) is an element inevitably added to steel, and when its content exceeds 0.02% by weight, the target composite corrosion resistance is greatly reduced There is a problem of Therefore, it is preferable to control the content of P to 0.02% by weight or less.

Sulfur (S): 0.02% by Weight or Less Sulfur (S) is an element which is solid-dissolved in steel to induce red shortness, so it is preferable to control its content as low as possible. If the content exceeds 0.02% by weight, there is a problem that the possibility of defects due to red shortness becomes high, so it is preferable to control the content of S at 0.02% by weight or less.

Aluminum (Al): 0.01 to 0.1% by weight
Aluminum (Al) is an element which is inevitably added at the time of production of aluminum-killed (Al-killed) steel, and it is preferable that 0.01% by weight or more is added for deoxidation effect. However, if the content of the above-mentioned aluminum exceeds 0.1% by weight, the possibility of inducing surface defects of the steel sheet becomes high, and there is a problem that the weldability is lowered. Therefore, in the present invention, it is preferable to limit the content of Al to 0.01 to 0.1% by weight.

Copper (Cu): 0.2 to 0.6% by weight
Copper (Cu) is an element added in consideration of the combined corrosion characteristics of sulfuric acid resistance and hydrochloric acid resistance, and if its content is too low, it becomes difficult to secure the target combined corrosion resistance, so 0.2% or more Is preferably added, and more preferably 0.3% or more. Although the composite corrosion resistance improves as the content of Cu increases, if the content is too high, the increase in corrosion resistance decreases greatly, the manufacturing cost sharply increases, and surface defects such as radial cracks (star cracks) are induced. Have the problem of Therefore, in the present invention, the upper limit of the content of Cu is preferably 0.6% by weight, and more preferably 0.5% by weight.

Antimony (Sb): 0.05 to 0.1% by weight
Antimony (Sb) is an essential element added to improve the composite corrosion resistance as in the case of the above Cu, and in particular, the composite corrosion resistance is effectively achieved by forming a Cu-Sb composite oxide in a corrosive environment. It is an element that can be improved. If the content of antimony is less than 0.05% by weight, the above-mentioned effect can not be obtained, and if it exceeds 0.1% by weight, not only the above-mentioned effect is saturated but also the manufacturing cost rises sharply. In view of this, it is preferable to add at 0.1 wt% or less.

  The balance other than the above composition consists of Fe and unavoidable impurities. On the other hand, other compositions may be included in addition to the above compositions, but the total content of W, Mo, Co and Ni is more preferably controlled to be less than 10 ppm. This is because these elements may deteriorate the material properties of the heat-rolled steel plate, such as ductility.

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

  At this time, the content of concentrated Cu and Sb is not particularly limited, but as described later, the extent to which an oxide layer having a thickness of 400 nm or more can be formed from the surface of a hot rolled steel sheet in a corrosive environment with sulfuric acid and hydrochloric acid. If it is If the thickness of the oxide layer is less than 400 nm, it becomes difficult to ensure the corrosion resistance aimed by the present invention. On the other hand, since the corrosion resistance is further 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, if it exceeds 500 nm, the effect of improving the corrosion resistance is lower than when a large amount of alloy is added, and furthermore, there is a problem that the manufacturing cost rises sharply, so the thickness of the oxide layer is 400 to 500 nm. Is more preferred.

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

  Hereinafter, the manufacturing method of the hot rolled sheet steel excellent in sulfuric acid and hydrochloric acid compound corrosion resistance which is other one mode of the present invention is explained in detail.

  First, after preparing the steel slab which satisfy | fills the composition mentioned above, it reheats at 1100-1300 degreeC. If the reheating temperature is less than 1100 ° C., there is a problem that it is difficult to secure the temperature during the subsequent hot rolling, and if the reheating temperature exceeds 1300 ° C., Cu having a low melting point is eluted and There is a problem that the possibility of the occurrence of cracks on the surface increases.

  Next, the reheated steel slab is hot-rolled and finished hot-rolled at 850 to 950 ° C. to obtain a hot-rolled steel sheet. If the finish hot rolling temperature is less than 850 ° C., the draw ratio may be greatly reduced due to the formation of stretched crystal grains, and the deviation of the material depending on the direction may become severe, and if it exceeds 950 ° C., austenite grain However, there is a problem that coarsening causes the curing ability to be greatly increased.

  Subsequently, the above hot rolled steel sheet is quenched at 120 to 150 ° C./s based on the surface temperature of the steel sheet. The quenching as described above can provide the necessary propulsive force for the alloying elements advantageous for corrosion resistance to move to the surface of the steel sheet after winding. If the cooling rate is less than 120 ° C./s, the surface temperature of the hot-rolled steel plate is too high, and the driving force for the transfer of the oxide-forming elements present inside the steel to the surface is low, and eventually the steel plate is composite. When exposed to various corrosive environments, there is a problem that sufficient oxides can not be obtained. On the other hand, if the cooling rate exceeds 150 ° C./s, the temperature inside the steel sheet becomes very low, and after coiling, recovery to the target temperature is not performed, and the movement of alloying elements advantageous for the formation of the oxide layer There is a problem that is not done smoothly. Therefore, the above-mentioned cooling rate is preferably 120 to 150 ° C./s.

  Thereafter, the cooled hot-rolled steel sheet is wound at 650 to 750 ° C. If the take-up temperature is less than 650 ° C., it is difficult to move atoms in the take-up process, so it is difficult to form a concentrated layer, and an oxide layer is not formed in a corrosive environment. It will be difficult. If the coiling temperature exceeds 750 ° C., the temperature to be recovered is too high and defects such as distortion may occur in the coiled steel sheet, so the coiling temperature is in the range of 650 to 750 ° C. It is preferable to have.

  In the case of the above-mentioned winding, it is preferred to make the surface of the above-mentioned steel plate become 720-750 ° C by a recuperation phenomenon. Even if the temperature inside the steel plate has a range of 650 to 750 ° C. through the cooling step, the surface of the steel plate will have a temperature lower than the above temperature range by quenching. Therefore, the migration of alloying elements advantageous for the formation of the oxide layer can be activated through the process of the above-mentioned recuperation, whereby the concentrated layer can be formed to a sufficient thickness. It is preferable that the surface temperature of the steel plate which passed through the said heat recovery is 720 degreeC or more, in order to fully acquire the said effect. However, it is difficult for the surface temperature of the steel plate to exceed 750 ° C., even after a sufficient process of heat recovery.

  The rolled steel sheet is gradually cooled to a cooling stop temperature of 350 to 400 ° C. at a rate of 30 to 40 ° C./hr. If the cooling rate is too fast, Cu, which is an element forming the concentrated layer, may not be sufficiently transferred, and the formation of a concentrated layer having a sufficient thickness may be difficult. Thus, the cooling rate is 40 ° C./hr. It is preferable to have the following range. On the other hand, if the temperature is less than 30 ° C./hr, the size of the crystal grains may be too large 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, if the cooling stop temperature is less than 350 ° C., there is a problem that the material property of the heat-rolled steel plate, eg, ductility, is deteriorated and the productivity is decreased. However, there may be problems such as inferior corrosion resistance. Therefore, it is preferable that said cooling stop temperature is the range of 350-400 degreeC.

  Hereinafter, the present invention will be more specifically described through examples. However, it should be noted that the following examples are only for illustrating and explaining the present invention in more detail, and not for limiting the scope of the present invention. This is because the scope of the present invention is determined by the matters described in the claims and the matters reasonably deduced therefrom.

  The steel ingots produced by melting into the component compositions shown in Table 1 below were maintained in a heating furnace at 1200 ° C. for 1 hour and then hot-rolled. At this time, finish hot rolling was performed at 900 ° C. to produce a hot-rolled steel plate having a final thickness of 4.5 mm. Thereafter, after cooling and winding under the conditions shown in Table 2 below, they were maintained. Then, it was gradually cooled to a cooling end temperature of 380 ° C. at a rate of 35 ° C./h to produce a final hot rolled steel sheet.

  In order to observe the corrosion characteristics of the hot-rolled steel plate manufactured according to the above, after immersing each specimen in a 16.9% by volume solution of sulfuric acid at 60 ° C. and 0.35% by volume of hydrochloric acid for 6 hours, The corrosion loss was measured, and the results are shown in Table 2.

  In addition, after the immersion under the condition of sulfuric acid-hydrochloric acid composite corrosion was completed, the thickness of the oxide layer (corrosion resistant layer) formed on the surface of the steel plate was measured and is shown in Table 2.

As can be seen from Tables 1 and 2 above, in Inventive Examples 1 to 3 satisfying the alloy composition and manufacturing condition proposed by the present invention, an oxide layer of 400 nm or more is formed, so that under corrosion environment by sulfuric acid and hydrochloric acid It can be confirmed that the weight loss of corrosion is less than 2.0 mg / cm ² / Hr, and has very excellent corrosion resistance characteristics.

Comparative Example 1 satisfies the alloy composition of the present invention, but the coiling temperature is as low as 500 ° C., so the oxide layer is not sufficiently formed, and thus the corrosion loss is 4.5 mg / cm ² / hr. , It can be seen that the corrosion resistance is very low.

Although Comparative Examples 2 to 4 satisfy the alloy composition of the present invention, since the cooling rate is as low as 10 ° C./s, the oxide layer is not sufficiently formed, and hence the corrosion loss is 3.2 mg. / Cm ² / hr or more, and it can be seen that the corrosion resistance is very low.

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

  While the present invention has been described with reference to the preferred embodiments, those skilled in the art will appreciate that the present invention may be practiced without departing from the spirit and scope of the invention as set forth in the appended claims. It can be understood that various modifications and changes can be made.

Claims (6)

By mass%, C: 0.05~0.1%, Mn : 0.5~1.5%, P: 0.02% or less, S: 0.02% or less, Al: 0.01~0. 1%, Cu: 0.2~0.6%, Sb: 0.05~0.1%, the balance being Fe and inevitable impurities, in a thickness direction from the surface of Cu and Sb within 500nm are concentrated The heat resistance excellent in sulfuric acid and hydrochloric acid combined corrosion resistance, which is less than 2.0 mg / cm ² / hr as a corrosion loss measured after being immersed in a 16.9 vol% sulfuric acid + 0.35 vol% hydrochloric acid solution at 60 ° C. Rolled steel plate.   The hot rolled steel sheet excellent in sulfuric acid and hydrochloric acid composite corrosion resistance according to claim 1, wherein the unavoidable impurities include W, Mo, Co and Ni, and the total of these contents is less than 10 ppm. The sulfuric acid and hydrochloric acid composite corrosion resistance according to claim 1 or 2 , characterized in that the concentrated Cu and Sb form an oxide layer containing a Cu-Sb complex oxide in a corrosive environment of sulfuric acid and hydrochloric acid. Excellent hot rolled steel sheet.   The hot rolled steel sheet excellent in sulfuric acid and hydrochloric acid composite corrosion resistance according to claim 3, wherein the oxide layer is formed in a thickness of 400 to 500 nm in the thickness direction from the surface of the hot rolled steel sheet. . By mass%, C: 0.05~0.1%, Mn : 0.5~1.5%, P: 0.02% or less, S: 0.02% or less, Al: 0.01~0. Reheating the steel slab consisting of 1%, Cu: 0.2 to 0.6%, Sb: 0.05 to 0.1%, the balance Fe and other unavoidable impurities at 1100 to 1300 ° C.
Hot rolling the reheated steel slab and finishing hot rolling at 850 to 950 ° C. to obtain a hot rolled steel sheet;
Quenching the hot rolled steel sheet at a rate of 120 to 150 ° C./s;
Winding the cooled hot rolled steel sheet at 650-750 ° C .;
Look including a step of gradually cooling to the cooling stop temperature of 350 to 400 ° C. at a rate of the winding has been hot-rolled steel sheet 30 to 40 ° C. / h,
Cu and Sb are concentrated within 500 nm in the thickness direction from the surface, and the corrosion loss measured after immersion for 6 hours in 16.9 vol% sulfuric acid + 0.35 vol% hydrochloric acid solution at 60 ° C. is 2.0 mg / The manufacturing method of the hot rolled sheet steel excellent in sulfuric acid and hydrochloric acid composite corrosion resistance which manufactures the hot rolled sheet steel which is cm < ² > / hr or less .   The method for producing a hot rolled steel sheet excellent in sulfuric acid and hydrochloric acid composite corrosion resistance according to claim 5, wherein the surface of the steel sheet is brought to 720 to 750 ° C by a recuperation phenomenon during the winding.