JP2005290476A - Low alloy steel having superior corrosion resistances for hydrochloric acid and for sulfuric acid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low alloy steel having superior corrosion resistance, which can be used in such a corrosive environment where dew containing an acid forms as in a refuse incinerator, an industrial waste incineration facility, an oil fired boiler, a funnel and a heat exchanger. <P>SOLUTION: The low alloy steel having superior corrosion resistances for hydrochloric acid and for sulfuric acid comprises, by mass%, 0.2% or less C, 0.5% or less Si, 1.6% or less Mn, 0.03-0.05% P, 0.03% or less S, 0.2-0.6% Cu, 0.05-0.3% Ni, 0.3-0.6% Cr, 0.15-0.45% Mo, 0.005-0.04% Sn, 0.01-0.03% Ti and the balance Fe with unavoidable impurities so that the contents of Cu, Sn, Ni, Cr and Mo can satisfy the relationship: Cu+10Sn+Ni/2+2Cr+3Mo≥1.5. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a low alloy steel excellent in hydrochloric acid corrosion resistance and sulfuric acid corrosion resistance used in a portion through which flue gas combusting heavy oil, coal, industrial waste, garbage, etc. passes, and in particular, hydrochloric acid corrosion resistance. The present invention relates to a low alloy steel having excellent properties.

  In an incinerator or a flue gas facility, a hydrochloric acid substance containing a large amount of hydrogen chloride may be generated in exhaust gas due to chlorine contained in the combustion substance. Hydrogen chloride contained in the exhaust gas becomes liquid and gaseous hydrochloric acid near the dew point, and condensation water and gas containing a lot of hydrochloric acid are condensed on the inner surface of the flue and heat exchanger, etc. Give rise to In addition, sulfur contained in the fuel becomes sulfur trioxide in the exhaust gas, and sulfuric acid corrosion may occur below the dew point temperature.

As measures against such acid dew point corrosion, there are a method of coating the surface of the steel material with a metal having excellent corrosion resistance by spraying or the like, and a method of improving the corrosion resistance of the steel material itself by modifying the steel material.
As the former method, as disclosed in Patent Document 1, a Ni alloy containing appropriate amounts of Cr, Si, Mo, and Cu is coated on the surface of ordinary carbon steel by thermal spraying such as plasma. This is very excellent in resistance to acid dew point corrosion because of the excellent corrosion resistance of the Ni alloy. However, since the manufacturing cost associated with thermal spraying or the coating material itself is expensive, it is difficult to apply to a portion having a large area.

In the latter method, there are two ways of thinking: a material based on so-called low alloy steel and a material based on high alloy steel such as stainless steel. However, high alloy steel contains about 30% by mass of Ni, and the amount of alloying elements is extremely large, which is disadvantageous in terms of cost. Therefore, a material based on low alloy steel is preferable.
As low alloy steel which improved the resistance with respect to acid dew point corrosion, there exist some which were indicated by patent documents 2-5. In Patent Document 2, Cr has an effect of improving corrosion resistance, but in order to promote local corrosion in an environment containing chlorine, the Cr content is reduced as much as possible to improve the corrosion resistance of steel in a combustion exhaust gas environment containing chlorine. P is to improve hydrochloric acid resistance and sulfuric acid resistance, and Mn, Ni, and Mo are toughness to steel materials, etc. In terms of mass%, C: 0.15% or less, Si: 0.07 %: Mn: 0.20-1.50%, P: 0.03-0.15%, S: 0.010% or less, Al: 0.010-0.10%, Cr: 0.10% Hereinafter, a low alloy steel containing Ni: 0.40 to 4.0%, Cu: 0.40% or less, Mo: 0.10 to 1.50%, the balance being Fe and inevitable impurities is disclosed. ing.

  In Patent Document 3, since the combined addition of Cu—Sb—Mg is extremely effective for improving the corrosion resistance, C: 0.003 to 0.15%, Si: 0.05 to 1.2%, Mn: 0.1 to 2.0%, P: 0.05% or less, S: 0.050% or less, Cu: 0.01 to 2.0%, Sb: 0.01 to 0.3%, Al : 0.005 to 0.10%, Mg: 0.0002 to 0.0150% is contained, and the balance is Fe and low alloy steels inevitable impurities are disclosed.

  Patent Document 4 discloses that by adding a very small amount of Mo within a range where the hydrochloric acid corrosion resistance index Al value is positive, the sulfuric acid dew point resistance is ensured while ensuring the sulfuric acid dew point corrosion resistance without making the amount of S extremely low. From the viewpoint that the corrosivity can be greatly improved, C: 0.001 to 0.2%, Si: 0.01 to 2.5%, Mn: 0.1 to 2%, Cu: 0.1 to 1% Mo: 0.001-1%, Sb: 0.01-0.2%, P: 0.05% or less, S: 0.05% or less, and Nb: 0.005-0. 1%, Ta: 0.005 to 0.1%, V: 0.005 to 0.1%, Ti: 0.005 to 0.1%, W: 0.05 to 1%, or one type A low alloy steel containing two or more types, the balance being Fe and inevitable impurities, and having an acid corrosion resistance index of 0 or more is disclosed.

In Patent Document 5, in order to improve workability and weldability, C: 0.07% or less, Si: 1.0% or less, Mn: 0.2 to 1.5%, P: 0.03% or less , S: 0.03% or less, Cu: 0.6% or less, Sb: 0.01 to 0.15%, Ni: 1.0% or less, with the balance being Fe and inevitable impurities Steel is disclosed.
JP-A-9-31576 Japanese Patent Laid-Open No. 11-131179 JP 2000-17382 A JP 2003-213367 A JP 2001-164335 A

Steel materials with higher hydrochloric acid corrosion resistance because industrial waste containing a large amount of plastic waste, such as medical waste, and waste containing a lot of plastic products are incinerated with an incinerator, especially because a large amount of chlorine gas is generated. However, the low alloy steels disclosed in Patent Documents 2 to 5 are still insufficient in terms of hydrochloric acid corrosion resistance.
Accordingly, an object of the present invention is to provide a low alloy steel having excellent acid corrosion resistance and particularly higher hydrochloric acid corrosion resistance.

The present inventor has conducted extensive experiments on the sulfuric acid corrosion resistance and hydrochloric acid corrosion resistance of the low alloy steel component composition. As a result, when Sn and Ti are added, the corrosiveness to hydrochloric acid and sulfuric acid is improved. I found out. Further, it has been found that if a certain relationship is given to the contents of Cu, Sn, Ni, Cr, and Mo, the hydrochloric acid gas corrosion resistance is particularly effective.
That is, Cu, Sn, Ni, Cr, Mo, and Ti are elements that improve acid corrosion resistance, and are elements that are added in combination when obtaining a low alloy steel excellent in acid corrosion resistance. The minimum addition amount and the maximum addition amount are determined for each of these elements. If an appropriate amount is added for each element, the best acid corrosion resistance should be obtained. However, since Ni, Cr, and Mo are expensive, it is desirable to reduce the addition amount if possible. In this case, by determining the addition amount of Ni, Cr, and Mo so as to have a certain relationship with the addition amount of other relatively inexpensive elements such as Cu and Sn, excellent acid corrosion resistance, In particular, it has been found that hydrochloric acid gas corrosion resistance can be obtained.

  From the above, the present invention is mass%, C: 0.2% or less, Si: 0.5% or less, Mn: 1.6% or less, P: 0.03-0.05%, S: 0.03% or less, Cu: 0.2-0.6%, Ni: 0.05-0.3%, Cr: 0.3-0.6%, Mo: 0.15-0.45%, Sn: 0.005-0.04%, Ti: 0.01-0.03%, the balance is Fe and inevitable impurities, and the contents of Cu, Sn, Ni, Cr, Mo are A low alloy steel excellent in hydrochloric acid resistance and sulfuric acid resistance characterized by satisfying the relationship of Cu + 10Sn + Ni / 2 + 2Cr + 3Mo ≧ 1.5%.

  According to the present invention, a low alloy steel having high corrosion resistance in a corrosive environment containing hydrochloric acid and sulfuric acid in a flue, a chimney, a heat exchanger, etc., such as a waste incineration facility, an industrial waste incineration facility or a heavy oil combustion facility. Can be provided.

Next, the reason for limitation to contain the above elements will be described.
C: C ensures the strength of the steel. If it exceeds 0.2%, weldability and toughness are lowered, and sulfuric acid resistance and hydrochloric acid resistance are lowered, so the upper limit is made 0.2%.
Si: Si is contained as a deoxidizer and a strength improving element in the steel making stage. If it is contained excessively, the toughness is remarkably lowered, so the upper limit was made 0.5%.

Mn: Mn is added to ensure the strength of the steel. If the content is excessive, the toughness of the steel decreases, so the upper limit was made 1.6%.
P: P has the effect of improving the corrosion resistance as well as improving the strength of the steel. However, if it is less than 0.03, the effect of improving the corrosion resistance is small. If it exceeds 0.05%, the corrosion resistance is lowered and the toughness of the steel is lowered. Therefore, the range is set to 0.03 to 0.05%. .

S: S is an unavoidable impurity element and adversely affects hydrochloric acid corrosion resistance. In addition, considering the cost for removing S in the steel making process, the upper limit is preferably made 0.03%.
Cu: Since Cu improves corrosion resistance, it is contained in a necessary amount. If it is less than 0.2%, the effect is low, and if it is excessively contained, it becomes harmful to hot workability, so the upper limit was made 0.6%.
Ni: Ni improves the corrosion resistance and toughness of steel. If it is less than 0.05%, the effect is not obtained, and if it is contained in a large amount, the cost increases, so the upper limit was made 0.3%.

Cr: Cr is added in an amount of 0.3% or more in order to improve corrosion resistance, high temperature oxidation resistance, and the like. However, if it is contained in a large amount, the corrosion resistance is rather lowered, so the upper limit was made 0.6%.
Mo: Mo improves corrosion resistance. If it is less than 0.15%, the effect is not obtained. However, if it exceeds 0.45%, the mechanical properties, particularly toughness, are impaired, so the range was made 0.15 to 0.45%.

Sn: Sn is added in a necessary amount for the purpose of improving the corrosion resistance, but if it is less than 0.005%, there is no effect. However, if it exceeds 0.04%, the toughness is lowered, so the range was made 0.005 to 0.04%.
Ti: Ti is added for the purpose of improving corrosion resistance. If it does not contain 0.01% or more, there will be no effect on hydrochloric acid corrosion resistance, and if it exceeds 0.03%, there will be no effect on sulfuric acid corrosion resistance, so the range was made 0.01 to 0.03%.

  Content of Cu, Sn, Ni, Cr, Mo: Cu, Sn, Ni, Cr, and Mo coexist and exhibit excellent acid corrosion resistance. When the content of these elements satisfies Cu + 10Sn + Ni / 2 + 2Cr + 3Mo ≧ 1.5%, the effect particularly excellent in hydrochloric acid gas corrosion resistance is exhibited.

  Examples 1 and 2 and Comparative Examples 1 to 5 having the compositions shown in Table 1 were smelted and made into slabs, and then the slabs were hot rolled to obtain steel plates with a thickness of 25 mm. After rolling, the product was air cooled to room temperature.

実施例品１，２および比較例品１〜５について、塩酸腐食試験、塩酸ガス腐食試験、硫酸腐食試験、排ガス雰囲気中での高温腐食試験、大気雰囲気中での高温腐食試験を行った。これら各試験の条件は次の通りである。

Examples 1 and 2 and Comparative Examples 1 to 5 were subjected to hydrochloric acid corrosion test, hydrochloric acid gas corrosion test, sulfuric acid corrosion test, high temperature corrosion test in exhaust gas atmosphere, and high temperature corrosion test in air atmosphere. The conditions for each of these tests are as follows.

(1) Hydrochloric acid corrosion test (hydrochloric acid corrosion resistance test)
This test was performed by immersing the test steel sheet in a hydrochloric acid solution having a concentration of 20% and a temperature of 80 ° C., and measuring the corrosion rate.
(2) Hydrochloric acid gas corrosion test (hydrochloric acid gas corrosion resistance test)
This test was carried out by exposing the test steel sheet to hydrochloric acid gas having a concentration of 30% and a temperature of 200 ° C. for 50 hours and measuring the corrosion mass.

(3) Sulfuric acid corrosion test (sulfuric acid corrosion resistance test)
This test was performed by immersing the test steel sheet in a sulfuric acid solution having a concentration of 80% and a temperature of 140 ° C., and measuring the corrosion rate.
The results of the hydrochloric acid corrosion test are shown in FIG. 1 in relation to the Cu content, and in FIG. 2 in relation to the Ti content. The results of the hydrochloric acid gas corrosion test are shown in FIG. 3 in relation to the Cr content, in FIG. 4 in relation to the Ti content, and in FIG. 5 in relation to (Cu + 10Sn + Ni / 2 + 2Cr + 3Mo). The results of the sulfuric acid corrosion test are shown in FIG. 6 in relation to the Mo content, in FIG. 7 in relation to the P content, and in FIG. 8 in relation to the Ti content. Hereinafter, the formula of (Cu + 10Sn + Ni / 2 + 2Cr + 3Mo) will be referred to as an effect element addition amount related formula.

As is apparent from FIGS. 1 to 8, Example Products 1 and 2 are superior in Comparative Examples 1 to 5 in hydrochloric acid corrosion resistance, hydrochloric acid gas corrosion resistance, and sulfuric acid corrosion resistance. It is understood that the acid resistance is excellent.
As shown in FIG. 1, Cu improves hydrochloric acid corrosion resistance. As shown in FIG. 3, Cr improves hydrochloric acid gas corrosion resistance. Moreover, Mo and P improve the sulfuric acid corrosion resistance as shown in FIGS.

  On the other hand, Ti improves hydrochloric acid corrosion resistance and hydrochloric acid gas corrosion resistance, as is apparent from FIGS. Further, as shown in FIG. 8, Ti improves the sulfuric acid corrosion resistance. However, if its content is too large, it inhibits the sulfuric acid corrosion resistance. For this reason, in this invention, content of Ti is 0.01 to 0.03% by mass%, and the upper limit is limited to 0.03% by mass to prevent acid resistance from decreasing.

  As described above, Cu, Cr, Mo, P, and Ti improve the acid corrosion resistance of steel. In addition to these Cu, Cr, Mo, P and Ti elements, Sn also improves the acid corrosion resistance of the steel. The figure which shows the relationship between the value (value of an effect element addition related formula) calculated by applying the addition amount (mass%) of Cu, Cr, Mo, Ni, and Sn to an effect element addition related equation and chlorine gas corrosion resistance According to No. 5, Examples 1 and 2 and Comparative Examples 2 and 5 in which the value of the expression related to the amount of addition of the effective element exceeds 1.5% are compared with Comparative Examples 1 and 3 and 4 in terms of hydrochloric acid gas corrosion resistance It is understood that the chlorine gas corrosion resistance can be improved by setting the amount of Cu, Cr, Mo, Ni, and Sn so that Cu + 10Sn + Ni / 2 + 2Cr + 3Mo ≧ 1.5. .

Figure showing the results of hydrochloric acid corrosion test in relation to Cu content Figure showing the results of hydrochloric acid corrosion test in relation to Ti content Figure showing the result of hydrochloric acid gas corrosion test in relation to Cr content Figure showing the results of hydrochloric acid gas corrosion test in relation to Ti content The figure which shows the result of hydrochloric acid gas corrosion test in relation to (Cu + 10Sn + Ni / 2 + 2Cr + 3Mo) Figure showing the result of sulfuric acid corrosion test in relation to Mo content Figure showing the result of sulfuric acid corrosion test in relation to P content Figure showing sulfuric acid corrosion test results in relation to Ti content

Claims (1)

In mass%, C: 0.2% or less, Si: 0.5% or less, Mn: 1.6% or less, P: 0.03-0.05%, S: 0.03% or less, Cu: 0 0.2-0.6%, Ni: 0.05-0.3%, Cr: 0.3-0.6%, Mo: 0.15-0.45%, Sn: 0.005-0.04 %, Ti: 0.01 to 0.03%, the balance being Fe and inevitable impurities, and the content of Cu, Sn, Ni, Cr, Mo is Cu + 10Sn + Ni / 2 + 2Cr + 3Mo ≧ 1.5% Low alloy steel excellent in hydrochloric acid corrosion resistance and sulfuric acid corrosion resistance characterized by satisfying the relationship.

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