JP4904847B2 - Steel material with excellent acid corrosion resistance - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a steel material having excellent acid corrosion resistance used for smoke power generation equipment such as thermal power plants, municipal waste, and industrial waste incineration equipment, and in particular, an environment where sulfuric acid dew point corrosion and hydrochloric acid dew point corrosion occur in a combustion exhaust gas atmosphere. The present invention relates to a steel material having excellent acid corrosion resistance.

  Combustion exhaust gas discharged from thermal power plants, municipal waste or industrial waste incineration equipment is mainly composed of moisture, sulfur oxides (sulfur dioxide, sulfur trioxide, etc.), hydrogen chloride, nitrogen oxides, carbon dioxide, It is composed of nitrogen, oxygen, etc. If the combustion exhaust gas contains sulfur trioxide even at 1 mass ppm, the dew point of the combustion exhaust gas rises to 100 ° C. or more and sulfuric acid condenses easily. So-called sulfuric acid dew point corrosion occurs in smoke exhaust facilities such as heat exchangers, desulfurizers, electrostatic precipitators, and induction fans.

  As countermeasures, sulfuric acid dew-point corrosion steel (sulfuric acid-resistant steel) as disclosed in Patent Document 1 and highly corrosion-resistant stainless steel as disclosed in Patent Document 2 are used. However, stainless steel is susceptible to stress corrosion cracking and crevice corrosion due to chloride concentration in addition to dew point corrosion in a hydrochloric acid corrosive environment. There is a problem of becoming a thing.

  On the other hand, combustion exhaust gas discharged from coal-fired boilers, general or industrial waste incineration facilities, etc. may contain a considerable amount of hydrogen chloride in addition to sulfur compounds such as sulfur trioxide. In this case, hydrochloric acid condensation occurs simultaneously with sulfuric acid condensation. Therefore, the material used for the flue gas facility that guides the exhaust gas is subject to severe sulfuric acid corrosion and hydrochloric acid corrosion.

  The sulfuric acid dew point temperature and the hydrochloric acid dew point temperature vary depending on the composition of the components constituting the combustion exhaust gas. In general, the dew point temperature of sulfuric acid is about 100 to 150 ° C, and the dew point temperature of hydrochloric acid is 50 to 80 ° C. Therefore, depending on the structure and location of the same flue gas facility, and even if the temperature of the combustion exhaust gas passing through is constant, the location where the sulfuric acid dew point corrosion is dominant and the location where the hydrochloric acid dew point corrosion is dominant are generated depending on the wall surface temperature. become. Therefore, the material constituting the smoke exhausting facility is required not only to be excellent in sulfuric acid dew point corrosion resistance but also to be excellent in hydrochloric acid dew point corrosion resistance.

As a response to this demand, for example, in Patent Document 3, Cu, Mo or the like is added to steel with C: 0.03 mass% or less, and the resistance to sulfuric acid and hydrochloric acid is improved. Alloy steel is disclosed. Patent Document 4 discloses a steel excellent in acid dew point corrosion resistance that has improved resistance to hydrochloric acid dew point corrosion while ensuring resistance to sulfuric acid dew point corrosion by adding Sn and / or Sb to low S steel. It is disclosed.
Japanese Patent Publication No. 43-014585 JP 07-316745 A Japanese Examined Patent Publication No. 46-034772 Japanese Patent Application Laid-Open No. 09-025536

  However, the steel of Patent Document 3 has a problem that, when Mo is added excessively, sulfuric acid corrosion resistance at a sulfuric acid concentration of 10 to 40 mass% is significantly hindered, and also about hydrochloric acid corrosion resistance, There is a problem that it is inferior to Patent Document 1 depending on conditions. Further, the hydrochloric acid corrosion resistance of the steel of Patent Document 4 is equal to or less than the hydrochloric acid resistance of Patent Document 1 described above.

  Furthermore, in waste incineration equipment that burns vinyl chloride and household garbage, the concentration of hydrogen chloride contained in the exhaust gas may reach as much as 4000 massppm depending on the equipment, so that hydrochloric acid corrosion resistance is maintained while maintaining sulfuric acid corrosion resistance. Therefore, there is a strong demand for a steel material that is more excellent in acid corrosion resistance and more inexpensive than high-corrosion-resistant stainless steel.

  Therefore, an object of the present invention is to provide an inexpensive acid-corrosion-resistant steel material that has further improved hydrochloric acid corrosion resistance while maintaining excellent sulfuric acid corrosion resistance.

  Inventors repeated examination about the influence of the metallurgical factor on hydrochloric acid corrosion resistance. As a result, it is possible to improve hydrochloric acid corrosion resistance while ensuring excellent sulfuric acid corrosion resistance by adding an appropriate amount of W to the Cu-Sb type sulfuric acid steel material, and when the steel material is corroded with hydrochloric acid. In this case, an amorphous oxide layer having a special composition is formed on the surface of the steel material, and this amorphous oxide layer has an effect of further improving hydrochloric acid corrosion resistance. It has been found that the crystalline oxide layer has an effect of improving the hydrochloric acid corrosion resistance even by coating the surface of the steel material by some method. The present invention has been completed based on the above findings.

  That is, the present invention provides C: 5.0 to 40.0 mass%, Si: 0.1 to 3.0 mass%, Mn: 0.1 to 1.0 mass%, Cu: 5 on the steel material surface after hydrochloric acid corrosion. Component composition containing 0.0-25.0 mass%, W: 1.0-20.0 mass%, Sb: 1.0-25.0 mass%, Ni: 20.0 mass% or less, Sn: 2.0 mass% or less A steel material having an amorphous oxide layer made of and excellent in acid corrosion resistance.

  The steel materials of the present invention are: C: 0.001 to 0.2 mass%, Si: 0.01 to 2.5 mass%, Mn: 0.1 to 2 mass%, Cu: 0.05 to 0.5 mass%, W : 0.01-0.5 mass%, Sb: 0.01-0.2 mass%, P: 0.05 mass% or less, S: 0.05 mass% or less, Ni: 0.5 mass% or less, Sn: 0.2 mass % Or less, and the balance consists of Fe and inevitable impurities.

  In the present invention, C: 5.0 to 40.0 mass%, Si: 0.1 to 3.0 mass%, Mn: 0.1 to 1.0 mass%, Cu: 5.0 to 25 0.0 mass%, W: 1.0-20.0 mass%, Sb: 1.0-25.0 mass%, Ni: 20.0 mass% or less, and Sn: 2.0 mass% or less. It is a steel material excellent in acid corrosion resistance formed by forming a quality oxide layer.

  ADVANTAGE OF THE INVENTION According to this invention, the steel materials which are excellent in acid corrosion resistance which are excellent in both sulfuric acid corrosion resistance and hydrochloric acid corrosion resistance can be provided at low cost. Therefore, the steel material according to the present invention is a material (steel material) used for chimneys, flues, heat exchangers, casings, expansions, etc. of thermal power plants and waste incineration facilities that undergo severe hydrochloric acid dew point corrosion and sulfuric acid dew point corrosion. And can contribute to improvement of durability of these facilities and reduction of maintenance load.

The inventors have found that the hydrochloric acid corrosion resistance of a steel material can be remarkably improved by adding an extremely small amount of W to a Cu—Sb-based sulfuric acid-resistant steel. Specifically, this steel material has C: 0.001 to 0.2 mass%, Si: 0.01 to 2.5 mass%, Mn: 0.1 to 2 mass%, Cu: 0.05 to 0.5 mass%. , W: 0.01 to 0.5 mass%, Sb: 0.01 to 0.2 mass%, P: 0.05 mass% or less, S: 0.05 mass% or less, Ni: 0.5 mass% or less, Sn: 0 It is a steel material that contains 0.2 mass% or less and the balance consists of Fe and inevitable impurities.
Hereinafter, the reasons for limiting the component composition will be described.

C: 0.001 to 0.2 mass%
From the viewpoint of acid corrosion resistance and weldability, C is preferably as low as possible. However, since the reduction to less than 0.001 mass% only increases the steelmaking cost, the lower limit of C is set to 0.001 mass%. On the other hand, from the viewpoint of ensuring strength, it is preferable to add a large amount of C, but when it exceeds 0.2 mass%, the hydrochloric acid resistance decreases. Therefore, the C content is set to 0.001 to 0.2 mass%. Preferably, it is the range of 0.001-0.1 mass%.

Si: 0.01-2.5 mass%
Si is an element added as a deoxidizer and for increasing strength, and it is necessary to add 0.01 mass% or more. On the other hand, excessive addition causes scale fixation in hot rolling, and scale marks increase rapidly, so the upper limit is 2.5 mass%.

Mn: 0.1 to 2 mass%
Mn is an element that increases the strength of steel and is added in an amount of 0.1 mass% or more depending on the required strength. However, if it exceeds 2 mass%, the ductility decreases, so the upper limit is made 2 mass%.

P: 0.05 mass% or less P is an element mixed as an inevitable impurity, and is preferably as low as possible since it significantly impairs hydrochloric acid corrosion resistance. However, since the reduction of P causes an increase in steelmaking cost, it is set to 0.05 mass% or less.

S: 0.05 mass% or less S, like P, is an element mixed as an inevitable impurity. If it exceeds 0.05 mass%, hot workability and mechanical properties are significantly impaired, so the upper limit is 0.05 mass. %.

Cu: 0.05-0.5 mass%
Cu is an element that improves hydrochloric acid corrosion resistance and is an essential element in the present invention. In order to ensure the above effect, it is necessary to add 0.05 mass% or more. However, even if added in excess of 0.5 mass%, the effect is saturated, so the upper limit is made 0.5 mass%.

W: 0.01-0.5 mass%
W is an element that is particularly important in the present invention because it has the effect of significantly improving hydrochloric acid corrosion resistance by adding 0.01 mass% or more to Cu-Sb steel. However, even if added in excess of 0.5 mass%, the effect is saturated, so the upper limit is made 0.5 mass%.

Sb: 0.01 to 0.2 mass%
Sb is an important element for improving hydrochloric acid corrosion resistance, and in order to exhibit its effect, it is necessary to add 0.01 mass% or more. However, even if added in excess of 0.2 mass%, the effect is saturated, so the upper limit is 0.2 mass%.

Ni: 0.5 mass% or less Ni is an element that has an effect of preventing surface cracking during hot working, which is easily generated by the addition of Cu and Sb. However, even if added over 0.5 mass%, the effect is saturated, so it is added in the range of 0.5 mass% or less.

Sn: 0.2 mass% or less Sn is a component that improves hydrochloric acid corrosion resistance. However, if the Sn content exceeds 0.2 mass%, the effect is saturated, so the content is made 0.2 mass% or less.

  In the acid corrosion resistant steel material of the present invention, the components other than those described above are preferably composed of Fe and inevitable impurities. However, as long as the effect of the present invention is not impaired, it goes without saying that it does not refuse to contain components other than those described above.

Next, an oxide layer generated on the surface of the steel material when the acid corrosion resistant steel material of the present invention is corroded with hydrochloric acid will be described.
When a steel material conforming to the component composition of the present invention is corroded with hydrochloric acid, for example, when immersed in a 5 mass% hydrochloric acid aqueous solution at 80 ° C. for about 6 hours, C: 5.0 to 40. 0 mass%, Si: 0.1-3.0 mass%, Mn: 0.1-1.0 mass%, Cu: 5.0-25.0 mass%, W: 1.0-20.0 mass%, Sb: 1 An amorphous oxide layer having a component composition containing 0.0 to 25.0 mass%, Ni: 20.0 mass% or less, and Sn: 2.0 mass% or less is formed.

  The inventors' investigation has revealed that the amorphous oxide layer has an effect of improving hydrochloric acid corrosion resistance. The reason why this amorphous oxide layer has an effect of improving hydrochloric acid corrosion resistance is not yet clear, but it is considered that a barrier effect is produced by the formation of a dense surface layer. Yes.

  Therefore, hydrochloric acid corrosion resistance can be improved by forming this amorphous oxide layer coating on the surface of the steel material by any method. The steel material that forms the coating may be either a steel material excellent in acid resistance or a steel material of ordinary steel. The method for forming the coating of the amorphous oxide layer is not particularly limited, but a thermal spraying method such as plasma spraying, arc spraying, flame spraying, and explosion spraying can be most preferably used. Moreover, it is preferable that the film thickness of the film to be formed is in the range of 0.1 to 0.5 μm. If the thickness is less than 0.1 μm, the effect of improving hydrochloric acid corrosion resistance is small. On the other hand, if the film thickness is 0.5 μm, the effect of improving hydrochloric acid resistance is sufficiently obtained. As the amorphous oxide layer to be coated, a layer obtained by a physical vapor deposition method (PVD method) or a chemical vapor deposition method (CVD method) can be used. As described above, the amorphous oxide layer film can be formed not only by the above method but also by corrosive with hydrochloric acid.

18 types of steel having the composition shown in Table 1 were melted in a 50 kg vacuum melting furnace, cast into ingots, heated to 1200 ° C, and then hot rolled to a finish temperature of 900 ° C. A hot-rolled sheet having a thickness of 6 mm was used. Test pieces 1 to 18 having a size of 4 mmt × 20 mmW × 30 mmL were sampled from the hot-rolled sheet and subjected to the following hydrochloric acid corrosion test and sulfuric acid corrosion test.
<Hydrochloric acid corrosion test>
The test piece was immersed in a 5 mass% hydrochloric acid aqueous solution maintained at 80 ° C. for 24 hours, and the corrosion weight loss was measured from the mass change before and after the corrosion test.
<Sulfuric acid corrosion test>
The test piece was immersed in a 50 mass% sulfuric acid aqueous solution maintained at 70 ° C. for 6 hours, and the corrosion weight loss was measured from the mass change before and after the corrosion test.
The evaluation of hydrochloric acid corrosion resistance and sulfuric acid corrosion resistance is based on a test piece 11 taken from steel, which is a medium carbon ordinary steel not containing Cu, Ni, W, Sb, or Sn. Corrosion weight loss of other test pieces was relatively evaluated.

  The results of the corrosion test are shown together in Table 1. From this result, all of the test pieces 12 to 18 collected from the steel deviating from the component composition of the present invention had a hydrochloric acid corrosion weight loss of about 1/5 and sulfuric acid corrosion compared to the test piece 11 collected from the base steel. The test pieces 1 to 10 collected from the steel satisfying the component composition of the present invention are compared with the test pieces 11 collected from the base steel, while the weight loss is about the same to about 1/10. The hydrochloric acid corrosion weight loss is about 1/100 and the sulfuric acid corrosion weight loss is about 1/20, which shows that the acid corrosion resistance is remarkably excellent.

  From the hot rolled sheet of steel 11 (medium carbon ordinary steel) used in Example 1, 17 test pieces having the same dimensions as in Example 1 were collected, and these test pieces were pickled to remove the surface scale. Then, the corrosion test pieces 21 to 37 having an amorphous oxide film having a thickness of 0.3 μm were sprayed on the surface by an amorphous oxide having a composition shown in Table 2 by a plasma spraying method. did. Thereafter, these test pieces were subjected to the same hydrochloric acid corrosion test as in Example 1. The hydrochloric acid corrosion resistance was evaluated by relatively evaluating the corrosion weight loss of the other test pieces based on the same test piece 11 (no thermal spray coating) as in Example 1 as a reference (1000).

  The results of the corrosion test are shown together in Table 2. From this result, the test piece 11 which does not contain Cu, Ni, W, Sb, Sn and has no amorphous oxide film has the largest corrosion weight loss by the hydrochloric acid corrosion test, and does not satisfy the component composition of the present invention. The corrosion weight loss by the hydrochloric acid corrosion test of the test pieces 31 to 37 on which the amorphous oxide film is formed is equivalent to about 1/5 of the corrosion weight loss of the test piece 11. On the other hand, the corrosion weight loss by the hydrochloric acid corrosion test of the test pieces 21 to 30 on which the amorphous oxide film satisfying the component composition of the present invention is formed is about 1/100 of the corrosion weight loss of the test piece 11. It can be seen that it has acid corrosion resistance. As described above, it was confirmed that the hydrochloric acid corrosion resistance can be improved by forming an amorphous oxide film satisfying the composition of the present invention on ordinary steel.

  The technology of the present invention can also be suitably used for struts, rails, pipes and the like used inside and outside the mine.

Claims (3)

On the steel material surface after hydrochloric acid corrosion, C: 5.0 to 40.0 mass%, Si: 0.1 to 3.0 mass%, Mn: 0.1 to 1.0 mass%, Cu: 5.0 to 25.0 mass %, W: 1.0-20.0 mass%, Sb: 1.0-25.0 mass%, Ni: 20.0 mass% or less, Sn: 2.0 mass% or less Steel with excellent acid corrosion resistance with a layer. The steel materials are C: 0.001 to 0.2 mass%, Si: 0.01 to 2.5 mass%, Mn: 0.1 to 2 mass%, Cu: 0.05 to 0.5 mass%, W: 0.00. 01 to 0.5 mass%, Sb: 0.01 to 0.2 mass%, P: 0.05 mass% or less, S: 0.05 mass% or less, Ni: 0.5 mass% or less, Sn: 0.2 mass% or less The steel material excellent in acid corrosion resistance according to claim 1, wherein the steel material is contained and the balance is made of Fe and inevitable impurities. On the steel material surface, C: 5.0 to 40.0 mass%, Si: 0.1 to 3.0 mass%, Mn: 0.1 to 1.0 mass%, Cu: 5.0 to 25.0 mass%, W: An amorphous oxide layer having a composition containing 1.0 to 20.0 mass%, Sb: 1.0 to 25.0 mass%, Ni: 20.0 mass% or less, and Sn: 2.0 mass% or less is formed. Steel material with excellent acid corrosion resistance.