CARBIDE REFINING METHOD OF HIGH-CARBON HIGH-ALLOY STEEL

Abstract

The present disclosure provides a carbide refining method of a high-carbon high-alloy steel. The carbide refining method of a high-carbon high-alloy steel includes the following steps: formulating a raw material according to chemical element compositions of the high-carbon high-alloy steel, and smelting to obtain a high-carbon high-alloy molten steel; performing an overheat treatment on the high-carbon high-alloy molten steel to Tm+(50?100)? C., to obtain a high-carbon high-alloy melt, and making the high-carbon high-alloy melt to be deposited in a preset water-cooled copper mold at a speed of 30?160 g/s by an inert gas, to obtain a high-carbon high-alloy billet through solidification molding; and performing a heat treatment process on the high-carbon high-alloy billet.

Claims

1. A carbide refining method of a high-carbon high-alloy steel, comprising following steps: formulating a raw material according to chemical element compositions of the high-carbon high-alloy steel, and smelting the raw material to obtain a high-carbon high-alloy molten steel; performing an overheat treatment on the high-carbon high-alloy molten steel to Tm+(50?100) ? C., to obtain a high-carbon high-alloy melt, and making the high-carbon high-alloy melt deposited in a preset water-cooled copper mold at a speed of 30?160 g/s by an inert gas, to obtain a high-carbon high-alloy billet through solidification molding; and performing a heat treatment process on the high-carbon high-alloy billet.

2. The carbide refining method of a high-carbon high-alloy steel according to claim 1, wherein the high-carbon high-alloy steel comprises a following chemical element compositions by weight percentage: C: 1.5?2.5%, W: 2.5?10%, Mo: 3?7%, Cr: 4?6%, V: 2?10%, Si: 0.3?0.6%, Mn: 0.3?0.8%, and a balance of Fe.

3. The carbide refining method of a high-carbon high-alloy steel according to claim 1, wherein the heat treatment process comprises high-temperature solution treatment, low-temperature interrupted quenching, and tempering treatment performed in sequence, wherein the high-temperature solution treatment is to keep a temperature at 900?1050? C. for 15?60 minutes; the low-temperature interrupted quenching is to keep a temperature at 700?860? C. for 1?2 hours; and the tempering treatment is to keep a temperature at 520?580? C. for 3?4 hours.

4. The carbide refining method of a high-carbon high-alloy steel according to claim 3, wherein after the high-temperature solution treatment is completed, oil quenching is performed to room temperature, and then low-temperature interrupted quenching is performed; and/or after the low-temperature interrupted quenching is completed, water quenching is performed to a martensite transformation point, oil quenching is performed to room temperature, and then the tempering treatment is performed.

5. The carbide refining method of a high-carbon high-alloy steel according to claim 1, wherein a method for the overheat treatment comprises: vacuumizing a chamber where the high-carbon high-alloy molten steel is located to 100?400 Pa, subsequently filling an inert gas for protection, and then heating the high-carbon high-alloy molten steel to obtain the high-carbon high-alloy melt.

6. The carbide refining method of a high-carbon high-alloy steel according to claim 1, wherein the overheat treatment is performed by a coil heating method.

7. The carbide refining method of a high-carbon high-alloy steel according to claim 5, wherein a method of depositing the melt comprises: filling the inert gas for protection, and after heating the high-carbon high-alloy molten steel to obtain the high-carbon high-alloy melt, continuing to fill the inert gas to make the high-carbon high-alloy melt sprayed to an external chamber.

8. The carbide refining method of a high-carbon high-alloy steel according to claim 1, wherein the high-carbon high-alloy melt is deposited under an effect of pressure difference, and the pressure difference is 0.05?0.25 MPa.

9. The carbide refining method of a high-carbon high-alloy steel according to claim 1, wherein a distance between an outlet of a nozzle of the chamber where the high-carbon high-alloy melt is located and the water-cooled copper mold is 11?20 cm; and/or a water outlet of the water-cooled copper mold has a temperature of 30?45? C.

10. The carbide refining method of a high-carbon high-alloy steel according to claim 9, wherein an outlet of a nozzle is in a round hole shape or a slit shape, and all nozzles are arranged in an array.

11. The carbide refining method of a high-carbon high-alloy steel according to claim 5, wherein the overheat treatment is performed by a coil heating method.

12. The carbide refining method of a high-carbon high-alloy steel according to claim 7, wherein the high-carbon high-alloy melt is deposited under an effect of pressure difference, and the pressure difference is 0.05?0.25 MPa.

13. The carbide refining method of a high-carbon high-alloy steel according to claim 7, wherein a distance between an outlet of a nozzle of the chamber where the high-carbon high-alloy melt is located and the water-cooled copper mold is 11?20 cm; and/or a water outlet of the water-cooled copper mold has a temperature of 30?45? C.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0035] In order to more clearly illustrate technical solutions of examples of the present disclosure, drawings that need to be used in the examples of the present disclosure will be briefly introduced below. It should be understood that the following drawings only show some of the examples of the present disclosure, and therefore should not be regarded as limitation to the scope. For those ordinarily skilled in the art, other related drawings can also be obtained from these drawings without using any inventive efforts.

[0036] FIG. 1 is a microstructure diagram of a billet obtained in Example 1;

[0037] FIG. 2 is a microstructure diagram of a billet obtained in Example 2;

[0038] FIG. 3 is a microstructure diagram of a billet obtained in Comparative Example 1; and

[0039] FIG. 4 is a microstructure diagram of high-carbon high-alloy steel obtained in Example 1.

DETAILED DESCRIPTION OF EMBODIMENTS

[0040] The applicant found that, due to a high carbon content and alloy elements, the high-carbon high-alloy steel is easy to form coarse eutectic carbides, and has serious segregation. A casting state (casting obtained by molding) microstructure of the current high-carbon high-alloy steel is extremely non-uniform, and mainly consists of martensite, residual austenite, and various carbides. The various carbides (such as the commonest MC, M.sub.2C, and M.sub.6C) are non-uniformly distributed, with varied forms, and especially coarse reticulated eutectic carbides are distributed at grain boundary, split the matrix and worsen the service performance. With regard to the high-carbon high-alloy steel casting, refining the carbides and making the same uniformly distributed are particularly crucial for the subsequent thermal-mechanical deformation and improvement for mechanical performance. As the coarse reticulated eutectic carbides of the casting are fragmented by subsequent forging, rolling and other processes, the mechanical performance is seriously affected; and even if forging and rolling processes are used, it is still difficult to make the carbides refined evenly and distributed diffusively, and meanwhile the costs are increased.

[0041] In addition, most of high-carbon high-alloy steel products are castings, that is, thermal mechanical deformation is no longer performed subsequently. There is only the heat treatment, but the heat treatment cannot change the distribution or morphology of the coarse carbides at all. For example, the billet fabricated by the existing spray forming technology have inherent pores, and for cast alloy steel, since the forging process is not included subsequently, pores of the billets after the heat treatment still exist, then the service lifetime is greatly reduced. Therefore, by refining the coarse eutectic carbides, the high-carbon high-alloy steel casting has an initial microstructure with fine carbides, which is extremely important to improve the mechanical performance.

[0042] In the present disclosure, the liquid flow is used to rapidly impact the liquid-solid interface of a self-stirring molten pool, such that a high-speed impact force makes the dendrite fragmented, thereby adding nucleation particles, and creating condition for refining the grains. Then in combination with a specific heat treatment process, it has a significant effect on refining the primary carbides of the high-carbon high-alloy steel billet.

[0043] In order to make objectives, technical solutions, and advantages of the examples of the present disclosure clearer, the technical solutions in the examples of the present disclosure will be described below clearly and completely. If no specific conditions are specified in the examples, they are carried out under normal conditions or conditions recommended by manufacturers. If manufacturers of reagents or apparatuses used are not specified, they are conventional products commercially available.

[0044] A carbide refining method of a high-carbon high-alloy steel according to examples of the present disclosure is specifically described below.

[0045] An example of the present disclosure provides a carbide refining method of a high-carbon high-alloy steel, mainly including preparing a high-carbon high-alloy billet by a melt impact method and performing a heat treatment process, which includes the following steps.

[0046] (1) Preparing the High-Carbon High-Alloy Billet by the Melt Impact Method [0047] S1, formulating a raw material according to chemical element compositions of the high-carbon high-alloy steel by weight percentage, including C: 1.5?2.5%, W: 2.5?10%, Mo: 3?7%, Cr: 4?6%, V: 2?10%, Si: 0.3?0.6%, Mn: 0.3?0.8%, and balance of Fe, and smelting the raw material to obtain a high-carbon high-alloy molten steel; and [0048] S2, vacuumizing a chamber where the high-carbon high-alloy molten steel is located to 100?400 Pa, subsequently filling an inert gas for protection, so that the whole chamber is in an inert atmosphere protection state, and then heating the high-carbon high-alloy molten steel by a coil heating method, wherein overheat treatment is performed to a range higher than a temperature of melting point by 50?100? C., i.e., Tm+(50?100) ? C., so as to obtain a high-carbon high-alloy melt; and continuing to fill the inert gas so that a pressure difference of 0.05?0.25 MPa is formed between the chamber where the high-carbon high-alloy molten steel is located and an external chamber, so as to make the high-carbon high-alloy melt sprayed to the external chamber at a speed of 30?160 g/s under the effect of the pressure difference, and deposited in a pre-set water-cooled copper mold, wherein a distance between an outlet of a nozzle of the chamber where the high-carbon high-alloy melt is located and the water-cooled copper mold is 11?20 cm, and a water outlet of the water-cooled copper mold has a temperature of 30?45? C., thereby obtaining a high-carbon high-alloy billet through solidification molding.

[0049] In the examples of the present disclosure, the raw material is placed in a crucible. A medium-frequency induction furnace is used to smelt the raw material to obtain the high-carbon high-alloy molten steel. The chamber of the medium-frequency induction furnace is in a closed state. The raw material is heated into the molten steel by coil, and then the molten steel is overheated into the melt. A graphite nozzle is provided at the bottom of the crucible. The outlet of the nozzle is in a round hole shape or a slit shape, and all nozzles are arranged in an array. The melt is deposited in the water-cooled copper mold at a certain speed through the nozzles under the effect of pressure difference, and shaped and solidified, to render a high-carbon high-alloy billet with fine carbides.

[0050] (2) Heat Treatment Process [0051] S3, performing high-temperature solution treatment on the high-carbon high-alloy billet, keeping temperature at 900?1050? C. for 15?60 minutes, and performing oil quenching to room temperature; [0052] S4, performing low-temperature interrupted quenching on the billet having undergone step S3, keeping temperature at 700?860? C. for 1?2 hours, performing water quenching to martensite transformation point (point M), and then performing oil quenching to room temperature; and

[0053] S5, performing tempering treatment on the billet having undergone step S4, and keeping temperature at 520?580? C. for 3?4 hours, to obtain the high-carbon high-alloy steel.

EXAMPLE

[0054] The features and performances of the present disclosure are further described below in detail in combination with examples.

Example 1

[0055] The present example provided a high-carbon high-alloy steel, of which a preparation process is as follows: [0056] S1, formulating a raw material in a crucible according to chemical element compositions of the high-carbon high-alloy steel: C: 2.5%, W: 4.1%, Mo: 2.9%, Cr: 5.0%, V: 8.2%, Si: 0.5%, Mn: 0.3%, and balance of Fe, and smelting at a temperature of melting point 1398? C. in a medium-frequency induction furnace, to obtain a high-carbon high-alloy molten steel; [0057] S2, vacuumizing a chamber of the medium-frequency induction furnace to 200 Pa, subsequently filling an inert gas for protection, so that the whole chamber was in an inert atmosphere protection state, and then heating the high-carbon high-alloy molten steel, overheating to 1450? C., i.e., Tm+52? C., to obtain a high-carbon high-alloy melt; and continuing to fill the inert gas so that a pressure difference of 0.15 MPa was formed between the chamber and an external chamber, to promote the high-carbon high-alloy melt in the crucible to be sprayed to the external chamber at a speed of 100 g/s through a nozzle at the bottom of the crucible under the effect of the pressure difference, and deposited in a pre-set water-cooled copper mold, wherein a distance between an outlet of a nozzle and the water-cooled copper mold was 15 cm, and a water outlet of the water-cooled copper mold had a temperature of 40? C., such that a high-carbon high-alloy billet was obtained through solidification molding; [0058] S3, performing high-temperature solution treatment on the high-carbon high-alloy billet, keeping temperature at 1000? C. for 30 minutes, and then performing oil quenching to room temperature; [0059] S4, performing low-temperature interrupted quenching on the billet having undergone step S3, keeping temperature at 800? C. for 1.5 hours, and performing water quenching to martensite transformation point (point M), and then performing oil quenching to room temperature; and [0060] S5, performing tempering treatment on the billet having undergone step S4, and keeping temperature at 550? C. for 3.5 hours, to obtain the high-carbon high-alloy steel.

Example 2

[0061] The present example provided a high-carbon high-alloy steel, of which a preparation process was different from that of Example 1 in that the pressure difference was controlled to be 0.25 MPa.

Example 3

[0062] The present example provided a high-carbon high-alloy steel, of which a preparation process was different from that of Example 1 in that a spraying speed was 50 g/s.

Comparative Example 1

[0063] The present comparative example provided a high-carbon high-alloy steel, of which a preparation process was different from that of Example 1 in that the high-carbon high-alloy molten steel was heated to 1450? C., and poured according to the conventional die casting method to obtain a billet, and then the billet was cooled to room temperature.

Comparative Example 2

[0064] The present comparative example provided a high-carbon high-alloy steel, of which a preparation process was different from that of Example 1 in that the high-carbon high-alloy molten steel was heated to 1450? C., and poured according to the conventional die casting method to obtain a billet, and then a heat treatment process was performed in the same manner as that of Example 1.

Comparative Example 3

[0065] The present comparative example provided a high-carbon high-alloy steel, of which a preparation process was different from that of Example 1 in that the high-carbon high-alloy billet was heated to 800? C., kept at the temperature for 4 h, and naturally cooled with furnace.

Comparative Example 4

[0066] The present comparative example provided a high-carbon high-alloy steel, of which a preparation process was different from that of Example 1 in that the overheat treatment was not performed, while the molten steel obtained from the smelting was sprayed, but due to a high viscosity, the alloy melt could not be smoothly sprayed from the nozzle, and easily blocked the nozzle.

[0067] FIG. 1 is a microstructure diagram of the billet in Example 1, FIG. 2 is a microstructure diagram of the billet in Example 2, and FIG. 3 shows microstructure morphology of the billet in Comparative Example 1. It is noted that FIG. 1-FIG. 3 all show original microstructures having not undergone heat treatment.

[0068] It is found through analysis that carbides in the microstructure show two types, wherein gray carbides are MC-type carbides, and white carbides are M.sub.2C carbides. The billets in FIG. 1 and FIG. 2 are formed according to a specific melt impact method, wherein the gray carbides are in a uniformly dispersed granular shape, very fine and uniform, and the white carbides are in a strip shape or rod shape; and the billet in FIG. 2 is subjected to a stronger impact effect, the carbides are finer than the carbides of the billet in FIG. 1. The gray carbides in the billet in FIG. 3 are of various shapes, including petaloid shape and coarse reticulated shape, severely aggregated, and split the matrix, and the white carbides are in a strip shape or a rod shape, and larger in size than those in FIG. 1 and FIG. 2.

[0069] In addition, Image-Pro Plus was used to perform statistical analysis on the sizes of two types of carbides in different billet microstructures, as shown in the following table:

TABLE-US-00001 Average size (?m) MC-type carbide M.sub.2C carbide Example 1 3.4 9.6 Example 2 2.5 18.7 Example 3 4.9 28.1 Comparative Example 1 11.6 50.5 Comparative Example 2 13.8 / Comparative Example 4 / /

[0070] FIG. 4 is a microstructure diagram (optical micrograph) of the high-carbon high-alloy steel (the billet is subjected to a specific heat treatment) in Example 1. It can be seen from FIG. 4 that the microstructure in the final state mainly has MC and M.sub.6C carbides.

[0071] By comparing FIG. 1 and FIG. 4, it is analyzed that a reason of the microstructure change is that the MC-type carbides in the billet are stable, and have no change in the subsequent heat treatment; and the M.sub.2C carbides are in a metastable phase, and will be decomposed into MC and M.sub.6C in the subsequent heat treatment. After the billet has undergone the heat treatment, the size of the M.sub.2C carbides can not be counted, which mainly consist of the MC and M.sub.6C carbide.

[0072] The microstructure of the high-carbon high-alloy steel (the billet does not undergo a specific heat treatment) in Comparative Example 3 is composed of pearlites and granular carbides. Compared with the alloy steel in Example 1, the alloy steel can be considered as in an intermediate state (spheroidizing annealing), aiming at reducing the alloy hardness and preparing for subsequent quenching-tempering in structure.

[0073] To sum up, the carbide refining method of a high-carbon high-alloy steel of the examples of the present disclosure can render the high-carbon high-alloy steel with a dense structure and fine carbides.

[0074] The above is merely for examples of the present disclosure and not intended to limit the scope of protection of the present disclosure. For those skilled in the art, various modifications and variations could be made to the present disclosure. Any modifications, equivalent substitutions, improvements and so on, within the spirit and principle of the present disclosure, should be covered within the scope of protection of the present disclosure.