A method for manufacturing a wire rod for a cylinder honing coil of an automobile engine

Abstract

The application relates to a manufacturing method of a wire rod for a cylinder melting coil of an automobile engine, and belongs to the metallurgical field. The chemical composition of the wire rod is as follows in percentage by mass: C: 0.10-0.12%, Si: 0.25-0.40%, Mn: 1.6-1.8%, Cr<=0.1%, Mo<=0.05%, Ni<=0.1%, Cu<=0.1%, Ti<=0.01%, Al<=0.01%, P<=0.012%, S<=0.008%, and the balance is Fe and inevitable impurity elements. A Si deoxidation process is adopted during smelting of the molten steel, and the Al in the steel is controlled to be <=0.01%. The segregation index of the C element in the same cross section of the wire rod is between 0.95 and 1.05, the segregation index of the Mn element is between 0.98 and 1.02, and the microstructure is ferrite+pearlite+sporadic martensite which does not affect drawing. The tensile strength is 550-600 MPa, the area reduction is >=70%, the wire rod is ensured to be continuously drawn from Phi 6.5 mm to Phi 1.7 mm, and the tensile strength of the steel wire after drawing is between 1200 and 1300 MPa.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, specifically relating to a wire for automotive engine cylinder fusion coils and its manufacturing method. Background Technology

[0002] The engine is one of the core components of a car, and the engine block, as a crucial part of the engine, has a vital impact on its performance and lifespan due to its quality and manufacturing process. Therefore, the coating materials and processes used for the engine block are particularly important. Spray coating can improve the wear resistance and corrosion resistance of the engine block. The coating material should possess high hardness, high wear resistance, high corrosion resistance, and high adhesion to meet the requirements of the engine block under harsh operating conditions such as high temperature, high pressure, and high speed. This helps resist wear on the cylinder walls under high temperature and high pressure, extends cylinder life, improves engine performance, and simultaneously improves fuel economy and reduces emissions. Furthermore, to ensure the stability of the spraying process, the weld bead needs to have a certain degree of toughness to ensure the stability of the weld bead coil feeding. Summary of the Invention

[0003] In view of the above-mentioned technical status, the present invention provides a wire rod for engine cylinder spraying weld bead ring and a manufacturing method thereof. The wire rod for weld bead ring produced by the present invention has the characteristics of narrow element composition control range, low center segregation level, and the ability to be drawn directly from Φ6.5mm to Φ1.7mm.

[0004] The chemical composition of the wire rod of this invention, by mass percentage, is as follows: C: 0.10-0.12%, Si: 0.25-0.40%, Mn: 1.6-1.8%, Cr≤0.1%, Mo≤0.05%, Ni≤0.1%, Cu≤0.1%, Ti≤0.01%, Al≤0.01%, P≤0.012%, S≤0.008%, with the balance being Fe and unavoidable impurity elements.

[0005] The mechanisms of action of the above chemical elements are as follows:

[0006] Carbon (C) is the most critical element in materials used in weld bead wire. C improves the material's strength, hardness, and wear resistance. In weld bead wire, as the carbon content increases, the material's strength and hardness increase; however, as the carbon content continues to increase, the wire's plasticity decreases. Therefore, this invention controls the C content to 0.10%-0.12%.

[0007] As a reducing agent and deoxidizer in steelmaking, silicon (Si) has a strong solid solution strengthening effect, improving the strength, hardness, and elastic limit of steel. Simultaneously, Si can significantly alter the CCT curve of steel, increasing the nose temperature of the C-curve and raising the phase transformation temperature. Appropriately increasing the Si content can mitigate the low-temperature microstructure problems caused by excessive Mn addition. As a deoxidizer, Si produces harmless silicate inclusions, ensuring continuous wire drawing even with large reduction in surface area. Therefore, the Si content should be controlled at 0.25%-0.40%.

[0008] Manganese (Mn) is the most effective alloying element for improving the hardenability of steel. When dissolved in the matrix, it has a solid solution strengthening effect, which can effectively improve the strength of the matrix. However, adding excessive Mn to steel increases the difficulty of controlling the microstructure of the wire rod. Due to the high hardenability of Mn and its tendency to segregate, adding excessive Mn to steel can easily generate low-temperature martensitic structure, causing the wire rod to break during the drawing process. Therefore, the manganese content is controlled at 1.6%-1.8%.

[0009] Cr, Mo, Ni, and Cu exist as residual elements in steel without intentional addition. Their presence significantly improves the hardenability of the steel, shifting the CCT curve to the lower right and substantially increasing the cooling rate of the wire rod during phase transformation. During cooling, the wire rod is prone to low-temperature phase transformation structures such as martensite. Therefore, the recommended content is Cr ≤ 0.1%, Mo ≤ 0.05%, Ni ≤ 0.1%, and Cu ≤ 0.1%.

[0010] P and S are considered harmful elements in needle-cloth steel, significantly reducing its plasticity and toughness, thus deteriorating its properties. Furthermore, they tend to cause intragranular segregation during crystallization, leading to higher concentrations in localized areas. Therefore, the design concentrations are P ≤ 0.012% and S ≤ 0.008%, and should be as low as possible.

[0011] Al and Ti are usually added to steel as grain-refining elements. Adding Al and Ti to steel easily generates Al2O3 and TiO inclusions. These inclusions have a polygonal shape with sharp edges and are brittle inclusions in steel. They can easily cause wire breakage during the drawing process. Therefore, in this invention, Ti≤0.01% and Al≤0.01%.

[0012] The wire rod produced by this invention satisfies the requirement that the segregation index of C element at positions D / 2, D / 4, and D / 8 on the same cross-section of the steel is between 0.95 and 1.05, and the segregation index of Mn element is between 0.98 and 1.02, thus preventing large areas of low-temperature phase transformation martensite structure caused by local segregation during the cooling process of the wire rod.

[0013] The wire rod produced by this invention has a microstructure of ferrite + pearlite + sporadic martensite that does not affect drawing (the martensite ratio is ≤2% in the SEM image of the wire rod).

[0014] The wire rod produced by this invention has a tensile strength of 550-600MPa and a shrinkage of more than 70%. If the wire rod strength is too high, abnormal structure and wire breakage are likely to occur. If the wire rod strength is too low, it cannot meet the downstream wire drawing requirements and will affect the wire feeding stability of downstream customers.

[0015] To ensure that the wire produced by this invention does not break during wire drawing and to ensure the stability of the coating process during the melting and spraying process, the steelmaking process of this application adopts the Si deoxidation process, strictly controls the Al% in the steel to ≤0.01%, and controls the composition of inclusions to be mainly 40~50%SiO2+20~30%CaO+15~25%MnO+5~15%Al2O3.

[0016] Steelmaking includes molten iron pretreatment, converter, refining, and then continuous casting to obtain billets.

[0017] The rolling and cooling method for molten wire rods, with the specific process flow as follows:

[0018] When rolling billets, a suitable heating temperature is selected. Preferably, the temperature of the high-temperature section in the heating furnace before rolling is above 1250℃, the total heating time is above 120min, and the high-temperature time is above 60min. This ensures that the billet has sufficient temperature and time for diffusion, effectively improving the macroscopic and microscopic segregation of C and Mn elements in the billet.

[0019] The final rolling temperature of the wire rod is controlled at 800-900℃, the rolling speed is set at 95-120m / s, and the wire drawing temperature is 850-950℃.

[0020] After the wire rod is coiled, it is cooled using an air-cooling + slow-cooling process. The wire rod cooling process is divided into two stages, following a combination of air-cooling and slow-cooling. In the first stage, the air-cooling stage, all insulation covers 1-6# are opened. Within the recrystallization temperature range (preferably 700~830℃, with a cooling rate of 2~5℃ / s), air cooling accelerates recrystallization nucleation and inhibits ferrite grain growth. In the second stage, slow cooling (using insulation covers for slow cooling, with a temperature range of 680℃ to room temperature and a cooling rate of 0.5~2℃ / s) achieves a full phase transformation, resulting in uniform, fine lamellar sorbite, and suppressing the formation of large areas of low-temperature martensite due to excessively rapid cooling and low phase transformation temperature.

[0021] The wire rod produced by the above method can meet the requirements of tensile strength of 550-600MPa, shrinkage of area of ​​more than 70%, and ensure that the wire rod can be drawn from Φ6.5mm to Φ1.7mm without breaking the wire. At the same time, the tensile strength of the steel wire after drawing is between 1200-1300MPa.

[0022] Compared with the prior art, the advantages of the present invention are as follows:

[0023] 1. The wire rod produced by this invention is cooled using a two-step cooling process of air cooling + heat preservation. The designed wire rod strength is between 550-600MPa, and it is drawn from Φ6.5mm wire rod to Φ1.7mm. This ensures that the wire strength after drawing is between 1200-1300MPa.

[0024] 2. The wire rod produced by this invention satisfies the requirement that the segregation index of C element at positions D / 2, D / 4, and D / 8 on the same cross-section of the steel is between 0.95 and 1.05, and the segregation index of Mn element is between 0.98 and 1.02. This ensures that the wire rod structure is ferrite + pearlite + sporadic martensite (martensite content controlled at ≤2%) that does not affect drawing, thus avoiding the formation of a large amount of low-temperature martensite structure in some areas due to Mn segregation.

[0025] 3. Compared with existing similar welding wire processes, the wire rod produced by this invention adopts a Si deoxidation process to ensure that the wire does not break during drawing and to ensure the stability of the coating process during the melting and spraying process. The Al% in the steel is strictly controlled to be ≤0.01%, and the composition of inclusions is mainly 40~50%SiO2+20~30%CaO+15~25%MnO+5~15%Al2O3. Attached Figure Description

[0026] Figure 1 This is a microstructure diagram of the wire rod in Embodiment 1 of the present invention;

[0027] Figure 2 This is a microstructure diagram of the wire rod in Embodiment 2 of the present invention;

[0028] Figure 3 This is a microstructure diagram of the wire rod in Embodiment 3 of the present invention. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to the embodiments. The embodiments are exemplary and intended to explain the present invention, but should not be construed as limiting the present invention.

[0030] Smelting 100 tons of steel with different chemical compositions as described below, deoxidation is carried out using silicon-based agents during steelmaking, and the Al% in the steel is strictly controlled to be ≤0.01%. The composition of inclusions is mainly controlled to be...

[0031] 40~45%SiO2+20~25%CaO+15~20%MnO+5~10%Al2O3:

[0032] The chemical compositions of Examples 1-3 are shown in Table 1:

[0033] Table 1

[0034]

[0035] The billet is heated in the furnace to ensure that the uniform heating temperature is above 1250℃ and the high temperature above 1250℃ is maintained for more than 1 hour to ensure that the billet is fully heated and diffused.

[0036] The spinning temperature is controlled between 850-950℃, and the cooling after spinning adopts a two-step cooling method of air cooling + slow cooling. In the first stage of air cooling, all insulation covers 1-6 are opened, and in the second stage of slow cooling, all insulation covers are closed to prevent a large amount of low-temperature martensite transformation during the phase transformation process. The temperature range of the first stage of air cooling is 700~830℃, and the temperature range of the second stage of slow cooling is 680℃ to room temperature.

[0037] The production process parameters for Examples 1-3 are shown in Table 2:

[0038] Table 2

[0039]

[0040] The wire rod performance obtained in Examples 1-3 is shown in Table 3:

[0041] Table 3

[0042]

[0043] In addition to the above embodiments, the present invention also includes other embodiments. All technical solutions formed by equivalent transformation or equivalent substitution should fall within the protection scope of the claims of the present invention.

Claims

1. A method for manufacturing wire rod for automotive engine cylinder weld bead rings, characterized in that: The chemical composition of the wire rod, by mass percentage, is as follows: C: 0.10-0.12%, Si: 0.25-0.40%, Mn: 1.6-1.8%, Cr≤0.1%, Mo≤0.05%, Ni≤0.1%, Cu≤0.1%, Ti≤0.01%, Al≤0.01%, P≤0.012%, S≤0.008%, with the balance being Fe. Including unavoidable impurity elements; the segregation index of C element at positions D / 2, D / 4, and D / 8 on the same cross section is between 0.95 and 1.05, and the segregation index of Mn element is between 0.98 and 1.

02. The microstructure is ferrite + pearlite + sporadic martensite that does not affect drawing, with martensite ≤2%; tensile strength: 550-600MPa, area reduction ≥70%, ensuring that the wire rod does not break when drawn from Φ6.5mm to Φ1.7mm, and the tensile strength of the steel wire after drawing is between 1200-1300MPa; Manufacturing method: Steel is smelted according to chemical composition. During steel smelting, Si deoxidation process is adopted to strictly control Al in steel ≤ 0.01% and control the composition of inclusions to be mainly 40~50% SiO2 + 20~30% CaO + 15~25% MnO + 5~15% Al2O3. The molten steel is cast into billets, and the billets are heated and rolled into wire rods. The final rolling temperature is 800-900℃, the rolling speed is 95~120m / s, and the wire drawing temperature is 850~950℃. After the wire rod is coiled, it is cooled using an air-cooling + slow-cooling process, which is divided into two stages. The first stage is the air-cooling stage: the insulation cover is fully opened, and cooling is carried out within the recrystallization temperature range. Air cooling accelerates recrystallization nucleation and inhibits ferrite grain growth. The second stage is the slow-cooling stage: the insulation cover is closed, and slow cooling is carried out inside the insulation cover to achieve sufficient phase transformation, resulting in uniform fine lamellar sorbite and inhibiting the formation of large areas of low-temperature martensite due to excessively rapid cooling and low phase transformation temperature. The temperature range of the first stage air-cooling is 700~830℃, and the cooling rate is 2~5℃ / s. The temperature range of the second stage slow-cooling is 680℃ to room temperature, and the cooling rate is 0.5~2℃ / s.

2. The method according to claim 1, characterized in that: The chemical composition of the wire rod is as follows: Cr: 0.03-0.1%, Mo: 0.01-0.05%, Ni: 0.02-0.1%, Cu: 0.02-0.1%.

3. The method according to claim 1, characterized in that: The segregation index of C element at positions D / 2, D / 4, and D / 8 on the same cross-section of the wire rod is 1, and the segregation index of Mn element is 1.

4. The method according to claim 1, characterized in that: Pre-rolling heating of billet: The temperature in the high-temperature section of the heating furnace is above 1250℃, the total heating time is above 120min, and the high-temperature time is above 60min, to ensure that the billet has sufficient temperature and time for diffusion, effectively improving the macroscopic and microscopic segregation of C and Mn elements in the billet.

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