KR100928774B1 - Sulfuric acid and hydrochloric acid corrosion resistant steel with excellent sulfuric acid and hydrochloric acid corrosion resistance - Google Patents

Abstract

Provided are sulfuric acid and hydrochloric acid corrosion resistant steels and methods for producing the same.

Steels with excellent sulfuric acid and hydrochloric acid corrosion resistance, in weight%, C: 0.15% or less (not including 0%), Si: 1.0% or less (not including 0%), Mn: 2.0% or less ( Does not contain 0%), S: 0.03% or less (does not contain 0%), P: 0.02% or less (does not contain 0%), Al: 0.01-0.1%, Cu: 0.2-1.0%, It is composed of Co: 0.02 ~ 0.1%, Sb: 0.02 ~ 0.2%, Sn: 0.02 ~ 0.15%, W: 0.02 ~ 0.2%, and the remaining Fe and other unavoidable impurities. After reheating the steel at 1100 to 1300 ° C., hot rolling may be performed. The finish temperature at the time of hot rolling may be 850 to 950 ° C., and the winding temperature may be 560 to 660 ° C.

Description

Sulfuric acid and hydrochloric acid corrosion resistant steel with excellent sulfuric acid and hydrochloric acid corrosion resistance and its manufacturing method {STEEL HAVING EXCELLENT RESISTANCE TO CORROSION BY HYDROCHLORIC ACID AND SULFURIC ACID AND METHOD FOR MANUFACTURING THE SAME}

The present invention relates to sulfuric acid and hydrochloric acid corrosion resistant steels used for materials such as desulfurization ducts, gas gas heaters (GGH), electrostatic precipitators (EP), etc. in a desulfurization facility of a thermal power plant, and a method of manufacturing the same. More particularly, the present invention relates to sulfuric acid and hydrochloric acid corrosion resistant steels and a method for manufacturing the same, which can improve the corrosion resistance of sulfuric acid and hydrochloric acid in a low-low sulfuric acid concentration section in a desulfurization plant to extend the life of the plant.

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 less, creating 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. Accordingly, the problem of condensation of hydrochloric acid as well as sulfuric acid on the surface of the steel is generated, and thus there is a need for a material having improved corrosion resistance as well as sulfuric acid corrosion resistance.

As a low alloy corrosion resistant steel applied to thermal power plants, steel grades having excellent sulfuric acid corrosion resistance have been developed to date by complex addition of Cu and other corrosion resistant alloying elements.

The technology for improving sulfuric acid corrosion resistance by the addition of Cu-Co composite is an invention considering only sulfuric acid condensation corrosion, and shows a characteristic of poor corrosion resistance in hydrochloric acid atmosphere.

When alloying elements such as Cu-Cr- (Ti, Nb, V, Mo) are added, they exhibit mechanical properties suitable for high temperature facilities, but they are inferior in corrosion resistance in low-low sulfuric acid concentration range and in hydrochloric acid atmosphere. There is a problem with the result.

In the case of improving the hydrochloric acid corrosion resistance by adding an alloying component such as Cu-Sb- (Mo, Cr, Ni, Sn), steelmaking costs are increased by adding expensive Mo, and corrosion resistance is poor in sulfuric acid condensation atmosphere. .

Accordingly, an object of the present invention is to provide a steel having excellent sulfuric acid resistant and hydrochloric acid corrosion characteristics in a low temperature-low sulfuric acid concentration section and a method of manufacturing the same.

Steel having excellent sulfuric acid and hydrochloric acid corrosion characteristics of the present invention for achieving the above object, by weight, C: 0.15% or less (not including 0%), Si: 1.0% or less (not including 0%) ), Mn: 2.0% or less (without 0%), S: 0.03% or less (without 0%), P: 0.02% or less (without 0%), Al: 0.01-0.1 %, Cu: 0.2 ~ 1.0%, Co: 0.02 ~ 0.1%, Sb: 0.02 ~ 0.2%, Sn: 0.02 ~ 0.15%, W: 0.02 ~ 0.2%, remaining Fe and other unavoidable impurities.

Furthermore, the method for producing steel having excellent sulfuric acid and hydrochloric acid corrosion resistance of the present invention is, by weight, C: 0.15% or less (does not include 0%), Si: 1.0% or less (does not include 0%) , Mn: 2.0% or less (without 0%), S: 0.03% or less (without 0%), P: 0.02% or less (without 0%), Al: 0.01-0.1%, Cu: 0.2 ~ 1.0%, Co: 0.02 ~ 0.1%, Sb: 0.02 ~ 0.2%, Sn: 0.02 ~ 0.15%, W: 0.02 ~ 0.2%, steel made of the remaining Fe and other unavoidable impurities 1100 ~ 1300 ℃ After reheating in hot rolling, the hot rolling finish temperature is 850 ~ 950 ℃, the winding temperature is made to include 560 ~ 660 ℃.

There is a useful effect that the corrosion resistance of sulfuric acid and hydrochloric acid is improved in the low-low sulfuric acid concentration range.

Hereinafter, the reason for limitation of the composition range of this invention is demonstrated.

C content: 0.15% by weight or less (does not include 0% by weight)

When the C content is more than 0.15% by weight, sulfuric acid corrosion resistance and welding properties are greatly reduced, which may cause defects and shorten the life of equipment to which the present invention is applied.

Si content: 1.0 wt% or less (does not include 0 wt%)

Si is an element mainly added to improve the strength, but when the content exceeds 1.0% by weight, the corrosion property is greatly deteriorated in the low-low sulfuric acid concentration range and 1.0 weight is caused in the hot rolling process. It is preferable to add below%.

Mn content: 2.0 wt% or less (does not include 0 wt%)

Mn was usually added to precipitate the solid solution S in the steel as manganese sulfide to prevent red brittleness due to solid solution sulfur and to satisfy the required mechanical properties. When the content of Mn exceeds 2.0% by weight, sulfuric acid and composite corrosion characteristics are inhibited compared to the strength improving effect, so the upper limit is set to 2.0% by weight.

S content: 0.03% by weight or less (does not include 0% by weight)

It is preferable to add S as low as possible, and when it exceeds 0.03 weight%, it is preferable to set an upper limit to 0.03 weight% because the possibility of defects by hot brittleness is high.

P content: 0.02% by weight or less (does not include 0% by weight)

If P is added in excess of 0.02% by weight, strength synergistic effect can be expected, but sulfuric acid and composite corrosion characteristics are greatly reduced, especially P in grain boundary adversely affects not only material degradation but also surface quality. It is preferable to limit the weight percentage.

Al content: 0.01 ~ 0.1 wt%

Al is an element added for the purpose of deoxidation in order to suppress the occurrence of cracks in the continuous casting process in the refining process, and less than 0.01% by weight of the deoxidation effect is less than 0.1% by weight, the probability of surface defects due to the increase of Al oxide This upper limit was set at 0.1% by weight.

Cu content: 0.2 ~ 1.0 wt%

Cu is an element that must be added in consideration of sulfuric acid and complex corrosion characteristics, and the effect of corrosion resistance is large when its content is more than 0.2% by weight, but when added in excess of 1.0% by weight, the effect of improving corrosion resistance is increased compared to the increase in the added amount. Since it becomes less economical because it becomes less, it is preferable to set the upper limit to 1.0 weight%.

Co content: 0.02 ~ 0.1 wt%

Co is a representative element that improves the corrosion resistance by sulfuric acid condensation together with Cu. When Co is added, it is possible to secure sulfuric acid corrosion resistance far superior to the effect of adding Cu alone. In comparison, the effect of Co on the composite corrosion characteristics is not as great as that of sulfuric acid corrosion resistance, but the addition of Co is essential in consideration of sulfuric acid corrosion resistance. It is preferable to set the Co content to 0.02 to 0.1% by weight, because the effect is less when the Co content is less than 0.02% by weight, and when the content exceeds 0.1% by weight, the improvement of the corrosion resistance is insignificant compared to the addition amount, and the steelmaking cost is greatly increased. Height also has its drawbacks.

Sb content: 0.02 ~ 0.2% by weight

Sb is an element that is effective in complex corrosion resistance with sulfuric acid, and is an element that improves corrosion resistance by forming a corrosion product on the surface of steel. If the added amount is less than 0.02% by weight, the addition effect is insignificant, and as the added amount is increased, the corrosion resistance increases, but when it exceeds 0.2% by weight, there is little effect according to the increase of the added amount.

Sn content: 0.02 ~ 0.15 wt%

Sn, like Sb, is an effective element for complex corrosion resistance with sulfuric acid, and is an element that contributes particularly to sulfuric acid corrosion resistance improvement. When Sn is added below 0.02% by weight, the addition effect is insignificant. There is a tendency to inhibit the rolling property such as breaking due to grain boundary precipitation of Sn in hot rolling without improving.

W content: 0.02 ~ 0.2% by weight

W is also an element added in consideration of corrosion resistance properties and useful in complex corrosion properties and effective in securing sulfuric acid corrosion resistance. W is added in the range of 0.02 to 0.2% by weight, for the same reason as for the amount of Sb added.

Hereinafter, the formula of the present invention will be described.

The two formulas of the present invention mean limiting the content range and essential additive elements of the added element to obtain sulfuric acid and hydrochloric acid corrosion resistance.

First, the formula [W (wt%) × Sn (wt%)] / Sb (wt%) ≤ 0.2 is an essential element in which W, Sn, and Sb are all essential elements, but the range of addition amount is maximized to maximize the effect on the corrosion resistance of each element. it means. Among these elements, Sb is an element that is more effective than other elements. Therefore, it is advantageous to increase the content of Sb rather than to increase the content of W and Sn. In other words, it is preferable to increase the content of Sb. This not only has the effect of corrosion resistance, but also has the effect that can be produced at low cost by adding a low-cost Sb rather than the effect of the addition of expensive W.

The following formula [W (wt%) × Sn (wt%)] / Sb (wt%) ≠ 0 indicates that the multiplication or division of each element is not zero. This means not. In other words, all elements included in the formula are essential elements to secure corrosion resistance, meaning that W, Sn, and Sb must all be added. Sn is mainly contributing to sulfuric acid resistance to satisfy sulfuric acid and hydrochloric acid corrosion characteristics. Since W and Sb contribute greatly to the hydrochloric acid properties, it can be said that addition of these elements is essential in order to exhibit the effect of having complex corrosion resistance of sulfuric acid and hydrochloric acid as in the present invention.

Hereinafter, the manufacturing method of this invention is demonstrated.

By weight, C: 0.15% or less (does not contain 0%), Si: 1.0% or less (does not contain 0%), Mn: 2.0% or less (does not contain 0%), S: 0.03% (0% or less), P: 0.02% or less (0%), Al: 0.01% to 0.1%, Cu: 0.2% to 1.0%, Co: 0.02% to 0.1%, Sb: 0.02% to 0.2% %, Sn: 0.02 ~ 0.15%, W: 0.02 ~ 0.2%, characterized in that the composition of the remaining Fe and other unavoidable impurities, the content of Sb, Sn, W is the following formula, [W (wt%) × Sn Reheat the steel satisfying (wt%)] / Sb (wt%) ≤ 0.2 and [W (wt%) × Sn (wt%)] / Sb (wt%) ≠ 0 to 1100 ~ 1300 ℃ Finishing the rolling at 850 ~ 950 ℃, it is characterized by winding in a temperature range of 560 ~ 660 ℃.

(1) Reheating Temperature: 1100 ~ 1300 ℃

The reheating temperature in the hot rolling process for manufacturing steel is to maintain the slab at a constant temperature for rolling to control the structure in the slab or to reconstruct the precipitate 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 1100 ° C or higher. On the other hand, for the re-use of the additive elements, the temperature is different depending on the characteristics of the additive element, but when the precipitate is difficult to dissolve at high temperatures as in the present invention is heated to a temperature higher than the tissue control temperature. W added in the present invention is a relatively stable element, it is difficult to re-precipitate the precipitate at high temperature, it is necessary to increase the slab reheating temperature to 1300 ℃.

(2) Finishing temperature: 850 ~ 950 ℃

The finishing temperature is usually set to be slightly higher than the temperature at which austenite transforms into ferrite. This is to finish the rolling just above the transformation point temperature so that the structure transformed into ferrite is uniformly distributed. In order to suppress the local corrosion caused by the difference of the tissue under the same corrosion conditions through the homogenization of the structure and to allow the uniform corrosion to proceed, a temperature of 850 ° C. or higher is preferable. The upper limit of the finishing temperature is to prevent the surface defects caused by the formation of the scale to 950 ℃ or less because it is necessary to prevent the scale generated from the surface in the high temperature state.

(3) Winding temperature: 560 ~ 660 ℃

Winding process after finishing rolling is the process that dominates the transformation into ferrite. The higher the temperature, the more grains grow and the softer the material. 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. Therefore, in the present invention, the coiling temperature after rolling is limited to 560 ~ 660 ℃ range that satisfies the target material and does not occur surface defects.

Hereinafter, the present invention will be described in more detail with reference to Examples.

EXAMPLE

The steel ingots prepared by melting to satisfy the composition shown in Table 1 were reheated in a 1250 ° C. heating furnace for 1 hour, and then hot rolled. Hot rolling finish temperature was set to 870 ~ 890 ℃, winding temperature was set to 620 ℃ conditions, the final thickness of 3.2mm was aimed. In order to evaluate the corrosion resistance of sulfuric acid under low temperature and low concentration conditions, the hot rolled specimens were measured for 6 hours by immersing the specimen in 70 ℃ -50wt% sulfuric acid solution to measure the corrosion loss. After immersion for 6 hours in modified green death solution (16.9 Vol% sulfuric acid + 0.35 Vol% hydrochloric acid) that most closely simulates the actual corrosion environment of the desulfurization system, the corrosion loss was measured in the same way as the corrosion resistance of sulfuric acid. Indicated.

Chemical composition (% by weight) C Mn Si P S Al Cu Co Cr Ni Sb Mo W Sn Invention 1 Composition 1 0.07 0.7 0.25 0.01 0.01 0.033 0.30 0.05 - - 0.10 - 0.10 0.05 Invention 2 Composition 2 0.07 0.7 0.25 0.01 0.01 0.036 0.30 0.05 - - 0.10 - 0.05 0.10 Comparative Material 1 Composition 3 0.07 0.7 0.25 0.01 0.01 0.027 0.30 0.05 - 0.25 - - - - Comparative Material 2 Composition 4 0.07 0.7 0.25 0.01 0.01 0.043 0.30 - - 0.15 0.10 0.05 - - Comparative Material 3 Composition 5 0.07 0.7 0.25 0.01 0.01 0.031 0.30 - 0.30 - - - - - Comparative Material 4 Composition 6 0.07 0.7 0.25 0.01 0.01 0.035 0.30 0.05 0.30 - - - - - Comparative Material 5 Composition 7 0.07 0.7 0.25 0.01 0.01 0.041 0.30 0.05 - - 0.05 - - - Comparative Material 6 Composition 8 0.07 0.7 0.25 0.01 0.01 0.027 0.30 0.05 - - 0.05 - 0.10 - Comparative Material7 Composition 9 0.07 0.7 0.25 0.01 0.01 0.028 0.30 0.05 - - 0.05 - - 0.10 Comparative Material 8 Composition 10 0.07 0.7 0.25 0.01 0.01 0.036 0.30 0.05 - - 0.05 0.05 - - Comparative Material 9 Composition 11 0.07 0.7 0.25 0.01 0.01 0.040 0.30 0.05 - - - - 0.10 0.05

[W (wt%) × Sn (wt%)] / Sb (wt%) Sulfuric acid corrosion resistance (mg / cm2 / hr) 50wt% Sulfuric acid -70 ℃ Hydrochloric acid + sulfuric acid complex corrosion resistance (mg / cm2 / hr) 16.9 Vol% sulfuric acid-0.35 Vol% hydrochloric acid -70 Invention 1 Composition 1 0.05 22.48 1.49 Invention 2 Composition 2 0.05 21.95 1.78 Comparative Material 1 Composition 3 - 46.30 20.94 Comparative Material 2 Composition 4 0 28.09 2.69 Comparative Material 3 Composition 5 - 58.17 10.60 Comparative Material 4 Composition 6 - 26.57 9.35 Comparative Material 5 Composition 7 0 27.56 8.98 Comparative Material 6 Composition 8 0 26.51 2.47 Comparative Material7 Composition 9 0 24.44 3.05 Comparative Material 8 Composition 10 0 27.38 7.45 Comparative Material 9 Composition 11 - 32.16 8.51

The chemical composition of the invention materials 1 and 2 is characterized by adding all of Cu, Co, Sb, W, Sn, among which the content of Sb, Sn, W is [W (wt%) × Sn (wt%)] / By satisfying the formulas of Sb (wt%) ≤ 0.2 and ([W (wt%) × Sn (wt%)] / Sb (wt%) ≠ 0), sulfuric acid corrosion resistance as well as complex corrosion properties are excellent. . The addition of Sb, Sn, and W plays a key role in the composite corrosion characteristics. If any of these components is omitted, corrosion resistance as shown in the results of the deposition tests of Inventive Materials 1 and 2 and Comparative Materials 5, 6, 7, and 9 Characteristics are impaired.

Comparative materials 2 and 8 in which Sb and Mo are added together have good sulfuric acid and complex corrosion resistance, but when Mo is added, manufacturing cost increases, and corrosion resistance is also inferior to that of Sb, W and Sn composite additives.

The difference between the components of Comparative Materials 3 and 4 is the addition of Co, but it can be seen that the sulfuric acid corrosion resistance is remarkably decreased in Comparative Material 3, which is Co-free steel. It can be seen that Co is an element to be added in consideration of sulfuric acid corrosion resistance.

The poor sulfuric acid and composite corrosion characteristics of Comparative Material 1 are due to the addition of Ni and should be excluded as far as possible from the component design.

Claims (3)

By weight, C: 0.15% or less (does not contain 0%), Si: 1.0% or less (does not contain 0%), Mn: 2.0% or less (does not contain 0%), S: 0.03% (0% or less), P: 0.02% or less (0%), Al: 0.01% to 0.1%, Cu: 0.2% to 1.0%, Co: 0.02% to 0.1%, Sb: 0.02% to 0.2% %, Sn: 0.02 to 0.15%, W: 0.02 to 0.2%, sulfuric acid and hydrochloric acid corrosion resistant steel having excellent corrosion resistance of sulfuric acid and hydrochloric acid, characterized by consisting of the remaining Fe and other unavoidable impurities. The method according to claim 1, wherein the content of Sb, Sn, W is equal to the following formula: [W (wt%) × Sn (wt%)] / Sb (wt%) ≦ 0.2 and [W (wt%) × Sn ( sulfuric acid and hydrochloric acid corrosion resistant steel having excellent corrosion resistance to sulfuric acid and hydrochloric acid, characterized by satisfying wt%)] / Sb (wt%) ≠ 0. By weight, C: 0.15% or less (does not contain 0%), Si: 1.0% or less (does not contain 0%), Mn: 2.0% or less (does not contain 0%), S: 0.03% (0% or less), P: 0.02% or less (0%), Al: 0.01% to 0.1%, Cu: 0.2% to 1.0%, Co: 0.02% to 0.1%, Sb: 0.02% to 0.2% %, Sn: 0.02 ~ 0.15%, W: 0.02 ~ 0.2%, characterized in that the composition of the remaining Fe and other unavoidable impurities, the content of Sb, Sn, W is the following formula, [W (wt%) × Sn Reheat the steel satisfying (wt%)] / Sb (wt%) ≤ 0.2 and [W (wt%) × Sn (wt%)] / Sb (wt%) ≠ 0 to 1100 ~ 1300 ℃ A method for producing sulfuric acid and hydrochloric acid corrosion resistant steel having excellent corrosion resistance to sulfuric acid and hydrochloric acid, characterized in that rolling is finished at 850 to 950 ° C and wound at a temperature range of 560 to 660 ° C.