CN104838029A - Steel material having excellent alcohol-induced pitting corrosion resistance and alcohol-induced SCC resistance - Google Patents

Abstract

By configuring the steel composition as follows, a steel with excellent resistance to alcohol-induced pitting corrosion and alcohol-induced SCC is provided. The inherent resistance to pitting corrosion and SCC of the steel is improved, so the steel can be used for large structures without electroplating or the addition of corrosion inhibitors. The composition is as follows: by mass%, it contains 0.03-0.3% C, 0.01-1.0% Si, 0.1-2.0% Mn, less than 0.03% P, less than 0.01% S and less than 0.1% Al, and contains one or two of the following: 0.03-1.0% Mo and 0.03-1.0% W, and at least two of the following: 0.005-0.5% Sb, 0.01-0.3% Sn and 0.005-0.1% Nb, with the balance being Fe and unavoidable impurities.

Description

Steel with excellent resistance to alcohol-induced pitting corrosion and alcohol-induced SCC

technical field

The present invention relates to a steel material excellent in alcohol-induced corrosion resistance, especially excellent in alcohol-induced pitting corrosion resistance and alcohol-induced SCC resistance.

In particular, the present invention relates to a steel material excellent in alcohol-induced pitting corrosion resistance and alcohol-induced SCC resistance. The steel material is suitable for use in parts that are in direct contact with bioalcohols. The steel material is used for storing bioalcohols such as bioethanol. Steel used in tanks, inner tanks of ships for transportation purposes, steel used in tanks for automobiles, or steel used for pipeline transportation, etc.

Background technique

Among bioalcohols, for example, bioethanol is produced mainly by decomposing and purifying sugar substances contained in corn, wheat, and the like. In recent years, bioethanol has been widely used around the world as an alternative fuel to petroleum (gasoline) and as a fuel mixed with gasoline, and its usage tends to increase year by year.

Therefore, in the process of storing and transporting bioethanol or the process of mixing with gasoline, although the amount of bioethanol to be treated is gradually increasing, the localized corrosion of bioethanol is high, and pitting corrosion (pitting) and SCC (stress corrosion) are particularly likely to occur. Corrosion cracking, stress corrosion cracking), which makes it difficult to operate it.

In the case of bioethanol, acetic acid and chloride ions are present as extremely small amounts of impurities in the production process, and absorb water and take in dissolved oxygen during storage, which is one of the causes of increased corrosion.

Therefore, there is the following defect: it is necessary to utilize equipment that has been implemented for ethanol-resistant measures (for example, as the tank body, in order to use an organic coating material, stainless steel, stainless composite steel (stainless steel) that is resistant to ethanol-induced SCC, and is excellent. clad steel) for safe handling. In addition, there is also the problem that existing oil pipelines cannot be used for transportation.

As mentioned above, there is still a problem in that equipment for processing bioethanol requires a huge cost.

As a method to solve the above-mentioned problems, for example, Patent Document 1 proposes the following method for biofuels: zinc-nickel (containing 5 to 25% Ni) plating is performed on steel materials for biofuel tanks, or on the basis of this electroplating Carry out chemical conversion treatment without hexavalent chromium. This method is considered to improve the corrosion resistance of steel materials in ethanol-containing gasoline.

In addition, Patent Document 2 proposes a steel sheet for pipes having excellent corrosion resistance with respect to fuel vapor such as bioethanol, in which the surface of the steel sheet is subjected to a treatment of "relative to Zn in the plating layer Zn-Co-Mo plating with a Co composition ratio of 0.2 to 4.0 at%.

In addition, in Non-Patent Document 1, the corrosion inhibitor (inhibitor) effect of ammonium hydroxide on SCC (stress corrosion cracking) of steel materials in a bioethanol simulated liquid was investigated, and it was reported that by adding ammonium hydroxide, it is possible to inhibit Crack growth and relaxation of SCC.

Patent Document 1: Japanese Patent Laid-Open No. 2011-26669

Patent Document 2: Japanese Patent Laid-Open No. 2011-231358

Non-Patent Document 1: F.Gui, J.A.Beavers and N.Sridhar, Evaluation ofammonia hydroxide for mitigating stress corrosion cracking of carbonsteel in fuel grade ethanol, NACE Corrosion Paper, No.11138(2011)

Contents of the invention

It is considered that the zinc-nickel plating disclosed in Patent Document 1 is effective in improving corrosion resistance. However, since the Zn-Ni plating requires electroplating treatment, even if there is no problem with small fuel tanks for automobiles, for example, large structures (such as storage tanks, pipelines, etc. with a thickness of more than 1000kL) For wall steel), it cannot be applied due to the huge processing cost. In addition, when defective plating etc. occur, pitting corrosion tends to progress rather easily in this part, and SCC tends to generate|occur|produce easily, Therefore, it cannot be said that it is sufficient from the point of view of pitting corrosion resistance and SCC resistance.

The Zn—Co—Mo plating disclosed in Patent Document 2 still needs to be treated by electroplating. Therefore, for the same reason as Patent Document 1, it cannot be applied to thick-walled steel materials of large structures. Also, for the same reason as Patent Document 1, it cannot be said to be sufficient from the viewpoint of pitting resistance and SCC resistance.

Furthermore, in the description of Non-Patent Document 1, although the addition of a corrosion inhibitor certainly alleviates corrosion phenomena such as SCC, it cannot be said that the effect is sufficient. This is because the corrosion inhibitor exerts its effect by being adsorbed on the surface, but its adsorption behavior is greatly affected by the surrounding pH and the like. Therefore, when corrosion occurs locally, the adsorption may not be sufficient. In addition, there is a risk of contamination due to the leakage of the corrosion inhibitor into the environment, and it is difficult to say that the method of Non-Patent Document 1 is an appropriate anti-corrosion measure.

From the above, the anticorrosion method using electroplating is not suitable for large-scale structures, and the effect in terms of pitting corrosion resistance is not sufficient. In addition, the effect of corrosion inhibitors on average to reduce corrosion is not sufficient. Therefore, improving the corrosion resistance of steel itself in bioethanol is also advantageous in terms of cost in terms of application to large structures.

The present invention advantageously responds to the above-mentioned needs, and its purpose is: by improving the corrosion resistance of the steel itself, especially the pitting corrosion resistance and SCC resistance, it can be applied to steel without electroplating treatment and without adding corrosion inhibitors. A steel material with excellent alcohol-induced pitting resistance and alcohol-induced SCC resistance for large structures.

Therefore, in order to solve the above-mentioned problems, the inventors of the present application repeatedly studied the corrosion phenomenon of steel materials in a bioethanol simulated solution.

As a result, it was found that the addition of Mo and W was effective in inhibiting corrosion, especially pitting corrosion and SCC in bioethanol, and in addition, by adding Sb, Sn, Nb in addition to the addition of Mo and W, the Pitting and SCC were significantly inhibited.

The present invention is based on the above findings.

That is, the main configuration of the present invention is as follows.

1. A steel with excellent resistance to alcohol-induced pitting corrosion and alcohol-induced SCC, said steel containing the following components in mass %:

C: 0.03～0.3%,

Si: 0.01 to 1.0%,

Mn: 0.1 to 2.0%,

P: less than 0.03%,

S: 0.01% or less, and

Al: less than 0.1%,

and contain one or two of the following ingredients:

Mo: 0.03 to 1.0%, and

W: 0.03～1.0%,

Also contains at least 2 selected from the following ingredients:

Sb: 0.005～0.5%,

Sn: 0.01 to 0.3%, and

Nb: 0.005～0.1%,

The balance is Fe and unavoidable impurities.

2. The steel product as described in the above 1, wherein, in terms of mass%, the total amount of Mo, W, Sb, Sn, and Nb satisfies the range of 0.15%≤(Mo+W+Sb+Sn+Nb)≤1.0%, In addition, the total amount of Mo and W satisfies 0.08%≦(Mo+W) in mass%.

3. The steel material according to the above 1 or 2, wherein the steel material further contains Ca in a range of 0.01% or less in mass%, and satisfies the condition of Ca/S≧0.5.

4. The steel material according to any one of 1 to 3 above, wherein the steel material further contains B: 0.0002 to 0.03% in mass %.

5. The steel product as described in any one of the above 1 to 4, wherein, in mass %, the steel product further contains one or two or more selected from the following components:

Zr: 0.005～0.1%,

V: 0.005～0.1%, and

Ti: 0.005 to 0.1%.

According to the present invention, when used as steel materials for bioethanol storage tanks, transportation tanks, and pipelines, compared with existing steel materials, it can be used for a longer period of time, and it is possible to avoid pitting corrosion and SCC causing biological damage. Accidents caused by ethanol leakage, and the above-mentioned various facilities can be provided at low cost, which is extremely useful industrially.

Detailed ways

Hereinafter, the present invention will be specifically described.

First, the reason why the component composition of the steel material is limited to the above-mentioned range in the present invention will be described. In addition, the unit of the element content in the component composition of a steel material is "mass %", and below, unless otherwise specified, it will only be shown by "%".

C: 0.03 to 0.3%

C is an element necessary to ensure the strength of steel. In the present invention, in order to ensure the target strength (400MPa or more), it is set to contain at least 0.03% of C. On the other hand, if the content of C exceeds 0.3%, the weldability will deteriorate. If it is lowered, there will be more restrictions on welding, so 0.3% is set as the upper limit. It is preferably in the range of 0.03 to 0.2%.

Si: 0.01 to 1.0%

Si is an element added for deoxidation. When the content is less than 0.01%, the deoxidation effect is insufficient. On the other hand, if it is more than 1.0%, the toughness and weldability will be deteriorated. Therefore, the content of Si is set to 0.01. ~1.0%. It is preferably in the range of 0.05 to 0.5%.

Mn: 0.1 to 2.0%

Mn is an element added to improve strength and toughness. When the content is less than 0.1%, the effect is insufficient. On the other hand, if it exceeds 2.0%, the weldability will deteriorate. Therefore, the content of Mn is set to 0.1%. ~2.0%. It is preferably in the range of 0.3 to 1.6%.

P: less than 0.03%

P is an element contained as an unavoidable impurity, and since it degrades toughness and weldability, the P content is suppressed to 0.03% or less. Preferably it is 0.025% or less. In addition, since excessive dephosphorization leads to an increase in cost, it is preferable to set the lower limit to 0.0003%. Therefore, it is preferably in the range of 0.0003 to 0.03%.

S: less than 0.01%

S is also an element contained as an unavoidable impurity. If the content becomes higher, not only the toughness and weldability will decrease, but also the inclusions such as MnS will increase, which will become the starting point of SCC and reduce the SCC resistance. Therefore, it is desirable to reduce the SCC resistance as much as possible. The S content is acceptable as long as it is 0.01% or less. In addition, since excessive desulfurization leads to an increase in cost, it is preferable to set the lower limit to 0.0001%. Therefore, it is preferably in the range of 0.0001 to 0.01%.

Al: 0.100% or less

Al is an element added as a deoxidizer, and if it is contained at a content higher than 0.100%, the toughness of the welded metal part will decrease when welding is performed, so it is limited to 0.100% or less. In addition, from the viewpoint of securing the deoxidation effect, it is preferable to set the lower limit to 0.005%. More preferably, it exists in the range of 0.005-0.070%.

One or two selected from 0.03 to 1.0% of Mo and 0.03 to 1.0% of W

Mo: 0.03 to 1.0%

In the steel material of the present invention, Mo is an important element for improving pitting resistance and SCC resistance. Since Mo forms an oxysalt as a corrosion product, it has an effect that when a crack (which will become the starting point of stress corrosion cracking) occurs, the corrosion product quickly protects the front of the crack and suppresses the growth of the crack. In addition, by incorporating Mo into the oxide film on the surface of the steel material, the dissolution resistance of the oxide film in an acidic environment caused by acetic acid contained as an impurity in bioethanol is improved, uneven corrosion is reduced, and at the same time, it also serves as an inhibition point erosion effect. However, if the content is less than 0.03%, the effect of improving pitting resistance and SCC resistance is insufficient. On the other hand, if it exceeds 1.0%, it is disadvantageous in terms of cost. Therefore, the content of Mo is set to 0.03 to 1.0%. . In addition, in order to further prevent cost increase, it is preferable to set it in the range of 0.03-0.5%.

W: 0.03～1.0%

In the steel material of the present invention, W is an important element for improving pitting resistance and SCC resistance. Since W and Mo will also form oxo acid salts as corrosion products, they have the following effects: when a crack (which will become the starting point of stress corrosion cracking) occurs, the corrosion product quickly protects the front of the crack and inhibits development of cracks. In addition, by incorporating W into the oxide film on the surface of the steel material, the dissolution resistance of the oxide film in an acidic environment caused by acetic acid contained as an impurity in bioethanol is improved, uneven corrosion is reduced, and at the same time, it also serves as an inhibition point erosion effect. However, if the content is less than 0.03%, the effect of improving pitting resistance and SCC resistance is insufficient. On the other hand, if it exceeds 1.0%, it is disadvantageous in terms of cost. Therefore, the content of W is set at 0.03 to 1.0%. . In order to further prevent cost increase, it is preferable to set it within the range of 0.03 to 0.5%.

At least two selected from 0.005 to 0.5% of Sb, 0.01 to 0.3% of Sn, and 0.005 to 0.1% of Nb

Sb: 0.005～0.5%

Sb is an element effective in improving pitting resistance and SCC resistance in an acidic environment caused by acetic acid contained as an impurity in bioethanol. However, when the content is less than 0.005%, there is no such effect. On the other hand, when it is more than 0.5%, there will be restrictions on steel production. Therefore, the content of Sb is set within the range of 0.005 to 0.5%. It is preferably in the range of 0.01 to 0.3%.

Sn: 0.01～0.3%

Like Sb, Sn also improves pitting corrosion resistance and SCC resistance in acidic environments, but when the content is less than 0.01%, the addition effect is insufficient. On the other hand, when it is more than 0.3%, the effect is saturated, and steel Due to manufacturing constraints, the Sn content is set within a range of 0.01 to 0.3%. It is preferably in the range of 0.02 to 0.2%.

Nb: 0.005～0.1%

Nb is also an element effective in improving pitting corrosion resistance and SCC resistance in an acidic environment caused by acetic acid. However, when the content is less than 0.005%, the effect is not exhibited. On the other hand, if it is more than 1.0%, the mechanical properties of the welded part will be reduced. Therefore, the content of Nb is set within the range of 0.005 to 0.1%. It is preferably in the range of 0.005 to 0.05%.

For the present invention, among the above-mentioned components, Mo, W, and Sb, Sn, and Nb are particularly important, and by containing the above-mentioned elements in a total amount of 0.15 to 1.0%, and containing the total amount of Mo and W, which are particularly important at 0.08% or more, can further improve pitting resistance and SCC resistance.

As mentioned above, although basic components were demonstrated, in addition to this, this invention can contain the following components suitably as needed.

Ca: less than 0.01%, and Ca/S≥0.5

Ca is an element added for the purpose of controlling the morphology of precipitates of S (which is an unavoidable impurity) (MnS and the like) and preventing cracking of SCC and the like. Therefore, it is preferable to add Ca according to the amount of S, and by setting Ca/S (mass ratio) to 0.5 or more, an effect of preventing cracking can be produced. More preferably, it is 1.0 or more. However, if added in excess, coarse inclusions will be formed and the toughness of the base material will be deteriorated, so it is preferable to set the upper limit of the amount of Ca to 0.01%.

B: 0.0002～0.03%

B is an element that increases the strength of the steel material, and may be contained as necessary. In order to obtain the above effects, it is preferable to contain 0.0002% or more of B, but on the other hand, if the added amount exceeds 0.03%, the toughness will deteriorate. Therefore, it is preferable to contain B in the range of 0.0002 to 0.03%. More preferably, it exists in the range of 0.0003 to 0.003%.

Zr: 0.005-0.1%, V: 0.005-0.1%, Ti: 0.005-0.1%

Furthermore, in order to improve the mechanical properties of the steel material, one or two or more selected from Zr, V, and Ti may be contained. For any of these elements, when the content is less than 0.005%, the addition effect is insufficient. On the other hand, if it is more than 0.1%, the mechanical properties of the welded part will be reduced. Therefore, their content is set at In the range of 0.005 to 0.1%. In addition, it is preferable to exist in the range of 0.005-0.05%.

Furthermore, as long as the effect of this invention is not impaired, it is permissible to contain components other than the above-mentioned components. For example, in addition to these components, a small amount of REM can also be added as a deoxidizer.

In the steel material of the present invention, components other than the above-mentioned components are Fe and unavoidable impurities.

Next, a suitable manufacturing method of the steel material of the present invention will be described.

Melt molten steel having the above-mentioned suitable composition in known furnaces such as converters and electric furnaces, and use known methods such as continuous casting and ingot casting to produce slabs, billets, etc. raw steel. In addition, at the time of smelting, vacuum degassing refining, etc. can be implemented.

The method for adjusting the composition of molten steel can be in accordance with known steel smelting methods.

Then, when the above-mentioned raw material steel is hot-rolled into a desired size and shape, it is heated to a temperature of 1000 to 1350°C. When the heating temperature is lower than 1000° C., deformation resistance becomes large, and hot rolling becomes difficult. On the other hand, heating higher than 1350° C. may cause surface scratches or increase scale loss and fuel consumption rate. It is preferably in the range of 1050 to 1300°C. In addition, when the temperature of raw material steel exists in the range of 1000-1350 degreeC from the beginning, it can provide it for hot rolling as it is without heating.

In addition, in hot rolling, it is necessary to make the finish temperature of hot rolling suitable, and it is preferable to make it 600 degreeC or more and 850 degreeC or less. When the finishing temperature of the hot finish rolling is lower than 600°C, the increase of the deformation resistance increases the rolling load, and the rolling is difficult to implement. On the other hand, when it exceeds 850 degreeC, desired intensity|strength may not be acquired. The cooling after the hot finish rolling is preferably air cooling or accelerated cooling with a cooling rate of 150° C./s or less. It is preferable to make the cooling stop temperature at the time of accelerated cooling in the range of 300-750 degreeC. It should be noted that after cooling, reheating treatment may be performed.

Example

Next, examples of the present invention will be described. It should be noted that the present invention is not limited to these Examples.

For molten steel having the composition shown in Table 1, slabs were produced by continuous casting after melting in a vacuum melting furnace or converter melting. Then, after heating to 1230° C., hot rolling was performed at a finish rolling finish temperature of 820° C. to obtain a 13 mm-thick steel plate.

These steel sheets were subjected to the following pitting corrosion test and stress corrosion cracking test.

(1) Pitting corrosion test using bioethanol simulant solution

Cut the steel material into 10mm×25mm×3.5mm t, use emery paper to wet grind both sides to #2000, perform ultrasonic degreasing in acetone for 5 minutes, and use it as corrosion test material after air drying. As a bioethanol simulation liquid, a solution obtained by adding 10 ml of water, 5 ml of methanol, 560 mg of acetic acid, and 132 mg of NaCl to 985 ml of ethanol was used. This solution was filled into a test tube, and the test material was impregnated at room temperature. After immersion for 30 days, the test material was taken out, and the rust adhering to the surface was washed away with a sponge, etc., and the corrosion products were removed in acid with a corrosion inhibitor added. Then, after washing with pure water, it washed with ethanol and air-dried. Then, the pitting depth on the surface of the experimental material was measured using a stereo laser microscope, and the maximum pitting depth was evaluated.

In addition, if the above-mentioned maximum pitting depth is less than 70% of the maximum pitting depth of base steel (comparative example 1), it is evaluated that the pitting resistance is excellent.

(2) SSRT (slow strain rate method) stress corrosion cracking test in bioethanol simulated liquid

The steel material was processed into a round bar of 130mm×6.35mmΦ, thread cutting was performed on both ends, and at the same time, 3.81mmΦ was processed at intervals of 12.7mm from the center of the round bar. The experimental material was ultrasonically degreased in acetone for 5 minutes and then installed in the SSRT testing machine. As a bioethanol simulation liquid, a solution obtained by adding 10 ml of water, 5 ml of methanol, 56 mg of acetic acid, and 52.8 mg of NaCl to 985 ml of ethanol was used. A strain was applied at a strain rate of 2.54×10 ^-5 mm/s in a dry air atmosphere under the conditions of filling and not filling the bioethanol simulant liquid into the tank covering the test material. Then, the ratio of the total elongation until fracture ([total elongation with solution/total elongation without solution]×100(%)) was calculated, and the SCC resistance was evaluated using the following criteria .

◎: More than 95%

○: More than 90% and less than 95%

△: More than 85% and less than 90%

×: Less than 85%

The obtained results are described in Table 2.

[Table 1]

[Table 2]

Table 2

From Table 2, it can be confirmed that, in the invention examples, the pitting corrosion in the bioethanol simulant liquid was suppressed, and the SCC resistance was also greatly improved. On the other hand, in the comparative examples (the composition of which is outside the scope of the invention), the pitting depth could not be suppressed to the same extent as the inventive examples, and a large improvement in SCC resistance was not observed.

It can be seen from the comparison between the inventive example and the comparative example that the improvement effect of the present invention is obvious.

Claims (5)

1. A steel with excellent resistance to alcohol-induced pitting corrosion and alcohol-induced SCC, said steel containing the following components in mass %: C: 0.03～0.3%, Si: 0.01 to 1.0%, Mn: 0.1 to 2.0%, P: less than 0.03%, S: 0.01% or less, and Al: less than 0.1%, and contain one or two of the following ingredients: Mo: 0.03 to 1.0%, and W: 0.03～1.0%, Also contains at least 2 selected from the following ingredients: Sb: 0.005～0.5%, Sn: 0.01 to 0.3%, and Nb: 0.005～0.1%, The balance is Fe and unavoidable impurities. 2. The steel product according to claim 1, wherein, in terms of mass%, the total amount of Mo, W, Sb, Sn, and Nb satisfies the range of 0.15%≤(Mo+W+Sb+Sn+Nb)≤1.0% , and, in terms of mass%, the total amount of Mo and W satisfies 0.08%≦(Mo+W). 3. The steel material according to claim 1 or 2, wherein the steel material further contains Ca in a range of 0.01% or less in mass%, and satisfies the condition of Ca/S≧0.5. 4. The steel material according to any one of claims 1 to 3, wherein the steel material further contains B: 0.0002 to 0.03% in mass %. 5. The steel material according to any one of claims 1 to 4, wherein, in mass %, the steel material further contains one or two or more selected from the following components: Zr: 0.005～0.1%, V: 0.005～0.1%, and Ti: 0.005 to 0.1%.