JP7502594B2 - Steel - Google Patents

Description

The present invention relates to steel materials.

Furnaces at thermal power plants and incinerators at waste incineration facilities generate exhaust gases that contain water vapor, sulfur oxides, hydrogen chloride, etc. When this exhaust gas is cooled in the exhaust gas chimney or other facilities, it condenses into sulfuric acid and hydrochloric acid, which causes severe corrosion of the steel that makes up the exhaust gas flow path, a condition known as sulfuric acid dew-point corrosion and hydrochloric acid dew-point corrosion.

To address these problems, sulfuric acid/hydrochloric acid dew-point corrosion resistant steels and highly corrosion resistant stainless steels have been proposed. For example, Patent Documents 1 to 4 propose steel materials with excellent sulfuric acid dew-point corrosion resistance to which Cu, Sb, Co, Cr, etc. have been added. Patent Document 5 proposes highly corrosion resistant stainless steel to which Cr, Ni, etc. have been added.

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

Steel materials containing Cu, Sb, Cr, Co, etc. exhibit excellent corrosion resistance in corrosive sulfuric acid environments such as exhaust gas stacks. However, further improvements in corrosion resistance are expected to extend the life of power generation equipment and incineration equipment.

In addition to exhaust gas chimneys, the steel materials used in incinerator flues for gasification melting furnaces, heat exchangers, gas-gas heaters, desulfurization equipment, electric dust collectors, etc. are installed as steel plates or steel pipes, so they require not only corrosion resistance but also weldability.

The present invention aims to solve the above problems and provide a steel material that has excellent corrosion resistance and weldability in sulfuric acid and hydrochloric acid corrosive environments.

The present invention was made to solve the above problems, and the gist of the present invention is the following steel material.

(1) Chemical composition, in mass%,
C: 0.010% or more and less than 0.20%;
Si: 0.10 to 0.50%,
Mn: 0.10 to 1.20%,
S: 0.0005 to 0.015%,
Cu: 0.10 to 0.50%,
Ni: 0.01 to 0.50%,
Cr: 0.05 to 2.00%,
Ti: 0.006 to 0.150%,
Co: 0.010 to 0.30%,
Al: 0.005 to 0.10%,
P: 0.025% or less,
N: 0.0010 to 0.0080%,
O: 0.0005 to 0.0035%,
The balance is Fe and impurities.
Ti/N is 5.1 to 40.0,
The CI defined by the following formula (i) is 14.0 to 90.0,
Ceq defined by the following formula (ii) is 0.180 to 0.380;
Steel.
CI=(Cu/64)/(S/32) (i)
Ceq=C+Mn/6+(Cu+Ni)/5+(Cr+Mo+V)/15 (ii)
In the above formula, the element symbols represent the content (mass%) of each element contained in the steel material, and 0 is substituted when the element is not contained.

(2) The chemical composition is, in mass%, replacing a part of the Fe,
Mo: 0.50% or less,
W: 0.50% or less,
Sn: 0.30% or less,
Sb: 0.15% or less,
As: 0.30% or less; and Bi: 0.010% or less;
It contains one or more selected from
The steel material according to (1) above.

(3) The chemical composition contains, in mass%, a part of the Fe replaced by
Nb: 0.10% or less,
V: 0.10% or less,
Zr: 0.050% or less,
Ta: 0.050% or less; and B: 0.010% or less;
It contains one or more selected from
The steel material according to (1) or (2) above.

(4) The chemical composition is, in mass%, replacing a part of the Fe,
Ca: 0.010% or less,
Mg: 0.010% or less; and REM: 0.010% or less;
It contains one or more selected from
The steel material according to any one of (1) to (3) above.

The present invention makes it possible to provide steel materials that are corrosion resistant in acid corrosion environments and have excellent weldability.

In order to solve the above problems, the inventors conducted detailed research into the corrosion resistance and weldability of steel materials, and came to the following findings.

When the cause of corrosion that occurs in corrosion-resistant steel containing Cu, Sb, and Cr was investigated, it was found that the starting point is nitrides that form on the steel surface. Therefore, it was discovered that in order to suppress the formation of nitrides, it is important to control the Ti/N ratio, which is the ratio based on mass between the Ti content and the N content, to 5.1 to 40.0.

In addition, the formation of inclusions can be suppressed by reducing the S content. However, it has been found that when Cu and S are contained at the same time, a poorly soluble CuS coating is formed on the steel surface, improving the corrosion resistance of the steel more than expected. In other words, the balance of the Cu and S content is important, and by setting the value of the acid corrosion resistance index CI = (Cu/64)/(S/32) to 14.0 to 90.0, a CuS coating can be formed on the steel sheet surface while suppressing the formation of inclusions that are likely to become the starting point of corrosion.

Furthermore, in order to satisfy the above conditions and obtain steel with excellent weldability, it was found that it is important to set the carbon equivalent Ceq = C + Mn/6 + (Cu + Ni)/5 + (Cr + Mo + V)/15 to 0.180 to 0.380.

The present invention was made based on the above findings. Each aspect of the present invention will be explained in detail below.

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

C: 0.010% or more and less than 0.20% C is an element that improves the strength of steel. However, if C is contained in excess, carbides increase and corrosion resistance deteriorates. Therefore, the C content is set to 0.010% or more and less than 0.20%. The C content is preferably 0.030% or more, and more preferably 0.050% or more. In addition, the C content is preferably 0.15% or less, and more preferably 0.10% or less.

Si: 0.10 to 0.50%
Silicon is an element that contributes to deoxidation and strength improvement, and controls the form of oxides. However, if silicon is contained in excess, the amount of oxides increases, impairing corrosion resistance. Therefore, the silicon content is set to 0.10 to 0.50%. The silicon content is preferably 0.15% or more, and more preferably 0.20% or more. The silicon content is preferably 0.40% or less, and more preferably 0.30% or less.

Mn: 0.10 to 1.20%
Mn is an element that improves strength and toughness. However, if Mn is contained in excess, coarse MnS is generated, and corrosion resistance and mechanical properties deteriorate. Therefore, the Mn content is set to 0.10 to 1.20%. The Mn content is preferably 0.30% or more, and more preferably 0.50% or more. Moreover, the Mn content is preferably 1.00% or less, and more preferably 0.85% or less.

S: 0.0005 to 0.015%
S is an element that combines with Cu to form CuS, thereby exhibiting unexpected corrosion resistance. However, if S is contained in excess, it reduces the hot workability and mechanical properties of the steel. Therefore, the S content is set to 0.0005 to 0.015%. The S content is preferably 0.0010% or more, and more preferably 0.0050% or more. In addition, the S content is preferably 0.008% or less.

Cu: 0.10 to 0.50%
Cu is an extremely important element that, when contained together with Cr and Co, significantly exhibits corrosion resistance to sulfuric acid and hydrochloric acid. However, when Cu is contained in excess, hot workability is reduced, impairing manufacturability. Therefore, the Cu content is set to 0.10 to 0.50%. The Cu content is preferably 0.15% or more, and more preferably 0.20% or more. Moreover, the Cu content is preferably 0.40% or less, and more preferably 0.30% or less.

Ni: 0.01 to 0.50%
Ni exerts an effect of improving manufacturability in steel containing Cu. Cu has a large effect of improving corrosion resistance, but it is easily segregated, and when it is contained alone, it may promote cracking after casting. In contrast, Ni has an effect of reducing the surface segregation of Cu. By containing Ni, in addition to suppressing the segregation of Cu and the cracking of the cast piece, the occurrence of local corrosion due to segregation is also suppressed, so that the effect of improving corrosion resistance is significantly exerted. However, Ni is an expensive element, and the inclusion of a large amount leads to an increase in steelmaking costs. Therefore, the Ni content is set to 0.01 to 0.50%. The Ni content is preferably 0.05% or more, more preferably 0.10% or more, and even more preferably 0.15% or more. Moreover, the Ni content is preferably 0.30% or less, more preferably 0.25% or less.

Cr: 0.05 to 2.00%
Cr is an element that improves corrosion resistance, similar to Cu, Co, and Sb. In particular, by simultaneously containing Cr with Cu and Co, excellent corrosion resistance is exhibited in an acidic environment of high temperature and high concentration. However, if Cr is contained in excess, the corrosion resistance is impaired due to an increase in nitrides that are the starting point of corrosion. Therefore, the Cr content is set to 0.05 to 2.00%. The Cr content is preferably 0.10% or more. In addition, the Cr content is preferably 1.60% or less, and more preferably 1.00% or less.

Ti: 0.006 to 0.150%
Ti is an element that improves corrosion resistance. In particular, by simultaneously containing Ti with Cu and Co, excellent corrosion resistance is exhibited in an acidic environment. However, if Ti is contained in excess, the corrosion resistance is impaired due to an increase in nitrides that cause corrosion. Therefore, the Ti content is set to 0.006 to 0.150%. The Ti content is preferably 0.010% or more, and more preferably 0.015% or more. In addition, the Ti content is preferably 0.070% or less, and more preferably 0.050% or less.

Co: 0.010 to 0.30%
Co is an element that improves corrosion resistance in an acidic environment. In particular, when Co is contained simultaneously with Cu, it exhibits excellent corrosion resistance in an acidic environment. However, if an excessive amount of Co is contained, the economic efficiency decreases. Therefore, the Co content is set to 0.010 to 0.30%. The Co content is preferably 0.020% or more, more preferably 0.030% or more, and even more preferably 0.050% or more. Moreover, the Co content is preferably 0.20% or less, and more preferably 0.10% or less.

Al: 0.005 to 0.10%
Al is added as a deoxidizer. However, if an excessive amount of Al is contained, the corrosion resistance is impaired due to an increase in inclusions. Therefore, the Al content is set to 0.005 to 0.10%. The Al content is preferably 0.020% or more. Moreover, the Al content is preferably 0.050% or less.

P: 0.025% or less P is an impurity that reduces the mechanical properties and manufacturability of steel. Therefore, the upper limit of the P content is set to 0.025% or less. The P content is preferably 0.020% or less, and more preferably 0.015% or less. It is preferable to reduce the P content as much as possible, that is, the content may be 0%, but an extreme reduction leads to an increase in steelmaking costs. Therefore, the P content is preferably 0.001% or more.

N: 0.0010 to 0.0080%
N is an element that forms nitrides. However, when N is contained in excess, it forms coarse nitrides that become the starting point of corrosion in an acidic environment, reducing the corrosion resistance of the steel. Therefore, the N content is set to 0.0010 to 0.0080%. The N content is preferably 0.0015% or more, and more preferably 0.0020% or more. In addition, the N content is preferably 0.0075% or less, and more preferably 0.0070% or less.

O: 0.0005 to 0.0035%
O is an element that generates oxides, and by combining with MnS, it renders MnS harmless and has the effect of preventing deterioration of corrosion resistance and mechanical properties. However, if O is contained in excess, coarse oxides that become the starting point of corrosion in an acidic environment are generated. Therefore, the O content is set to 0.0005 to 0.0035%. The O content is preferably 0.0010% or more, and more preferably 0.0015% or more. In addition, the O content is preferably 0.0030% or less, and more preferably 0.0025% or less.

In addition to the above elements, the chemical composition of the steel of the present invention may further contain one or more elements selected from Mo, W, Sn, Sb, As and Bi within the ranges shown below. The reasons for limiting each element are explained below.

Mo: 0.50% or less Mo is an element that improves corrosion resistance in an acidic environment when contained simultaneously with Cu and Sb, so it may be contained as necessary. However, Mo is an expensive element, and the inclusion of a large amount of Mo leads to an increase in steelmaking costs. Therefore, the Mo content is set to 0.50% or less. The Mo content is preferably 0.30% or less. In particular, when the corrosion resistance to hydrochloric acid is to be improved, the Mo content is preferably 0.01% or more, and more preferably 0.10% or more.

W: 0.50% or less Like Mo, W is an element that improves corrosion resistance in an acidic environment when contained simultaneously with Cu and Sb, so it may be contained as necessary. However, W is an expensive element, and the inclusion of a large amount of W increases the steelmaking cost. Therefore, the W content is set to 0.50% or less. The W content is preferably 0.30% or less. In particular, when the corrosion resistance to hydrochloric acid is to be improved, the W content is preferably 0.01% or more, and more preferably 0.10% or more.

Sn: 0.30% or less Sn is an element that improves corrosion resistance in an acidic environment, so it may be contained as necessary. However, if Sn is contained in excess, hot workability decreases. Therefore, the Sn content is set to 0.30% or less. The Sn content is preferably 0.20% or less. In order to obtain the above effects, the Sn content is preferably 0.01% or more, more preferably 0.02% or more, and even more preferably 0.05% or more.

Sb: 0.15% or less Sb is an element that improves corrosion resistance in an acidic environment, so it may be contained as necessary. However, if Sb is contained in excess, hot workability decreases. Therefore, the Sb content is set to 0.15% or less. The Sb content is preferably 0.13% or less. In order to obtain the above effects, the Sb content is preferably 0.03% or more, and more preferably 0.05% or more.

As: 0.30% or less As is not as effective as Sb and Sn, but it is an effective element for improving corrosion resistance in an acidic environment, so it may be contained as necessary. However, if As is contained in excess, hot workability decreases. Therefore, the As content is set to 0.30% or less. The As content is preferably 0.20% or less, and more preferably 0.10% or less. In addition, when it is desired to obtain the above-mentioned effect, the As content is preferably 0.01% or more, more preferably 0.02% or more, and even more preferably 0.05% or more.

Bi: 0.010% or less Bi does not have a significant effect compared to Sb and Sn, but since it is an element that improves corrosion resistance in an acidic environment, it may be contained as necessary. However, if Bi is contained in excess, hot workability decreases. Therefore, the Bi content is set to 0.010% or less. The Bi content is preferably 0.007% or less, and more preferably 0.005% or less. In addition, when it is desired to obtain the above effect, the Bi content is preferably 0.001% or more, more preferably 0.002% or more, and even more preferably 0.005% or more.

In addition to the above elements, the chemical composition of the steel of the present invention may further contain one or more elements selected from Nb, V, Zr, Ta and B within the ranges shown below in order to improve mechanical properties, etc. The reasons for limiting each element are explained below.

Nb: 0.10% or less Nb, like Ti, is an element that forms nitrides, and may be included as necessary for the purpose of refining crystal grains and improving strength. However, if Nb is excessively included, mechanical properties may deteriorate. Therefore, 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. In addition, when it is desired to obtain the above effects, the Nb content is preferably 0.001% or more, and more preferably 0.005% or more.

V: 0.10% or less V, like Ti and Nb, is an element that forms nitrides, and may be included as necessary, mainly to improve strength by precipitation strengthening. However, if V is included in excess, mechanical properties may deteriorate. Therefore, the V content is set to 0.10% or less. The V content is preferably 0.050% or less, more preferably 0.030% or less, and even more preferably 0.020% or less. In addition, if it is desired to obtain the above effects, the V content is preferably 0.005% or more.

Zr: 0.050% or less Zr, like Ti, Nb and V, is an element that forms nitrides, and may be included as necessary, mainly to improve strength by precipitation strengthening. However, Zr is an expensive element, and a large amount of Zr increases the steelmaking cost. Therefore, the Zr content is set to 0.050% or less. The Zr content is preferably 0.040% or less, more preferably 0.030% or less, and even more preferably 0.020% or less. In order to obtain the above effects, the Zr content is preferably 0.005% or more.

Ta: 0.050% or less Ta is an element that contributes to improving strength, and also contributes to improving corrosion resistance, although the mechanism is not necessarily clear, so it may be contained as necessary. However, Ta is an expensive element, and the inclusion of a large amount of Ta leads to an increase in steelmaking costs. Therefore, the Ta content is set to 0.050% or less. The Ta content is preferably 0.040% or less, more preferably 0.030% or less, and even more preferably 0.020% or less. In addition, when it is desired to obtain the above effect, the Ta content is preferably 0.001% or more, and more preferably 0.005% or more.

B: 0.010% or less B is an element that improves hardenability and increases strength, so it may be contained as necessary. However, even if B is contained in excess, the effect is saturated and the toughness of the base material and HAZ may decrease. Therefore, the B content is set to 0.010% or less. The B content is preferably 0.0050% or less, more preferably 0.0030% or less, and even more preferably 0.0020% or less. In addition, if it is desired to obtain the above effect, the B content is preferably 0.0003% or more, and more preferably 0.0005% or more.

In addition to the above elements, the chemical composition of the steel of the present invention may further contain one or more elements selected from Ca, Mg, and REM within the ranges shown below for the purpose of deoxidization and inclusion control. The reasons for limiting each element are explained below.

Ca: 0.010% or less Ca is an element mainly used to control the form of sulfides, and may be contained as necessary to form fine oxides. However, if Ca is contained in excess, mechanical properties may be impaired. Therefore, the Ca content is set to 0.010% or less. The Ca content is preferably 0.005% or less. In order to obtain the above effects, the Ca content is preferably 0.0005% or more, more preferably 0.0010% or more, and even more preferably 0.0020% or more.

Mg: 0.010% or less Mg may be contained as necessary to form fine oxides. However, excessive addition of Mg leads to increased steelmaking costs. Therefore, the Mg content is set to 0.010% or less. The Mg content is preferably 0.005% or less, and more preferably 0.003% or less. In order to obtain the above effects, the Mg content is preferably 0.0001% or more, more preferably 0.0003% or more, and even more preferably 0.0005% or more.

REM: 0.010% or less REM (rare earth elements) are elements mainly used for deoxidation, and may be contained as necessary to form fine oxides. However, excessive addition of REM leads to increased steelmaking costs. Therefore, the REM content is set to 0.010% or less. The REM content is preferably 0.005% or less, and more preferably 0.003% or less. In addition, when it is desired to obtain the above-mentioned effects, the REM content is preferably 0.0001% or more, more preferably 0.0003% or more, and even more preferably 0.0005% or more. Here, REM represents Sc, Y, and lanthanoids, and the REM content represents the total content of these elements.

In the chemical composition of the steel of the present invention, the balance is Fe and impurities. Here, impurities refer to components that are mixed in from raw materials such as ores and scraps and other factors during the industrial production of steel, and are acceptable within the range that does not adversely affect the steel material of the present invention.

Ti/N: 5.1 to 40.0
As described above, Ti and N affect the corrosion resistance of steel materials. If the N content is excessive, the Ti/N ratio becomes small, and if the Ti content is excessive, the Ti/N ratio becomes large. In either case, nitrides are generated and tend to become the starting point of corrosion. Therefore, Ti/N is set to 5.1 to 40.0. Ti/N is preferably 6.0 or more, and more preferably 8.0 or more. Also, Ti/N is preferably 35.0 or less, and more preferably 30.0 or less.

CI: 14.0-90.0
Cu and S affect the corrosion resistance of steel materials. When the CI defined by the following formula (i) exceeds 90.0, it becomes difficult for a CuS coating to form on the steel material surface, and sufficient corrosion resistance cannot be obtained. However, when the CI is less than 14.0, the inclusions tend to become the starting point of corrosion, and the corrosion resistance may decrease. Therefore, the CI is set to 14.0 to 90.0. The CI is preferably 21.0 or more, and more preferably 27.0 or more. The CI is preferably 85.0 or less, and more preferably 80.0 or less.
CI=(Cu/64)/(S/32) (i)

Ceq: 0.180 to 0.380
In addition, C, Mn, Cu, Ni, Cr, Mo and V affect the weldability of steel. Ceq defined by the following formula (ii) is an index showing the deterioration of weldability due to an increase in the hardness of steel, and is set to 0.380 or less in order to ensure weldability. However, if Ceq is less than 0.180, the mechanical properties become insufficient. Therefore, Ceq is set to 0.180 to 0.380. Ceq is preferably 0.190 or more, and more preferably 0.200 or more. In addition, Ceq is preferably 0.340 or less.
Ceq=C+Mn/6+(Cu+Ni)/5+(Cr+Mo+V)/15 (ii)
However, in formula (ii), when the steel does not contain Mo and V, the calculation is performed assuming that these elements are 0.

(B) Manufacturing Method There are no particular limitations on the manufacturing method of the steel material according to the present invention, but examples include steel plates, steel sections, steel pipes, etc., which are manufactured by hot rolling and, if necessary, cold rolling.

When manufacturing steel, the steel is melted in the usual way, the components are adjusted, and the resulting steel billet is cast, hot rolled, and then cold rolled as necessary. After hot rolling, the steel may be water-cooled as is, or air-cooled, and then reheated and quenched. After hot rolling, the steel may be wound into a coil. After hot rolling, the steel may be cold-rolled and then further heat-treated.

When manufacturing steel pipes, steel plates may be formed into a tubular shape and welded, and can be made into UO steel pipes, electric resistance welded steel pipes, forged steel pipes, spiral steel pipes, etc. Seamless steel pipes manufactured by subjecting steel pieces to hot extrusion or piercing rolling are also included in the steel materials of the present invention.

The present invention will be explained in more detail below with reference to examples. Note that the conditions in the examples shown below are one example of conditions adopted to confirm the feasibility and effects of the present invention, and the present invention is not limited to this one example of conditions. Furthermore, various conditions may be adopted in the present invention as long as they do not deviate from the gist of the present invention and achieve the object of the present invention.

Steel having the chemical composition shown in Tables 1 and 2 was melted, and the steel ingot was heated at 1150°C for 2 hours, after which it was hot-rolled and air-cooled to produce a steel plate 20 mm thick.

The obtained steel plates were used to carry out the various performance evaluation tests shown below.

<Sulfuric acid resistance, hydrochloric acid resistance>
A test piece having a thickness of 4 mm, a width of 25 mm, and a length of 25 mm was taken from the center of each steel plate and finished by wet polishing with #400 to prepare a test piece for evaluating corrosion resistance. The corrosion resistance was evaluated by a sulfuric acid immersion test and a hydrochloric acid immersion test. In the sulfuric acid immersion test, the test piece was immersed in a 50% sulfuric acid aqueous solution at 70° C. for 6 hours, and in the hydrochloric acid immersion test, the test piece was immersed in a 10% hydrochloric acid aqueous solution at 80° C. for 5 hours.

Then, the corrosion weight loss of the test pieces after the sulfuric acid immersion test and the hydrochloric acid immersion test was calculated. Using Comparative Example AA as the standard, the sulfuric acid resistance and hydrochloric acid resistance were evaluated as follows: those with a corrosion weight loss of 60% or less were marked with ◎, those with a corrosion weight loss of more than 60% and less than 80% were marked with ○, and those with a corrosion weight loss of more than 80% were marked with ×.

<Weld cracks>
A y-type weld cracking test was carried out in accordance with JIS Z 3158: 2016. A test piece having a thickness of 20 mm 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 48 hours later.

<Tensile strength>
Tensile test pieces were prepared in accordance with JIS Z 2241:2011, and tensile tests were performed to determine the tensile strength. Tensile strengths of 400 MPa or more were evaluated as ◯, and those of less than 400 MPa were evaluated as ×.

Table 3 shows the measurement results of the sulfuric acid immersion test, hydrochloric acid immersion test, weld crack test, and tensile test.

As shown in Table 3, steels A to Z have good results in terms of corrosion resistance to hydrochloric acid and sulfuric acid, weldability, and tensile strength, because their chemical composition, Ti/N, CI, and Ceq are within the ranges of the present invention. On the other hand, steels AA to AI have poor results in terms of at least one of corrosion resistance to hydrochloric acid and sulfuric acid, weldability, and tensile strength, because their chemical composition, Ti/N, CI, and Ceq are outside the ranges of the present invention.

Steel AA was the steel used as the standard for evaluation in hydrochloric acid corrosion tests and sulfuric acid corrosion tests, but because its Ti/N was high, its corrosion resistance to hydrochloric acid and sulfuric acid was reduced compared to the steels of the present invention. Steel AB had reduced corrosion resistance because its Ti/N was low. Steel AC, which had a CI below the specified value, Steel AD, which had a CI above the specified value, Steel AG, which had a low Cu content, Steel AH, which had a low Cr content, and Steel AI, which had a low Co content, also had reduced corrosion resistance to hydrochloric acid and sulfuric acid compared to the steels of the present invention.

Furthermore, Steel AF had an excessive Ceq value, which caused weld cracks, and Steel AE had insufficient tensile strength because its Ceq was too low.

The steel material of the present invention can be used in smoke exhaust equipment for boilers that burn fossil fuels such as heavy oil and 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. Specifically, it can be suitably used for smoke exhaust equipment flue ducts, casings, heat exchangers, gas-gas heaters consisting of two heat exchangers (heat recovery unit and reheater), desulfurization equipment, electric dust collectors, induced draft fans, basket materials and heat transfer element plates and fin materials for rotary regenerative air preheaters, etc.

Claims (4)

The chemical composition, in mass%, is
C: 0.010% or more and less than 0.20%;
Si: 0.10 to 0.50%,
Mn: 0.10 to 1.20%,
S: 0.0005 to 0.015%,
Cu: 0.10 to 0.50%,
Ni: 0.01 to 0.50%,
Cr: 0.05 to 2.00%,
Ti: 0.006 to 0.150%,
Co: 0.010 to 0.30%,
Al: 0.005 to 0.10%,
P: 0.025% or less,
N: 0.0010 to 0.0080%,
O: 0.0005 to 0.0035%,
The balance is Fe and impurities.
Ti/N is 5.1 to 40.0,
The CI defined by the following formula (i) is 14.0 to 90.0,
Ceq defined by the following formula (ii) is 0.200 to 0.380;
Steel.
CI=(Cu/64)/(S/32) (i)
Ceq=C+Mn/6+(Cu+Ni)/5+(Cr+Mo+V)/15 (ii)
In the above formula, the element symbols represent the content (mass%) of each element contained in the steel material, and 0 is substituted when the element is not contained. O content is 0.0005 to 0.0023 %,
The Co content is 0.010 to 0.30% (excluding 0.020% or less),
The chemical composition is, in mass %, replacing a part of the Fe,
Mo: 0.50% or less,
W: 0.50% or less,
Sn: 0.30% or less,
Sb: 0.15% or less,
As: 0.30% or less; and Bi: 0.010% or less;
It contains one or more selected from
The steel material according to claim 1. The chemical composition is, in mass %, replacing a part of the Fe,
Nb: 0.10% or less,
V: 0.10% or less,
Zr: 0.050% or less,
Ta: 0.050% or less; and B: 0.010% or less;
It contains one or more selected from
The steel material according to claim 1 or 2. The chemical composition is, in mass %, replacing a part of the Fe,
Ca: 0.010% or less,
Mg: 0.010% or less; and REM: 0.010% or less;
It contains one or more selected from
The steel material according to any one of claims 1 to 3.