Wire rod for fusion coil of automobile engine cylinder and manufacturing method of wire rod

Abstract

The invention relates to a wire rod for a fusion coil of an automobile engine cylinder and a manufacturing method of the wire rod, and belongs to the field of metallurgy. The wire rod comprises the following chemical components in percentage by mass: 0.10-0.12% of C, 0.25-0.40% of Si, 1.6-1.8% of Mn, less than or equal to 0.1% of Cr, less than or equal to 0.05% of Mo, less than or equal to 0.1% of Ni, less than or equal to 0.1% of Cu, less than or equal to 0.01% of Ti, less than or equal to 0.01% of Al, less than or equal to 0.012% of P, less than or equal to 0.008% of S and the balance of Fe and inevitable impurity elements. A Si deoxidation process is adopted during molten steel smelting, and Al% in the steel is controlled to be smaller than or equal to 0.01%. The segregation index of the C element of the same cross section of the wire rod ranges from 0.95 to 1.05, the segregation index of the Mn element ranges from 0.98 to 1.02, and the microstructure is ferrite, pearlite and sporadic martensite which does not affect drawing. The tensile strength is 550-600 MPa, the area reduction is larger than or equal to 70%, it is guaranteed that the wire rod is not broken when the wire rod is straightly pulled from the phi 6.5 mm to the phi 1.7 mm, and the tensile strength of the drawn steel wire ranges from 1200 MPa to 1300 MPa.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy, and in particular relates to a wire material for a melting wire coil of an automobile engine cylinder and a manufacturing method thereof. Background Art

[0002] The engine is one of the core components of a car. As an important part of the engine, the quality and manufacturing process of the engine block have a vital impact on the performance and life of the engine. Therefore, the spraying material and spraying process of the engine block are also particularly important. The wear resistance and corrosion resistance of the engine block can be improved by spraying. The spraying material should have high hardness, high wear resistance, high corrosion resistance, and high adhesion to meet the use requirements of the engine block under harsh working conditions such as high temperature, high pressure, and high speed, resist the wear of the cylinder wall under high temperature and high pressure environment, extend the service life of the cylinder, and improve engine performance, while improving fuel economy and reducing emissions. In addition, in order to ensure the stability of the spraying process during the spraying operation, the melting line needs to have a certain toughness to ensure the stability of the melting line coil wire feeding. Summary of the invention

[0003] In view of the above technical status, the present invention provides a wire rod for engine cylinder spraying fused-metal wire coil and a manufacturing method. The wire rod for fused-metal wire coil produced by the present invention has the following characteristics: narrow element composition control range, low center segregation level, and can be directly pulled from Φ6.5mm to Φ1.7mm.

[0004] The chemical composition of the wire rod of the present invention is calculated by mass percentage 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%, and the remainder is Fe and unavoidable impurity elements.

[0005] The mechanism of action of the above chemical elements is as follows:

[0006] C is the most critical element in the material of the fused wire coil. C can improve the strength, hardness and wear resistance of the material. As the carbon content in the fused wire increases, the material strength and hardness increase, but when the carbon content continues to increase, the plasticity of the steel wire decreases, so the present invention controls the C content to 0.10%-0.12%.

[0007] As a reducing agent and deoxidizer in the steelmaking process, Si element has a strong solid solution strengthening effect, which improves the strength, hardness and elastic limit of steel. At the same time, Si element in steel can significantly change the CCT curve of steel, increase the temperature of the nose of the C curve, and increase the phase transition temperature. Properly increasing Si can improve the low-temperature structure problem caused by adding excessive Mn to the steel. Si element is added to steel as a deoxidizer to produce harmless silicate inclusions, which can ensure that the wire rod has a large reduction rate and deep drawing without breaking the wire. Therefore, the Si content is controlled to 0.25%-0.40%

[0008] Mn is the most effective alloying element for improving the hardenability of steel. It has a solid solution strengthening effect when dissolved in the matrix and can effectively improve the matrix strength. However, adding excessive Mn to the steel makes it more difficult to control the organization of the wire rod. Since Mn has strong hardenability and is an element that easily segregates, adding excessive Mn to the steel is prone to 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 in steel as residual elements and are not intentionally added. Their presence will greatly improve the hardenability of steel, move the steel CCT curve to the lower right, and significantly increase the cooling rate of the wire rod during the phase change process. Low-temperature phase transformation structures such as martensite are prone to occur in the wire rod during the cooling process. Therefore, Cr≤0.1%, Mo≤0.05%, Ni≤0.1%, and Cu≤0.1%.

[0010] P and S are harmful elements in card clothing steel, which significantly reduce the plasticity and toughness of steel and deteriorate its performance. At the same time, they are prone to intracrystalline segregation during the crystallization process, making the content in local areas too high. Therefore, P is designed to be less than 0.012%, S less than 0.008% and 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, which are polygonal and angular in shape and are brittle inclusions in steel. They easily cause wire rod breakage during drawing. Therefore, in the present invention, Ti≤0.01% and Al≤0.01%.

[0012] The wire rod produced by the present invention satisfies that the C element segregation index 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 Mn element segregation index is between 0.98 and 1.02, thereby preventing large pieces of low-temperature phase transformation martensite structure caused by local segregation of the wire rod during cooling.

[0013] The wire rod produced by the present invention has a structure of ferrite+pearlite+sporadic martensite which does not affect drawing (in the SEM image of the wire rod, the proportion of martensite is ≤2%).

[0014] The wire rod produced by the present invention meets the tensile strength of 550-600MPa and the area shrinkage of more than 70%. If the wire rod strength is too high, abnormal tissue breakage is likely to occur, and if the wire rod strength is too low, it cannot meet the downstream wire drawing requirements, affecting the wire feeding stability of downstream customers.

[0015] The wire rod produced by the present invention is to ensure that the steel wire is not broken during drawing and to ensure the stability of the spraying process of the steel wire during the spraying process. For this reason, the present invention adopts Si deoxidation process in molten steel smelting, strictly controls Al% in steel ≤ 0.01%, and controls the inclusion composition to be mainly 40-50% SiO2+20-30% CaO+15-25% MnO+5-15% Al2O3.

[0016] Molten steel smelting includes molten iron pretreatment - converter - refining, and then continuous casting to obtain billets.

[0017] Rolling cooling method for wire rod for fusion coil, specific process flow:

[0018] Select appropriate heating temperature for billet rolling. Preferably, the temperature of the high temperature section in the heating furnace before rolling is above 1250°C, the total heating time is above 120 minutes, and the high temperature time is above 60 minutes, to ensure that the billet has sufficient temperature and time to diffuse, and effectively improve the macro and micro 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 spinning temperature is 850-950℃.

[0020] After the wire rod is spun, it is cooled by air cooling + slow cooling process. The wire rod cooling process is divided into two stages, following the combination of air cooling and slow cooling. In the first step, all the insulation covers of the air cooling section 1-6# are opened. In the recrystallization temperature range (the preferred air cooling temperature range is 700-830℃, and the cooling rate is 2-5℃ / s), air cooling is used to accelerate the recrystallization nucleation and inhibit the growth of ferrite grains. In the second step, slow cooling (insulation cover slow cooling method, slow cooling method, cover cooling, slow cooling temperature range 680 to room temperature, cooling rate 0.5-2℃ / s) is used to achieve full phase transformation, obtain uniform fine-flaked troostite, and inhibit the formation of large pieces of low-temperature phase martensite structure due to too fast cooling and low phase transformation temperature.

[0021] The wire rod produced by the above method can meet the tensile strength requirement of 550-600MPa and the area shrinkage of more than 70%, ensuring that the wire rod can be straight-drawn from Φ6.5mm to Φ1.7mm without breaking the wire, while meeting the tensile strength of the steel wire after drawing between 1200-1300MPa.

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

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

[0024] 2. The wire rod produced by the present invention satisfies the requirements that the C element segregation index 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 Mn element segregation index is between 0.98 and 1.02, thereby ensuring that the wire rod structure is ferrite + pearlite + sporadic martensite that does not affect drawing (the martensite content is controlled at ≤2%), and avoiding Mn segregation causing a large amount of local low-temperature martensite structure.

[0025] 3. The wire rod produced by the present invention is compared with the existing similar welding wire process. In order to ensure that the steel wire is not broken when drawn and the spraying process stability of the steel wire is ensured during the spraying process, the Si deoxidation process is adopted, and the Al% in the steel is strictly controlled to be ≤0.01%, and the inclusion composition is controlled to be mainly 40-50% SiO2+20-30% CaO+15-25% MnO+5-15% Al2O3. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0028] Figure 3 This is the microstructure diagram of the wire rod according to Example 3 of the present invention. DETAILED DESCRIPTION

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

[0030] Smelt 100 tons of molten steel with different chemical compositions as follows. During the smelting of molten steel, silicon agent is used for deoxidation. Al% in 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 time 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. The 1st air cooling section 1-6# insulation covers are all opened, and the 2nd slow cooling section insulation covers are all closed to prevent a large amount of low-temperature transformation martensite from appearing during the phase change process. The temperature range of the first air cooling section is 700-830℃, and the temperature range of the second slow cooling section is 680 to room temperature.

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

[0038] Table 2

[0039] Heating temperature ℃ Spinning temperature ℃ Fan 1-6# Fan 7-20# Example 1 1250 860 Insulation cover open Insulation cover closed Example 2 1252 865 Insulation cover open Insulation cover closed Example 3 1248 850 Insulation cover open Insulation cover closed

[0040] The wire rod properties obtained corresponding to Examples 1-3 are shown in Table 3:

[0041] Table 3

[0042]

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

Claims

1. A wire rod for automobile engine cylinder fusion wire coil, characterized in that: The chemical composition of the wire rod is calculated by mass percentage 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%, and the remainder is Fe and unavoidable impurity elements.

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

3. The wire rod according to claim 1, characterized in that: On the same cross section, the segregation index of C element at positions D / 2, D / 4 and D / 8 is between 0.95-1.05, the segregation index of Mn element is between 0.98-1.02, and the microstructure is ferrite + pearlite + sporadic martensite that does not affect drawing, and martensite is ≤2%.

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

5. The wire rod according to claim 1, characterized in that: Tensile strength: 550-600MPa, surface shrinkage ≥70%, ensuring that the wire rod is pulled straight from Φ6.5mm to Φ1.7mm without breaking. The tensile strength of the steel wire after drawing is between 1200-1300MPa.

6. A method for manufacturing the wire rod according to claim 1, characterized in that: Molten steel is smelted according to the chemical composition, Si deoxidation process is adopted during molten steel smelting, Al% in steel is strictly controlled to be ≤0.01%, and the composition of inclusions is controlled to be mainly 40-50% SiO2+20-30% CaO+15-25% MnO+5-15% Al2O3, the molten steel is cast into billets, 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 laying temperature is: 850-950℃; After the wire rod is spun, it is cooled by air cooling + slow cooling process. The cooling process is divided into two stages. The first step is air cooling: all the insulation covers are opened and cooled in the recrystallization temperature range. Air cooling accelerates the recrystallization nucleation and inhibits the growth of ferrite grains. The second step is slow cooling: the insulation cover is closed and slow cooling is carried out in the insulation cover to achieve sufficient phase transformation and obtain uniform fine-flaked troostite, which inhibits the formation of large pieces of low-temperature martensite structure due to low phase transformation temperature caused by excessive cooling.

7. The method according to claim 6, characterized in that: Heating of billet before rolling: The temperature of the high temperature section in 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 to diffuse, and effectively improve the macro and micro segregation of C and Mn elements in the billet.

8. The method according to claim 6, characterized in that: In the first step of air cooling, the air cooling temperature range is 700-830°C, and the cooling rate is 2-5°C / s.

9. The method according to claim 6, characterized in that: The second step is the slow cooling stage, the slow cooling temperature range is 680°C to room temperature, and the cooling rate is 0.5-2°C / s.

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