A smelting method for improving the purity of molten steel of an acid-resistant and corrosion-resistant pipeline steel

Abstract

The present application relates to the technical field of pipeline steel smelting, in particular to a smelting method for improving the purity of molten steel of acid-resistant and corrosion-resistant pipeline steel, which comprises the following steps: magnesium metallurgical treatment is carried out on the molten steel after refining, so as to obtain inclusions mainly composed of MgO·Al2O3 and MgO, the inclusions are removed by floating through static stirring and setting, and the purity of the molten steel is improved; high-temperature tapping is carried out during smelting, so as to reduce the sulfur content in the molten steel; a low-melting-point, high-fluidity and low-oxidizing refining slag system is prepared during refining, so as to improve the adsorption of inclusions, modify and refine oxide inclusions, disperse hydrogen atom adsorption points, refine grains by using fine inclusions, hinder the expansion of micro-cracks, and realize the performance of hydrogen-induced cracking resistance of the acid-resistant and corrosion-resistant pipeline steel.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of pipeline steel smelting, in particular to a smelting method for improving the purity of molten steel of acid-resistant and corrosion-resistant pipeline steel. BACKGROUND

[0002] With the continuous development of economy, the dependence of human beings on energy is becoming more and more serious, and oil resources are the main energy that human beings cannot get rid of at present. Among them, the proportion of crude oil transportation in oil natural transportation is increasing, and most of the steel plates need to have acid resistance and corrosion resistance for transportation. H2S is one of the most harmful media with corrosion effect in oil and natural gas. When the transportation pipeline is exposed to fluid medium containing wet H2S, H2S acid corrosion is prone to occur, which causes the pipe wall to be thinned, corroded, even broken, etc., and seriously affects the service life and safe operation of the pipeline. Hydrogen-induced cracking (HIC) and sulfide stress corrosion cracking (SSCC) are the main forms of H2S acid corrosion.

[0003] In order to ensure the good HIC resistance of the pipeline steel, the low carbon content and high purity of the molten steel must be ensured in the smelting process, and the total amount of inclusions is reduced as much as possible and is subjected to modification treatment. Therefore, the present application provides a smelting method for improving the purity of molten steel of acid-resistant and corrosion-resistant pipeline steel, which improves the purity of the molten steel to improve the HIC resistance of the pipeline steel. SUMMARY

[0004] The present application overcomes the shortcomings of the prior art and provides a smelting method for improving the purity of molten steel of acid-resistant and corrosion-resistant pipeline steel. The chemical elements and mass percentage of the molten steel are as follows: C:≤0.05%, Mn:≤1.50%, Al:0.02%~0.05%, O<0.0015%, S<0.0015%, Mg:0.0010%~0.0020%, Ca≤0.0004%, and the balance is Fe and other unavoidable impurities. The smelting method further includes using low-sulfur scrap steel in the converter smelting, controlling the S content to be <0.005%, and controlling the tapping temperature to be 1670~1720 degrees. A low-melting-point, high-fluidity, and low-oxidizing refining slag system is formed in the refining process, and magnesium metallurgical treatment is performed after the refining treatment.

[0005] The technical solution of the present application is further defined as follows:

[0006] Further, LF+RH mode is used for molten steel refining, RH uses high vacuum degree ≤3.0mbar for vacuum operation; no oxygen is blown during RH refining, and natural decarburization is realized by using carbon-oxygen reaction under vacuum; after the carbon content is reduced to the target steel composition, the oxygen content in the molten steel is 0.03%~0.05%; after decarburization, aluminum is added for deoxidization, and the molten steel is circulated and the bottom blowing argon is used to promote the floating removal of the deoxidization products; and the vacuum is broken after ensuring that the activity oxygen in the molten steel is below 5ppm after alloying.

[0007] Further, LF refining process adds slagging agent, and through slag-steel reaction, the S content in the steel is controlled to be less than 0.0015% after the refining is finished, and the LF refining process adds aluminum particles on the slag surface, and the aluminum wire is fed into the ladle.

[0008] Further, magnesium treatment is carried out after the refining alloying, the magnesium-aluminum cored wire is fed into the molten steel to deeply purify the molten steel and modify the inclusions in the steel; after the cored wire is fed, the Mg and Al contents in the steel satisfy the following relationship: w Mg satisfies 2.2*10 -3 w Al +2.2*10 -6 satisfies 5.7*10 -3 w Al +1.2*10 -5 .

[0009] Further, the cored wire core material is composed of 8%-15% Mg, 25%-40% Al, and the rest is Fe and inevitable impurities, wherein the Mg and Al are in the form of binary alloy particles, and the Fe is single iron powder.

[0010] Further, the casting process adopts low superheat casting of 20-35 DEG C, the drawing speed is 0.5-0.8 m / min, the dynamic soft reduction technology is adopted to ensure the compactness of the structure, and the slow cooling process is adopted after continuous casting.

[0011] Further, the low-melting-point, high-fluidity and low-oxidation refining slag system is controlled in the following ranges: CaO: 45%-55%, SiO2: 8%-10%, Al2O3: 20%-25%, MgO: 8%-10%, MnO+FeO<1%, CaF2<6%, the slag basicity is between 5 and 7, and the mannese index is between 0.25 and 0.35.

[0012] The beneficial effects of the present application are:

[0013] (1) The present application adopts metallurgical technology to modify the inclusions, the magnesium core inclusions pin the grain boundaries, inhibit the growth of austenite grains, and can also be used as a heterogeneous nucleation point in the solidification process to induce the formation of intracrystalline acicular ferrite, thereby refining the grains and inhibiting the expansion of micro-cracks, thereby improving the hydrogen-induced cracking resistance of the pipeline steel;

[0014] (2) The present application adopts high-temperature desulfurization technology, reduces the production amount of sulfides in the steel, and the actual activity product of manganese and sulfur in the liquid phase during the solidification process of the molten steel is less than the equilibrium activity product, thereby avoiding the precipitation of type II MnS in the form of sulfur at the end of solidification, the sulfides are precipitated in the solid phase and uniformly and dispersedly distributed, the production amount of plastic sulfides in the steel is reduced, and the sulfide morphology and distribution are improved, thereby reducing the risk of hydrogen-induced cracking;

[0015] (3) The present application adopts magnesium metallurgy technology, which can modify the alumina or calcium aluminate in the steel into MgO·Al2O3, MgO and a small amount of (Mn, Mg) S, the critical nucleation radius of MgO·Al2O3 and MgO is smaller than that of Al2O3, the nucleation rate is high, and they are distributed in a more fine and dispersed state in the molten steel, the interface energy between MgO·Al2O3 and MgO and the molten steel is smaller than that between Al2O3 and the molten steel, the wetting angle is also small, the attraction between the particles is also smaller than that of Al2O3, and they are not easy to aggregate and grow, thus avoiding the formation of cluster-shaped inclusions, so they are also more fine and dispersed in the final product, small-size inclusions usually have less harm to the steel, and can disperse hydrogen atom adsorption points, reduce local hydrogen enrichment, and thus avoid hydrogen-induced cracking;

[0016] (4) In the refining process of the present application, the slag basicity is a low-melting-point, high-fluidity, low-oxidizing refining slag system, the range is controlled as follows: CaO: 45% to 55%, SiO2: 8% to 10%, Al2O3: 20% to 25%, MgO: 8% to 10%, MnO + FeO < 1%, CaF2 < 6%, the slag basicity is between 5 and 7, the mannese index is between 0.25 and 0.35, the slag has a low melting point and high fluidity, the adsorption capacity of the slag to inclusions is improved, and the purity of the molten steel is improved;

[0017] (5) The MgO·Al2O3 and MgO inclusions obtained by the present application are beneficial to pinning the grain boundary, inhibiting the growth of austenite grains, heterogeneous nucleation points in the solidification and cooling process, promoting the generation of acicular ferrite, refining the grain structure, and playing a role of regulating the structure and inhibiting crack propagation. DETAILED DESCRIPTION

[0018] Example 1

[0019] In this example, the content of main elements in the molten steel in the steel is as follows: C: 0.03%, Mn: 1.23%, Al: 0.03%, O: 0.009%, S: 0.0011%, Mg: 0.0013%, Ca: 0.0002%, the balance being Fe and other unavoidable impurities; low-sulfur scrap steel S: 0.003% is used in the converter smelting, the tapping temperature is 1696 degrees, high-temperature and high-alkalinity slag is used for tapping, which effectively reduces the original sulfur content in the molten steel, provides good kinetic conditions for refining, reduces the refining treatment time, and the molten steel is refined by LF+RH mode, RH uses high vacuum degree 1.0 mbar for vacuum operation; no oxygen is blown during RH refining process, natural decarburization is realized by carbon-oxygen reaction under vacuum, after the carbon content is reduced to the target steel composition, the oxygen content in the molten steel is 0.04%; after decarburization, aluminum is added for deoxidation, the molten steel is circulated and 120 L / min bottom blowing argon is used to promote the floating removal of deoxidation products; after alloying, the composition and temperature are qualified and the activity oxygen in the molten steel is ensured to be below 5 ppm after breaking the vacuum. A slagging agent is added during the LF refining process to form suitable refining white slag, and through the slag-steel reaction, the S in the steel after refining is 0.0010%, the LF refining process uses slag surface aluminum particles and feeding aluminum wire in the ladle for composite deoxidation. After the refining and alloying, magnesium treatment is carried out, magnesium-aluminum cored wire is fed into the molten steel for deep purification and modification of inclusions in the steel; after the cored wire is fed, the Mg and Al contents in the steel satisfy the following relationship: Mg 2.2 x 10 -3 w Al + 2.2 x 10 -6 between 5.7 x 10 -3 w Al + 1.2 x 10 -5 .

[0020] During the casting process, low superheat casting of 30°C is used, the drawing speed is 0.65 m / min, dynamic soft reduction technology is used to ensure the compactness of the structure, and slow cooling process is used after continuous casting. The core material of the cored wire is 13% Mg, 26% Al, and the balance is Fe and unavoidable impurities, among which Mg and Al exist in the form of binary alloy particles, and Fe is single iron powder. The low-melting-point, high-fluidity, and low-oxidizing refining slag system is controlled as follows: CaO: 51%, SiO2: 9%, Al2O3: 23%, MgO: 9%, MnO+FeO: 0.3%, CaF2: 0.06%, slag basicity 5.7, Mnsen's index 0.30, the molten steel is purified and the inclusion composition is controlled through slag-steel reaction.

[0021] Example 2

[0022] In this embodiment, the content of main elements in the molten steel is as follows: C: 0.02%, Mn: 1.15%, Al: 0.03%, O: 0.0010%, S: 0.0010%, Mg: 0.0015%, Ca: 0.0002%, and the balance is Fe and other inevitable impurities; low-sulfur scrap steel S: 0.003% is used in the converter smelting, the tapping temperature is 1696 degrees, high-temperature and high-alkalinity slag is used for tapping, which effectively reduces the original sulfur content in the molten steel, provides good kinetic conditions for refining, reduces the refining treatment time, and the molten steel is refined by LF+RH mode, and RH uses high vacuum degree 1.0 mbar for vacuum operation; no oxygen is blown during RH refining process, and natural decarburization is realized by carbon-oxygen reaction under vacuum, and after the carbon content is reduced to the target steel composition, the oxygen content in the molten steel is 0.04%; after decarburization, aluminum is added for deoxidation, and the molten steel is circulated and 120 L / min bottom blowing argon is used to promote the floating removal of deoxidation products; after alloying, the composition and temperature are qualified and the activity oxygen in the molten steel is ensured to be below 5 ppm, and then the vacuum is broken. The LF refining process adds slag forming agent to form suitable refining white slag, and through slag-steel reaction, the S in the steel after refining is 0.0010%, and the LF refining process uses slag surface aluminum particles and feeding aluminum wire in the ladle for composite deoxidation. After the refining alloying, magnesium treatment is carried out, magnesium-aluminum cored wire is fed into the molten steel for deep purification and modification of inclusions in the steel; after the cored wire is fed, the Mg and Al contents in the steel satisfy the following relationship: Mg 2.2 x 10 -3 w Al + 2.2 x 10 -6 between 5.7 x 10 -3 w Al + 1.2 x 10 -5 .

[0023] In the casting process, low superheat casting of 30°C is used, the drawing speed is 0.65 m / min, dynamic soft reduction technology is used to ensure the compactness of the structure, and slow cooling process is used after continuous casting. The core material of the cored wire is 13% Mg, 26% Al, and the balance is Fe and inevitable impurities, among which Mg and Al exist in the form of binary alloy particles, and Fe is single iron powder. The low-melting-point, high-fluidity, and low-oxidizing refining slag system is controlled in the following ranges: CaO: 51%, SiO2: 9%, Al2O3: 23%, Mg: O: 9%, MnO+FeO: 0.3%, CaF2: 0.06%, slag basicity is 61, and mannese index is 0.27. The molten steel is purified and the inclusion composition is adjusted through slag-steel reaction.

[0024] Example 3

[0025] In this embodiment, the content of main elements in the molten steel is as follows: C: 0.03%, Mn: 1.43%, Al: 0.03%, O: 0.0009%, S: 0.0012%, Mg: 0.0017%, Ca: 0.0002%, and the balance is Fe and other inevitable impurities; low-sulfur scrap steel S: 0.003% is used in the converter smelting, the tapping temperature is 1696 degrees, high-temperature and high-alkalinity slag is used for tapping, which effectively reduces the original sulfur content in the molten steel, provides good kinetic conditions for refining, reduces the refining treatment time, and the molten steel is refined by LF+RH mode, and RH is operated under high vacuum degree of 1.0 mbar; no oxygen is blown during RH refining process, and natural decarburization is realized by carbon-oxygen reaction under vacuum, and after the carbon content is reduced to the target steel composition, the oxygen content in the molten steel is 0.04%; after decarburization, aluminum is added for deoxidization, and the molten steel is circulated and 120 L / min bottom blowing argon is used to promote the floating and removal of deoxidization products; after alloying, the composition and temperature are qualified and the activity oxygen in the molten steel is ensured to be below 5 ppm, and then the vacuum is broken. The LF refining process adds slag forming agent to form suitable refining white slag, and through slag-steel reaction, the S in the steel after refining is 0.0010%, and the LF refining process uses slag surface aluminum particles and feeding aluminum wire in the ladle for composite deoxidization. After refining and alloying, magnesium treatment is carried out, magnesium-aluminum cored wire is fed into the molten steel for deep purification and modification of inclusions in the steel; after feeding the cored wire, the contents of Mg and Al in the steel satisfy the following relationship: Mg 2.2 x 10 -3 w Al + 2.2 x 10 -6 between 5.7 x 10 -3 w Al + 1.2 x 10 -5 .

[0026] The casting process uses low superheat casting of 30°C, the drawing speed is 0.65 m / min, the dynamic soft reduction technology is used to ensure the compactness of the structure, and the slow cooling process is used after continuous casting. The core material of the cored wire is 13% Mg, 26% Al, and the balance is Fe and inevitable impurities, among which Mg and Al exist in the form of binary alloy particles, and Fe is single iron powder. The low-melting-point, high-fluidity, and low-oxidizing refining slag system is controlled as follows: CaO: 51%, SiO2: 9%, Al2O3: 23%, Mg: 0.0019%, MnO+FeO: 0.3%, CaF2: 0.06%, slag basicity is 5.9, and mannese index is 0.33. The molten steel is purified and the inclusion composition is controlled through slag-steel reaction.

[0027] Table 1: Detection content of various inclusions in each embodiment (in percentage)

[0028] Embodiments Class A Class B Class C Class D Class DS 1 0.5 0.5 0 0.5 0 2 0 0 0 0.5 0 3 0.5 0.5 0 0 0

[0029] In combination with Table 1, it can be known that the molten steel purity is obviously improved by the process improvement, the B-type inclusion rating small inclusion organization is dispersedly distributed in the steel grade, has no adverse effect on the molten steel, can improve the organizational grain size to a certain extent, improve the steel plate strength, and improve the product quality.

[0030] In addition to the above embodiments, the present application can have other implementation manners. Any technical solution formed by equivalent replacement or equivalent transformation falls within the protection scope required by the present application.

Claims

1. A method of improving the steel cleanliness of an acid-resistant corrosion-resistant pipeline steel, characterized in that, The chemical elements and mass percentage of the molten steel are: C:≤0.05%, Mn:≤1.50%, Al:0.02%-0.05%, O<0.0015%, S<0.0015%, Mg:0.0010%-0.0020%, Ca≤0.0004%, the balance being Fe and other inevitable impurities; wherein the smelting method further comprises using low-sulfur scrap steel in converter smelting, controlling S content <0.005%, tapping temperature 1670-1720 degrees, creating a low-melting-point, high-fluidity, low-oxidizing refining slag system in the refining process, and performing magnesium metallurgical treatment after refining treatment; LF refining process adds slagging agent, and through slag-steel reaction, the S content in the steel is controlled <0.0015% after refining is completed, and aluminum particles are added to the slag surface in the LF refining process, and aluminum wire is fed into the ladle; After refining and alloying, magnesium treatment is performed. Magnesium-aluminum cored wire is then fed into the molten steel to deeply purify it and modify and control inclusions. After feeding the cored wire, the Mg and Al content in the steel satisfies the following relationship: w Mg Satisfies 2.2×10 -3 w Al +2.2×10 -6 Up to 5.7×10 -3 w Al +1.2×10 -5 between; The core material of the cored wire is 8%-15% Mg, 25%-40% Al, and the balance being Fe and inevitable impurities, wherein Mg and Al are in the form of binary alloy particles, and Fe is single iron powder; The low-melting-point, high-fluidity, low-oxidizing refining slag system is controlled as follows: CaO:45%-55%, SiO2:8%-10%, Al2O3:20%-25%, MgO:8%-10%, MnO+FeO<1%, CaF2<6%, slag basicity is between 5 and 7, and the mannese index is between 0.25 and 0.

35.

2. The smelting method of claim 1, wherein, The molten steel is refined by LF+RH mode, RH uses high vacuum degree ≤3.0 mbar for vacuum operation; no oxygen is blown in the RH refining process, and natural decarburization is realized by carbon-oxygen reaction under vacuum, after the carbon content is reduced to the target steel composition, the oxygen content in the molten steel is 0.03%-0.05%; after decarburization, aluminum is added for deoxidization, and the molten steel is circulated and the bottom argon blowing is used to promote the floating removal of deoxidization products; after alloying, the molten steel activity oxygen is ensured to be below 5 ppm before breaking the vacuum.

3. The smelting method of claim 1, wherein, During casting, low superheat casting of 20-35°C is adopted, the drawing speed is 0.5-0.8 m / min, dynamic soft reduction technology is used to ensure the compactness of the structure, and slow cooling process is used after continuous casting.