Preparation process of dual-material tappet with wear resistance and toughness

Abstract

The invention discloses a preparation process of a dual-material tappet with both wear resistance and toughness, and relates to the technical field of engine tappet manufacturing, the preparation process comprises the steps of matrix pretreatment, gradient heating, infiltration compounding, diffusion heat preservation, subsection cooling and finish machining, and a wear-resistant alloy material comprises the following chemical components in percentage by weight: 3.2-3.6% of C, 0.4-0.6% of Ni, 2.4-2.5% of Si, 0.9-1.3% of Cr, 0.6-0.9% of Mn and the balance of Fe and inevitable impurities. Mo is equal to 0.4%-0.65%, and Slt is equal to 0.1%, Plt; 0.1%, with the balance being Fe and inevitable impurities. Compared with the prior art, the method has the advantages that the performance can be flexibly matched according to different engine requirements; the comprehensive performance of the working face is remarkably improved by adopting an infiltration composite process; the strength and the toughness of the matrix are improved; the double-metal bonding strength is consistent; the cost of the infiltration composite process is lower than that of brazing; the matrix in the semi-molten state and the wear-resistant material form metallurgical bonding, and the bonding strength is higher; the combined steel and the gradient cooling process jointly improve the impact resistance.

Description

Technical Field

[0001] The present invention relates to the technical field of engine tappet manufacturing, and in particular to a process for preparing a dual-material tappet that takes both wear resistance and toughness into consideration. Background Art

[0002] As a key component of the engine's valvetrain, the performance of the tappet directly impacts the engine's reliability and service life. During engine operation, the tappet's working surface is exposed to harsh conditions, subject to complex working conditions such as lack of lubricant, high temperatures, high-frequency impacts, and seizure. Therefore, the tappet material must possess excellent wear resistance, impact toughness, and seizure resistance. Currently, the most common tappet types on the market include chilled cast iron tappets, welded tappets, and brazed tappets, which suffer from the following deficiencies:

[0003] (1) The working surface performance flexibility of the chilled cast iron tappet is poor, and it is difficult to flexibly match it according to the specific requirements of different engines; the overall performance improvement space of the working surface is limited, and it is difficult to meet the increasing performance requirements of the engine; in the manufacturing process, processes such as resin-coated sand sintering and quenching oil heat treatment are involved, which will produce VOCs harmful gases and pollute the environment.

[0004] (2) The welded tappet generally uses ordinary structural steel as the substrate, which has relatively low strength and toughness, limiting its scope of use. During the manufacturing process, it is difficult to ensure the consistency of the bimetallic bonding strength, and it is impossible to accurately determine the cooling parameters according to the actual use environment of the tappet, making it difficult to obtain friction pair performance that matches the working parts.

[0005] (3) The brazed tappet has the problem of high manufacturing cost, and the bonding strength of the two materials needs to be improved. The impact resistance is also relatively insufficient, making it difficult to adapt to high-intensity working environments.

[0006] In summary, existing tappet technologies struggle to simultaneously meet the comprehensive performance requirements for tappets in harsh operating environments, and they also suffer from numerous deficiencies in manufacturing processes, costs, and environmental protection. Therefore, developing a dual-material tappet manufacturing process that balances wear resistance and toughness is of great practical significance. Summary of the Invention

[0007] To solve the above technical problems, the present invention provides a technical solution: a process for preparing a dual-material tappet that takes into account both wear resistance and toughness, comprising the following steps:

[0008] Step 1: Matrix pretreatment: Process shallow flat pits with a depth of 1.5-3mm on the working surface of the alloy steel matrix, with a surface roughness of Ra ≤ 6.3μm;

[0009] Step 2: Gradient heating: heating the substrate to 1100-1250°C to make its working surface in a semi-molten state;

[0010] Step 3: Infiltration and compounding: Heat the wear-resistant alloy material to 1300-1500℃ to melt it into liquid state, and then drip it into the shallow pit in a dripping manner at a dripping speed of 3-5 drops / second. The volume of each drop is 0.05-0.15cm 3 ;

[0011] Step 4: Diffusion and insulation: Maintain the composite area temperature at 1200-1300°C for 10-30 minutes in a flux protection environment;

[0012] Step 5: Segmented cooling: Gradient cooling is performed using a water-based coolant;

[0013] Step 6: Finishing: Machining the composite working surface to the target size, with a final surface roughness of Ra ≤ 0.4 μm. Phosphating treatment can be performed to further increase wear resistance.

[0014] The advantages of the present invention over the prior art are: (1) the working surface performance is adjustable through a dual-material composite design, and the performance can be flexibly matched according to the requirements of different engines; the melt infiltration composite process is used to significantly improve the comprehensive performance of the working surface; the harmful gas emissions in the traditional casting process are avoided, which is more environmentally friendly; (2) alloy steel is selected as the matrix material, which improves the matrix strength and toughness; the consistency of the bimetallic bonding strength is ensured by gradient heating and diffusion insulation process; the friction pair performance matching the working conditions is obtained by using a segmented cooling process; (3) the melt infiltration composite process is lower in cost than brazing; the matrix in a semi-molten state forms a metallurgical bond with the wear-resistant material, and the bonding strength is higher; the alloy steel matrix and the gradient cooling process jointly improve the impact resistance.

[0015] As an improvement, the chemical composition of the wear-resistant alloy material is as follows by weight: C = 3.0-3.8%, Ni = 0.2-0.8%, Si = 2.2-2.7%, Cr = 0.7-1.5%, Mn = 0.4-1.1%, Mo = 0.2-0.85%, S < 0.3%, P < 0.3%, and the remainder is Fe and unavoidable impurities.

[0016] As an improvement, the chemical composition of the wear-resistant alloy material is as follows by weight: C = 2.2 ~ 3.2%, Ni = 0.1 ~ 0.5%, Cr = 11 ~ 14%, Mn = 0.2 ~ 0.7%, Mo = 0.5 ~ 2.0%, S < 0.2%, P < 0.2%, and the balance is Fe and unavoidable impurities.

[0017] As an improvement, the chemical composition of the wear-resistant alloy material is as follows by weight: C = 3.2-3.7%, Ni = 0.4-0.6%, Si = 2.4-2.7%, Cr = 0.5-0.9%, Mn = 0.5-0.9%, Mo = 0.4-0.8%, Cu0.4-0.8, S < 0.12%, P < 0.2%, and the remainder is Fe and unavoidable impurities.

[0018] As an improvement, in step 3, the fusion zone of the liquid wear-resistant alloy and the substrate forms a transition zone with a width of 50-200 μm, and the Cr and Mo element contents in the transition zone are distributed in a gradient.

[0019] As an improvement, the water-based coolant contains 6 wt % sodium nitrate, 4 wt % polyether polyol, 0.2 wt % nanographene, and 4 wt % sodium chloride.

[0020] As an improvement, the heating in step 2 adopts segmented induction heating, with heating to 600°C at 80-100°C / s in the first stage and heating to the target temperature at 30-50°C / s in the second stage.

[0021] As an improvement, the hardness of the composite working surface is ≥62HRC, the hardness of the matrix is ​​38-52HRC, and the slope of the Vickers hardness gradient change in the transition zone is ≤15HV / μm.

[0022] As an improvement, the thickness of the composite working surface is 15-25% of the total thickness of the substrate, and the bonding strength with the substrate is ≥400 MPa.

[0023] As an improvement, step 5 includes three stages: the first stage is cooling to 900°C at a rate of 15-20°C / s, the second stage is cooling to 600°C at a rate of 8-12°C / s, and the third stage is air cooling to room temperature. DETAILED DESCRIPTION

[0024] In a specific embodiment of the present invention, a dual-material tappet formulation is provided, wherein the chemical composition of the wear-resistant alloy material is, by weight, C = 3.2%, Ni = 0.4%, Si = 2.4%, Cr = 0.9%, Mn = 0.6%, Mo = 0.4%, S = 0.05%, P = 0.05%, with the remainder being Fe and unavoidable impurities. The process flow includes:

[0025] 1. Matrix pretreatment stage

[0026] 1. The round steel is cold drawn to the blank size with a tolerance of ±0.05

[0027] 2. Perform straightening and roundness control Within, the curvature in free state is not greater than 5mm / 3 meters,

[0028] 3. Cut the plane and control the verticality of the size within 0.05.

[0029] 4. Use a pit furnace to heat and keep warm to anneal to below HB105.

[0030] 5. The surface is treated with molybdenum disulfide, soap solution, etc. for immersion lubrication.

[0031] 6. Use a hydraulic press to cold extrude the blank and control the depth of the ball socket.

[0032] 7. Use CNC drilling machine and CNC lathe to process oil holes and shape the base.

[0033] 2. Gradient heating stage

[0034] The IGBT-100kW segmented induction heating system is used. The first stage heats the substrate to 600°C at 90°C / s, and the second stage heats the substrate to 1150°C at 40°C / s, achieving a semi-molten state on the working surface. The segmented induction heating system has a power output of 100kW, a frequency range of 1-20kHz, and a cooling method using water-cooled coils. This equipment is suitable for gradient heating, ensuring a uniform semi-molten state on the substrate working surface and avoiding localized overheating or unmelted areas.

[0035] 3. Infiltration and compounding stage

[0036] A medium-frequency induction furnace, model: GP100-C, is used. The wear-resistant alloy materials are added to the crucible in sequence according to the ratio and heated to 1450°C. They are melted into liquid and kept warm for 15 minutes to ensure complete melting. The rated capacity of the medium-frequency induction furnace is: 100-500kg, suitable for batch melting of wear-resistant alloys, melting temperature: maximum 1600°C, temperature control accuracy: ±5°C, tilting method: hydraulic tilting, and slowly pouring into the casting mold for finalization.

[0037] In order to ensure the uniformity and consistency of composition and process and avoid segregation on the wear-resistant surface, the present invention uses induction heating equipment to remelt the wear-resistant alloy material twice, and adopts synchronous linkage with the substrate heating to ensure that the substrate and liquid alloy temperatures match. The secondary melted alloy is then dripped into the shallow flat pit at a dripping rate of 4 drops / second, and the volume of each drop is 0.5-1.5cm 3 The fusion zone between the liquid wear-resistant alloy and the substrate forms a transition zone with a width of 100μm, in which the Cr and Mo element contents are distributed in a gradient. 3 / Drop quantitative pouring.

[0038] 4. Diffusion and insulation stage

[0039] The diffusion and insulation stage is crucial to the bonding strength, stability and consistency of the weld overlay layer and the substrate. The present invention uses a digital induction heating device with an infrared temperature measuring device, sets the insulation parameters, uses a far-infrared temperature measuring gun to collect temperature, and automatically controls the digital induction heating device with a microcomputer to insulate and supplement the temperature of the substrate carrying the melt, thereby promoting the gradient diffusion of the Cr / Mo elements.

[0040] 5. Segmented cooling stage

[0041] The water-based cooling equipment utilizes a high-pressure precision atomizing cooling unit, model MistCool JET-3000. It features a spray pressure of 0.8-1.5 MPa, a flow rate control range of 10-50 L / min, a mist particle size of 20-50 μm, and a cooling rate adjustment range of 5-25°C / s. This equipment features a multi-nozzle array layout, enabling targeted spraying on the tappet working surface, achieving gradient cooling. Its control system, interlocked with the induction heating system, automatically triggers a three-stage cooling process. The coolant utilizes a water-based coolant composed of 6wt% sodium nitrate, 4wt% polyether polyol, 0.2wt% nanographene, and 4wt% sodium chloride. This cooling process is a gradient cooling process consisting of three stages: the first stage cooling to 900°C at a rate of 18°C / s, the second stage cooling to 600°C at a rate of 10°C / s, and the third stage air cooling to room temperature.

[0042] Through these controls, the composite working surface can achieve a maximum hardness of 66 HRC. By adjusting parameters, the hardness can be customized to the range of 55-65 HRC based on the specific camshaft requirements. The ball socket surface hardness is HRC 50+, with a measured depth of 1mm reaching HRC ≥ 40. The Vickers hardness gradient in the transition zone is 12 HV / μm. The composite working surface is 20% of the total thickness of the substrate, and the bond strength with the substrate is 420 MPa. It can withstand a 1000-hour engine overload durability test, outperforming cold engine cast iron tappets.

[0043] 6. Finishing stage

[0044] 1. Use a CNC hard rail lathe to turn off the surface residue layer on the end face of the tappet.

[0045] 2. A dedicated spherical grinder grinds the composite work surfaces to a final surface roughness of Ra = 0.3μm. Suitable for batch processing, it features a spindle power of 15kW and a feed accuracy of 0.001mm, ensuring a surface roughness of Ra ≤ 0.4μm. The cooling system utilizes high-pressure grinding fluid filtration to prevent nanographene residue. The CNC system utilizes a FANUC 31i-B, supporting programming for 3D surface grinding. This unit is suitable for finishing, efficiently grinding composite work surfaces to target dimensions. Equipped with a MarSurfLD 260 measuring instrument, it monitors surface quality in real time.

[0046] Comparative experiment

[0047] Control group 1: A common chilled cast iron tappet on the market was selected, model: LQ-01.

[0048] Experimental results: The hardness of the chilled cast iron tappet working surface is 58HRC, and the wear rate under simulated harsh working conditions is 0.015mm 3 / h, while the wear rate of the dual-material tappet prepared in this embodiment is 0.008mm 3 / h, impact toughness increased by 25%.

[0049] Control group 2: using existing surfacing tappets, model: Bosch FV-12.

[0050] Experimental results: The bonding strength of the surfacing welded tappet is 350 MPa. Under simulated high-frequency impact conditions, cracks appear on the surfacing welded tappet, while no cracks appear on the dual-material tappet prepared in this embodiment. Its impact resistance is significantly better than that of the surfacing welded tappet.

[0051] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A process for preparing a dual-material tappet with both wear resistance and toughness, characterized in that The following steps are involved: Step 1: Matrix pretreatment: Process shallow flat pits with a depth of 1.5-3mm on the working surface of the alloy steel matrix, with a surface roughness of Ra ≤ 6.3μm; Step 2: Gradient heating: heating the substrate to 1100-1250°C to make its working surface in a semi-molten state; Step 3: Infiltration and compounding: Heat the wear-resistant alloy material to 1300-1500℃ to melt it into liquid state, and then drip it into the shallow pit in a dripping manner at a dripping speed of 3-5 drops / second. The volume of each drop is 0.05-0.15cm 3 ; Step 4: Diffusion and insulation: Maintain the composite area temperature at 1200-1300°C for 10-30 minutes in a flux protection environment; Step 5: Segmented cooling: Gradient cooling is performed using a water-based coolant; Step 6: Finishing: Machining the composite working surface to the target size, with a final surface roughness of Ra ≤ 0.4 μm. Phosphating treatment can be performed to further increase wear resistance.

2. The process for preparing a dual-material tappet with both wear resistance and toughness according to claim 1, characterized in that: The chemical composition of the wear-resistant alloy material is as follows by weight: C=3.0-3.8%, Ni=0.2-0.8%, Si=2.2-2.7%, Cr=0.7-1.5%, Mn=0.4-1.1%, Mo=0.2-0.85%, S<0.3%, P<0.3%, and the balance is Fe and unavoidable impurities.

3. The process for preparing a dual-material tappet with both wear resistance and toughness according to claim 2, characterized in that: The chemical composition of the wear-resistant alloy material is as follows by weight: C=2.2-3.2%, Ni=0.1-0.5%, Cr=11-14%, Mn=0.2-0.7%, Mo=0.5-2.0%, S<0.2%, P<0.2%, and the balance is Fe and unavoidable impurities.

4. The process for preparing a dual-material tappet with both wear resistance and toughness according to claim 3, characterized in that: The chemical composition of the wear-resistant alloy material is as follows by weight: C=3.2-3.7%, Ni=0.4-0.6%, Si=2.4-2.7%, Cr=0.5-0.9%, Mn=0.5-0.9%, Mo=0.4-0.8%, Cu0.4-0.8, S<0.12%, P<0.2%, and the balance is Fe and unavoidable impurities.

5. The process for preparing a dual-material tappet with both wear resistance and toughness according to claim 1, characterized in that: In the step 3, the fusion zone of the liquid wear-resistant alloy and the substrate forms a transition zone with a width of 50-200 μm, and the contents of Cr and Mo elements in the transition zone are distributed in a gradient.

6. The process for preparing a dual-material tappet with both wear resistance and toughness according to claim 1, characterized in that: The water-based coolant contains 6 wt % of sodium nitrate, 4 wt % of polyether polyol, 0.2 wt % of nanographene, and 4 wt % of sodium chloride.

7. The process for preparing a dual-material tappet with both wear resistance and toughness according to claim 1, characterized in that: The heating in step 2 adopts segmented induction heating, with heating to 600°C at 80-100°C / s in the first stage and heating to the target temperature at 30-50°C / s in the second stage.

8. The process for preparing a dual-material tappet with both wear resistance and toughness according to claim 1, characterized in that: The hardness of the composite working surface is ≥62HRC, the hardness of the matrix is ​​38-52HRC, and the slope of the Vickers hardness gradient change in the transition zone is ≤15HV / μm.

9. The process for preparing a dual-material tappet with both wear resistance and toughness according to claim 8, characterized in that: The thickness of the composite working surface is 15-25% of the total thickness of the substrate, and the bonding strength with the substrate is ≥400 MPa.

10. The process for preparing a dual-material tappet with both wear resistance and toughness according to claim 1, characterized in that The step 5 includes three stages: the first stage is cooling to 900° C. at a rate of 15-20° C. / s, the second stage is cooling to 600° C. at a rate of 8-12° C. / s, and the third stage is air cooling to room temperature.