CN109055772B

CN109055772B - Electroslag remelting process method

Info

Publication number: CN109055772B
Application number: CN201811256569.9A
Authority: CN
Inventors: 冯朝源; 冯英育
Original assignee: Individual
Current assignee: Beijing Hsb Tooling Material Technology Co ltd
Priority date: 2018-10-25
Filing date: 2018-10-25
Publication date: 2020-03-17
Anticipated expiration: 2038-10-25
Also published as: CN109055772A

Abstract

The invention relates to an electroslag remelting process method, and belongs to the technical field of electroslag remelting. The electroslag remelting process method comprises the following steps: placing a sandwich type cooler in a through hole which is arranged on an electrode blank used for electroslag remelting along the vertical direction, wherein the sandwich type cooler is in insulated connection with a cooling circulation system; in the electroslag remelting process, the distance between the sandwich cooler and the electroslag ingot is adjusted to reduce the temperature of the central part of the electroslag ingot. The temperature of the surface of the inner hole of the electrode blank is close to the temperature of the outer surface under the action of the interlayer type cooler, and in the electroslag remelting process, the distance between the interlayer type cooler and an electroslag ingot is adjusted to reduce the temperature of the central part of the electroslag ingot, so that a metal molten pool is in a shallow flat shape, a liquid phase line is basically vertical to the longitudinal direction, equiaxial crystals are promoted to be formed, and the phenomenon that alloy metal elements are unevenly distributed on the cross section due to crystallization segregation is avoided.

Description

Electroslag remelting process method

Technical Field

The invention belongs to the technical field of electroslag remelting, and particularly relates to an electroslag remelting process method.

Background

At present, widely used die steel and high-speed steel have toughness and isotropy which cannot meet the changing customer requirements. Especially in the aspects of large-scale die-casting, large-section nonferrous metal (aluminum alloy) extrusion, precision forging dies and complex cutting tools, along with the development of automation and intellectualization of equipment, the working condition of the dies is worsened more and more, and the traditional die steel and high-speed steel cannot meet the market demand. The large-section hot-working die steel with high toughness and high isotropy is produced, and large dies and cutting tools with high quality and long service life are manufactured by taking the die steel as a raw material, which is the development requirement of modern automobiles, electronic home appliances and rail transit transportation industries.

The reasons for the insufficient toughness and isotropy of large-section die steel and high-speed steel are liquated carbides necessarily generated in the crystallization process of alloy steel, segregation generated by selective crystallization of dendrites, and carbon elements and other alloy elements are enriched in certain local areas in the steel in the form of aggregation. After the steel ingot is heated and forged, liquated carbides and black-white strip-shaped structures can be seen through metallographic observation, and the phenomenon is particularly serious in the center of the large-section electroslag ingot. The research shows that: increasing the number of liquated carbides above 3 μm from 1 to 2 per square millimeter reduces the ductility of the steel by nearly a factor of two. Accordingly, the North American die casting Association and other organizations promulgate high-grade die casting mold material acceptance standards and define acceptable grades of band-shaped structures, non-metallic inclusions, impact toughness, and the like. Eliminating liquated carbide and banded structure, high temperature diffusion annealing and powerful forging are effective means. In the electroslag remelting process, a process method of directional solidification as much as possible is adopted, the quality of an electroslag ingot is improved, segregation and secondary dendrite spacing are reduced, and the improvement of isotropy of an internal structure is influenced.

Disclosure of Invention

In view of the above, the present invention provides an electroslag remelting process to effectively solve the above problems.

The embodiment of the invention is realized by the following steps:

the embodiment of the invention provides an electroslag remelting process method, wherein a sandwich type cooler is arranged in a through hole which is arranged on an electrode blank used for electroslag remelting along the vertical direction, and the sandwich type cooler is connected with a cooling circulation system in an insulating way; in the electroslag remelting process, the distance between the sandwich cooler and the electroslag ingot is adjusted to reduce the temperature of the central part of the electroslag ingot.

In an alternative embodiment of the present invention, the adjusting the distance between the sandwich-type cooler and the electroslag ingot in the electroslag remelting process includes: in the initial stage of electroslag remelting, adjusting the sandwich cooler to enable the distance between the sandwich cooler and the electroslag ingot to be a first distance; and adjusting the distance between the sandwich type cooler and the electroslag ingot to be a second distance along with the progress of the electroslag remelting process, wherein the second distance is smaller than the first distance.

In an alternative embodiment of the present invention, the adjusting the distance between the sandwich-type cooler and the electroslag ingot comprises: in the electroslag remelting process, the distance between the sandwich cooler and an electroslag ingot is adjusted according to the temperature of a thermocouple arranged on the inner surface of the sandwich cooler.

In an alternative embodiment of the present invention, before placing a sandwich cooler in the through hole opened in the vertical direction on the electrode blank for electroslag remelting, the method further comprises: and a through hole is formed in the electrode blank used for electroslag remelting along the vertical direction.

In an optional embodiment of the present invention, the forming of the through hole in the vertical direction on the electrode blank used for electroslag remelting includes: and a through hole with the diameter of 50-120 mm is formed in the center of the electrode blank used for electroslag remelting along the vertical direction.

In an alternative embodiment of the invention, the sandwich cooler comprises: the cooling device comprises an outer pipe and a hollow inner pipe arranged in the outer pipe, wherein the top end of the hollow inner pipe exceeds the top end of the outer pipe, the bottom end of the hollow inner pipe is communicated with the outer pipe, an outlet is formed in one side, close to the top end, of the outer pipe, and during cooling, a cooling medium enters from the top end of the hollow inner pipe, flows through an interlayer between the hollow inner pipe and the outer pipe, and is discharged through the outlet.

In an alternative embodiment of the invention, a plurality of side holes are spaced on the wall of the hollow inner tube near the bottom end.

In an alternative embodiment of the invention, the diameter of the side hole is one eighth of the diameter of the hollow inner tube.

In an alternative embodiment of the invention, the outer tube has a wall thickness of between 3 and 10 mm.

In an optional embodiment of the present invention, the hollow inner tube is made of stainless steel, and the outer tube is made of low carbon steel.

The electroslag remelting process method provided by the embodiment of the invention comprises the following steps: placing a sandwich type cooler in a through hole which is arranged on an electrode blank used for electroslag remelting along the vertical direction, wherein the sandwich type cooler is in insulated connection with a cooling circulation system; in the electroslag remelting process, the distance between the sandwich cooler and the electroslag ingot is adjusted to reduce the temperature of the central part of the electroslag ingot. The temperature of the surface of the inner hole of the electrode blank is close to the temperature of the outer surface under the action of the interlayer type cooler, and in the electroslag remelting process, the distance between the interlayer type cooler and an electroslag ingot is adjusted to reduce the temperature of the central part of the electroslag ingot, so that a metal molten pool is in a shallow flat shape, a liquid phase line is basically vertical to the longitudinal direction, equiaxial crystals are promoted to be formed, and the phenomenon that alloy metal elements are unevenly distributed on the cross section due to crystallization segregation is avoided.

Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the embodiments of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts. The above and other objects, features and advantages of the present invention will become more apparent from the accompanying drawings. Like reference numerals refer to like parts throughout the drawings. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.

Fig. 1 shows a schematic flow chart of an electroslag remelting process method provided by an embodiment of the invention.

Fig. 2 shows a schematic view of a conventional electroslag remelting process.

Fig. 3 is a schematic diagram illustrating an electroslag remelting process according to an embodiment of the present invention.

Fig. 4 shows a schematic structural diagram of a sandwich-type cooler source provided by an embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. The components of embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations.

Thus, the following detailed description of the embodiments of the present invention, presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

It should be noted that: like reference numbers and letters refer to like items in the following figures, and thus, once an item is defined in one figure, it need not be further defined and explained in subsequent figures.

In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings or the orientations or positional relationships that the products of the present invention are conventionally placed in use, and are only used for convenience in describing the present invention and simplifying the description, but do not indicate or imply that the devices or elements referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus, should not be construed as limiting the present invention. Furthermore, the terms "first," "second," "third," and the like are used solely to distinguish one from another and are not to be construed as indicating or implying relative importance. Further, the term "and/or" in the present application is only one kind of association relationship describing the associated object, and means that three kinds of relationships may exist, for example, a and/or B may mean: a exists alone, A and B exist simultaneously, and B exists alone.

Furthermore, the terms "horizontal", "vertical", "overhang" and the like do not imply that the components are required to be absolutely horizontal or overhang, but may be slightly inclined. For example, "horizontal" merely means that the direction is more horizontal than "vertical" and does not mean that the structure must be perfectly horizontal, but may be slightly inclined.

In the description of the present invention, it should also be noted that, unless otherwise explicitly specified or limited, the terms "disposed," "mounted," "connected," and "connected" are to be construed broadly and may, for example, be fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.

The hot work die steel generally contains alloy elements such as Cr, Mo, V, etc. which improve the red hardness of the steel, and liquated carbides and a band-shaped structure due to dendrite segregation are generated during solidification. The liquated carbide and dendritic crystal segregation greatly reduce the toughness and isotropy of steel, the die material adopting the structure can not meet the requirements of severe operating environments such as die-casting, extrusion, precision forging and the like, the service life of the die is very short, and even the phenomenon of integral cracking of the die occurs. The method for homogenizing and strongly forging the high-tropism and high-toughness die steel is developed in China and abroad in recent 20 years, and the typical production process is electric arc furnace (intermediate frequency furnace) → ladle refining → vacuum degassing → ingot casting → electroslag remelting → homogenization → forging → grain refinement → complete annealing. In this method, the homogenization treatment is carried out at 1240-1300 ℃ for a long time (20 hours) in the case of large-section hot-work die steel for electroslag ingots (sections having a thickness of more than 200 mm), and nevertheless, the segregation of liquid carbide and a band-shaped structure due to dendrite segregation are found in the central portion of the steel structure.

It should be noted that the defects existing in the above solutions are the results obtained after the inventors have practiced and studied carefully, and therefore, the discovery process of the above problems and the solutions proposed by the following embodiments of the present invention to the above problems should be the contribution of the inventors to the present invention in the course of the present invention.

In view of this, the present invention employs an electroslag remelting process shown in fig. 1 for a liquid precipitated carbide and a banded structure generated by dendrite segregation of high-grade die steel, so as to substantially eliminate the liquid precipitated carbide and shorten the distance between secondary dendrites. Thereby relieving the pressure of the homogenization process. At the same homogenization treatment temperature and the same homogenization time, the structure is more uniform, and the liquated carbide and the banded structure generated by dendrite segregation are thoroughly eliminated. The steps described in connection with fig. 1 will be described below.

Step S101: and a sandwich type cooler is arranged in a through hole which is arranged on an electrode blank used for electroslag remelting along the vertical direction, and the sandwich type cooler is in insulated connection with a cooling circulation system.

In the embodiment of the application, a sandwich cooler is placed in a through hole which is vertically arranged on an electrode blank used for electroslag remelting, and the temperature of the surface of an inner hole of the electrode blank is close to the temperature of the outer surface under the action of the sandwich cooler, so that a flat metal molten pool is formed.

The interlayer cooler is connected with the cooling circulation system in an insulating way, and a large amount of heat energy generated in the electroslag remelting process is taken away in an air cooling or water cooling mode, so that the central structure of an electroslag remelting steel ingot is improved.

Wherein, after the electrode blank used for electroslag remelting is annealed, a through hole with the diameter of 50-120 mm is processed in the center of the electrode blank along the vertical direction according to the size of the electrode blank. The size of the through hole is determined according to the diameter of the electrode blank, for example, the diameter of the electrode blank is less than 300 mm, and the diameter of the central through hole is 50 mm; 300-500 mm diameter of electrode blank, 80 mm diameter of central through hole; the diameter of the electrode blank exceeds 500 mm, and the diameter of the central through hole is 120 mm.

Wherein, because the center of the electrode blank is processed with a center hole with the diameter of phi 50-120 mm, the center hole of the electrode blank can not be subjected to arc discharge during electroslag remelting, thereby reducing the heat supply of the center part and being beneficial to the formation of a shallow and flat molten pool. Meanwhile, under the action of the sandwich cooler, the overheating temperature near the central hole of the electrode blank is controlled, namely the temperature of the metal melted at the central part of the cooling hole is lower, so that the temperature of the center of a molten pool is reduced, and the whole crystal approaches to the horizontal direction.

Step S102: in the electroslag remelting process, the distance between the sandwich cooler and the electroslag ingot is adjusted to reduce the temperature of the central part of the electroslag ingot.

In the electroslag remelting process, the distance between the interlayer cooler and the electroslag ingot is adjusted to reduce the temperature of the central part of the electroslag ingot, so that the temperature of the central part of the electroslag ingot is controlled, and a molten pool is always in a shallow and flat state in the whole electroslag remelting process from bottom to top. Under the crystallization conditions, the crystallization quality of the whole electroslag ingot can be ensured.

When the distance between the sandwich-type cooler and the slag surface or the surface of the metal molten pool is adjusted along with the melting process of electroslag remelting, the distance between the sandwich-type cooler and an electroslag ingot can be adjusted according to the temperature of a thermocouple placed on the inner surface of the sandwich-type cooler. Optionally, in the initial stage of electroslag remelting, adjusting the distance between the sandwich-type cooler and the electroslag ingot to be a first distance; and adjusting the distance between the sandwich type cooler and the electroslag ingot to be a second distance along with the progress of the electroslag remelting process, wherein the second distance is smaller than the first distance. Further, in the initial stage of electroslag remelting, because the crystallization front edge is close to the bottom seeding plate, the crystallization surface is in a shallow flat state, and the distance between the sandwich cooler and the remelting slag or the metal molten pool is far. Along with the remelting process, the distance between the crystallization surface and the bottom surface is more and more far, the heat transmitted from the bottom surface is less and less, the temperature of the central part of the electroslag ingot is higher and higher, the distance between the cooler and the slag surface or the surface of the metal molten pool is closer and closer (the distance between the cooler and the slag surface is shortened along with the adjustment of the sandwich type cooler), and the central crystallization temperature of the electroslag ingot is controlled to be at a relatively lower level. Under the condition of improving the melting speed of electroslag remelting, the distance between the sandwich cooler and a metal melting pool or a slag surface is properly shortened, so that the internal crystallization quality of an electroslag ingot is ensured.

In order to facilitate understanding of the above process, the description may be made with reference to the schematic diagrams illustrated in fig. 2 and 3. Wherein, fig. 2 is a schematic diagram of the principle of the existing electroslag remelting process; fig. 3 is a schematic view of the principle of an electroslag remelting process according to an embodiment of the present invention.

The above-described sandwich cooler can be described with reference to the schematic structural diagram shown in fig. 4. Wherein the sandwich cooler comprises: the cooling device comprises an outer pipe and a hollow inner pipe arranged in the outer pipe, wherein the top end of the hollow inner pipe exceeds the top end of the outer pipe, the bottom end of the hollow inner pipe is communicated with the outer pipe, an outlet is formed in one side, close to the top end, of the outer pipe, and during cooling, a cooling medium enters from the top end of the hollow inner pipe, flows through an interlayer between the hollow inner pipe and the outer pipe, and is discharged through the outlet.

Optionally, a plurality of side holes are spaced apart on the wall of the hollow inner tube near the bottom end, for example, 8-12 side holes are spaced apart on the wall of the hollow inner tube near the bottom end. In the embodiment, in order to increase the flow of the cooling medium, 8-12 side holes are processed at the lower part of the inner pipe.

Optionally, the diameter of the side hole is one eighth of the diameter of the hollow inner tube. In this embodiment, the outer diameter of the sandwich cooler is smaller than the diameter of the inner hole of the electrode blank, and an air-cooling or water-cooling mode can be adopted according to the requirement. The cooling circulation system is connected with a sandwich type cooler arranged in the electrode blank in an insulating way. The cooling medium absorbs the heat of the center of the electrode blank through heat conduction, convection and heat radiation, so that the temperature difference between the center of the section of the electrode blank and the surface of the excircle is greatly reduced, and the metal molten pool is shallow and flat. Wherein the outer diameter of the sandwich cooler is 45-115 mm, and the outer diameter of the sandwich cooler is smaller than the diameter of an inner hole of the electrode blank.

Optionally, the hollow inner tube is made of stainless steel, and the outer tube is made of low-carbon steel. Optionally, the outer tube has a tube wall thickness of between 3-10 mm. In this embodiment, the cooling medium enters from the top end of the hollow inner tube with poor thermal conductivity, flows through the interlayer between the hollow inner tube and the outer tube, and is discharged through the outlet. Wherein the outer pipe of the sandwich cooler is made of low-carbon steel with good heat conductivity, and the wall thickness is 3-10 mm.

It should be noted that the sandwich cooler is kept at a distance from the metal or remelted slag surface throughout the electroslag remelting process, and the distance needs to be adjusted in the early, middle and late remelting stages. Under the condition of safe production, the distance between the sandwich cooler and the surface of the liquid metal or the remelting slag surface is shortened as much as possible, and the temperature of the central part of the electroslag ingot in the remelting process is reduced. The position of the sandwich cooler is positioned above the slag surface, the position of the sandwich cooler is adjusted according to the requirement, and the sandwich cooler moves upwards along with the remelting process.

It should be noted that, in the present specification, the embodiments are all described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments may be referred to each other.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. An electroslag remelting process method is characterized by comprising the following steps:

placing a sandwich type cooler in a through hole which is arranged on an electrode blank used for electroslag remelting along the vertical direction, wherein the sandwich type cooler is in insulated connection with a cooling circulation system;

in the electroslag remelting process, through adjusting sandwich-type cooler and electroslag ingot's distance to reduce electroslag ingot central part's temperature, wherein, through adjusting sandwich-type cooler and electroslag ingot's distance includes:

adjusting the distance between the sandwich cooler and an electroslag ingot according to the temperature of a thermocouple placed on the inner surface of the sandwich cooler, wherein the distance between the sandwich cooler and the electroslag ingot is adjusted to be a first distance at the initial stage of electroslag remelting; and adjusting the distance between the sandwich type cooler and the electroslag ingot to be a second distance along with the progress of the electroslag remelting process, wherein the second distance is smaller than the first distance.

2. The method according to claim 1, wherein before placing a sandwich cooler in the through hole opened in the vertical direction in the electrode blank for electroslag remelting, the method further comprises:

and forming a through hole on an electrode blank used for electroslag remelting along the vertical direction.

3. The method according to claim 2, wherein the step of forming a through hole in the electrode blank for electroslag remelting in a vertical direction comprises:

and a through hole with the diameter of 50-120 mm is formed in the center of the electrode blank used for electroslag remelting along the vertical direction.

4. The method of claim 1, wherein the sandwich cooler comprises: the cooling device comprises an outer pipe and a hollow inner pipe arranged in the outer pipe, wherein the top end of the hollow inner pipe exceeds the top end of the outer pipe, the bottom end of the hollow inner pipe is communicated with the outer pipe, an outlet is formed in one side, close to the top end, of the outer pipe, and during cooling, a cooling medium enters from the top end of the hollow inner pipe, flows through an interlayer between the hollow inner pipe and the outer pipe, and is discharged through the outlet.

5. The method of claim 4, wherein the hollow inner tube near the bottom end has a plurality of side holes spaced apart in the wall of the tube.

6. The method of claim 5, wherein the diameter of the side hole is one-eighth of the diameter of the hollow inner tube.

7. A method according to any of claims 4-6, wherein the outer tube has a wall thickness of between 3-10 mm.

8. The method of claim 7, wherein the hollow inner tube is made of stainless steel and the outer tube is made of mild steel.