A continuous casting method for ultra-thick martensitic stainless steel

Abstract

The present invention provides a method for continuous casting of ultra-thick martensitic stainless steel; including: (1) determining the time of refining soft blowing and argon blowing; (2) controlling the composition of molten steel; (3) controlling the trace elements and inclusions of the finished product; (4) controlling the superheat of casting; (5) blowing argon gas throughout the casting process to ensure that the argon blowing of the long nozzle, the tundish and the submerged nozzle is normal; (6) confirmation of key parameters during continuous casting: (7) adopting the end electromagnetic stirring technology; (8) using the dynamic light pressure reduction technology in the secondary cooling zone to control the pressure reduction to 1.5mm / m. The total pressure reduction is controlled at 5-8mm; (9) implementing the heavy pressure reduction technology at the end of the secondary cooling, and the pressure reduction is controlled at 3-5mm / m. The method for continuous casting of ultra-thick martensitic stainless steel involved in the present invention not only meets the production of thicker martensitic stainless steel, but also solves the technical problems of defects such as central porosity and central segregation inside.

Description

Technical Field

[0001] The invention relates to the field of martensitic stainless steel, and in particular to a continuous casting method of ultra-thick martensitic stainless steel. Background Art

[0002] The maximum thickness of martensitic stainless steel currently available in the domestic market does not exceed 300mm, and most of them are below 240mm. Under normal circumstances, to meet the requirements of rolled material flaw detection, the rolling ratio must be above 300mm to obtain rolled materials with good internal quality. Therefore, the continuous casting billets of stainless steel currently on the market can only be rolled below 80mm.

[0003] In order to obtain thicker rolled products, such as rolled products with a thickness of more than 100 mm, the quality requirements for the rolled products become higher, such as: defects such as central looseness and central segregation appear inside. In order to provide thicker rolled products while not having the above technical defects inside, a production method that satisfies both internal and external requirements is required. Therefore, in the current market, a method that can produce martensitic stainless steel products with a thickness of more than 300 mm is an urgent need of the market. Summary of the invention

[0004] The purpose of the invention is to provide a continuous casting method for ultra-thick martensitic stainless steel.

[0005] The present invention is achieved through the following technical solutions:

[0006] The present invention relates to a continuous casting method of ultra-thick martensitic stainless steel, comprising the following steps:

[0007] (1) Determine the time for refining soft blowing and argon blowing: the time for refining soft blowing is more than 20 minutes, the time for argon blowing is more than 60 minutes, and the total calming time is more than 20 minutes; only when the quality of molten steel refining is up to standard can continuous casting produce qualified ingots;

[0008] (2) Control the composition of molten steel: Use 4Cr13, the contents of which are shown in Table 1:

[0009] Table 1

[0010]

[0011] The composition of molten steel determines the performance of the later products. Only by strictly controlling the composition of molten steel can it be possible to produce qualified ingots. The performance of the later products can be guaranteed. In particular, the S content in molten steel must be strictly controlled to prevent MnS segregation;

[0012] (3) Control trace elements and inclusions; their contents are shown in Table 2:

[0013] Table 2

[0014]

[0015] The purity of molten steel directly affects the internal quality of the ingot;

[0016] (4) Control the superheat of casting: the liquidus temperature is 1470℃, the steel temperature on the turntable is 1570℃, and the superheat of the tundish is controlled at 20℃-30℃; the tundish temperature is 1490℃;

[0017] If conditions permit, the superheat of the tundish can be lowered and controlled at around 20°. The superheat of the molten steel in the tundish must be strictly controlled, otherwise the produced ingots will be particularly prone to central porosity and shrinkage holes.

[0018] (5) Argon is blown throughout the casting process, specifically: argon blowing in the long nozzle, argon blowing in the tundish, and argon blowing in the submerged nozzle;

[0019] (6) Confirmation of key parameters during continuous casting:

[0020] Check the taper of the crystallizer before pouring. The taper of the wide side of the crystallizer is 1.22%, and the taper of the narrow side is 0.82%;

[0021] According to the high temperature characteristics of steel, the final shrinkage roll gap is determined by taking into full consideration the solidification shrinkage in the secondary cooling zone. In the active section and the area where light pressure is not applied, the roll gap shrinkage is implemented at 0.4mm / m.

[0022] Select reasonable protective slag and control the basicity of the protective slag.

[0023] Within 300 seconds after pouring, the pulling speed is increased from 0.2 to the target pulling speed, which is 0.6 m / min.

[0024] The cooling water flow rate of the crystallizer is 5.8m / s; the cooling water temperature difference of the crystallizer is 6℃; the control of the water flow rate and the cooling water temperature difference of the crystallizer directly determines the thickness and temperature of the shell after leaving the crystallizer, and affects the magnitude of the light pressure and heavy pressure of the fan-shaped segment behind. The water flow rate and temperature difference are very critical.

[0025] The hydraulic vibration of the crystallizer is non-sinusoidal vibration, A (amplitude) = 1.5 + 1.5 * V, f (frequency) = 130-10 * V, and the deflection rate is 20%;

[0026] The second cooling zone adopts weak cooling mode, and the specific water volume is 0.25L / Kg;

[0027] The submerged nozzle is a double-outlet type on both sides, and the nozzle insertion depth is 100mm;

[0028] The secondary cooling water table is shown in Table 3 below;

[0029] Table 3

[0030]

[0031] The nozzle layout of the second cooling zone strictly controls the width range of the nozzle coverage. The principle of nozzle angle design is that the area sprayed by the nozzle in each zone can just reach the position of the billet shell, so as to prevent corners from being overcooled and cracked, and to avoid corners and edges from being too cold, which makes it difficult to implement light pressure and heavy pressure later. From the high temperature mechanical properties of 4Cr13, its high temperature deformation resistance increases by 3 times between 950° and 750°, so the surface temperature of the billet must be strictly controlled in the second cooling zone.

[0032] (7) Use end electromagnetic stirring technology; the first pair of electric stirring rollers use 250A / 5Hz, and the second pair of electric stirring rollers use 300A / 5Hz to prevent segregation and looseness at the end of solidification. The total calculation and arrangement of the position of the end electromagnetic stirring can effectively improve the looseness problem in the center of the ingot;

[0033] (8) Dynamic soft reduction technology is used in the secondary cooling zone to control the reduction amount at 1.5 mm / m. The total reduction amount is controlled at 5-8 mm;

[0034] (9) Implement heavy pressure reduction technology at the end of the secondary cooling process, and control the reduction amount to 3-5 mm / m.

[0035] In order to further improve the center quality of the ingot, heavy pressure reduction technology is implemented at the end of the secondary cooling, and the reduction is controlled at 3-5mm / m. The total reduction of light pressure reduction and heavy pressure reduction is controlled at more than 12mm to effectively solve the problems of looseness and shrinkage in the center of the ingot.

[0036] The present invention has the following advantages: the continuous casting method of ultra-thick martensitic stainless steel involved in the present invention not only meets the production of thicker martensitic stainless steel, but also solves the technical problems of defects such as central porosity and central segregation inside. DETAILED DESCRIPTION

[0037] The present invention is described in detail below in conjunction with specific embodiments. It should be noted that the following embodiments are only further descriptions of the present invention, but the protection scope of the present invention is not limited to the following embodiments. Example

[0038] This embodiment relates to a continuous casting method for ultra-thick martensitic stainless steel. Taking the martensitic stainless steel with a cross section of 300X610 produced by a steel plant as an example, the specific steps are as follows:

[0039] (1) Ensure that the refining soft blowing time is more than 20 minutes, the total Ar time is more than 60 minutes, and the total calming time is more than 20 minutes. Only when the quality of molten steel refining is up to standard can continuous casting produce qualified ingots;

[0040] (2) Strictly control the composition of molten steel. The composition of 4Cr13 is shown in Table 1.

[0041] The composition of molten steel determines the performance of the subsequent products. Only by strictly controlling the composition of molten steel can it be possible to produce qualified ingots. The performance of subsequent products can be guaranteed. In particular, the S content in molten steel must be strictly controlled to prevent MnS segregation.

[0042] (3) Strictly control the trace elements and inclusions of the finished product. The trace elements are shown in Table 2. The purity of molten steel directly affects the internal quality of the ingot.

[0043] (4) According to the steel composition, the liquidus temperature is calculated to be 1470℃, and the steel temperature on the turntable is ensured to be above 1570℃. The superheat of the tundish is controlled at about 20℃-30℃. If conditions permit, the superheat of the tundish can be lowered to about 20℃, and the tundish temperature is controlled at about 1490℃. The superheat of the molten steel in the tundish must be strictly controlled, otherwise the produced ingots are prone to central porosity and shrinkage.

[0044] (5) Argon should be blown throughout the casting process to ensure that the argon blowing of the long nozzle, the tundish and the submerged nozzle is normal.

[0045] (6) Confirmation of key parameters during continuous casting: Strictly check the taper of the crystallizer before pouring to ensure that the wide side taper is 1.22% and the narrow side taper is 0.82%; according to the high temperature characteristics of steel, fully consider the solidification shrinkage in the secondary cooling zone and determine the final shrinkage roll gap. In the active section and the area where light pressure is not implemented, the roll gap shrinkage is implemented at 0.4mm / m, and a reasonable protective slag is selected to control the basicity of the protective slag;

[0046] After pouring begins, the pulling speed is increased from 0.2 to the target pulling speed within 300 seconds, and the target pulling speed is controlled at 0.6m / min.

[0047] The crystallizer cooling water flow rate is controlled at 5.8m / s; the crystallizer cooling water temperature difference is controlled at about 6°. The control of the crystallizer water flow rate and cooling water temperature difference directly determines the thickness and temperature of the billet shell after leaving the crystallizer, and affects the magnitude of the force of the subsequent fan-shaped segment under light pressure and heavy pressure. The water flow rate and temperature difference are very critical.

[0048] The hydraulic vibration of the crystallizer adopts non-sinusoidal vibration, A (amplitude) = 1.5 + 1.5 * V, f (frequency) = 130-10 * V, and the deflection rate is 20%.

[0049] The secondary cooling zone adopts weak cooling mode, and the water volume is controlled at 0.25L / Kg.

[0050] The submerged nozzle adopts a double-outlet type on both sides, and the nozzle insertion depth is controlled at about 100mm.

[0051] The secondary cooling water table is shown in Table 3 below.

[0052] (7) The end electromagnetic stirring technology is used. The first pair of electric stirring rollers use 250A / 5Hz, and the second pair of electric stirring rollers use 300A / 5Hz to prevent segregation and loosening at the end of solidification.

[0053] (8) Dynamic light reduction technology is used in the secondary cooling zone to improve the looseness of the center of the billet. The reduction is controlled at 1.5mm / m. The total reduction is controlled at 5-8mm.

[0054] (9) In order to further improve the center quality of the ingot, heavy pressure reduction technology is implemented at the end of the secondary cooling, and the reduction is controlled at 3mm / m. The total reduction of light pressure reduction and heavy pressure reduction is controlled at more than 12mm to effectively solve the problems of looseness and shrinkage in the center of the ingot.

[0055] The invention relates to a continuous casting method for ultra-thick martensitic stainless steel, which not only meets the production requirements of thicker martensitic stainless steel, but also solves the technical problems of defects such as central porosity and central segregation inside the steel.

[0056] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art may make various modifications or variations within the scope of the claims, which will not affect the essence of the present invention.

Claims

1. A continuous casting method for ultra-thick martensitic stainless steel, characterized in that: The following steps are involved: (1) Determine the refining soft blowing and argon blowing time: the refining soft blowing time is more than 20 minutes, the argon blowing time is more than 60 minutes, and the total sedation time is more than 20 minutes; (2) Control of molten steel composition: 4Cr13 is used, and the contents of its components are as follows: C 0.4%, Si 0.45%, Mn 0.6%, P0.025%, S 0.003%, Cr 13.2%, Ni 0.25%, Mo 0.15%, Cu 0.25%, N 0.045%; (3) Control trace elements and inclusions; their contents are as follows: Pb 0.41%, Sn 0.45%, As 0.6%, Sb 0.025%, Bi0.003%, W 13.2%, Co 0.25%, Nb 0.51%; (4) Control the superheat of casting: the liquidus temperature is 1470℃, the steel temperature on the turntable is 1570℃, and the superheat of the tundish is controlled at 20℃-30℃; (5) Argon is blown throughout the casting process, specifically: argon blowing at the long nozzle, argon blowing at the tundish, and argon blowing at the submerged nozzle; (6) Confirmation of key parameters during continuous casting: Check the taper of the crystallizer before pouring. The taper of the wide side of the crystallizer is 1.22%, and the taper of the narrow side is 0.82%; Within 300 seconds after pouring, the pulling speed is increased from 0.2 m / min to the target pulling speed, which is 0.6 m / min. The cooling water flow rate of the crystallizer is 5.8m / s; the cooling water temperature difference of the crystallizer is 6℃; The hydraulic vibration of the crystallizer is a non-sinusoidal vibration; The second cooling zone adopts weak cooling mode, and the specific water volume is 0.25L / Kg; The immersion nozzle is a double-outlet type on both sides, and the nozzle insertion depth is 100mm; (7) Adopt end electromagnetic stirring technology; the first pair of electric stirring rollers adopts 250A / 5Hz, and the second pair of electric stirring rollers adopts 300A / 5Hz; (8) Dynamic soft reduction technology is used in the secondary cooling zone to control the reduction at 1.5 mm / m and the total reduction at 5-8 mm; (9) Implement heavy pressure reduction technology at the end of the secondary cooling, and control the pressure reduction to 3-5 mm / m; The ultra-thick martensitic stainless steel is specifically a continuously cast ingot having a thickness of 300 mm or more.

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