KR20030047470A - The hot rolled sheet steel with the excellent anti-corrosion resistance to sulfuric acid - Google Patents

Abstract

PURPOSE: A hot rolled sheet steel with excellent anti-corrosion resistance to sulfuric acid is provided. CONSTITUTION: The hot rolled sheet steel comprises 0.15 wt.% or less of C, 1.0 wt.% or less of Si, 1.5 wt.% or less of Mn, 0.03 wt.% or less of S, 0.02 wt.% or less of P, Al 0.01 to 0.1 wt.%, Cu 0.2 to 1.0 wt.%, Co 0.02 to 0.1 wt.%, Cr 0.05 to 0.5, Ni 0.1 to 2.0 wt.%, a balance of Fe and incidental impurities, wherein atomic ratio of Ni/Cu is 0.5 to 2.0.

Description

Hot rolled sheet steel with the excellent anti-corrosion resistance to sulfuric acid}

The present invention relates to a hot rolled steel sheet having excellent sulfuric acid corrosion resistance, which is used as a material for power plant preheater, boiler pipe, and peripheral parts. More specifically, the corrosion rate is greatly improved in the low-low sulfuric acid concentration range, and high-temperature oxidation is delayed. The present invention relates to a hot rolled steel sheet having excellent sulfuric acid corrosion resistance in a high temperature-low sulfuric acid concentration range by adding an appropriate amount of other additive elements to prevent surface defects caused by a large amount of Cu in continuous casting or hot rolling.

Steels with excellent sulfuric acid corrosion resistance are used as materials used in low temperature parts below 300 ° C of thermal power plant preheaters that come into contact with exhaust gas containing sulfurous acid gas, and components that are highly corrosive by sulfuric acid, such as boiler piping. In general, sulfuric acid resistant steel has been known to add a large amount of Cu in the steel in order to retard the corrosion rate in the sulfuric acid atmosphere than ordinary steel. Although Cu has a great effect of significantly delaying the corrosion rate of sulfuric acid compared to other additive elements, a steel has been developed that adds an appropriate amount of Cu and complexly adds other elements due to cracking during hot rolling. Representative examples thereof include Japanese Patent Laid-Open Nos. 9-25536 and 10-110237.

Japanese Patent Application Laid-open No. Hei 9-25536 adds alloying elements of Ni, Cr, V, Nb, Ti, Sn, Sb, and B to the basic component system of C-Si-Mn-PS-Al-Cu to secure hot workability. It is a technology to improve sulfuric acid corrosion resistance. Japanese Patent Application Laid-Open No. 10-110237 discloses hot workability by adding alloying elements of Ni, Cr, V, Nb, Ti, Sn, Sb, B, and Mo to the basic component system of C-Si-Mn-PS-Al-Cu. It is a technology to improve sulfuric acid corrosion resistance while securing

However, these prior art has a problem that the corrosion rate is still high in the low-temperature sulfuric acid concentration range while adding a large amount of alloying elements. In addition, there is a problem that the surface defects during corrosion and continuous casting or hot rolling caused by oxidation occurring at a high temperature.

Therefore, in order to solve the problem, the present invention greatly improves the corrosion rate in the low-low sulfuric acid concentration section, delays high temperature oxidation, and prevents surface defects due to the addition of a large amount of Cu in continuous casting or hot rolling. In order to provide a hot rolled steel sheet excellent in sulfuric acid corrosion resistance in the high temperature-low sulfuric acid concentration range by adding an appropriate amount, the purpose.

Hot-rolled steel sheet of the present invention for achieving the above object, by weight% C: 0.15% or less, Si: 1.0% or less, Mn: 1.5% or less, 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: 0.05-0.5, Ni: 0.1-2.0%, Ni / Cu atomic ratio: 0.5-2.0, satisfying the composition of remaining Fe and other unavoidable impurities do.

Hereinafter, the present invention will be described in detail.

· C: 0.15% or less

When the amount of C added exceeds 0.15%, weldability is greatly deteriorated when welding is used, and thus defects are high. Therefore, it is preferable to make the upper limit of C content into 0.15%.

· Si: 1.0% or less

Since Si is an element mainly added to improve strength, the sulfuric acid corrosion resistance is greatly deteriorated at more than 1.0%, so the upper limit is preferably 1.0%.

· Mn: 1.5% or less

The Mn is usually added to prevent hot shortness due to solid solution of precipitated sulfur in steel as manganese sulfide in the present invention. If the Mn content is more than 1.5%, sulfuric acid corrosion resistance is deteriorated, so the upper limit is preferably 1.5%.

· P: 0.02% or less

When P is more than 0.02%, sulfuric acid corrosion resistance is greatly reduced, so it is preferable to limit the upper limit to 0.02%.

· S: 0.03% or less

It is preferable to add the S as low as possible, and if it is added 0.03% or more, the upper limit is preferably 0.03% because the possibility of defects due to hot brittleness is high.

· Al: 0.01 ~ 0.1%

The Al is added as a deoxidizer, but less than 0.01% has a low deoxidation effect, and in the case of more than 0.1%, Al has a high probability of surface defects.

· Cu: 0.2 ~ 1.0%

The Cu is added to increase the sulfuric acid corrosion resistance greatly, but the effect is noticeable from 0.2% or more, but in the case of more than 1.0%, the effect of improving the corrosion resistance is not large compared to the increase of the addition amount.

· Co: 0.02 ~ 0.1%

The Co is added with Cu, particularly in the low temperature-low sulfuric acid concentration section, thereby greatly improving the corrosion resistance. The effect is prominent from 0.02% or more, but when it exceeds 0.1%, the improvement of corrosion resistance is insignificant compared to the added amount.

· Cr: 0.05 ~ 0.5%

The Cr is added to improve the corrosion resistance by the formation of Cr-based oxide on the surface at a high temperature, almost no anticorrosive coating is produced when the addition amount is less than 0.05%, the anticorrosive coating is easy to develop as the addition amount is increased, but the anticorrosive effect is large. If it is more than 0.5%, there is little effect by the increase of the addition amount.

· Ni: 0.1 ~ 2.0%

The Ni is added to prevent surface defects occurring during continuous casting or hot rolling in Cu-added steel, and there is no surface defects in the Ni addition amount of 0.1% or more, and when it exceeds 2.0%, the manufacturing cost increases greatly, so the upper limit value is 1.0. It is desirable to limit to%.

· Ni / atomic ratio of Cu: 0.5 ~ 2.0

The atomic ratio of Ni / Cu is to prevent the occurrence of surface defects during continuous casting or hot rolling, and to reduce the production cost by reducing expensive Ni additions. Surface defects are likely to occur at the Ni / Cu atomic ratio of 0.5 or less. When the atomic ratio of Ni / Cu is 2.0 or more, the manufacturing cost is greatly increased, so it is preferable to limit the atomic ratio of Ni / Cu to 2.0 or less.

The steel formed as described above is heated by a conventional method and hot rolled to a desired thickness to produce a hot rolled sheet. Even under hot rolling under normal conditions, there is little change in sulfuric acid corrosion resistance.

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

EXAMPLE

The steel ingot prepared by dissolving the composition as shown in Table 1 was maintained for 1 hour in a 1250 ° C. heating furnace, and then hot rolled. At this time, the hot finish rolling start temperature was 1100 ° C, the winding temperature was 650 ° C, and the final thickness was 3.2mm. In order to investigate the corrosion resistance of sulfuric acid at low temperature and low concentration, hot-rolled specimens were immersed in 70 ℃ -50% and 140 ℃ -80% sulfuric acid solution for 1 hour to measure the corrosion loss of each specimen.

Sample Number Chemical composition (% by weight) Ni / Cu atomic ratio C Si Mn P S Al Cu Co Ni Cr Invention steel One 0.053 0.45 0.65 0.010 0.012 0.045 0.28 0.052 0.22 0.18 0.85 2 0.053 0.43 0.67 0.013 0.013 0.042 0.30 0.051 0.28 0.25 1.01 3 0.055 0.45 0.63 0.013 0.011 0.042 0.32 0.045 0.34 0.36 1.15 4 0.051 0.44 0.65 0.011 0.012 0.045 0.32 0.055 0.42 0.48 1.42 Comparative steel One 0.052 0.45 0.67 0.014 0.009 0.043 0.31 0.005 0.32 0.19 1.12 2 0.054 0.46 0.65 0.013 0.010 0.041 0.25 0.054 0.32 0.03 1.12 3 0.052 0.45 0.65 0.012 0.011 0.045 0.10 0.021 0.12 0.12 1.30 4 0.052 0.45 0.65 0.012 0.011 0.042 0.30 0.053 0.02 0.21 0.07

Sample Number Corrosion loss (mg / cm ² hr) Surface condition 50% -70 ^o C 80% -140 ^o C Average Invention steel One 18.9 10.2 14.55 Good 2 16.9 8.6 12.75 Good 3 16.5 7.4 11.95 Good 4 15.3 7.2 11.25 Good Comparable One 35.6 20.9 28.25 Good 2 19.8 25.9 22.85 Good 3 45.2 35.6 40.4 Good 4 17.5 11.3 14.4 Surface Defects

In Tables 1 and 2, the steels belonging to the present invention have an average corrosion loss of 15 mg / cm ² hr or less, and exhibit very excellent sulfuric acid corrosion resistance. The amount of addition is outside the scope of the present invention, the corrosion loss is very high under the conditions of 50% -70 ^o C and 80% -140 ^o C sulfuric acid solution, the average corrosion loss is very high, 28.25mg / cm ² hr. Comparative steel 2 is good in the low temperature-low concentration range, but the Cr content is out of the scope of the present invention, the corrosion loss is very high under the condition of 80% -140 ^o C sulfuric acid solution, the average corrosion loss is very high, 22.85mg / cm ² hr. . In case of Comparative Steel 3, the Cu content is out of the scope of the present invention and the corrosion loss is very high under the conditions of 50% -70 ^o C and 80% -140 ^o C sulfuric acid solution, and the average corrosion loss is very high as 40.4 mg / cm ² hr. . In the case of Comparative Steel 4, Cu, Co, and Cr belonged to the range of the present invention, so that sulfuric acid corrosion resistance was good, but Ni was lower than the range limited by the present invention, resulting in surface defects.

As described above, according to the present invention, a hot rolled steel sheet having excellent sulfuric acid corrosion resistance is provided, which greatly extends the lifespan of materials requiring relatively thick thicknesses of power plant preheaters where sulfuric acid dew point corrosion occurs and materials of boiler piping and peripheral devices. The effect is to have a useful effect.

Claims (1)

By weight% C: 0.15% or less, Si: 1.0% or less, Mn: 1.5% or less, S: 0.03% or less, P: 0.02% or less, Al: 0.01-0.1%, Cu: 0.2-1.0%, Co: 0.02 Hot rolled steel sheet with excellent sulfuric acid corrosion resistance that satisfies -0.1%, Cr: 0.05-0.5, Ni: 0.1-2.0%, Ni / Cu atomic ratio: 0.5-2.0 and is composed of the remaining Fe and other unavoidable impurities.