Steel for blast furnace gas pipeline and preparation method thereof

Abstract

The invention provides steel for blast furnace gas pipeline and a preparation method thereof, and relates to the field of steel smelting. The method comprises molten steel smelting, KR pre-desulfurization, BOF converter smelting, LF refining, RH refining, CCM continuous casting, rolling, heating descaling, rolling cooling and tempering treatment. The chemical composition of the steel for blast furnace gas pipeline comprises C: 0.03-0.06%, Si: 0.10-0.25%, Mn: 0.80-1.50%, Nb: 0.02-0.05%, Ni: 2.00-3.00%, Mo: 0.30-0.50%, Cr: 1.00-1.50, Al: 0.030-0.050%, P≤0.010%, S≤0.005%, and the rest is Fe and inevitable impurities. The invention obtains ultra-large volume steel for blast furnace gas transportation through the synergistic effect of Cr and Ni component design and rolling heat treatment.

Description

Technical Field

[0001] The invention relates to the technical field of steel smelting, and in particular to steel for blast furnace gas pipelines and a preparation method thereof. Background Art

[0002] Blast furnace gas is a by-product produced by steel companies during the blast furnace ironmaking process. The main components of blast furnace gas are about 8%~12% carbon dioxide, 20%~30% carbon monoxide, 1%~5% hydrogen, and 40%~55% nitrogen. In addition to the above components, blast furnace gas also contains some dust particle impurities, a small amount of chlorides and sulfates, carbonates and nitrates, etc. Because its components contain combustible gases such as carbon monoxide and hydrogen, the measures currently commonly adopted by steel companies are to first carry out dust reduction treatment on the blast furnace gas, and then transport it to the rolling mill or steelmaking plant through a gas pipeline, and use it as a combustible gas for heating fuel for ingots and ladles, thereby realizing the recycling of energy. At present, blast furnace gas transmission pipelines are generally welded with plain carbon steel plates such as Q235. Since plain carbon steel is not corrosion-resistant, sulfides such as SO2 and SO3 in the gas and CO 3- , Cl - Plasma in a humid pipeline environment causes serious corrosion of gas pipelines. Thin steel plates are very likely to be perforated due to corrosion, resulting in gas leakage accidents, which poses a major safety hazard. Therefore, it is necessary to develop a steel plate resistant to strong acid corrosion to replace ordinary carbon steel, so as to improve the corrosion resistance of blast furnace gas pipelines.

[0003] At present, there are not many technical solutions disclosed in China about blast furnace gas corrosion-resistant steel and its preparation method. For example, patent application CN103924159A discloses a high-toughness acid-resistant steel for gas pipelines and its preparation method. The corrosion resistance of the obtained steel plate is 6.8 times that of Q345B steel, but because it is manufactured by hot rolling coil process, the thickest specification of the steel plate is 10mm; patent CN113046638B discloses SNS acid-resistant steel high-quality ingot for gas pipelines and its production method, and patent application CN118002617A discloses a method for preparing steel for gas pipelines. Both adopt hot rolling coil process to manufacture steel for gas pipelines, and its maximum thickness specification is 12mm. For another example, the high-toughness acid-resistant steel for gas pipelines obtained by patent CN111321347A also adopts hot rolling coil process, and its maximum thickness is 12mm. Although the steel produced by some of the above technical solutions can meet the corrosion resistance requirements of steel for gas pipelines, most of them are manufactured by hot rolling coil process, which limits the maximum thickness of steel plates to less than 18 mm. Thin steel plates are easily perforated under acid gas corrosion and cannot meet the application problems of thick and large-diameter gas pipelines, especially in recent years, most newly built blast furnaces are 5000 m 3 Large volume above 5000 m 3The large amount of blast furnace gas produced by the above-mentioned super-large volume blast furnaces requires thick-gauge and large-diameter gas pipelines to meet the transportation requirements. However, there is currently a lack of corrosion-resistant steel for thick-gauge gas pipelines in China.

[0004] Therefore, in response to the demand for steel for transporting ultra-large volumes of blast furnace gas, a new steelmaking method needs to be proposed to solve the technical problem that the current blast furnace gas pipelines have poor corrosion resistance and cannot meet application requirements. Summary of the invention

[0005] The purpose of the present invention is to provide a steel for blast furnace gas pipeline and a preparation method thereof. By designing a new alloy composition and rolling process and utilizing wide and thick plate hot rolling production technology, high-strength corrosion-resistant steel plates with a thickness of more than 18 mm are successfully manufactured to meet the demand for steel for ultra-large volume blast furnace gas transportation.

[0006] To achieve the above object, the present invention proposes the following technical solutions:

[0007] In a first aspect, a method for preparing steel for a blast furnace gas pipeline is provided, comprising the following steps:

[0008] S1: Smelting to obtain target molten steel, and casting to obtain a continuous casting billet with a thickness of 220 mm and a width of 1500-2300 mm; wherein the chemical composition of the target molten steel includes C: 0.03-0.06%, Si: 0.10-0.25%, Mn: 0.80-1.50%, Nb: 0.02-0.05%, Ni: 2.00-3.00%, Mo: 0.30-0.50%, Cr: 1.00-1.50, Al: 0.030-0.050%, P≤0.010%, S≤0.005%, and the rest is Fe and unavoidable impurities;

[0009] S2: stacking the continuous casting billets for slow cooling for no less than 72 hours, loading them into a furnace for heating and keeping them warm to a preset condition, and then descaling them to obtain slabs; the center segregation of the slabs is no higher than Class C 0.5 level, and the center porosity is no higher than 0.5 level;

[0010] S3: rolling the slab into steel plate;

[0011] S4: The steel plate is reheated to 580-600°C for tempering, with a thermal insulation coefficient of 2.5-3min / mm. After tempering, it is air-cooled to obtain steel for blast furnace gas pipelines.

[0012] Furthermore, the process of smelting and obtaining the target molten steel in step S1 comprises the following steps:

[0013] S11: smelting to obtain initial molten steel;

[0014] S12: performing KR pre-desulfurization treatment on the initial molten steel, wherein the weight percentage of chemical component S in the molten steel after desulfurization is no more than 0.0010%, and the temperature of the molten steel after desulfurization is controlled to be 1300-1380°C;

[0015] S13: Scrap steel is added to the desulfurized molten iron to adjust the composition of the molten steel and continue smelting in the converter, with the weight ratio of scrap steel being 15-20%; the temperature of the molten steel is 1580-1640°C when the converter is slag-dumped, and the chemical composition of the converter molten steel includes P≤0.008%, C: 0.03-0.05%, slag basicity 4.0-6.5, and T.Fe in the slag: 25-35%;

[0016] S14: tapping from the converter. When the tapping rate is 20-30%, aluminum particles, ferrosilicon, metallic manganese, ferrochrome, ferrovanadium and ferroniobium are added for deoxidation and alloying. When the tapping rate is 70-80%, lime and fluorite are added for slag making. After the tapping rate is over, calcium aluminate is added to the slag surface to synthesize the slag. In addition, during the tapping process, the ladle is blown and stirred at the bottom. After the tapping rate is over, stirring is continued for 3-5 minutes. The molten steel is transported to LF for refining.

[0017] S15: LF refining: Turn on the power to raise the temperature, add calcium carbide, lime and fluorite to adjust the slag, and start bottom blowing and stirring to desulfurize. Add alloy according to the composition of the incoming molten steel, adjust the alloy composition to the required molten steel composition, and transport it to RH vacuum treatment after the molten steel composition, slag composition and temperature meet the standards;

[0018] S16: RH vacuum treatment, RH station starts vacuum treatment to control the vacuum degree less than 2mbar, maintain for 5-10min, add titanium iron according to weight percentage, maintain net circulation treatment for not less than 15min, break the air to tap, feed pure calcium wire into the molten steel after tapping, control the Ca content in the molten steel to 15-25ppm; and the chemical composition of the molten steel after RH vacuum treatment includes C: 0.03~0.06%, Si: 0.10~0.25%, Mn: 0.80~1.50%, Nb: 0.02~0.05%, Ni: 2.00~3.00%, Mo: 0.30~0.50%, Cr: 1.00~1.50, Al: 0.030~0.050%, P≤0.010%, S≤0.005%, and the rest is Fe and unavoidable impurities;

[0019] S17: The molten steel after RH vacuum treatment is poured to obtain a continuous casting slab with a thickness of 220 mm and a width of 1500-2300 mm.

[0020] Furthermore, the process of heating and keeping the temperature in the furnace to the preset conditions in step S2 is: heating the furnace to 1100-1180° C. and keeping the temperature for 270-420 min.

[0021] Furthermore, the process of steel plate rolling in step S3 is as follows: the slab is rolled in the first stage to obtain an intermediate slab, the single-pass reduction rate of the first-stage rolling is not less than 12% and the thickness of the intermediate slab is not less than 100 mm; the intermediate slab is rolled in the second stage to obtain a steel plate and water-cooled to room temperature, the reduction rate of at least two passes in the second stage rolling is not less than 18%, and the reduction rate of the last pass is 4-8%; the compression ratio of the steel plate is not less than 8.

[0022] Furthermore, the scrap steel in step S13 includes nickel plate and ferromolybdenum.

[0023] Furthermore, in the step S14, the bottom blowing flow rate of the ladle during bottom blowing and stirring in the steel tapping process is 600-800NL / min.

[0024] Furthermore, in the step S17, the superheat of the molten steel in the intermediate ladle during the pouring process is 15-25°C, and the crystallizer uses a low-melting-point alkaline protective slag with a melting point of 1150-1200°C.

[0025] In a second aspect, a steel for a blast furnace gas pipeline is proposed, which is prepared by the above-mentioned preparation method of the steel for a blast furnace gas pipeline.

[0026] Further, the chemical composition of the steel for blast furnace gas pipeline includes, by weight percentage, C: 0.03-0.06%, Si: 0.10-0.25%, Mn: 0.80-1.50%, Nb: 0.02-0.05%, Ni: 2.00-3.00%, Mo: 0.30-0.50%, Cr: 1.00-1.50, Al: 0.030-0.050%, P≤0.010%, S≤0.005%, and the rest is Fe and unavoidable impurities;

[0027] The central segregation of the steel used for blast furnace gas pipeline is not higher than Class C 0.5 level, and the central porosity is not higher than 0.5 level.

[0028] Furthermore, the yield strength of the steel for blast furnace gas pipeline is greater than 600MPa, the tensile strength reaches 700MPa, and the impact energy at -20°C is greater than 250J.

[0029] It can be seen from the above technical solutions that the technical solutions of the present invention have the following beneficial effects:

[0030] The invention provides a steel for blast furnace gas pipeline and a preparation method thereof, and relates to the field of steel smelting; the method comprises molten steel smelting, KR pre-desulfurization, BOF converter smelting, LF refining, RH refining, CCM continuous casting, rolling, heating descaling, rolling cooling and tempering treatment, and the chemical composition of the steel for blast furnace gas pipeline comprises C: 0.03-0.06%, Si: 0.10-0.25%, Mn: 0.80-1.50%, Nb: 0.02-0.05%, Ni: 2.00-3.00%, Mo: 0.30- 0.50%, Cr: 1.00-1.50%, Al: 0.030-0.050%, P≤0.010%, S≤0.005%, and the rest are Fe and inevitable impurities; the present invention obtains a high-strength steel plate for gas pipelines with a yield strength greater than 600MPa, a tensile strength of 700MPa, and an impact energy greater than 250J at -20°C through the composition design of Cr and Ni and the synergistic effect of rolling heat treatment; according to the performance test of the steel plate, the acid corrosion resistance of the steel plate is as high as 25.5 times that of ordinary carbon steel Q235B.

[0031] Compared with the prior art, the alloy composition designed in the present invention and the forming process adopted are not only economical in composition design, but also can produce characteristic steel plates with superior performance by utilizing the synergistic effect of the two, meet the application requirements of thick-gauge corrosion-resistant gas pipelines, and improve the safety of blast furnace gas transportation.

[0032] It should be appreciated that all combinations of the foregoing concepts, as well as additional concepts described in greater detail below, may be considered to be part of the inventive subject matter of the present disclosure, provided such concepts are not mutually inconsistent.

[0033] The foregoing and other aspects, embodiments and features of the present invention can be more fully understood from the following description in conjunction with the accompanying drawings. Other additional aspects of the present invention, such as the features and / or beneficial effects of the exemplary embodiments, will be apparent from the following description or learned from the practice of the specific embodiments according to the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The accompanying drawings are not intended to be drawn to scale. In the accompanying drawings, each identical or nearly identical component shown in various figures may be represented by the same reference numeral. For clarity, not every component is labeled in each figure. Embodiments of various aspects of the present invention will now be described by way of example and with reference to the accompanying drawings, in which:

[0035] Figure 1 This is a surface morphology image of the steel plate after corrosion according to Example 1 of the present invention;

[0036] Figure 2 This is a surface morphology of the steel plate after corrosion in Comparative Example 2 of the present invention;

[0037] Figure 3 This is the surface morphology of the Q235B steel plate after corrosion in the prior art. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solution and advantages of the embodiment of the present invention clearer, the technical solution of the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings of the embodiment of the present invention. Obviously, the described embodiment is a part of the embodiment of the present invention, not all of the embodiments. Based on the described embodiment of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. Unless otherwise defined, the technical terms or scientific terms used herein should be the common meaning understood by people with general skills in the field to which the present invention belongs.

[0039] The words "first", "second" and similar words used in the patent application specification and claims of the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. Similarly, unless the context clearly indicates otherwise, the singular form of "a", "an" or "the" and other similar words do not indicate a quantitative limitation, but indicate the existence of at least one. "Include" or "comprises" and other similar words mean that the elements or objects appearing before "include" or "comprises" include the features, wholes, steps, operations, elements and / or components listed after "include" or "comprises", and do not exclude the existence or addition of one or more other features, wholes, steps, operations, elements, components and / or their collections.

[0040] In order to meet the corrosion resistance requirements of steel for gas pipelines, the prior art proposes several steel plates manufactured by hot rolling coiling process, but the process limits the thickness of the steel plates to 18 mm, and therefore cannot meet the application problems of thick-gauge and large-diameter gas pipelines. Based on the lack of thick-gauge and large-diameter steel for gas pipelines in the prior art, the present invention aims to propose a steel for furnace gas pipelines and a preparation method thereof, and successfully manufactures a steel plate whose thickness, corrosion resistance and strength meet the requirements of thick-gauge and large-diameter steel for gas pipelines through alloy composition design and coordinated forming process design.

[0041] Specifically, the method for preparing steel for blast furnace gas pipeline disclosed in the present invention comprises the following steps:

[0042] S1: Smelting to obtain target molten steel, and casting to obtain a continuous casting billet with a thickness of 220 mm and a width of 1500-2300 mm; wherein the chemical composition of the target molten steel includes C: 0.03-0.06%, Si: 0.10-0.25%, Mn: 0.80-1.50%, Nb: 0.02-0.05%, Ni: 2.00-3.00%, Mo: 0.30-0.50%, Cr: 1.00-1.50, Al: 0.030-0.050%, P≤0.010%, S≤0.005%, and the rest is Fe and unavoidable impurities;

[0043] S2: stacking the continuous casting billet for slow cooling for no less than 72 hours, charging the billet into a furnace and heating it to 1100-1180°C, keeping the temperature for 270-420 minutes, and then descaling the billet to obtain a slab; the center segregation of the billet is not higher than Class C 0.5 level, and the center porosity is not higher than 0.5 level;

[0044] S3: rolling the slab into a steel plate, including: rolling the slab in the first stage to obtain an intermediate billet, wherein the single pass reduction rate of the first stage rolling is not less than 12% and the thickness of the intermediate billet is not less than 100 mm; rolling the intermediate billet in the second stage to obtain a steel plate and water cooling it to room temperature, wherein the reduction rate of at least two passes in the second stage rolling is not less than 18%, and the reduction rate of the last pass is 4-8%; the compression ratio of the steel plate is not less than 8;

[0045] S4: The steel plate is reheated to 580-600℃ for tempering, with a thermal insulation coefficient of 2.5-3min / mm. After tempering, it is air-cooled to obtain steel for blast furnace gas pipelines.

[0046] The process of smelting the target molten steel in step S1 and casting to obtain the continuous casting billet comprises the following steps:

[0047] S11: smelting to obtain initial molten steel;

[0048] S12: performing KR pre-desulfurization treatment on the initial molten steel, wherein the weight percentage of chemical component S in the molten steel after desulfurization is no more than 0.0010%, and the temperature of the molten steel after desulfurization is controlled to be 1300-1380°C;

[0049] S13: Scrap steel is added to the desulfurized molten iron to adjust the composition of the molten steel and continue smelting in the converter. The weight ratio of the scrap steel added is 15-20%, and the scrap steel includes nickel plate and ferromolybdenum. The temperature of the molten steel is 1580-1640℃ when the converter is slaged. The chemical composition of the converter molten steel includes P≤0.008%, C: 0.03-0.05%, slag basicity 4.0-6.5, and T.Fe in the slag: 25-35%;

[0050] S14: tapping from the converter. When the tapping rate is 20-30%, aluminum particles, ferrosilicon, metallic manganese, ferrochrome, ferrovanadium and ferroniobium are added for deoxidation and alloying. When the tapping rate is 70-80%, lime and fluorite are added for slag making. After the tapping rate is reached, calcium aluminate is added to the slag surface to synthesize the slag. In addition, during the tapping process, the ladle is bottom blown and stirred. The bottom blowing flow rate is 600-800NL / min. After the tapping rate is reached, stirring is continued for 3-5 minutes. The molten steel is transported to LF for refining.

[0051] S15: LF refining: Turn on the power to raise the temperature, add calcium carbide, lime and fluorite to adjust the slag, and start bottom blowing and stirring to desulfurize. Add alloy according to the composition of the incoming molten steel, adjust the alloy composition to the required molten steel composition, and transport it to RH vacuum treatment after the molten steel composition, slag composition and temperature meet the standards;

[0052] S16: RH vacuum treatment, RH station starts vacuum treatment to control the vacuum degree less than 2mbar, maintain for 5-10min, add titanium iron according to weight percentage, maintain net circulation treatment for not less than 15min, break the air to tap, feed pure calcium wire into the molten steel after tapping, control the Ca content in the molten steel to 15-25ppm; and the chemical composition of the molten steel after RH vacuum treatment includes C: 0.03~0.06%, Si: 0.10~0.25%, Mn: 0.80~1.50%, Nb: 0.02~0.05%, Ni: 2.00~3.00%, Mo: 0.30~0.50%, Cr: 1.00~1.50, Al: 0.030~0.050%, P≤0.010%, S≤0.005%, and the rest is Fe and unavoidable impurities;

[0053] S17: pouring the molten steel after RH vacuum treatment to obtain a continuous casting slab with a thickness of 220 mm and a width of 1500-2300 mm; wherein, the superheat of the molten steel in the intermediate ladle during the pouring process is 15-25°C, and the crystallizer uses a low-melting-point alkaline protective slag with a melting point of 1150-1200°C.

[0054] The steel for blast furnace gas pipeline and the preparation method thereof disclosed in the present invention are further specifically introduced below in conjunction with the accompanying drawings and specific embodiments.

[0055] Example 1

[0056] S1: Initial molten steel is obtained by smelting. The chemical composition of the initial molten steel is calculated by weight percentage, including Si: 0.18%, Mn: 0.22%; P: 0.08%, S: 0.034%;

[0057] S2: The initial molten steel is subjected to KR pre-desulfurization treatment, the weight percentage of the chemical component S in the molten steel after desulfurization is 0.0012%, and the temperature of the molten steel after desulfurization is controlled to be 1352°C;

[0058] S3: Scrap steel is added to the desulfurized molten iron to adjust the composition of the molten steel and continue to be smelted in the converter. The weight ratio of scrap steel added is 20%, and the scrap steel includes nickel plate and ferromolybdenum. The temperature of the molten steel is 1631°C when the converter is slaged. The chemical composition of the converter molten steel includes P: 0.008%, C: 0.035%, S: 0.0011% by weight, the slag basicity is 5.0, and T.Fe in the slag is 28%;

[0059] S4: tapping from the converter. When the tapping rate is 25%, aluminum particles, ferrosilicon, metallic manganese, ferrochrome, ferrovanadium and ferroniobium are added for deoxidation and alloying. When the tapping rate is 70%, lime and fluorite are added for slag making. After the tapping rate is reached, calcium aluminate is added to the slag surface to synthesize the slag. In addition, during the tapping process, the ladle is bottom blown for stirring. The bottom blowing flow rate is 700NL / min. After the tapping rate is reached, stirring is continued for 5 minutes. The molten steel is transported to LF for refining.

[0060] S5: LF refining: Turn on the power to raise the temperature, add calcium carbide, lime and fluorite to adjust the slag, and start bottom blowing and stirring to desulfurize. Add alloy according to the composition of the incoming molten steel, adjust the alloy composition to the required molten steel composition, and transport it to RH vacuum treatment after the molten steel composition, slag composition and temperature meet the standards;

[0061] S6: RH vacuum treatment, RH station starts vacuum treatment to control the vacuum degree less than 2mbar, maintain for 8min, add titanium iron according to weight percentage, maintain net circulation treatment for not less than 15min, break the air to tap, feed pure calcium wire into the molten steel after tapping, control the Ca content in the molten steel to 18ppm; and the chemical composition of the molten steel after RH vacuum treatment, by weight percentage, includes C: 0.035%, Si: 0.21%, Mn: 0.85%, Nb: 0.025%, Ni: 2.10%, Mo: 0.35%, Cr: 1.05%, Al: 0.037%, P: 0.009%, S: 0.0011%, and the rest is Fe and unavoidable impurities;

[0062] S7: The molten steel after RH vacuum treatment is poured to obtain a continuous casting slab with a thickness of 220 mm and a width of 2260 mm; wherein, the superheat of the molten steel in the intermediate ladle during the pouring process is 25°C, and the crystallizer adopts a low-melting-point alkaline protective slag with a melting point of 1180°C.

[0063] S8: stacking the continuous casting billet for slow cooling for no less than 72 hours, charging the billet into a furnace, heating it to 1160° C., keeping it warm for 270 minutes, and then descaling the billet to obtain a slab; the center segregation of the billet is no higher than Class C 0.5 level, and the center porosity is no higher than 0.5 level;

[0064] S9: rolling the slab into a steel plate, including: rolling the slab into an intermediate slab in the first stage to obtain the intermediate slab, the intermediate slab having a thickness of 110 mm after the first stage rolling, the first stage rolling being performed in 7 passes, with reduction rates of 12.5%, 14.3%, 12.5%, 14.3%, 13.9%, 16.1%, and 15.4% respectively; rolling the intermediate slab into a steel plate in the second stage and cooling the steel plate to room temperature with water, the second stage rolling being performed in 11 passes, with reduction rates of 22.7%, 23.5%, 18.5%, 13.2%, 13.0%, 10.0%, 16.7%, 16.7%, 12.0%, 13.6%, and 5.3% respectively; the compression ratio of the steel plate is 17.8;

[0065] S10: The steel plate is reheated to 580°C for tempering, with a thermal insulation coefficient of 3.0 min / mm and a thermal insulation period of 45 min. After tempering, the steel plate is air-cooled to obtain a blast furnace gas pipeline steel with a thickness of 18 mm.

[0066] The method steps of Examples 2-4 and Comparative Examples 1-2 disclosed in Table 1 below are the same as those of Example 1 for preparing steel for blast furnace gas pipelines, and the only difference is the process parameters for preparing the continuous casting billet and the alloy composition of the obtained continuous casting billet. The specific data are shown in Tables 1-3 below.

[0067] Table 1 Chemical composition data of Examples 1-4 and Comparative Examples 1-2

[0068]

[0069] Table 2 Process parameters for preparing continuous casting billets in Examples 1-4 and Comparative Examples 1-2

[0070]

[0071] Through composition design and smelting process control, Examples 1-4 and Comparative Examples 1-2 respectively produced continuous casting billets with a thickness of 220 mm, and then produced steel plates of different thicknesses; wherein, the difference between Examples 1-4 and Comparative Examples 1-2 lies in the actual smelting composition and specific process parameters, as shown in Tables 2 and 3 below; Table 1 above is the chemical composition results of the continuous casting billets produced in each embodiment, Table 2 is the process parameters of the steps before producing the continuous casting billets in each embodiment, and Table 3 is the process parameters of the steps of producing corrosion-resistant steel from the continuous casting billets in each embodiment.

[0072] Table 3 Rolling process parameters of test steel of Examples 1-4 and Comparative Examples 1-2

[0073]

[0074] Table 4 Phase ratio of the microstructure of steel plates after rolling in Examples 1-4 and Comparative Examples 1-2

[0075]

[0076] Table 4 above shows the proportions of each phase in the microstructure of the steel plates obtained in each embodiment after water cooling, which was obtained by metallographic observation.

[0077] The following is a further analysis of the mechanical properties and acid corrosion resistance tests of the steel plates obtained in the above-mentioned Examples 1-4 and Comparative Examples 1-2, and the results of the tensile properties test of the standard full-thickness plate specimens and the standard CVN low-temperature impact properties are shown in Table 5. Among them, the yield strength of the steel plates in Examples 1-4 reaches about 700MPa, while the tensile strength is close to 800MPa, and the yield strength ratio is less than 90%, which indicates that the steel plates obtained in the embodiments of the present invention have good pipe forming properties; the low-temperature CVN impact properties at -20°C and -40°C are in the range of 227~287J, that is, the steel plates obtained in the embodiments have excellent low-temperature crack arrest properties. Comparative Examples 1-2 are weaker than Examples 1-4 in terms of strength and low-temperature impact properties, which indicates that suitable alloy composition and process parameters can ensure the stability of the performance of the steel for blast furnace gas pipelines of the present invention.

[0078] The corrosion resistance test was carried out according to the test method specified in JB / T 7901. A mixed solution of 20% sulfuric acid + 1% concentrated HCl was prepared with deionized water and placed in a 1000ml ground glass bottle. The sample was processed into a 50mm x 25mm x 5mm standard sample. The sample was fully immersed in the prepared mixed solution. The test temperature was kept at a constant range of 25±2℃. After being completely immersed for 48 hours, the sample was cleaned and weighed, and the corrosion rate was calculated according to the following formula:

[0079]

[0080] Where: is the corrosion rate, in millimeters per year (mm / a); b is the conversion factor, 8760 (1a=8760h); m is the mass of the sample before the test, in grams (g); is the mass of the sample after the test, in grams (g); A is the total surface area of ​​the sample, in square millimeters (mm 2 ); t is the test time, in hours (h); is the density of the sample steel (g / mm 3 ). The corrosion resistance test results of Examples 1-4 and Comparative Examples 1-2 are shown in Table 6. Due to the good combination of Cr, Ni and Mo elements, Examples 1-4 have excellent corrosion resistance, with an average corrosion rate of 5.08-7.59 mm / a. Compared with Comparative Examples 1-2, the corrosion resistance is improved by 10.3-15.6 times, and compared with the corrosion resistance of Q235B plain carbon steel, the corrosion resistance is improved by 17.0-25.5 times.

[0081] Table 5 Mechanical properties data of corrosion resistant steel of Examples 1-4 and Comparative Examples 1-2

[0082]

[0083] Combined with Table 6, it can be found from the examples and comparative examples that the strength, toughness and corrosion resistance of the steel plate are greatly improved by increasing the content of Ni, Cr and Mo elements. Figures 1 to 3 The following are the surface morphology pictures of Example 1, Comparative Example 2 and Q235B steel plates after corrosion. It can be seen that the surface of the sample in Example 1 is relatively smooth, with only shallow rust on the surface, while the surface corrosion layer of the sample in Comparative Example 2 is thicker and has more corrosion pits. The surface of Q235B plain carbon steel has thick corrosion products, and large and deep corrosion pits cover the surface of the sample.

[0084] Table 6 Corrosion resistance performance data of corrosion-resistant steel of Examples 1-4 and Comparative Examples 1-2

[0085]

[0086] In summary, the present invention develops a high-strength, corrosion-resistant steel for blast furnace gas pipelines through the synergistic effect of alloying component design and manufacturing process, which not only solves the problem of poor corrosion resistance of thick-gauge and ultra-large-volume blast furnace gas pipelines in the prior art, but also improves the safety of blast furnace gas transportation, and fills the gap in domestic corrosion-resistant steel for thick-gauge gas pipelines.

[0087] Although the present invention has been disclosed as above with preferred embodiments, it is not intended to limit the present invention. A person with ordinary knowledge in the technical field to which the present invention belongs may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be determined by the definition of the claims.

Claims

1. A method for preparing steel for blast furnace gas pipeline, characterized in that: The steps include: S1: Smelting to obtain target molten steel, and casting to obtain a continuous casting billet with a thickness of 220 mm and a width of 1500-2300 mm; wherein the chemical composition of the target molten steel includes C: 0.03-0.06%, Si: 0.10-0.25%, Mn: 0.80-1.50%, Nb: 0.02-0.05%, Ni: 2.00-3.00%, Mo: 0.30-0.50%, Cr: 1.00-1.50, Al: 0.030-0.050%, P≤0.010%, S≤0.005%, and the rest is Fe and unavoidable impurities; S2: stacking the continuous casting billet for slow cooling for not less than 72 hours, heating and keeping the billet in a furnace to a preset condition, and then descaling the billet to obtain a slab; the center segregation of the billet is not higher than Class C 0.5 level, and the center porosity is not higher than 0.5 level; wherein the process of heating and keeping the billet in a furnace to a preset condition is: heating the billet in a furnace to 1100-1180°C, and keeping the temperature for 270-420 min; S3: rolling the slab into steel plate; S4: The steel plate is reheated to 580-600°C for tempering, with a thermal insulation coefficient of 2.5-3min / mm. After tempering, it is air-cooled to obtain steel for blast furnace gas pipelines.

2. The method for preparing steel for blast furnace gas pipeline according to claim 1, characterized in that: The process of smelting and obtaining the target molten steel in step S1 comprises the following steps: S11: smelting to obtain initial molten steel; S12: performing KR pre-desulfurization treatment on the initial molten steel, wherein the weight percentage of chemical component S in the molten steel after desulfurization is no more than 0.0010%, and the temperature of the molten steel after desulfurization is controlled to be 1300-1380°C; S13: Scrap steel is added to the desulfurized molten iron to adjust the composition of the molten steel and continue smelting in the converter, with the weight ratio of scrap steel being 15-20%; the temperature of the molten steel is 1580-1640°C when the converter is slag-dumped, and the chemical composition of the converter molten steel includes P≤0.008%, C: 0.03-0.05%, slag basicity 4.0-6.5, and T.Fe in the slag: 25-35%; S14: tapping from the converter. When the tapping rate is 20-30%, aluminum particles, ferrosilicon, metallic manganese, ferrochrome, ferrovanadium and ferroniobium are added for deoxidation and alloying. When the tapping rate is 70-80%, lime and fluorite are added for slag making. After the tapping rate is over, calcium aluminate is added to the slag surface to synthesize the slag. In addition, during the tapping process, the ladle is blown and stirred at the bottom. After the tapping rate is over, stirring is continued for 3-5 minutes. The molten steel is transported to LF for refining. S15: LF refining: Turn on the power to raise the temperature, add calcium carbide, lime and fluorite to adjust the slag, and start bottom blowing and stirring to desulfurize. Add alloy according to the composition of the incoming molten steel, adjust the alloy composition to the required molten steel composition, and transport it to RH vacuum treatment after the molten steel composition, slag composition and temperature meet the standards; S16: RH vacuum treatment, RH station starts vacuum treatment to control the vacuum degree less than 2mbar, maintain for 5-10min, add titanium iron according to weight percentage, maintain net circulation treatment for not less than 15min, break the air to tap, feed pure calcium wire into the molten steel after tapping, control the Ca content in the molten steel to 15-25ppm; and the chemical composition of the molten steel after RH vacuum treatment includes C: 0.03~0.06%, Si: 0.10~0.25%, Mn: 0.80~1.50%, Nb: 0.02~0.05%, Ni: 2.00~3.00%, Mo: 0.30~0.50%, Cr: 1.00~1.50, Al: 0.030~0.050%, P≤0.010%, S≤0.005%, and the rest is Fe and unavoidable impurities; S17: The molten steel after RH vacuum treatment is poured to obtain a continuous casting slab with a thickness of 220 mm and a width of 1500-2300 mm.

3. The method for preparing steel for blast furnace gas pipeline according to claim 1, characterized in that: The process of the steel plate rolling in step S3 is as follows: the slab is rolled in the first stage to obtain an intermediate slab, the single-pass reduction rate of the first-stage rolling is not less than 12% and the thickness of the intermediate slab is not less than 100 mm; the intermediate slab is rolled in the second stage to obtain a steel plate and water-cooled to room temperature, the reduction rate of at least two passes in the second stage rolling is not less than 18%, and the reduction rate of the last pass is 4-8%; the compression ratio of the steel plate is not less than 8.

4. The method for preparing steel for blast furnace gas pipeline according to claim 2, characterized in that: The scrap steel in step S13 includes nickel plates and ferromolybdenum.

5. The method for preparing steel for blast furnace gas pipeline according to claim 2, characterized in that: In the step S14, the bottom blowing flow rate of the ladle during bottom blowing and stirring during the steel tapping process is 600-800NL / min.

6. The method for preparing steel for blast furnace gas pipeline according to claim 2, characterized in that: In the step S17, the superheat of the molten steel in the intermediate ladle is 15-25°C, and the crystallizer uses a low-melting-point alkaline protective slag with a melting point of 1150-1200°C.

7. A steel for blast furnace gas pipeline, characterized in that: The steel is prepared by the method for preparing steel for blast furnace gas pipelines as described in any one of claims 1 to 6.

8. The steel for blast furnace gas pipeline according to claim 7, characterized in that: The chemical composition of steel for blast furnace gas pipelines includes C: 0.03~0.06%, Si: 0.10~0.25%, Mn: 0.80~1.50%, Nb: 0.02~0.05%, Ni: 2.00~3.00%, Mo: 0.30~0.50%, Cr: 1.00~1.50, Al: 0.030~0.050%, P≤0.010%, S≤0.005%, and the rest is Fe and unavoidable impurities; The central segregation of the steel for blast furnace gas pipeline is not higher than Class C 0.5 level, and the central porosity is not higher than 0.5 level.

9. The steel for blast furnace gas pipeline according to claim 7, characterized in that: The yield strength of the steel for blast furnace gas pipeline is greater than 600MPa, the tensile strength reaches 700MPa, and the impact energy at -20°C is greater than 250J.

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