CN114990425A - Cutter for crushing scrap steel and preparation and repair method thereof - Google Patents

Abstract

The application provides hot work die steel, which comprises the following components in percentage by weight: 0.35-0.4%, Si: 1.2-2.2%, Mn: 2.1-2.8%, Cr: 4.5-5.8%, S: 0.03% or less, Al: 0.01-0.2%, V: 0.01-0.15%, Mo: 0.1-0.3%, RE: 0.05 to 0.15 percent; ni: 0.2-0.4%, Nb 0.45-0.85%, Ti: 0.1-0.3, and the balance of Fe and inevitable impurity elements. Wherein the ratio of Ni: al = 1-1.5, (Nb + V + Ti): 3/4C is between 2.5 and 3.5. The tensile strength of the hot-work die steel can reach over 1960MPa, the yield strength reaches over 1650MPa, and the Charpy U-shaped notch impact power is not less than 38J/cm ² The hardness can reach more than 57 HRC. The die steel made of the die steel is subjected to laser remelting repair by using high-entropy alloy powder with the component of CoCrNbFeMnCx, wherein x is 0.1-0.5.

Description

Cutter for crushing scrap steel and preparation and repair method thereof

Technical Field

The invention belongs to the technical field of material crushing equipment, and particularly relates to the field of a cutter for crushing scrap steel.

Background

At present, with the continuous development of green economy in China, the recycling of steel materials becomes an important part in circular economy. However, in the process of crushing and recycling scrap steel, as hardening materials are inevitably mixed in scrap iron and scrap steel bars, the crushing cutter is easy to collapse, break corners, crack and the like, so that the cutter is very high in consumption in the use process, the cutter needs to be disassembled and replaced once being damaged, the cost of the crushing cutter is high, the cutter replacement influences the working time of the crushing machine, great influence is brought to the continuity of production of enterprises, and meanwhile, the production cost of the enterprises is greatly improved. The existing cutter has low strength, quick abrasion, short service life and easy fracture, and can not meet the existing market demand.

Therefore, the development of a cutter with excellent comprehensive performance and long service life and convenient repair is a problem to be solved urgently.

Disclosure of Invention

The invention provides a cutter suitable for recycling scrap iron, which has excellent hardness uniformity and good matching of strength and toughness, and the service life of the cutter is obviously prolonged compared with that of the existing cutter for crushing. Another object of the present invention is to provide a method for manufacturing the tool, and a method for repairing a tool manufactured using the tool steel.

According to the tool steel, the tool steel with high strength, high toughness, high wear resistance and hardness uniformity is obtained by the compound addition of Nb, V, Ti and RE and the cooperation of an online subcritical spheroidizing annealing and quenching process, the addition amount of V, Mo is reduced, the cost is obviously reduced, and the tool steel is suitable for large-scale popularization and use. Meanwhile, the application also provides a method for repairing the cutter by adopting the high-entropy alloy matched with the cutter steel, so that the whole service life of the cutter is prolonged, and the production cost of an enterprise is obviously reduced.

The specific technical scheme is as follows:

a cutter is prepared from the following steel, and comprises the following components in percentage by mass:

c: 0.35-0.4%, Si: 1.2-2.2%, Mn: 2.1-2.8%, Cr: 4.5-5.8%, S: 0.03% or less, Al: 0.01-0.2%, V: 0.01-0.15%, Mo: 0.1-0.3%, RE: 0.05 to 0.15 percent; ni: 0.2-0.4%, Nb 0.45-0.85%, Ti: 0.1-0.3, and the balance of Fe and inevitable impurity elements.

Preferably, the alloy composition satisfies the following formula:

ni: al = 1-1.5 equation 1

(Nb + V + Ti): 3/4C is in the range of 2.5-3.5 formula 2

The steel for the cutter is manufactured by the following process steps:

(1) smelting and alloying, smelting in an electric furnace, tapping, and refining outside an LF furnace, wherein Al-Si wires are firstly added into steel for deoxidation treatment during the refining outside the furnace, and then Al-RE intermediate alloy is added into the steel for treatment;

(2) casting under a protective atmosphere to obtain a casting blank;

(3) reheating the steel billet at 1180-1230 ℃, and controlling soaking time at 2-8 h;

(4) rolling: controlling the initial rolling temperature to be 1120-1200 ℃, the final rolling temperature to be 820-890 ℃, the cooling rate to be 5-15 ℃/s and the final cooling temperature to be 520-580 ℃;

(5) an online isothermal spheroidizing annealing process: after finishing rolling, raising the temperature to a first-stage isothermal annealing temperature of 820-840 ℃ on line, wherein the temperature raising rate is 2-4 ℃/s, and the annealing time is 1-2 h; the isothermal annealing temperature of the second stage is 720-760 ℃, and the annealing time is 4-8 h;

(6) quenching: the quenching temperature is 980-1040 ℃, the temperature is kept for 30-60min, and vacuum quenching is adopted;

(7) and (3) tempering immediately after quenching, wherein in the tempering process, firstly, the precipitation of carbide is promoted through high-temperature tempering at 520-580 ℃, the hardness of the steel is effectively improved, and then, the stress of the steel is reduced through low-temperature tempering at 280-320 ℃, the toughness is improved, so that the cutter steel with the toughness meeting the requirement is obtained.

The tensile strength of the steel for the cutter can reach over 1960MPa, the yield strength reaches over 1650MPa, and the Charpy U-shaped 5mm notch impact toughness is more than or equal to 38J/cm ² The hardness can reach more than 57 HRC.

Laser surface alloying is a surface repairing technique, which uses high-energy laser beam as heat source to quickly heat and melt the base material, and injects reinforcing powder into molten pool, so as to form a new surface alloying layer based on the original base material. The technology can effectively repair the damage shown by the cutter, and obtain a new repair layer with high hardness and wear resistance. The invention also provides a repair method for preparing the cutter by the cutter steel, which adopts high-entropy alloy powder with the components of CoCrNbFeMnCx to carry out laser remelting repair, wherein x is 0.1-0.5, Body Centered Cubic (BCC) + Face Centered Cubic (FCC) can be formed in rapid cooling after laser remelting, a two-phase solid solution can be formed, the strength and the hardness are considered, M23C6 or M7C3 type carbide is formed, and the carbide is dispersed in an alloy structure to generate a dispersion strengthening effect, so that the hardness and the wear resistance of the high-entropy alloy are improved.

The specific laser remelting repair process comprises the following steps:

1): carrying out pretreatment such as cleaning, sand blasting and the like on the surface of a tool to be repaired;

2): performing stress relief annealing on the cutter, and performing stress relief annealing at the temperature of 220-;

3): performing remelting repair with laser power of 2200-;

4) and (5) repairing the cutter for subsequent treatment, and grinding the repaired cutter to reach the designed size and precision of the cutter.

The function of each element of the invention is as follows:

C：0.35-0.4%

the main austenitizing element and the main strengthening element have more obvious precipitation hardening effect along with the increase of the carbon content, and in order to ensure the precipitation of enough carbides and the secondary hardening phenomenon caused by dispersion precipitation on a quenched martensite matrix in the tempering process, the C content in the invention is not less than 0.35 percent.

Si：1.2-2.2%

Si is a deoxidizing element, does not form carbide in steel, and can be dissolved in ferrite to affect the strength of steel. After the steel is tempered at 450-650 ℃, the secondary hardening effect of the steel can be promoted, the high-temperature strength of the steel is improved, the oxidation resistance of the steel at high temperature can be effectively improved, and the corrosion resistance of the steel in an oxidation medium is improved. In order to obtain the above properties, the Si content is controlled to be 1.2-2.2% in the present invention.

Mn：2.1-2.8%

Mn plays a role of solid solution strengthening in steel, and also strongly lowers the Ms point of steel, thereby increasing the hardenability of steel.

Cr：3.5-5.0%

Cr is an essential element for improving the phase transformation behavior (hardenability) and at the same time increasing the strength of the steel by forming carbides. If the Cr amount is less than 3.5%, the effects of lowering the transformation temperature and refining the microstructure are insufficient, and the hardness and impact value cannot be sufficiently obtained. Furthermore, the corrosion resistance required of the tool exposed to a corrosive environment increases with the amount of Cr.

V：0.01-0.15%

Vanadium, a carbide-forming element, the use of low vanadium content in the present invention reduces the number of potential crack initiation sites, thus also improving the high temperature impact toughness of the material of the present invention.

Ni：0.4-0.6%

Ni can reduce the heat conductivity of the matrix, intermetallic compounds are precipitated with Al in the heat treatment process, and the precipitated phases can keep coherent relation with the matrix, thereby improving the heat conductivity. The average size of precipitated phases is less than 10nm, so that the comprehensive performance of the steel can be improved.

Al：

The aluminum element and the nickel element can form a NiAl intermetallic compound in a secondary tempering process at 400-550 ℃. Al is added in an amount of 0.4 or less, and Ni: al is between 1 and 1.5.

Ti：0.1-0.3%，Nb:0.1-0.25%

The precipitation of large amounts of Cr carbides in tool steels leads to a decrease in thermal conductivity and, in addition, the dimensions are typically of the order of 100nm, which also reduces toughness. Through the reasonable proportioning design of the alloy (Nb + V + Ti): 3/4C is 2.5 to 3.5, the volume fraction of carbide is controlled, the size of Nb + V + Ti precipitates is small, and when this condition is satisfied, the size of Mo and W primary precipitates is less than 100nm, and the size of secondary precipitates is less than 10nm, so the toughness is good. Ti, V and Nb are all strong carbide forming elements, when the three elements are added in a composite way, the secondary hardening effect of the steel is further improved, and when the following formula is met,

2.5≤(Nb+V+Ti)：3/4C≤3.5

can ensure the precipitation of enough fine carbide in the steel and improve the toughness under the condition of meeting the hardness requirement.

Mo：0.1-0.3%

Mo is an important carbide-forming element, and particularly, it is possible to greatly improve the hardness of a tempered steel material by temper hardening and to improve the wear resistance of the steel material.

RE：0.05-0.15%

RE can purify steel, change the form of inclusions, and enable the inclusions to be dispersed and distributed in the crystal instead of sulfide inclusions distributed along the grain boundary, thereby improving the toughness.

By adopting a subcritical on-line isothermal spheroidizing annealing process and utilizing the waste heat after rolling, the production efficiency is improved. And a pearlite structure with fine interlamellar spacing is obtained through a low-temperature spheroidizing process, and spheroidized granular pearlite is fine and dispersedly distributed and is prepared for pre-structure quenching. The quenching process after the quenching is matched, the structure of the steel is a mixed structure of ferrite and martensite, and the martensite is finely dispersed and distributed, and during the period of the ferrite being mixed, the cutter steel with good combination of hardness and toughness is obtained.

In the tempering process, firstly, the precipitation of carbide is promoted through high-temperature tempering at 520-580 ℃, the hardness of steel is effectively improved, and then the stress of the steel is reduced through low-temperature tempering at 280-320 ℃, so that the toughness is improved, and the cutter steel with the toughness meeting the requirement is obtained.

Description of the figures

FIG. 1 shows the structure after on-line isothermal spheroidizing annealing using subcritical.

Detailed Description

The specific components of examples 1-5 and comparative examples 1-5 are shown in Table 1 below and were prepared according to the following procedure:

smelting and alloying, smelting in an electric furnace, tapping, LF external refining, wherein during the external refining, Al-Si wires are firstly added into steel for deoxidation treatment, and then Al-RE intermediate alloy is added into the steel for treatment;

casting under a protective atmosphere to obtain a cast ingot;

the reheating temperature of the steel billet is 1180-1230 ℃, and the soaking time is controlled to be 2-8 h.

Rolling: controlling the initial rolling temperature to be 1120-1200 ℃, the final rolling temperature to be 820-890 ℃, the cooling rate to be 5-15 ℃/s and the final cooling temperature to be 520-580 ℃;

an online isothermal spheroidizing annealing process: after the rolling finish cooling is finished, immediately heating to the first-stage isothermal annealing temperature of 820-840 ℃, wherein the heating rate is 2-4 ℃/s, and the annealing time is 1-2 h; the isothermal annealing temperature of the second stage is 720-760 ℃, and the annealing time is 4-8 h.

Quenching: the quenching temperature is 980-1040 ℃, the temperature is kept for 30-60min, and vacuum quenching is adopted;

and tempering immediately after quenching, wherein in the tempering process, firstly, the precipitation of carbide is promoted through high-temperature tempering at the temperature of 520-580 ℃, the hardness of the steel is effectively improved, and then the stress of the steel is reduced through low-temperature tempering at the temperature of 280-320 ℃, the toughness is improved, so that the cutter steel with the toughness meeting the requirement is obtained.

TABLE 1

The mechanical properties of the samples 1 to 5 and B1 to B5 after the secondary tempering treatment were performed. See table 2 for specific results.

TABLE 2

As can be seen from table 2, B1 has a significant decrease in hardness due to the absence of Nb and Mo, B2 has a significant decrease in toughness due to the absence of RE, and B3 and B5 have a significant decrease in hardness and toughness due to the fact that they do not satisfy the requirement of equation 2. B4 does not satisfy formula 1 and the hardness is insufficient.

Cutter a was made from the cutter steel described in example 1, and the use test was performed under the same conditions as those of cutter B made from H13 steel, which is commonly used in the art. The service life of the cutter A can reach 13000-15000 tons of crushing amount, and the service life of the cutter B is 7000-9000 tons of crushing amount.

Repairing the damaged cutter A, wherein the laser remelting repair process comprises the following steps:

1): carrying out pretreatment such as cleaning, sand blasting and the like on the surface of a tool to be repaired;

2): performing stress relief annealing on the cutter, and performing stress relief annealing at the temperature of 220-;

3): remelting repair is carried out, the laser power is 3200W, the scanning speed is controlled to be 20mm/s under the condition that the flow of inert protective gas is 25L/min, the powder feeding amount is 5.5g/s, and the lap joint amount is 55%, wherein the remelting powder is CoCrNbFeMnC0.3;

4) and (5) repairing the cutter for subsequent treatment, and grinding and polishing the repaired cutter to reach the designed size and precision of the cutter.

The service life of the repaired cutter can still reach about 0.8 time of that of the original cutter, the service life of the whole cutter is obviously prolonged, and the cost is effectively reduced.

The invention has been described in an illustrative manner, and it is to be understood that the invention is not limited to the specific embodiments described, and that various modifications may be made without departing from the spirit and scope of the invention.

Claims (6)

1. A steel for a cutting tool, characterized in that: the composite material comprises the following components in percentage by mass:

c: 0.35-0.4%, Si: 1.2-2.2%, Mn: 2.1-2.8%, Cr: 4.5-5.8%, S: 0.03% or less, Al: 0.01-0.2%, V: 0.01-0.15%, Mo: 0.1-0.3%, RE: 0.05 to 0.15 percent; ni: 0.2-0.4%, Nb 0.45-0.85%, Ti: 0.1-0.3, and the balance of Fe and inevitable impurity elements.

2. A die steel according to claim 1, wherein the composition satisfies the following formula:

ni: al = 1-1.5 formula 1

(Nb + V + Ti): 3/4C is in the range of 2.5 to 3.5, equation 2.

3. A method for producing the steel for cutting tools according to claim 1 or 2, characterized in that:

the manufacturing method comprises the following steps:

(1) smelting and alloying, smelting in an electric furnace, tapping, LF external refining, wherein during the external refining, Al-Si wires are firstly added into steel for deoxidation treatment, and then Al-RE intermediate alloy is added into the steel for treatment;

(2) casting under a protective atmosphere to obtain a casting blank;

(3) reheating the steel billet at 1180-1230 ℃, and controlling soaking time at 2-8 h;

(4) rolling: controlling the initial rolling temperature to be 1120-1200 ℃, the final rolling temperature to be 820-890 ℃, the cooling rate to be 5-15 ℃/s and the final cooling temperature to be 520-580 ℃;

(5) an online isothermal spheroidizing annealing process: after the rolling finish cooling is finished, immediately heating to the first-stage isothermal annealing temperature of 820-840 ℃, wherein the heating rate is 2-4 ℃/s, and the annealing time is 1-2 h; the isothermal annealing temperature of the second stage is 720-760 ℃, and the annealing time is 4-8 h;

(6) quenching: the quenching temperature is 980-1040 ℃, the temperature is kept for 30-60min, and vacuum quenching is adopted;

(7) and (3) tempering immediately after quenching, wherein in the tempering process, firstly, the precipitation of carbide is promoted through high-temperature tempering at 520-580 ℃, the hardness of the steel is effectively improved, and then, the stress of the steel is reduced through low-temperature tempering at 280-320 ℃, the toughness is improved, so that the die steel with the toughness meeting the requirement is obtained.

4. A method for producing the steel for cutting tools according to claim 3, characterized in that:

the tensile strength of the prepared steel for the cutter can reach over 1960MPa, the yield strength reaches over 1650MPa, and the Charpy U-shaped 5mm notch impact toughness is more than or equal to 38J/cm ² The hardness can reach more than 57 HRC.

5. A cutting tool made of the cutting tool steel according to claims 1 and 2 or the cutting tool steel obtained by the method of manufacturing the cutting tool steel according to any one of claims 3 to 4.

6. A process for repairing a cutting tool according to claim 5, wherein:

the specific laser remelting repair process comprises the following steps:

1): carrying out pretreatment such as cleaning, sand blasting and the like on the surface of a tool to be repaired;

2): performing stress relief annealing on the cutter, and performing stress relief annealing at the temperature of 220-;

3): performing remelting repair with laser power of 2200-;

4) and repairing the cutter for subsequent treatment, and grinding the repaired cutter to achieve the designed size and precision of the cutter.

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