WO2021005960A1 - 耐硫酸露点腐食性に優れる継目無鋼管およびその製造方法 - Google Patents
耐硫酸露点腐食性に優れる継目無鋼管およびその製造方法 Download PDFInfo
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- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/10—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies
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- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
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- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- C22C38/008—Ferrous alloys, e.g. steel alloys containing tin
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
Definitions
- the present invention relates to a seamless steel pipe having excellent sulfuric acid dew point corrosion resistance and a method for manufacturing the same. More specifically, the present invention is a seamless steel pipe suitable for piping used in a sulfuric acid dew point corrosion environment generated by combustion exhaust gas of a boiler, a gasification melting furnace, etc., and particularly in an exhaust heat recovery boiler.
- the present invention relates to a seamless steel pipe for piping, which is useful for preventing scattering of corrosion products caused by dew point corrosion and has excellent corrosion resistance to dew point corrosion, and a method for manufacturing the same.
- Patent Document 2 W, Sn, and Cr are added to steel having C: 0.01 to 0.12 mass%, Cu: 0.03 to 1.0 mass%, and Sb: 0.002 to 0.7 mass%.
- C, Sb, and W so as to satisfy a specific relationship, a sulfuric acid dew point corrosive steel having improved sulfuric acid dew point corrosiveness as well as hydrochloric acid dew point corrosive property is disclosed.
- Patent Documents 1 and 2 reduce the dew point corrosion rate of sulfuric acid or the dew point corrosion rate of hydrochloric acid, which is a problem in exhaust heat recovery boilers and the like. It is considered to be effective in suppressing the occurrence. However, in a harsher environment where the sulfuric acid concentration is 70% by mass, it is difficult to sufficiently suppress the sulfuric acid dew point corrosion. Furthermore, no mention is made of exfoliation of corrosion products generated in the environment. Furthermore, there is no detailed description regarding the production of seamless steel pipes suitable for exhaust heat recovery boiler piping, and it is not possible to find the optimum conditions for achieving both sulfuric acid dew point corrosiveness and seamless steel pipe manufacturability.
- the present invention has been made in view of the above circumstances, is excellent in sulfuric acid dew point corrosion resistance, is suitable for piping used in a sulfuric acid dew point corrosion environment such as an exhaust heat recovery boiler, and has excellent manufacturability.
- the purpose is to provide steel-free pipes.
- Another object of the present invention is to provide a suitable manufacturing method for the above-mentioned seamless steel pipe.
- the present inventors first diligently studied the exfoliation property of the corrosion product generated in the sulfuric acid dew point corrosion environment.
- the basic chemical composition is C: 0.04%, Si: 0.2%, Mn: 1.4%, Al: 0.02% in mass%, which is further effective for acid resistance.
- a seamless steel pipe having an outer diameter of 138.9 mm and a wall thickness of 10.8 mm is obtained from a base steel pipe material having a component composition in which Cu and Sb are added, and further from a steel pipe material having a component composition in which Sn, W, and Cr are appropriately added.
- Manufactured After normalizing heat treatment of these seamless steel pipes at a normalizing temperature of 950 ° C., corrosion test pieces were collected from the outer surface side of the steel pipes.
- a corrosion test piece (length) is collected from the outer surface side of the steel pipe so as to include the outer surface of the steel pipe, and the surface corresponding to the outer surface side of the steel pipe is ground by 0.5 mm to remove scale and the like. 30 mm in width ⁇ 20 mm in width ⁇ 5 mm in thickness) was prepared. Subsequently, a sulfuric acid dew point corrosion test was carried out according to the procedure schematically shown in FIG. 1, and the peelability of the corrosion product produced in the corrosion test was evaluated.
- a sulfuric acid aqueous solution adjusted to a concentration of 70% by mass is injected into a container, the liquid temperature is kept heated to 50 ° C. by an external constant temperature bath, and then a corrosion test piece (test piece in FIG. 1). 1) was immersed. The immersion time was 96 hours. After immersion for 96 hours, the sulfuric acid aqueous solution was discharged from the container, the corrosion test piece 1 was dried, carefully taken out, and the corrosion product generated on the surface of the corrosion test piece was photographed with a digital camera 2 on a photographing table. The imaging surface was the surface that was on the outer surface side of the steel pipe when the corrosion test piece was processed.
- Photographed image analysis performing appropriate image processing on the image by (NIH using the development of the Image J software) to calculate the area S I of the resulting corrosion product (mm 2).
- a transparent adhesive film manufactured by NICHIBAN, cellophane tape (registered trademark), product number CT-24, width 24 mm
- the corrosion products produced by peeling the film were peeled off.
- Corrosion products that are easily affected were collected on the adhesive surface of the adhesive film.
- the corrosion product collected on the adhesive surface of the adhesive film is photographed with a digital camera 2, the image is analyzed, the area of the corrosion product collected on the adhesive surface of the adhesive film is calculated, and this is calculated from the corrosion test piece.
- the area of the peeled corrosion product was defined as S II (mm 2 ).
- the generated corrode ratio [(S II / S I) ⁇ 100] of the area of corrosion products were stripped from the corrosion test piece to an area of the corrosion products formed corrode the test piece surface (S I) (S II) It was defined as the peeling rate (%).
- FIG. 2 shows a comparison of corrosion product peeling rates after the sulfuric acid dew point corrosion test of seamless steel pipes with different amounts of Cu, Sb, Sn, W, and Cr used in the experiment.
- the basic chemical components 0.04% C-0.2% Si-1.4% Mn-0.02% Al
- Cu 0.3%
- Sb 0.1
- the amount of Sb added was increased to “0.3% Cu-0.2% Sb”.
- No significant difference was observed in the corrosion product peeling rate of the "0.3% Cu-0.1% Sb-0.05% Sn" material to which the "material” and Sn were added.
- the corrosion product peeling rate changes depending on the manufacturing method of the steel pipe material even with the same composition.
- the steel pipe material obtained by continuously casting directly into a slab having a circular cross section (hereinafter, also referred to as “directly cast steel pipe material”) is formed and heat-treated to form a seam.
- directly cast steel pipe material a steel pipe obtained by melting steel in a rotary furnace, once continuously casting it into a slab having a rectangular cross section, and then heating and hot rolling it to form a circular cross section.
- the material hereinafter also referred to as "steel piece rolled steel pipe material” had a better corrosion product peeling rate.
- the present inventors have conducted extensive research in order to clarify the difference in the corrosion product peeling rate between the above steel pipe materials (straight-cast steel pipe material, steel piece rolled steel pipe material). As a result, it was found that the difference was in the concentration of alloying elements on the outer surface of the seamless steel pipe. Specifically, in the seamless steel pipe of the "0.3% Cu-0.1% Sb-0.6% Cr" material used for measuring the corrosion product peeling rate, the adjacent portion of the region where the corrosion test piece was collected. A sample was taken and the cross section orthogonal to the longitudinal direction of the steel pipe was mirror-polished. Next, a quantitative ray analysis of Cr was performed by an electron probe microanalyzer (EPMA).
- EPMA electron probe microanalyzer
- the measurement conditions for EPMA are an acceleration voltage of 20 kV, a beam current of 0.5 ⁇ A, and a beam diameter of 10 ⁇ m. Using a calibration curve prepared in advance from the X-ray intensity, it was converted to Cr concentration (mass%).
- FIG. 3 shows EPMA of a sample collected from a seamless steel pipe produced by forming and heat-treating a steel pipe material as it is directly cast, and a sample collected from a seamless steel pipe produced by forming and heat-treating a rolled steel pipe material.
- the line analysis results are compared and shown.
- the sample collected from the seamless steel pipe produced by forming and heat-treating the steel pipe material as it is directly cast has almost the same Cr in the region from the outer surface of the steel pipe to 4 mm in the wall thickness center direction. The concentration was shown.
- the steel pipe material subjected to the same heat treatment as the heat treatment applied when the slab having a rectangular cross section is converted into the steel piece rolled steel pipe material from the straight cast steel pipe material (hereinafter, also referred to as "slab heat-treated steel pipe material").
- the sample collected from the seamless steel pipe manufactured by forming and heat-treating the steel piece can obtain the same increase in Cr concentration as the sample collected from the seamless steel pipe produced by forming and heat-treating the steel piece rolled steel pipe material. I understood.
- the present inventors performed the same EPMA measurement for alloying elements other than Cr.
- the relationship with the corrosion product peeling rate of the corrosion test was investigated diligently. As a result, the alloying elements that affect the peeling rate of corrosion products were narrowed down when Cu, Cr, and Sb were added and when W was added together with Cu, Cr, and Sb, and the seamless steel pipe obtained by EPMA measurement was narrowed down.
- the present invention has been completed based on these findings, and has the following gist.
- the average Cu concentration (mass%), average Cr concentration (mass%), and average Sb concentration (mass%) in the region of 0.5 to 2.0 mm from the outer surface of the steel pipe toward the center of the wall thickness are Cu * and Cr, respectively.
- Cu * , Cr * , and Sb * satisfy the following equation (1).
- the cooled steel pipe material is heated to 1100 to 1300 ° C. and then hot-rolled at 800 ° C. or higher to obtain a seamless steel pipe having a predetermined shape, cooled, and then cooled.
- a method for producing a seamless steel pipe having excellent sulfuric acid dew point corrosion resistance which is subjected to normalizing heat treatment by heating at a normalizing temperature of 850 to 1050 ° C.
- a method for manufacturing a seamless steel pipe with excellent sulfuric acid dew point corrosiveness is a method for manufacturing a seamless steel pipe with excellent sulfuric acid dew point corrosiveness.
- a method for producing a seamless steel pipe having excellent sulfuric acid dew point corrosion resistance which is subjected to normalizing heat treatment by heating at a normalizing temperature of 850 to 1050 ° C.
- the resistance according to [6] wherein when a slab having a circular cross section is heated to a heating temperature in a temperature range of 1000 to 1200 ° C., the heating time from 900 ° C. to the heating temperature is 1.5 hours or more.
- the present invention it is possible to provide a seamless steel pipe having excellent sulfuric acid dew point corrosion resistance, suitable for piping used in a sulfuric acid dew point corrosion environment such as an exhaust heat recovery boiler, and excellent in manufacturability. Further, according to the present invention, it is possible to provide a suitable manufacturing method for the seamless steel pipe.
- the seamless steel pipe of the present invention is excellent in sulfuric acid dew point corrosion resistance, and is excellent in the effect of suppressing peeling of corrosion products generated in a harsher environment where the sulfuric acid concentration is 70% by mass in an exhaust heat recovery boiler or the like. Further, the seamless steel pipe of the present invention has a predetermined yield strength and tensile strength and is suitable for piping. Further, the seamless steel pipe of the present invention is excellent in the effect of suppressing defects generated in the manufacturing process thereof and is excellent in manufacturability.
- FIG. 1 is a schematic view illustrating a method for measuring a corrosion product peeling rate.
- FIG. 2 is a graph showing the results of investigation of the corrosion product peeling rate of the seamless steel pipe experimental materials having different amounts of Cu, Sb, Sn, W, and Cr added.
- FIG. 3 is a graph showing the results of EPMA line analysis of a region of the outer surface to 4 mm of a seamless steel pipe manufactured from different steel pipe materials.
- FIG. 4 is a graph showing the correlation between the regression equation of Cu, Cr, Sb, and W concentrations (Cu * , Cr * , Sb * , W * ) near the outer surface of the seamless steel pipe and the corrosion product exfoliation rate. is there.
- the seamless steel pipe having excellent sulfuric acid dew point corrosion resistance of the present invention is also simply referred to as the seamless steel pipe of the present invention.
- C 0.02 to 0.12% C is an element that enhances the strength of steel, and in the present invention, the content of C is required to be 0.02% or more in order to satisfy the yield strength and tensile strength particularly required for seamless steel pipes for piping. Therefore, the C content is set to 0.02% or more.
- the C content is preferably 0.021% or more, more preferably 0.022% or more.
- the content of C exceeding 0.12% adversely affects the hot ductility at high temperature. Specifically, it causes surface defects during hot rolling of seamless steel pipes. Therefore, the upper limit of the C content is set to 0.12%. From the viewpoint of preventing surface defects, the C content is preferably 0.08% or less, more preferably 0.04% or less.
- Si 0.010 to 1.00%
- Si is an element that acts as a deoxidizer and dissolves in steel to increase the strength of steel.
- 0.010% or more of Si content is required. Therefore, the Si content is 0.010% or more.
- the Si content is preferably 0.05% or more, more preferably 0.20% or more.
- the content of Si exceeding 1.00% adversely affects the hot ductility at high temperature. Therefore, the upper limit of the Si content is set to 1.00%.
- the Si content is preferably 0.80% or less, more preferably 0.60% or less.
- Mn 0.10 to 2.00%
- Mn is an element that enhances the strength of steel by improving hardenability, and in the present invention, in order to satisfy the yield strength and tensile strength particularly required for seamless steel pipes for piping, 0.10% or more.
- Mn content is required. Therefore, the Mn content is set to 0.10% or more.
- the Mn content is preferably 0.50% or more, more preferably 1.10% or more.
- the upper limit of the Mn content is set to 2.00%.
- the Mn content is preferably 1.80% or less, more preferably 1.40% or less.
- P 0.050% or less P causes significant central segregation during continuous casting and causes internal defects during drilling during hot rolling of seamless steel pipes. Therefore, in the present invention, it is desirable to reduce as much as possible, but up to 0.050% is acceptable. Therefore, the P content is set to 0.050% or less.
- the P content is preferably 0.030% or less, more preferably 0.015% or less.
- the lower limit of the P content is not particularly limited, but since excessive de-P causes an increase in manufacturing cost, it is preferable that the lower limit of the P content is about 0.004%.
- S 0.004% or less S also has a remarkable central segregation during continuous casting, which causes internal defects during drilling in hot rolling of seamless steel pipes. Therefore, in the present invention, it is desirable to reduce as much as possible, but up to 0.004% is acceptable. Therefore, the S content is set to 0.004% or less.
- the S content is preferably 0.003% or less, more preferably 0.002% or less.
- the lower limit of the S content is not particularly limited, but since excessive removal of S causes an increase in manufacturing cost, it is preferable that the lower limit of the S content is about 0.0004%.
- Al 0.010 to 0.100%
- Al is an element that acts as a deoxidizing material. In order to reduce solid solution oxygen and prevent a decrease in the amount of effective Cr due to Cr oxide formation when Cr is contained, 0.010% or more is required. Therefore, the Al content is set to 0.010% or more.
- the Al content is preferably 0.015% or more, more preferably 0.020% or more.
- the upper limit of the Al content is set to 0.100%.
- the Al content is preferably 0.080% or less, more preferably 0.040% or less.
- Cu 0.03 to 0.80% Cu is an element effective in preventing corrosion of steel in a sulfuric acid dew point environment. Further, when it is concentrated on the outer surface of the steel pipe by the combined addition with Cr, it works to improve the peelability of the corrosion product. In order to obtain such an effect, Cu needs to be contained in an amount of 0.03% or more. Therefore, the Cu content is set to 0.03% or more.
- the Cu content is preferably 0.10% or more, more preferably 0.20% or more.
- Cu lowers the high temperature ductility of steel, and when it is contained in excess of 0.80%, outer surface defects occur significantly during hot rolling, so the upper limit of the Cu content is high. Is 0.80%.
- the Cu content is preferably 0.60% or less, more preferably 0.40% or less.
- Ni 0.02 to 0.50%
- Ni is an element that suppresses a decrease in high-temperature ductility of Cu when compoundly added to Cu-containing steel. In order to obtain such an effect, a content of 0.02% or more is required. Therefore, the Ni content is set to 0.02% or more.
- the Ni content is preferably 0.08% or more, more preferably 0.10% or more.
- the upper limit of the Ni content is set to 0.50%.
- the Ni content is preferably 0.45% or less, and more preferably 0.30% or less.
- Cr 0.55 to 1.00% Cr does not contribute significantly to the prevention of corrosion in a sulfuric acid dew point environment, but as shown in FIG. 2, it is an important element that contributes to the improvement of the peelability of corrosion products by the combined addition of Cu and Sb. .. In order to obtain such an effect, a content of 0.55% or more is required. Therefore, the Cr content is set to 0.55% or more.
- the Cr content is preferably 0.57% or more, more preferably 0.60% or more.
- the upper limit of the Cr content is set to 1.00%.
- the Cr content is preferably 0.90% or less, and more preferably 0.80% or less.
- Sb 0.005 to 0.20%
- Sb is an element effective in preventing steel corrosion in a sulfuric acid dew point corrosion environment. Further, when it is concentrated on the outer surface of the steel pipe by the combined addition with Cr, it works to improve the peelability of the corrosion product. In order to obtain such an effect, Sb needs to be contained in an amount of 0.005% or more. Therefore, the Sb content is set to 0.005% or more.
- the Sb content is preferably 0.02% or more, more preferably 0.05% or more.
- the upper limit of the Sb content is set to 0.20%.
- the Sb content is preferably 0.15% or less, more preferably 0.09% or less.
- W 0.003 to 0.040%
- Sn 0.005 to 0.5%
- W 0.003 to 0.040%
- W like Cr
- W improves the exfoliation property of corrosion products produced in a sulfuric acid dew point environment.
- it since it is an expensive element unlike Cr, it may be contained for the purpose of further improving the exfoliation property of the corrosion product by adding it in combination with Cr.
- W needs to be contained in an amount of 0.003% or more. Therefore, when W is contained, the W content is set to 0.003% or more.
- the W content is preferably 0.005% or more, more preferably 0.008% or more.
- the content exceeds 0.040%, the occurrence of internal defects during drilling in hot rolling of seamless steel pipes is promoted, especially in the central segregation portion during continuous casting. Therefore, when W is contained, the upper limit of the W content is set to 0.040%.
- the W content is preferably 0.030% or less, and more preferably 0.015% or less.
- Sn 0.005 to 0.5%
- Sn does not significantly affect the improvement of the peeling rate of the corrosion product generated in the sulfuric acid dew point environment, but may be contained for the purpose of reducing the corrosion itself in the sulfuric acid dew point corrosion environment. ..
- Sn needs to be contained in an amount of 0.005% or more. Therefore, when Sn is contained, the Sn content is set to 0.005% or more.
- the Sn content is preferably 0.02% or more.
- the upper limit of the Sn content is set to 0.5%.
- the Sn content is preferably 0.05% or less.
- the rest other than the above components are Fe and unavoidable impurities.
- Specific unavoidable impurity elements include H, O, Co, As, Zr, Ag, Ta, Pb and the like.
- the permissible upper limit of each unavoidable impurity element is H: 0.0005%, O: 0.004%, Co: 0.001%, As: 0.006%, Zr: 0.0004%, Ag: 0. 001%, Ta: 0.004%, Pb: 0.005%.
- the seamless steel pipe of the present invention has an average Cu concentration (mass%), an average Cr concentration (mass%), and an average Sb concentration in a region of 0.5 to 2.0 mm from the outer surface of the seamless steel pipe in the central direction of the wall thickness.
- (mass%) and average W concentration (mass%) are Cu * , Cr * , Sb * , and W * , respectively, when W is not added, 1.7 ⁇ Cu * + 11 ⁇ Cr * +3.8 ⁇ Sb * ⁇ 13.5 ⁇ ⁇ ⁇ (1)
- the filling In the case of W addition 1.7 ⁇ Cu * + 11 ⁇ Cr * +3.8 ⁇ Sb * +5.2 ⁇ W * ⁇ 13.5 ⁇ ⁇ ⁇ (2) Meet.
- the exfoliation property of the corrosion product generated in the sulfuric acid dew point environment is related to the concentration of Cu, Cr, Sb and W on the surface of the steel pipe.
- the steel pipe surface referred to here refers to a region up to 2 mm from the outer surface of the steel pipe.
- the composition of the corrosion product corresponds to Cu, Cr, Sb, and W that elute when this region is corroded in a sulfuric acid dew point environment, and when these elements are concentrated on the steel pipe surface, the peelability is improved. Conceivable.
- the present inventor collects samples for EPMA analysis from various steel pipes, sets the measurement conditions to an acceleration voltage of 20 kV, a beam current of 0.5 ⁇ A, and a beam diameter of 10 ⁇ m, from the outer surface side of the steel pipe of the sample toward the center of the wall thickness.
- Concentration (% by mass) of Cu, Cr, Sb, and W obtained by performing EPMA line analysis measurement in a 2 mm region using a calibration curve prepared in advance from the characteristic X-ray intensity of each element. was calculated.
- the arithmetic average of the concentrations (mass%) of Cu, Cr, Sb, and W calculated every 0.25 mm in the region of 0.5 to 2.0 mm from the outer surface of the steel pipe toward the center of the wall thickness is calculated.
- the value calculated on the left side of the equation (1) must satisfy 13.5 or more when W is not added.
- the value calculated on the left side of the equation (1) is preferably 14.0 or more, and more preferably 15.0 or more.
- the corrosion product peeling rate can be further reduced, and for example, a corrosion product peeling rate of 8% or less can be obtained.
- the corrosion product peeling rate can be further reduced, and for example, a corrosion product peeling rate of 5% or less can be obtained.
- the value calculated on the left side of the equation (2) must satisfy 13.5 or more.
- the value calculated on the left side of the equation (2) is preferably 14.0 or more, and more preferably 15.0 or more.
- the corrosion product peeling rate can be further reduced, and for example, a corrosion product peeling rate of 8% or less can be obtained.
- the corrosion product peeling rate can be further reduced, and for example, a corrosion product peeling rate of 5% or less can be obtained.
- the Cu, Cr, Sb, and W contents of the steel should be appropriately combined, and the steel pipe manufacturing method described later, particularly the steel piece rolling or slab heat treatment to be carried out after continuous casting of the steel pieces, is optimal. It is achieved by doing it under various conditions.
- the seamless steel pipe of the present invention has a yield strength of 230 MPa or more and a tensile strength of 380 MPa or more in order to have sufficient strength when used for piping.
- the yield strength is preferably 250 MPa or more.
- the tensile strength is preferably 400 MPa or more.
- the yield strength and tensile strength can be measured by the method described in Examples.
- the method for melting steel is not particularly limited.
- molten steel having the above-mentioned composition can be melted by a commonly known melting method such as a converter, an electric furnace, or a vacuum melting furnace.
- the molten steel casting method is preferably a continuous casting method.
- continuous casting there are cases where continuous casting is performed on slabs having a rectangular cross section such as general slabs and blooms, and cases where continuous casting is performed directly on slabs having a circular cross section more suitable for hot rolling into seamless steel pipes.
- the manufacturing conditions in the subsequent manufacturing process change.
- a slab having a rectangular cross section has a substantially square columnar outer shape
- a slab having a circular cross section has a substantially cylindrical outer shape.
- the slab having the rectangular cross section is heated to a predetermined heating temperature and then hot-rolled to obtain a steel pipe material having a circular cross section.
- the heating temperature is as follows.
- the temperatures such as slab, steel pipe material, heating temperature of steel pipe, hot rolling temperature, quenching temperature, cooling stop temperature, etc. are the surface temperatures of slab, steel pipe material, steel pipe, etc. (In the case of a steel pipe, the temperature of the outer surface) can be measured with a radiation thermometer or the like.
- Heating temperature Temperature range of 1000 to 1200 ° C.
- rolling is performed hot and in the temperature range of the austenite phase of steel.
- elements such as Cu, Cr, Sb, and W are concentrated on the outer surface of the seamless steel pipe after the steel pipe heat treatment described later. The heating temperature during rolling of steel pieces affects this thickening.
- the heating temperature during rolling of the steel piece is less than 1000 ° C.
- the above-mentioned elements are not sufficiently concentrated on the outer surface of the slab (surface of the slab), and the outer surface of the seamless steel pipe after the final heat treatment of the steel pipe is used.
- the required Cu, Cr, Sb, and W enrichment cannot be obtained. Therefore, a slab having a rectangular cross section is heated to a heating temperature in a temperature range of 1000 ° C. or higher, and hot rolling is performed. That is, the heating temperature at the start of hot rolling (during steel piece rolling) is set to 1000 ° C. or higher.
- the heating temperature is preferably 1050 ° C. or higher, more preferably 1100 ° C. or higher.
- the upper limit of the heating temperature is 1200 ° C. This is because the concentration of the alloying elements described above saturates at about 1180 ° C. or higher, and thus it is economically disadvantageous to consume a large fuel cost and raise the heating temperature.
- the heating temperature is preferably 1190 ° C. or lower, more preferably 1180 ° C. or lower.
- Heating time from 900 ° C to heating temperature 1.5 hours or more (optimal conditions)
- the heating time is particularly long at a temperature exceeding 900 ° C.
- the heating time is more preferably 2.0 hours or more.
- the upper limit is preferably 3.0 h.
- hot rolling (steel piece rolling) is immediately performed.
- the steel piece is rolled within 60 seconds.
- the hot rolling end temperature is not particularly limited, but the hot rolling temperature end temperature (steel piece rolling end temperature) is 800 ° C. or higher in consideration of the load of the rolling mill due to the rolling load. It is preferably, more preferably 900 ° C. or higher.
- room temperature means 25 ° C.
- the cooling method at this time is not particularly limited. Normally, air cooling is performed on a cooling bed or the like, but weak water cooling may be performed for the purpose of shortening the cooling time to room temperature and increasing the number of rollings per hour.
- air cooling means cooling by leaving it to stand naturally without taking any cooling means, and the cooling rate is usually 1 ° C./s or less.
- the slab is once heated (shard heat treatment) to be used as a steel pipe material before rolling the steel pipe (pipe making).
- the heating temperature in this slab heat treatment is as follows.
- Heating temperature of slab heat treatment Temperature range of 1000 to 1200 ° C. In order to obtain the same effect as steel slab rolling, the heating temperature of slab heat treatment is also the same. That is, when the heating temperature during the slab heat treatment is less than 1000 ° C., the above-mentioned elements such as Cu, Cr, Sb, and W are insufficiently concentrated on the slab outer surface (slab surface), and the final steel pipe heat treatment is performed. The required Cu, Cr, Sb, and W enrichment cannot be obtained on the outer surface of the subsequent seamless steel pipe. Therefore, the heating temperature of the slab heat treatment is set to 1000 ° C. or higher. The heating temperature is preferably 1050 ° C. or higher, more preferably 1100 ° C. or higher.
- the upper limit of the heating temperature of the slab heat treatment is 1200 ° C. This is because the concentration of the above-mentioned elements saturates at about 1180 ° C. or higher, and therefore it is economically disadvantageous to consume a large fuel cost and raise the heating temperature.
- the heating temperature of the slab heat treatment is preferably 1190 ° C. or lower, more preferably 1180 ° C. or lower.
- Heating time from 900 ° C to heating temperature 1.5 hours or more (optimal conditions)
- the heating time is particularly long at a temperature exceeding 900 ° C.
- the heating time from 900 ° C. to the heating temperature of the slab heat treatment is 1.5 hours or more.
- the heating time is more preferably 2.0 hours or more.
- the upper limit is preferably 3.0 h.
- the cooling method after the slab heat treatment is not particularly limited. Normally, air cooling is performed on a cooling bed or the like, but weak water cooling may be performed for the purpose of shortening the cooling time to room temperature and increasing the number of heat treatments per hour.
- a seamless steel pipe having a predetermined shape is formed hot (pipe making process).
- the pipe making process as a method of forming a seamless steel pipe having a predetermined shape from a steel pipe material, the steel pipe material is heated and hot-rolled (after drilling a piercer, mandrel mill rolling or plug mill rolling to obtain a predetermined wall thickness. After molding, the diameter is reduced to an appropriate diameter).
- the heating temperature and hot rolling temperature of the steel pipe material are as follows.
- Heating temperature of steel pipe material 1100 to 1300 ° C
- the steel pipe material is heated and then hot-rolled to obtain a seamless steel pipe having a predetermined shape.
- the heating temperature of the steel pipe material is set to 1100 ° C. or higher.
- the heating temperature of the steel pipe material is preferably 1150 ° C. or higher, more preferably 1200 ° C. or higher.
- the upper limit of the heating temperature of the steel pipe material is set to 1300 ° C.
- the heating temperature of the steel pipe material is preferably 1290 ° C. or lower, more preferably 1280 ° C. or lower.
- Hot rolling temperature 800 ° C. or higher
- the hot rolling temperature of hot rolling is lower than 800 ° C.
- the high-temperature ductility of steel decreases and defects occur on the outer surface during hot rolling. These defects remain even after the heat treatment of the steel pipe, and the defects detected by the non-destructive inspection are rejected even if the maintenance and refinement are performed. Therefore, the hot rolling temperature is set to 800 ° C. or higher from the viewpoint of defect prevention. That is, the hot rolling (steel pipe rolling) end temperature is set to 800 ° C. or higher.
- the rolling end temperature of the diameter reduction rolling is set to 800 ° C. or higher.
- the hot rolling temperature is preferably 830 ° C. or higher, more preferably 850 ° C. or higher.
- the cooling method at this time is not particularly limited. Normally, air cooling is performed on a cooling bed or the like, but weak water cooling may be performed for the purpose of shortening the cooling time to room temperature and increasing the number of rollings per hour.
- normalizing heat treatment is performed on the seamless steel pipe cooled to room temperature (steel pipe heat treatment process).
- the purpose of the normalizing heat treatment is to adjust the hardness of the seamless steel pipe to a predetermined strength suitable for piping.
- the heat treatment temperature (normalizing temperature) of the normalizing heat treatment is as follows.
- Normalizing temperature 850-1050 ° C
- the normalizing temperature is preferably 880 ° C. or higher, more preferably 900 ° C. or higher.
- the quasi-temperature shall be 1050 ° C or lower.
- the normalizing temperature is preferably 1000 ° C. or lower, more preferably 950 ° C. or lower.
- Air cooling on a cooling floor or the like is preferable for cooling after the completion of the normalizing heat treatment.
- weak water cooling is performed for the purpose of increasing the number of rollings per hour, it is preferable to start from 500 ° C. or lower, which is sufficiently lower than the transformation end temperature.
- a slab having a rectangular cross section was heated at a predetermined heating temperature and formed into a steel pipe material (steel piece rolled steel pipe material) having a diameter of 190 mm or a diameter of 140 mm by hot rolling.
- the seamless steel pipe manufactured using the steel pipe material is described as "steel piece rolling" in the columns of the steel pipe material classification in Tables 3, 4, and 5. Further, the heating temperature at the time of rolling the steel pieces, the heating time from 900 ° C. to the heating temperature, and the end temperature of the rolling of the steel pieces were carried out under the conditions shown in Tables 3, 4 and 5.
- the slab having a circular cross section was made into a steel pipe material by heat-treating the slab except for some comparative materials.
- Steel pipes manufactured using steel pipe materials that have undergone slab heat treatment are described as "shard heat treatment” in the columns of steel pipe material categories in Tables 3, 4, and 5.
- the seamless steel pipe manufactured without performing the slab heat treatment is described as "as straight cast” in the column of steel pipe material classification in Tables 3, 4 and 5.
- the heating temperature of the slab heat treatment and the heating time from 900 ° C. to the heating temperature were carried out under the conditions shown in Tables 3, 4 and 5.
- non-destructive inspection is "excellent” without defects
- non-destructive inspection finds defects but those that meet the acceptance criteria by maintenance are "good”
- non-destructive inspection finds defects and maintenance is not possible.
- those that did not meet the acceptance criteria even after maintenance were evaluated as "impossible”
- excellent and "good” were evaluated as excellent in manufacturability.
- the manufacturability is more preferably "excellent”.
- maintenance means removing defects such as flaws using, for example, a cutting device.
- the EPMA analysis sample had a cross section orthogonal to the longitudinal direction of the steel pipe on the measurement surface, and was mirror-polished.
- the measurement conditions of EPMA were an acceleration voltage of 20 kV, a beam current of 0.5 ⁇ A, and a beam diameter of 10 ⁇ m, and measurement was performed in a region of 2 mm from the outer surface side of the steel pipe of the sample toward the center of the wall thickness.
- the reason why the measurement region is set to 2 mm from the outer surface of the steel pipe is that the composition of the corrosion product generated in the sulfuric acid dew point environment corresponds to the concentration of the alloying element eluted when this region is corroded in the sulfuric acid dew point environment.
- the measurement elements were Cu, Cr, Sb, and W.
- the concentration (mass%) was calculated using a calibration curve prepared in advance from the characteristic X-ray intensity of each element. Specifically, the arithmetic of the concentrations (mass%) of each of 7 Cu, Cr, Sb, and W calculated every 0.25 mm in the region of 0.5 to 2.0 mm from the outer surface of the steel pipe toward the center of the wall thickness. Calculate the average, average Cu concentration (Cu * ) [mass%], average Cr concentration (Cr * ) [mass%], average Sb concentration (Sb * ) [mass%], average W concentration (W * ) [mass] %].
- Table 6, Table 7, and Table 8 show Cu * , Cr * , Sb * , and W * .
- the calculated values on the left side of the formula (1) or the formula (2) calculated from these Cu * , Cr * , Sb * , and W * are also described.
- the applicable range of the present invention is 13.5 or more. It is preferably 14.0 or more, and more preferably 15.0 or more. The reason why 0.5 mm from the outer surface of the steel pipe is excluded from the measurement area is that it is too close to the sample surface to perform accurate line analysis.
- Tensile test pieces are sampled from arbitrary positions in the longitudinal and circumferential directions of steel pipes, and processed into JIS Z2241 12B test pieces for steel pipes with an outer diameter of less than 170 mm and JIS Z2241 12C test pieces for steel pipes with an outer diameter of 170 mm or more.
- a tensile test was conducted based on JIS Z2241.
- the yield strength and tensile strength obtained in the tensile test are shown in Tables 6, 7 and 8.
- a yield strength of 230 MPa or more and a tensile strength of 380 MPa or more were accepted. More preferably, the yield strength is 250 MPa or more, and the tensile strength is 400 MPa or more.
- a corrosion test piece used for the corrosion test under the sulfuric acid dew point environment As a corrosion test piece used for the corrosion test under the sulfuric acid dew point environment, a corrosion test was taken from the outer surface side of the steel pipe so as to include the outer surface of the steel pipe, and the surface corresponding to the outer surface side of the steel pipe was ground by 0.5 mm to remove scale and the like. A piece (length 30 mm ⁇ width 20 mm ⁇ thickness 5 mm) was prepared. Subsequently, the peelability of the corrosion product produced in the sulfuric acid dew point corrosion test was evaluated by the procedure schematically shown in FIG. First, a sulfuric acid aqueous solution adjusted to a concentration of 70% by mass was injected into a container, the liquid temperature was kept at 50 ° C. by an external constant temperature bath, and then the corrosion test piece 1 was immersed.
- the immersion time was 96 hours. After the completion of the immersion for 96 hours, the sulfuric acid aqueous solution was discharged from the container, the corrosion test piece 1 was dried, carefully taken out, and the corrosion product formed on the surface of the corrosion test piece 1 was photographed by the digital camera 2 on the photographing table.
- the imaging surface was the surface that was on the outer surface side of the steel pipe when the corrosion test piece was processed. Photographed image analysis performing appropriate image processing on the image by (NIH using the development of the Image J software) to calculate the area S I of the resulting corrosion product (mm 2).
- a transparent adhesive film manufactured by NICHIBAN, cellophane tape (registered trademark), product number CT-24, width 24 mm
- Corrosion products that are easily affected were collected on the adhesive surface of the adhesive film.
- the corrosion product collected on the adhesive surface of the adhesive film is photographed by the digital camera 2, the image is analyzed, the area of the corrosion product collected on the adhesive surface of the adhesive film is calculated, and this is used as the corrosion test piece 1.
- the area of the corrosion product exfoliated from S II (mm 2 ) was defined.
- the generated corrode ratio [(S II / S I) ⁇ 100] of the area of corrosion products were stripped from the corrosion test piece to an area of the corrosion products formed corrode the test piece surface (S I) (S II) It was defined as the peeling rate (%).
- the results are shown in Tables 6, 7 and 8.
- a corrosion product peeling rate of 10% or less was regarded as acceptable.
- the corrosion product peeling rate is preferably 8% or less, and more preferably 5% or less.
- Examples of the invention (steel pipe Nos. 1-1 to 1-22) in which the composition of steel components and the production conditions are within the scope of the present invention and satisfy the requirements of the formula (1) or the formula (2) of the present invention are described.
- From the viewpoint of pipe defects there were no defects on the inner and outer surfaces of the steel pipe, or even if defects were found, they were minor and met the acceptance criteria after maintenance, and were excellent in manufacturability. Furthermore, it satisfies the yield strength and tensile strength required for seamless steel pipes for piping, and in addition, it has excellent sulfuric acid dew point corrosion resistance with a corrosion product peeling rate of 10% or less after immersion for 96 hours in a sulfuric acid dew point corrosion environment. Indicated.
Abstract
Description
1.7×Cu*+11×Cr*+3.8×Sb* ・・・(A)
の回帰式となる。
1.7×Cu*+11×Cr*+3.8×Sb*+5.2×W* ・・・(B)
の回帰式となる。
[1]質量%で、
C:0.02~0.12%、
Si:0.010~1.00%、
Mn:0.10~2.00%、
P:0.050%以下、
S:0.004%以下、
Al:0.010~0.100%、
Cu:0.03~0.80%、
Ni:0.02~0.50%、
Cr:0.55~1.00%、
Sb:0.005~0.20%、
を含有し、残部がFeおよび不可避的不純物からなる成分組成を有し、
鋼管の外表面から肉厚中央方向に0.5~2.0mmの領域における平均Cu濃度(質量%)、平均Cr濃度(質量%)、平均Sb濃度(質量%)を、それぞれCu*、Cr*、Sb*としたとき、Cu*、Cr*、Sb*が以下の式(1)を満たし、
降伏強度が230MPa以上、引張強度が380MPa以上である、耐硫酸露点腐食性に優れる継目無鋼管。
1.7×Cu*+11×Cr*+3.8×Sb*≧ 13.5 ・・・(1)
[2]質量%で、
C:0.02~0.12%、
Si:0.010~1.00%、
Mn:0.10~2.00%、
P:0.050%以下、
S:0.004%以下、
Al:0.010~0.100%、
Cu:0.03~0.80%、
Ni:0.02~0.50%、
Cr:0.55~1.00%、
Sb:0.005~0.20%、
W:0.003~0.040%、
を含有し、残部がFeおよび不可避的不純物からなる成分組成を有し、
鋼管の外表面から肉厚中央方向に0.5~2.0mmの領域における平均Cu濃度(質量%)、平均Cr濃度(質量%)、平均Sb濃度(質量%)、平均W濃度(質量%)を、それぞれCu*、Cr*、Sb*、W*としたとき、Cu*、Cr*、Sb*、W*が以下の式(2)を満たし、
降伏強度が230MPa以上、引張強度が380MPa以上である、耐硫酸露点腐食性に優れる継目無鋼管。
1.7×Cu*+11×Cr*+3.8×Sb*+5.2×W*≧ 13.5 ・・・(2)
[3]前記成分組成が、さらに、質量%で、
Sn:0.005~0.5%
を含有する、[1]または[2]に記載の耐硫酸露点腐食性に優れる継目無鋼管。
[4]前記[1]~[3]のいずれかに記載の耐硫酸露点腐食性に優れる継目無鋼管の製造方法であって、
前記成分組成を有する鋼を、矩形断面を有する鋳片に鋳造し、
次いで、前記矩形断面を有する鋳片を1000~1200℃の温度域の加熱温度に加熱し、熱間圧延を施して円形断面を有する鋼管素材としてから冷却し、
前記冷却した鋼管素材を、1100~1300℃に加熱後、800℃以上で熱間圧延して、所定の形状の継目無鋼管とし、冷却した後、
850~1050℃の焼準温度で加熱する焼準熱処理を行う、耐硫酸露点腐食性に優れる継目無鋼管の製造方法。
[5]矩形断面を有する鋳片を1000~1200℃の温度域の加熱温度に加熱する際、900℃から前記加熱温度までの加熱時間が1.5h以上である、[4]に記載の耐硫酸露点腐食性に優れる継目無鋼管の製造方法。
[6]前記[1]~[3]のいずれかに記載の耐硫酸露点腐食性に優れる継目無鋼管の製造方法であって、
前記成分組成を有する鋼を、円形断面を有する鋳片に鋳造し、
次いで、前記円形断面を有する鋳片を1000~1200℃の温度域の加熱温度に加熱して鋼管素材とした後、冷却し、
前記冷却した鋼管素材を、1100~1300℃に加熱後、800℃以上で熱間圧延して、所定の形状の継目無鋼管とし、冷却した後、
850~1050℃の焼準温度で加熱する焼準熱処理を行う、耐硫酸露点腐食性に優れる継目無鋼管の製造方法。
[7]円形断面を有する鋳片を1000~1200℃の温度域の加熱温度に加熱する際、900℃から前記加熱温度までの加熱時間が1.5h以上である、[6]に記載の耐硫酸露点腐食性に優れる継目無鋼管の製造方法。
Cは鋼の強度を高める元素であり、本発明では、特に配管用継目無鋼管として要求される降伏強度、および引張強度を満足させるため、0.02%以上のCの含有を必要とする。よって、C含有量は0.02%以上とする。C含有量は、好ましくは0.021%以上であり、より好ましくは0.022%以上である。一方、0.12%を超えるCの含有は、高温での熱間延性に悪影響する。具体的には、継目無鋼管の熱間圧延時の表面欠陥発生の原因となる。このため、C含有量の上限を0.12%とする。表面欠陥防止の観点から、C含有量は、好ましくは0.08%以下であり、より好ましくは0.04%以下である。
Siは脱酸剤として作用するとともに、鋼中に固溶して鋼の強度を高める元素であり、本発明では、特に配管用継目無鋼管として要求される降伏強度、および引張強度を満足させるため、0.010%以上のSiの含有を必要とする。よって、Si含有量は0.010%以上とする。Si含有量は、好ましくは0.05%以上であり、より好ましくは0.20%以上である。一方、1.00%を超えるSiの含有は、高温での熱間延性に悪影響する。このため、Si含有量の上限を1.00%とする。Si含有量は、好ましくは0.80%以下であり、より好ましくは0.60%以下である。
Mnは、焼入れ性の向上を介して、鋼の強度を高める元素であり、本発明では、特に配管用継目無鋼管として要求される降伏強度、および引張強度を満足させるため、0.10%以上のMnの含有を必要とする。よって、Mn含有量は0.10%以上とする。Mn含有量は、好ましくは0.50%以上であり、より好ましくは1.10%以上である。一方、2.00%を超えてMnを含有させた場合、連続鋳造時の中心偏析が著しく、継目無鋼管の熱間圧延における穿孔時の内部欠陥の原因となる。このため、Mn含有量の上限を2.00%とする。Mn含有量は、好ましくは1.80%以下であり、より好ましくは1.40%以下である。
Pは、連続鋳造時の中心偏析が著しく、継目無鋼管の熱間圧延における穿孔時の内部欠陥の原因となる。そのため、本発明ではできるだけ低減することが望ましいが、0.050%までは許容できる。このため、P含有量は0.050%以下とする。P含有量は、好ましくは0.030%以下であり、より好ましくは、0.015%以下である。P含有量の下限は、特に限定されないが、過度の脱Pは製造コストの増加を招くため、P含有量の下限は0.004%程度とすることが好適である。
Sもまた、連続鋳造時の中心偏析が著しく、継目無鋼管の熱間圧延における穿孔時の内部欠陥の原因となる。そのため、本発明ではできるだけ低減することが望ましいが、0.004%までは許容できる。このため、S含有量は0.004%以下とする。S含有量は、好ましくは0.003%以下であり、より好ましくは、0.002%以下である。S含有量の下限は、特に限定されないが、過度の脱Sは製造コストの増加を招くため、S含有量の下限は0.0004%程度とすることが好適である。
Alは脱酸材として作用する元素である。固溶酸素を低減し、後述するCr含有時に、Cr酸化物生成による有効Cr量の低下を防止するため、0.010%以上の含有を必要とする。よって、Al含有量は0.010%以上とする。Al含有量は、好ましくは0.015%以上であり、より好ましくは0.020%以上である。一方、0.100%を超えてAlを含有させた場合、Al2O3が鋼中に多く発生し、鋼の高温での熱間延性に悪影響する。このことから、Al含有量の上限を0.100%とする。Al含有量は、好ましくは0.080%以下であり、より好ましくは0.040%以下である。
Cuは硫酸露点環境下での鋼の腐食防止に有効な元素である。さらに、Crとの複合添加で、鋼管外表面に濃化した場合、腐食生成物の剥離性を改善する働きをする。このような効果を得るため、Cuは0.03%以上の含有を必要とする。よって、Cu含有量は0.03%以上とする。Cu含有量は、好ましくは0.10%以上であり、より好ましくは0.20%以上である。一方、Cuは鋼の高温延性を低下させることも良く知られており、0.80%を超えて含有させた場合、熱間圧延時の外表面欠陥発生が著しいことから、Cu含有量の上限を0.80%とする。Cu含有量は、好ましくは0.60%以下であり、より好ましくは0.40%以下である。
Niは、Cu含有鋼に複合添加した場合、Cuの高温延性低下を抑制する元素である。このような効果を得るため、0.02%以上の含有を必要とする。よって、Ni含有量は0.02%以上とする。Ni含有量は、好ましくは0.08%以上であり、より好ましくは0.10%以上である。一方、0.50%を超えて含有させても効果が飽和し、かつ、添加コストが高い元素であることから、Ni含有量の上限を0.50%とする。Ni含有量は、好ましは0.45%以下であり、より好ましは0.30%以下である。
Crは硫酸露点環境下での腐食防止自体には大きく寄与しないが、図2に示すように、CuおよびSbとの複合添加によって、腐食生成物の剥離性の改善に寄与する重要な元素である。このような効果を得るため、0.55%以上の含有を必要とする。よって、Cr含有量は0.55%以上とする。Cr含有量は、好ましくは0.57%以上であり、より好ましくは0.60%以上である。一方、1.00%を超えて含有させた場合、特に連続鋳造時の中心偏析部において、継目無鋼管の熱間圧延における穿孔時の内部欠陥の発生を助長する。このことから、Cr含有量の上限を1.00%とする。Cr含有量は、好ましは0.90%以下であり、より好ましは0.80%以下である。
SbはCuと同様、硫酸露点腐食環境下での鋼の腐食防止に有効な元素である。さらに、Crとの複合添加で鋼管外表面に濃化した場合、腐食生成物の剥離性を改善する働きをする。このような効果を得るためには、Sbは0.005%以上の含有を必要とする。よって、Sb含有量は0.005%以上とする。Sb含有量は、好ましくは0.02%以上であり、より好ましくは0.05%以上である。一方、0.20%を超えて含有させた場合、高温延性を著しく低下させ、熱間圧延時の外表面欠陥発生が著しいことから、Sb含有量の上限を0.20%とする。Sb含有量は、好ましは0.15%以下であり、より好ましは0.09%以下である。
Wは、Crと同様、硫酸露点環境下で生成した腐食生成物の剥離性を改善することを本発明者らは見出した。ただし、Crと異なり高価な元素であるため、Crと複合添加させることで、さらなる腐食生成物剥離性を改善させることを目的に含有させてもよい。このような効果を得るために、Wは0.003%以上の含有を必要とする。よって、Wを含有する場合、W含有量は0.003%以上とする。W含有量は、好ましくは0.005%以上であり、より好ましくは0.008%以上である。一方、0.040%を超えて含有させた場合、特に連続鋳造時の中心偏析部において、継目無鋼管の熱間圧延における穿孔時の内部欠陥の発生を助長する。このことから、Wを含有する場合、W含有量の上限を0.040%とする。W含有量は、好ましは0.030%以下であり、より好ましは0.015%以下である。
Snは、図2に示すように硫酸露点環境下で生成した腐食生成物の剥離率の改善にはあまり影響しないが、硫酸露点腐食環境下での腐食そのものを低減する目的に含有させても良い。硫酸露点腐食の改善のためには、Snは0.005%以上の含有を必要とする。よって、Snを含有する場合、Sn含有量は0.005%以上とする。Sn含有量は、0.02%以上が好ましい。一方、SnはSbと同様に鋼の高温延性を低下させるため、Snを含有する場合、Sn含有量の上限を0.5%とする。Sn含有量は、好ましくは0.05%以下とする。
1.7×Cu*+11×Cr*+3.8×Sb*≧ 13.5 ・・・(1)
を満たし、
W添加の場合は、
1.7×Cu*+11×Cr*+3.8×Sb*+5.2×W*≧ 13.5 ・・・(2)
を満たす。
矩形断面を有する鋳片を円形断面の鋼管素材へ圧延(鋼片圧延)によって成形する際、熱間で、かつ鋼のオーステナイト相の温度域で圧延を行う必要がある。加えて、本発明の課題である、硫酸露点環境下で生成した腐食生成物を剥離しにくくするため、後述する鋼管熱処理後の継目無鋼管外表面にCu、Cr、Sb、Wといった元素を濃化させる必要があり、鋼片圧延時の加熱温度がこの濃化に影響する。すなわち、鋼片圧延時の加熱温度が1000℃未満の場合、上述の元素の鋳片外面(鋳片表面)への濃化が不十分で、最終的な鋼管熱処理後の継目無鋼管外表面で必要なCu、Cr、Sb、W濃化が得られない。そのため、矩形断面を有する鋳片を1000℃以上の温度域の加熱温度に加熱し、熱間圧延を施す。すなわち、熱間圧延開始時(鋼片圧延時)の加熱温度を1000℃以上とする。なお、前記加熱温度は、好ましくは1050℃以上であり、より好ましくは1100℃以上である。一方で、前記加熱温度の上限は1200℃とする。上述の合金元素の濃化はおよそ1180℃以上で飽和するため、多大な燃料コストを消費して加熱温度を上げることは経済的に不利となるためである。前記加熱温度は、好ましくは1190℃以下であり、より好ましくは1180℃以下である。
より効果的に継目無鋼管の外表面にCu、Cr、Sb、Wといった元素を濃化させるため、特に900℃を超える温度での加熱時間が長いことが好ましい。具体的には、900℃から目標とする鋼片圧延時の加熱温度までの加熱時間を1.5h以上とすることで、鋼片圧延時の加熱温度が同一であってもCu、Cr、Sb、Wといった元素の濃化が著しくなる。よって、900℃から鋼片圧延時の加熱温度までの加熱時間を1.5h以上とすることが好ましい。前記加熱時間は、より好ましくは2.0h以上である。一方で、この加熱時間を3.0h以上としても効果は飽和し、かつ、燃料費等で経済的に不利となるため、上限は3.0hとすることが好ましい。
鋼片圧延と同等の効果を得るために、鋳片熱処理の加熱温度も同様とする。すなわち、鋳片熱処理時の加熱温度が1000℃未満の場合、Cu、Cr、Sb、Wといった上述の元素の鋳片外面(鋳片表面)への濃化が不十分で、最終的な鋼管熱処理後の継目無鋼管の外表面で必要なCu、Cr、Sb、W濃化が得られない。よって、鋳片熱処理の加熱温度は、1000℃以上とする。なお、前記加熱温度は、好ましくは1050℃以上であり、より好ましくは1100℃以上である。一方で、鋳片熱処理の加熱温度の上限は1200℃とする。上述の元素の濃化はおよそ1180℃以上で飽和するため、多大な燃料コストを消費して加熱温度を上げることは経済的に不利となるためである。鋳片熱処理の加熱温度は、好ましくは1190℃以下であり、より好ましくは1180℃以下である。
より効果的に継目無鋼管の外表面にCu、Cr、Sb、Wといった元素を濃化させるため、特に900℃を超える温度での加熱時間が長いことが好ましい。具体的には、900℃から目標とする鋳片熱処理の加熱温度までの加熱時間を1.5h以上とすることで、鋳片熱処理の加熱温度が同一であってもCu、Cr、Sb、Wといった元素の濃化が著しくなる。よって、900℃から鋳片熱処理の加熱温度までの加熱時間を1.5h以上とすることが好ましい。前記加熱時間は、より好ましくは2.0h以上である。一方で、この加熱時間を3.0h以上としても効果は飽和し、かつ、燃料費等で経済的に不利となるため、上限は3.0hとすることが好ましい。
造管工程では、鋼管素材を加熱した後、熱間圧延して所定の形状の継目無鋼管とする。この際、鋼管素材の加熱温度が1100℃未満の場合、ピアサー穿孔時の内部欠陥の発生が著しく、最終の鋼管熱処理後に非破壊検査で検出された欠陥は手入れ精整を行っても不合格となるため、欠陥防止の観点から鋼管素材の加熱温度は1100℃以上とする。鋼管素材の加熱温度は、好ましくは1150℃以上であり、より好ましくは1200℃以上である。一方で、鋼管素材の加熱温度が1300℃超えの場合、鋼表面の酸化ロスや、燃料費の上昇等、経済的に不利益となるため、鋼管素材の加熱温度の上限を1300℃とする。鋼管素材の加熱温度は、好ましくは1290℃以下であり、より好ましくは1280℃以下である。
熱間圧延(鋼管圧延)の圧延温度が800℃を下回ると、鋼の高温延性が低下し熱間圧延中の外表面に欠陥が発生する。これらの欠陥は鋼管熱処理後も残存し、非破壊検査で検出された欠陥は手入れ精整を行っても不合格となるため、欠陥防止の観点から熱間圧延温度は800℃以上とする。すなわち、熱間圧延(鋼管圧延)終了温度を800℃以上とする。例えば、熱間圧延として、ピアサー穿孔、マンドレルミル圧延あるいはプラグミル圧延し、その後、縮径圧延する場合、縮径圧延の圧延終了温度を800℃以上とする。熱間圧延温度は、好ましくは830℃以上であり、より好ましくは850℃以上である。
焼準熱処理の焼準温度が850℃未満の場合、鋼の一部がオーステナイト変態を終了せず、未変態のフェライトやパーライト組織のまま高温で保持される。この結果、これらのフェライトやパーライト組織が強度低下の原因となるため、焼準温度は850℃以上とする。焼準温度は、好ましくは880℃以上であり、より好ましくは900℃以上である。一方、焼準温度が1050℃を超える場合、オーステナイト変態終了後の粒成長が著しく、焼準熱処理終了後の冷却過程で変態生成するフェライト粒が粗大化し、降伏強度低下の原因となるため、焼準温度は1050℃以下とする。焼準温度は、好ましくは1000℃以下であり、より好ましくは950℃以下である。
2 デジタルカメラ
Claims (7)
- 質量%で、
C:0.02~0.12%、
Si:0.010~1.00%、
Mn:0.10~2.00%、
P:0.050%以下、
S:0.004%以下、
Al:0.010~0.100%、
Cu:0.03~0.80%、
Ni:0.02~0.50%、
Cr:0.55~1.00%、
Sb:0.005~0.20%、
を含有し、残部がFeおよび不可避的不純物からなる成分組成を有し、
鋼管の外表面から肉厚中央方向に0.5~2.0mmの領域における平均Cu濃度(質量%)、平均Cr濃度(質量%)、平均Sb濃度(質量%)を、それぞれCu*、Cr*、Sb*としたとき、Cu*、Cr*、Sb*が以下の式(1)を満たし、
降伏強度が230MPa以上、引張強度が380MPa以上である、耐硫酸露点腐食性に優れる継目無鋼管。
1.7×Cu*+11×Cr*+3.8×Sb*≧ 13.5 ・・・(1) - 質量%で、
C:0.02~0.12%、
Si:0.010~1.00%、
Mn:0.10~2.00%、
P:0.050%以下、
S:0.004%以下、
Al:0.010~0.100%、
Cu:0.03~0.80%、
Ni:0.02~0.50%、
Cr:0.55~1.00%、
Sb:0.005~0.20%、
W:0.003~0.040%、
を含有し、残部がFeおよび不可避的不純物からなる成分組成を有し、
鋼管の外表面から肉厚中央方向に0.5~2.0mmの領域における平均Cu濃度(質量%)、平均Cr濃度(質量%)、平均Sb濃度(質量%)、平均W濃度(質量%)を、それぞれCu*、Cr*、Sb*、W*としたとき、Cu*、Cr*、Sb*、W*が以下の式(2)を満たし、
降伏強度が230MPa以上、引張強度が380MPa以上である、耐硫酸露点腐食性に優れる継目無鋼管。
1.7×Cu*+11×Cr*+3.8×Sb*+5.2×W*≧ 13.5 ・・・(2) - 前記成分組成が、さらに、質量%で、
Sn:0.005~0.5%
を含有する、請求項1または2に記載の耐硫酸露点腐食性に優れる継目無鋼管。 - 請求項1~3のいずれかに記載の耐硫酸露点腐食性に優れる継目無鋼管の製造方法であって、
前記成分組成を有する鋼を、矩形断面を有する鋳片に鋳造し、
次いで、前記矩形断面を有する鋳片を1000~1200℃の温度域の加熱温度に加熱し、熱間圧延を施して円形断面を有する鋼管素材としてから冷却し、
前記冷却した鋼管素材を、1100~1300℃に加熱後、800℃以上で熱間圧延して、所定の形状の継目無鋼管とし、冷却した後、
850~1050℃の焼準温度で加熱する焼準熱処理を行う、耐硫酸露点腐食性に優れる継目無鋼管の製造方法。 - 矩形断面を有する鋳片を1000~1200℃の温度域の加熱温度に加熱する際、900℃から前記加熱温度までの加熱時間が1.5h以上である、請求項4に記載の耐硫酸露点腐食性に優れる継目無鋼管の製造方法。
- 請求項1~3のいずれかに記載の耐硫酸露点腐食性に優れる継目無鋼管の製造方法であって、
前記成分組成を有する鋼を、円形断面を有する鋳片に鋳造し、
次いで、前記円形断面を有する鋳片を1000~1200℃の温度域の加熱温度に加熱して鋼管素材とした後、冷却し、
前記冷却した鋼管素材を、1100~1300℃に加熱後、800℃以上で熱間圧延して、所定の形状の継目無鋼管とし、冷却した後、
850~1050℃の焼準温度で加熱する焼準熱処理を行う、耐硫酸露点腐食性に優れる継目無鋼管の製造方法。 - 円形断面を有する鋳片を1000~1200℃の温度域の加熱温度に加熱する際、900℃から前記加熱温度までの加熱時間が1.5h以上である、請求項6に記載の耐硫酸露点腐食性に優れる継目無鋼管の製造方法。
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CN114182180A (zh) * | 2021-12-13 | 2022-03-15 | 马鞍山钢铁股份有限公司 | 一种含Sn、Sb耐硫酸及氯离子腐蚀的钢板及其制造方法 |
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CN115637391B (zh) * | 2022-11-07 | 2023-05-12 | 鞍钢股份有限公司 | 550MPa级耐硫酸露点腐蚀用稀土钢及其制造方法 |
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BR112022000052A2 (pt) | 2022-02-22 |
JP6822623B1 (ja) | 2021-01-27 |
MX2022000386A (es) | 2022-02-10 |
EP3998356A4 (en) | 2023-01-04 |
JPWO2021005960A1 (ja) | 2021-09-13 |
EP3998356A1 (en) | 2022-05-18 |
KR20220016981A (ko) | 2022-02-10 |
US20220411890A1 (en) | 2022-12-29 |
KR102654713B1 (ko) | 2024-04-03 |
CN114096692A (zh) | 2022-02-25 |
AR119363A1 (es) | 2021-12-15 |
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