JP7099041B2 - Steel material - Google Patents

Description

The present invention relates to steel materials.

Boiler smoke exhaust equipment and gasification melting furnaces that burn various fuels, waste, sewage sludge, etc. are exposed to the atmosphere of combustion exhaust gas, and are exposed to sulfuric acid dew point corrosion, hydrochloric acid dew point corrosion environment, or aqueous solution of sulfuric acid or hydrochloric acid. It will be an environment of contact. Steel materials exposed to such a severely corrosive environment are required to have excellent acid resistance for a long period of time.

To solve such problems, sulfuric acid / hydrochloric acid dew point corrosion resistant steel and highly corrosion resistant stainless steel have been proposed. (For example, refer to Patent Documents 1 to 5.). Among these, Patent Documents 1 to 4 propose steel materials having excellent sulfuric acid dew point corrosion resistance to which Cu, Sb, Co, Cr and the like are added. Further, Patent Document 5 proposes a highly corrosion-resistant stainless steel to which Cr, Ni and the like are added.

Japanese Unexamined Patent Publication No. 2001-164335 Japanese Patent Application Laid-Open No. 2003-213367 Japanese Unexamined Patent Publication No. 2007-239094 Japanese Unexamined Patent Publication No. 2012-57221 Japanese Unexamined Patent Publication No. 7-316745

Steel materials containing Cu, Sb, Cr, etc. have excellent sulfuric acid dew point corrosion resistance, and exhibit excellent corrosion resistance in sulfuric acid corrosion environments such as boilers and exhaust gas chimneys of incineration facilities. However, in order to extend the life of boilers and incinerators, further improvement in corrosion resistance is expected.

Further, steel materials used for applications such as heat exchangers, gas-gas heaters, desulfurization devices, and electrostatic precipitators are required to have not only acid resistance but also weldability. Further, from the viewpoint of manufacturability, hot workability is also required.

In view of such circumstances, it is an object of the present invention to provide a steel material having excellent manufacturability, long-term corrosion resistance and excellent weldability in an acid corrosion environment of sulfuric acid dew point corrosion and hydrochloric acid dew point corrosion. be.

The present inventors focused on oxides and nitrides that are the starting points of corrosion, and conducted studies to improve the corrosion resistance of steel materials in an acid-corroded environment. It was found that the formation of oxides, which are the starting points of corrosion, was suppressed by setting the Si / Al ratio in the range of 7.0 to 15.0.

Furthermore, it was found that when the content of Cr and N, which is effective for improving acid resistance, increases, the nitride containing Cr becomes the starting point of corrosion. Therefore, further studies were conducted on Cr and N, and it was found that corrosion resistance exceeding expectations is exhibited by setting the value of the acid corrosion resistance index BI obtained by the following formula (1) to 0.55 to 30.00. Obtained.
BI = (Cr / 52) / (N / 14) ... (1)

Further, when Cu and Sb are contained at the same time, the acid resistance is improved, but the hot workability is lowered. On the other hand, the value of the processability coefficient EI obtained by the following formula (2) is 1.0 to 6.0, and the Ceq obtained by the following formula (3) is 0.150 to 0.400. Therefore, it was found that excellent acid resistance, hot workability and weldability can be obtained.
EI = (Cu / 64) / (Sb / 122) ... Equation (2)
Ceq = C + Mn / 6 + (Cu + Ni) / 5+ (Cr + Mo + V) / 15 ... (3)

The present invention has been made based on such findings, and the gist thereof is as follows.
[1] By mass%,
C: 0.01-0.10%,
Si: 0.04 to 0.40%,
Mn: 0.30 to 1.50%,
Cu: 0.05 to 0.50%,
Sb: 0.03 to 0.30%,
Ni: 0.01-0.50%,
Cr: 0.02 to 0.50%,
Al: 0.005 to 0.055%,
N: 0.002 to 0.010%,
P: 0 to 0.020%,
S: 0 to 0.015%, and O: 0 to 0.0035%
The balance consists of Fe and impurities.
The content of Si and the content of Al are mass ratios.
Si / Al: 7.0 to 15.0
Satisfied,
The BI required in (1) below is 0.55 to 30.00.
The EI required in (2) below is 1.0 to 6.0.
A steel material having a Ceq obtained by the following equation (3) of 0.150 to 0.400.
BI = (Cr / 52) / (N / 14) ... Equation (1)
EI = (Cu / 64) / (Sb / 122) ... Equation (2)
Ceq = C + Mn / 6 + (Cu + Ni) / 5+ (Cr + Mo + V) / 15 ... Equation (3)
Here, in the formula, C, Mn, Cu, Sb, Ni, Cr, V, and N indicate the content based on the mass% of each element, and when they are not contained, they are 0.
[2] Furthermore, by mass%,
Mo: 0.50% or less,
W: 0.50% or less,
Sn: 0.30% or less,
The steel material according to the above [1], which contains one or more selected from the group consisting of As: 0.30% or less and Co: 0.30% or less.
[3] Furthermore, by mass%,
Ti: 0.050% or less,
Nb: 0.10% or less,
V: 0.10% or less,
Zr: 0.050% or less,
The steel material according to the above [1] or [2], which contains one or more selected from the group consisting of Ta: 0.050% or less and B: 0.010% or less.
[4] Furthermore, by mass%,
Ca: 0.010% or less,
Described in any one of the above [1] to [3], which comprises one or more selected from the group consisting of Mg: 0.010% or less and REM: 0.010% or less. Steel material.

According to the present invention, excellent corrosion resistance is exhibited in a sulfuric acid corrosion environment such as an exhaust gas chimney of a boiler or an incinerator or a hydrochloric acid corrosion environment such as an exhaust gas chimney of a waste incinerator, and the manufacturability and weldability are improved. Will also be able to provide excellent steel materials. Therefore, the present invention makes an extremely remarkable industrial contribution.

Hereinafter, preferred embodiments of the present invention will be described in detail.
From the studies by the present inventors, it has been found that in order to improve the acid resistance of acid-resistant steel containing Cu, Sb, and Cr, it is effective to suppress nitrides and oxides that tend to be corrosion starting points on the surface of the steel material. .. First, it was found that it is effective to utilize Si, which has a weaker oxidizing power than Al, in order to suppress the formation of oxides, and that the Si / Al ratio is important.

Next, if the content of Cr, which is effective for improving acid resistance, is excessive, it becomes easy to form a nitride, which can be a starting point of corrosion. As a result of the study by the present inventors, it was found that the balance of the contents of Cr and N is important, and it is necessary to set the acid resistance corrosion index BI obtained by the following formula (1) in an appropriate range. ..
BI = (Cr / 52) / (N / 14) ... Equation (1)

Further, it was found that the ratio of the contents of Cu and Sb is important for the steel containing Cu and Sb at the same time in order to secure the hot workability. Then, it was found that the hot workability can be ensured so as not to impair the manufacturability by setting the workability coefficient EI obtained by the following formula (2) in an appropriate range. In addition to these, by setting the Ceq required by the following formula (3) to an appropriate range, we succeeded in obtaining a steel material having excellent acid resistance, hot workability and weldability.
EI = (Cu / 64) / (Sb / 122) ... Equation (2)
Ceq = C + Mn / 6 + (Cu + Ni) / 5+ (Cr + Mo + V) / 15 ... Equation (3)

The components of the steel material according to this embodiment will be described. The notation of% means mass% unless otherwise specified.

(C: 0.01 to 0.10%)
C is an element that improves the strength, and it is necessary to contain 0.01% or more. The amount of C is preferably 0.03% or more, more preferably 0.05% or more. On the other hand, if the amount of C exceeds 0.10%, carbides increase and acid resistance deteriorates, so the amount of C is set to 0.10% or less. The amount of C is preferably 0.09% or less, more preferably 0.08% or less.

(Si: 0.04 to 0.40%)
Si is an element that contributes to deoxidation and improvement of strength, and it is necessary to contain 0.04% or more in order to control the morphology of the oxide. The amount of Si is preferably 0.05% or more, and more preferably 0.10% or more. On the other hand, if the Si content exceeds 0.40%, the oxide increases and the acid resistance is impaired, so the Si amount is set to 0.40% or less. The amount of Si is preferably 0.30% or less.

(Mn: 0.30 to 1.50%)
Mn is an element that improves strength and toughness, and contains 0.30% or more. The amount of Mn is preferably 0.50% or more, more preferably 0.80% or more. On the other hand, if an amount of Mn exceeding 1.50% is contained, coarse MnS is generated and the corrosion resistance and mechanical properties are deteriorated. Therefore, the amount of Mn is set to 1.50% or less. The amount of Mn is preferably 1.20% or less, more preferably 1.00% or less.

(Cu: 0.05 to 0.50%)
Cu is an extremely important element that remarkably exhibits corrosion resistance to sulfuric acid and hydrochloric acid when contained at the same time as Sb. In order to ensure corrosion resistance in an acidic environment, it is necessary to set the Cu amount to 0.05% or more. The amount of Cu is preferably 0.10% or more, more preferably 0.150% or more, still more preferably 0.20% or more. On the other hand, if the amount of Cu exceeds 0.50%, the hot workability is lowered and the manufacturability is impaired, so the content is set to 0.50% or less. The amount of Cu is preferably 0.40% or less, more preferably 0.30% or less.

(Sb: 0.03 to 0.30%)
As described above, Sb is an extremely important element that improves acid resistance when contained at the same time as Cu, and it is necessary to contain 0.03% or more in order to secure corrosion resistance in an acidic environment. The amount of Sb is preferably 0.05% or more, more preferably 0.08% or more, still more preferably 0.10% or more. On the other hand, if the amount of Sb exceeds 0.30%, the hot workability deteriorates, so the amount is set to 0.30% or less. The amount of Sb is preferably 0.15% or less.

(Ni: 0.01-0.50%)
Ni is an element that improves corrosion resistance in an acidic environment, and the amount of Ni is 0.01% or more. When Cu is contained, Ni exhibits the effect of enhancing manufacturability. Cu has a great effect of improving corrosion resistance, but it is easily segregated, and when it is contained alone, it may promote cracking after casting. On the other hand, Ni has the effect of reducing the segregation of Cu. When Ni is contained, in addition to suppressing cracking of the slab due to Cu segregation, the occurrence of local corrosion due to segregation is also suppressed, so that the effect of improving corrosion resistance is remarkably exhibited. The amount of Ni is preferably 0.03% or more, more preferably 0.05% or more, still more preferably 0.10% or more. On the other hand, since Ni is an expensive element, the amount of Ni is set to 0.50% or less from the viewpoint of cost. The amount of Ni is preferably 0.30% or less, more preferably 0.25% or less.

(Cr: 0.02 to 0.50%)
Cr is an element that improves corrosion resistance like Cu and Sb. In particular, by containing Cr at the same time as Cu and Sb, excellent corrosion resistance is exhibited in an acidic environment where the temperature and concentration are high. Therefore, from the viewpoint of ensuring corrosion resistance, it is necessary to contain Cr of 0.02% or more. The amount of Cr is preferably 0.05% or more. On the other hand, if Cr is excessively contained, the amount of Cr is set to 0.50% or less because the increase in the nitride that is the starting point of corrosion impairs the acid resistance. More preferably, the amount of Cr is 0.30% or less, and more preferably the amount of Cr is 0.20% or less.

(Al: 0.005 to 0.055%)
Al is a deoxidizing agent and needs to contain 0.005% or more. The amount of Al is preferably 0.010% or more, more preferably 0.020% or more. On the other hand, if Al is excessively contained, acid resistance is impaired due to an increase in inclusions, so the amount of Al is set to 0.055% or less. The amount of Al is preferably 0.050% or less, more preferably 0.040% or less.

(N: 0.002 to 0.010%)
N is an element that forms a nitride, and when Cr is contained, the corrosion resistance decreases when the amount of N becomes excessive, so the amount of N is set to 0.010% or less. The amount of N is preferably 0.008% or less, more preferably 0.006% or less. On the other hand, since fine nitrides are effective in improving mechanical properties and the like, the amount of N is set to 0.002% or more. The amount of N is preferably 0.003% or more.

(P: 0 to 0.020%)
P is an impurity and reduces the mechanical properties and manufacturability of the steel material, so the amount of P is 0.020% or less. The lower limit of the P amount is not limited and may be 0%, but the P amount may be 0.001% or more from the viewpoint of cost.

(S: 0 to 0.015%)
Since S is an impurity and deteriorates hot workability and mechanical properties of steel materials, the amount of S is set to 0.015% or less. The lower limit of the amount of S is not limited and may be 0%. When S is contained at the same time as Cu and Sb, the corrosion resistance in an acidic environment is improved. Therefore, the amount of S may be 0.001% or more. The amount of S may be more preferably 0.005% or more, still more preferably 0.01% or more.

(O: 0 to 0.0035%)
O is an element that produces an oxide. The amount of O is set to 0.0035% or less in order to suppress the formation of coarse oxides that are the starting points of corrosion in an acidic environment. The amount of O is preferably 0.0030% or less, more preferably 0.0025% or less. The lower limit of the O amount is not limited and may be 0%, but the O amount may be 0.0005% or more from the viewpoint of cost.

Further, in order to improve the corrosion resistance in an acidic environment, one or more selected from the group consisting of Mo, W, Sn, As and Co may be contained. Since these elements are not always essential in steel materials, the lower limit of the content is set to 0%.

(Mo: 0.50% or less)
Mo is an element that improves corrosion resistance in an acidic environment by containing Cu, Sb, and Cr at the same time. In particular, the amount of Mo can be 0.01% or more in order to enhance the corrosion resistance to hydrochloric acid. The amount of Mo is more preferably 0.05% or more, still more preferably 0.10% or more. On the other hand, since Mo is an expensive element, the Mo content is set to 0.50% or less from the viewpoint of cost. It is more preferably 0.30% or less, still more preferably 0.10% or less.

(W: 0.50% or less)
W is an element that improves corrosion resistance in an acidic environment by containing Cu, Sb, and Cr at the same time as Mo. In particular, the amount of W can be 0.01% or more in order to enhance the corrosion resistance to hydrochloric acid. The amount of W is more preferably 0.05% or more, still more preferably 0.10% or more. On the other hand, since W is also an expensive element, the Mo content is set to 0.50% or less from the viewpoint of cost. It is more preferably 0.30% or less, still more preferably 0.10% or less.

(Sn: 0.30% or less)
Sn is an element that improves corrosion resistance in an acidic environment, and may contain 0.01% or more. The Sn amount is more preferably 0.02% or more, and further preferably the Sn amount is 0.05% or more. On the other hand, if Sn is excessively contained, the hot workability is lowered, so the Sn amount is set to 0.30% or less. More preferably, the Sn amount is 0.20% or less.

(As: 0.30% or less)
Although the effect of As is not remarkable as compared with Sb and Sn, it is an element effective for improving corrosion resistance in an acidic environment, and may contain 0.01% or more. The amount of As is more preferably 0.02% or more, and further preferably the amount of As is 0.05% or more. On the other hand, if As is excessively contained, the hot workability is deteriorated, so the amount of As is set to 0.30% or less. The amount of As is more preferably 0.20% or less, still more preferably 0.10% or less.

(Co: 0.30% or less)
Although the effect of Co is not remarkable as compared with Sb and Sn, Co is an element that improves corrosion resistance in an acidic environment, and may contain 0.01% or more. The Co amount is more preferably 0.02% or more, and further preferably the Co amount is 0.05% or more. On the other hand, since the economic efficiency of excessively containing Co is lowered, the amount of Co is set to 0.30% or less. The amount of Co is more preferably 0.20% or less, still more preferably 0.10% or less.

Further, in order to improve mechanical properties and the like, one or more selected from the group consisting of Ti, Nb, V, Zr, Ta and B may be contained. Since these elements are not always essential in steel materials, the lower limit of the content is set to 0%.

(Ti: 0.050% or less)
Ti is an element that forms a nitride and contributes to the miniaturization of crystal grains and the improvement of strength, and may contain 0.001% or more. More preferably, the amount of Ti is 0.005% or more. On the other hand, if Ti of more than 0.050% is contained, the nitride becomes coarse and the mechanical properties may be deteriorated. Therefore, the Ti amount is set to 0.050% or less. The amount of Ti is more preferably 0.040% or less, further preferably 0.030% or less, and even more preferably 0.020% or less.

(Nb: 0.10% or less)
Like Ti, Nb is an element that forms a nitride, and may contain 0.001% or more for the purpose of refining crystal grains and improving the strength. More preferably, the amount of Nb is 0.005% or more. On the other hand, if Nb of more than 0.10% is contained, the mechanical properties may be deteriorated, so the amount of Nb is set to 0.10% or less. The amount of Nb is more preferably 0.050% or less, further preferably 0.030% or less, and even more preferably 0.020% or less.

(V: 0.10% or less)
Like Ti and Nb, V is an element that forms a nitride, and may be contained mainly for improving the strength by strengthening precipitation. In order to obtain the effect, the amount of V is preferably 0.005% or more. On the other hand, if V of more than 0.10% is contained, the mechanical properties may be deteriorated, so the amount of V is set to 0.10% or less. The amount of V is more preferably 0.050% or less, further preferably 0.030% or less, and even more preferably 0.020% or less.

(Zr: 0.050% or less)
Like Ti, Nb, and V, Zr is an element that forms a nitride, and may be contained mainly for improving the strength by strengthening precipitation. In order to obtain the effect, the amount of Zr is preferably 0.005% or more. On the other hand, Zr is an expensive element, and if Zr of more than 0.050% is contained, the mechanical properties may deteriorate. Therefore, the amount of Zr is set to 0.050% or less. The amount of Zr is more preferably 0.040% or less, further preferably 0.030% or less, and even more preferably 0.020% or less.

(Ta: 0.050% or less)
Ta is an element that contributes to the improvement of strength, and may contain 0.001% or more. Further, although the mechanism is not always clear, Ta also contributes to the improvement of corrosion resistance, and more preferably, the amount of Ta is 0.005% or more. On the other hand, if Ta is excessively contained, the cost increases, so the amount of Ta is set to 0.050% or less. The amount of Ta is more preferably 0.040% or less, further preferably 0.030% or less, and even more preferably 0.020% or less.

(B: 0.010% or less)
B is an element that improves hardenability and enhances strength. In order to obtain the effect, the amount of B is preferably 0.003% or more. More preferably, the amount of B is 0.0005% or more. On the other hand, even if B containing more than 0.010% is contained, the effect may be saturated and the toughness of the base material and HAZ may decrease, and the amount of B is set to 0.010% or less. The amount of B is more preferably 0.0050% or less, further preferably 0.0030% or less, and even more preferably 0.0020% or less.

Further, for the purpose of deoxidation and control of inclusions, one or more selected from the group consisting of Ca, Mg and REM may be contained. Since these elements are not always essential in steel materials, the lower limit of the content is set to 0%.

(Ca: 0.010% or less)
Ca is an element mainly used for controlling the morphology of sulfide, and may contain 0.0005% or more in order to form a fine oxide. The amount of Ca is preferably 0.001% or more, more preferably 0.002% or more. On the other hand, if Ca of more than 0.010% is contained, the mechanical properties may be impaired, so the amount of Ca is set to 0.010% or less. More preferably, the amount of Ca is 0.005% or less.

(Mg: 0.010% or less)
Mg may be contained in an amount of 0.0001% or more in order to form a fine oxide. The amount of Mg is preferably 0.0003% or more, more preferably 0.0005% or more. On the other hand, from the viewpoint of manufacturing cost, the amount of Mg is set to 0.010% or less. The amount of Mg is more preferably 0.005% or less, still more preferably 0.003% or less.

(REM: 0.010% or less)
REM (rare earth element) is an element mainly used for deoxidation, and may contain 0.0001% or more in order to form a fine oxide. The REM amount is preferably 0.0003% or more, more preferably 0.0005% or more. On the other hand, from the viewpoint of manufacturing cost, the REM amount is 0.010% or less. The REM amount is more preferably 0.005% or less, still more preferably 0.003% or less.

The balance of the chemical composition of the steel material according to this embodiment is iron (Fe) and impurities. The term "impurity" means a component mixed by raw materials such as ore and scrap and other factors when the steel material is industrially manufactured, and is permitted as long as it does not adversely affect the steel material according to the present embodiment. do. However, among impurities, it is necessary to limit the upper limit for O, P, and S as described above.

In the steel material according to this embodiment, it is necessary to control the relationship of specific elements in order to improve the acid resistance.
(Si / Al: 7.0 to 15.0)
The Si / Al ratio (mass ratio) is an important index for suppressing oxides that tend to be corrosion starting points on the surface of steel materials. In order to suppress the formation of oxides, it is effective to utilize Si, which has a weaker oxidizing power than Al, and the acid resistance is remarkably improved by setting the Si / Al ratio to 7.0 or more. The Si / Al ratio is preferably 8.0 or more, more preferably 9.0 or more. On the other hand, even if the Si / Al ratio exceeds 15.0, the effect is saturated, and as the amount of Al decreases, deoxidation becomes insufficient, and the acid resistance may decrease due to the oxide. Is 15.0. The Si / Al ratio is preferably 14.0 or less, more preferably 13.0 or less.

(BI: 0.55 to 30.00)
The acid resistance corrosion index BI is important for suppressing nitrides that tend to be corrosion origins on the surface of steel materials. Although Cr is effective in improving acid resistance, if the content is excessive, it becomes easy to form a nitride that is a starting point of corrosion. Therefore, in order to significantly improve acid resistance, the acid resistance corrosion index BI is used. It is necessary to make it 30.00 or less. The BI is preferably 30.00 or less, more preferably 15.00 or less, still more preferably 10.00 or less, and even more preferably 5.00 or less. On the other hand, if Cr is insufficient, the effect of improving acid resistance becomes insufficient, so it is necessary to set the acid resistance corrosion index BI to 0.55 or more. The BI is preferably 0.60 or more, more preferably 0.70 or more.

The acid resistance corrosion index BI is a ratio of the total number of Cr atoms and N atoms to the number of carbon atoms, as shown in the following formula (1). That is, Cr / 52 and N / 14 are terms obtained by dividing the contents of Cr and N by the mass number of each element, respectively.
BI = (Cr / 52) / (N / 14) ... Equation (1)

In the steel material according to the present embodiment, it is necessary to control the relationship between specific elements in order to improve hot workability and weldability.
(EI: 1.0 to 6.0)
The workability index EI is an index considering the influence of Sb that promotes the deterioration of hot workability due to Cu, and is important for ensuring hot workability. If the content of Sb is too large with respect to the content of Cu, the hot workability deteriorates, so the workability index EI needs to be 1.0 or more. The EI is preferably 2.0 or more, more preferably 3.0 or more. Increasing the workability index EI is preferable for ensuring hot workability, but the effect is saturated even if it exceeds 6.0. Further, it is necessary to set the processability index EI to 6.0 or less so that the effect of improving acid resistance is not insufficient due to insufficient Sb. The EI is preferably 5.9 or less, more preferably 5.8 or less.

The processability index EI is a ratio of the number of Cu atoms to the number of Sb atoms, as shown in the following formula (2). That is, Cu / 64 and Sb / 122 are terms obtained by dividing the contents of Cu and Sb by the mass number of each element, respectively.
EI = (Cu / 64) / (Sb / 122) ... Equation (2)

(Ceq: 0.150 to 0.400)
Ceq is an index indicating deterioration of weldability due to an increase in hardness, and is set to 0.400 or less in order to ensure weldability. Ceq is preferably 0.350 or less, more preferably 0.330 or less. On the other hand, if Ceq is too low, the mechanical properties will be insufficient, so the value should be 0.150 or higher. Ceq is preferably 0.180 or more, more preferably 0.200 or more. Ceq is a known index as shown in the following formula (3).
Ceq = C + Mn / 6 + (Cu + Ni) / 5+ (Cr + Mo + V) / 15 ... Equation (3)

In the above formulas (1) to (3), C, Mn, Cu, Sb, Mo, W, Ni, Cr, V, and N indicate the content based on the mass% of each element, and if they are not contained, they are 0. Is.

A method for manufacturing a steel material according to this embodiment will be described. The steel material according to the present embodiment includes steel plates, shaped steels, steel pipes and the like manufactured by hot rolling and, if necessary, cold rolling. A thick steel plate having a plate thickness of 3 mm or more, more preferably 6 mm or more is preferable.

The steel material according to the present embodiment is manufactured by melting steel by a conventional method, adjusting the components, hot rolling the steel pieces obtained by casting, and cold rolling if necessary. .. 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 may be formed into a tubular shape and welded, and may be a UO steel pipe, an electrosewn steel pipe, a forge welded steel pipe, a spiral steel pipe, or the like. A seamless steel pipe manufactured by hot-extruding or drilling and rolling a steel piece is also included in the present embodiment.

Hereinafter, the technical contents of the present invention will be further described with reference to examples of the present invention. The conditions in the examples shown below are one condition example adopted for confirming the feasibility and effect of the present invention, and the present invention is not limited to this one condition example. Further, the present invention can adopt various conditions as long as the gist of the present invention is not deviated and the object of the present invention is achieved.

Steels having the components shown in Tables 1 and 2 were melted, the ingots were heated at 1150 ° C. for 2 hours, and then hot-rolled and air-cooled to produce a steel sheet having a thickness of 20 mm. The balance of the components of each steel shown in Tables 1 and 2 is iron and impurities.

A 25 × 25 × 4 mm test piece was collected from the obtained steel sheet from the central part of the plate thickness and finished by wet # 400 polishing to obtain a test piece for corrosion resistance evaluation. The corrosion resistance was evaluated by a sulfuric acid immersion test and a hydrochloric acid immersion test. The sulfuric acid immersion test was performed at two levels, one immersed in a 50% sulfuric acid aqueous solution at 70 ° C. for 6 hours and the one immersed in an 80% sulfuric acid aqueous solution at 140 ° C. for 6 hours, and the hydrochloric acid immersion test was performed at 3 mol / at 60 ° C. It was immersed in an aqueous solution of L-hydrochloric acid for 6 hours at one level, and each was evaluated by reducing the amount of corrosion.

Based on Comparative Example AA, those with improved corrosion resistance by 30% or more (corrosion loss decreased to 70% or less of Comparative Example AA) were marked with ○, and those with improved corrosion resistance by 50% or more (corrosion loss was 50% of Comparative Example AA). Those (decreased below) were marked with ⊚, and those with less than 30% (corrosion loss was more than 70% of Comparative Example AA) were marked with x.

As for the hot workability (workability), the presence or absence of cracks was visually determined on the surface of the hot rolled material rolled under the above conditions.
In addition, as a weldability evaluation, a y-type weld crack test was performed based on JIS Z 3158. A 16 mmt test piece was used, and after welding from both sides with a current of 170 A, the presence or absence of cracks on the surface and cross section was confirmed after a predetermined time had elapsed.

In addition, a tensile test piece was prepared in accordance with JIS Z 2241, and a tensile test was performed to determine the tensile strength. Those having a tensile strength of 400 MPa or more were evaluated as ◯, and those having a tensile strength of less than 400 MPa were evaluated as x. The above results are shown in Table 3.

As shown in Table 3, Steel No. In A to Z, the components, Si / Al ratio, BI value, EI value, and Ceq are within the range of the present invention, and corrosion resistance to hydrochloric acid and sulfuric acid, processability, weldability, and strength are all good. On the other hand, Steel No. Any of the components, Si / Al ratio, BI value, EI value, and Ceq of AA to AJ is outside the scope of the present invention, and any of corrosion resistance, processability, weldability, and strength against hydrochloric acid and sulfuric acid is lowered. There is.

Steel No. AA is a steel used as a reference for evaluation of hydrochloric acid corrosion test and sulfuric acid corrosion test, but since it does not contain Cr, its corrosion resistance to hydrochloric acid and sulfuric acid is lower than that of the steel of the present invention. Steel No. with a small amount of Cu AB, Steel No. with Si / Al ratio out of range. Steel No. with AC, AD, and BI out of range. AE and AF also have lower corrosion resistance to hydrochloric acid and sulfuric acid than the steel of the present invention.

Steel No. Since AG has a low EI value, its workability is lowered. On the other hand, Steel No. Since AH has a high EI value, its corrosion resistance to hydrochloric acid and sulfuric acid is lowered. Steel No. AI has a small Ceq and insufficient strength. On the other hand, the steel No. with a large Ceq. AJ has reduced weldability.

Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to such examples. It is clear that a person having ordinary knowledge in the field of the art to which the present invention belongs can come up with various modifications or modifications within the scope of the technical idea described in the claims. , These are also naturally understood to belong to the technical scope of the present invention.

The steel material of the present invention is a boiler that burns heavy oil, fossil fuels such as coal, gas fuels such as liquefied natural gas, general waste such as municipal waste, industrial waste such as waste oil, plastics and exhaust tires, and sewage sludge. It can be used for smoke exhaust equipment. Specifically, a gas-gas heater composed of a flue duct, a casing, a heat exchanger, and two heat exchangers (heat recovery device and reheater) for smoke exhaust equipment, a scrubbering device, an electrostatic dust collector, and an attracting blower. , Can be suitably used for basket materials of rotary regeneration type air preheaters, heat transfer element plates, and the like.

Claims (3)

By mass%,
C: 0.01-0.10%,
Si: 0.04 to 0.40%,
Mn: 0.30 to 1.50%,
Cu: 0.05 to 0.50%,
Sb: 0.03 to 0.30%,
Ni: 0.01-0.50%,
Cr: 0.02 to 0.50%,
Al: 0.005 to 0.055%,
N: 0.002 to 0.010%,
P: 0 to 0.020%,
S: 0 to 0.015%, and O: 0 to 0.0035%
The balance consists of Fe and impurities.
The content of Si and the content of Al are mass ratios.
Si / Al: 7.0 to 15.0
Satisfied,
The BI required in (1) below is 0.55 to 30.00.
The EI required in (2) below is 1.0 to 6.0.
A steel material having a Ceq obtained by the following equation (3) of 0.150 to 0.400.
BI = (Cr / 52) / (N / 14) ... Equation (1)
EI = (Cu / 64) / (Sb / 122) ... Equation (2)
Ceq = C + Mn / 6 + (Cu + Ni) / 5+ (Cr + Mo + V) / 15 ... Equation (3)
Here, in the formula, C, Mn, Cu, Sb, Ni, Cr, V, and N indicate the content based on the mass% of each element, and when they are not contained, they are 0. Furthermore, by mass%,
Mo: 0.02 to 0.50% (excluding 0.02%),
The steel material according to claim 1, wherein the steel material contains. Furthermore, by mass%,
W: 0.50% or less,
Sn: 0.30% or less,
As: 0.30% or less,
Co: 0.30% or less,
Ti: 0.050% or less,
Nb: 0.10% or less,
V: 0.10% or less,
Zr: 0.050% or less,
Ta: 0.050% or less ,
B: 0.010% or less ,
Ca: 0.010% or less,
Mg: 0.010% or less, and
REM: 0.010% or less
The steel material according to claim 2 , wherein the steel material contains one kind or two or more kinds selected from the group consisting of.