WO2024087788A1 - Steel for forged bucket teeth of excavator, and preparation method therefor - Google Patents

Abstract

Disclosed in the present invention are steel for forged bucket teeth of an excavator, and a preparation method therefor. The steel for forged bucket teeth of an excavator comprises the following chemical components in percentages by mass: 0.30-0.37% of C, 1.25-1.55% of Si, 1.00-1.30% of Mn, less than or equal to 0.035% of P, less than or equal to 0.035% of S, 1.20-1.50% of Cr, 0.020-0.050% of Al and the balance of Fe and inevitable impurities. The preparation process therefor comprises converter smelting, LF refining, RH vacuum treatment, continuous casting, heating, rolling and cooling. Low-cost alloy elements are used in the present invention for component design, and the optimal component proportion is used, so as to obtain the steel for forged bucket teeth with a yield strength larger than or equal to 1500 MPa, a tensile strength larger than or equal to 1800 MPa, a 20°C longitudinal impact absorbing energy larger than or equal to 45 J, a rolling-state hardness of 220-240 HB and good hardenability.

Description

Steel for forging bucket teeth of excavator and preparation method thereof Technical Field

The invention relates to a steel material and a preparation method thereof, and in particular to a steel material for forging bucket teeth of an excavator and a preparation method thereof.

Background technique

Bucket teeth are consumable parts in excavator operation. According to different working scenarios, a pair of bucket teeth can usually be used for 15-45 days in earthwork operations and 5-10 days in mining operations. Their failure is mainly due to the continuous wear of the tooth tip until the tooth root is exposed and completely scrapped. A pair of wear-resistant bucket teeth with excellent performance can greatly reduce the replacement and maintenance time and improve operating efficiency. This requires that the steel used for bucket teeth has good structural uniformity, high hardenability, wear resistance and excellent mechanical properties. Low-cost and high hardenability design and matching with the feeding and water quenching process of downstream users are the key difficulties in the design and production of forged bucket tooth steel.

Summary of the invention

Purpose of the invention: The present invention aims to provide a steel for forged bucket teeth of an excavator having excellent mechanical properties; another purpose of the present invention is to provide a method for preparing the steel for forged bucket teeth of an excavator, which adopts the composition design of low-cost alloys C, Mn, Si, Cr and the most optimized production process, so that the steel has good structural uniformity, high hardenability, wear resistance and excellent mechanical properties.

Technical solution: The chemical composition of the steel for forging bucket teeth of excavators described in the present invention contains, by mass percentage, the following: C: 0.30-0.37%, Si: 1.25-1.55%, Mn: 1.00-1.30%, P: ≤0.035%, S: ≤0.035%, Cr: 1.20-1.50%, Al: 0.020-0.050%, and the remainder is Fe and unavoidable impurities.

The method for preparing the steel for forging bucket teeth of an excavator comprises the following steps:

(1) Converter smelting: The main furnace materials are scrap steel + molten iron. During the smelting process, lime and magnesite are added to adjust the slag system, silicon manganese, ferrosilicon and ferrochrome are added to roughly adjust the composition, and aluminum blocks are used for deoxidation after steel is tapped;

(2) LF refining: Complete composition adjustment to control each element within the internal control range, deoxidize and remove inclusions, feed aluminum wire, and use silicon carbide to deoxidize the slag surface throughout the LF process;

(3) RH vacuum treatment: vacuum treatment is used to remove impurities and avoid hydrogen embrittlement;

(4) Continuous casting: large square billet continuous casting machine is used for production, full protection casting is used to prevent secondary oxidation of molten steel, and low superheat casting is used;

(5) Heating: The billet is first preheated to make the surface temperature of the billet basically consistent with the core temperature, and then heated to above 1200°C;

(6) Rolling and cooling: After the ingot leaves the heating furnace, high-pressure water is used to remove phosphorus. The rolling temperature is controlled at 1040-1140℃. The final rolling is controlled by a KOCKS unit. After rolling, a long cooling bed is used for slow cooling, and the cooling bed is covered with an insulation cover. The cooling bed is shaken at a uniform speed to cool the round steel slowly, improve the straightness of the material and release stress.

Furthermore, the hydrogen content in the molten steel after the vacuum treatment in step (3) is ≤2ppm.

Furthermore, in the continuous casting process described in step (4), the superheat of the first furnace of the tundish is controlled to be ≤40°C, the continuous casting furnace is controlled at 10-30°C, and the casting speed is maintained at 0.80-0.90m/min.

Furthermore, the heating temperature in step (5) is specifically ≤950°C in the preheating stage, 1050-1180°C in the first heating stage, 1200-1290°C in the second heating stage, 1200-1270°C in the equalizing stage, and the total heating time is ≥210min.

Furthermore, in step (6), the dephosphorization pressure is controlled to be greater than 18 MPa; and the final rolling temperature is 800-870°C.

Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: the steel for forging bucket teeth of excavators described in the present invention does not add high-cost alloy elements such as Mo, Ni, Ti, and W, has the advantage of low cost, and at the same time has excellent performance, yield strength ≥1500MPa, tensile strength ≥1800MPa, 20℃ longitudinal impact absorption energy ≥45J, hardenability J1.5: 54-56HRC, J8: 52-55HRC, J15: 50-52HRC, J20: 48-50HRC, J30: 47-49HRC, rolled hardness 220-240HB.

Detailed ways

The technical solution of the present invention is further described below in conjunction with embodiments.

Take 5 batches of production as examples, namely Examples 1 to 5, and the preparation method is as follows:

(1) Converter smelting

The main furnace materials are scrap steel + molten iron. During the smelting process, lime, magnesite, etc. are added to adjust the slag system. Some silicon manganese, ferrosilicon and ferrochrome are added to roughly adjust the composition. Aluminum blocks are used for deoxidation after steelmaking.

The specific process parameters are as follows:

(2) LF refining

Complete the composition adjustment to control each element within the internal control range, deoxidize and remove inclusions, feed aluminum wire according to the content of sample 1 (Alt) to make (Alt) ≥ 0.040%, use silicon carbide to deoxidize the slag surface during the LF process, and feed aluminum wire before entering the RH to make (Alt) Reaching 0.035%.

The specific process parameters are as follows:

(3) RH vacuum treatment

Through vacuum treatment, degassing and inclusion removal, the hydrogen content in the molten steel is reduced to ≤2ppm to avoid hydrogen embrittlement.

The specific process parameters are as follows:

(4) Continuous casting

It is produced by a 5-machine 5-strand large square billet continuous casting machine, with full protection casting to prevent secondary oxidation of molten steel, low superheat casting, superheat of the first furnace of the tundish is controlled at ≤40℃, the continuous casting furnace is controlled at 10-30℃, the casting speed is kept constant at 0.85m/min, the crystallizer electromagnetic stirring adopts 380A*2HZ, the end electromagnetic stirring parameter is 520A*6HZ, and the automatic liquid level control keeps the crystallizer liquid level fluctuation within ±5mm. If it exceeds, it will be scrapped.

(5) Heating

Due to the high alloy content of the steel, the continuous casting billet has large structural stress and cooling stress, which is prone to heating defects. In terms of heating process. The billet is first fully preheated before entering the furnace, so that the surface temperature of the billet is basically consistent with the core temperature, and then quickly heated to above 1200℃. The production of bucket tooth steel is controlled according to the preheating section ≤950℃, heating section 1100℃, heating section 2 1220℃, soaking section 1220℃, and total heating time ≥210min.

(6) Rolling

After the ingot is taken out of the heating furnace, high-pressure water is used to remove phosphorus, and the dephosphorization pressure is controlled to be greater than 18MPa. The rolling temperature is controlled at 1040-1140℃, and the final rolling is controlled by a KOCKS unit. After rolling, a long large cooling bed is used for slow cooling. The cooling bed is covered with a heat preservation cover, and the cooling bed is shaken at a uniform speed to slowly cool the round steel, thereby improving the flatness of the material and releasing the stress. Under the process of the present invention, the steel does not need to be slowly put into the pit.

The specific process parameters are as follows:

Finished product test results

(1) Chemical composition

The chemical composition and content of the steel for forging bucket teeth of the excavator described in Examples 1-5 are as follows (%):

(2) Low magnification

The low multiples of rolled materials are as follows (grades):

(3) Hardness and mechanical properties of rolled materials

Control the final rolling temperature and slow cooling in the insulation cover of the cooling bed to reduce the internal stress of the rolled material. After the round steel is processed into a Φ25mm blank, it is quenched at 930±15℃ water cooling and tempered at 230±10℃ water cooling, and the mechanical properties are as follows.

(4) Non-metallic inclusions

The non-metallic inclusions are as follows (grade):

(5) Hardenability

Hardenability data are as follows (HRC):

The bucket tooth steel produced according to the above process can be cold sheared by users to improve their production efficiency. After heat treatment, the bucket tooth products have uniform hardness, stable product performance, good wear resistance and great cost advantages.

Claims (7)

A steel for forging bucket teeth of an excavator, characterized in that its chemical composition, in terms of mass percentage, contains: C: 0.30-0.37%, Si: 1.25-1.55%, Mn: 1.00-1.30%, P: ≤0.035%, S: ≤0.035%, Cr: 1.20-1.50%, Al: 0.020-0.050%, and the remainder is Fe and unavoidable impurities. A method for preparing the steel for forging bucket teeth of an excavator according to claim 1, characterized in that the method comprises the following steps: (1) Converter smelting: The main furnace materials are scrap steel + molten iron. During the smelting process, lime and magnesite are added to adjust the slag system, silicon manganese, ferrosilicon and ferrochrome are added to roughly adjust the composition, and aluminum blocks are used for deoxidation after steel is tapped; (2) LF refining: Complete composition adjustment to control each element within the internal control range, deoxidize and remove inclusions, feed aluminum wire, and use silicon carbide to deoxidize the slag surface throughout the LF process; (3) RH vacuum treatment: vacuum treatment is used to remove impurities and avoid hydrogen embrittlement; (4) Continuous casting: large square billet continuous casting machine is used for production, full protection casting is used to prevent secondary oxidation of molten steel, and low superheat casting is used; (5) Heating: The billet is first preheated to make the surface temperature of the billet basically consistent with the core temperature, and then heated to above 1200°C; (6) Rolling and cooling: After the ingot leaves the heating furnace, high-pressure water is used to remove phosphorus. The rolling temperature is controlled at 1040-1140℃. The final rolling is controlled by a KOCKS unit. After rolling, a long cooling bed is used for slow cooling. The cooling bed is covered with an insulation cover and shaken at a uniform speed to slowly cool the round steel, thereby improving the straightness of the material and releasing stress. The method for preparing steel for forged bucket teeth of excavators according to claim 2 is characterized in that the hydrogen content in the molten steel after the vacuum treatment in step (3) is ≤2ppm. The method for preparing steel for forged bucket teeth of excavators according to claim 2 is characterized in that, during the continuous casting process in step (4), the superheat of the first furnace of the tundish is controlled to be ≤40°C, the continuous casting furnace is controlled at 10-30°C, and the casting speed is maintained at 0.80-0.90m/min. The method for preparing steel for forged bucket teeth of excavators according to claim 2 is characterized in that the heating temperature in step (5) is specifically ≤950°C in the preheating section, 1050-1180°C in the first heating section, 1200-1290°C in the second heating section, 1200-1270°C in the soaking section, and the total heating time is ≥210min. The method for preparing steel for forged bucket teeth of excavators according to claim 2 is characterized in that the dephosphorization pressure in step (6) is controlled to be greater than 18 MPa. The method for preparing steel for forged bucket teeth of excavators according to claim 2 is characterized in that the final rolling temperature in step (6) is 800-870°C.