KR100946148B1 - Steel excellent in resistance to corrosion by sulfuric acid and method for manufacturing the same - Google Patents

Abstract

Provided is a steel having excellent corrosion characteristics by sulfuric acid condensation and a method of manufacturing the same.

Sulfuric acid corrosion resistant steels are, by weight, C: 0.15% or less (excluding 0%), Si: 1.0% or less (excluding 0%), Mn: 2.0% or less (excluding 0%), S: 0.03% P: 0.02% or less, Al: 0.01% to 0.1%, Cu: 0.2% to 1.0%, Co: 0.02% to 0.1%, Cr: 0.1% to 1.0%, Ni: 0.1% or less (excluding 0%), Nb: It is composed of 0.02 ~ 0.1%, remaining Fe and other unavoidable impurities. The steel may have a tissue of polygonal ferrite, or may include at least one selected from low temperature tissues of excicular ferrite, bainitic ferrite, and bainite. When the low temperature tissue is included, it exhibits excellent mechanical properties in various temperature ranges from room temperature to 500 ° C.

Sulfuric acid corrosion resistant steel, low temperature structure, high temperature strength

Description

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

The present invention relates to sulfuric acid corrosion-resistant steel used as a material for ducts, air preheaters, boiler pipes and peripheral parts of power plant boilers and a method of manufacturing the same. More specifically, it relates to sulfuric acid corrosion-resistant steel and a method for manufacturing the sulfuric acid corrosion resistance that can improve the corrosion resistance of sulfuric acid in the low temperature-low sulfuric acid concentration section to extend the life of the equipment.

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 reaches a dew point of sulfuric acid of about 160 ° C., a severe corrosive environment is created by sulfuric acid condensing on the steel surface. Materials used for low temperature parts below 200 ° C in thermal power plants are required to have excellent sulfuric acid condensation corrosion properties, but mechanical properties can be applied if they meet the level of conventional low alloy steels. However, boiler ducts and air preheaters operating at temperatures above 200 ° C. also require excellent high temperature tensile properties in addition to sulfuric acid corrosion resistance.

In general, steel has been developed to secure corrosion resistance by adding a combination of Cu and other corrosion-resistant alloy elements in steel, and the representative conventional techniques are Korean Patent Publications 2001-010931, 2003-0047470, 2003-0047469, Japan Published Patent Publication No. 2002-327236.

Korean Unexamined Patent Publication No. 2001-010931 is a technique for improving sulfuric acid corrosion resistance by the addition of Cu-Co composite. In 2003-0047470, Cr is added to Ni in terms of surface defects in terms of corrosion resistance in Cu-Co-based corrosion steel, and in 2003-0047469, Nb is added in Cu-Co to secure strength. These are improving sulfuric acid corrosion resistance in Cu-Co system. However, since sulfuric acid corrosion resistance is required in the low temperature-low concentration range, the characteristics need to be improved. In addition, the mechanical properties of the material is insufficient to be applied to a high temperature environment, so it is not suitable for a facility such as a boiler duct or an air preheater.

In the case of the Japanese Laid-Open Patent Publication No. 2002-327236, an alloy component such as Cu-Cr- (Ti, Nb, V, Mo, W) is added to exhibit mechanical properties suitable for high temperature facilities, but in the low temperature-low sulfuric acid concentration range The corrosion resistance of the product has the problem of showing poor results.

Accordingly, the present invention is to solve the above problems, to provide a steel with excellent strength while improving the sulfuric acid corrosion resistance in the low temperature-low concentration range, the object is.

Furthermore, the object of the present invention is to provide a high-temperature guarantee high strength steel showing excellent mechanical properties in a temperature range of room temperature to 500 ° C. or less, and a method of manufacturing the same.

In order to achieve the above object, the steel having excellent sulfuric acid corrosion resistance in the low temperature-low concentration range of the present invention is, by weight, C: 0.15% or less (excluding 0%), Si: 1.0% or less (excluding 0%) , Mn: 2.0% or less (excluding 0%), S: 0.03% or less, P: 0.02% or less, Al: 0.01 to 0.1%, Cu: 0.2 to 1.0%, Co: 0.02 to 0.1%, Cr: 0.1 ~ 1.0%, Ni: 0.1% or less (except 0%), Nb: 0.02 ~ 0.1%, remaining Fe and other inevitable impurities.

In addition, high-temperature warranty high-strength sulfuric acid corrosion-resistant steel, in weight%, C: 0.15% or less (excluding 0%), Si: 1.0% or less (excluding 0%), Mn: 2.0% or less (excluding 0%) ), S: 0.03% or less, P: 0.02% or less, Al: 0.01 to 0.1%, Cu: 0.2 to 1.0%, Co: 0.02 to 0.1%, Cr: 0.1 to 1.0%, Ni: 0.1% or less (0% Nb: 0.02 to 0.1%, consisting of the remaining Fe and other unavoidable impurities, at least 1 selected from the low temperature tissues of the excicular ferrite, bainitic ferrite and bainite. Paper is included.

The high-temperature warranty high strength sulfuric acid corrosion resistant steel of the present invention, in weight%, C: 0.15% or less (excluding 0%), Si: 1.0% or less (excluding 0%), Mn: 2.0% or less (0% S: 0.03% or less, P: 0.02% or less, Al: 0.01 ~ 0.1%, Cu: 0.2 ~ 1.0%, Co: 0.02 ~ 0.1%, Cr: 0.1 ~ 1.0%, Ni: 0.1% or less ( 0%), Nb: 0.02 ~ 0.1%, the steel consisting of the remaining Fe and other unavoidable impurities, hot-rolled after accelerated cooling and winding to a temperature of 500 ~ 660 ℃.

The Mn content in the steel of the present invention is most preferably 1.51-2.0%. In addition, the sulfuric acid corrosion resistant steel may further include V.

Sulfuric acid corrosion resistant steel for high temperature strength guarantee of the present invention is 20% or more of at least one selected from the low temperature tissue of the excicular cooler (accicular ferrite), bainitic ferrite (bainitic ferrite), bainite (bainite).

를 만족하는 것이 바람직하다. In the steel of the present invention, Mn, Cr, Ni, and Nb have the following relationship,

It is desirable to satisfy.

According to the present invention, there is a useful effect of improving the room temperature strength and the high temperature strength while improving the corrosion resistance in the low temperature-low sulfuric acid concentration section.

Hereinafter, the present invention will be described in detail.

The present invention is derived from the process of deriving the optimal component design in the Cu-Co component system in order to improve the corrosion resistance and strength characteristics in the low-temperature sulfuric acid concentration corrosion zone. In the present invention, in order to improve the strength characteristics in Cu-Co-based sulfuric acid steel, while raising the Mn to 2.0% level and adding Nb, the lowering of the corrosion resistance is lower than the upper limit of Ni to 0.1% (excluding 0%). To control the Cr in the range of 0.1-1.0%. Thus, in the present invention, unlike the Cu-Co-based sulfuric acid corrosion-resistant steel known so far, in the present invention, the corrosion resistance and strength in the low-temperature sulfuric acid concentration corrosion zone by the organic management of the components of Mn, Nb, Cr, Ni We are improving the characteristics together. In order to solve the problem of surface defects due to the addition of Cu in the Cu-Co system, it is necessary to add more than 0.1% of Ni. However, according to the present invention, the problem of surface defects in Nb-Cr additive steel does not occur and Ni is 0.1. If it is less than% (except 0%), corrosion resistance will improve further.

Furthermore, it is a feature of the present invention to further improve the strength at high temperatures by the process of accelerated cooling-cold winding in such component designed steels. In other words, by forming a low temperature structure with the precipitation strengthening effect to improve the high temperature strength.

The content of C is preferably 0.15% or less (excluding 0%).

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

The content of Si is preferably 1.0% or less (excluding 0%).

Si is an element mainly added to improve the strength, but if the content is higher than 1.0%, it is preferable to add it to 1.0% or less (excluding 0%) because the corrosion property is significantly worsened in the low-low sulfuric acid concentration section. Do.

The content of Mn is preferably 2.0% or less (excluding 0%).

Mn is usually added to precipitate solid solution S in steel as manganese sulfide to prevent red brittleness due to solid solution sulfur. In the present invention, Mn is also added for preventing red brittleness and improving strength at room temperature and high temperature. When the Mn content exceeds 2.0%, the sulfuric acid corrosion resistance is inhibited in comparison with the strength improving effect, so the upper limit is preferably 2.0%. In order to improve the strength at room temperature and high temperature, the Mn content is preferably set to 1.51-2.0%. In this range, the strength is improved while the toughness is not reduced. Of course, the content of Mn may be appropriately selected according to the desired strength, and if necessary, the content of Mn may be 0.5-1.50%.

The content of S is preferably 0.03% or less.

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

The content of P is preferably 0.02% or less.

When P exceeds 0.02%, strength synergistic effect can be expected, but since sulfuric acid corrosion resistance is greatly reduced, it is preferable to limit the upper limit to 0.02%.

The content of Al is preferably 0.01-0.1%.

Al is an element added for deoxidation purposes in the refining process, and less than 0.01% deoxidation effect, Al exceeds 0.1% increase the probability of surface defects due to the increase of Al oxide.

The content of Cu is preferably 0.2-1.0%.

Cu is an element that must be added in consideration of sulfuric acid corrosion resistance, the effect of the corrosion resistance is large when the content is more than 0.2%. If the Cu content is more than 1.0%, the effect of improving the corrosion resistance is small compared to the increase in the amount of addition, so the upper limit is preferably 1.0%.

The content of Co is preferably 0.02-0.1%.

Co is a characteristic element of sulfuric acid steel together with Cu, and when Co is added, it is possible to secure much better corrosion resistance than the effect of adding Cu alone. If the Co content is less than 0.02%, the effect is less, if more than 0.1% not only does not improve the corrosion resistance compared to the addition amount, there is also a disadvantage that greatly increases the steelmaking cost.

The content of Cr is preferably 0.1-1.0%.

Cr is added to improve the corrosion resistance by forming Cr-based oxide on the surface at a high temperature, and almost no anticorrosive coating is formed when the added amount is less than 0.1%. As the amount of Cr is increased, the anticorrosive coating is easier to develop, and the anticorrosive effect is large.

The content of Ni is preferably 0.1% or less (excluding 0%).

Ni is an element that significantly inhibits sulfuric acid corrosion resistance. In the past, Ni was added to prevent surface defects that may occur during continuous casting or hot rolling of Cu-added steel. However, even when Ni of 0.1% or less (except 0%) was added, the surface was good and corrosion resistance was improved at the same time. In addition, manufacturing costs can be saved.

The content of Nb is preferably 0.02-0.1%.

Nb is an element that greatly contributes to improving room temperature and high temperature strength by the effect of fine NbC precipitates. The target strength can be ensured when the amount of Nb added is 0.02% or more, and the strength increases as the amount added. However, when the amount of Nb added exceeds 0.1%, not only the ductility is greatly reduced, but also the NbC precipitation effect cannot be expected due to the depletion of solid solution C. Therefore, the upper limit is preferably limited to 0.1%. In the case of Nb, it is most suitable because it is an optimum element which improves strength effectively and does not reduce corrosion resistance compared with other alloy components.

An alloy component may be added to the steel satisfying the above components as necessary. As a representative example, the addition of V may be considered for increasing the strength.

The content of V is preferably 0.02-0.1%.

When the V content is added less than 0.02%, the strength synergistic effect is insufficient, and when the content of V exceeds 0.1%, the corrosion resistance tends to be lowered.

The steel satisfying the above component system may have a polygonal ferrite single phase structure. In this case, the strength characteristics are good along with the corrosion resistance in the low temperature-low concentration range. Furthermore, when the low temperature tissue is included through accelerated cooling, the high temperature tensile property is further improved. In the present invention, the low-temperature tissue is an excimer ferrite (accicular ferrite), bainitic ferrite (bainitic ferrite), bainite (bainite), at least one of them are included. The proportion of cold tissue is most preferably 20-100%.

* In the steel that satisfies the component system of the present invention, when the components of Mn, Nb, Ni, and Cr are organically controlled in the following relationship, the corrosion characteristics and the strength characteristics are optimized. However, the present invention is not limited thereto.

Hereinafter, the manufacturing method of the steel of this invention is demonstrated.

In the present invention, the steel of the composition can be reheated and hot-rolled to produce a hot rolled sheet, or a cold rolled hot rolled sheet can be manufactured by a conventional method.

The steel of the present invention may have a polygonal ferrite single phase structure. In this case, the strength characteristics are good along with the corrosion resistance in the low temperature-low concentration range. Furthermore, when the low temperature tissue is included through accelerated cooling, the high temperature tensile property is further improved. In the present invention, the low-temperature tissue includes at least one selected from the group consisting of an excicular cooler (accicular ferrite), bainitic ferrite, and bainite.

The method for producing steel having a single-phase structure of polygonal ferrite is not a special method, but a conventional method. In other words, accelerated cooling and cold winding are not applied. Therefore, according to the present invention will be described in more detail with respect to the steel manufacturing method including a low-temperature structure through accelerated cooling.

First, after hot rolling a steel which satisfies the component system of the present invention, it is acceleratedly cooled and wound up at a temperature of 500 to 660 ° C. These manufacturing conditions are for obtaining a low temperature structure. Preferred accelerated cooling is at a rate of 30 ° C / s or more on average, and more preferably 30-50 ° C / s. In the present invention, the accelerated cooling condition is sufficient as long as it is a condition capable of obtaining a low temperature structure at the coiling temperature, and is not necessarily limited to the accelerated cooling rate.

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. The hot rolling finish temperature was set at 870 ~ 890 ℃, and the winding temperature was set by dividing each composition into two conditions of 560 ℃ and 660 ℃, and the final thickness was set to 6.0mm in consideration of the customer use thickness. In order to evaluate the corrosion resistance of sulfuric acid under low temperature and low concentration conditions, the hot rolled specimen was measured for 3 hours by immersing the specimen in 70 ℃ -50% sulfuric acid solution and measuring the corrosion loss. The properties were evaluated and the results are shown in Table 2. During the high temperature tensile test, the temperature specimen was minimized by maintaining the tensile test specimen to the target temperature for 30 minutes. In Table 1, the Al content is 0.03% in the steel grades A1-A12.

division Chemical composition (% by weight) C Mn Si P S Cu Co Cr Ni Nb V Ti (Mn + Cr + Nb) / Ni A1 0.07 0.5 0.2 0.015 0.012 0.35 0.1 0.25 2 A2 0.1 0.7 0.25 0.015 0.012 0.35 0.6 0.04 - A3 0.07 1.53 0.2 0.015 0.012 0.35 0.05 0.5 0.05 0.04 40 A4 0.07 1.53 0.2 0.015 0.012 0.35 0.05 0.5 0.05 0.02 40.4 A5 0.07 1.53 0.2 0.055 0.012 0.35 0.05 0.5 0.25 0.02 6.08 A6 0.07 1.53 0.2 0.015 0.012 0.35 0.05 0.25 0.04 6 A7 0.07 1.53 0.2 0.015 0.012 0.35 0.05 0.1 0.05 0.04 32.8 A8 0.07 1.53 0.2 0.015 0.012 0.35 0.05 0.5 0.05 0.04 40.8 A9 0.07 1.80 0.2 0.015 0.012 0.35 0.05 0.5 0.05 0.04 46.8 A10 0.07 0.8 0.2 0.015 0.012 0.35 0.05 0.5 0.05 0.03 26.6 A11 0.07 1.0 0.2 0.015 0.012 0.35 0.05 0.5 0.05 0.03 30.6 A12 0.07 1.2 0.2 0.015 0.012 0.35 0.05 0.5 0.05 0.03 34.6

division Hot rolled coiling temperature Average cooling rate (℃ / s) Mechanical Properties: Room Temperature (Mpa,%) Mechanical Properties: 500 ℃ (Mpa,%) Corrosion rate Remarks YS TS El YS TS El Mg / cm2 / hr Target material ≥400 ≥500 ≥15 ≥250 ≥310 ≥15 ≤40 A1 560 40 326 437 33.8 186 228 41.1 39.1 Comparative Material 1 660 25 295 414 40.9 167 216 41.7 39.6 Comparative Material 2 A2 560 40 487 572 20.9 340 395 40.3 55.4 Comparative Material 3 660 25 401 497 24.4 215 287 46.0 56.8 Comparative Material 4 A3 560 40 496 569 24.9 339 389 23.5 42.5 Comparative Material 5 660 25 323 432 32.2 195 307 27.0 48.2 Comparative Material 6 A4 560 40 546 643 20.4 413 470 15.3 31.7 Invention 1 660 25 407 504 25.3 269 368 28.0 36.1 Invention Material 8 A5 560 40 518 613 21.4 376 441 18.0 57.9 Comparative Material7 660 25 426 527 29.0 267 327 32.8 76.3 Comparative Material 8 A6 560 40 489 549 14.6 328 378 16.5 49.2 Comparative Material 9 660 25 319 421 34.6 183 282 32.8 51.9 Comparative Material 10 A7 560 40 541 617 18.6 384 426 19.6 36.3 Invention 2 660 25 431 511 27.6 288 378 26.1 39.4 Invention Material 9 A8 560 40 549 671 18.3 420 472 16.9 34.3 Invention 3 660 25 441 529 25.5 257 358 28.0 38.2 Invention 10 A9 560 40 558 667 21.1 439 502 20.8 39.4 Invention 4 660 25 434 529 24.7 291 398 26.7 39.6 Invention Material 11 A10 560 40 534.3 605.3 24.9 343.0 375.7 25.6 36.23 Invention 5 660 25 446.2 517.9 25.3 279.3 307.3 21.5 34.19 Invention Material12 A11 560 40 537.6 617.4 24.3 357.7 393.0 24.3 35.31 Invention 6 660 25 456.4 532.8 32.4 269.0 319.3 33.3 32.07 Invention Material 13 A12 560 40 545.8 635.8 23.6 386.0 421.3 20.0 33.49 Invention Material7 660 25 485.7 553.6 32.6 262.7 317.0 33.9 31.78 Invention 14

As can be seen from the results in Table 2, in the case of A4, A7, A8, A9, A10, A11, and A12 satisfying the steel component system of the present invention, the target material is secured even when hot winding or accelerated cooling-low temperature winding. In particular, in the case of accelerated cooling-low temperature winding, the strength at room temperature and high temperature is greatly improved. Figure 1 shows the microstructure change of the steel of A4 according to the manufacturing conditions of high temperature odor and accelerated cooling-low temperature odor. Looking at Figure 1b, it can be seen that the low temperature tissue is distributed.

A2 is Ti-added steel, and the material level is satisfactory, but sulfuric acid corrosion resistance is inferior. It is proved that Ti is not an optimal alloying element when considering corrosion resistance. A5 is a P-added steel, but the strength increase effect is satisfactory, but it can be seen that it is a harmful element in terms of corrosion resistance.

1 is a photograph showing the microstructure according to the winding temperature of the invention steel

Figure 1a is a case of high temperature winding

1B is a case of winding at low temperature.

Claims (12)

By weight, C: 0.15% or less (excluding 0%), Si: 1.0% or less (excluding 0%), Mn: 2.0% or less (excluding 0%), S: 0.03% or less, P: 0.02% Al: 0.01 ~ 0.1%, Cu: 0.2 ~ 1.0%, Co: 0.02 ~ 0.1%, Cr: 0.1 ~ 1.0%, Ni: 0.1% or less (excluding 0%), Nb: 0.02 ~ 0.1%, rest Sulfuric acid corrosion resistant steel with excellent sulfuric acid corrosion resistance composed of Fe and other unavoidable impurities. The method according to claim 1, wherein Mn, Cr, Ni, Nb by weight% is

Sulfuric acid corrosion resistant steel excellent sulfuric acid corrosion resistance, characterized in that to satisfy. By weight, C: 0.15% or less (excluding 0%), Si: 1.0% or less (excluding 0%), Mn: 2.0% or less (excluding 0%), S: 0.03% or less, P: 0.02% Al: 0.01 ~ 0.1%, Cu: 0.2 ~ 1.0%, Co: 0.02 ~ 0.1%, Cr: 0.1 ~ 1.0%, Ni: 0.1% or less (excluding 0%), Nb: 0.02 ~ 0.1%, rest Sulfuric acid corrosion resistant steel having excellent corrosion resistance to sulfuric acid, which is composed of Fe and other unavoidable impurities, and includes at least one selected from low temperature tissues of excicular ferrite, bainitic ferrite, and bainite. The sulfuric acid corrosion-resistant steel of claim 1 or 3, wherein the Mn content is 1.51-2.0%. 4. The sulfuric acid corrosion resistant steel having excellent sulfuric acid corrosion resistance according to claim 1, wherein the Mn content is 0.5-1.50%. The sulfuric acid corrosion-resistant steel having excellent sulfuric acid corrosion resistance according to claim 1 or 3, wherein the sulfuric acid corrosion-resistant steel contains V in an amount of 0.02-0.1%. 4. The sulfuric acid corrosion resistant steel having excellent sulfuric acid corrosion resistance according to claim 3, wherein at least one selected from the excicular ferrite, bainitic ferrite, and bainite is 20% or more. . By weight, C: 0.15% or less (excluding 0%), Si: 1.0% or less (excluding 0%), Mn: 2.0% or less (excluding 0%), S: 0.03% or less, P: 0.02% Al: 0.01 ~ 0.1%, Cu: 0.2 ~ 1.0%, Co: 0.02 ~ 0.1%, Cr: 0.1 ~ 1.0%, Ni: 0.1% or less (excluding 0%), Nb: 0.02 ~ 0.1%, rest A method for producing sulfuric acid corrosion resistant steel having excellent sulfuric acid corrosion resistance, comprising: cold rolling a steel composed of Fe and other unavoidable impurities after accelerated cooling, and winding it at a temperature of 500 to 660 ° C. to have a low temperature structure. The method of claim 8, wherein the accelerated cooling is performed at an average speed of 30 to 50 ° C./s. 9. The method for producing sulfuric acid corrosion resistant steel having excellent sulfuric acid corrosion resistance according to claim 8, wherein the content of Mn is 1.51-2.0%. 9. The method for producing sulfuric acid corrosion resistant steel having excellent sulfuric acid corrosion resistance according to claim 8, wherein the content of Mn is 0.5-1.50%. 10. The method of claim 8, wherein the sulfuric acid corrosion resistant steel includes V in an amount of 0.02-0.1%.

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