High-Vanadium High-Speed Steel and Preparation Method Therefor, and Use Thereof

The present disclosure claims priority to Chinese Patent Application No. 2024105568452, entitled “HIGH-VANADIUM HIGH-SPEED STEEL AND PREPARATION METHOD THEREFOR, AND USE THEREOF” filed on May 7, 2024 with the China Patent Office, the entire contents of which are incorporated herein by reference.

The present disclosure relates to the technical field of high-vanadium high-speed steel, and specifically to a high-vanadium high-speed steel and preparation method therefor, and use thereof.

The high-vanadium high-speed steel is easy to form coarse eutectic carbides due to its high contents of carbon and alloying elements, so that the segregation is serious and the microstructure is uneven, which seriously limits the mechanical property and the wear resistance. Therefore, the critical factors to improve comprehensive performances of the high-speed steel are defining the size of the carbide and improving the morphology and the microstructure homogeneity of the carbide. The manufacturing methods mainly include the conventional casting, electroslag remelting, spray molding, and powder metallurgy. The conventional casting and electroslag remelting in the above methods are widely used in mass industrial production, but the high-speed steel ingot by the two methods has coarse carbides, which are distributed in a continuous network. In the subsequent heat treatment process, the coarse and continuous network carbides are difficult to eliminate, which results in embrittlement of the grain boundary, so that the strength and toughness are reduced. The spray molding is a rapid solidification technology, which utilizes the refined liquid metal to form the droplet spraying flow after atomization, so that the semi-solidified particles are deposited on the base. The microstructure refinement and the uniform composition of the metal can be realized by the rapid solidification, which eliminates the macro-segregation. However, this method has problems of overspray of the spraying droplets, a low yield, a loose microstructure, and the inherent porosity. Importantly, as the roll material for hot rolling, the high-vanadium high-speed steel exists in the form of the ingot (i.e., it does not have the subsequent thermal mechanical deformation and only needs to carry out the heat treatment). The ingot by the spray molding has a porosity up to about 20%, which is difficult to satisfy the use.

In the above preparation methods, the microstructure is coarse; the distribution is uneven; the heat treatment process is complex and time-consuming, so that it is difficult to realize the desired comprehensive performance.

In view of this, the present disclosure is proposed.

The object of the present disclosure is to provide a high-vanadium high-speed steel and preparation method therefor, and use thereof.

The present disclosure is realized in the following ways.

In a first aspect, the present disclosure provides a preparation method of a high-vanadium high-speed steel, including:

In an optional embodiment, the cooling rate is 45-75° C./h.

In an optional embodiment, the high-vanadium high-speed steel casting billet is heated with a furnace in a tube furnace protected by an inert gas.

In an optional embodiment, the raw materials are smelted by using an intermediate frequency induction furnace at a smelting temperature of 1480-1520° C.; the intermediate frequency induction furnace is vacuumized to 100-400 Pa when smelting; and subsequently the inert gas is filled for protection.

In an optional embodiment, a pressure difference between an inner chamber of the melt and an outer chamber during the melt impacting is 0.05-0.25 MPa, and a spraying speed is 0.75-1.75 m/s.

In an optional embodiment, a speed of the cooling platform moving downward is 50-120 mm/s.

In an optional embodiment, the quenching and tempering treatment includes: preheating the annealing ingot at 600-750° C. for 5-15 min; then carrying out a quenching and holding a temperature at 1000-1230° C., wherein a holding duration is 10-30 min, and then carrying out the quenching in oil to a room temperature; and then tempering 1-4 times at 520-600° C. for 1 h each time, wherein the tempering is carried out each time after air cooling to the room temperature.

In an optional embodiment, the annealed ingot is preheated in a muffle furnace, and quenched in a tube furnace filled with an inert atmosphere.

In a second aspect, the present disclosure provides a high-vanadium high-speed steel ingot, which is prepared by the using preparation method of the high-vanadium high-speed steel as described in any one of the foregoing embodiments.

Preferably, an annealing hardness of the high-vanadium high-speed steel is 315-360 HV.

Preferably, a tempering hardness of the high-vanadium high-speed steel is 863-980 HV.

Preferably, a tempering bending strength of the high-vanadium high-speed steel is 1157-1404 MPa.

Preferably, a vanadium content in the high-vanadium high-speed steel is 4-10%.

Preferably, after the high-vanadium high-speed steel is annealed, vanadium carbide in the ingot is in a shape of sphere, and is uniformly distributed in the base.

Preferably, after the high-vanadium high-speed steel is tempered, the vanadium carbide in the ingot is in a shape of sphere and block, and is distributed dispersedly, wherein vanadium carbide with a coarse size and an irregular shape does not appear.

In a third aspect, the present disclosure provides the use of the high-vanadium high-speed steel, wherein the high-vanadium high-speed steel is as described in the foregoing embodiments, and can be used in the preparation of a roll, a hammer head, a ball mill liner, or a rotor body. The present disclosure includes the following beneficial effects.

The preparation method of the high-vanadium high-speed steel provided by the present disclosure prepares the high-vanadium high-speed steel casting billet by adopting the melt impact method first, which can play roles of crushing grains and crushing primary carbides when performing the melt impacting, so as to improve the strength, toughness, and wear resistance of the high-vanadium high-speed steel, so as to improve the service life. Compared with the prior spray molding method, the biggest difference is that the formed ingot microstructure is dense and uniform, and the carbide is fine. The ingot prepared by the prior spray molding technique has inherent voids. For casting the high-vanadium high-speed steel, the ingot porosity still exists after the heat treatment since the forging process is not included in subsequence, so that the service life is greatly reduced. The method of the present disclosure refines the grains and carbides, and greatly reduces the generation of porosity. The utilization rate of the melt is higher, and there is no waste of the alloy melt. The solidified ingot microstructure is uniform and dense. Additionally, the high-vanadium high-speed steel casting billet prepared by the melt impact method has fine and uniform carbide particles. In order to prevent the aggregation and growth of the carbide, it adopts the rapid spheroidizing annealing process, wherein after it is heated to 820-910° C. with the furnace and held for 2-4 h, it is cooled down to 450-550° C. at a cooling rate larger than 40° C./h; and then it is air cooled to a room temperature, wherein the temperature cooling speed is fast, so as to realize the rapid annealing, so that the carbide in the high-vanadium high-speed steel is not easily agglomerated, and is uniformly distributed in conglobate shape, wherein the rapid spheroidizing annealing process is time-saving and high-efficient, and compared with the conventional annealing process, it greatly shortens the duration; and next, the quenching and tempering are carried out, which comprehensively improves the mechanical property of the high-vanadium high-speed steel.

In order to make the purpose, 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 clearly and completely in the following. Where specific conditions are not indicated in the examples, they shall be performed based on the usual conditions or those recommended by manufacturers. The reagents or instruments used without indication of the manufacturers are conventional products that can be purchased commercially.

The present disclosure provides a preparation method of a high-vanadium high-speed steel, including the following steps.

The raw materials is smelted to form a melt.

In the present disclosure, the raw materials are prepared according to the chemical element composition of vanadium, and are smelted to obtain the melt of the high-vanadium high-speed steel, wherein the raw materials in mass percentage include C: 2.0-2.5%, Cr: 4-6%, W: 2.5-6%, Mo: 3-7%, V: 4-10%, Si: 0.3-0.6%, Mn: 0.3-0.8%, and a balance of Fe.

The raw material is smelted by using an intermediate frequency induction furnace at a smelting temperature of 1480-1520° C.; the intermediate frequency induction furnace is vacuumized to 100-400 Pa when smelting; and subsequently the inert gas is filled for protection.

The melt is impacted to a cooling platform to form a high-vanadium high-speed steel casting billet.

Specifically, when the smelting reaches a preset temperature (1480-1520° C.), the melt is deposited on a pre-cooled cooling platform (such as a water-cooled copper mold) at a spraying speed of 0.75-1.75 m/s by the inert gas, at which time the melt is rapidly solidified and molded, so as to form the high-vanadium high-speed steel casting billet.

The impacting temperature of the high-vanadium high-speed steel of the above composition melt is controlled to be 1480-1520° C., wherein the superheat should not be too high, otherwise the grain of solidification microstructure will be coarse; and the fluidity is poor when it is lower than this temperature, which is not easy to realize the rapid impacting and easy to block the nozzle.

A pressure difference between an inner chamber of the melt and an outer chamber during the melt impacting is 0.05-0.25 MPa, wherein the pressure difference refers to a pressure difference between the chamber of the melt in the crucible and the outer chamber. The specific realizing step can be described as: vacuumizing the chamber formed by the intermediate frequency induction furnace, and filling the inert atmosphere subsequently, at which time there is still a certain pressure difference with the outside; and filling the inert gas flow into the melt when the melt reaches the holding temperature, so as to promote the rapid spraying of the melt. The structure is mainly controlled by means of airflow, which is easy to realize and operate.

The cooling platform can move up and down under the driving of the movement mechanism, so as to control a distance between the cooling platform and the nozzle of the intermediate frequency induction furnace, so as to perform the melt impacting better, wherein the speed of the downward movement of the cooling platform is 50-120 mm/s. The present disclosure found by research that when lower than 50 mm/s, it will have the problem of the lower quality of metallurgical bonding between layers, which is easy to cause a large amount of porosity defects; and when higher than 120 mm/s, the melt of the next layer has arrived before the melt of the last layer forms a valid solidification thickness, which cannot play a crushing effect on the dendritic crystal.

The spheroidizing annealing treatment is carried out on the high-vanadium high-speed steel casting billet to obtain an annealed ingot, wherein the spheroidizing annealing treatment includes heating the high-vanadium high-speed steel casting billet to 820-910° C.; holding for 2-4 h; then cooling down to 450-550° C. at a cooling rate larger than 40° C./h; then air cooling to a room temperature.

In the present disclosure, the high-vanadium high-speed steel casting billet is prepared by the melt impact method based on step S2 first, wherein the microstructure of the formed high-vanadium high-speed steel casting billet is uniform, and the size of the carbide is small. It needs to develop a new annealing process, which can meet the cutting condition, and at the same time prevent the aggregation and growth of the fine carbides. Therefore, the present disclosure adopts the above spheroidizing annealing treatment, which rapidly reduces the temperature to 450-550° C. by a high-speed cooling method. It not only can shorten the duration of the annealing process (the duration of this process is only ¼-⅓ of the duration of the conventional annealing process), which is energy saving and high-efficient, but also can realize that the vanadium carbide in the high-vanadium high-speed steel casting billet is in a shape of sphere; is uniformly distributed; has suitable hardness; and is convenient for the subsequent machining.

The cooling rate can be, for example, 45-75° C./h. In other embodiments of the present disclosure, the cooling rate can be, for example, any one of 45° C./h, 50° C./h, 55° C./h, 60° C./h, 65° C./h, 70° C./h, 75° C./h, or a range value between any two.

The high-vanadium high-speed steel casting billet is heated with a furnace in the tube furnace protected by the inert gas, and is protected by the inert gas, which can avoid the reaction between the chemical elements in the raw material and the oxygen, and at the same time the heating with the furnace can be better controlled.

The quenching and tempering treatment is performed on the annealed ingot, so as to obtain a resultant.

The quenching and tempering treatment includes: preheating the annealed ingot at 600-750° C. for 5-15 min; then carrying out a quenching when holding a temperature at 1000-1230° C., wherein a holding duration is 10-30 min, and carrying out the quenching in oil to a room temperature; and then tempering 1-4 times at 520-600° C. for 1 h each time, wherein the tempering is carried out each time after air cooling to the room temperature. The annealed ingot is preheated in a muffle furnace, and quenched in the tube furnace filled with the inert atmosphere.

Since the high-vanadium high-speed steel contains a large amount of high-melting-point brittle carbides, in the quenching and tempering treatment of the present disclosure, the annealed ingot is fully preheated in 600-750° C. first, which can prevent the annealed ingot from directly cracking during the heat preservation at 1000-1230° C. The large amounts of carbides can be fully dissolved by quenching in the heat preservation at 1000-1230° C.; and the carbides were sphered and isolated due to the high temperature diffusion dissolution and the driving from the interfacial tension, which is beneficial to improving the morphology of the carbide and to improving its toughness. Additionally, the dissolved alloying element is dissolved in the austenite to increase the hardenability of the alloy, and at the next quenching and cooling process, the base transforms to the strong martensite base. During the tempering at 520-600° C., the stress can be eliminated, so as to promote the dispersion and the precipitation of the secondary carbides, which improves the strength and hardness of the base. The multiple tempering process allows the incomplete residual austenite to transform completely, so as to improve the strength and the hardness of the base. The performance of the high-vanadium high-speed steel is improved by multiple quenching and tempering treatments, so that it has a high hardness, and the good strength and toughness.

The high-vanadium high-speed steel prepared by using the above preparation method of the high-vanadium high-speed steel has the excellent mechanical property, wherein the annealing hardness of the high-vanadium high-speed steel is 315-360 HV; the tempering hardness of the high-vanadium high-speed steel is 863-980 HV; and the tempering bending strength of the high-vanadium high-speed steel is 1157-1404 MPa. Meanwhile, the vanadium content in the high-vanadium high-speed steel is 4-10%. After the high-vanadium high-speed steel is annealed, the vanadium carbide in the ingot is in a shape of sphere, and is uniformly distributed in the base. After the high-vanadium high-speed steel is tempered, the vanadium carbide in the ingot is mainly in a shape of sphere and block, and is distributed dispersedly, wherein the vanadium carbide with a coarse size and an irregular shape does not appear.

In the present disclosure, the grain and the primary carbide are crushed by using the impacting effect of the melt, which in turn can improve the strength, toughness, and wear resistance of the high carbon alloy steel, so as to improve the service life. Compared with the prior spray molding method, the biggest difference is that the formed ingot microstructure is dense and uniform, and the carbide is fine. The ingot prepared by the prior spray molding technique has inherent voids. For casting the high-vanadium high-speed steel, the ingot porosity still exists after the heat treatment since the forging process is not included in subsequence, so that the service life is greatly reduced. The preparation method of the high-vanadium high-speed steel provided by the present disclosure prepares the high-vanadium high-speed steel casting billet by using the melt impact method. It refines the grains and carbides, and greatly reduces the generation of porosity. The utilization rate of the melt is higher, and there is no waste of the alloy melt. The solidified ingot microstructure is uniform and dense. Additionally, the high-vanadium high-speed steel casting billet prepared by the melt impact method has fine and uniform carbide particles. In order to prevent the aggregation and growth of the carbide, it adopts the rapid spheroidizing annealing process, which is time-saving and high-efficient, and compared with the conventional annealing process, it greatly shortens the duration. Next, the quenching and tempering treatment is carried out, which can comprehensively improve the mechanical property of the high-vanadium high-speed steel. The high-vanadium high-speed steel obtained can be widely used to prepare the roll, hammer head, ball mill liner, or rotor body.

The features and performance of the present disclosure are described in further detail below in connection with the examples.

The example provided a preparation method of the high-vanadium high-speed steel, including the following steps.

The Example is basically the same as Example 1, and the only difference is that the parameters of step (3) and step (4) are different.

Specifically, the example provided a preparation method of the high-vanadium high-speed steel, including the following steps.

The Example is basically the same as Example 1, and the only difference is that the parameters of step (3) and step (4) are different.

Specifically, the example provided a preparation method of the high-vanadium high-speed steel, including the following steps.

The Example is basically the same as Example 1, and the only difference is that the parameters of step (3) and step (4) are different.