High-carbon martensitic stainless steel refined with carbides and method for producing the same

Abstract

The application discloses a carbide-refined high-carbon martensitic stainless steel and a preparation method thereof, and belongs to the technical field of stainless steel production. The chemical components of the carbide-refined high-carbon martensitic stainless steel are controlled as follows in percentage by mass: 0.45%<=C<=0.55%, Si<=1.00%, Mn<=1.00%, P<=0.040%, S<=0.015%, 14.00%<=Cr<=15.00%, Mo<=0.70%, Cu+N+Ni+Co<=1.00%, and the balance of Fe and inevitable impurities. The application provides a production system of a low-carbide-precipitated stainless steel strip, which can further ensure that the above material obtains a lower carbide quantity and a smaller carbide size, and meets the requirements of polishing performance of market processing.

Description

Technical Field

[0001] This invention belongs to the field of stainless steel production technology, specifically relating to a high-carbon martensitic stainless steel with refined carbides and its preparation method. Background Technology

[0002] Because traditional high-carbon martensitic stainless steels such as 50Cr15 have high carbon content, the carbides formed during the production process are relatively large. For example, during continuous casting, due to separation and crystallization, there is a severe uneven distribution of carbon elements on the cross-section of the billet, especially in the center of the billet where the carbon content is even higher. Moreover, the high carbon content further leads to more and larger carbides in the center of the billet. These carbides cause problems such as easy cracking and uneven color after polishing during subsequent processing and use. Even when using ingot casting, this problem cannot be eliminated, and the carbides in the core of the ingot are even larger during ingot casting. Summary of the Invention

[0003] To address the aforementioned technical problems in the prior art, this invention provides a high-carbon martensitic stainless steel with refined carbides and its preparation method.

[0004] In a first aspect of the invention, a high-carbon martensitic stainless steel with refined carbides is provided, the chemical composition of which is controlled by mass percentage as follows: 0.45%≤C≤0.55%, Si≤1.00%, Mn≤1.00%, P≤0.040%, S≤0.015%, 14.00%≤Cr≤15.00%, Mo≤0.70%, Cu+N+Ni+Co≤1.00%, with the balance being Fe and unavoidable impurities, wherein the austenite stability coefficient S is calculated by the following formula: S=Ni+0.68×Cr+0.55×Mn+0.45×Si+27×(C+N)+Mo+0.2×Co, wherein S=23~28.

[0005] Furthermore, the chemical composition of the above-mentioned carbide-refined high-carbon martensitic stainless steel is controlled by mass percentage as follows: 0.46%≤C≤0.48%, 0.25%≤Si≤0.32%, 0.67%≤Mn≤0.71%, 0.036%≤P≤0.038%, 0.005%≤S≤0.006%, 14.69%≤Cr≤14.78%, Mo≤0.61%, Cu+N+Ni+Co≤1.00%, with the balance being Fe and unavoidable impurities. The austenite stability coefficient S is calculated by the following formula: S=Ni+0.68×Cr+0.55×Mn+0.45×Si+27×(C+N)+Mo+0.2×Co, where S=23.49~23.55.

[0006] In a second aspect of the invention, the method for preparing carbide-refined high-carbon martensitic stainless steel includes the following steps: (1) Refining treatment: The molten steel after converter smelting is sent to VD furnace for secondary refining, then transferred to LF furnace, lime and fluorite are added to form slag, and after weak stirring with argon, it is sent out. (2) Continuous casting: The refined molten steel is sent to the slab continuous casting machine for casting. The superheat of the tundish is controlled to be ≤25℃. The secondary cooling adopts strong cooling and the secondary cooling water volume is controlled to be 0.80~0.85L / kg. The casting is to obtain the slab. (3) Heat treatment of billet: The cut billet is sent into the heat treatment furnace and the temperature is raised from room temperature. When the furnace temperature reaches 1000℃ or above, the holding time is started. The holding time is ≥1.2 min / mm based on the billet thickness. After the holding time is completed, the billet is cooled to room temperature with the furnace. (4) Hot rolling: The heat-treated billet is hot rolled. The rough rolling stage is rolled in 5 passes, with the first pass having a reduction rate of ≥40% and the single-pass deformation rate of each subsequent pass being ≥30%. After rough rolling, it is rolled into strip with a thickness of 3-4 mm by finish rolling. (5) Finished product processing: The hot-rolled strip is annealed and pickled to obtain the finished strip.

[0007] Furthermore, in the above-mentioned method for preparing high-carbon martensitic stainless steel with refined carbides, in step (2), the superheat of the tundish is controlled to be 22-25°C.

[0008] Furthermore, in the above-mentioned method for preparing high-carbon martensitic stainless steel with refined carbides, in step (2), the secondary cooling water volume is 0.82 to 0.83 L / kg.

[0009] Furthermore, in the above-mentioned method for preparing high-carbon martensitic stainless steel with refined carbides, in step (3), the holding time is 1.25 to 1.35 min / mm based on the thickness of the billet.

[0010] Furthermore, in the above-mentioned method for preparing high-carbon martensitic stainless steel with refined carbides, in step (4), the first pass reduction rate is 40% to 43%, and the single-pass deformation rate of each subsequent pass is 30% to 34%.

[0011] Furthermore, in the above-mentioned method for preparing high-carbon martensitic stainless steel with refined carbides, the finished strip obtained by the method for preparing high-carbon martensitic stainless steel has a carbide size of less than 5 μm.

[0012] The carbide-refined high-carbon martensitic stainless steel and its preparation method of the present invention have the following advantages and beneficial effects: (1) This invention improves the structural stability of the material by controlling the composition of the steel, thereby reducing the precipitation of carbides. Then, the precipitation time of carbides is reduced by continuous casting with low superheat and high cooling water intensity. Finally, through heat treatment and large deformation hot rolling process, the control target of low carbides and small size is achieved, which greatly reduces the degree of surface defects after the material is polished. (2) The present invention provides a production system for stainless steel strip with low carbide precipitation, which can further ensure that the above materials obtain a lower carbide quantity and smaller carbide size, and meet the market processing requirements for polishing performance. Detailed Implementation

[0013] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0014] In a first aspect of the invention, a high-carbon martensitic stainless steel with refined carbides is provided, which meets the market requirements for polishing performance.

[0015] Specifically, the chemical composition of the carbide-refined high-carbon martensitic stainless steel of the present invention is controlled by mass percentage as follows: 0.45%≤C≤0.55%, Si≤1.00%, Mn≤1.00%, P≤0.040%, S≤0.015%, 14.00%≤Cr≤15.00%, Mo≤0.70%, Cu+N+Ni+Co≤1.00%, with the balance being Fe and unavoidable impurities. The austenite stability coefficient S is calculated by the following formula: S=Ni+0.68×Cr+0.55×Mn+0.45×Si+27×(C+N)+Mo+0.2×Co, where S=23~28.

[0016] Preferably, the chemical composition of the carbide-refined high-carbon martensitic stainless steel of the present invention is controlled by mass percentage as follows: 0.46%≤C≤0.48%, 0.25%≤Si≤0.32%, 0.67%≤Mn≤0.71%, 0.036%≤P≤0.038%, 0.005%≤S≤0.006%, 14.69%≤Cr≤14.78%, Mo≤0.61%, Cu+N+Ni+Co≤1.00%, with the balance being Fe and unavoidable impurities. The austenite stability coefficient S is calculated by the following formula: S=Ni+0.68×Cr+0.55×Mn+0.45×Si+27×(C+N)+Mo+0.2×Co, where S=23.49~23.55.

[0017] The role of the required elemental and content control ranges in the carbide-refined high-carbon martensitic stainless steel of this invention is described below: (1) Carbon can enhance the influence of precipitates and the mechanical properties of materials: Carbon readily forms iron carbides in steel, commonly known as cementite. In stainless steel, due to the presence of chromium, it is also more likely to combine with Cr to form metallic carbon compounds MxCy. These carbides include Fe3C, (Fe,Cr)23C6, (Fe,Cr)7C3, etc. To reduce carbide precipitation, it is necessary to improve the stability of austenite and thus reduce the amount and size of precipitates during the austenite-to-martensite transformation process.

[0018] (2) The effect of chromium on the mechanical properties of martensitic stainless steel: Chromium is the most critical element to ensure the corrosion resistance of the material; Chromium has a certain influence on the austenite stability coefficient of the material. The higher the chromium content, the greater the austenite stability coefficient. Therefore, the chromium content needs to be greater than 14.00 wt.% and less than 15.00 wt.%.

[0019] (3) Carbon is a key element for the formation of a stable austenitic phase in materials. At the same time, because it can provide high hardness, it can maintain good sharpness and wear resistance after the material is processed. Therefore, the carbon content should be controlled between 0.45 and 0.55 wt.%.

[0020] In a second aspect of the present invention, a method for preparing carbide-refined high-carbon martensitic stainless steel is provided, comprising the following steps: (1) Refining treatment: The molten steel after converter smelting is sent to VD furnace for secondary refining, then transferred to LF furnace, lime and fluorite are added to form slag, and after weak stirring with argon, it is sent out. (2) Continuous casting: The refined molten steel is sent to the slab continuous casting machine for casting. The superheat of the tundish is controlled to be ≤25℃. The secondary cooling adopts strong cooling and the secondary cooling water volume is controlled to be 0.80~0.85L / kg. The casting is to obtain the slab. (3) Heat treatment of billet: The cut billet is sent into the heat treatment furnace and the temperature is raised from room temperature. When the furnace temperature reaches 1000℃ or above, the holding time is started. The holding time is ≥1.2 min / mm based on the billet thickness. After the holding time is completed, the billet is cooled to room temperature with the furnace. (4) Hot rolling: The heat-treated billet is hot rolled. The rough rolling stage is rolled in 5 passes, with the first pass having a reduction rate of ≥40% and the single-pass deformation rate of each subsequent pass being ≥30%. After rough rolling, it is rolled into strip with a thickness of 3-4 mm by finish rolling. (5) Finished product processing: The hot-rolled strip is annealed and pickled to obtain the finished strip.

[0021] Preferably, in the method for preparing high-carbon martensitic stainless steel with carbide refinement of the present invention, in step (2), the superheat of the tundish is controlled to be 22-25°C.

[0022] Preferably, in the method for preparing high-carbon martensitic stainless steel with carbide refinement of the present invention, in step (2), the secondary cooling water volume is 0.82 to 0.83 L / kg.

[0023] Preferably, in the method for preparing high-carbon martensitic stainless steel with carbide refinement of the present invention, in step (3), the holding time is 1.25 to 1.35 min / mm based on the thickness of the billet.

[0024] Preferably, in the method for preparing carbide-refined high-carbon martensitic stainless steel of the present invention, in step (4), the first pass reduction rate is 40% to 43%, and the single-pass deformation rate of each subsequent pass is 30% to 34%.

[0025] Preferably, in the method for preparing high-carbon martensitic stainless steel with refined carbides according to the present invention, the finished strip obtained by the method for preparing high-carbon martensitic stainless steel has a carbide size of less than 5 μm.

[0026] The following detailed description of the carbide-refined high-carbon martensitic stainless steel and its preparation method is illustrated in conjunction with specific embodiments.

[0027] Example 1 The chemical composition of the carbide-refined high-carbon martensitic stainless steel of Example 1, by mass percentage, is: C: 0.48 wt.%, Si: 0.25 wt.%, Mn: 0.67 wt.%, P: 0.038 wt.%, S: 0.006 wt.%, Cr: 14.78 wt.%, with the remainder being Fe and unavoidable impurities. Specifically, the austenite stability coefficient S is 23.49.

[0028] The specific process of preparing carbide-refined high-carbon martensitic stainless steel in Example 1 includes: (1) Refining treatment: The molten steel after converter smelting is sent to VD furnace for secondary refining, then transferred to LF furnace, lime and fluorite are added to form slag, and after weak stirring with argon, it is sent out.

[0029] (2) Continuous casting: The refined molten steel is sent to the slab continuous casting machine for casting. The superheat of the tundish is controlled at 23℃ (≤25℃). The secondary cooling adopts strong cooling and the secondary cooling water ratio is controlled at 0.82L / kg. The casting is then used to obtain the slab.

[0030] (3) Heat treatment of billet: The cut billet is sent into the heat treatment furnace and the temperature is raised from room temperature. When the furnace temperature reaches 1000℃ or above, the holding time is started. The billet thickness is 200mm and the actual holding time is 260min (1.3min / mm based on thickness, which meets ≥1.2min / mm). After the holding time is completed, the billet is cooled to room temperature with the furnace.

[0031] (4) Hot rolling: The heat-treated billet is hot rolled. The rough rolling stage is rolled in 5 passes, with the first pass having a reduction rate of 42% (≥40%), and the billet is rolled from 200mm to 114mm thickness. The single-pass deformation rates of the subsequent 4 passes are 32%, 33%, 32%, and 31% (all ≥30%). After rough rolling, the strip is rolled into a thickness of 3.5mm by finish rolling.

[0032] (5) Finished product processing: The hot-rolled strip is annealed and pickled to obtain the finished strip.

[0033] The material produced in this embodiment has no large primary carbides, and the size of the carbides is less than 5μm.

[0034] Example 2 The chemical composition of the carbide-refined high-carbon martensitic stainless steel of Example 2, by mass percentage, is as follows: C: 0.46 wt.%, Si: 0.32 wt.%, Mn: 0.71 wt.%, P: 0.036 wt.%, S: 0.005 wt.%, Cr: 14.69 wt.%, Mo: 0.61 wt.%, with the remainder being Fe and unavoidable impurities. Specifically, the austenite stability coefficient S is 23.55.

[0035] The specific process of preparing carbide-refined high-carbon martensitic stainless steel in Example 2 includes: (1) Refining treatment: The molten steel after converter smelting is sent to VD furnace for secondary refining, then transferred to LF furnace, lime and fluorite are added to form slag, and after weak stirring with argon, it is sent out.

[0036] (2) Continuous casting: The refined molten steel is sent to the slab continuous casting machine for casting. The superheat of the tundish is controlled at 24℃ (≤25℃). The secondary cooling adopts strong cooling and the secondary cooling water ratio is controlled at 0.83L / kg. The casting is then used to obtain the slab.

[0037] (3) Heat treatment of billet: The cut billet is sent into the heat treatment furnace and the temperature is raised from room temperature. When the furnace temperature reaches 1000℃ or above, the holding time is started. The billet thickness is 200mm and the actual holding time is 255min (1.275min / mm based on thickness, which meets ≥1.2min / mm). After the holding time is completed, the billet is cooled to room temperature with the furnace.

[0038] (4) Hot rolling: The heat-treated billet is hot rolled. The rough rolling stage is rolled in 5 passes, with the first pass having a reduction rate of 41% (≥40%), and the billet is rolled from 200mm to 118mm in thickness. The single-pass deformation rates of the subsequent 4 passes are 33%, 32%, 31%, and 31% (all ≥30%). After rough rolling, the strip is rolled into a thickness of 3.5mm by finish rolling.

[0039] (5) Finished product processing: The hot-rolled strip is annealed and pickled to obtain the finished strip.

[0040] The material produced in this embodiment has no large primary carbides, and the size of the carbides is less than 5μm.

[0041] In summary, compared with the prior art, the carbide-refined high-carbon martensitic stainless steel and its preparation method of the present invention have the following advantages and positive effects: (1) This invention improves the structural stability of the material by controlling the composition of the steel, thereby reducing the precipitation of carbides. Then, the precipitation time of carbides is reduced by continuous casting with low superheat and high cooling water intensity. Finally, through heat treatment and large deformation hot rolling process, the control target of low carbides and small size is achieved, which greatly reduces the degree of surface defects after the material is polished. (2) The present invention provides a production system for stainless steel strip with low carbide precipitation, which can further ensure that the above materials obtain a lower carbide quantity and smaller carbide size, and meet the market processing requirements for polishing performance.

[0042] In the description of this specification, the term "embodiment" means a specific feature, structure, material, or characteristic described in connection with that embodiment is included in at least one embodiment of the invention. The illustrative expressions of the above terms in this specification do not necessarily refer to the same embodiment. Furthermore, those skilled in the art can combine or combine the different embodiments and features described in this specification without creating contradiction.

[0043] It should be noted that, unless otherwise specified, the terms used herein have the meanings commonly understood by those skilled in the art. Furthermore, when a numerical range is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum. Further, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Moreover, when multiple ranges are provided to describe features, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0044] It should also be noted that, in this document, the term "comprising" or any other variation thereof is intended to cover non-exclusive inclusion, such that an article or device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or device.

[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the present invention.

Claims

1. A high-carbon martensitic stainless steel with refined carbides, characterized in that, The chemical composition of the carbide-refined high-carbon martensitic stainless steel is controlled by mass percentage as follows: 0.45%≤C≤0.55%, Si≤1.00%, Mn≤1.00%, P≤0.040%, S≤0.015%, 14.00%≤Cr≤15.00%, Mo≤0.70%, Cu+N+Ni+Co≤1.00%, with the balance being Fe and unavoidable impurities. The austenite stability coefficient S is calculated by the following formula: S=Ni+0.68×Cr+0.55×Mn+0.45×Si+27×(C+N)+Mo+0.2×Co, where S=23~28.

2. The carbide-refined high-carbon martensitic stainless steel according to claim 1, characterized in that, The chemical composition of the carbide-refined high-carbon martensitic stainless steel is controlled by mass percentage as follows: 0.46%≤C≤0.48%, 0.25%≤Si≤0.32%, 0.67%≤Mn≤0.71%, 0.036%≤P≤0.038%, 0.005%≤S≤0.006%, 14.69%≤Cr≤14.78%, Mo≤0.61%, Cu+N+Ni+Co≤1.00%, with the balance being Fe and unavoidable impurities. The austenite stability coefficient S is calculated by the following formula: S=Ni+0.68×Cr+0.55×Mn+0.45×Si+27×(C+N)+Mo+0.2×Co, where S=23.49~23.

55.

3. A method for preparing high-carbon martensitic stainless steel with refined carbides, characterized in that, Includes the following steps: (1) Refining treatment: The molten steel after converter smelting is sent to VD furnace for secondary refining, then transferred to LF furnace, lime and fluorite are added to form slag, and after weak stirring with argon, it is sent out. (2) Continuous casting: The refined molten steel is sent to the slab continuous casting machine for casting. The superheat of the tundish is controlled to be ≤25℃. The secondary cooling adopts strong cooling and the secondary cooling water volume is controlled to be 0.80~0.85L / kg. The casting is to obtain the slab. (3) Heat treatment of billet: The cut billet is sent into the heat treatment furnace and the temperature is raised from room temperature. When the furnace temperature reaches 1000℃ or above, the holding time is started. The holding time is ≥1.2min / mm based on the billet thickness. After the holding time is completed, the billet is cooled to room temperature with the furnace. (4) Hot rolling: The heat-treated billet is hot rolled. The rough rolling stage is rolled in 5 passes, with the first pass having a reduction rate of ≥40% and the single-pass deformation rate of each subsequent pass being ≥30%. After rough rolling, it is rolled into strip with a thickness of 3-4 mm by finish rolling. (5) Finished product processing: The hot-rolled strip is annealed and pickled to obtain the finished strip.

4. The method for preparing carbide-refined high-carbon martensitic stainless steel according to claim 3, characterized in that, In step (2), the superheat of the intermediate tundish is controlled to be 22-25°C.

5. The method for preparing carbide-refined high-carbon martensitic stainless steel according to claim 3, characterized in that, In step (2), the secondary cooling water volume is 0.82 to 0.83 L / kg.

6. The method for preparing carbide-refined high-carbon martensitic stainless steel according to claim 3, characterized in that, In step (3), the heat preservation time is 1.25 to 1.35 min / mm based on the thickness of the billet.

7. The method for preparing carbide-refined high-carbon martensitic stainless steel according to claim 3, characterized in that, In step (4), the first pass reduction rate is 40% to 43%, and the single-pass deformation rate of each subsequent pass is 30% to 34%.

8. The method for preparing carbide-refined high-carbon martensitic stainless steel according to claim 3, characterized in that, The finished strip prepared by the method described above has a carbide size of less than 5 μm.