CN120485472A

CN120485472A - A clean smelting process and production process for L485M pipeline steel

Info

Publication number: CN120485472A
Application number: CN202510635036.5A
Authority: CN
Inventors: 陈传磊; 刘熙章; 李洪翠; 张英杰; 马淑梅; 丁中; 张波; 陈耀; 邵明海; 刘飞; 潘振华; 赵友虎; 赵登报; 刘建伟; 杨光维
Original assignee: SD Steel Rizhao Co Ltd
Current assignee: SD Steel Rizhao Co Ltd
Priority date: 2025-05-16
Filing date: 2025-05-16
Publication date: 2025-08-15

Abstract

The invention relates to the technical field of pipeline steel smelting, in particular to a clean smelting process and a production process of L485M pipeline steel. The clean smelting process at least comprises the following steps of carrying out RH refining on pipeline steel molten steel, carrying out rinsing on cold steel attached in an RH vacuum tank by using high-temperature molten steel before pipeline steel production, controlling the high-temperature molten steel inlet temperature of a rinsing heat to be more than or equal to 1610 ℃, maintaining the vacuum pressure for more than or equal to 16 minutes, adopting a special tank production mode after rinsing, feeding pure calcium wires after RH emptying, carrying out accurate calcium treatment on the pipeline steel molten steel, controlling the Ca content of the pipeline steel molten steel to be 0.0015% -0.0025%, and carrying out soft blowing for 12-15 minutes after wire feeding. The invention is beneficial to improving the cleanliness level of pipeline steel, improving the flaw detection qualification rate of the steel plate and improving the delivery speed of ordered products.

Description

Clean smelting process and production process of L485M pipeline steel

Technical Field

The invention relates to the technical field of pipeline steel smelting, in particular to a clean smelting process and a production process of L485M pipeline steel.

Background

The pipeline steel has flaw detection of about 5-7 times in the pipe manufacturing process, and in the pipeline construction process, the pipeline steel also needs to be subjected to repeated detection within the range of 100 mm at two ends of the pipeline steel by adopting special flaw detection equipment such as phased array or TOFT and the like, so that the quality requirement is strict. The quality problem of the pipeline steel produced in the past occurs, and most of sampling anatomical analysis is that B-class and D-class inclusion exceeds standard, so that flaw detection does not meet acceptance standards. Since aluminum (Al) is the most economical metal element with strong deoxidizing ability and cost consumption, al metal is generally used as the main and final deoxidizing element in the current steel smelting, so that the main purpose of promoting the aluminum deoxidizing products to float up into slag in the RH refining and soft blowing, and continuous casting processes is to be achieved. Although various process optimization measures are adopted, the removal rate of alumina and calcium aluminate inclusions is not stable all the time due to a plurality of influencing factors.

CN118291708a discloses a smelting method of hydrogen-transporting pipeline steel, which comprises the steps of carrying out KR desulfurization on molten iron, controlling the end sulfur content of the KR desulfurization, carrying out slag skimming operation, controlling the slag skimming rate of the slag skimming operation to obtain first molten steel, carrying out converter smelting on the first molten steel, carrying out slag formation dephosphorization by adopting a double slag method in the converter smelting, controlling the technological parameters of slag formation dephosphorization, carrying out tapping after the technological parameters of slag formation dephosphorization are controlled, carrying out slag blocking operation and slag charge addition in the tapping, controlling the technological parameters of the slag charge to obtain second molten steel, carrying out LF refining on the second molten steel, controlling the technological parameters of the slag formation desulfurization stage of the LF refining to obtain third molten steel, carrying out VD vacuum refining on the third molten steel, controlling the time of the VD vacuum refining and the bottom blowing argon flow to obtain clean molten steel, and controlling the moisture of alloy and raw materials in the whole smelting process.

CN117778864A discloses a preparation method of pipeline steel, which comprises the steps of S1, adding quicklime into a liquid Fe material for slagging and supplying oxygen, adding Al and Mn alloy, adding slag forming materials for uniform mixing to obtain molten steel, S2, transferring the molten steel into an LF refining furnace, adjusting Si, mn, cr, ni, mo, V, nb content, controlling slag system binary alkalinity to be 5-10, blowing argon for removing impurities to obtain refined molten steel, S3, transferring the refined molten steel into a VD vacuum furnace for vacuumizing to obtain cast molten steel, S4, continuously casting round billets to obtain continuously cast round billets, S5, sequentially cutting, heating, spraying water for dephosphorization, cooling, perforating and rolling the continuously cast round billets, and then sequentially cooling, heating, quenching, heating and cooling to obtain the pipeline steel.

CN116855843a discloses a smelting method for improving the purity of molten steel of acid-resistant corrosion-resistant pipeline steel, which is characterized in that through metallurgical treatment of molten steel magnesium after refining molten steel, inclusions mainly comprising MgO.Al ₂O₃ and MgO are obtained, floating is removed through static stirring and sedation, the purity of molten steel is improved, high-temperature tapping is smelted, the sulfur content in molten steel is reduced, a low-melting-point, high-fluidity and low-oxidization refining slag system is produced in the refining process, the adsorption effect on the inclusions is improved, oxide inclusions are modified and refined, hydrogen atom adsorption points are dispersed, fine inclusion refinement grains are utilized to prevent the expansion of microcracks, and the hydrogen-induced cracking resistance of the acid-resistant corrosion-resistant pipeline steel is realized.

CN116516235A discloses a control method for B-type inclusion in pipeline steel, which comprises the steps of converter smelting, LF refining, calcium treatment, RH vacuum refining, magnesium treatment, soft blowing, continuous casting and rolling, wherein the molten steel component and slag alkalinity are regulated in the LF refining process, a Si-Ca alloy cored wire is fed into the molten steel for calcium treatment after LF refining, and a Mg-Al alloy cored wire is fed into the molten steel for magnesium treatment after RH refining. The molten steel does not contain large-size CaO-Al ₂O₃ inclusion, the inclusion is mainly CaO-Al ₂O₃ -MgO-CaS with high MgO content, and after hot rolling, the inclusion is dispersed small-particle magnesia-alumina spinel.

According to the technical scheme, clean molten steel is obtained mainly through conventional processes of molten steel magnesium metallurgical treatment after molten steel refining, si-Ca wire calcium treatment, mg-Al wire magnesium treatment, slag system binary alkalinity control of 5-10, argon blowing impurity removal, VD vacuum treatment, double slag method slag formation dephosphorization slag blocking, LF slag formation desulfurization VD vacuum refining, and the like, and the influence of cold steel attached in an RH vacuum tank on cleanliness is not paid attention to mainly by conventional processes of calcium treatment, magnesium treatment, slag alkalinity control, double slag method refining process improvement and the like.

Disclosure of Invention

Aiming at the technical problem of poor cleanliness of pipeline steel smelting, the invention provides a clean smelting process and production process of L485M pipeline steel, which are beneficial to improving the cleanliness level of the pipeline steel, improving the flaw detection qualification rate of the steel plate and improving the delivery speed of ordered products.

The technical scheme of the invention is as follows:

in a first aspect, the invention provides a clean smelting process of L485M pipeline steel, which at least comprises the following steps:

carrying out RH refining on pipeline steel molten steel, carrying out rinsing on cold steel attached in an RH vacuum tank by using high-temperature molten steel in a furnace before pipeline steel production, controlling the entering temperature of the high-temperature molten steel in a rinsing heat to be more than or equal to 1610 ℃, maintaining the vacuum pressure for more than or equal to 16 minutes, and adopting a special production mode of a special tank after rinsing;

Feeding a pure calcium wire after RH breaking, performing accurate calcium treatment on the pipeline steel molten steel, controlling the Ca content of the pipeline steel molten steel to be 0.0015% -0.0025%, and soft blowing for 12-15 minutes after wire feeding.

Further, during RH refining, the incoming temperature of molten steel of pipeline steel is 1595-1615 ℃, RH vacuum degree is less than or equal to 200 Pa, dwell time is more than or equal to 12 minutes, pure degassing time is more than or equal to 7 minutes, outgoing temperature is 1560-1580 ℃, aluminum burning loss control in RH process is ensured to be less than or equal to 0.008%, and H content is controlled to be less than 0.0002%.

Further, the pipeline molten iron is subjected to RH refining after KR pretreatment, converter smelting and LF refining.

Further, the KR pretreatment procedure controls the sulfur content of molten iron entering the converter to be below 0.002%, the slag skimming bright surface is controlled according to more than 80%, and the temperature of the treated molten iron is 1380-1410 ℃.

Further, in the converter smelting process, the converter endpoint temperature is more than or equal to 1620 ℃, endpoint oxygen is less than or equal to 0.050%, endpoint sulfur content is less than or equal to 0.015%, als in steel after tapping deoxidation is more than or equal to 0.015%, slag charge in the tapping process is aligned to a steel flow impact area, the added ladle top slag is ensured to be fully melted, early slag formation is achieved, and slag samples are white slag or ash-white slag.

Further, in the LF refining process, the inlet temperature is more than or equal to 1540 ℃, the outlet temperature is 1610-1630 ℃, the heating time is less than or equal to 30 minutes, the LF slag system optimization target is to control the binary alkalinity to be in the range of 5.0-8.0, the CaO/Al ₂O₃ to be in the range of 1.7-1.9, the slag system is ensured to have better fluidity, the white slag holding time is more than or equal to 15 minutes, and the aim of rapidly absorbing and removing impurities in molten steel is fulfilled.

In a second aspect, the invention also provides a production process of the L485M pipeline steel, which comprises a KR pretreatment process, a converter smelting process, an LF refining process, an RH refining process, a casting process and a rolling process;

In the RH refining process, a furnace is used before pipeline steel production, cold steel adhered in an RH vacuum tank is rinsed by using high-temperature molten steel, the high-temperature molten steel entering temperature of rinsing heat is controlled to be more than or equal to 1610 ℃, the vacuum pressure maintaining time is controlled to be more than or equal to 16 minutes, and a special production mode for a special tank is adopted after rinsing;

Feeding pure calcium wires after RH breaking, carrying out accurate calcium treatment on molten steel, controlling the Ca content of the molten steel to be 0.0015% -0.0025%, and carrying out soft blowing for 12-15 minutes after wire feeding.

Further, the specific steps of the production process of the L485M pipeline steel are as follows:

(1) KR pretreatment, namely, adopting a KR molten iron deep desulfurization process, controlling the sulfur content of molten iron entering a converter to be 0.002% or less, and controlling the slag skimming bright surface according to 80% or more, wherein the temperature of the treated molten iron is 1380-1410 ℃;

(2) Converter smelting, wherein the finishing temperature of the converter is more than or equal to 1620 ℃, the finishing oxygen is less than or equal to 0.050%, the finishing sulfur content is less than or equal to 0.015%, als in steel is more than or equal to 0.015% after steel tapping and deoxidization, slag materials in the steel tapping process are aligned to a steel flow impact area, the added ladle top slag is ensured to be melted sufficiently, early slag formation is realized, and a slag sample is white slag or ash-white slag;

(3) LF refining, namely LF refining in-station temperature is more than or equal to 1540 ℃, out-station temperature is 1610-1630 ℃, heating time is less than or equal to 30 minutes, LF slag system optimization target is to control binary alkalinity in a range of 5.0-8.0, caO/Al ₂O₃ is controlled in a range of 1.7-1.9, good fluidity of slag system is ensured, white slag holding time is more than or equal to 15 minutes, and rapid adsorption removal of impurities in molten steel is achieved;

(4) RH refining, namely, a furnace before pipeline steel production, namely, using high-temperature molten steel to clean cold steel of a vacuum tank in advance, wherein the entering temperature of molten steel in the tank rinsing furnace time is more than or equal to 1610 ℃, the vacuum pressure maintaining time is more than or equal to 16 minutes, and a special production mode of a special tank is kept during the production period of the pipeline steel after tank rinsing;

The inlet temperature of the pipeline steel heat is 1595-1615 ℃, the RH vacuum degree is less than or equal to 200 Pa, the dwell time is more than or equal to 12 minutes, the pure degassing time is more than or equal to 7 minutes, the outlet temperature is 1560-1580 ℃, the aluminum burning loss control in the RH process is less than or equal to 0.008%, and the H content is controlled below 0.0002%;

feeding pure calcium wires after RH breaking, carrying out accurate calcium treatment on molten steel, controlling the Ca content of the molten steel to be 0.0015% -0.0025%, and carrying out soft blowing for 12-15 minutes after wire feeding;

(5) Casting into casting blank in continuous casting machine, wherein dynamic soft reduction technology is applied in casting process to improve internal quality of casting blank, ensure that low-power segregation C class is superior to 1.5 grade, cut the casting blank into fixed length, and slowly cool for at least 48 hours;

(6) And rolling, namely cold casting, namely rolling the steel plate with the thickness of 12 mm-30 mm after heating for 4-6 hours in a heating furnace, wherein the initial rolling temperature of rough rolling is 1100-1180 ℃, the thickness of a rolled intermediate billet is 3 times of the thickness of a finished product, the final rolling temperature of finish rolling is 790-830 ℃, the initial cooling temperature is not lower than 780 ℃, and the cooling speed is 8-18 ℃ per second.

Further, the rolled steel plate is subjected to flaw detection, and the flaw detection qualification rate is more than 99.5%.

The invention has the beneficial effects that:

According to the clean smelting process provided by the invention, the temperature of the high-temperature molten steel in the rinsing heat is controlled to be more than 1610 ℃, the rinsing time is properly prolonged, the circulation frequency of the high-temperature molten steel in the rinsing heat in the RH vacuum tank is increased, the reinforcement of the rinsing process is realized, the full removal of cold steel in the RH vacuum tank is ensured, and the technical problem of poor smelting cleanliness due to the existence of the cold steel is solved. Multiple production practices show that by using the same strict flaw detection standard, the flaw detection qualification rate of the pipeline steel heat produced after the RH rinsing of the groove is improved by more than 10% compared with that of the pipeline steel heat after the rinsing of the groove, the steel plate corresponding to the heat after the rinsing of the groove basically does not generate defect waves, and the steel plate corresponding to the production heat after the rinsing of the groove is easy to generate continuous defect waves.

The clean smelting process provided by the invention can further reduce the condition that the molten steel of the refined high-quality pipeline steel with high oxidizing property is added into the residual cold steel strip to affect the stabilized acid-soluble aluminum, avoid the aluminum in the molten steel from being oxidized again, reduce the content of regenerated Al ₂O₃ inclusion, provide more stable conditions for the subsequent calcium treatment, convert the residual Al ₂O₃ in the molten steel into 12 CaO.7Al ₂O₃ by the subsequent calcium treatment process, reduce the generation of CaS inclusion, improve the purity level of the molten steel, and provide process support for the production of the pipeline steel.

The invention also provides a process for producing the pipeline steel L485M by adopting the clean smelting process, which covers a complete flow from the pretreatment of molten iron KR to rolling, and the parameters of each step are accurately controlled. Besides the effect of clean smelting process, the production process improves the internal quality of the casting blank by using a dynamic soft reduction technology in the continuous casting process, and obtains good steel plate structure and performance by controlling parameters such as heating time, starting rolling temperature, finishing rolling temperature, starting cooling temperature, cooling speed and the like in the rolling process.

Detailed Description

In order to better understand the technical solutions of the present invention, the following description will clearly and completely describe the technical solutions of the embodiments of the present invention, and it is obvious that the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present invention without making any inventive effort, shall fall within the scope of the present invention.

The invention firstly provides a clean smelting process of L485M pipeline steel, which at least comprises the following steps:

As a preferred embodiment of the invention, when RH refining, the entering temperature of the molten steel of the pipeline steel is 1595-1615 ℃, the RH vacuum degree is less than or equal to 200 Pa, the dwell time is more than or equal to 12 minutes, the pure degassing time is more than or equal to 7 minutes, the exiting temperature is 1560-1580 ℃, the aluminum burning loss in the RH process is ensured to be controlled at a lower level (less than or equal to 0.008 percent) by controlling parameters such as the entering temperature, the exiting temperature, the RH vacuum degree, the dwell time, the pure degassing time and the like of the molten steel of the pipeline steel, and the H content is also controlled to be in an extremely low range (less than 0.0002 percent). The method is favorable for stabilizing the components of the molten steel, reducing the content of impurity gas, improving the quality of the molten steel and laying a foundation for the subsequent production of high-quality pipeline steel.

As a preferred embodiment of the invention, the invention adopts a mode of combining a plurality of refining procedures, molten iron is firstly subjected to KR pretreatment and deep desulfurization, then smelting is carried out in a converter, and then LF refining and RH refining are sequentially carried out, so that a complete smelting flow is formed. Pretreatment, converter smelting, LF refining and RH refining cooperate to produce high quality pipeline steel molten steel.

In a preferred embodiment of the present invention, the KR pretreatment step controls the sulfur content of molten iron charged into the converter to be 0.002% or less, the slag-off bright surface to be 80% or more, and the temperature of the molten iron after treatment to be 1380 ℃ to 1410 ℃. The low sulfur content is beneficial to reducing the formation of sulfide inclusions in the steel, improving the purity and the performance of the steel, and the proper slag skimming bright surface and molten iron temperature can provide good conditions for subsequent converter smelting.

As a preferable implementation mode of the invention, in the converter smelting process, the converter endpoint temperature is more than or equal to 1620 ℃, the endpoint oxygen is less than or equal to 0.050%, the endpoint sulfur content is less than or equal to 0.015%, als in steel after tapping deoxidation is more than or equal to 0.015%, slag in the tapping process is aligned to a steel flow impact zone, parameters such as the converter endpoint temperature, endpoint oxygen, endpoint sulfur content, als in steel after tapping deoxidation and the adding mode of slag in the tapping process are controlled, so that the molten steel components are ensured to meet the requirements, the slag can be fully melted to form white slag or ash and white slag during tapping, the adsorption of impurities in the molten steel is facilitated, and the purity of the molten steel is improved.

As a preferred embodiment of the invention, in the LF refining process, the inlet temperature is more than or equal to 1540 ℃, the outlet temperature is 1610 ℃ to 1630 ℃, the heating time is less than or equal to 30 minutes, the LF slag system optimization target is to control the binary alkalinity to be in the range of 5.0 to 8.0, the CaO/Al ₂O₃ to be in the range of 1.7 to 1.9, the white slag holding time is more than or equal to 15 minutes, and the slag system performance is optimized by controlling parameters such as the inlet temperature, the outlet temperature, the heating time, the binary alkalinity of the LF slag system, the CaO/Al ₂O₃ ratio, the white slag holding time and the like of the LF refining, so that the LF slag system has good fluidity, the impurities in molten steel can be quickly adsorbed and removed, and the cleanliness of the molten steel is further improved.

The invention also provides a process for producing the L485M pipeline steel by utilizing the clean smelting process, which comprises a KR pretreatment process, a converter smelting process, an LF refining process, an RH refining process, a casting process and a rolling process;

As a preferred embodiment of the invention, the specific steps of the L485M pipeline steel production process are as follows:

As a preferable implementation mode of the invention, the quality and the performance of the pipeline steel L485M steel plate prepared by adopting the production process of the invention are proved to meet the high standard requirements by carrying out flaw detection on the rolled steel plate, and the flaw detection qualification rate is more than 99.5%, so that the reliability and the safety of the pipeline steel in practical application can be met.

Example 1

An L485M pipeline steel plate with the thickness of 26 mm comprises the following chemical elements in percentage by weight:

C 0.078%、Si 0.23%,Mn 1.59%,P 0.01%,S 0.0009%,Alt 0.031%（Als 0.028%）,Ti 0.015%,Nb 0.056%,Cr 0.246%,Ca 0.0019%,Mo 0.12%, The balance being Fe and unavoidable impurities.

The L485M pipeline steel plate is prepared according to the following production process steps:

(1) KR pretreatment, namely adopting a KR molten iron deep desulfurization process, wherein the slag skimming bright surface is 87%, and the temperature of the treated molten iron is 1395 ℃ so that the sulfur content of molten iron entering a converter is 0.0010%;

(2) 210 ton converter smelting, wherein the converter endpoint temperature is 1635 ℃, endpoint oxygen is 0.043%, endpoint sulfur content is 0.012%, als in steel after tapping deoxidation is 0.018%, slag charge in the tapping process is aligned to a steel flow impact zone, added ladle top slag is fully melted, and slag sample is white slag;

(3) LF refining, namely LF refining at an inbound temperature of 1560 ℃ and an outbound temperature of 1625 ℃ for 26 minutes, wherein the LF slag system optimization target is to control the binary alkalinity at 6.0, caO/Al ₂O₃ at 1.85, the slag system has better fluidity, and the white slag retention time is 16 minutes, so that the aim of rapidly absorbing and removing impurities in molten steel is fulfilled;

(4) RH refining, namely, a furnace before pipeline steel production, namely, using high-temperature molten steel with the entering temperature of 1625 ℃ and controlling the vacuum pressure maintaining time to be 16 minutes, cleaning cold steel of a vacuum tank in advance, and keeping a special production mode of a special tank during the production period of the pipeline steel after the tank is cleaned;

The inlet temperature of the pipeline steel heat is 1610 ℃, the RH vacuum degree is 180 Pa, the dwell time is 16 minutes, the pure degassing time is 10 minutes, the outlet temperature is 1568 ℃, the burning loss of aluminum in the RH process is 0.006%, and the H content is controlled at 0.00015%;

Feeding a pure calcium wire 175 m after RH is broken, performing accurate calcium treatment on molten steel, detecting the Ca content in the molten steel to be 0.0019%, and performing soft blowing for 12 minutes after wire feeding;

(5) Casting into a casting blank with the thickness of 300 mm on a continuous casting machine, improving the internal quality of the casting blank by using a dynamic soft reduction technology in the casting process, ensuring that the low-power segregation C class is 1.0 grade, cutting the cast casting blank into a fixed length, and slowly cooling for 50 hours;

(6) And rolling, namely cold casting, namely heating the steel plate in a heating furnace for 4.8 hours, rolling the steel plate into a steel plate with the thickness of 26 mm on a 4300 production line, wherein the initial rolling temperature of rough rolling is 1170 ℃, the thickness of a rolled intermediate billet is more than 3 times of the thickness of a finished product, the finish rolling temperature of finish rolling is 810 ℃, the initial cooling temperature is not lower than 795 ℃, and the cooling speed is 15 ℃ per second.

And (3) detecting the flaw of the rolled steel plate in the step (6), wherein the flaw detection qualification rate is 99.8%.

Comparative example 1

C 0.071%、Si 0.25%,Mn 1.58%,P 0.01%,S 0.0010%,Alt 0.032%（Als 0.029%）,Ti 0.016%,Nb 0.055%,Cr 0.238%,Ca 0.0019%,Mo 0.11%, The balance being Fe and unavoidable impurities.

(4) RH refining, namely, the inlet temperature of a pipeline steel heat is 1610 ℃, the RH vacuum degree is 180 Pa, the dwell time is 16 minutes, the pure degassing time is 10 minutes, the outlet temperature is 1568 ℃, the burning loss of aluminum in the RH process is 0.006%, and the H content is controlled to be 0.00015%;

Comparative example 1 is different from example 1 in that there is no rinsing tank before RH refining, and cold steel adheres to the inside of the RH vacuum tank, and thus, the purity of smelting and the inclusion content of the final product are affected. And (3) detecting the flaw of the rolled steel plate in the step (6), wherein the flaw detection qualification rate is 86.2%.

Comparative example 2

C 0.060%、Si 0.23%,Mn 1.55%,P 0.01%,S 0.0010%,Alt 0.032%（Als 0.028%）,Ti 0.015%,Nb 0.057%,Cr 0.257%,Ca 0.0019%,Mo 0.11%, The balance being Fe and unavoidable impurities.

(4) RH refining, namely, one furnace before pipeline steel production, namely, controlling the vacuum pressure maintaining time to be 12 minutes by using molten steel with the entering temperature of 1608 ℃, rinsing the cold steel of a vacuum tank clean in advance, and keeping a special production mode of a special tank during the production period of the pipeline steel after rinsing the tank;

Comparative example 2 differs from example 1 in that the molten steel used in the rinsing bath stage is low in temperature and the vacuum dwell time is different, and the condition has a limited effect of removing cold steel adhering to the inside of the RH vacuum bath, and thus affects the cleanliness of smelting and the inclusion content of the final product. And (3) detecting the flaw of the rolled steel plate in the step (6), wherein the flaw detection qualification rate is 89.6%.

Example 2

An L485M pipeline steel plate with the thickness of 15 mm comprises the following chemical elements in percentage by weight:

C 0.055%、Si 0.24%,Mn 1.56%,P 0.01%,S 0.0012%,Alt 0.034%（Als 0.032%）,Ti 0.016%,Nb 0.055%,Cr 0.255%,Ca 0.0015%,Mo 0.10%, The balance being Fe and unavoidable impurities.

(1) KR pretreatment, namely adopting a KR molten iron deep desulfurization process, wherein the slag skimming bright surface is 85%, and the temperature of the treated molten iron is 1390 ℃ so that the sulfur content of molten iron entering a converter is 0.0009%;

(2) 210 ton converter smelting, wherein the converter endpoint temperature is 1627 ℃, the endpoint oxygen is 0.040%, the endpoint sulfur content is 0.014%, als in steel after tapping deoxidation is 0.022%, slag charge in the tapping process is aligned to a steel flow impact zone, added ladle top slag is fully melted, and slag sample is white slag;

(3) LF refining, namely LF refining at an inbound temperature of 1563 ℃ and an outbound temperature of 1625 ℃ for 25 minutes, wherein the LF slag system optimization target is to control the binary alkalinity at 6.6, caO/Al ₂O₃ at 1.8, the slag system has better fluidity, and the white slag retention time is 19 minutes, so that the impurities in molten steel can be quickly adsorbed and removed;

(4) RH refining, namely, a furnace before pipeline steel production, namely, using high-temperature molten steel with the entering temperature of 1622 ℃ and controlling the vacuum pressure maintaining time to be 18 minutes, cleaning cold steel of a vacuum tank in advance, and keeping a special production mode of a special tank during the production period of the pipeline steel after the tank is cleaned;

The inlet temperature of the pipeline steel heat is 1605 ℃, the RH vacuum degree is 175 Pa, the dwell time is 15 minutes, the pure degassing time is 9 minutes, the outlet temperature is 1572 ℃, the burning loss of aluminum in the RH process is 0.005%, and the H content is controlled to be 0.00010%;

Feeding a pure calcium wire 168 m after RH is broken, performing accurate calcium treatment on molten steel, detecting the Ca content in the molten steel to be 0.0015%, and performing soft blowing for 13 minutes after wire feeding;

(5) Casting into a casting blank with the thickness of 300 mm on a continuous casting machine, improving the internal quality of the casting blank by using a dynamic soft reduction technology in the casting process, ensuring that the low-power segregation C class is 1.0 grade, cutting the cast casting blank into a fixed length, and slowly cooling for 48 hours;

(6) And rolling, namely cold casting, namely heating the steel plate in a heating furnace for 4.6 hours, rolling the steel plate into a steel plate with the thickness of 15 mm ℃ in a 4300 production line, wherein the initial rolling temperature of rough rolling is 1165 ℃, the thickness of a rolled intermediate billet is 3 times of the thickness of a finished product, the finish rolling temperature of finish rolling is 825 ℃, the initial cooling temperature is not lower than 810 ℃, and the cooling speed is 15 ℃ per second.

Example 3

An L485M pipeline steel plate with the thickness of 30 mm comprises the following chemical elements in percentage by weight:

C 0.056%、Si 0.23%,Mn 1.56%,P 0.01%,S 0.0008%,Alt 0.034%（Als 0.032%）,Ti 0.014%,Nb 0.056%,Cr 0.258%,Ca 0.0015%,Mo 0.13%, The balance being Fe and unavoidable impurities.

(1) KR pretreatment, namely adopting a KR molten iron deep desulfurization process, wherein the slag skimming bright surface is 80%, and the temperature of the treated molten iron is 1380 ℃ so that the sulfur content of molten iron entering a converter is 0.002%;

(2) Smelting in a 210 ton converter, wherein the finishing temperature of the converter is 1620 ℃, the finishing oxygen is 0.050%, the finishing sulfur content is 0.015%, als in steel after tapping deoxidation is 0.016%, slag materials in the tapping process are aligned to a steel flow impact zone, added ladle top slag is fully melted, and slag samples are white slag;

(3) LF refining, namely LF refining at an inbound temperature of 1540 ℃ and an outbound temperature of 1610 ℃ for 30 minutes, wherein the LF slag system optimization target is to control the binary alkalinity at 8.0, caO/Al ₂O₃ at 1.7, the slag system has better fluidity, and the white slag retention time is 15 minutes, so that the impurities in molten steel are removed by rapid adsorption;

(4) RH refining, namely, a furnace before pipeline steel production, namely, using high-temperature molten steel with the entering temperature of 1610 ℃ to control the vacuum pressure maintaining time to be 19 minutes, cleaning cold steel of a vacuum tank in advance, and keeping a special production mode of a special tank during the production period of the pipeline steel after tank cleaning;

The inlet temperature of the pipeline steel heat is 1595 ℃, the RH vacuum degree is 200 Pa, the dwell time is 12 minutes, the pure degassing time is 7 minutes, the outlet temperature is 1560 ℃, the burning loss of aluminum in the RH process is 0.008%, and the H content is controlled to be 0.0002%;

feeding pure calcium wires after RH breaking, carrying out accurate calcium treatment on molten steel, detecting the Ca content in the molten steel to be 0.0015%, and carrying out soft blowing for 15 minutes after wire feeding;

(6) And rolling, namely cold casting, namely heating the steel plate in a heating furnace for 4 hours, and rolling the steel plate into a steel plate with the thickness of 30 mm ℃ in a 4300 production line, wherein the initial rolling temperature of rough rolling is 1180 ℃, the thickness of a rolled intermediate billet is more than 3 times of the thickness of a finished product, the finish rolling temperature is 830 ℃, the initial cooling temperature is not lower than 780 ℃, and the cooling speed is 8 ℃ per second.

And (3) detecting the flaw of the rolled steel plate in the step (6), wherein the flaw detection qualification rate is 99.6%.

Example 4

An L485M pipeline steel plate with the thickness of 20 mm comprises the following chemical elements in percentage by weight:

C 0.063%、Si 0.25%,Mn 1.58%,P 0.01%,S 0.0010%,Alt 0.033%（Als 0.031%）,Ti 0.012%,Nb 0.052%,Cr 0.249%,Ca 0.0025%,Mo 0.12%, The balance being Fe and unavoidable impurities.

(1) KR pretreatment, namely adopting a KR molten iron deep desulfurization process, wherein the slag skimming bright surface is 85%, and the temperature of the treated molten iron is 1410 ℃ so that the sulfur content of molten iron entering a converter is 0.001%;

(2) 210 ton converter smelting, wherein the end point temperature of the converter is 1650 ℃, the end point oxygen is 0.032%, the end point sulfur content is 0.010%, als in steel after tapping deoxidation is 0.018%, slag charge in the tapping process is aligned to a steel flow impact zone, added ladle top slag is fully melted, and slag sample is white slag;

(3) LF refining, namely LF refining at an inbound temperature of 1555 ℃, an outbound temperature of 1630 ℃ and a heating time of 30 minutes, wherein an LF slag system optimization target is to control the binary alkalinity at 5.0, caO/Al ₂O₃ at 1.75, the slag system has better fluidity, and the white slag retention time is 20 minutes, so that impurities in molten steel can be quickly adsorbed and removed;

(4) RH refining, namely, a furnace before pipeline steel production, namely, using high-temperature molten steel with the entering temperature of 1630 ℃ and controlling the vacuum pressure maintaining time to be 18 minutes, cleaning cold steel of a vacuum tank in advance, and keeping a special production mode of a special tank during the production period of the pipeline steel after the tank is cleaned;

The inlet temperature of the pipeline steel heat is 1615 ℃, the RH vacuum degree is 180 Pa, the dwell time is 15 minutes, the pure degassing time is 9 minutes, the outlet temperature is 1580 ℃, the burning loss of aluminum in the RH process is 0.006%, and the H content is controlled to be 0.00010%;

feeding pure calcium wires after RH breaking, carrying out accurate calcium treatment on molten steel, detecting the Ca content in the molten steel to be 0.0025%, and carrying out soft blowing for 12 minutes after wire feeding;

(5) Casting into a casting blank with the thickness of 300 mm on a continuous casting machine, improving the internal quality of the casting blank by using a dynamic soft reduction technology in the casting process, ensuring that the low-power segregation C class is 1.0 grade, cutting the cast casting blank into a fixed length, and slowly cooling for 60 hours;

(6) And rolling, namely cold casting, namely heating the steel plate in a heating furnace for 6 hours, rolling the steel plate into a steel plate with the thickness of 20 mm on a 4300 production line, wherein the initial rolling temperature of rough rolling is 1100 ℃, the thickness of a rolled intermediate billet is more than 3 times of the thickness of a finished product, the finish rolling finishing temperature is 790 ℃, the initial cooling temperature is not lower than 785 ℃, and the cooling speed is 18 ℃ per second.

And (3) detecting the flaw of the rolled steel plate in the step (6), wherein the flaw detection qualification rate is 99.7%.

Although the present invention has been described in detail by way of preferred embodiments, the present invention is not limited thereto. Various equivalent modifications and substitutions may be made in the embodiments of the present invention by those skilled in the art without departing from the spirit and scope of the present invention, and it is intended that all such modifications and substitutions be within the scope of the present invention/be within the scope of the present invention as defined by the appended claims.

Claims

1. The clean smelting process of the L485M pipeline steel is characterized by at least comprising the following steps:

2. The clean smelting process of L485M pipeline steel according to claim 1, wherein the entering temperature of the pipeline steel molten steel is 1595 ℃ to 1615 ℃, the RH vacuum degree is less than or equal to 200 Pa, the dwell time is more than or equal to 12 minutes, the pure degassing time is more than or equal to 7 minutes, the exiting temperature is 1560 ℃ to 1580 ℃, the burning loss of the RH process is less than or equal to 0.008%, and the H content is less than 0.0002%.

3. The clean smelting process of L485M pipeline steel, as set forth in claim 1, characterized in that the pipeline molten iron is subjected to RH refining after KR pretreatment, converter smelting and LF refining.

4. The clean smelting process of L485M pipeline steel according to claim 1, wherein the KR pretreatment procedure controls the sulfur content of molten iron entering a converter to be below 0.002%, slag skimming bright surface is controlled according to more than 80%, and the temperature of the molten iron after treatment is 1380-1410 ℃.

5. The clean smelting process of the L485M pipeline steel, as set forth in claim 1, characterized in that in the converter smelting process, the converter endpoint temperature is not less than 1620 ℃, the endpoint oxygen is not more than 0.050%, the endpoint sulfur content is not more than 0.015%, als in the steel after tapping deoxidation is not less than 0.015%, the slag in the tapping process is aligned to the steel flow impact zone, the top slag of the ladle is fully melted, and the slag sample is white slag or ash-white slag.

6. The clean smelting process of L485M pipeline steel according to claim 1, wherein in the LF refining process, the inlet temperature is more than or equal to 1540 ℃, the outlet temperature is 1610 ℃ to 1630 ℃, the heating time is less than or equal to 30 minutes, the LF slag system optimization target is to control the binary alkalinity to be in the range of 5.0 to 8.0, the CaO/Al ₂O₃ to be in the range of 1.7 to 1.9, and the white slag holding time is more than or equal to 15 minutes.

7. The production process of the L485M pipeline steel is characterized by comprising a KR pretreatment process, a converter smelting process, an LF refining process, an RH refining process, a casting process and a rolling process;

8. The production process of the L485M line steel according to claim 7, characterized in that the production process of the L485M line steel comprises the following specific steps:

(2) Converter smelting, wherein the finishing temperature of the converter is more than or equal to 1620 ℃, the finishing oxygen is less than or equal to 0.050%, the finishing sulfur content is less than or equal to 0.015%, als in steel is more than or equal to 0.015% after steel tapping and deoxidization, slag materials in the steel tapping process are aligned to a steel flow impact area, added ladle top slag is fully melted, and slag samples are white slag or ash-white slag;

(3) LF refining, wherein the incoming temperature of LF refining is more than or equal to 1540 ℃, the outgoing temperature is 1610-1630 ℃, the heating time is less than or equal to 30 minutes, the LF slag system optimization target is to control the binary alkalinity to be in the range of 5.0-8.0, caO/Al ₂O₃ to be in the range of 1.7-1.9, and the white slag holding time is more than or equal to 15 minutes;

The inlet temperature of the pipeline steel heat is 1595-1615 ℃, the RH vacuum degree is less than or equal to 200 Pa, the dwell time is more than or equal to 12 minutes, the pure degassing time is more than or equal to 7 minutes, the outlet temperature is 1560-1580 ℃, the aluminum burning loss in the RH process is less than or equal to 0.008%, and the H content is less than 0.0002%;

(5) Casting into casting blank in continuous casting machine, wherein dynamic soft reduction technology is applied in casting process to improve internal quality of casting blank, low-power segregation C class is superior to 1.5 grade, the casting blank is cut into fixed length, and slow cooling is carried out for at least 48 hours;

(6) Rolling, namely rolling a casting blank into a steel plate with the thickness of 12 mm-30 mm after heating for 4-6 hours in a heating furnace, wherein the initial rolling temperature of rough rolling is 1100-1180 ℃, the thickness of a rolled intermediate blank is 3 times of the thickness of a finished product, the finish rolling temperature of finish rolling is 790-830 ℃, the cooling temperature is not lower than 780 ℃, and the cooling speed is 8-18 ℃ per second.

9. The production process of the L485M pipeline steel, as set forth in claim 8, characterized in that the flaw detection is carried out on the rolled steel plate, and the flaw detection qualification rate is more than 99.5%.