Steel material having excellent corrosion resistance in sulfide-containing condensation environments and method for producing same

Abstract

The invention relates to steel with excellent corrosion resistance for oil tankers, crude oil storage tanks and the like, in particular to steel with excellent corrosion resistance in a condensation environment containing sulfide gas and a production method of the steel.

Description

[0001] This application is a divisional application of the application filed on December 21, 2017, with application number 201780078973.9, entitled "Steel with excellent corrosion resistance in a condensation environment containing sulfides and a method for producing the same" (PCT / KR2017 / 015294, national phase entry date June 20, 2019). Technical Field

[0002] This disclosure relates to steel with excellent corrosion resistance for use in oil tankers, crude oil storage tanks, etc., and more specifically to steel with excellent corrosion resistance in dew condensation environments containing sulfide gases, and a method for producing the steel. Background Technology

[0003] Among the various types of steel used in ships, the steel used in crude oil storage tanks for oil tankers can suffer considerably severe corrosion damage due to the internal environment of the tanks. In crude oil storage tanks, various types of corrosion occur due to volatile components in the crude oil, inert gases introduced into the tank for explosion protection, seawater mixtures, salts in oilfield brine, or condensation caused by internal temperature differences. Furthermore, the corrosion rate is significantly higher than in typical brine environments.

[0004] In the top plate of crude oil storage tanks, hydrogen sulfide gas evaporated from crude oil and gases such as CO2, SO2, and O2 from inert gases introduced for explosion protection can react with condensation formed on the steel surface due to temperature differences, resulting in a high content of hydrogen sulfide and sulfur dioxide. This leads to corrosion. Because corrosion occurs at a thin water film, the corrosion caused by condensation (i.e., condensate) is similar to atmospheric corrosion of atmospheric-resistant steels, and due to the daily temperature range, moisture condenses and dries periodically and repeatedly. Therefore, corrosion caused by condensate can be classified separately as dew point corrosion.

[0005] During the daytime, condensation does not occur on the top deck of crude oil tankers carrying crude oil because the internal temperature rises to approximately 50°C. At night, however, evaporation occurs on the lower part of the top deck as the internal temperature drops to approximately 25°C. In the case of a 300,000-ton crude oil tanker, up to 30 tons of water may condense on the upper part of the top deck, causing corrosion. Therefore, corrosion caused by condensation is not negligible.

[0006] In addition, carbon dioxide, sulfur dioxide, and flammable gases are injected into the empty spaces of the storage tanks of crude oil tankers to prevent hull explosions. These gases, along with the sulfur and hydrogen sulfide already contained in the crude oil, dissolve in moisture, creating an atmosphere similar to that caused by acidic condensation when condensation occurs. Typically, as acidity increases, the amount of H₂ participating in the corrosion reaction increases. + The amount of ions increases. Therefore, the corrosion rate can be further increased.

[0007] Patent documents 1 and 2 have been proposed to improve the corrosion resistance of marine steel. However, the marine steel in patent document 1 is designed without considering corrosion caused by hydrogen sulfide when crude oil contains hydrogen sulfide, and therefore the marine steel is insufficient for use in actual crude oil storage tanks.

[0008] (Patent Document 1) Japanese Patent Publication 2000-017381 Summary of the Invention

[0009] Technical issues

[0010] One aspect of this disclosure is to provide a steel and a method for producing the steel, which can optimize the steel composition and determine the relationship between the components to ensure improved corrosion resistance, even in condensation environments containing sulfides.

[0011] The problems to be solved by the present invention are not limited to those described above. Other problems not mentioned will be clearly understood by those skilled in the art from the following description.

[0012] Technical solution

[0013] According to one aspect of this disclosure, a steel with excellent corrosion resistance in a condensation environment containing sulfide gases is provided, the steel comprising, by weight percent (wt%), 0.02% to 0.2% carbon (C), 0.1% to 1.0% silicon (Si), 0.2% to 2.0% manganese (Mn), 0.03% or less phosphorus (P), 0.03% or less sulfur (S), 0.05% to 0.5% copper (Cu), 0.05% to 0.5% nickel (Ni), 0.02% to 0.5% molybdenum (Mo), 0.1% or less aluminum (Al), 0.05% to 0.5% chromium (Cr), 0.001% to 0.01% calcium (Ca), and the balance iron (Fe) and unavoidable impurities.

[0014] The sulfide dew point corrosion susceptibility index given by relational expression 1 is above 1.7 and below 2.5.

[0015] (Relational Expression 1)

[0016] Sulfide dew point corrosion susceptibility index =

[0017] (Where Ca, S, Cr, Mo, Cu, Ni and Mn represent the content (by weight) of the corresponding elements).

[0018] According to another aspect of this disclosure, a method is provided for producing steel with excellent corrosion resistance in a condensation environment containing sulfide gases by hot rolling and cooling a slab, the steel comprising, by weight percent (wt%), 0.02% to 0.2% carbon (C), 0.1% to 1.0% silicon (Si), 0.2% to 2.0% manganese (Mn), 0.03% or less phosphorus (P), 0.03% or less sulfur (S), 0.05% to 0.5% copper (Cu), 0.05% to 0.5% nickel (Ni), 0.02% to 0.5% molybdenum (Mo), 0.1% or less aluminum (Al), 0.05% to 0.5% chromium (Cr), 0.001% to 0.01% calcium (Ca), and the balance iron (Fe) and unavoidable impurities, with a sulfide dew point corrosion susceptibility index of more than 1.7 and less than 2.5, as given by relational expression 1.

[0019] (Relational Expression 1)

[0020] Sulfide dew point corrosion susceptibility index =

[0021] (Where Ca, S, Cr, Mo, Cu, Ni and Mn represent the content (by weight) of the corresponding elements).

[0022] Cooling is carried out at a cooling rate of 10°C / s or higher between a cooling start temperature higher than or equal to Ar3 temperature and a cooling end temperature between (Ae1-30°C) and 600°C.

[0023] Beneficial effects

[0024] As described above, according to an exemplary embodiment of this disclosure, the steel composition can be optimized to meet the sulfide dew point corrosion susceptibility index. Therefore, resistance to sulfide dew point corrosion can be improved. Attached Figure Description

[0025] Figure 1 A test apparatus for simulating the sulfide condensation test in this disclosure is shown.

[0026] Figure 2 This is an image showing the results of a 100-day sulfide dew point corrosion test according to one exemplary embodiment of this disclosure. Detailed Implementation

[0027] This disclosure will be described in detail below.

[0028] The inventors have conducted research to solve the aforementioned problems in the related art. The inventors have discovered that, in order to improve corrosion resistance in condensation environments containing sulfide gases, it is necessary to appropriately control the composition of each component, as described below. Furthermore, the inventors have discovered that it is necessary to appropriately control the relationships between components such as Ca, S, Cr, Mo, Ni, and Mn that affect dew point corrosion sensitivity. For these reasons, the inventors conceived this invention.

[0029] First, the alloy composition range of the steel according to this disclosure will be described in detail. The steel contains, by weight percentage (wt%), 0.02% to 0.2% carbon (C), 0.1% to 1.0% silicon (Si), 0.2% to 2.0% manganese (Mn), 0.03% or less phosphorus (P), 0.03% or less sulfur (S), 0.05% to 0.5% copper (Cu), 0.05% to 0.5% nickel (Ni), 0.02% to 0.5% molybdenum (Mo), 0.1% or less aluminum (Al), 0.05% to 0.5% chromium (Cr), 0.001% to 0.01% calcium (Ca), and the balance iron (Fe) and unavoidable impurities.

[0030] Carbon (C): 0.02% to 0.2% by weight

[0031] Carbon (C) is an element added to improve strength. Increasing the carbon (C) content can increase hardenability and thus improve strength. However, with increasing carbon content, overall corrosion resistance decreases. Furthermore, it also affects localized corrosion resistance by promoting the precipitation of carbides and the like. Therefore, the carbon (C) content should be reduced to improve both overall and localized corrosion resistance. However, when the carbon (C) content is less than 0.02 wt%, it is difficult to ensure strength. When the carbon (C) content is greater than 0.2 wt%, weldability deteriorates, making it unsuitable for steels specifically designed for welded structures. Therefore, the carbon (C) content is specifically set from 0.02 wt% to 0.2 wt%. From a corrosion resistance perspective, the carbon (C) content can be specifically set to 0.16 wt% or less, and more specifically, 0.14 wt% or less, to improve casting cracking and reduce carbon equivalent.

[0032] Silicon (Si): 0.1 wt% to 1.0 wt%

[0033] Silicon (Si) needs to be present in an amount of 0.1 wt% or more to act as a deoxidizer and to increase the strength of steel. Additionally, increasing the silicon (Si) content is advantageous because it contributes to improved overall corrosion resistance. However, when the silicon (Si) content exceeds 1.0 wt%, toughness and weldability deteriorate. Furthermore, the oxide scale causes surface defects because it is difficult to separate during rolling. Therefore, the silicon (Si) content is specifically limited to 0.1 wt% to 1.0 wt%. More specifically, silicon (Si) is added in an amount of 0.2 wt% or more to improve corrosion resistance.

[0034] Manganese (Mn): 0.2% to 2.0% by weight

[0035] Manganese (Mn) is an element that effectively increases strength without reducing toughness. However, when excessive manganese (Mn) is added, it can increase the electrochemical reaction rate on the steel surface during corrosion reactions, thus reducing corrosion resistance. When manganese (Mn) is added in amounts less than 0.2 wt%, it is difficult to ensure the durability of structural steel. Increasing the manganese (Mn) content increases hardenability and improves strength. However, when manganese (Mn) is added in amounts greater than 2.0 wt%, weldability and corrosion resistance decrease. Therefore, the manganese (Mn) content is specifically set between 0.2 wt% and 2.0 wt%.

[0036] Phosphorus (P): 0.03% by weight or less

[0037] Phosphorus (P) is an impurity element. When phosphorus (P) is added in amounts greater than 0.03% by weight, weldability is significantly reduced and toughness is deteriorated. Therefore, the content of phosphorus (P) is specifically limited to 0.03% by weight or less.

[0038] Sulfur (S): 0.03% by weight or less

[0039] Sulfur (S) is also an impurity element. When the sulfur (S) content exceeds 0.03% by weight, the ductility, impact toughness, and weldability of the steel deteriorate. Therefore, the sulfur (S) content is specifically limited to 0.03% by weight or less. Sulfur (S) readily reacts with manganese (Mn) to form elongated inclusions such as manganese sulfide (MnS), and the voids formed at the ends of these inclusions can be the starting point for localized corrosion. Therefore, the sulfur (S) content is more specifically limited to 0.01% by weight or less.

[0040] Copper (Cu): 0.05% to 0.5% by weight

[0041] When copper (Cu) is included with nickel (Ni) in an amount of 0.05 wt% or more, the precipitation of iron (Fe) is delayed, which effectively improves both overall and localized corrosion resistance. However, when the amount of copper (Cu) is greater than 0.5 wt%, the copper (Cu) melts into the grain boundaries in a liquid state during slab production. This results in cracking during hot working, a phenomenon known as "hot shortness." Therefore, the copper (Cu) content is specifically set at 0.05 wt% to 0.5 wt%. Since the frequency of surface cracking during slab production may vary depending on the content of each element, it is more specific to set the copper (Cu) content at 0.5 wt% or less.

[0042] Nickel (Ni): 0.05 wt% to 0.5 wt%

[0043] Similar to copper (Cu), the inclusion of nickel (Ni) at 0.05 wt% or more effectively improves both overall and localized corrosion resistance. Furthermore, when nickel (Ni) is added together with copper (Cu), the reaction between nickel (Ni) and copper (Cu) inhibits the formation of the copper (Cu) phase, thus preventing hot brittleness. Nickel (Ni) is also an effective element for improving the toughness of the matrix material. However, since nickel (Ni) is an expensive element, adding it at 0.5 wt% or more is disadvantageous in terms of economic efficiency and weldability. Therefore, the nickel (Ni) content is specifically set at 0.05 wt% to 0.5 wt%.

[0044] Since nickel (Ni) has no greater effect on improving corrosion resistance than copper (Cu), the nickel (Ni) content is greater than or equal to the copper (Cu) content. Specifically, the nickel (Ni) content is 1.5 times or less of the copper (Cu) content to suppress surface cracking caused by the addition of copper (Cu), rather than using a large amount of nickel (Ni) to improve corrosion resistance. More specifically, the nickel (Ni) content is limited to 0.3% by weight or less.

[0045] Molybdenum (Mo): 0.02 wt% to 0.5 wt%

[0046] Molybdenum (Mo) is an element that helps improve corrosion resistance and strength, and should be added in amounts of 0.02% by weight or more to achieve this effect. However, molybdenum (Mo) should be dissolved in the steel to improve corrosion resistance. For example, dissolved molybdenum (Mo) improves resistance to condensate containing hydrogen sulfide. However, molybdenum (Mo) included in amounts exceeding the solubility limit can react with sulfur (S), forming Mo₂S and reducing corrosion resistance. Therefore, adding excessive amounts of molybdenum (Mo) may reduce resistance to condensate containing hydrogen sulfide. Thus, the upper limit for molybdenum (Mo) is specifically 0.5% by weight. Additionally, molybdenum (Mo) precipitates are used to improve strength, but coarsely precipitated molybdenum (Mo) can cause localized corrosion of the steel. Therefore, more specifically, molybdenum (Mo) should be added in amounts of 0.1% by weight or less.

[0047] Aluminum (Al): 0.1% by weight or less

[0048] Aluminum (Al) is an element added for deoxidation, and it reacts with nitrogen (N) in steel to form aluminum nitride (AlN) and refine the austenite grains to improve toughness. However, when aluminum (Al) is included in amounts greater than 0.1% by weight, inclusions are formed in coarse oxides during the steelmaking process, and during rolling, stretched inclusions are formed based on the characteristics of alumina. Since the formation of these elongated inclusions promotes the formation of voids around the inclusions, and these voids serve as initiation points for localized corrosion, the elongated inclusions contribute to reduced localized corrosion resistance. Therefore, the aluminum (Al) content is specifically set at 0.1% by weight or less. Since deoxidation effects can be achieved even with the addition of aluminum (Al) through other deoxidizing elements such as silicon (Si), there is no lower limit for the aluminum (Al) content. However, at least 0.001% by weight or more of aluminum (Al) can be specifically added to anticipate the deoxidation effect achieved by aluminum (Al).

[0049] Chromium (Cr): 0.05% to 0.5% by weight

[0050] Chromium (Cr) is an element that enhances corrosion resistance by forming a chromium oxide layer on the surface of steel in corrosive environments. Chromium (Cr) should be included in an amount of 0.05 wt% or more to exhibit corrosion resistance effects dependent on the amount of chromium (Cr) added. However, when chromium (Cr) is included in an amount greater than 0.5 wt%, toughness and weldability are adversely affected. Therefore, the chromium (Cr) content is specifically set to 0.05 wt% to 0.5 wt%.

[0051] Calcium (Ca): 0.001% by weight to 0.01% by weight

[0052] Calcium (Ca) reacts with aluminum (Al), silicon (Si), and oxygen (O) in molten steel to form a complex oxide, which then reacts with sulfur (S) to form calcium sulfide (CaS). This calcium sulfide (CaS) inclusion dissolves in water in condensing environments, increasing the pH of the steel surface. Therefore, while inhibiting the electrochemical reactions in the steel to improve corrosion resistance, it also promotes the formation of a stable phase. To improve corrosion resistance, the amount of calcium (Ca) added should be at least 0.001% by weight. However, when the calcium (Ca) content is greater than 0.01% by weight, the refractory material may melt during steelmaking. Therefore, the Ca content is specifically set to 0.001% by weight to 0.01% by weight. Furthermore, the amount of calcium (Ca) added is more specifically 0.002% by weight or more to ensure the sulfide dew point corrosion susceptibility index.

[0053] In addition to the above-mentioned components, the balance includes iron (Fe) and unavoidable impurities. However, the addition of other alloying elements is not excluded without departing from the scope of this disclosure.

[0054] In the steels disclosed herein, the sulfide condensation corrosion susceptibility index, as defined in relational expression 1, specifically satisfies 1.7 to 2.3.

[0055] [Relational Expression 1]

[0056] Sulfide dew point corrosion susceptibility index =

[0057] (Where Ca, S, Cr, Mo, Cu, Ni and Mn represent the content (by weight) of the corresponding elements).

[0058] The aforementioned Ca, Cr, Mo, Cu, Ni, and Mn are components whose addition amounts affect corrosion resistance in sulfide condensation environments. The effect of each of these components on corrosion resistance is quantitatively derived, and the relationships between the components are expressed by Relationship Expression 1. When the sulfide dew point corrosion susceptibility index, as defined by Relationship Expression 1, is between 1.7 and 2.5, improved corrosion resistance in the corresponding environment can be ensured.

[0059] The steel of this disclosure having an advantageous composition can be readily produced by those skilled in the art using knowledge in the art without excessive repetitive testing. This disclosure presents a production method more advantageous than, for example, methods discovered by the inventors, namely, a method for producing steel.

[0060] The method for producing steel according to this disclosure is a method of producing steel by conventional hot rolling and cooling, and the method is characterized in that the cooling is carried out at a cooling rate of 10°C / s or lower, with a cooling start temperature of Ar3 or higher and a cooling end temperature ranging from (Ae1-30°C) to 600°C. The cooling conditions of this disclosure will be described below.

[0061] Cooling section: Cooling from Ar3 temperature or higher to (Ae1-30℃) up to 600℃

[0062] According to the results of experiments conducted by the inventors, when molybdenum (Mo) is added to achieve beneficial effects, a large amount of precipitates are formed, and the added molybdenum (Mo) has adverse effects on overall corrosion and localized corrosion. Furthermore, when excessive molybdenum (Mo) dissolves, it negatively impacts corrosion resistance in environments containing hydrogen sulfide. Therefore, the ratio of molybdenum (Mo) forming precipitates to dissolved molybdenum (Mo) must be properly controlled. Since molybdenum (Mo) tends to form precipitates at temperatures between 700°C and 550°C, a portion of this section requires rapid cooling to prevent molybdenum (Mo) precipitation, while other portions of the section require slow cooling to prevent excessive dissolution of molybdenum (Mo).

[0063] When cooling begins at temperatures below or equal to Ar3, copper (Cu) segregates into pearlite, accelerating corrosion caused by the galvanic pair of pearlite and ferrite. Therefore, cooling must begin at or above Ar3 and continue until temperatures adequately forming precipitates such as molybdenum (Mo) without pearlite formation (Ae1-30°C) or lower. When cooling proceeds to sufficiently low temperatures, molybdenum (Mo) is not properly precipitated and dissolves excessively. Consequently, molybdenum (Mo) may combine with sulfur (S) in a condensate atmosphere containing hydrogen sulfide to form Mo2S, potentially degrading the corrosion resistance of the steel. Consequently, cooling must be completed at 600°C or higher.

[0064] Cooling rate: 10℃ / s or higher

[0065] Because the time required to traverse the temperature range where molybdenum (Mo) precipitates easily form increases when the cooling rate is low, excessive precipitate formation may occur. Therefore, a cooling rate of 10 °C / s or higher is required. Even at higher cooling rates, achieving the objectives of this disclosure is not a problem. Therefore, it is not necessary to determine an upper limit for the cooling rate. However, considering the limitations of the cooling equipment's capacity and the constraints on the ability to apply considerably high cooling rates, an upper limit of 50 °C / s can be determined.

[0066] Invention Embodiments

[0067] Exemplary embodiments of this disclosure will be described in detail below. However, this disclosure is not limited to the exemplary embodiments described herein.

[0068] (Implementation Plan)

[0069] After preparing molten steel with the composition listed in Table 1 (weight percentage (wt%), the balance including iron (Fe) and unavoidable impurities), continuous casting is used to produce billets. The produced billets are hot-rolled under standard conditions and then cooled under the conditions in Table 2.

[0070] [Table 1]

[0071]

[0072] Table 2

[0073]

[0074] As can be seen from Table 1, the steel of the present invention refers to steel plates having a composition that meets the composition range defined in this disclosure. However, comparative steels 1, 5, and 6 show cases where necessary additive elements selected from this disclosure, such as Mo, Cu, and Cr, are not added. Comparative steels 2, 3, 4, 7, and 8 show cases where necessary elements are added but the sulfide dew point corrosion susceptibility index, as expressed by relational expression 1, does not meet the required range because the susceptibility index is less than 1.7 or greater than 2.5, as described later. The corrosion resistance of these components of the comparative steels is significantly lower than that of the steel of the present invention. Therefore, since corrosion of the steel in a sulfide dew point corrosive environment cannot be prevented, corrosion resistance may be reduced and replacement cycles may be increased.

[0075] Table 3 below lists the measurement results of the sulfide dew point corrosion susceptibility index and corrosion rate of the steel of the present invention and the comparative steel. The corrosion rates listed in Table 3 are obtained through... Figure 1 The results measured by the test apparatus shown. For example, as... Figure 1 As shown, to simulate a sulfide condensation environment, distilled water was filled into an airtight container, and corrosive gases such as SO2, H2S, CO2, and O2 were continuously blown into the distilled water. A sample with dimensions of 60 mm × 20 mm × 5 mm, used to measure the corrosion rate, was then polished with #600 sandpaper and placed on top of the airtight container. The airtight container's lid was equipped with an inlet, outlet, and a heating / cooling water circulation system. After airtightening, the airtight container was installed in a thermostat and subjected to a 100-day temperature cycle of (50°C, 20 hours) → (25°C, 4 hours). The gas introduced into the test apparatus was a gas simulating the sulfide dew point corrosion environment of the upper deck of a crude oil storage tank, and this gas had the following composition.

[0076] Gas composition by volume percentage: 5% O2 - 15% CO2 - 0.011% SO2 - 0.055% H2S - balance N2

[0077] After 100 days of corrosion testing, rust removal was performed in a corrosion product removal solution. The mass loss of each sample was divided by the initial surface area of ​​the sample. For relative comparison, the corrosion rate of comparison steel 1 was set to 100, and the relative corrosion rates are listed in Table 3.

[0078] Table 3

[0079]

[0080] As can be seen from Table 2, when corrosion-resistant elements such as Mo, Cu, and Cr are not added at all or in insufficient amounts, and the sulfide condensation sensitivity index does not meet the range of 1.7 to 2.3 proposed in this disclosure, the relative corrosion rate is at most twice that of the steel of the present invention. This phenomenon occurs in all comparative steels, although the degree varies slightly, which is determined by the fact that the sulfide condensation sensitivity index proposed in this disclosure is not met.

[0081] Figure 2 Images of samples of the steels 1 to 7 of the present invention and the comparative steels 1 to 8, observed after a 100-day sulfide dew point corrosion test. As described above, the steels 1 to 7 of the present invention, with a sulfide dew point corrosion susceptibility index in the range of 1.7 or higher to 2.5 or lower as proposed in relational expression 1 of this disclosure, have a dense structure, wherein the corrosion products have a bright color. In the case of the comparative steels 1 to 8, dark-colored corrosion products are visible to the naked eye.

[0082] As mentioned above, as shown in Table 3 and Figure 2 As shown, the sulfide corrosion susceptibility index proposed in this disclosure should be met to prevent sulfide dew point corrosion. When the susceptibility index is not met, sufficient corrosion resistance cannot be ensured for the stable use of the steel in the corresponding environment, and therefore the service life of the corresponding structure may not be guaranteed.

[0083] This application also relates to the following aspects:

[0084] 1. A steel exhibiting excellent corrosion resistance in a condensation environment containing sulfide gases, said steel comprising, by weight percent (wt%), 0.02% to 0.2% carbon (C), 0.1% to 1.0% silicon (Si), 0.2% to 2.0% manganese (Mn), 0.03% or less phosphorus (P), 0.03% or less sulfur (S), 0.05% to 0.5% copper (Cu), 0.05% to 0.5% nickel (Ni), 0.02% to 0.5% molybdenum (Mo), 0.1% or less aluminum (Al), 0.05% to 0.5% chromium (Cr), 0.001% to 0.01% calcium (Ca), and the balance iron (Fe) and unavoidable impurities.

[0085] Among them, the sulfide dew point corrosion susceptibility index given by relational expression 1 is 1.7 or higher to 2.5 or lower.

[0086] (Relational Expression 1)

[0087] Sulfide dew point corrosion susceptibility index =

[0088] Where Ca, S, Cr, Mo, Cu, Ni and Mn represent the content of the corresponding elements in weight percent.

[0089] 2. The steel according to aspect 1, wherein the Ni content is greater than or equal to the Cu content, and the Ni content is 1.5 times or less than the Cu content.

[0090] 3. The steel according to aspect 1, wherein Ca is 0.002% to 0.01%.

[0091] 4. A method for producing steel with excellent corrosion resistance in a condensation environment containing sulfide gases, comprising hot rolling and cooling a slab, said slab comprising, by weight percent (wt%), 0.02% to 0.2% carbon (C), 0.1% to 1.0% silicon (Si), 0.2% to 2.0% manganese (Mn), 0.03% or less phosphorus (P), 0.03% or less sulfur (S), 0.05% to 0.5% copper (Cu), 0.05% to 0.5% nickel (Ni), 0.02% to 0.5% molybdenum (Mo), 0.1% or less aluminum (Al), 0.05% to 0.5% chromium (Cr), 0.001% to 0.01% calcium (Ca), and the balance iron (Fe) and unavoidable impurities.

[0092] Among them, the sulfide dew point corrosion susceptibility index given by relational expression 1 is 1.7 or higher to 2.5 or lower.

[0093] (Relational Expression 1)

[0094] Sulfide dew point corrosion susceptibility index =

[0095] Where Ca, S, Cr, Mo, Cu, Ni, and Mn represent the content of the corresponding elements in weight percent, and

[0096] The cooling is performed at a cooling rate of 10°C / second or higher between a cooling start temperature higher than or equal to Ar3 temperature and a cooling end temperature of Ae1-30°C to 600°C.

[0097] 5. The method according to aspect 4, wherein the content of Ni is greater than or equal to the content of Cu, and the content of Ni is 1.5 times or less than the content of Cu.

[0098] 6. The method according to aspect 4, wherein Ca is 0.002% to 0.01%.

Claims

1. A steel exhibiting excellent corrosion resistance in a condensation environment containing sulfide gases, said steel comprising, by weight percentage (wt%): 0.02% to 0.2% carbon (C), 0.1% to 1.0% silicon (Si), 0.2% to 2.0% manganese (Mn), 0.03% or less phosphorus (P), 0.03% or less but excluding 0% sulfur (S), 0.05% to 0.5% copper (Cu), 0.05% to 0.5% nickel (Ni), 0.02% to 0.5% molybdenum (Mo), 0.1% or less aluminum (Al), 0.05% to 0.5% chromium (Cr), 0.001% to 0.01% calcium (Ca), and the balance iron (Fe) and unavoidable impurities. Among them, the sulfide dew point corrosion susceptibility index given by relational expression 1 is 1.78 or higher to 2.25 or lower. Relational expression 1: Sulfide dew point corrosion susceptibility index = Where Ca, S, Cr, Mo, Cu, Ni, and Mn represent the content of the corresponding elements in weight percent. The content of Ni is greater than that of Cu, and the content of Ni is 1.5 times or less than that of Cu.

2. The steel according to claim 1, wherein, The Ca content ranges from 0.002% to 0.01%.

3. A method for producing steel with excellent corrosion resistance in a condensation environment containing sulfide gases, comprising hot rolling and cooling a slab, said slab comprising, by weight percentage (wt%): 0.02% to 0.2% carbon (C), 0.1% to 1.0% silicon (Si), 0.2% to 2.0% manganese (Mn), 0.03% or less phosphorus (P), 0.03% or less but excluding 0% sulfur (S), 0.05% to 0.5% copper (Cu), 0.05% to 0.5% nickel (Ni), 0.02% to 0.5% molybdenum (Mo), 0.1% or less aluminum (Al), 0.05% to 0.5% chromium (Cr), 0.001% to 0.01% calcium (Ca), and the balance iron (Fe) and unavoidable impurities. Among them, the sulfide dew point corrosion susceptibility index given by relational expression 1 is 1.78 or higher to 2.25 or lower. Relational expression 1: Sulfide dew point corrosion susceptibility index = Where Ca, S, Cr, Mo, Cu, Ni, and Mn represent the content of the corresponding elements in weight percent, and The cooling is carried out at a cooling rate of 10°C / second or higher between a cooling start temperature higher than or equal to Ar3 temperature and a cooling end temperature of Ae1-30°C to 600°C. The content of Ni is greater than that of Cu, and the content of Ni is 1.5 times or less than that of Cu.

4. The method according to claim 3, wherein, The Ca content ranges from 0.002% to 0.01%.

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