JP6992499B2 - Steel material - Google Patents

Description

The present invention relates to steel materials.

High acid resistance is required for steel materials used in chemical plant equipment and the like. Therefore, it is common to secure the corrosion resistance of the steel material by containing an expensive element such as Mo or W. In recent years, it has been found that in steel materials exposed to the environment containing ammonium ions such as ammonium sulfate mixed liquid, pipes and the like are seriously damaged by corrosion even though they contain expensive elements.

Conventionally, various highly corrosion-resistant stainless steels have been proposed for such problems. For example, Patent Document 1 proposes a corrosion-resistant steel for a chimney inner cylinder of a coal-fired power plant containing Mo, W and the like.

Japanese Unexamined Patent Publication No. 2001-262285

Steel materials containing W, Mo, etc. have excellent acid resistance and exhibit excellent corrosion resistance in a corrosive environment such as an exhaust gas chimney of an incinerator. However, the studies of the present inventors have found that the corrosion resistance is not sufficient in the environment where ammonium sulfate is produced, even though it contains Mo and W.

An object of the present invention is to solve the above-mentioned problems and to provide a steel material having long-term corrosion resistance at a low cost in an environment containing ammonium ions such as an ammonium sulfate-resistant mixed solution.

The present invention has been made to solve the above problems, and the following steel materials are the gist of the present invention.

(1) The chemical composition is mass%.
C: 0.02 to 0.15%,
Si: 0.10 to 0.35%,
Mn: 2.0-3.0%,
Al: 0.20 to 1.20%,
N: 0.001 to 0.10%,
Cr: 0.10 to 9.0%,
Mo: less than 0.05%,
W: Less than 0.05%,
P: 0.020% or less,
S: 0.015% or less,
Cu: 0 to 0.20%,
Ni: 0 to 0.20%,
Sn: 0 to 0.20%,
Sb: 0 to 0.20%,
Ti: 0 to 0.10%,
Nb: 0 to 0.10%,
Zr: 0 to 0.10%,
V: 0 to 0.20%,
B: 0 to 0.0030%,
Ca: 0 to 0.010%,
Mg: 0 to 0.010%,
REM: 0-0.010%,
Remaining: Fe and impurities,
The value of Rc represented by the following equation (i) is 0.010 to 1.70.
Steel material.
Rc = (Cr + Al) / (3Mn + 4000S) ... (i)
However, the element symbol in the formula represents the content (mass%) of each element, and if it is not contained, it is set to 0.

(2) The chemical composition is mass%.
Cu: 0.03 to 0.20%, and
Ni: 0.03 to 0.20%,
Contains one or two selected from,
The steel material according to (1) above.

(3) The chemical composition is mass%.
Sn: 0.05 to 0.20%, and
Sb: 0.05 to 0.20%,
Contains one or two selected from,
The steel material according to (1) or (2) above.

(4) The chemical composition is mass%.
Ti: 0.001 to 0.10%,
Nb: 0.005 to 0.10%,
Zr: 0.005 to 0.10%, and
V: 0.005 to 0.20%,
Contains one or more selected from
The steel material according to any one of (1) to (3) above.

(5) The chemical composition is mass%.
B: 0.0003 to 0.0030%,
Contains,
The steel material according to any one of (1) to (4) above.

(6) The chemical composition is mass%.
Ca: 0.00005 to 0.010%,
Mg: 0.0001 to 0.010%, and
REM: 0.0001 to 0.010%,
Contains one or more selected from
The steel material according to any one of (1) to (5) above.

According to the present invention, it is possible to obtain a steel material that exhibits excellent corrosion resistance in a corrosive environment containing ammonium ions such as an ammonium sulfate mixed solution such as a chemical plant.

The present inventors investigated the cause of severe corrosion in the coke gas piping generated in the steelworks. In particular, when the components of the sediment and drain water in the severely corroded area _were investigated, it was found that they contained a large amount of ^NH ₄₊ and SO ^4-2 .

Therefore, the polarization was measured in an aqueous solution containing various elements in iron and containing ammonium sulfate and ammonium chloride, respectively, to investigate the suppression of corrosion. As a result, it was found that Cr suppresses the reduction of ammonium ions. In addition, elements such as Mo, W, and Ni are advantageous elements that improve corrosion resistance in ordinary corrosion-resistant steel, but if the content is excessive, they will significantly improve corrosion resistance in an environment containing ammonium ions such as an ammonium sulfate mixed solution. It became clear that it deteriorated. Furthermore, it was found that the corrosion resistance deteriorates depending on the content of C.

As a result of further studies by the present inventors, the balance of the contents of Cr, Al, Mn, and S is important, and it is necessary to set the corrosion resistance index Rc represented by the following formula (i) in an appropriate range. I understood.
Rc = (Cr + Al) / (3Mn + 4000S) ... (i)

The present invention has been made based on the above findings. Hereinafter, each requirement of the present invention will be described in detail.

(A) Chemical composition The reasons for limiting each element are as follows. In the following description, "%" for the content means "mass%".

C: 0.02 to 0.15%
C is an element that improves the strength and needs to be contained in an amount of 0.02% or more. On the other hand, if the C content exceeds 0.15%, carbides increase and acid resistance deteriorates, so the C content is set to 0.15% or less. The C content is preferably 0.03% or more, and more preferably 0.05% or more. The C content is preferably 0.14% or less, more preferably 0.13% or less.

Si: 0.10 to 0.35%
Si is an element that contributes to deoxidation and improvement of strength, and needs to be contained in an amount of 0.10% or more in order to control the morphology of the oxide. On the other hand, if an amount of Si exceeding 0.35% is contained, the oxide increases and the acid resistance is impaired, so the Si content is limited to 0.35% or less. The Si content is preferably 0.15% or more, more preferably 0.20% or more. Further, the Si content is preferably 0.30% or less.

Mn: 2.0-3.0%
Mn is an element that suppresses the reduction of ammonium ions, and must be contained in an amount of 2.0% or more. On the other hand, even if it is excessively contained, the corrosion resistance effect in the environment containing ammonium ions is saturated, so the Mn content is set to 3.0% or less. The Mn content is preferably 2.4% or more. The Mn content is preferably 2.8% or less.

Al: 0.20 to 1.20%
Al is an element that suppresses the reduction of ammonium ions, and needs to be contained in an amount of 0.20% or more. On the other hand, even if it is excessively contained, the corrosion resistance effect in the environment containing ammonium ions is saturated, so the Al content is set to 1.20% or less. The Al content is preferably 0.60% or more, and preferably 1.10% or less.

N: 0.001 to 0.10%
N is effective in suppressing the coarsening of γ grains in slab heating during rolling due to the fine nitride, and it is necessary to contain N in an amount of 0.001% or more. On the other hand, if N is excessively contained, coarse nitrides are formed and the mechanical properties of the base metal are deteriorated. Therefore, the N content is set to 0.10% or less. The N content is preferably 0.002% or more in order to sufficiently suppress the coarsening of γ grains by the pinning effect of the nitride even at high temperature heating.

Cr: 0.10 to 9.0%
Cr is an element that suppresses the reduction of ammonium ions, and needs to be contained in an amount of 0.10% or more. On the other hand, even if it is excessively contained, the corrosion resistance effect in the environment containing ammonium ions is saturated, so the Cr content is set to 9.0% or less. The Cr content is preferably 0.50% or more. The Cr content is preferably 8.0% or less, more preferably 7.0% or less, and even more preferably 6.0% or less.

Mo: less than 0.05% W: less than 0.05% In an environment containing ammonium ions, if a large amount of Mo and W are contained, the corrosion resistance is significantly deteriorated, so it is necessary to limit the content thereof. Therefore, the contents of Mo and W are set to less than 0.05%, respectively.

P: 0.020% or less P is an impurity and deteriorates the mechanical properties and productivity of steel materials. Therefore, the P content is 0.020% or less. The lower limit of the P content is not limited and may be 0%, but the P content may be 0.001% or more from the viewpoint of cost.

S: 0.015% or less S is generally contained as an impurity and deteriorates hot workability and mechanical properties of steel materials. Therefore, the S content is set to 0.015% or less. The lower limit of the S content is not limited and may be 0%. When S is contained together with Cu, the corrosion resistance in an acidic environment is improved. Therefore, the S content may be 0.0002% or more. When the above effect is desired, the S content is preferably 0.001% or more, more preferably 0.002% or more.

Since the elements shown below are optional additives, the lower limit may be 0%.

Cu: 0 to 0.20%
Cu is an element that deteriorates corrosion resistance in an environment containing ammonium ions. In particular, if the Cu content exceeds 0.20%, the corrosion resistance is significantly reduced in an environment containing ammonium ions, so the content is 0.20% or less. The Cu content is preferably 0.15% or less, more preferably 0.10% or less. However, since the corrosion resistance in an acidic environment is improved by containing Cu together with S, the Cu content is preferably 0.03% or more.

Ni: 0 to 0.20%
Like Cu, Ni is an element that deteriorates corrosion resistance in an environment containing ammonium ions. In particular, if the Ni content exceeds 0.20%, the corrosion resistance is significantly reduced in an environment containing ammonium ions, so the content is set to 0.20% or less. The Ni content is preferably 0.15% or less, more preferably 0.10% or less. However, since Ni has the effect of improving corrosion resistance in an acidic environment, the Ni content is preferably 0.03% or more.

Sn: 0 to 0.20%
Since Sn is an element that suppresses the reduction of ammonium ions, it may be contained if necessary. However, if it is contained in an excessive amount, the toughness of the steel is significantly lowered, so that the Sn content is 0.20% or less. In order to further increase the toughness, the Sn content is preferably 0.15% or less. If the above effect is desired, the Sn content is preferably 0.05% or more.

Sb: 0 to 0.20%
Since Sb is an element that suppresses the reduction of ammonium ions like Sn, it may be contained if necessary. However, if it is contained in an excessive amount, the toughness of the steel is significantly lowered, so that the Sb content is 0.20% or less. In order to further increase the toughness, the Sb content is preferably 0.15% or less. When the above effect is desired, the Sb content is preferably 0.05% or more.

Ti: 0 to 0.10%
Since Ti is an element that forms a nitride in the same manner as Nb and contributes to the refinement of crystal grains and the improvement of strength, it may be contained as necessary. However, if an amount of Ti exceeding 0.10% is contained, the nitride becomes coarse and the mechanical properties may deteriorate. Therefore, the Ti content is set to 0.10% or less. The Ti content is preferably 0.080% or less, more preferably 0.050% or less, and even more preferably 0.040% or less. When the above effect is desired, the Ti content is preferably 0.001% or more.

Nb: 0 to 0.10%
Nb is an element that forms a nitride, and may be contained as necessary for the purpose of refining the crystal grains and improving the strength. However, if an amount of Nb exceeding 0.10% is contained, the mechanical properties are deteriorated, so the Nb content is set to 0.10% or less. The Nb content is preferably 0.050% or less, more preferably 0.030% or less, and even more preferably 0.020% or less. When the above effect is desired, the Nb content is preferably 0.005% or more.

Zr: 0 to 0.10%
Like Ti and Nb, Zr is an element that forms a nitride and is an element that mainly contributes to the improvement of strength by strengthening precipitation, and therefore may be contained as necessary. However, Zr is an expensive element, and if it is contained in an excessive amount, the mechanical properties deteriorate. Therefore, the Zr content is set to 0.10% or less. The Zr content is preferably 0.080% or less, more preferably 0.050% or less, and even more preferably 0.040% or less. When the above effect is desired, the Zr content is preferably 0.005% or more.

V: 0 to 0.20%
Like Nb, Ti, and Zr, V is an element that forms a nitride and is an element that mainly contributes to the improvement of strength by strengthening precipitation, and therefore may be contained as necessary. However, if it is contained in an excessive amount, the mechanical properties are deteriorated, so the V content is set to 0.20% or less. The V content is preferably 0.15% or less, more preferably 0.10% or less, still more preferably 0.050% or less. When the above effect is desired, the V content is preferably 0.005% or more.

B: 0 to 0.0030%
Since B is an element that improves hardenability and enhances strength, it may be contained as necessary. However, even if an amount of B exceeding 0.0030% is contained, the effect is saturated and the toughness of the base material and HAZ is lowered, so the B content is set to 0.0030% or less. The B content is preferably 0.0020% or less, more preferably 0.0010% or less. When the above effect is desired, the B content is preferably 0.0003% or more, more preferably 0.0005% or more.

Ca: 0 to 0.010%
Ca is an element mainly used for controlling the morphology of sulfides, and may be contained as necessary in order to form fine oxides. However, if an amount of Ca exceeding 0.010% is contained, the mechanical properties are impaired, so the Ca content is set to 0.010% or less. The Ca content is preferably 0.005% or less. When the above effect is desired, the Ca content is preferably 0.00005% or more, more preferably 0.0001% or more, and further preferably 0.00015% or more. ..

Mg: 0 to 0.010%
Since Mg forms a fine oxide, it may be contained if necessary. However, from the viewpoint of manufacturing cost, the Mg content is 0.010% or less. The Mg content is preferably 0.005% or less, more preferably 0.003% or less. When the above effect is desired, the Mg content is preferably 0.0001% or more, more preferably 0.0003% or more, and further preferably 0.0005% or more. ..

REM: 0 to 0.010%
REM (rare earth element) is an element mainly used for deoxidation, and may be contained as necessary in order to form a fine oxide. However, from the viewpoint of manufacturing cost, the REM content is 0.010% or less. The REM content is preferably 0.005% or less, more preferably 0.003% or less. When the above effect is desired, the REM content is preferably 0.0001% or more, more preferably 0.0003% or more, and further preferably 0.0005% or more. ..

Here, REM is a general term for 17 elements in which Y and Sc are combined with 15 elements of lanthanoids. One or more of these 17 elements can be contained in the steel material, and the REM content means the total content of these elements.

In the chemical composition of the steel material of the present invention, the balance is Fe and impurities. Here, the "impurity" is a component mixed with raw materials such as ore and scrap, and various factors in the manufacturing process when manufacturing steel materials industrially, and is allowed as long as it does not adversely affect the present invention. Means something.

In the present invention, in addition to having the above-mentioned chemical composition, the corrosion resistance index Rc shown below needs to satisfy a predetermined condition.

Rc: 0.010 to 1.70
The Rc value is an index experimentally found by the present inventor, and is a value calculated by the following formula (i) based on the contents of Cr, Al, Mn and S.
Rc = (Cr + Al) / (3Mn + 4000S) ... (i)
However, the element symbol in the formula represents the content (mass%) of each element, and if it is not contained, it is set to 0.

Among the elements used in the formula (i), Cr, Al and Mn have an action of suppressing the reduction of ammonium ions and suppressing the corrosion of steel materials as described above. On the other hand, MnS existing as an inclusion in the steel material serves as a starting point of the reduction reaction of ammonium ions, promotes the reaction, and promotes corrosion. Therefore, when a large amount of S is contained in the steel, a large amount of MnS is formed, so that the effect of suppressing the reduction of ammonium ions is offset even when Cr, Al and Mn are sufficiently contained.

When the Rc value of the above formula (i) is less than 0.010, the suppression of the reduction reaction of ammonium ions becomes unstable, and MnS becomes the starting point of corrosion. Since the corrosion resistance of the steel material improves as the Rc value increases, the upper limit of the Rc value is not particularly limited, but the upper limit of the Cr amount (9.0%), the upper limit of the Al amount (1.20%), and the Mn amount. It becomes 1.70 from the lower limit value (2.0%) and the lower limit value (0%) of the S amount. The corrosion resistance effect gradually saturates as the Rc value is increased. The upper limit of the more preferable Rc value, in which the effect of improving the corrosion resistance during this period is remarkably exhibited, is 1.50, and more preferably 1.00.

(B) Applications The use of the steel material according to the present invention does not need to be particularly limited, but as described above, it is suitable for use in an environment containing ammonium ions. Specifically, the steel material according to the present invention is suitable as a material used in equipment of a chemical factory exposed to ammonium sulfate.

More specifically, the steel material according to the present invention is (1) equipment of a manufacturing plant for pharmaceuticals, reagents, etc. by neutralization synthesis of sulfuric acid and ammonia, and (2) a plant for recovering by-product ammonium sulfate from coke oven gas. Equipment, (3) equipment for synthesizing caprolactam, which is a raw material for nylon, (4) equipment for synthesizing acrylamide, (5) equipment for exhaust gas from coal boilers, (6) equipment for regenerating powder fire extinguishing agents (using ammonium phosphate and ammonium sulfate), It is suitable as a material used in chemical plants such as (7) nitrogen oxide reduction equipment and (8) urethane production equipment.

(C) Shape / Dimensions The shape and dimensions of the steel material according to the present invention are not particularly limited. Steel materials include, for example, steel plates, shaped steels, and steel pipes. When used as a steel sheet, the plate thickness is preferably 3 mm or more, more preferably 6 mm or more. Similarly, when used as a steel pipe, the wall thickness is preferably 3 mm or more, and more preferably 6 mm or more.

(D) Manufacturing Method The manufacturing conditions of the steel material according to the present invention are not particularly limited, but can be manufactured by, for example, the following method.

When manufacturing a steel sheet, first, a steel having the above-mentioned chemical composition is melted by a conventional method and cast into a steel piece. Subsequently, the obtained steel pieces are hot-rolled and, if necessary, cold-rolled. After hot rolling, it may be water-cooled as it is, or it may be air-cooled and then reheated and quenched. After hot rolling, it may be wound into a coil. After hot rolling, cold rolling may be performed and further heat treatment may be performed.

When manufacturing a steel pipe, the steel plate obtained by the above method may be formed into a tubular shape and welded, or may be a UO steel pipe, an electrosewn steel pipe, a forge welded steel pipe, a spiral steel pipe or the like. Alternatively, the steel piece may be hot-extruded or drilled and rolled to form a seamless steel pipe.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

The steel having the chemical composition shown in Table 1 was melted, the ingot was heated at 1150 ° C. for 2 hours, hot-rolled to a thickness of 20 mm, and then air-cooled to produce a steel sheet.

A test piece having a length of 50 mm, a width of 25 mm, and a thickness of 3 mm was collected from the obtained steel sheet from the central part of the plate width and the plate thickness of 1/4 t, and finished by wet # 600 polishing to prepare a test piece for corrosion resistance evaluation. The corrosion resistance was evaluated by an ammonium sulfate immersion test. The concentration of the ammonium sulfate aqueous solution was 1 mol, the liquid temperature was heated to 80 ° C., and the mixture was immersed for 1 week, and then the corrosion weight was measured. Then, the corrosion resistance was evaluated using the above-mentioned corrosion reduction as an index. The specific liquid volume was 20 mL / cm ² .

In the evaluation of corrosion resistance, the test No. of Comparative Example was used. Based on 27, those having a corrosion weight loss of 50% or less were marked with ⊚, those with a corrosion weight loss of more than 50% and 70% or less were marked with ◯, and those with a corrosion weight of more than 70% were marked with x. The results are shown in Table 2.

As is clear from Table 2, the test No. that satisfies the chemical composition specified in the present invention. It can be seen that the steel materials 1 to 26 have good corrosion resistance. On the other hand, the test No. of the comparative example which deviates from the specification of the present invention. The steel materials of 28 to 33 had inferior corrosion resistance.

According to the present invention, it is possible to obtain a steel material that exhibits excellent corrosion resistance in a corrosive environment containing ammonium ions such as an ammonium sulfate mixed solution such as a chemical plant.

Claims (6)

The chemical composition is by mass%,
C: 0.02 to 0.15%,
Si: 0.10 to 0.35%,
Mn: 2.0-3.0%,
Al: 0.20 to 1.20% (excluding 1.20%) ,
N: 0.001 to 0.10%,
Cr: 0.10 to 9.0%,
Mo: less than 0.05%,
W: Less than 0.05%,
P: 0.020% or less,
S: 0.015% or less (excluding 0.003% or less) ,
Cu: 0.03 to 0.20%,
Ni: 0 to 0.20%,
Sn: 0 to 0.20%,
Sb: 0 to 0.20%,
Ti: 0 to 0.10%,
Nb: 0 to 0.10%,
Zr: 0 to 0.10%,
V: 0 to 0.20%,
B: 0 to 0.0030%,
Ca: 0 to 0.010%,
Mg: 0 to 0.010%,
REM: 0-0.010%,
Remaining: Fe and impurities,
The value of Rc represented by the following equation (i) is 0.010 to 1.70.
Steel material.
Rc = (Cr + Al) / (3Mn + 4000S) ... (i)
However, the element symbol in the formula represents the content (mass%) of each element, and if it is not contained, it is set to 0. The chemical composition is by mass% .
Ni: 0.03 to 0.20%,
Contains ,
The steel material according to claim 1. The chemical composition is by mass%.
Sn: 0.05 to 0.20%, and
Sb: 0.05 to 0.20%,
Contains one or two selected from,
The steel material according to claim 1 or 2. The chemical composition is by mass%.
Ti: 0.001 to 0.10%,
Nb: 0.005 to 0.10%,
Zr: 0.005 to 0.10%, and
V: 0.005 to 0.20%,
Contains one or more selected from
The steel material according to any one of claims 1 to 3. The chemical composition is by mass%.
B: 0.0003 to 0.0030%,
Contains,
The steel material according to any one of claims 1 to 4. The chemical composition is by mass%.
Ca: 0.00005 to 0.010%,
Mg: 0.0001 to 0.010%, and
REM: 0.0001 to 0.010%,
Contains one or more selected from
The steel material according to any one of claims 1 to 5.