CN102021498B - Low-alloy sulfuric acid dew point corrosion resistant steel plate and manufacturing method thereof - Google Patents

Abstract

The invention discloses a low-alloy sulfuric acid dew-point corrosion-resistant steel plate and a manufacturing method thereof. The composition weight percentage ratio (Wt%) of the steel is: C: 0.02%-0.15%, Si: 0.15%-0.55%, Mn: 0.50 %～1.60%, P: ≤0.020%, S: ≤0.020%, Ni: 0.08%～0.30%, Cu: 0.20%～0.60%, Cr: 0.30%～1.50%, Bi: 0.02%～0.30%, Als : 0.015% to 0.045%, the balance being Fe and unavoidable impurities. The steel ingot smelted according to the above ratio is soaked at 1220-1250°C, rolled, and the final rolling temperature is greater than 850°C, and air-cooled after rolling. The present invention is characterized in that it can have good corrosion resistance in the sulfuric acid dew point corrosion environment of the exhaust gas produced by the combustion of high-sulfur fuel. It can be widely used in boiler preheaters and gas-saving equipment that are prone to sulfuric acid dew point corrosion in petroleum, chemical, electric power and other industries, as well as on pipelines and chimneys.

Description

A kind of low alloy sulfuric acid dew point corrosion resistant steel plate and its manufacturing method

technical field

The invention relates to a low-alloy sulfuric acid dew-point corrosion-resistant steel plate, in particular to a steel plate with good corrosion resistance and a manufacturing method thereof in a sulfuric acid dew-point corrosion environment generated by combustion of high-sulfur fuel.

Background technique

In the installations of petroleum, chemical industry, electric power and other industries, resistance to sulfuric acid dew point corrosion generally appears in boiler preheaters and gas-saving equipment, as well as transmission pipelines and stacks. The fuel used in boilers, such as heavy oil and coal, contains a large amount of sulfur (S), which is decomposed into sulfur dioxide (SO ₂ ) and sulfur trioxide (SO ₃ ) by combustion, and combines with water vapor at the dew point temperature to become sulfuric acid (H ₂ SO ₄ ) The change from thin to thick has a strong corrosive effect on equipment.

Sulfuric acid dew point resistant steel is a kind of steel resistant to both sulfuric acid dew point corrosion and atmospheric corrosion. Sulfuric acid dew point corrosion-resistant steel alloy composition design Following the weathering steel born in the United States in 1933, the research on the dew point condensation of sulfuric acid found that CORTEN steel containing certain alloy elements such as Cu, P, Cr, and Ni has certain corrosion resistance. This was the starting point for the first use of this low-alloy steel in the air preheater of a boiler. It was initially found that adding 0.2% to 0.5% copper to steel can greatly improve the corrosion resistance of steel to various concentrations of sulfuric acid, and copper has become one of the basic components of sulfuric acid dew point corrosion resistant steel.

The sulfuric acid dew point corrosion-resistant steel developed in Japan is mainly divided into two categories according to the use environment: (1) with 0.2% ~ 0.5% Cu, > 0.010% S as the matrix, adding a small amount of Sn and Sb elements, and its compounds become reactive to hydrogen Inhibitor; (2) For the IV corrosion environment of high temperature and high concentration sulfuric acid, it is developed based on Cu, Cr or Cu, Cr, Ni of the same system as CORTEN steel. As stated in the Japanese Patent Publication No. 43-14585, the composite addition of Cu and Sb has the ability to resist sulfuric acid dew point corrosion and has been proven in application.

Domestic research and development of sulfuric acid dew-point corrosion-resistant steel started relatively late, and the composition system and use standards generally refer to Japanese steel grades, among which B485NL of Baosteel Co., Ltd., 10Cr1Cu of Anshan Iron and Steel Co., Ltd., and ND (09CuCrSb) of Jiangyin Special Steel are generally used for reference. Steel, 12MnCuCr of Jinan Iron and Steel Co., Ltd. and NS sulfuric acid dew point corrosion resistant steel products of Baosteel No. 1 Steel Company.

Aiming at the problem of sulfuric acid dew point corrosion, corrosion-resistant steel in sulfuric acid environment has been developed at home and abroad. As stated in the Special Publication No. 43-14585, the compound addition of Cu and Sb has the performance of sulfuric acid dew point corrosion resistance and has been proved by application. China's "sulfuric acid dew point resistance Low-alloy steel 09CuCrSb (ND steel) for corroded seamless steel pipes" (public number: 03130825.2) and above, although the alloy ratio of corrosion-resistant elements is considered, the processing performance of the steel is affected due to the Sb element; CORTEN steel in the United States and domestic B485NL of Baosteel Co., Ltd., 10CrlCu of Anshan Iron and Steel Co., Ltd., and 12MnCuCr of Jinan Iron and Steel Co., Ltd. are Cr and Cu-based steels (publication number: 90101258.0). Its corrosion resistance is not ideal in the environment of high sulfur fuel.

For high-sulfur fuels with a sulfur content of more than 2%, when the sulfur content increases, the concentration of sulfuric acid in the exhaust increases, and as the temperature decreases, the condensation of sulfuric acid increases, which is much harsher than that of low-sulfur fuels. The corrosion resistance to steel is also stronger. Therefore, it can play a corrosion-resistant steel grade in a relatively mild environment with less than 2% sulfur, and it is difficult to achieve the role of corrosion resistance in an environment with high-sulfur fuel.

As mentioned above, there is no more suitable production technology for the desired steel plate that can exhibit good corrosion resistance no matter under the condition of low sulfur or high sulfur (sulfur content exceeds 2%).

Contents of the invention

The present invention aims at the problems existing in the sulfuric acid dew point corrosion-resistant steel plate, and provides a steel plate with good corrosion resistance and a manufacturing method in a sulfuric acid dew point corrosion environment of sulfuric acid dew point corrosion generated by combustion of fuel containing high sulfur.

Its composition weight percentage distribution ratio (Wt%) of steel of the present invention is:

C: 0.02%～0.15%, Si: 0.15%～0.55%, Mn: 0.50%～1.60%, P: ≤0.020%, S: ≤0.020%, Ni: 0.08%～0.30%, Cu: 0.20%～0.60 %, Cr.0.30%-1.50%, Bi: 0.02%-0.30%, Als: 0.015%-0.045%, and the balance is Fe and unavoidable impurities.

One or two or more trace elements such as Nb, Ti and V can also be added to the steel composition of the present invention, the total amount not exceeding 0.22%.

The production process of the steel plate is:

The steel ingot smelted according to the above ratio is soaked at 1220-1250°C, rolled, and the final rolling temperature is greater than 850°C, and air-cooled after rolling. It can be used to produce low alloy sulfuric acid dew point corrosion resistant steel plate.

Due to the addition of Bi to the alloy of the present invention, it forms a dense oxide film on the surface that is several times higher than that of the matrix and is rich in elements such as Bi, Ti, Cu, Cr, etc., so it has high resistance to sulfuric acid dew point corrosion and corrosion. Application confirmed; play an unexpected effect.

The addition of specific elements of the invention is explained as follows:

For the selection of C element, the maximum carbon content should not exceed 0.30% by weight percentage. C element is a strengthening element, and low carbon content will damage the strength of the material. The carbon content is selected at 0.02% to 0.15%. The reduction of carbon content, on the one hand, is conducive to improving the toughness, and at the same time, it can significantly improve the welding performance of the steel plate.

Si strengthening element is dissolved in ferrite to improve the yield strength of steel, if it is less than 0.15%, it will increase the cost of steelmaking process. More than 0.50%, in this combination of ingredients, it is easy to cause the slab to produce recycled iron scale that is difficult to remove, which will affect the surface quality of the finished steel plate. Therefore, it is determined that its range is 0.15% to 0.55%.

Mn is mainly dissolved in ferrite to strengthen and improve the hardenability of steel, and it is an element that must exist in steel during smelting. Its content range is determined according to the strength level to be achieved, but making it less than 0.15% requires high smelting and increases costs. However, when the content is too high, it is easy to cause segregation, so the range is determined to be 0.50% to 1.60%.

P tends to cause segregation and is detrimental to weldability and formability. In order to ensure the requirements of weldability and formability, the present invention controls it to be less than 0.020%.

S is a harmful element. From the perspective of mechanical properties, the lower the better, but too low will lead to increased process costs. The present invention controls it to be less than 0.020%.

Ni is a precious metal element, which improves hardenability, increases the strength of steel without reducing its toughness, and the scope of its obvious corrosion resistance is more than 1.0%. Appropriate addition of this element can also prevent Cu on the surface of the slab when it is heated. crack phenomenon. In order to control costs, the range is limited to 0.08% to 0.30%.

Cu has a good effect on improving corrosion resistance, and the necessary content is 0.20%, but if the content exceeds 0.60%, its effect is saturated, so the range is limited to 0.20% to 0.60%.

Cr is an element that strongly improves hardenability and is a strong carbide forming element. It is used in conjunction with Cu to improve the corrosion resistance of steel. The necessary amount is 0.30%, so the content range is limited to 0.30% to 1.50%.

Bi is an effective element for improving corrosion resistance. It forms a dense oxide film on the surface that is several times higher than that of the matrix and is rich in Bi, Ti, Cu, Cr and other elements, so it has high resistance to sulfuric acid dew point corrosion corrosion; low It has no effect at 0.01%, and more than 0.30% has a tendency of thermal processing deterioration, so its content is preferably between 0.01% and 0.30%.

Als is a traditional nitrogen-fixing element, and the formation of AlN can refine the austenite grains, so its content range is limited to 0.015% to 0.045%.

Ti is a strong carbonitride forming element, and the formation of TiN and TiC can prevent the growth of austenite grains and refine the austenite grains during soaking and reheating. It is preferable to limit its content range to 0.010-0.050%.

The characteristic of the production process of the present invention is that the heating temperature is limited to 1230±20°C, and the rolling is carried out in the austenite recrystallization zone and the non-recrystallization zone. The oxidation loss of the billet is large. Therefore, the heating temperature is determined to be 1230±20°C; the starting rolling temperature is limited to above 1200°C, the steel has good plasticity, low strength, and is easy to roll. Poor shape will affect the normal progress of the next process.

The final rolling temperature is greater than 850°C, and air-cooled after rolling. When the final rolling temperature is higher than 950℃, the grain refinement is insufficient, which affects the strengthening effect. Below 850°C, the load on the rolling mill will increase. However, the difference in the horizontal and vertical properties of the steel plate becomes larger.

The present invention is characterized in that it can have good corrosion resistance in the sulfuric acid dew point corrosion environment of the exhaust gas produced by the combustion of high-sulfur fuel. It overcomes the shortcomings of traditional low-alloy sulfuric acid dew-point corrosion-resistant steels that cannot exert sufficient corrosion resistance in equipment using high-sulfur fuels with a sulfur content exceeding 2%, and can be widely used in equipment in petroleum, chemical, electric power and other industries. Sulfuric acid dew point corrosion on boiler preheaters and gas saving equipment, as well as on delivery pipes and chimneys.

Detailed ways

Its composition weight percent (Wt%) of steel of the present invention is:

C: 0.02%～0.15%, Si: 0.15%～0.55%, Mn: 0.50%～1.60%, P: ≤0.020%, S: ≤0.020%, Ni: 0.08%～0.30%, Cu: 0.20%～0.60 %, Cr: 0.30% to 1.50%, Bi: 0.02% to 0.30%, Als: 0.015% to 0.045%, and the balance is Fe and unavoidable impurities.

One or two or more trace elements such as Nb, Ti and V can also be added to the steel composition of the present invention, the total amount not exceeding 0.22%.

The production process of the steel plate is:

The steel ingot smelted according to the above ratio is soaked at 1220-1250°C, rolled, and the final rolling temperature is greater than 850°C, and air-cooled after rolling. It can be used to produce low alloy sulfuric acid dew point corrosion resistant steel plate.

According to the composition ratio of the steel technical scheme of the present invention, 80kg is used for smelting and rolling in the laboratory.

The chemical composition is shown in Table 1, 2.

Table 1 Comparison of similar products and steel composition of the present invention (surplus is Fe)

Table 3 Contrast steel and actual performance of steel of the present invention

Rel(MPa) Rm(MPa) A(%) KV ₂ (20℃)(J) 70℃, 50% H2SO4 solution, corrosion rate (g/m ² .h) Contrast Steel 1 385 542 25.6 63 25.0 Contrast Steel 2 320 430 38.0 - 11.4 Example 1 385 530 26.0 115 8.58 Example 2 370 490 29.5 180 5.21 Example 3 390 575 26.5 266 4.61 Example 4 420 510 32.0 223 5.10 Example 5 400 525 26.0 177 3.88

Table 4 steel production process of the present invention

serial number Heating temperature ℃  Rolling temperature °C  Finish rolling temperature ℃ Example 1 1230 ＞1200 860 Example 2 1220 ＞1200 880 Example 3 1225 ＞1200 850 Example 4 1250 ＞1200 890 Example 5 1235 ＞1200 860

Claims (2)

1. a low-alloy steel resisting dew-point corrosion of sulfuric acid plate, is characterized in that, moiety is by weight percentage:

C:0.04%, Si:0.53%, Mn:1.49%, P:0.010%, S:0.006, Ni:0.30%, Cu:0.26%, Cr:1.2%, Bi:0.15%, Als:0.045%, Nb:0.048, V:0.030, surplus is Fe and inevitable impurity, impelling strength 177J during 20 ℃ of its steel plate, at 70 ℃, 50%H ₂sO ₄under solution, erosion rate 3.88g/m ².h.

2. the manufacture method of a kind of low-alloy steel resisting dew-point corrosion of sulfuric acid plate as claimed in claim 1, is characterized in that: the steel ingot after smelting by said ratio is 1235 ℃ of soaking, and start rolling temperature is more than 1200 ℃, and 860 ℃ of finishing temperatures, roll rear air cooling.