JP7091968B2 - 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.

For such problems, sulfuric acid / hydrochloric acid dew point corrosion resistant steel and highly corrosion resistant stainless steel have been proposed (see, for example, 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 carbides 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 Al / O in the range of 3.0 to 35.0.

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 (1) is 1.4 to 6.0, and the Ceq obtained by the following formula (2) is 0.180 to 0.330. Therefore, it was found that excellent acid resistance, hot workability and weldability can be obtained.

EI = (Cu / 64) / (Sb / 122) ... Equation (1)
Ceq = C + Mn / 6 + (Cu + Ni) / 5+ (Cr + Mo + V) / 15 ... Equation (2)

The present invention has been made based on such findings, and the gist thereof is as follows.
[1] By mass%,
C: 0.010 to 0.20%,
Si: 0.040 to 0.70%,
Mn: 0.20 to 1.00%,
Cu: 0.10 to 1.00%,
Sb: 0.010 to 0.30%,
Al: 0.005 to 0.050%,
Cr: 0.10 to 2.00%,
P: 0.020% or less,
S: 0.015% or less,
N: 0.010% or less, O: 0.0035% or less, the balance consists of Fe and impurities, and Al / O, which is the ratio based on the mass of Al content and O content, is
Al / O: 3.0 to 35.0
The steel material is characterized in that the EI obtained by the following formula (1) is 1.4 to 6.0 and the Ceq obtained by the following formula (2) is 0.180 to 0.330. ..
EI = (Cu / 64) / (Sb / 122) ... Equation (1)
Ceq = C + Mn / 6 + (Cu + Ni) / 5+ (Cr + Mo + V) / 15 ... Equation (2)
Here, in the formula, Cu, Sb, C, Mn, Ni, Cr, Mo, and V indicate the content based on the mass% of each element, and when they are not contained, they are 0.
[2] Furthermore, by mass%,
Mo: 0.10% or less,
W: 0.10% or less,
Ni: 1.00% or less,
Sn: 0.30% or less,
As: 0.30% or less, and
Co: The steel material according to [1], which contains one kind or two or more kinds selected from the group consisting of 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,
Ta: 0.050% or less, and
B: The steel material according to [1] or [2], which contains one kind or two or more kinds selected from the group consisting of 0.010% or less.
[4] Furthermore, by mass%,
Ca: 0.010% or less,
Mg: 0.010% or less, and
REM: The steel material according to any one of [1] to [3], which contains one kind or two or more kinds selected from the group consisting of 0.010% or less.

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 incineration facility and an acid corrosion environment such as 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 and Sn, it is effective to suppress carbides and oxides that tend to be corrosion starting points on the surface of the steel material. First, it was found that it is important to control Al / O, which is a ratio based on the mass of the Al content and the O content, in an appropriate range in order to suppress the formation of oxides. That is, if there is too much oxygen, Al / O becomes small, and if there is too much Al, Al / O becomes large, and in either case, the generated oxide tends to be the starting point of corrosion.

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, by setting the workability coefficient EI obtained by the following formula (1) and the Ceq value obtained by the following formula (2) within an appropriate range, hot workability, acid resistance, and acid resistance are maintained so as not to impair the manufacturability. It was found that weldability and strength can be ensured. By setting these in an appropriate range, we succeeded in obtaining a steel material having excellent acid resistance, hot workability and weldability.

EI = (Cu / 64) / (Sb / 122) ... Equation (1)
Ceq = C + Mn / 6 + (Cu + Ni) / 5+ (Cr + Mo + V) / 15 ... Equation (2)

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

(C: 0.010 to 0.20%)
C is an element that improves the strength, and it is necessary to contain 0.010% or more. The amount of C is preferably 0.030% or more, more preferably 0.050% or more. On the other hand, if the amount of C exceeds 0.20%, carbides increase and acid resistance deteriorates, so the amount of C is set to 0.20% or less. The amount of C is preferably 0.15% or less, more preferably 0.10% or less.

(Si: 0.040 to 0.70%)
Si is an element that contributes to deoxidation and improvement of strength, and it is necessary to contain 0.040% or more in order to control the morphology of the oxide. The amount of Si is preferably 0.050% or more, and more preferably 0.10% or more. On the other hand, if the Si content exceeds 0.70%, the oxide increases and the acid resistance is impaired, so the Si amount is set to 0.70% or less. The amount of Si is preferably 0.50% or less.

(Mn: 0.20 to 1.00%)
Mn is an element that improves strength and toughness, and contains 0.20% or more. The amount of Mn is preferably 0.30% or more. On the other hand, if an amount of Mn exceeding 1.00% is contained, coarse MnS is generated and the corrosion resistance and mechanical properties are deteriorated. Therefore, the amount of Mn is set to 1.00% or less. The amount of Mn is preferably 0.90% or less, more preferably 0.80% or less.

(Cu: 0.10 to 1.00%)
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 0.10% or more. The amount of Cu is preferably 0.15% or more, more preferably 0.20% or more. On the other hand, if the amount of Cu exceeds 1.00%, the hot workability is lowered and the manufacturability is impaired, so the content is set to 1.00% or less. The amount of Cu is preferably 0.90% or less, more preferably 0.80% or less.

(Sb: 0.010 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 0.010% or more in order to secure corrosion resistance in an acidic environment. The amount of Sb is preferably 0.050% 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.

(Al: 0.005 to 0.050%)
Al is a deoxidizing agent and needs to contain 0.005% or more. The amount of Al is 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 0.050% or less. The amount of Al is preferably 0.040% or less.

(Cr: 0.10 to 2.00%)
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 0.10% or more. The amount of Cr is preferably 0.15% or more. On the other hand, if Cr is excessively contained, the amount of Cr is set to 2.00% or less because the increase in nitrides, which is the starting point of corrosion, impairs acid resistance. More preferably, the amount of Cr is 1.80% or less, and more preferably, the amount of Cr is 1.50% or less.

(P: 0.020% or less)
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, but the P amount may be 0.001% or more from the viewpoint of cost.

(S: 0.015% or less)
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. Although the lower limit of the amount of S is not limited, the amount of S may be 0.001% or more because when S is contained at the same time as Cu and Sb, the corrosion resistance in an acidic environment is improved. The amount of S is more preferably 0.005% or more, still more preferably 0.01% or more.

(N: 0.010% or less)
N is an impurity and reduces the mechanical properties and manufacturability of the steel material, so the amount of N is 0.010% or less. The lower limit of the N amount is not limited, but the N amount may be 0.001% or more from the viewpoint of cost. When the fine nitride is used for improving the mechanical properties and the like, the amount of N may be 0.002% or more.

(O: 0.0035% or less)
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. From the viewpoint of cost, the amount of O is 0.0005% or more.

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

(Mo: 0.10% 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 0.02% or more, still more preferably 0.03% or more. On the other hand, since Mo is an expensive element, the Mo content is set to 0.10% or less from the viewpoint of cost. It is more preferably 0.08% or less, still more preferably 0.05% or less.

(W: 0.10% 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, in order to enhance the corrosion resistance to hydrochloric acid, the W amount may be contained in an amount of 0.01% or more. On the other hand, since W is also an expensive element, the content of W is set to 0.10% or less from the viewpoint of cost. It is more preferably 0.08% or less, still more preferably 0.05% or less.

(Ni: 1.00% or less)
Ni is an element that improves corrosion resistance in an acidic environment, and when Cu is contained, Ni exhibits the effect of improving 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 0.10% or more, more preferably 0.15% or more, still more preferably 0.20% or more. On the other hand, since Ni is an expensive element, the amount of Ni is set to 1.00% or less from the viewpoint of cost. More preferably, it is 0.80% 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 amount of Sb is more preferably 0.02% or more, and more preferably the amount of Sn is 0.05% or more. On the other hand, if Sb 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)
Co is an element that improves corrosion resistance in an acidic environment, although its effect is not remarkable as compared with Sb and Sn, 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, if Co is excessively contained, the economic efficiency is lowered, so 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 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 0.10% or more is contained, the mechanical properties may deteriorate, 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 can 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 it contains 0.050% or more of Zr, 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 Ta amount 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 (rare earth element) may be contained. Since these elements are not always essential in steel materials, the lower limit of the content is 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 amount of REM is more preferably 0.005% or less, still more preferably 0.003% or less.

Specific examples of the REM include Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, and one of them. Can be contained alone or in combination of two or more. When two or more kinds of rare earth elements are contained, for example, a mixed rare earth element (mish metal) before separation and purification, or a mixture or compound of rare earth elements such as a dizim alloy (alloy consisting of Nd and Pr) may be used. .. Further, when two or more kinds of rare earth elements are contained, the above-mentioned REM amount means the total amount of all rare earth elements.

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 with 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 P, S, N and O as described above.

The steel material according to the present embodiment needs to control the relationship between specific elements in order to improve acid resistance, hot workability, weldability and strength.

(Al / O: 3.0 to 35.0)
Al / O (mass ratio) is an important index for suppressing oxides that tend to be corrosion starting points on the surface of steel materials. It was found that it is important to control Al / O within an appropriate range in order to suppress the formation of oxides. If it is less than 3.0 or more than 35.0, an oxide that tends to be a corrosion starting point may be produced. Further, when Al / O is larger than 35.0, the hot workability is lowered. Al / O is preferably 3.5 or more, more preferably 4.0 or more. The Al / O is preferably 30.0 or less, more preferably 25.0 or less.

(EI: 1.4-6.0)
The index EI is an index considering the influence of Sb that promotes the deterioration of hot workability due to Cu, and is mainly important for ensuring hot workability and acid resistance. If the content of Sb is too large with respect to the content of Cu, the hot workability deteriorates, so the index EI needs to be 1.4 or more. The index EI is preferably 1.5 or more, more preferably 2.0 or more. Increasing the index EI is preferable for ensuring hot workability, but the effect is saturated even if it exceeds 6.0. In addition, it is necessary to set the index EI to 6.0 or less so that the effect of improving acid resistance is not insufficient due to insufficient Sb. The index EI is preferably 5.9 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 (1). That is, Cu / 64 and Sb / 122 are terms obtained by dividing the contents of Cu and Sb by the atomic weight of each element, respectively.
EI = (Cu / 64) / (Sb / 122) ... Equation (1)

(Ceq: 0.180 to 0.330)
Ceq is an index showing deterioration of weldability due to an increase in hardness, and is set to 0.330 or less, preferably 0.320 or less in order to secure weldability. on the other hand. If Ceq is too low, the strength becomes insufficient, so the strength is 0.180 or more, preferably 0.200 or more, and more preferably 0.250 or more. Ceq is an index represented by the following formula (2).
Ceq = C + Mn / 6 + (Cu + Ni) / 5+ (Cr + Mo + V) / 15 ... Equation (2)

In the above formulas (1) and (2), Cu, Sb, C, Mn, Ni, Cr, Mo, and V indicate the content based on the mass% of each element, and if they are not contained, they are calculated as 0. ..

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. The steel material is preferably a thick steel plate having a plate thickness of 3 mm or more, more preferably 6 mm or more.

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 each of the obtained steel sheets 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 carried out by immersing in a 50% aqueous sulfuric acid solution at 70 ° C. for 5 hours, and the hydrochloric acid immersion test was carried out by immersing in a 3.6% aqueous hydrochloric acid solution at 40 ° C. for 5 hours, 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 reduction decreased to 70% or less of Comparative Example AA) were marked with ○, and those with improved corrosion resistance by 50% or more (corrosion reduction 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, the presence or absence of cracks was visually determined on the surface of the hot rolled material rolled under the above conditions.

In addition, a y-type weld crack test was conducted based on JIS Z 3158. A 20 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 results are shown in Table 3.

As shown in Table 3, Steel No. The components, Al / O, EI value, and Ceq value of A to Z are within the range of the present invention, and the corrosion resistance, processability, weldability, and strength against hydrochloric acid and sulfuric acid are all good. On the other hand, Steel No. In AA to AI, any of the components, Al / O, EI value, Ceq value, Cu, Cr or Sb is out of the scope of the present invention, and any of corrosion resistance, processability, weldability and strength against hydrochloric acid and sulfuric acid is obtained. It is declining.

Steel No. AA is a steel used as a reference for evaluation of hydrochloric acid corrosion test and sulfuric acid corrosion test, but since the EI value exceeds the upper limit specified in the present invention, the corrosion resistance to hydrochloric acid and sulfuric acid is higher than that of the steel of the present invention. It is declining. Steel No. 1 whose Al / O is outside the range specified in the present invention. The steel No. which is below the lower limit of AC and AD and Cu, Cr and Sb specified in the present invention. AG, AH, and AI also have lower corrosion resistance to hydrochloric acid and sulfuric acid than the steel of the present invention.

Steel No. AB and Steel No. Since AG has a low EI value, its hot workability is lowered. Steel No. In AC, the hot workability is deteriorated because Al / O exceeds the upper limit of the range specified in the present invention.

Steel No. with a large Ceq AE has reduced weldability. Steel No. AF has a small Ceq and insufficient strength.

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 consisting 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 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 (4)

By mass%,
C: 0.010 to 0.20%,
Si: 0.040 to 0.70%,
Mn: 0.20 to 1.00%,
Cu: 0.10 to 1.00%,
Sb: 0.010 to 0.30%,
Al: 0.005 to 0.050%,
Cr: 0.10 to 2.00%,
P: 0.020% or less,
S: 0.015% or less,
N: 0.010% or less, and
O: 0.0035% or less,
Al / O, which is a ratio based on the mass of Al content and O content, is composed of Fe and impurities, and has an Al / O content.
Al / O: 3.0 to 35.0
The steel material is characterized in that the EI obtained by the following formula (1) is 1.4 to 6.0 and the Ceq obtained by the following formula (2) is 0.180 to 0.330. ..
EI = (Cu / 64) / (Sb / 122) ... Equation (1)
Ceq = C + Mn / 6 + (Cu + Ni) / 5+ (Cr + Mo + V) / 15 ... Equation (2)
Here, in the formula, Cu, Sb, C, Mn, Ni, Cr, Mo, and V indicate the content based on the mass% of each element, and when they are not contained, they are 0. Furthermore, by mass%,
Mo: 0.10% or less,
W: 0.10% or less,
Ni: 1.00% or less,
Sn: 0.30% or less,
As: 0.30% or less, and
The steel material according to claim 1, wherein Co: contains one kind or two or more kinds selected from the group consisting of 0.30% or less. Furthermore, by mass%,
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, and
B: The steel material according to claim 1 or 2, which contains one kind or two or more kinds selected from the group consisting of 0.010% or less. Furthermore, by mass%,
Ca: 0.010% or less,
Mg: 0.010% or less, and
REM: The steel material according to any one of claims 1 to 3, which contains one kind or two or more kinds selected from the group consisting of 0.010% or less.