KR101372794B1 - Steel sheet having excellent corrosion resistance by sulfuric acid and hydrochloric acid and weldability and method for manufacturing the same - Google Patents

Abstract

In the present invention, C: 0.15% or less, Si: 0.2-1.0%, Mn: 0.5-1.5%, P: 0.02% or less, S: 0.02% or less, Al: 0.01-0.1%, Cu: 0.2-1.0 It provides a steel sheet excellent in sulfuric acid and hydrochloric acid composite corrosion resistance and weldability including%, Ni: 0.1-0.5%, Co: 0.03-0.1%, Sb: 0.05-0.15%, balance Fe and other unavoidable impurities. In addition, Cu and Ni satisfy 0.4 ≦ Ni / Cu ≦ 0.7, and Sb, Co and Cu satisfy 0.2 ≦ (Sb / 122 + Co / 59) / (Cu / 64) ≦ 1.0, and the Co And Sb provides a steel sheet satisfying 1 ≦ (Co / 59) / (Sb / 122) ≦ 3.

Description

Sulfuric acid and hydrochloric acid composite corrosion resistance and weldable steel sheet and its manufacturing method {STEEL SHEET HAVING EXCELLENT CORROSION RESISTANCE BY SULFURIC ACID AND HYDROCHLORIC

The present invention relates to a steel sheet used as a thermal power plant piping that is susceptible to corrosion due to sulfuric acid and hydrochloric acid generated by the reaction of sulfur dioxide and chlorine gas generated by burning fossil fuels such as coal or petroleum with water. The present invention relates to a steel sheet excellent in sulfuric acid and hydrochloric acid composite corrosion resistance and weldability, and a method of manufacturing the same.

Combustion of sulfur-containing fuels forms SOx in the exhaust gas, resulting in sulfuric acid through chemical bonding with moisture in the exhaust gas. When the temperature of the exhaust gas drops to about 160 ° C. and reaches the dew point of sulfuric acid, sulfuric acid condensed on the surface of the river creates a severe corrosive environment. In addition, chlorine ions (Cl ⁻ ) contained in the exhaust gas are also condensed with hydrochloric acid together with sulfuric acid at a temperature of about 80 ° C. or lower to create a more corrosive environment. The current trends in the design of environmental facilities for domestic thermal power plants show a trend toward lowering operating temperatures for increased dust collection and desulfurization efficiency. As a result, the problem of condensation of hydrochloric acid as well as sulfuric acid on the surface of the steel is generated. Therefore, there is a need for a material having improved hydrochloric acid corrosion resistance as well as sulfuric acid corrosion resistance.

In general, sulfuric acid-hydrochloric acid corrosion resistant steel has been known to add a large amount of Cu in the steel in order to delay the corrosion rate than the general steel in sulfuric acid and hydrochloric acid atmosphere. Cu has a superior effect of significantly delaying the corrosion rate of sulfuric acid compared to other additive elements, but if the content is excessively excessive, there is a problem in that cracking occurs during hot rolling.

To solve this problem, steel (Japanese Laid-Open Patent Publication No. 1997-025536, Japanese Laid-Open Patent Publication No. 1998-110237, Korean Laid-Open Patent Publication No. 2009-0070249, etc.) has been developed in which an appropriate amount of Cu is added and other elements are added in combination. , Cu has relatively low melting point and Cu is crystallized when a large amount is added, causing cracks on the corners of slabs, and remaining as surface defects after hot rolling. There is a problem.

In order to solve this problem, lowering the amount of added Cu causes a problem of lowering corrosion resistance. In addition, since sulfuric acid / hydrochloric acid composite corrosion resistant steel is mostly used by welding, it is difficult to use unless the welding quality is secured.

Existing steel does not consider the welding quality has a problem that it is very difficult to work due to defects in the welded portion or poor weldability.

One aspect of the present invention is a sulfuric acid and hydrochloric acid composite corrosion resistance to improve the weldability by minimizing the surface defects caused by Cu added to improve the corrosion resistance in the sulfuric acid atmosphere or sulfuric acid-hydrochloric acid complex atmosphere to improve the corrosion resistance And to provide a steel sheet excellent in weldability and a method of manufacturing the same.

Sulfuric acid and hydrochloric acid composite corrosion resistance and weldability of the aspect of the present invention is excellent in weight percent C: 0.15% or less, Si: 0.2-1.0%, Mn: 0.5-1.5%, P: 0.02% or less, S: 0.02% Hereinafter, Al: 0.01-0.1%, Cu: 0.2-1.0%, Ni: 0.1-0.5%, Co: 0.03-0.1%, Sb: 0.05-0.15%, balance Fe and other unavoidable impurities.

Cu and Ni preferably satisfy 0.4 ≦ Ni / Cu ≦ 0.7.

It is preferable that Sb, Co, and Cu satisfy 0.2≤ (Sb / 122 + Co / 59) / (Cu / 64) ≤1.0.

Co and Sb preferably satisfy 1 ≦ (Co / 59) / (Sb / 122) ≦ 3.

In another aspect of the present invention, a method for manufacturing a steel sheet having excellent sulfuric acid and hydrochloric acid composite corrosion resistance and weldability is C: 0.15% or less, Si: 0.2-1.0%, Mn: 0.5-1.5%, P: 0.02% or less, S: 0.02% or less, Al: 0.01-0.1%, Cu: 0.2-1.0%, Ni: 0.1-0.5%, Co: 0.03-0.1%, Sb: 0.05-0.15%, balance Fe and other unavoidable impurities ,

Cu and Ni satisfy 0.4 ≦ Ni / Cu ≦ 0.7,

Sb, Co and Cu satisfy 0.2≤ (Sb / 122 + Co / 59) / (Cu / 64) ≤1.0,

Reheating the steel slab satisfying 1≤ (Co / 59) / (Sb / 122) ≤3 at 1200 ° C or higher;

Finishing rolling the reheated steel slab at 900 ° C. or higher; And

And winding the finished rolled steel sheet at 600 ° C. or higher.

According to an aspect of the present invention, it is possible to provide a hot-rolled steel sheet excellent in sulfuric acid-hydrochloric acid composite corrosion resistance and weldability, and denitrification equipment, desulfurization equipment, flue gas piping and preheater of a power plant where sulfuric acid-hydrochloric acid composite corrosion occurs. It is effective to greatly extend the life of the material of the piping and peripheral devices requiring a relatively thick thickness.

The present inventors studied a steel sheet excellent in complex corrosion resistance and weldability and a method of manufacturing the same in sulfuric acid and hydrochloric acid atmosphere, and realized that excellent corrosion resistance and weldability can be secured by appropriately controlling the component system of the steel sheet.

Hereinafter, the steel sheet excellent in sulfuric acid and hydrochloric acid composite corrosion resistance and weldability of the present invention will be described in detail.

Carbon (C): 0.15 wt% or less (excluding 0)

Carbon is a composition that improves the strength, but if the content exceeds 0.15% by weight, weldability is greatly deteriorated during welding, so defects are likely to occur, and corrosion resistance is also greatly reduced. Therefore, the carbon content is preferably 0.15% by weight or less.

Silicon (Si): 0.2-1.0 wt%

The said silicon is an element added mainly to improve strength. When the content of the silicon is less than 0.2% by weight, internal defects may occur during welding, resulting in poor welding joints. On the other hand, when the content exceeds 1.0% by weight, the silicon content is too high, the silicon oxide is generated on the surface of the steel sheet can increase the surface defect occurrence rate. Therefore, the content of the silicon is preferably controlled to 0.2-1.0% by weight.

Manganese (Mn): 0.5-1.5 wt%

The manganese is typically added to prevent hot shortness due to solid solution sulfur precipitated as manganese sulfide in the steel in the present invention is added for the purpose of preventing redness brittleness and improved weldability. When the content of the manganese is less than 0.5% by weight, a defect occurs after welding, and thus there is a problem in that the weld is not sound. On the other hand, when the content of the manganese exceeds 1.5% by weight, there is no possibility that red brittleness will occur anymore, so the upper limit may be limited to 1.5% by weight in consideration of cost. Therefore, the content of the manganese is preferably controlled to 0.5-1.5% by weight.

Aluminum (Al): 0.01-0.1 wt%

The aluminum typically acts as a deoxidizer and has a lower limit of 0.01% by weight of the amount added during the production of Al-killed steel. On the other hand, when the content of aluminum exceeds 0.1% by weight, the probability of occurrence of defects on the surface of the steel sheet increases and the elongation decreases, so the upper limit is made 0.1% by weight. Therefore, the content of aluminum is preferably controlled to 0.01-0.1% by weight.

Copper (Cu): 0.2-1.0 wt%

The copper is an element that must be added in consideration of sulfuric acid and complex corrosion properties, the content of which is greater than 0.2% by weight, the effect of corrosion resistance is large. However, when the content of copper exceeds 1.0% by weight, the effect of improving the corrosion resistance is small compared to the increase in the amount of addition, so it is uneconomical, and the upper limit is preferably 1.0% by weight. Therefore, the content of copper is preferably controlled to 0.2-1.0% by weight.

Nickel (Ni): 0.1-0.5 wt%

Nickel is an element capable of improving corrosion resistance, and the lower limit thereof is preferably added in an amount of 0.1% by weight or more. However, when the nickel content is more than 0.5% by weight, the effect of improving the corrosion resistance is small compared to the increase in the amount of addition, so it is uneconomical, and the upper limit is preferably 0.5% by weight. Therefore, the content of nickel is preferably controlled to 0.1-0.5% by weight.

Cobalt (Co): 0.03-0.1 wt%

The high balt is an element that activates copper in a corrosive environment and easily deposits on a surface to improve corrosion resistance. In addition, it is particularly effective in corrosion resistance of hydrochloric acid, which is effective in improving sulfuric acid / hydrochloric acid corrosion resistance rather than sulfuric acid corrosion resistance. In order to properly show this effect, the content is preferably 0.03% by weight or more. However, as the addition amount increases, the effect increases, but when the amount exceeds 0.1% by weight, the effect no longer rises, so the upper limit is made 0.1% by weight. Therefore, the content of cobalt is preferably controlled to 0.03-0.1% by weight.

Antimony (Sb): 0.05-0.15 wt%

The antimony is added to the steel to produce antimony oxide to serve to greatly improve the sulfuric acid / hydrochloric acid corrosion resistance. In order to properly show this effect, the content is preferably 0.05% by weight or more. However, as the addition amount increases, the corrosion resistance is improved, but when it exceeds 0.15% by weight, there is almost no increase effect, so the upper limit is limited to 0.15% by weight. Therefore, the content of the antimony is preferably controlled to 0.05-0.15% 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): 0.02 wt% or less

Since phosphorus is an impurity contained inevitably, it is contained in steel, and thus there is a problem of degrading weldability and sulfuric acid-hydrochloric acid composite corrosion resistance, and it is preferable to control it 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

Sulfur is an inevitable impurity, which increases the possibility of defects caused by hot brittleness, so it is desirable to suppress the content as much 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%.

According to an aspect of the present invention, by satisfying the above component system, it is possible to provide a steel sheet excellent in sulfuric acid and hydrochloric acid composite corrosion resistance and weldability. However, when the relationship between the alloying elements described below is satisfied, the effect of the present invention can be further improved.

Ni / Cu (weight ratio): 0.4-0.7

When the Ni / Cu is less than 0.4, defects are easily generated on the surface of the steel sheet, which greatly reduces the corrosion resistance of the defect-generating site and may cause cracks during processing. On the other hand, when the Ni / Cu exceeds 0.7, the corrosion resistance is rather low. Therefore, it is preferable to control Ni / Cu to 0.4-0.7.

(Sb / 122 + Co / 59) / (Cu / 64): 0.2-1.0

When (Sb / 122 + Co / 59) / (Cu / 64) is less than 0.2, the amount of antimony or cobalt oxide remaining on the surface is so small that the composite corrosion resistance is low. On the other hand, when the value is greater than 1.0, the amount of antimony or cobalt oxide is too high, which lowers the corrosion resistance by copper oxide, thereby lowering the composite corrosion resistance. Therefore, it is preferable to control (Sb / 122 + Co / 59) / (Cu / 64) to 0.2-1.0.

(Co / 59) / (Sb / 122): 1-3

When the cobalt is too small as compared to antimony, the hydrochloric acid corrosion resistance is lowered, and the composite corrosion resistance is lowered. Therefore, the lower limit thereof is preferably controlled to one. In addition, when the (Co / 59) / (Sb / 122) exceeds 3 because the cobalt is too much compared to antimony, the complex corrosion resistance may also be lowered by lowering the sulfuric acid corrosion resistance. Therefore, it is preferable to control (Co / 59) / (Sb / 122): 1-3.

Another aspect of the present invention relates to a method for manufacturing a steel sheet excellent in sulfuric acid and hydrochloric acid composite corrosion resistance and weldability, it is possible to provide a hot rolled steel sheet by hot rolling a steel satisfying the above component system. Although general hot rolling conditions can be applied, it is more preferable to satisfy the conditions described below.

Hereinafter, a method for producing a steel sheet excellent in sulfuric acid and hydrochloric acid composite corrosion resistance and weldability of the present invention will be described in detail.

Reheating Step: Above 1200 ℃

The reheating temperature in the hot rolling process is intended to control the texture in the slab by maintaining the slab at a constant temperature for rolling or to reuse the precipitates formed by the additive elements. Therefore, the temperature required for reheating satisfies the target rolling finish temperature, and a range for eliminating columnar structure in performance is required, and is usually set to 1200 ° C or higher. In order to reuse the added elements, the temperature may be changed according to the characteristics of the added element, and the upper limit can be controlled in consideration of this. The heating temperature is preferably carried out at 1300 ℃ or less in consideration of heating economics.

Rolling step: 900 ℃ or more

It is important to control the finish rolling temperature during hot rolling. The finish rolling temperature is set to be slightly higher than the temperature at which the austenite is transformed into ferrite. This is to finish the rolling immediately above the transformation point temperature so that the structure transformed into ferrite is uniformly distributed. In order to suppress the local corrosion due to the tissue difference and to allow the uniform corrosion to proceed under the same corrosion conditions through the homogenization of the structure, a temperature of 900 ° C or higher is preferable.

Winding stage: 600 ℃ or more

Winding is performed after the said rolling. At this time, it is preferable to perform coiling temperature at 600 degreeC or more. The winding process is a process that controls the stage of transformation into ferrite. As the temperature is higher, grains grow and the material becomes soft. However, at low temperatures where grain growth is difficult, oxidation occurs in the surface layer part during hardening due to the formation of fine grains or during winding. Likewise, when the coiling temperature is high, scales are formed to easily cause surface defects.

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 ingot prepared by dissolving in the composition as shown in Table 1 was held in a heating furnace at 1250 占 폚 for 1 hour and then subjected to hot rolling. At this time, the hot finish rolling temperature was 900 ℃, the coiling temperature was 650 ℃ hot rolling to a final thickness of 4.5mm. The hot rolled specimens were immersed in a 16.9 vol.% Sulfuric acid + 0.35 vol.% Sulfuric acid solution at 60 ° C. for 6 hours in order to investigate the corrosion characteristics under the complex corrosion condition of sulfuric acid-hydrochloric acid. Shown in In addition, weldability is shown in Table 2 by judging whether the cracking occurred by bending the welding workability and 180 degrees after welding. In addition, the occurrence of surface defects were evaluated and shown in Table 2 below.

division C Si Mn P S Al Cu Ni Sb Co Ni /
Cu (Sb / 122 + Co / 59) / (Cu / 64) (Co / 59) /
(Sb / 122) Inventory 1 0.065 0.35 0.82 0.011 0.012 0.039 0.38 0.18 0.08 0.06 0.47 0.28 1.55 Inventive Example 2 0.073 0.44 0.92 0.009 0.014 0.042 0.45 0.25 0.09 0.05 0.56 0.23 1.15 Inventory 3 0.068 0.39 1.22 0.009 0.01 0.042 0.28 0.13 0.1 0.07 0.46 0.46 1.45 Honorable 4 0.075 0.28 0.55 0.011 0.011 0.044 0.52 0.28 0.09 0.06 0.54 0.22 1.38 Comparative Example 1 0.065 0.15 0.22 0.014 0.009 0.049 0.33 0.18 0.11 0.06 0.55 0.37 1.13 Comparative Example 2 0.072 0.42 0.66 0.011 0.012 0.053 0.35 - 0.09 - 0.00 0.13 - Comparative Example 3 0.068 0.38 0.73 0.011 0.012 0.045 0.45 0.23 - - 0.51 - - Comparative Example 4 0.072 0.45 0.93 0.013 0.009 0.035 0.42 0.28 0.03 0.05 0.67 0.17 3.45

(However, the content unit of each component in Table 1 is weight%.)

division Corrosion loss (mg / cm 2 / hr.) Weld crack
(After bending test) Surface defect Inventory 1 4.5 none Good Inventive Example 2 3.9 none Good Inventory 3 4.3 none Good Honorable 4 3.8 none Good Comparative Example 1 4.3 Cracking Good Comparative Example 2 3.9 none Surface Defects Occurred Comparative Example 3 20.8 none Good Comparative Example 4 10.2 none Good

As shown in Tables 1 and 2, Inventive Examples 1 to 4 satisfying the conditions of the present invention exhibit a very excellent corrosion resistance characteristics of less than 5 mg / ㎠ / hr sulfuric acid / hydrochloric acid corrosion and bending test welds after welding There was no crack at all, and it was confirmed that the surface condition was also very good because no defects occurred.

On the other hand, Comparative Example 1 has no corrosion resistance and surface defects of the base material but very poor weldability. This is an experimental example of the content of silicon and manganese out of the range controlled by the present invention, it can be seen that cracks occur in the bending specimen after welding is poor weldability. Such steel may be broken due to stress concentration at actual welding sites, and may also be dangerous because the corrosion resistance is greatly reduced.

In addition, in Comparative Example 2, a surface defect occurred in the base material because the amount of nickel added was outside the range controlled by the present invention, and the Ni / Cu ratio was also outside the range controlled by the present invention. If surface defects occur in a product, not only the appearance is bad, but stress may be concentrated in the area during processing, and cracks may occur due to the concentration of stress in the area.

In addition, Comparative Example 3 is excellent in surface quality and weldability, but corrosion resistance is significantly lower than the present invention steel. The antimony and cobalt content is out of the range controlled by the present invention, and additionally, the (Sb / 122 + Co / 59) / (Cu / 64) ratio and (Co / 59) / (Sb / 122) ratio are also within the scope of the present invention. Because you are out of.

In addition, in Comparative Example 4, the antimony content was outside the range controlled by the present invention, and additionally (Sb / 122 + Co / 59) / (Cu / 64) ratio and (Co / 59) / (Sb / 122). The ratio is out of the range controlled by the present invention. Comparative Example 4 was excellent in surface quality and weldability, but it was confirmed that the corrosion resistance is very low compared to the invention example because the corrosion loss is very high.

Claims (5)

By weight% C: 0.15% or less (excluding 0), Si: 0.2-1.0%, Mn: 0.5-1.5%, P: 0.02% or less, S: 0.02% or less, Al: 0.01-0.1%, Cu: 0.2 -1.0%, Ni: 0.1-0.5%, Co: 0.03-0.1%, Sb: 0.05-0.15%, balance Fe and other unavoidable impurities,
Cu and Ni satisfy 0.4 ≦ Ni / Cu ≦ 0.7, and Sb, Co, and Cu satisfy 0.2 ≦ (Sb / 122 + Co / 59) / (Cu / 64) ≦ 1.0, and Co and Sb Satisfies 1≤ (Co / 59) / (Sb / 122) ≤3,
Steel plate with excellent corrosion resistance and weldability of sulfuric acid and hydrochloric acid with a corrosion loss of 16.9% by volume of sulfuric acid and 0.35% by volume of hydrochloric acid of 5 mg / Cm 2 / hr or less.
delete delete delete By weight% C: 0.15% or less (excluding 0), Si: 0.2-1.0%, Mn: 0.5-1.5%, P: 0.02% or less, S: 0.02% or less, Al: 0.01-0.1%, Cu: 0.2 -1.0%, Ni: 0.1-0.5%, Co: 0.03-0.1%, Sb: 0.05-0.15%, balance Fe and other unavoidable impurities,
Cu and Ni satisfy 0.4 ≦ Ni / Cu ≦ 0.7,
Sb, Co and Cu satisfy 0.2≤ (Sb / 122 + Co / 59) / (Cu / 64) ≤1.0,
Reheating the steel slab satisfying 1≤ (Co / 59) / (Sb / 122) ≤3 at 1200 ° C or higher;
Finishing rolling the reheated steel slab at 900 ° C. or higher; And
Winding the finished rolled steel sheet at 600 ° C. or higher,
A method for producing a steel sheet having excellent corrosion resistance and weldability of sulfuric acid and hydrochloric acid having a corrosion loss of 5% / cm 2 / hr or less in a solution of 16.9% by volume of sulfuric acid and 0.35% by volume of hydrochloric acid.