JPH07316745A - High alloy stainless steel having excellent corrosion resistance in dew point environment simultaneously producing sulfuric acid and hydrochloric acid - Google Patents

Abstract

PURPOSE:To produce a high alloy stainless steel excellent in corrosion resistance environments of sulfuric acid and hydrochloric acid produced at the dew point of acid in an environment of the exhaust gas of a fuel boiler for fossil fuel and city garbage. CONSTITUTION:This high alloy stainless steel consists of a compsn. contg. 12.0 to 16.0% Cr, 28.0 to 30.0% Ni, 1.5 to 3.0% Cu and <=3.0% Mo, simultaneously satisfying >=39 sulfuric acid corrosion resisting index prescribed by GI (H2 SO4)=[Cr]+0.8[Ni]+[Mo]+0.5+[Cu] and >=9 hydrochloric acid corrosion resisting index prescribed by GI(HCI)=-[Cr]+0.7 [Ni]-0.8[Mo]+1.8[Cu], and contg., as impurities, 6<=0.01% C, <=0.5% Si, <=1.0% Mn, <=0.015% P and <=0.01% S, and the balance Fe with inevitable impurities. Thus, the stainless steel having excellent uniform corrosion resistance can be obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high alloy stainless steel having excellent corrosion resistance in a sulfuric acid and hydrochloric acid environment generated by an acid dew point in a combustion boiler exhaust gas environment of fossil fuels and municipal waste.

[0002]

2. Description of the Related Art Conventionally, in a combustion boiler for fossil fuels and municipal waste, a large amount of sulfur dioxide and hydrogen chloride are contained in combustion exhaust gas due to sulfur and chlorine contained in the fuel.
Sulfur dioxide is further oxidized to sulfur trioxide, which raises the dew point of the system together with hydrogen chloride and condenses acidic dew condensation water on the walls of chimneys, flues and flue gas desulfurization equipment. Is known to cause severe general corrosion in acidic environments known as sulfuric acid dew point corrosion and hydrochloric acid dew point corrosion.

In order to prevent sulfuric acid dew point corrosion and hydrochloric acid dew point corrosion of this steel, as a conventional technique, a method of suppressing the generation of sulfur dioxide or hydrogen chloride in terms of operation technology (use of low sulfur content fuel, change of combustion method, Measures such as heat retention at low temperature parts) and adoption of corrosion resistant materials for low temperature members (low alloy steel such as sulfuric acid resistant steel, hydrochloric acid resistant steel and sulfuric acid resistant stainless steel) have been used.

However, in the above-mentioned case, it is difficult to constantly maintain operational management, and it requires a great deal of labor and cost for sorting municipal waste. Under the present circumstances, unexpected corrosion occurs and a large amount of corrosion products are released from the chimney together with the emission of exhaust gas, which is becoming a social problem such as environmental pollution.

As described above, low alloy steel and stainless steel which have been used as materials for chimneys and flues in order to ensure long-term corrosion resistance not only in the sulfuric acid dew point environment but also in the hydrochloric acid dew point environment are sufficient for the equipment. Not suitable as a material that secures corrosion resistance and safety.

[0006]

In view of these circumstances, the present invention newly investigates and analyzes the chimneys and flues of a combustion boiler for fossil fuel and municipal waste that are actually used, and the corrosion obtained by the analysis results. Under the environmental conditions, the effects of Cr, Ni, Mo, and Cu components, which are the main components for improving the corrosion resistance of stainless steel, on the general corrosion are studied in detail, and the effects of each element are clarified. It is an object of the present invention to provide a high alloy stainless steel which is more excellent in general corrosion resistance than alloy steel and stainless steel and is less likely to cause dew point corrosion.

The steel of the present invention is a high alloy stainless steel having excellent general corrosion resistance, which is used in exhaust gas treatment equipment incidental to a combustion boiler for fossil fuels and municipal waste, and chimney / flue equipment, and has a long life. It has become possible to ensure long-term compliance, safety, and environmental pollution prevention.

[0008]

The present invention is based on C, in weight percent.
r: 12.0% or more and 16.0% or less, Ni: 28.0%
Or more, including 30.0% or less, Cu: 1.5% or more and 3.0% or less, Mo: 3.0% or less, and GI (H ₂ SO ₄ ) = [Cr] +0.8 [Ni] + [ Mo] +
Sulfuric acid corrosion resistance index specified by 0.5 [Cu] is 39 or more, GI (HCl) =-[Cr] +0.7 [Ni] -0.8 [M
o] +1.8 [Cu] satisfying the hydrochloric acid corrosion resistance index of 9 or more at the same time,
As impurities, C: 0.01% or less, Si: 0.5% or less, Mn: 1.0% or less, P: 0.015% or less, S:
A high alloy stainless steel having excellent corrosion resistance in a dew point environment in which sulfuric acid and hydrochloric acid are simultaneously produced, which is characterized by containing 0.01% or less and the balance Fe and unavoidable impurities.

The basic feature of the present invention is that in order to secure general corrosion resistance in a dew point environment where sulfuric acid or hydrochloric acid is generated, C
GI based on the composite addition of 4 components of r, Ni, Mo and Cu
That is, the (H ₂ SO ₄ ) value and the GI (HCl) value are regulated. The effect of adding these alloy elements will be described below. The present inventors analyzed the condensed condensed water collected from the exhaust gas chimney and the flue of a fossil fuel / urban waste combustion boiler. As a result, it was clarified that the dew-point environment is mainly composed of condensed sulfuric acid and hydrochloric acid, in which ferric ion, ammonium ion, calcium ion, etc. are mixed. When the boiler is stopped, the temperature of incidental equipment such as a chimney and a flue gradually becomes low, and when the temperature falls to a temperature below the acid dew point, dew condensation water is generated. In such a low temperature part, general corrosion due to condensed water of sulfuric acid and hydrochloric acid becomes a problem.

From the results of the above environmental analysis, the present inventors
Focus on sulfuric acid and hydrochloric acid as factors that control corrosion in dew point environments
In a sulfuric acid aqueous solution and a hydrochloric acid aqueous solution simulating this.
A corrosion weight loss measurement test was performed. That is, 18Cr-1
2Ni-2.5Mo-1Cu composition stainless steel
Steel with different Cr, Ni, Mo, and Cu in the base
Corrosion rate and alloying element composition in the above environment using seeds
The relationship with the amount was obtained by multiple regression analysis, and general corrosion resistance
The corrosion resistance index (GI) was clarified. That conclusion
Fruits, sulfuric acid corrosion resistance index, which is an index of corrosion resistance in sulfuric acid environment:
GI (H₂SO _Four) Is GI (H₂SO_Four) = [Cr] +0.8 [Ni] + [Mo] +
Hydrochloric acid corrosion resistance, which is indicated by 0.5 [Cu] and is an index of corrosion resistance in a hydrochloric acid environment.
Food index: GI (HCl) is GI (HCl) =-[Cr] +0.7 [Ni] -0.8 [M
It has been found that it is given by o] +1.8 [Cu].

These GI values show the general corrosion resistance in sulfuric acid.
The coexistence effect of Cr, Ni, Mo and Cu is effective for improving the property.
N is necessary to improve the general corrosion resistance in hydrochloric acid.
i and Cu are effective, but on the contrary, addition of Cr and Mo is
It shows that the surface corrosion is deteriorated. Like this
Sulfuric acid corrosion resistance index obtained by: GI (H₂SO_Four) And rot
Relationship with food rate and hydrochloric acid corrosion resistance index: GI (HC
The relationship between l) and the corrosion rate is shown in FIG. Resistance to general corrosion
When the food limit is 1 mm / y, GI (H₂S
O _Four) Value is 39 or more, and in hydrochloric acid, CI (HC
If the value of l) is 9 or more, sufficient general corrosion resistance can be secured.
Became clear.

As described above, the corrosion-resistant stainless steel required in the dew-point environment must simultaneously satisfy two general corrosion resistances: sulfuric acid general corrosion resistance and hydrochloric acid general corrosion resistance. Table 1 shows GI (H ₂ S
An example of a material obtained as a high alloy stainless steel having an O ₄ ) value of 39 or more and a GI (HCl) value of 9 or more at the same time is shown. Further, FIG. 2 shows the range of the present invention (area indicated by hatching) in comparison with the conventional steel.

The general corrosion resistance index mentioned here: GI
Is a general term for sulfuric acid corrosion resistance index: GI (H ₂ SO ₄ ) and hydrochloric acid corrosion resistance index: GI (HCl). GI below
The reasons for limiting the components that satisfy the (H ₂ SO ₄ ) value and the GI (HCl) value will be described. Cr: 12.0 to 16.0% Cr is a basic component of the steel of the present invention. Cr improves the sulfuric acid corrosion resistance, but on the other hand, it is a conflicting element that deteriorates the hydrochloric acid corrosion resistance. Therefore, it is necessary to add at least 12% to secure sulfuric acid corrosion resistance, but 16% or less is preferable to secure hydrochloric acid corrosion resistance.

Ni: 28.0-30.0% Ni, together with Cr, is a basic component of the steel of the present invention. Ni is an element that improves corrosion resistance by adding Cu together with sulfuric acid or hydrochloric acid. If it is less than 28%, both sulfuric acid corrosion resistance and hydrochloric acid corrosion resistance cannot be secured at the same time. Also,
Even if added in excess of 30%, the general corrosion resistance is saturated and it becomes economically expensive, so the upper limit was made 30.0%.

Mo: 3.0% or less Mo improves the sulfuric acid corrosion resistance, but on the other hand, it is also an element that deteriorates the hydrochloric acid corrosion resistance. Even if added in excess of 3%, general corrosion resistance is improved, but since Mo is a strong ferrite-forming element, the material becomes brittle and industrial production becomes difficult. It was set to 0.0%.

Cu: 1.5 to 3.0% Cu, together with Cr and Ni, is a basic component of the steel of the present invention.
It is an element that improves the general corrosion resistance by adding Ni together in sulfuric acid or hydrochloric acid. If it is less than 1.5%, both sulfuric acid corrosion resistance and hydrochloric acid corrosion resistance cannot be satisfied at the same time. Further, even if added in excess of 3%, the general corrosion resistance is improved, but the hot workability deteriorates and industrial production becomes difficult, so the upper limit was made 3.0%.

C: 0.01% or less C lowers the better because it precipitates carbides at the grain boundaries of the weld and induces intergranular corrosion. Further, it is preferable that the base material is low in strength, workability and toughness. In order to improve the general corrosion resistance, which is a feature of the present invention, it is limited to an extremely low value of 0.01% or less.

Si: 0.5% or less Si has a deoxidizing effect, but if less than 0.01%, no effect can be expected. Further, if it exceeds 0.5%, the workability is significantly deteriorated. From the viewpoint of workability, the upper limit was set to 0.5%. Mn: 1.0% or less Mn is an element that deteriorates general corrosion resistance, but if it is 1% or less, its adverse effect becomes very small, so the upper limit was made 1.0%.

P: 0.015% or less Since P deteriorates the general corrosion resistance in the above environment, the smaller the content, the better. If it exceeds 0.015%, the general corrosion resistance rapidly deteriorates. S: 0.01% or less Since S deteriorates the general corrosion resistance in the above environment, the smaller the content, the better. If it exceeds 0.01%, the general corrosion resistance is significantly deteriorated.

[0020]

EXAMPLES Table 1 shows the chemical compositions of the steels of the present invention and comparative steels. Electric furnace-AOD and electric furnace-
It was melted by the VAC method. These molten steels were cast into continuous cast slabs under normal conditions. From 1150 ° C to 1250
Soaking treatment was performed at 0 ° C. for 0.5 to 1 hour. After surface cleaning, hot rolling was performed under the conditions for stainless steel. These steels were subjected to solution treatment and then subjected to a test.

Table 2 compares the sulfuric acid corrosion resistance and the hydrochloric acid corrosion resistance of the steel of the present invention and the comparative steel. Corrosion test is 25m
# 3 on the entire surface of the test piece measuring m × 25 mm × 4 mm thick
The wet-polished material up to No. 20 was used and immersed in a 20% sulfuric acid aqueous solution and a 10% hydrochloric acid solution at 80 ° C. for 1 hour. The corrosion rate was converted into the plate thickness from the weight difference before and after the test and displayed.
It is clear from Table 2 that the steel of the present invention is a material that is excellent in both sulfuric acid corrosion resistance and hydrochloric acid corrosion resistance at the same time as compared with the comparative steel.

[0022]

[Table 1]

[0023]

[Table 2]

[0024]

As described above, the conventional steel materials for chimneys, flues, and other incidental equipment are corroded by condensed water containing sulfuric acid and hydrochloric acid generated by burning fossil fuel and municipal waste. Was inevitable. The steel of the present invention has excellent general corrosion resistance even in these acids as compared with the conventional steel, and is economically excellent because it contains the minimum amount of alloying elements.

[Brief description of drawings]

FIG. 1 GI (H ₂ SO ₄ ) and corrosion rate and GI (H
It is a figure which shows the relationship between Cl) and a corrosion rate.

FIG. 2 is a diagram showing a sulfuric acid corrosion resistance index and a hydrochloric acid corrosion resistance index of a conventional steel and a steel of the present invention.

Claims (1)

[Claims] 1. By weight%, Cr: 12.0% or more and 16.0% or less, Ni: 28.0% or more and 30.0% or less, Cu: 1.5% or more and 3.0% or less, Mo: 3.0% or less, and GI (H ₂ SO ₄ ) = [Cr] +0.8 [Ni] + [Mo] +
Sulfuric acid corrosion resistance index specified by 0.5 [Cu] is 39 or more, GI (HCl) =-[Cr] +0.7 [Ni] -0.8 [M
o] +1.8 [Cu] satisfying the hydrochloric acid corrosion resistance index of 9 or more at the same time,
As impurities, C: 0.01% or less, Si: 0.5% or less, Mn: 1.0% or less, P: 0.015% or less, S: 0.01% or less, including the balance Fe and unavoidable impurities. A high-alloy stainless steel that exhibits excellent corrosion resistance in a dew point environment that simultaneously produces sulfuric acid and hydrochloric acid.