CN110629124A - Rare-sulfuric-acid-corrosion-resistant microalloyed steel and heat treatment method of steel plate/steel pipe thereof - Google Patents
Rare-sulfuric-acid-corrosion-resistant microalloyed steel and heat treatment method of steel plate/steel pipe thereof Download PDFInfo
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- CN110629124A CN110629124A CN201810658840.5A CN201810658840A CN110629124A CN 110629124 A CN110629124 A CN 110629124A CN 201810658840 A CN201810658840 A CN 201810658840A CN 110629124 A CN110629124 A CN 110629124A
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0226—Hot rolling
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- 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
- C21D8/105—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies of ferrous alloys
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/08—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for tubular bodies or pipes
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/005—Ferrite
Abstract
A heat treatment method for dilute sulfuric acid corrosion resistant microalloyed steel and a steel plate/steel pipe thereof comprises the following chemical components in percentage by mass: c: 0.01 to 0.20%, Mn: 0.2-0.70%, S: 0.01-0.04%, P is less than or equal to 0.018%, Cu: 0.10 to 0.40%, and the balance of Fe and inevitable impurities, and the elements further satisfy the following relational expression: Mn/S is less than or equal to 24. The microalloyed steel has the ratio of 20G to 10#、20#The carbon steel has better dilute sulfuric acid corrosion resistance, and the specific performance indexes are as follows: under the conventional dilute sulphuric acid pickling condition, namely 60-10.3 wt%, the corrosion rate of 24h is less than or equal to50g/m2H, the yield strength Rel is more than or equal to 250MPa, the tensile strength Rm is more than or equal to 350MPa, and the elongation is more than or equal to 25 percent.
Description
Technical Field
The invention belongs to the field of metal materials, and particularly relates to a dilute-sulfuric-acid-corrosion-resistant microalloyed steel and a heat treatment method of a steel plate/steel pipe thereof.
Background
Firstly, the sulfuric acid corrosion mechanism is oxidation corrosion and electrochemical corrosion according to different concentrations, for example, high-concentration fuming sulfuric acid is oxidation, carbon steel can generate a passive film to resist corrosion, and dilute sulfuric acid is electrochemical corrosion, so that not only is carbon steel seriously corroded, but also stainless steel is corroded; secondly, the corrosivity of sulfuric acid is also changed greatly with the temperature and is not in a linear relationship, so that the development of sulfuric acid corrosion resistant materials, especially materials, is always a hotspot and a difficult point.
The flue gas produced throughout the year by petrochemical plants, coal power plants, steel smelting plants and the like contains a large amount of SO3、SO2Iso-acid gas, SO2Further generation of SO under catalysis3And then a sulfuric acid corrosion environment is formed. In addition, many carbon steel manufacturing equipment in the industries of smelting, chemical engineering and the like are in a non-acid environment during normal operation, but the scale is usually removed by acid washing with dilute sulfuric acid, namely, the equipment is corroded by the dilute sulfuric acid only during scale removal. For example, in an alkaline aluminum smelter, a conventional carbon steel is usually adopted to manufacture a heat exchanger tube bundle, and the tube bundle is often leaked and fails during acid cleaning and descaling, so that a material with dilute sulfuric acid corrosion resistance needs to be selected. Although the corrosion problem of the environment can be solved by adopting a material upgrading mode such as high alloy, the performance-price ratio of the high alloy is poor, and the carbon steel system material is still adopted in the industry generally. The existing low alloy steel with sulfuric acid corrosion resistance generally improves the corrosion resistance mainly by alloying Cr, Cu, Sb, Mo, Al, Ni, Ti, V, B, Sn and the like, does not exert the common heat treatment method and process of steel to realize the structure optimization, and further improves the corrosion resistance of the material, namely the existing heat treatment of the acid-resistant steel mainly aims at improving the mechanical property and the like, and does not give consideration to the minimization of pearlite and achieves the dilute sulfuric acid corrosion resistance.
Disclosure of Invention
The invention aims to provide a micro-alloyed steel resisting dilute sulphuric acid corrosion and a steel plate/steel pipe thereofA heat treatment method, the microalloyed steel has a ratio of 20G to 10#、20#The carbon steel has better dilute sulfuric acid corrosion resistance, and the specific performance indexes are as follows: under the conventional dilute sulphuric acid pickling condition, namely 60-10.3 wt%, the corrosion rate of 24h is less than or equal to 50g/m2H, the yield strength Rel is more than or equal to 250MPa, the tensile strength Rm is more than or equal to 350MPa, the elongation is more than or equal to 25 percent, and the steel can be used in a dilute sulfuric acid corrosion environment.
In order to achieve the purpose, the technical scheme of the invention is as follows:
the general inventive concept of the present invention is to improve the dilute sulfuric acid corrosion resistance of steel materials with the help of heat treatment, which is dominated by micro-alloying. Firstly, the novel material resistant to dilute sulfuric acid corrosion belongs to a microalloyed steel system, and elements such as Cr, Mo, Ni, Ti, V and the like do not need to be additionally added; the invention mainly depends on trace element Cu, conventional residual element S and the like and Mn/S ratio to realize corrosion resistance. Secondly, conventional carbon steel is a ferrite + pearlite two-phase structure, the two phases have different potentials, and dilute sulfuric acid corrosion is electrochemical corrosion, so the two-phase structure is harmful to dilute sulfuric acid corrosion resistance. The invention can reduce or even eliminate the potential difference of a corrosion interface by melting pearlite to convert the pearlite into micro carbide through heat treatment, thereby improving the electrochemical corrosion resistance of dilute sulfuric acid, namely improving the mechanical property and further improving the dilute sulfuric acid corrosion resistance of steel through heat treatment.
Specifically, the microalloyed steel resisting the corrosion of dilute sulfuric acid comprises the following chemical components in percentage by mass: c: 0.01 to 0.20%, Mn: 0.2-0.70%, S: 0.01-0.04%, P is less than or equal to 0.018%, Cu: 0.10 to 0.40%, and the balance of Fe and inevitable impurities, and the elements further satisfy the following relational expression: Mn/S is less than or equal to 24.
Preferably, the content of C in the chemical components of the microalloyed steel resisting the dilute sulfuric acid corrosion is 0.06-0.18% by mass percent.
Preferably, the chemical composition of the microalloyed steel resisting the dilute sulfuric acid corrosion contains 0.27 to 0.60 percent of Mn by mass percent.
Preferably, the content of S in the chemical components of the microalloyed steel resisting the dilute sulfuric acid corrosion is 0.015-0.035% by mass.
Preferably, the chemical composition of the microalloyed steel resisting the dilute sulfuric acid corrosion is less than or equal to 0.015 percent by mass.
Preferably, the chemical composition of the microalloyed steel resisting the dilute sulfuric acid corrosion is 0.15-0.30% of Cu by mass percent.
Preferably, the chemical composition of the microalloyed steel resisting the dilute sulphuric acid corrosion is Mn/S less than or equal to 21.
Further, the heat treatment structure of the microalloyed steel resisting the dilute sulphuric acid corrosion is ferrite and tiny carbides.
The yield strength of the microalloyed steel resisting the dilute sulfuric acid corrosion is more than or equal to 250MPa, the tensile strength is more than or equal to 350MPa, and the 24h corrosion rate under the conventional dilute sulfuric acid pickling condition, namely 60-10.3 wt%, is less than or equal to 50g/m2.h。
In the composition design of the steel sheet of the present invention:
c: c is easy to form carbide, particularly forms pearlite with a potential obviously different from that of ferrite, and is not beneficial to resisting electrochemical corrosion of dilute sulfuric acid, and the lower the potential is, the better the potential is in conventional control. Secondly, the invention eliminates pearlite by heat treatment to make carbide into tiny particles, namely, the adverse effect caused by high carbon content is eliminated by heat treatment to optimize the structure. Furthermore, C is the most economical element for improving strength and is objectively present, and lowering C excessively is an uneconomical solution. Therefore, the content of C is controlled to be 0.01 to 0.20 wt%, preferably 0.06 to 0.18 wt% in the present invention.
Mn: mn is likely to form inclusions with S, and decreases corrosion resistance, that is, the effectiveness of S, but increases the strength of the steel, but if the Mn content is too high, the tendency of structure segregation increases. Therefore, the Mn content is controlled to be 0.2 to 0.70 wt%, preferably 0.27 to 0.60 wt% in the present invention.
S: the S element generally needs to be strictly controlled in the conventional steel, but is a beneficial element for resisting sulfuric acid corrosion, and can form Cu for inhibiting electrochemical corrosion together with Cu and other elementsmSnCompounds and contributes to the formation of a surface film resistant to sulfuric acid corrosion, but the S content is too high and is liable to crack during hot rolling. Thus, the present invention controls SThe content is 0.01-0.04 wt%, preferably 0.015-0.035 wt%.
Mn: mn is easy to form impurities which are unfavorable to corrosion resistance, mechanical property and the like with S, and the formation of Cu with Cu is reducedmSnThe effective S content of the compound is reduced, thereby reducing CumSnThe amount of the compound generated and the integrity and compactness of the corrosion-resistant surface film, therefore, in order to improve the effective content of S element resisting sulfuric acid corrosion, the Mn/S is required to be less than or equal to 24, and the Mn/S is preferably less than or equal to 21.
P: p is not beneficial to the sulfur acid resistance, but is residual element objectively existing, the material economy is influenced too low, and the invention controls P to be less than or equal to 0.018 wt%, preferably P to be less than or equal to 0.015 wt%.
Cu: cu is a conventional residual element in steel, and is strictly controlled in heat-resistant steel and the like, but is advantageous for improving the sulfuric acid resistance. To prevent the tendency to roll cracking, the maximum Cu content should be strictly controlled. Therefore, the Cu content is strictly controlled to be 0.10 to 0.40 wt%, preferably 0.15 to 0.30 wt%.
The invention also provides a heat treatment method for manufacturing the steel plate/steel pipe by the microalloyed steel resisting the dilute sulphuric acid corrosion, which comprises the following steps: the heat treatment temperature is 720-790 ℃, and the heat preservation time is more than or equal to 15 min.
Preferably, the heat treatment temperature is 740-780 ℃, and the heat preservation time is more than or equal to 25 min.
Further, the heat-treated structure of the steel sheet/pipe made of the microalloyed steel resistant to the dilute sulfuric acid corrosion is ferrite + fine carbides.
The yield strength of a steel plate/steel pipe manufactured by the microalloyed steel resisting the dilute sulfuric acid corrosion is more than or equal to 250MPa, the tensile strength is more than or equal to 350MPa, and the 24h corrosion rate under the conventional dilute sulfuric acid pickling condition, namely 60-10.3 wt percent, is less than or equal to 50g/m2.h。
Specifically, the invention also provides a manufacturing method of the microalloyed steel plate resistant to the dilute sulfuric acid corrosion, which mainly comprises the following steps:
(1) smelting and casting
Smelting and casting according to the chemical components;
(2) heating: heating temperature is 1150-1280 ℃, and the heat preservation time is more than or equal to 45 min;
(3) rolling: the finishing temperature is more than or equal to 800 ℃;
(4) and (3) heat treatment: the heat treatment temperature is 720-790 ℃, and the heat preservation time is more than or equal to 15 min.
Preferably, in the step (2), the heating temperature is 1180-1250 ℃, and the heat preservation time is more than or equal to 60 min.
Preferably, in the step (3), the finishing temperature is more than or equal to 850 ℃.
Preferably, in the step (4), the heat treatment temperature is 740-780 ℃, and the heat preservation time is more than or equal to 25 min.
Further, the heat treatment structure of the microalloyed steel plate resisting the dilute sulphuric acid corrosion is ferrite and micro carbide.
The yield strength of the microalloyed steel plate resistant to the dilute sulfuric acid corrosion is more than or equal to 250MPa, the tensile strength is more than or equal to 350MPa, and the 24h corrosion rate under the conventional dilute sulfuric acid pickling condition, namely 60-10.3 wt%, is less than or equal to 50g/m2.h。
The invention also provides a manufacturing method of the microalloyed welded pipe resistant to the dilute sulfuric acid corrosion, which mainly comprises the following steps:
(1) smelting and casting
Smelting and casting according to the chemical components;
(2) heating: heating temperature is 1150-1280 ℃, and the heat preservation time is more than or equal to 45 min; obtaining a hot-rolled coil or plate;
or heating and rolling: heating temperature is 1150-1280 ℃, and the heat preservation time is more than or equal to 45 min; temperature of finish rolling
More than or equal to 800 ℃; obtaining a heat treatment state coil/plate;
(3) the coiled sheet or the plate is formed and welded into a pipe;
(4) thermal treatment
The heat treatment temperature is 720-790 ℃, and the heat preservation time is more than or equal to 15 min.
Preferably, in the step (2), the heating temperature is 1180-1250 ℃, and the heat preservation time is more than or equal to 60 min.
Preferably, in the step (2), the finishing temperature is more than or equal to 850 ℃.
Preferably, in the step (4), the heat treatment temperature is 740-780 ℃, and the heat preservation time is more than or equal to 25 min.
Further, the heat treatment structure of the microalloyed welded pipe resistant to the dilute sulfuric acid corrosion is ferrite and micro carbide.
The yield strength of the microalloyed welded pipe resistant to the dilute sulfuric acid corrosion is more than or equal to 250MPa, the tensile strength is more than or equal to 350MPa, and the 24h corrosion rate under the conventional dilute sulfuric acid pickling condition, namely 60-10.3 wt%, is less than or equal to 50g/m2.h。
The invention also provides a manufacturing method of the microalloyed seamless steel tube resistant to the dilute sulfuric acid corrosion, which mainly comprises the following steps:
(1) smelting and casting
Smelting and casting according to the chemical components;
(2) heating: heating at 1200-1300 ℃, and keeping the temperature for more than or equal to 45 min;
(3) perforating: the perforation temperature is 1100-1190 ℃;
(4) rolling: the finishing temperature is more than or equal to 800 ℃;
(5) and (3) heat treatment: the heat treatment temperature is 720-790 ℃, and the heat preservation time is more than or equal to 15 min.
Preferably, in the step (2), the heating temperature is 1220-1260 ℃, and the heat preservation time is more than or equal to 60 min.
Preferably, in the step (3), the perforation temperature is 1150-1180 ℃.
Preferably, in the step (4), the finishing temperature is more than or equal to 850 ℃.
Preferably, in the step (5), the heat treatment temperature is 740-780 ℃, the heat preservation time is more than or equal to 25min, and the heat preservation time is preferably selected according to the thickness of the product.
Further, the step (3) also comprises the steps of empty reduction and continuous rolling, and the production line configuration of the empty reduction and the continuous rolling is not necessarily provided with working procedures.
And before the rolling in the step (4), reheating treatment is also included: the reheating temperature is 940-980 ℃, and the heat preservation time is more than or equal to 30 minutes; reheating is not necessarily a process step depending on the line configuration.
Preferably, the reheating temperature is 950-970 ℃, and the heat preservation time is more than or equal to 45 minutes.
And the heat treatment structure of the microalloyed seamless steel pipe resisting the dilute sulfuric acid corrosion is ferrite and micro carbide.
The yield strength of the microalloyed seamless steel tube resistant to the dilute sulfuric acid corrosion is more than or equal to 250MPa, the tensile strength is more than or equal to 350MPa, and the 24-hour corrosion rate under the conventional dilute sulfuric acid pickling condition, namely 60-10.3 wt%, is less than or equal to 50g/m2.h。
The invention has the beneficial effects that:
the invention has the outstanding characteristics in the aspect of component design that the corrosion resistance of the microalloyed steel is realized by adding the element Cu, reasonably utilizing the residual element S and controlling the Mn/S ratio.
On the basis of the above-mentioned element composition and its effective content the structure obtained by utilizing conventional heat treatment of carbon steel is ferrite + pearlite. In order to melt and convert pearlite in the microstructure of the steel material into micro carbide, thereby reducing or even eliminating potential difference of a corrosion interface and ensuring electrochemical corrosion resistance of dilute sulfuric acid, the invention adopts the following heat treatment process: the heat treatment temperature is 720-790 ℃, and the heat preservation time is more than or equal to 15 min. If the heat treatment temperature is less than 720 ℃ and the holding time is less than 15min, pearlite cannot be transformed into fine carbides, while if the heat treatment temperature is more than 790 ℃, although pearlite can be transformed into fine carbides, the fine carbides are excessively grown, and the corrosion resistance is lowered.
Drawings
FIG. 1 shows a metallographic structure of a seamless tube in example 1 of the present invention.
FIG. 2 shows that inventive and comparative examples are at 60-10.3 wt% H2SO4The corrosion rate of the solution after long-period soaking tends to change.
FIG. 3 shows that inventive and comparative examples are at 60-10.3 wt% H2SO4And comparing the corrosion resistance of the electrochemical method in the solution.
FIG. 4 shows inventive example 1 at 25 deg.C-10.3 wt% H2SO4And (5) soaking for 48 h.
Detailed Description
The invention will be further explained below with reference to the examples and the accompanying drawings.
Table 1 shows the components of inventive examples 1 to 5, Table 2 shows the resistances and currents of inventive examples 1 and 4, and Table 3 shows the room-temperature tensile properties of inventive examples 1 to 5 and comparative examples 1 to 3.
The manufacturing method of the microalloyed steel plate/steel pipe resisting the dilute sulfuric acid corrosion provided by the embodiment of the invention comprises the following steps:
the invention provides a method for manufacturing a microalloyed steel plate resistant to dilute sulfuric acid corrosion, which mainly comprises the following steps:
(1) smelting and casting
Smelting and casting according to the chemical components;
(2) heating: heating temperature is 1150-1280 ℃, and the heat preservation time is more than or equal to 45 min;
(3) rolling: the finishing temperature is more than or equal to 800 ℃;
(4) and (3) heat treatment: the heat treatment temperature is 720-790 ℃, and the heat preservation time is more than or equal to 15 min.
Preferably, in the step (2), the heating temperature is 1180-1250 ℃, and the heat preservation time is more than or equal to 60 min.
Preferably, in the step (3), the finishing temperature is more than or equal to 850 ℃.
Preferably, in the step (4), the heat treatment temperature is 740-780 ℃, and the heat preservation time is more than or equal to 25 min.
The invention also provides a manufacturing method of the microalloyed welded pipe resistant to the dilute sulfuric acid corrosion, which mainly comprises the following steps:
(1) smelting and casting
Smelting and casting according to the chemical components;
(2) heating: heating temperature is 1150-1280 ℃, and the heat preservation time is more than or equal to 45 min; obtaining a hot-rolled coil or plate;
or heating and rolling: heating temperature is 1150-1280 ℃, and the heat preservation time is more than or equal to 45 min; temperature of finish rolling
More than or equal to 800 ℃; obtaining a heat treatment state coil/plate;
(3) the coiled sheet or the plate is formed and welded into a pipe;
(4) thermal treatment
The heat treatment temperature is 720-790 ℃, and the heat preservation time is more than or equal to 15 min.
Preferably, in the step (2), the heating temperature is 1180-1250 ℃, and the heat preservation time is more than or equal to 60 min.
Preferably, in the step (2), the finishing temperature is more than or equal to 850 ℃.
Preferably, in the step (4), the heat treatment temperature is 740-780 ℃, and the heat preservation time is more than or equal to 25 min.
The invention also provides a manufacturing method of the microalloyed seamless steel tube resistant to the dilute sulfuric acid corrosion, which mainly comprises the following steps:
(1) smelting and casting
Smelting and casting according to the chemical components;
(2) heating: heating at 1200-1300 ℃, and keeping the temperature for more than or equal to 45 min;
(3) perforating: the perforation temperature is 1100-1190 ℃;
(4) rolling: the finishing temperature is more than or equal to 800 ℃;
(5) and (3) heat treatment: the heat treatment temperature is 720-790 ℃, and the heat preservation time is more than or equal to 15 min.
Preferably, in the step (2), the heating temperature is 1220-1260 ℃, and the heat preservation time is more than or equal to 60 min.
Preferably, in the step (3), the perforation temperature is 1150-1180 ℃.
Preferably, in the step (4), the finishing temperature is more than or equal to 850 ℃.
Preferably, in the step (5), the heat treatment temperature is 740-780 ℃, the heat preservation time is more than or equal to 25min, and the heat preservation time is preferably selected according to the thickness of the product.
Further, the step (3) also comprises the steps of empty reduction and continuous rolling, and the production line configuration of the empty reduction and the continuous rolling is not necessarily provided with working procedures.
And before the rolling in the step (4), reheating treatment is also included: the reheating temperature is 940-980 ℃, and the heat preservation time is more than or equal to 30 minutes; reheating is not necessarily a process step depending on the line configuration.
The specific embodiment is as follows:
inventive example 1: the components of the seamless tube are shown in the table 1, molten steel is smelted according to the weight percentage of chemical elements, particularly the preferred percentage; casting to obtain a tube blank, and performing macroscopic inspection to obtain a defect-free tube blank, wherein the tube blank needs to be polished if the tube blank has defects; heating the tube blank to 1250 ℃, and preserving heat for 150 min; perforating at 1160 ℃, and then carrying out air reduction and continuous rolling; heating to 960 deg.C, and maintaining for 45 min; controlling the finishing temperature to be more than or equal to 860 ℃ and hot rolling to reach the product thickness, or hot rolling to form a mother pipe and then rolling and drawing to reach the product thickness. The heat treatment temperature is 760 ℃, and the heat preservation time is 30 min. As shown in fig. 1, the microstructure of the seamless tube of inventive example 1 is ferrite + fine carbide as seen from fig. 1.
Inventive example 2: the components of the welded pipe are shown in the table 1, and molten steel is smelted according to the weight percentage of chemical elements, particularly the preferred percentage; casting to obtain a slab, and performing macroscopic inspection to obtain a defect-free slab; heating the plate blank to 1200 ℃, and preserving heat for 65 minutes; controlling the finish rolling temperature, and carrying out hot rolling to reach the product thickness, wherein the finish rolling temperature is 880 ℃; cutting into a coil or a plate with proper specification; the coiled sheet or the plate is formed and welded into a pipe; the heat treatment process of the product comprises the following steps: the temperature is 770 ℃, and the temperature is kept for 35 min.
Inventive examples 3 to 5: the components of the plate are shown in table 1, and molten steel is smelted according to the weight percentage of chemical elements, particularly the preferred percentage; casting to obtain a slab, and performing macroscopic inspection to obtain a defect-free slab; heating the plate blank to 1210 ℃, and preserving heat for 60 minutes; controlling the finish rolling temperature, and carrying out hot rolling to reach the product thickness, wherein the finish rolling temperature is 885 ℃; the heat treatment process of the product comprises the following steps: the heat treatment temperature is 775 ℃, and the heat preservation time is 30 min.
Comparative example 1: the components are shown in the table 1 and are mixed according to the weight percentage of chemical elements; casting to obtain a slab, and performing macroscopic inspection to obtain a defect-free slab; heating the plate blank to 1200 ℃, and preserving heat for 65 minutes; controlling the finish rolling temperature, and carrying out hot rolling to reach the product thickness, wherein the finish rolling temperature is 880 ℃; the heat treatment process comprises the following steps: the temperature is 770 ℃, and the temperature is kept for 35min, so that the steel plate of the comparative example 1 is obtained.
Comparative example 2: the components are shown in Table 1, and the welded pipe of comparative example 2 is obtained by the above-mentioned process flow of invention example 2.
Comparative example 3: the seamless pipe of comparative example 3 was produced according to the process flow of invention example 1 as shown in Table 1.
The verification proves that the corrosion resistance of the comparative examples 1-3 is far lower than that of the invention examples under the same process conditions due to the difference of the components and the mixture ratio thereof.
When the Mn content is the same, as in comparative example 1 and invention example 2, the S content of invention example 2 is high, and the Mn/S is low, so that invention example 2 can form a compound with high S content with Cu, that is, more Cu can be formedmSnThereby contributing to corrosion resistance. The results of comparison of corrosion resistance are shown in FIG. 2, and it is understood from FIG. 2 that the corrosion resistance of inventive example 2 is superior to that of comparative example 1. Secondly, as in comparative example 2, even though the Mn content is reduced, since the S content is reduced more greatly, Mn/S becomes large and the corrosion resistance is not good even with a high Cu content (see FIG. 2, FIG. 3). Furthermore, in comparative example 3, the content of S is high and the Mn/S ratio is low, but the content of Cu is too low, and corrosion resistance is not good (see FIGS. 2 and 3), because corrosion resistance depends on the formation of CumSnThat is, the ratio of Cu to S is required, i.e., both Cu and S are required to reach a certain content. Therefore, for the chemical composition of the present invention, a certain S and Cu content and Mn/S ratio can achieve high sulfuric acid resistance.
1. Corrosion resistance to dilute sulfuric acid
(1) Weightlessness corrosion resistance evaluation
The conventional dilute sulfuric acid pickling temperature and concentration of an Australia aluminum smelter are respectively 40-60 ℃ and 10.3 wt%, the service life is designed according to 5 years, pickling is carried out for 1h every week, and the accumulated pickling time of the whole service life is about 216 h. Invention and 10#Comparative examples of steels between 60 and 10.3 wt% H2SO4The corrosion rate change trend during 312h soaking is shown in fig. 2, the corrosion mechanism is uniform corrosion, and the corrosion resistance is reliably evaluated by a weight loss method. The corrosion rates of comparative examples 1 and 2 correspond up to 214.31g/m at 24h2H and 86.58g/m2H, while the corrosion rates of comparative examples 1 and 2 decreased with time, at 144h, they were also 77.34g/m, respectively2H and 69.26g/m2H, are all higher than the set 50g/m2H pass cut point, then comparative examples 1 and 2 are fail. Comparative example 3 was relatively stable over time, fluctuating near the cut point, and comparative example 3 was essentially acceptable. In the inventive example, the maximum corrosion rate is 43.31g/m2H (invention examples 4 and 24h), therefore, the corrosion rates of invention examples 1 to 5 in the whole test period are all lower than the set target, and all are qualified.
(2) Electrochemical evaluation of corrosion resistance
Compared with the comparative example, the invention examples 1-5 are 60-10.3 wt% of H2SO4The more the impedance multiple is shown in FIG. 3The better the large corrosion resistance. Comparative example 2 is similar to comparative example 1, comparative example 3 is slightly better (1.5 times of comparative example 1), and invention examples 1 to 5 are about 4.4 to 5.3 times of comparative example 1, so that invention examples 1 to 5 are far more corrosion resistant than comparative example in this corrosive environment.
At 25-10.3% H2SO4The results of the impedance test in (1) are shown in table 2. As can be seen from table 2, the impedance of invention example 1 is about 9.8 times that of invention example 4, and as can be seen from fig. 3, the impedance of invention example 1 is about 1.2 times that of invention example 4 at 60 ℃. The lower the temperature, the better the corrosion resistance of invention example 1. Inventive example 1 at 25 deg.C-10.3% H2SO4The polarization curve for the medium immersion time of 48h is shown in FIG. 4. As can be seen from fig. 4, in the case of a long-term corrosive environment, inventive example 1 has a strong polarization capability, i.e., the corrosion resistance is stable.
In conclusion, the results of the weight loss method and the electrochemical method are mutually verified, and the results of the weight loss method and the electrochemical method both show that the invention examples 1-5 have dilute sulfuric acid corrosion resistance which is far higher than that of conventional carbon steel.
2. Tensile Properties
The heat-treated tensile properties of inventive examples 1 to 5 and comparative examples 1 to 3 are shown in Table 3, and the yield strength Re of inventive examples 1 to 5 having good corrosion resistance is not less than 315MPa, and the tensile strength Rm is not less than 408 MPa.
Table 1 units: wt.%
| C | Mn | P | S | Cu | Ratio of Mn to S | |
| Comparative example 1 (10)#) | 0.08 | 0.60 | 0.01 | 0.02 | 0.10 | 30.0 |
| COMPARATIVE EXAMPLE 2(20G) | 0.2 | 0.50 | 0.015 | 0.008 | 0.30 | 62.5 |
| Comparative example 3 (20)#) | 0.15 | 0.64 | 0.012 | 0.028 | 0.05 | 22.8 |
| Inventive example 1 | 0.09 | 0.41 | 0.005 | 0.02 | 0.28 | 20.5 |
| Inventive example 2 | 0.13 | 0.60 | 0.008 | 0.025 | 0.15 | 24.0 |
| Inventive example 3 | 0.20 | 0.27 | 0.009 | 0.017 | 0.10 | 15.9 |
| Inventive example 4 | 0.18 | 0.34 | 0.01 | 0.028 | 0.4 | 12.1 |
| Inventive example 5 | 0.01 | 0.20 | 0.007 | 0.015 | 0.35 | 13.3 |
TABLE 2
| Rp/ohm | Zx/ohm | Ecorr/mA | I/mA | |
| Inventive example 1 | 170 | 164.9 | -280.72 | -0.248 |
| Inventive example 4 | 17.37 | 9.65 | -377.72 | -2.67 |
TABLE 3
Claims (8)
1. A microalloyed steel resisting dilute sulfuric acid corrosion comprises the following chemical components in percentage by mass: c: 0.01 to 0.20%, Mn: 0.2-0.70%, S: 0.01-0.04%, P is less than or equal to 0.018%, Cu: 0.10 to 0.40%, and the balance of Fe and inevitable impurities, and the elements further satisfy the following relational expression: Mn/S is less than or equal to 24.
2. The microalloyed steel capable of resisting the dilute sulfuric acid corrosion according to claim 1, wherein the microalloyed steel for resisting the dilute sulfuric acid corrosion comprises the following chemical components in percentage by mass: c: 0.06-0.18%, Mn: 0.27-0.60%, S: 0.015-0.035%, P is less than or equal to 0.015%, Cu: 0.15 to 0.30% and the balance of Fe and unavoidable impurities, wherein the elements further satisfy the following relation: Mn/S is less than or equal to 21.
3. The dilute sulfuric acid corrosion resistant microalloyed steel as claimed in claim 1 or 2, wherein the heat treated structure of the dilute sulfuric acid corrosion resistant microalloyed steel is ferrite + fine carbides.
4. The microalloyed steel resisting dilute sulfuric acid corrosion according to any one of claims 1 to 3, wherein the microalloyed steel resisting dilute sulfuric acid corrosion has a yield strength of not less than 250MPa, a tensile strength of not less than 350MPa, and a 24-hour corrosion rate of not more than 50g/m under the conventional dilute sulfuric acid pickling condition of 60 to 10.3 wt%2.h。
5. The heat treatment process for manufacturing steel plates/tubes made of microalloyed steel resistant to dilute sulfuric acid corrosion according to any one of claims 1 to 4, characterized in that it comprises: the heat treatment temperature is 720-790 ℃, and the heat preservation time is more than or equal to 15 min.
6. The heat treatment method according to claim 5, wherein the heat treatment temperature is 740 to 780 ℃ and the holding time is not less than 25 min.
7. The heat treatment method according to claim 5 or 6, wherein the heat-treated structure of the steel sheet/pipe is ferrite + fine carbide.
8. The heat treatment method according to any one of claims 5 to 7, wherein the yield strength of the steel plate/pipe is not less than 250MPa, the tensile strength is not less than 350MPa, and the 24-hour corrosion rate under the conventional dilute sulfuric acid pickling condition, i.e. 60-10.3 wt%, is not more than 50g/m2.h。
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| CN101372733A (en) * | 2003-12-23 | 2009-02-25 | Posco公司 | Bake-hardenable cold rolled steel sheet having excellent formability, and method of manufacturing the same |
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