A smelting method for producing ferritic stainless steel for vehicles using conventional plate production facilities

Abstract

A smelting method for producing ferritic stainless steel for vehicles using conventional plate production facilities, the process steps include smelting molten iron in BF blast furnace → desulfurization by KR → re-blowing in BOF converter → refining in LF ladle → cyclic degassing by RH → continuous casting by CC; by tapping the steel at high temperature in converter and heating up LF furnace to melt chromium-containing alloy, deep desulfurization of molten iron by KR and slag desulfurization by LF, low-sulfur control of molten steel composition is achieved; decarbonization and chromium preservation of molten steel are achieved by selecting low-carbon micro-carbon chromium iron for deoxidation and alloying and blowing oxygen under RH extreme vacuum conditions. That is, ferritic stainless steel is produced by optimizing the functional allocation of conventional plate steelmaking production facilities and selecting suitable chromium alloying materials.

Description

Technical Field

[0001] The invention relates to the technical field of stainless steel, and in particular to a smelting method for producing ferritic stainless steel for vehicles using conventional plate production facilities. Background Art

[0002] In recent years, the development and application of ferritic stainless steel for vehicles has received widespread attention at home and abroad. It can reduce the vehicle's own weight, increase the vehicle's load capacity, and extend the service life of the vehicle's steel structure. It has low cost during the vehicle's life cycle and is green and environmentally friendly with no pollution to the environment.

[0003] In 2008, the Ministry of Railways issued the "Technical Requirements (Provisional) for T4003 Stainless Steel Plates (Strips) for Railway Freight Car Bodies" (Transportation Freight Car

[2008] No. 186, Technical Requirements for Chemical Composition of T4003 See Table 1

[0004] Table 1 Chemical composition of T4003:

[0005]

[0006] Domestic and foreign stainless steel production mainly has two-step and three-step process flows, and the common feature is that they are all produced using AOD furnaces. According to the characteristics of T4003 composition design, the alloy addition amount is large and the carbon content, nitrogen content and sulfur content requirements are low, which is very difficult to produce in conventional plate production facilities. Summary of the invention

[0007] In view of the above-mentioned defects of the prior art, the technical problem to be solved by the present invention is how to develop a smelting method for producing ferritic stainless steel for vehicles using conventional plate production facilities, so as to utilize the optimized allocation of functions of conventional plate steelmaking production facilities and the selection of suitable chromium alloying materials to realize the production of ferritic stainless steel for vehicles.

[0008] To achieve the above object, the present invention provides a smelting method for producing ferritic stainless steel for vehicles using conventional plate production facilities, comprising the following steps:

[0009] S1, KR furnace desulfurization

[0010] The blast furnace molten iron is deeply desulfurized by mechanical stirring in a KR furnace. The mass percentage of S in the molten iron after KR desulfurization is ≤0.0010%;

[0011] S2, BOF furnace combined blowing

[0012] The desulfurized molten iron is added to the BOF converter for double blowing to produce high-temperature low-carbon steel. The mass percentage of C in the crude steel liquid after the converter is controlled to be ≤0.04%, and the temperature of the crude steel liquid after the steel is produced is 1660 ~ 1680℃;

[0013] S3, LF furnace ladle refining

[0014] The crude steel liquid from the converter is transported to the LF refining furnace, a low carbon ferrochrome alloy is added, the temperature is raised to melt the low carbon ferrochrome alloy, and LF slag making and desulfurization are performed to form alloy steel liquid, wherein the mass percentage of the low carbon ferrochrome alloy component is:

[0015] C: 0.058%, Cr: 62.12%, Si: 0.86%, the rest is Fe and unavoidable substances;

[0016] S4, RH furnace degassing

[0017] The molten steel from the LF furnace is transported to the RH furnace for refining. Under the vacuum conditions of a vacuum chamber pressure of ≤133Pa and a circulating flow rate of 150-180 Nm³ / h, oxygen is blown to remove carbon and retain chromium. The carbon content is adjusted to reach the target carbon content, and other components are fine-tuned to meet the standard requirements of ferritic stainless steel for vehicles. Silicon, aluminum, niobium and titanium are alloyed. The weight percentage of the components of the molten steel formed is controlled at:

[0018] C≤0.03%, Si:0.2~0.5%, Mn:1.3~1.8%, P≤0.035%, S≤0.003%, Ti:0.12~0.18%, N:0.008~0.02%, Cr:11.0~12.5%, Nb:0.04~0.08%;

[0019] S5, continuous casting

[0020] The molten steel is poured into the tundish for continuous casting to produce ferritic stainless steel for vehicles.

[0021] In one embodiment, in the step S3 of LF furnace ladle refining, the tapping temperature of the alloy steel liquid is controlled to be 1580 ~ 1620 °C.

[0022] In one embodiment, in the RH furnace degassing step S4, the outlet molten steel temperature is controlled at 1550-1560°C.

[0023] In one of the embodiments, in the continuous casting step S5, the casting speed is controlled to be ≥ 0.8 m / min.

[0024] In one embodiment, in the continuous casting step S5, stainless steel protection slag is added during the cutting of the ingot, and the physical and chemical indicators of the stainless steel protection slag include:

[0025] Melting point: 1060~1090℃, basicity: 0.7 0.9, viscosity: 0.3 0.5Pas, bulk density: 0.60 0.66g / cm³.

[0026] The present invention discloses a smelting method for producing ferritic stainless steel for vehicles using conventional plate production facilities. The method includes: high-temperature steel tapping in a converter and heating up an LF furnace to melt a chromium-containing alloy, deep desulfurization of molten iron by KR and slag desulfurization by LF, so as to achieve low-sulfur control of molten steel composition; and decarbonization and chromium preservation of molten steel are achieved by selecting low-carbon micro-carbon chromium iron for deoxidation and alloying and blowing oxygen under RH extreme vacuum conditions. That is, the method utilizes the optimized allocation of functions of conventional plate steelmaking production facilities and the selection of appropriate chromium alloying materials to produce ferritic stainless steel, opening a precedent for smelting stainless steel using conventional plate steelmaking facilities, and the chromium recovery rate is high in RH decarbonization and chromium preservation, with a chromium recovery rate of more than 97%. DETAILED DESCRIPTION

[0027] The embodiments of the present invention are described in detail below. In these descriptions, some specific implementations in the embodiments of the present invention are specifically disclosed to represent some ways of implementing the principles of the embodiments of the present invention, but it should be understood that the scope of the embodiments of the present invention is not limited thereto. On the contrary, the embodiments of the present invention include all changes, modifications and equivalents that fall within the spirit and connotation of the appended claims.

[0028] A smelting method for producing ferritic stainless steel for vehicles in a conventional plate production facility adopts a process path design of: BF blast furnace smelting molten iron → KR desulfurization → BOF converter re-blowing → LF ladle refining → RH cycle degassing → CC continuous casting. The specific process steps include:

[0029] S1, KR furnace desulfurization

[0030] The blast furnace molten iron is deeply desulfurized by mechanical stirring in a KR furnace. The mass percentage of S in the molten iron after KR desulfurization is ≤0.0010%.

[0031] S2, BOF furnace combined blowing

[0032] The desulfurized molten iron is added to the BOF converter for double blowing to produce high-temperature low-carbon steel. The mass percentage of C in the crude steel liquid after converter steelmaking is controlled to be ≤0.04%, and the temperature of the crude steel liquid after steelmaking is 1660 ~1680℃.

[0033] S3, LF furnace ladle refining

[0034] The crude steel liquid from the converter is transported to the LF refining furnace, a low carbon ferrochrome alloy is added, the temperature is raised to melt the low carbon ferrochrome alloy, and LF slag making and desulfurization are performed to form alloy steel liquid, wherein the mass percentage of the low carbon ferrochrome alloy component is:

[0035] C: 0.058%, Cr: 62.12%, Si: 0.86%, the rest is Fe and unavoidable substances;

[0036] S4, RH furnace degassing

[0037] The molten steel from the LF furnace is transported to the RH furnace for refining. Under the vacuum conditions of ≤133Pa in the vacuum chamber and 150~180 Nm³ / h of vacuum flow, oxygen is blown to remove carbon and retain chromium. The carbon content is adjusted to the target carbon content, and other components are fine-tuned to meet the standard requirements of ferritic stainless steel for vehicles. Silicon, aluminum, niobium and titanium are alloyed. The weight percentage of the components of the molten steel formed is controlled at:

[0038] C≤0.03%, Si:0.2~0.5%, Mn:1.3~1.8%, P≤0.035%, S≤0.003%, Ti:0.12~018%, N:0.008~0.02%, Cr:11.0~12.5%, Nb:0.04~0.08%.

[0039] S5, continuous casting

[0040] The molten steel is poured into the tundish for continuous casting to produce ferritic stainless steel for vehicles.

[0041] The present invention discloses a smelting method for producing ferritic stainless steel for vehicles using conventional plate production facilities, which realizes low-sulfur control of molten steel composition by high-temperature steel tapping from a converter and heating and melting a chromium-containing alloy in an LF furnace, deep desulfurization of molten iron by KR and slag desulfurization by LF; and decarbonization and chromium preservation of molten steel are realized by selecting low-carbon micro-carbon chromium iron for deoxidation and alloying and blowing oxygen under RH extreme vacuum conditions.

[0042] The present invention utilizes the function optimization allocation of conventional plate steelmaking production facilities to select suitable chromium alloying materials to produce ferritic stainless steel without professional stainless steel production facilities such as AOD and VOD, thus opening a precedent for smelting stainless steel with conventional plate steelmaking facilities. The chromium recovery rate is high during RH decarburization and chromium preservation, and the chromium recovery rate is greater than 97%.

[0043] In one embodiment, in the step S3 of LF furnace ladle refining, the tapping temperature of the alloy steel liquid is controlled to be 1580 ~ 1620 °C.

[0044] In one embodiment, in the RH furnace degassing step S4, the outlet molten steel temperature is controlled at 1550-1560°C.

[0045] In one of the embodiments, in the continuous casting step S5, the casting speed is controlled to be ≥ 0.8 m / min.

[0046] In one embodiment, in the continuous casting step S5, stainless steel protection slag is added during the cutting of the ingot, and the physical and chemical indicators of the stainless steel protection slag include:

[0047] Melting point: 1060 ~1090℃, basicity: 0.7 ~0.9, viscosity: 0.3 ~0.5Pas, bulk density: 0.60 0.66g / cm³.

[0048] In order to verify the effectiveness of the method described in this application, a test experiment was carried out using a specific embodiment. Example

[0049] Steelmaking: KR1 deep desulfurization, hot metal after desulfurization [S]: 0.0001%. Steelmaking furnace 2 is a 210-ton converter with top and bottom combined blowing, with a steel output of 172 tons, a steel carbon weight percentage of 0.026%, and a steel tapping temperature of 1660°C. The molten steel from the steelmaking furnace is refined in the ladle refining furnace LF furnace 3, heated to melt the ferrochrome alloy and slag desulfurization, and the LF furnace outlet temperature is 1608°C. The molten steel from the LF furnace is refined in the ladle refining furnace 4RH. Under the extreme vacuum degree (pressure in the vacuum chamber: 73Pa; circulation flow rate: 1650 Nm³ / h), oxygen is blown to remove carbon and retain chromium, and other elements are deoxidized and alloyed. After the refining, the weight percentage of the molten steel components is controlled to be [C]0.01, [Si]0.32, [Mn]1.60, [P]0.015, [S]0.003, [Ti]0.15, [N]0.01, [Cr]11.50, [Nb]0.07, and the outlet molten steel temperature is 1557℃.

[0050] Continuous casting: Molten steel is injected into the tundish 6 through the sliding water inlet at the bottom of the ladle 5. The capacity of the tundish is 60 tons, and the temperature of the molten steel in the tundish is 1540℃. When the weight of the molten steel reaches 25 tons, the stopper rod is opened, and the molten steel is injected into the crystallizer 7 from the tundish. The vibration of the crystallizer is electric cylinder vibration, the billet pulling speed is 0.9m / min, the billet thickness out of the crystallizer is 230mm, and the billet cutting is "natural gas + oxygen + iron powder" mode. Use special protective slag for ferrite, and the physical and chemical indicators of the protective slag are: melting point 1072℃, basicity 0.75, viscosity 3

[0051] 0.415 Pas, volume density 0.64g / cm. The composition of the continuous casting tundish is [C]0.01, [Si]0.32, [Mn]1.60, [P]0.015, [S]0.003, [Ti]0.14, [N]0.01, [Cr]11.50, [Nb]0.07; Example

[0052] Steelmaking: KR1 deep desulfurization, hot metal after desulfurization [S]: 0.0001%. Steelmaking furnace 2 is a 210-ton converter with top and bottom double blowing, with a steel output of 174 tons, a steel carbon weight percentage of 0.031%, and a steel tapping temperature of 1675°C. The molten steel from the steelmaking furnace is refined in the ladle refining furnace LF furnace 3, heated to melt the ferrochrome alloy and slag desulfurization, and the LF furnace outlet temperature is 1585°C. The molten steel from the LF furnace is refined in the ladle refining furnace 4RH. Under the extreme vacuum degree (pressure in the vacuum chamber: 70Pa; circulation flow rate: 1780 Nm3 / h), oxygen is blown to remove carbon and retain chromium, and other elements are deoxidized and alloyed. After the refining, the weight percentage content of the molten steel components is controlled to be [C]0.01, [Si]0.35, [Mn]1.68, [P]0.014, [S]0.001, [Ti]0.17, [N]0.01, [Cr]12.38, [Nb]0.06, and the outlet molten steel temperature is 1552℃.

[0053] Continuous casting: Molten steel is injected into the tundish 6 through the sliding water inlet at the bottom of the ladle 5. The capacity of the tundish is 60 tons, and the temperature of the molten steel in the tundish is 1537℃. When the weight of the molten steel reaches 25 tons, the stopper rod is opened, and the molten steel is injected into the crystallizer 7 from the tundish. The vibration of the crystallizer is electric cylinder vibration, the billet pulling speed is 1.25m / min, the billet thickness out of the crystallizer is 230mm, and the billet cutting is in the "natural gas + oxygen + iron powder" mode. Ferrite special protective slag is used, and the physical and chemical indicators of the protective slag are: melting point 1072℃, basicity 0.75, viscosity 0.415 Pas, and bulk density 0.64 g / cm³. The composition of the continuous casting tundish is [C]0.01, [Si]0.35, [Mn]1.68, [P]0.014, [S]0.001, [Ti]0.16, [N]0.01, [Cr]12.38, [Nb]0.06;

[0054] Ingot structure: The macrostructure of ingots in Example 1 and Example 2 is both Class C.

[0055] The performance and composition test results of the above embodiments are shown in the following table:

[0056]

[0057] It can be seen from the above test results that the smelting method of producing ferritic stainless steel for vehicles using conventional plate production facilities applied for by the present invention utilizes the optimized allocation of functions of conventional plate steelmaking production facilities and the selection of suitable chromium alloying materials to produce ferritic stainless steel, and the performance and composition of the ferritic stainless steel meet the standard requirements.

[0058] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that for a person of ordinary skill in the art, several modifications and improvements made without departing from the concept of the present invention all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A smelting method for producing ferritic stainless steel for vehicles using conventional plate production facilities, characterized in that: The following steps are involved: S1, KR furnace desulfurization The blast furnace molten iron is deeply desulfurized by mechanical stirring in the KR furnace. The mass percentage of S in the molten iron after KR desulfurization is ≤0.0010%; S2, BOF furnace combined blowing The desulfurized molten iron is added to the BOF converter for double blowing to produce high-temperature low-carbon steel. The mass percentage of C in the crude steel liquid after the converter is controlled to be ≤0.04%, and the temperature of the crude steel liquid after the steel is produced is 1660~1680℃; S3, LF furnace ladle refining The crude steel liquid from the converter is transported to the LF refining furnace, a low carbon ferrochrome alloy is added, the temperature is raised to melt the low carbon ferrochrome alloy, and LF slag making and desulfurization are performed to form alloy steel liquid, wherein the mass percentage of the low carbon ferrochrome alloy components is: C: 0.058%, Cr: 62.12%, Si: 0.86%, and the rest is Fe and unavoidable substances; S4, RH furnace degassing The molten steel from the LF furnace is transported to the RH furnace for refining. Under the vacuum conditions of the vacuum chamber pressure ≤133Pa and the circulating flow rate of 150-180Nm³ / h, oxygen is blown to remove carbon and retain chromium, the carbon content is adjusted to reach the target carbon content, and other components are fine-tuned to meet the standard requirements of ferritic stainless steel for vehicles, and silicon, aluminum, niobium and titanium are alloyed. The weight percentage of the components of the formed molten steel is controlled at: C≤0.03%, Si:0.2~ 0.5%, Mn:1.3 ~1.8%, P≤0.035%, S≤0.003%, Ti:0.12 ~0.18%, N:0.008~ 0.02%, Cr:11.0~12.5%, Nb:0.04~ 0.08%; S5, continuous casting The molten steel is poured into the tundish for continuous casting to produce ferritic stainless steel for vehicles; In the step S3 of LF furnace ladle refining, the tapping temperature of the alloy steel liquid is controlled to be 1580-1620° C.; In the RH furnace degassing step S4, the outlet molten steel temperature is controlled at 1550-1560°C; In the continuous casting step S5, the casting speed is controlled to be ≥ 0.8 m / min; In the continuous casting step S5, stainless steel protection slag is added when the ingot is cut, and the physical and chemical indicators of the stainless steel protection slag include: melting point: 1060-1090°C, basicity: 0.7-0.9, viscosity: 0.3-0.5 Pas, and bulk density: 0.60-0.66 g / cm³.

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