阅读说明：本技术 一种通过熔体处理控制高碳马氏体不锈钢一次碳化物的处理剂和方法 (Treating agent and method for controlling primary carbide of high-carbon martensitic stainless steel through melt treatment ) 是由 闫志杰 樊玮荟 陈永安 李大赵 王睿 康燕 苗芳 于 2020-12-31 设计创作，主要内容包括：本发明公开了一种通过熔体处理改善高碳马氏体不锈钢铸坯的铸态组织,从而控制一次碳化物的方法,所述控制方法包括如下步骤：感应炉或转炉、电炉→LF精炼→RH精炼→喂线加入适量熔体处理剂→铸坯；其中根据钢种的精炼工艺要求选择性进行LF精炼,如果不需要,直接进入下一步；根据钢种的精炼工艺要求选择性进行RH精炼,如果不需要,直接进入下一步；在选择性的LF精炼后或RH精炼后通过喂线加入适量熔体处理剂；铸坯根据钢种和生产工艺要求采用相应的铸造方法和正常的工艺参数生产。本发明能在有效细化高碳马氏体不锈钢一次碳化物的同时改善铸坯的成分偏析,为后续通过塑性变形进一步细化碳化物,以及通过回火实现二次碳化物的有效强化提供组织和成分基础。(The invention discloses a method for improving the cast structure of a high-carbon martensitic stainless steel casting blank through melt treatment so as to control primary carbides, which comprises the following steps: induction furnace or converter, electric furnace → LF refining → RH refining → wire feeding with proper amount of melt treating agent → casting blank; wherein, LF refining is selectively carried out according to the refining process requirement of the steel grade, and if the LF refining is not required, the next step is directly carried out; selectively carrying out RH refining according to the refining process requirement of the steel grade, and directly entering the next step if the RH refining is not required; adding a proper amount of melt treating agent through a wire feeding after selective LF refining or RH refining; the casting blank is produced by adopting a corresponding casting method and normal process parameters according to the steel grade and the production process requirements. The method can effectively refine the primary carbide of the high-carbon martensitic stainless steel, improve the component segregation of the casting blank, and provide a structure and component basis for further refining the carbide through plastic deformation and effectively strengthening the secondary carbide through tempering.)

1. The melt treatment agent for controlling the primary carbides of the high-carbon martensitic stainless steel is characterized by comprising the following components in percentage by weight: 20-70% of rare earth ferrosilicon, 5-30% of silicon-calcium alloy, 5-30% of aluminum-calcium alloy and 5-20% of other trace alloy elements M.

2. The melt processing agent according to claim 1, wherein the trace element M comprises the following raw materials in percentage by weight: v1-20%, W1-20%, Cu 5-30%, Bi 5-30%, Co 5-20%, Mo 2-20%, Nb 1-10%, N1-5%, and B1-5%.

3. A method for controlling primary carbides of high carbon martensitic stainless steel by melt processing, the control method comprising the steps of: induction furnace, converter or electric furnace → adding melt processing agent into the feed wire;

adding a melt treatment agent into a wire feeding way, and adding the melt treatment agent into the wire feeding way according to the components of the steel grade, wherein the melt treatment agent comprises the following components in percentage by weight: 20-70% of rare earth ferrosilicon, 5-30% of calcium-silicon alloy, 5-30% of aluminum-calcium alloy and 5-20% of other trace alloy elements M.

4. The method for controlling the primary carbides of the high-carbon martensitic stainless steel according to claim 3, wherein the trace element M consists of the following raw materials in percentage by weight: v1-20%, W1-20%, Cu 5-30%, Bi 5-30%, Co 5-20%, Mo 2-20%, Nb 1-10%, N1-5%, and B1-5%.

5. The method for controlling the primary carbides of the high-carbon martensitic stainless steel according to claim 3 or 4, wherein an LF refining and/or an RH refining are included between the induction furnace, converter or electric furnace process and the wire feeding process.

6. The method of controlling primary carbides of high-carbon martensitic stainless steel according to claim 5, wherein said LF refining control comprises: the refining slag comprises the following components in percentage by mass: 10-60% CaO, 15-50% SiO₂、10～30％Al₂O₃5-15% of MgO and the like, and the LF refining period is controlled to be 20-60 min.

7. The method of controlling primary carbides of high carbon martensitic stainless steel according to claim 5, wherein said RH refining includes: refining for 20-60 min under the vacuum degree of not less than 67 Pa; after RH vacuum refining, Als is controlled to be 0.01-0.035%, H is less than or equal to 10ppm, and O is less than or equal to 25 ppm.

8. The method of controlling primary carbides in high carbon martensitic stainless steel according to claim 5, wherein said wire feeding a melt processing agent comprises: feeding a melt treating agent line of 1.0-15 kg/ton of molten steel; and after the wire feeding is finished, argon blowing and stirring are carried out, the slag surface is slightly moved, the molten steel is not exposed, and the time is controlled to be 5-30 min.

Technical Field

The invention relates to the technical field of steel smelting, in particular to a high-carbon martensitic stainless steel carbide control technology, which improves the as-cast structure of a casting blank through melt treatment to achieve the purpose of refining primary as-cast carbide.

Background

The martensitic stainless steel can change the performance of the material through heat treatment, and has great market demands in the fields of aviation industry, heavy transportation, nuclear power, medical treatment, cutters and the like. In order to meet the requirements of high strength and high corrosion resistance, high carbon and high chromium are an important development direction of martensitic stainless steel (the carbon content is not less than 0.4 wt%). The high-carbon martensitic stainless steel contains more than 10% of Cr and a small amount of carbide-forming elements such as Mo, V, W, Nb and the like, and is intended to precipitate fine secondary carbides as a strengthening phase during tempering to improve the strength of the material. The morphology, size and distribution of carbides are closely related to the performance of the high-carbon martensitic stainless steel. However, the primary carbides precipitated during solidification of the high carbon martensitic stainless steel melt are generally distributed in bulk or even in a network form in the matrix. The primary carbides contain a large amount of alloy elements, the content of the alloy elements in the matrix is reduced, the tempering secondary hardening effect is weakened, and meanwhile, the coarse carbides are crack sources during plastic deformation, so that the corrosion resistance and the mechanical property of the material are greatly reduced. Therefore, the control and refinement of primary carbides is a key common technical problem in the production of high quality high carbon martensitic stainless steels.

The conventional method for improving the carbide is to crush and refine the carbide through repeated thermoplastic deformation, and although the method is effective, the carbide is still unevenly distributed, and meanwhile, the generation efficiency is low and the cost is high. It is desirable to control and refine primary carbides in the ingot, which is a way to solve for the coarseness and uneven distribution of carbides at the source. From the invention patents published in China at present, the carbide morphology of steel types such as tool and die steel, high-carbon steel, bearing steel and the like is improved by methods such as electroslag remelting, refining, along with stream deterioration during pouring and the like (such as recently published invention patents: CN 106282750A, CN 106756437A, CN 101768655A and the like), and certain effects are achieved. The existing research results show that electroslag remelting and refining can obviously purify molten steel, reduce inclusions, inhibit heterogeneous nucleation of carbides to a certain extent, but have no obvious effect on inhibiting aggregation and growth of the carbides. The rheological method is generally used for the production of cast iron and cast steel, and the method can possibly improve the morphology of carbide, but simultaneously precipitates a large amount of impurities, so that the rheological method is not suitable for clean production.

Disclosure of Invention

The invention aims to solve the key common technical problem of controlling the carbide of the high-carbon martensitic stainless steel and provide a method for controlling the as-cast structure of a casting blank by controlling the solidification behavior of molten steel through melt treatment so as to achieve the purpose of refining primary carbide. The invention adds a melt treating agent designed and prepared by a self-designed and prepared method in the smelting production process of high-carbon stainless steel, and controls the nucleation and growth of carbide in the solidification process of steel melt under the action of the melt treating agent, thereby achieving the purpose of controlling carbide and homogenizing components and realizing the refinement of primary carbide.

In order to achieve the purpose, the invention is realized by the following technical scheme:

the invention discloses a method for controlling and refining primary carbides by improving the as-cast structure of a high-carbon martensitic stainless steel casting blank through melt treatment, which comprises the following steps: induction furnace (or converter, electric furnace) → LF refining (selectivity) → RH refining (selectivity) → melt processing (wire feed with appropriate amount of melt processing agent) → casting blank.

Wherein:

LF refining (selectivity), wherein the LF refining is selectively adopted according to the refining process requirement of the steel grade;

RH refining (selectivity), wherein RH refining is selectively adopted according to the refining process requirement of steel grades;

adding a proper amount of melt treating agent into the wire feeding, and adding a proper amount of melt treating agent in a wire feeding mode according to the components of the steel grade;

casting blank, and selecting a casting method according to steel types and production processes.

According to the control method provided by the invention, the LF refining (selectivity) comprises the following steps: and (3) selectively adopting LF refining according to the refining process requirement of the steel grade, and if the LF refining is adopted, adopting a refining slag system with the alkalinity of 5-9 and adding a proper amount of calcium. The refining slag system comprises the following components in percentage by weight: 10-60% CaO, 15-50% SiO₂、10～30％Al₂O₃5-15% MgO. And the LF refining period is controlled to be 20-60 min. And adjusting the argon flow to be in a soft blowing stirring state after LF refining is finished, wherein the soft blowing state is a slag surface micro-motion state, molten steel is not exposed, and the weak stirring soft blowing time is controlled to be 5-10 min. If LF refining is not adopted, the RH refining or the stage of adding the melt treating agent is directly carried out.

According to the control method provided by the invention, the RH refining (selectivity) comprises the following steps: and selectively adopting RH refining according to the refining process requirement of the steel grade, and refining for 30-60 min under the vacuum degree of not less than 67Pa if the RH refining is adopted. After RF vacuum refining, Als is controlled to be 0.01-0.035%, H is less than or equal to 10ppm, and O is less than or equal to 25 ppm. If RH refining is not adopted, the step of adding the melt treating agent is directly carried out.

According to the control method provided by the invention, the melt treatment, namely the wire feeding, is added with a proper amount of melt treatment agent, and comprises the following steps: and after the selective LF refining or RH refining is finished, adding 1.0-15 kg/ton of molten steel melt treatment agent according to the component characteristics of the steel grade. And after the wire feeding is finished, continuously blowing argon for stirring, slightly moving the slag surface, and controlling the time to be 5-30 min, wherein the molten steel is not exposed. The melt treating agent comprises the following components in percentage by weight: 20-70% of rare earth ferrosilicon, 5-30% of calcium-silicon alloy, 5-30% of aluminum-calcium alloy and 5-20% of other trace alloy elements M, wherein the trace elements M comprise the following raw materials in percentage by weight: v1-20%, W1-20%, Cu 5-30%, Bi 5-30%, Co 5-20%, Mo 2-20%, Nb 1-10%, N1-5%, and B1-5%. The purpose of adding the melt treating agent is to control the nucleation and growth behavior of carbides in the solidification process of molten steel, inhibit the precipitation and aggregation growth of the carbides and realize the refinement of primary carbides.

According to the control method provided by the invention, the casting blank adopts normal process parameters of the selected casting method according to the steel grade and the production process.

The carbide control method has the advantages that the carbide of the high-carbon martensitic stainless steel can be effectively controlled, the component segregation of the casting blank is improved while the primary carbide of the casting blank is refined, and a structure and component basis is provided for further refining the carbide through plastic deformation and effectively strengthening the secondary carbide through tempering.

Drawings

FIG. 1 shows the metallographic structure of a 7Cr14 high-carbon stainless steel casting blank according to the present invention;

FIG. 2 shows the metallographic structure of a cast slab of 7Cr14 high-carbon stainless steel not used in the present invention

FIG. 3 is an SEM image of extracted carbides of a 7Cr14 high-carbon stainless steel billet adopting the invention;

FIG. 4 is an SEM image of extracted carbides of a 7Cr14 high carbon stainless steel billet not using the present invention;

FIG. 5 is a graph showing the size distribution of extracted carbides of cast 7Cr14 high carbon stainless steel ingots with and without the present invention.

Detailed Description

Any feature disclosed in this specification may be replaced by alternative features serving equivalent or similar purposes, unless expressly stated otherwise. Unless expressly stated otherwise, each feature is only an example of a generic series of equivalent or similar features. The description is only for the purpose of facilitating understanding of the present invention and should not be construed as specifically limiting the present invention.

The invention is further illustrated by the following description and the accompanying drawings.

Example 1:

selecting 7Cr14 martensitic stainless steel (the components are C: 0.65-0.75%, Cr: 13.5-15.5%, Mn: 0.45-0.65%, Si: 0.25-0.45%, Mo: 0.35-0.45%, V: 0.35-0.45%), and implementing the primary carbide control of the 7Cr14 martensitic stainless steel according to the method for controlling the carbide, wherein the method mainly comprises the following steps:

smelting 200kg of molten steel in the atmosphere by adopting a 200kg intermediate frequency furnace, and controlling the components to be on-line in an allowable range in consideration of the burning loss of alloy elements;

after complete melting and heat preservation for 5min, refining in a furnace, wherein the refining slag system comprises the following components in percentage by weight: 30% CaO, 40% SiO₂、25％Al₂O₃5% of MgO and the like.

After refining for 20min, feeding the wire and adding a melt treating agent, wherein the melt treating agent comprises the following components: 40% of rare earth ferrosilicon, 30% of silicon-calcium alloy, 10% of aluminum-calcium alloy and other trace alloy elements M20%, wherein the trace elements M comprise the following raw materials in percentage by weight: v8%, W2%, Cu 10%, Bi 20%, Co 5%, Mo 10%, Nb 5%, N3% and B2%, the addition amount of the melt processing agent is 1.0kg (5 kg/ton molten steel);

preserving the heat for 10min, and pouring into a steel die after slagging off to obtain a casting blank.

FIGS. 1 and 2 show the metallographic structure of the cast slab of 7Cr14 high carbon stainless steel with and without the use of the present invention, and it can be seen that the net carbides of the cast slab with the use of the wire feed of the present invention added with the melt processing agent are reduced; FIGS. 3 and 4 are SEM images of extracted carbides of a 7Cr14 high carbon stainless steel ingot with and without the invention, and it can be seen that the carbide of the ingot with the invention is obviously refined and the edges and corners of the carbide are passivated; FIG. 5 is a graph of the distribution of the size of extracted carbides of cast 7Cr14 high carbon stainless steel ingots with and without the present invention, further demonstrating the refinement of carbides with the present invention ingots and the disappearance of carbides with a size greater than 200 μm after melt processing.

Example 2:

selecting 7Cr14 martensitic stainless steel (the components are C: 0.65-0.75%, Cr: 13.5-15.5%, Mn: 0.45-0.65%, Si: 0.25-0.45%, Mo: 0.35-0.45%, V: 0.35-0.45%), and implementing the primary carbide control of the 7Cr14 martensitic stainless steel according to the method for controlling the carbide, wherein the method mainly comprises the following steps:

smelting 200kg of molten steel in the atmosphere by adopting a 200kg intermediate frequency furnace, and controlling the components to be on-line in an allowable range in consideration of the burning loss of alloy elements;

after complete melting and heat preservation for 5min, refining in a furnace, wherein the refining slag system comprises the following components in percentage by weight: 10% CaO, 50% SiO₂、25％Al₂O₃15% MgO, etc.

After refining for 20min, feeding the wire and adding a melt treating agent, wherein the melt treating agent comprises the following components: 70% of rare earth ferrosilicon, 20% of silicon-calcium alloy, 5% of aluminum-calcium alloy and other trace alloy elements M5%, wherein the trace elements M comprise the following raw materials in percentage by weight: v20%, W1%, Cu 7%, Bi 30%, Co 20%, Mo 2%, Nb 10%, N5% and B5%, the addition amount of the melt processing agent is 1.0kg (5 kg/ton molten steel);

preserving the heat for 10min, and pouring into a steel die after slagging off to obtain a casting blank.

Example 3:

selecting 7Cr14 martensitic stainless steel (the components are C: 0.65-0.75%, Cr: 13.5-15.5%, Mn: 0.45-0.65%, Si: 0.25-0.45%, Mo: 0.35-0.45%, V: 0.35-0.45%), and implementing the primary carbide control of the 7Cr14 martensitic stainless steel according to the method for controlling the carbide, wherein the method mainly comprises the following steps:

smelting 200kg of molten steel in the atmosphere by adopting a 200kg intermediate frequency furnace, and controlling the components to be on-line in an allowable range in consideration of the burning loss of alloy elements;

after complete melting and heat preservation for 5min, refining in a furnace, wherein the refining slag system comprises the following components in percentage by weight: 60% of CaO and 15% of SiO₂、10％Al₂O₃15% MgO, etc.

After refining for 20min, feeding the wire and adding a melt treating agent, wherein the melt treating agent comprises the following components: 20% of rare earth ferrosilicon, 30% of silicon-calcium alloy, 30% of aluminum-calcium alloy and other trace alloy elements M20%, wherein the trace elements M comprise the following raw materials in percentage by weight: v1%, W20%, Cu 30%, Bi 5%, Co 21%, Mo 20%, Nb 1%, N1% and B1%, and the amount of the melt processing agent added is 1.0kg (5 kg/ton molten steel);

preserving the heat for 10min, and pouring into a steel die after slagging off to obtain a casting blank.