Fire grate bar of sintering machine and manufacturing method of fire grate bar

Abstract

The invention provides a sintering machine fire grate bar and a manufacturing method thereof, and aims to solve the problems that an existing fire grate bar is insufficient in high temperature resistance, poor in wear resistance and short in service life. Specifically, the sintering machine fire grate comprises the following chemical components in percentage by mass: 0.70-1.00% of C, 1.5-2.5% of Si, 0.20-0.4% of Mn, less than or equal to 0.03% of S, less than or equal to 0.03% of P, 18-21% of Cr, 0-0.5% of Mo and 0.010-0.025% of RE, and the design is combined with specific casting and rapid cooling processes, so that the metallographic structure of the fire grate is mainly ferrite and austenite, and the high temperature resistance and wear resistance of the fire grate are remarkably improved. According to verification of the embodiment, the service life of the manufactured fire grate bar on a sintering machine can reach 15-18 months, the service life of the discharging grate is prolonged to 18 months, the problems in the prior art are effectively solved, and remarkable technical advantages and economic benefits are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of manufacturing parts used in the sintering system of ironmaking furnace charge in the metallurgical industry, and in particular to a sintering machine grate bar and a manufacturing method thereof. The grate bar has excellent high temperature resistance and is suitable for various ironmaking furnace charge sintering machine working conditions. Background Art

[0002] In the metallurgical industry, sintering of charge before ironmaking is a key step, which involves sintering a variety of powdered raw materials into blocks through high-temperature treatment to remove impurities, improve charge quality, enhance its mechanical strength and reducibility, and ensure that the charge composition is uniform and stable, thereby improving the charge quality of the iron-making blast furnace, and then improving the smelting efficiency and pig iron quality. The sintering machine is the core equipment in this process, and the grate bars installed on its trolley play a vital role. The grate bars need to withstand high-temperature thermal cycles and high-temperature friction of the charge for a long time. The working environment is extremely harsh, so strict requirements are placed on its material: it must have excellent high-temperature resistance, wear resistance and long service life at the same time to meet the needs of continuous operation of the iron-making blast furnace and sintering machine, and avoid huge economic losses caused by downtime.

[0003] As a casting product, the grate bar can be used directly without subsequent machining. The design of its chemical composition is the core technology to improve the heat resistance and wear resistance. At present, there are many patent technologies on the material of sintering machine grate bars, each with its own characteristics. For example, CN103849819A discloses a chemical composition of a grate bar, in which the carbon content is high and the chromium content is low, resulting in insufficient heat resistance; at the same time, the high manganese content will cause a large amount of heat-intolerant pearlite to be produced in the metallographic structure of the grate bar. Although another patent, CN115109995A, has increased the chromium content, the carbon and manganese content is still high, which limits its high temperature resistance. In addition, patents such as CN102605289A, CN101935805A, and CN104611634A all have the problem of excessively high carbon content, resulting in insufficient high temperature strength and oxidation resistance.

[0004] In view of the above-mentioned defects in the prior art, the present invention proposes a new chemical composition and manufacturing method of grate bars. This method reduces the carbon content to less than 1%, but still higher than the carbon content of ordinary cast steel, while increasing the silicon content, so that the carbon equivalent is maintained at a high level, and introduces a high content of chromium. This innovative design not only ensures that the molten steel has good casting properties, but also significantly improves the performance of the grate bars at high temperatures, effectively overcomes the shortcomings of the prior art, and can better meet the actual working conditions of the sintering machine. Summary of the invention

[0005] In view of the technical problems of the existing sintering machine grate bars, such as insufficient high temperature resistance and short service life, the present invention aims to provide a sintering machine grate bar and a manufacturing method thereof. The sintering machine grate bars in the prior art are prone to failure in high temperature and harsh environments due to unreasonable chemical composition design, which seriously affects the operating efficiency and production cost of the sintering machine. Therefore, it is particularly important to develop a sintering machine grate bar with excellent high temperature performance and long service life and a manufacturing method thereof.

[0006] The present invention proposes a sintering machine grate bar and a manufacturing method thereof, characterized in that the chemical composition of the grate bar includes (mass percentage): C=0.70-1.00%, Si=1.5-2.5%, Mn=0.20-0.4%, S≤0.03, P≤0.03%, Cr=18-21%, Mo=0-0.5%, RE=0.010-0.025%. For grate bars with a length of ≥400 mm, 0.3%-1% nickel (Ni) and a trace amount of cobalt (Co) can be added on the basis of the above to improve the high temperature strength. This chemical composition design is different from the traditional technology, and its characteristics are: although the carbon content is lower than the existing technology, it is still higher than ordinary carbon steel, combined with a higher silicon content, so that the carbon equivalent (carbon% + 1 / 3 silicon) is maintained at a higher level, thereby ensuring that the molten steel has good casting performance and a low-cost production process can be adopted. In addition, the high silicon content significantly improves the high-temperature oxidation resistance of the grate bar. The chromium content is controlled above 18%, forming an optimized chromium / carbon ratio (21-25), which not only ensures excellent high-temperature oxidation resistance, but also realizes the effective utilization of ferrochrome resources. The molybdenum element in the chemical composition helps to improve the high-temperature strength of the grate bars. For long-sized grate bars, their high-temperature performance can be further enhanced by adding nickel and cobalt. At the same time, the present invention reduces the manganese content to avoid the formation of excessive pearlite that is easily decomposed at high temperatures and has poor oxidation resistance, thereby ensuring the high-temperature strength of the grate bars. Through the specific chemical composition design, the metallographic structure of the grate bars after casting is mainly ferrite and austenite. This is achieved by taking special measures to rapidly cool the molten steel after pouring, which effectively prevents the precipitation of carbon and the formation of pearlite, thereby improving the high-temperature performance of the grate bars.

[0007] In terms of manufacturing method, the present invention adopts the following key technologies: (1) Raw material preparation and smelting: According to the size and performance requirements of the grate bars required by the user, the chemical composition is designed, and high-quality raw and auxiliary materials are selected accordingly. Subsequently, these raw materials are put into the smelting equipment, and through the high-temperature smelting process, molten steel with specific chemical composition is obtained. These chemical compositions include: carbon (C) content is controlled between 0.70 and 1.00%, silicon (Si) content is in the range of 1.5 to 2.5%, manganese (Mn) content is maintained at 0.20 to 0.4%, and the sulfur (S) and phosphorus (P) contents are strictly controlled not to exceed 0.03%, and 18 to 21% of chromium (Cr) and appropriate amounts of molybdenum (Mo) are added. For grate bars with longer lengths, such as length ≥400mm, consider adding 0.3% to 1% nickel (Ni) and trace amounts of cobalt (Co) to further improve high-temperature strength; (2) Casting: The molten steel is cast into the shape of grate bars. This process requires strict control of the casting temperature and speed to avoid internal defects; (3) Inoculation treatment: When the molten steel is discharged from the furnace, rare earth ferrosilicon alloy is added to the ladle as an inoculant, and the addition amount is 0.1% of the mass of the molten steel. At the same time, silicon-calcium alloy is added as an inoculant, and the addition amount is 0.12% of the mass of the molten steel. This step is aimed at optimizing the casting performance of the molten steel, improving the metallurgical quality of the molten steel, and improving the high temperature resistance, mechanical properties and wear resistance of the grate bars. (4) Cooling treatment: After casting, when the temperature of the grate bars naturally drops to 950-1000°C, quickly open the box and shake off the sand attached to the surface. Then, use an industrial fan to blow air strongly, or combine blowing and spraying to cool the grate bars quickly and evenly to room temperature. This rapid cooling process is crucial to ensure that the metallographic structure of the grate bars is mainly ferrite and austenite, thereby effectively improving its high temperature performance and wear resistance; (5) Post-processing: After cooling to room temperature, the grate bars are carefully polished and smoothed to remove surface burrs and defects, improve their surface finish and service life. The finished grate bars are strictly inspected for quality, including appearance inspection, dimension measurement, mechanical property testing, and high temperature resistance and wear resistance evaluation, and are put into storage only when they meet the standard requirements.

[0008] The present invention achieves the optimization adjustment of carbon content through a carefully designed combination of chemical components, which is lower than the traditional technology and higher than ordinary carbon steel, while increasing the silicon content, and combining the joint inoculation treatment of rare earth ferrosilicon and silicon calcium alloy and the timely high-temperature unpacking and rapid cooling process, successfully obtains the cast metallographic structure dominated by ferrite and austenite. This innovation not only significantly improves the high temperature resistance and wear resistance of the grate bar, but also effectively overcomes the limitations of the existing technology and fully meets the strict requirements of the sintering machine on the performance of the grate bar. Compared with the existing technology, the alloy grate bar and its manufacturing method provided by the present invention have the following significant advantages: (1) Significantly improved high temperature resistance: Through scientific chemical composition design and special cooling method, the grate bars have excellent antioxidant and thermal fatigue resistance at high temperatures; (2) Enhanced wear resistance: The optimized chemical composition and special cooling method make the metallographic structure of the grate bars mainly ferrite and austenite, avoiding the formation of heat-sensitive pearlite, thereby improving the wear resistance of the grate bars; (3) Extended service life: The improvement of comprehensive performance enables the grate bars to maintain a longer service life in high temperature and harsh environment, reducing production and maintenance costs; (4) Improved production efficiency: The optimized manufacturing method improves the production efficiency and quality stability of grate bars, which is conducive to industrial production.

[0009] In summary, the grate bar and the manufacturing method thereof provided by the present invention not only solve the problems existing in the prior art, but also significantly improve the performance and production efficiency of the grate bar, and have broad market application prospects and significant economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 This is the production process flow chart of sintering machine grate bars.

[0011] Figure 2 This is a diagram of the grate bar casting.

[0012] Figure 3 This is the drawing of the grate casting for blanking. DETAILED DESCRIPTION

[0013] The present invention provides a sintering machine grate bar having excellent oxidation resistance and wear resistance at high temperature and a manufacturing method thereof. The technical solution of the present invention is described in detail through two specific embodiments below. Example 1

[0014] This embodiment involves the furnace charge sintering workshop of the special steel company under the group company. The workshop has a complete furnace charge sintering production line, in which the grate bars used on the sintering machine are the specific application objects of the technology of the present invention; (1) Specifications and chemical composition of grate bars: Figure 1 shows the grate bar casting. Figure 2As shown, the weight of a single piece is 5.5kg and the length is 490mm. According to this size, the chemical composition of the grate bar is determined as follows: carbon (C) content 0.75-0.9%, silicon (Si) content 1.8-2.0%, manganese (Mn) content 0.20-0.35%, sulfur (S) content not more than 0.03%, phosphorus (P) content not more than 0.03%, chromium (Cr) content 18.5-21%, molybdenum (Mo) content 0.35-0.5%, nickel (Ni) content 0.5-0.8%, rare earth element (RE) content 0.015-0.025%; (2) Casting and cooling process: Sand casting method is used, and four grate bar castings are placed in each box. After the molten steel is poured, wait for about 8 minutes. When the temperature of the grate bar drops to 950-1000℃, open the box and shake off the sand. Then use a fan to blow strong air to achieve rapid cooling, ensuring that the metallographic structure of the grate bar is mainly ferrite and austenite; (3) Use effect: After the grate bars manufactured by the above process are installed and used on the sintering machine, their service life reaches 15 to 18 months, with significant effects, effectively improving production efficiency and reducing maintenance costs. Example 2

[0015] This embodiment involves the unloading grate of the sintering plant of the special steel company under this group company: (1) Specifications and chemical composition of blanking grate: The blanking grate casting is shown in the figure below: Figure 3 As shown, the overall dimensions are length × width × height = 1300 × 1150 × 200mm, and the weight is 1443kg. Since it needs to work in a high temperature environment, it was originally cast with heat-resistant ductile iron, and its service life was only 3 months. Later, the heat-resistant steel produced using the technology of the present invention has the following chemical composition: carbon (C) content 0.75-0.9%, silicon (Si) content 1.6-1.8%, manganese (Mn) content 0.20-0.35%, sulfur (S) content not more than 0.03%, phosphorus (P) content not more than 0.03%, chromium (Cr) content 18.5-21%, molybdenum (Mo) content 0.35-0.5%, rare earth element (RE) content 0.015-0.025%; (2) Casting and cooling process: After pouring the molten steel, wait for about 13 minutes. When the temperature of the grate drops to 950-1000℃, open the box and shake off the sand. Use a fan to blow air and spray to cool rapidly to ensure that the metallographic structure of the grate is also ferrite and austenite; (3) Use effect: The unloading grate produced by the technology of the present invention has an installed service life of 18 months, which is significantly improved compared with the original material. It also performs stably during use and meets the use requirements in high temperature environments.

[0016] It should be noted that the above-listed embodiments are only specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and similar changes or modifications made therewith can be directly derived or easily associated with by those skilled in the art from the contents disclosed in the present invention, and should all fall within the protection scope of the present invention.

Claims

1. A sintering machine grate bar, characterized in that: The chemical composition of the sintering machine grate bar includes the following elements in mass percentage: C=0.70-1.00%, Si=1.5-2.5%, Mn=0.20-0.4%, S≤0.03%, P≤0.03%, Cr=18-21%, Mo=0-0.5%, RE=0.010-0.025%, and the balance is Fe and unavoidable impurities.

2. A sintering machine grate bar according to claim 1, characterized in that: The sintering machine grate bar further contains nickel (Ni) in an amount of 0.3% to 1% by mass.

3. A sintering machine grate bar according to claim 2, characterized in that: The microstructure of the sintering machine grate bars is mainly composed of ferrite and austenite.

4. A method for manufacturing a sintering machine grate bar according to any one of claims 1 to 3, characterized in that: The following steps are involved: (1) Smelting: placing raw materials into a smelting device to obtain molten steel containing the chemical composition of any one of claims 1 to 3; (2) Casting: Casting molten steel into the shape of grate bars; (3) Inoculation treatment: When the molten steel is discharged from the furnace, rare earth ferrosilicon alloy is added into the ladle as an inoculant, and the amount added is 0.1% of the mass of the molten steel. At the same time, silicon-calcium alloy is added as an inoculant, and the amount added is 0.12% of the mass of the molten steel. (4) Cooling treatment: After the molten steel is poured, when the temperature of the grate bars drops to 950-1000°C, the box is opened to remove the sand, and the steel is quickly cooled to room temperature by fan blowing and spraying; (5) Post-processing: The cooled grate bars are polished and smoothed to obtain finished grate bars.

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