CN113236435A - High-performance friction welding cast iron piston and preparation method thereof - Google Patents

High-performance friction welding cast iron piston and preparation method thereof Download PDF

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Publication number
CN113236435A
CN113236435A CN202110548352.0A CN202110548352A CN113236435A CN 113236435 A CN113236435 A CN 113236435A CN 202110548352 A CN202110548352 A CN 202110548352A CN 113236435 A CN113236435 A CN 113236435A
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China
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piston
cast iron
cooling oil
friction welding
blank
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CN202110548352.0A
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CN113236435B (en
Inventor
张亮亮
刘亚辉
薛斌斌
宋朋虎
张勇
刘干师
牛建华
张晓帅
王鹏霏
高扬
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Zhongnei Keith Automobile New Power System Co ltd
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Zhongnei Keith Automobile New Power System Co ltd
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02F—CYLINDERS, PISTONS OR CASINGS, FOR COMBUSTION ENGINES; ARRANGEMENTS OF SEALINGS IN COMBUSTION ENGINES
    • F02F3/00—Pistons 
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K20/00—Non-electric welding by applying impact or other pressure, with or without the application of heat, e.g. cladding or plating
    • B23K20/12—Non-electric welding by applying impact or other pressure, with or without the application of heat, e.g. cladding or plating the heat being generated by friction; Friction welding
    • B23K20/122—Non-electric welding by applying impact or other pressure, with or without the application of heat, e.g. cladding or plating the heat being generated by friction; Friction welding using a non-consumable tool, e.g. friction stir welding
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C1/00—Refining of pig-iron; Cast iron
    • C21C1/10—Making spheroidal graphite cast-iron
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C21D1/19—Hardening; Quenching with or without subsequent tempering by interrupted quenching
    • C21D1/20—Isothermal quenching, e.g. bainitic hardening
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/0068—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for particular articles not mentioned below
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C33/00—Making ferrous alloys
    • C22C33/08—Making cast-iron alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C37/00—Cast-iron alloys
    • C22C37/04—Cast-iron alloys containing spheroidal graphite
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C37/00—Cast-iron alloys
    • C22C37/10—Cast-iron alloys containing aluminium or silicon
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02F—CYLINDERS, PISTONS OR CASINGS, FOR COMBUSTION ENGINES; ARRANGEMENTS OF SEALINGS IN COMBUSTION ENGINES
    • F02F3/00—Pistons 
    • F02F3/0084—Pistons  the pistons being constructed from specific materials
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02F—CYLINDERS, PISTONS OR CASINGS, FOR COMBUSTION ENGINES; ARRANGEMENTS OF SEALINGS IN COMBUSTION ENGINES
    • F02F3/00—Pistons 
    • F02F3/16—Pistons  having cooling means
    • F02F3/18—Pistons  having cooling means the means being a liquid or solid coolant, e.g. sodium, in a closed chamber in piston
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02F—CYLINDERS, PISTONS OR CASINGS, FOR COMBUSTION ENGINES; ARRANGEMENTS OF SEALINGS IN COMBUSTION ENGINES
    • F02F3/00—Pistons 
    • F02F3/16—Pistons  having cooling means
    • F02F3/20—Pistons  having cooling means the means being a fluid flowing through or along piston
    • F02F3/22—Pistons  having cooling means the means being a fluid flowing through or along piston the fluid being liquid
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Combustion & Propulsion (AREA)
  • General Engineering & Computer Science (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Thermal Sciences (AREA)
  • Fluid Mechanics (AREA)
  • Pistons, Piston Rings, And Cylinders (AREA)

Abstract

The invention provides a cast iron piston, which comprises a piston skirt part and a piston head part, wherein the piston head part is friction welded at the upper end of the piston skirt part; the bottom of the piston head is provided with a part of cooling oil duct; the top of the piston skirt part is provided with a cooling oil channel matched with the piston head part; and a closed cooling oil passage cavity is formed between the piston head and the piston skirt through friction welding. The ferrite nodular cast iron piston provided by the invention is characterized in that cooling oil passages of the head part and the skirt part of the piston are processed in advance, and then a closed cooling oil passage is formed; the required shape of the cooling oil channel can be processed according to the requirement, and the surface quality of the oil channel is good. The invention can reduce the compression height of the traditional cast iron piston by more than 20 percent, fills the technical blank in the industry, greatly reduces the cost of the piston, improves the service performance, can meet the severe technical requirements of the current internal combustion engine such as large explosion pressure, direct injection in the cylinder and the like, and further prolongs the service life of the piston, the cylinder sleeve, the piston ring and even the engine.

Description

High-performance friction welding cast iron piston and preparation method thereof
Technical Field
The invention belongs to the technical field of cast iron piston manufacturing, relates to a cast iron piston and a preparation method thereof, and particularly relates to a novel high-performance friction welding cast iron piston and a preparation method thereof.
Background
The engine of automobile is a heart part of automobile and is composed of two major mechanisms of crank link mechanism and valve actuating mechanism, and five major systems of cooling, lubricating, igniting, fuel supplying and starting system. The piston is a reciprocating element in the cylinder body of the automobile engine, and the basic structure of the piston can be divided into a top part, a head part and a skirt part. The piston is used as a key core part of an engine, mainly has the functions of bearing gas pressure and driving a crankshaft to rotate through a piston connecting rod mechanism so as to provide power, and in addition, the piston, a cylinder cover and a cylinder wall jointly form a combustion chamber. When working, the piston bears alternating mechanical load and thermal load and is in the conditions of high temperature, high pressure, high speed and poor lubrication for a long time, and the working condition is severe.
At present, three types of aluminum pistons, steel pistons and cast iron pistons are mainly used in the market, and along with the updating and upgrading of an engine, the explosion pressure and the liter power are continuously improved, namely along with the implementation of national emission, the explosion pressure of the engine is more than 200bar, and after the liter power reaches 32-40 kW/L, the aluminum pistons cannot be used due to the characteristics of materials. Therefore, steel pistons and cast iron pistons are gradually favored by main engine factories, but the steel pistons have high material cost, high processing cost and poor cutting performance, and the problems of pin hole occlusion, throat oxidation and the like often occur in the actual operation process of an engine. The ferrite ball-milling cast iron piston is low in cost and good in machining performance, the lubricating effect of a pin hole area can be effectively improved due to the existence of the spherical graphite, the risks of piston occlusion and locking are greatly reduced, the weight of the piston can be further reduced due to the use of the ball-milling cast iron, and the effective power of an engine can be improved. Thus, cast iron pistons have many advantages over other pistons in this regard and have received much attention in the industry
However, the existing nodular cast iron piston, especially the cooling oil duct thereof, is formed by lost foam casting, the size of the blind hole of the oil duct which can be formed is limited, the surface quality is poor, the casting process is complex, the rejection rate is high, and the batch automatic production is difficult to realize. Particularly, with the implementation of the emission standard of the country vi, the engines need to be updated, however, for the same type of engines, in order to further increase the displacement and increase the explosion pressure, the height of the piston is usually reduced, i.e., the compression height is reduced, and further, the volume of the combustion chamber of the engine is increased, so that the power and the explosion pressure of the engine are continuously increased. However, the conventional cast iron piston with the internal cooling oil passage has the technical characteristics that the blind hole of the oil passage cannot be cast, so that the piston is high in height, and the compression height of the piston is difficult to reduce.
Therefore, how to find a suitable processing method, which overcomes the above problems of the existing ball-milling cast iron piston in production, simplifies the process, is more suitable for automated industrial mass production, and becomes one of the problems to be solved in various large host factories and accessory production enterprises.
Disclosure of Invention
In view of the above, the technical problem to be solved by the present invention is to provide a cast iron piston and a method for manufacturing the same, and in particular, to a novel high-performance friction-welded cast iron piston and a method for manufacturing the same. The high-performance friction welding cast iron piston provided by the invention can be processed into the shape of a required cooling oil duct according to the design requirement, the surface quality of the oil duct is good, the cost of the piston can be greatly reduced, the service performance is improved, and meanwhile, the preparation process is simple and stable, is easy for industrial automation popularization and use, and has good market prospect.
The invention provides a cast iron piston, which comprises a piston skirt part and a piston head part, wherein the piston head part is friction welded at the upper end of the piston skirt part;
the bottom of the piston head is provided with a part of cooling oil duct;
the top of the piston skirt part is provided with a cooling oil channel matched with the piston head part;
and a closed cooling oil passage cavity is formed between the piston head and the piston skirt through friction welding.
Preferably, the friction welding comprises second order friction welding;
the cast iron piston is obtained by friction welding of a piston skirt blank which is processed independently and a piston head blank which is processed independently;
the volume proportion of the partial cooling oil passage in the cooling oil passage cavity is 20-80%;
the bottom of the cooling oil duct cavity is provided with an oil inlet and an oil outlet;
the oil inlet and/or the oil outlet are/is obtained by electrochemical corrosion processing;
the shape of the cooling oil channel cavity and/or the cooling oil channel can be adjusted;
the diameter of the cooling oil duct cavity is 4-15 mm.
Preferably, the cast iron piston comprises, by mass:
C：3.70wt％～3.95wt％；
Si：2.0wt％～2.5wt％；
P：0～0.01wt％；
S：0～0.02wt％；
Mn：0～0.1wt％；
Cu：0.2wt％～0.5wt％；
Ni：0.5wt％～1.0wt％；
Nb：0.02wt％～0.06wt％；
Mo：0.1wt％～0.2wt％；
Mg：0.03wt％～0.06wt％；
Ce：0.01wt％～0.03wt％；
the balance being Fe.
Preferably, the cast iron piston comprises a ferritic spheroidal graphite cast iron piston;
the ferrite content of the cast iron piston is more than or equal to 90 percent;
the spheroidization rate of the cast iron piston is more than or equal to 95 percent;
the graphite sphere diameter of the cast iron piston is less than or equal to 0.06 mm;
the as-cast hardness of the cast iron piston is 160-200 HBW;
the cast strength of the cast iron piston is more than or equal to 500 Mpa;
the elongation of the cast iron piston is more than or equal to 7 percent;
the cast iron piston has a metallographic structure composed of acicular ferrite and copper-rich austenite.
Preferably, the cast iron piston further comprises a manganese-based phosphate coating compounded on the surface of the cast iron piston;
the thickness of the manganese series phosphating coating is 2-10 mu m;
the cast iron piston also comprises a nano coating compounded on the manganese series phosphating coating;
the nanocoating comprises a graphite nanocoating comprising titanium dioxide;
the thickness of the nano coating is 6-16 mu m;
the compression height of the cast iron piston is 40-100 mm.
The invention provides a preparation method of a cast iron piston, which comprises the following steps:
1) mixing and smelting cast iron piston raw materials to obtain molten iron, then sending the molten iron into a mold for cooling, then carrying out hot rolling to obtain a ferrite ball-milling cast iron bar, and carrying out rough machining to obtain a cast iron piston skirt blank;
mixing and smelting cast iron piston raw materials to obtain molten iron, then carrying out centrifugal casting to obtain a ferrite ball-milling cast iron pipe, and carrying out rough machining to obtain a cast iron piston head blank;
2) friction welding the cast iron piston skirt blank and the cast iron piston head blank obtained in the step to obtain a cast iron piston semi-finished product;
3) and (3) carrying out isothermal quenching treatment on the cast iron piston semi-finished product obtained in the step, then carrying out electrochemical corrosion, processing an oil inlet and outlet hole of the cast iron piston, and then carrying out heat treatment and finish machining to obtain the cast iron piston.
Preferably, the smelting mode comprises medium-frequency induction furnace smelting;
the smelting temperature is 1550-1650 ℃;
the cooling mode of the die comprises copper die water cooling;
the diameter of the ferrite ball-milling cast iron bar is 100-160 mm;
the diameter of the ferrite ball-milling cast iron pipe is 100-160 mm;
the wall thickness of the ferrite ball-milling cast iron pipe is 15-40 mm.
Preferably, the welding surface roughness Rz of the rough machined skirt blank and/or the rough machined head blank is equal to or greater than 100;
the edge of the welding surface of the rough machined skirt blank and/or the rough machined head blank is added with an arc chamfer of R1.5-R2.0 mm;
a part of cooling oil duct is processed at the bottom of the head blank after rough machining;
the roughly machined skirt blank is also provided with a cooling oil duct matched with the piston head blank;
the welding surface roughness Rz of a part of the cooling oil channel of the roughly machined head blank and/or the cooling oil channel of the roughly machined skirt blank, which is matched with the piston head blank, is more than or equal to 100;
and the welding surface of the part of the cooling oil channel of the roughly machined head blank and/or the cooling oil channel matched with the piston head blank of the roughly machined skirt blank is set to be an arc or a plane of R18-R25 mm.
Preferably, the friction welding is specifically second-order friction welding under nitrogen protection;
the flow rate of the nitrogen is 8-10L/m3；
The pressure of the nitrogen is 0.8-1 MPa;
the rotating speed of the friction welding is 800-1800 r/min;
the pressure of the first-order friction welding of the second-order friction welding is 250-270 Bar;
the pressure maintaining time of the first-stage friction welding of the second-stage friction welding is 1-6 seconds;
the pressure of second-order friction welding of the second-order friction welding is 85-95 Bar;
the second-order friction welding of the second-order friction welding has the pressure maintaining time of 3-8 seconds;
the inner welding surface of the second-order friction welding is an arc surface or a plane from R18 to R25.
Preferably, the quenching temperature of the isothermal quenching treatment is 890-910 ℃;
the quenching time of the isothermal quenching treatment is 30-180 minutes;
the isothermal temperature of the isothermal quenching treatment is 355-375 ℃;
the isothermal time of the isothermal quenching treatment is 30-180 minutes;
the temperature of the heat treatment is 340-380 ℃;
the heat treatment time is 2.5-3.5 hours;
the heating rate of the heat treatment is 150-300 ℃/h;
the fine finishing also comprises a manganese series phosphating treatment step and a composite nano coating step.
The invention provides a cast iron piston, which comprises a piston skirt part and a piston head part, wherein the piston head part is friction welded at the upper end of the piston skirt part; the bottom of the piston head is provided with a part of cooling oil duct; the top of the piston skirt part is provided with a cooling oil channel matched with the piston head part; and a closed cooling oil passage cavity is formed between the piston head and the piston skirt through friction welding. Compared with the prior art, the invention aims at the existing nodular cast iron piston and the internal cooling oil duct thereof, and is formed by casting processes such as a lost foam casting process, and the problems of limited size of oil duct blind holes (oil inlet holes and oil outlet holes), poor surface quality, high piston height, complex casting process, high rejection rate, difficulty in realizing batch automatic production and the like exist. The invention particularly selects a friction welding process for feasibility study, although the prior art also adopts a friction welding process for a steel piston, the friction welding of the cast iron piston is more complex than that of steel because the welding carbon equivalent of the cast iron piston is high, the structural stress after welding is larger, the graphite is cut apart, and the welding performance is poorer due to the influence of impurity elements such as sulfur, phosphorus and the like, and the prior friction welding process is difficult to realize.
The invention creatively provides a ferritic nodular cast iron piston obtained by friction welding, which can be used for forming a closed cooling oil duct by pre-processing the cooling oil ducts of the head part and the skirt part of the piston and then connecting the head part and the skirt part in a welding manner; the required shape of the cooling oil channel can be processed according to the design requirement, and the surface quality of the oil channel is good. The cast iron piston designed by the invention can reduce the height (compression height) of the traditional cast iron piston by more than 20 percent, is a novel high-performance ultralow-compression high-friction welding cast iron piston, fills the technical blank in the cast iron piston industry, can greatly reduce the piston cost, improves the service performance, can meet the severe technical requirements of the current internal combustion engine such as large explosion pressure, direct injection in a cylinder and the like, and further prolongs the service life of the piston, a cylinder sleeve, a piston ring and even an engine.
The novel high-performance friction welding cast iron piston obtained by adjusting the formula and the production process of the cast iron piston has the advantages of high welding strength, low width of a heat affected zone, ultralow welding quantity, low oxidation, low stress and good cutting processability, the throat of the combustion chamber of the piston has good high temperature resistance and oxidation resistance, and the working face has good wear resistance, wear reduction and thermal fatigue resistance, can effectively prolong the service life of the piston, obviously reduce the frequency of replacement of the piston due to failure such as abrasion, corrosion, thermal fatigue and the like, but also can further reduce the weight of the diesel engine (the density of the nodular cast iron is less than that of steel), improve the effective power and the heat efficiency of the engine, play a good role in energy conservation and emission reduction, meanwhile, the preparation process is simple and stable, is easy for industrial automation popularization and use, and has better market prospect.
The experimental result shows that the cast iron piston prepared by the invention has low stress and good cutting processability relative to a steel piston, the throat of a combustion chamber of the piston has good high temperature resistance and oxidation resistance, the working face has good wear resistance, wear reduction and thermal fatigue resistance, the service life of the piston can be effectively prolonged, the frequency of replacement of the piston due to failure such as wear, corrosion and thermal fatigue can be obviously reduced, the weight of a diesel engine (the density of nodular cast iron is less than that of steel) can be further reduced, the effective power and the thermal efficiency of the engine can be improved, good effects of energy conservation and emission reduction can be achieved, and meanwhile, the preparation process is simple and stable, the industrial automation popularization and use are easy, and the market prospect is good.
Drawings
FIG. 1 is a schematic diagram of a cross-sectional structure of a cooling oil passage of a piston of a high-performance friction-welded cast iron piston according to the present invention;
FIG. 2 is a schematic cross-sectional view of the appearance of a high performance friction welded cast iron piston according to the present invention;
FIG. 3 is a schematic, diagrammatic illustration of the construction of the piston head prior to welding as provided by the present invention;
FIG. 4 is a schematic, diagrammatic illustration of the construction of the skirt portion of the piston prior to welding as provided by the present invention;
FIG. 5 is a schematic view of the production process of the high performance friction welded cast iron piston according to the present invention;
FIG. 6 is a graphite photograph (100 times) of a semi-finished product before friction welding of the ball-milling cast iron head skirt prepared by the present invention;
FIG. 7 is a photograph (100 times) of the matrix structure of a semi-finished product before friction welding of the ball-milling cast iron head skirt prepared by the present invention;
FIG. 8 is a photograph (500 times) of the matrix structure of a semi-finished product before friction welding of the ball-milled cast iron head skirt prepared by the present invention;
FIG. 9 is a photograph (500 times) of the metallographic structure of a friction welded cast iron piston product prepared according to the invention.
Detailed Description
For a further understanding of the invention, reference will now be made to the preferred embodiments of the invention by way of example, and it is to be understood that the description is intended to further illustrate features and advantages of the invention, and not to limit the scope of the claims.
All of the starting materials of the present invention, without particular limitation as to their source, may be purchased commercially or prepared according to conventional methods well known to those skilled in the art.
The raw material used in the present invention is not particularly limited in purity, and the present invention is preferably industrial pure or of purity conventional in the field of cast iron piston materials.
All the raw materials, the marks and the acronyms thereof belong to the conventional marks and acronyms in the field, each mark and acronym is clear and definite in the field of related application, and the raw materials can be purchased from the market or prepared by a conventional method by the technical staff in the field according to the marks, the acronyms and the corresponding application.
In all the processes of the invention, the abbreviations thereof belong to the common abbreviations in the art, each abbreviation is clearly clear in the field of its associated use, and the ordinary process steps thereof can be understood by those skilled in the art from the abbreviations.
The invention provides a cast iron piston, which comprises a piston skirt part and a piston head part, wherein the piston head part is friction welded at the upper end of the piston skirt part;
the bottom of the piston head is provided with a part of cooling oil duct;
the top of the piston skirt part is provided with a cooling oil channel matched with the piston head part;
and a closed cooling oil passage cavity is formed between the piston head and the piston skirt through friction welding.
In the present invention, the friction welding preferably comprises second order friction welding. The present invention is in principle not particularly limited to the definition and concept of the second order friction welding, as is known to the person skilled in the art.
In the present invention, the cast iron piston includes a piston skirt and a piston head friction welded to an upper end of the piston skirt. Specifically, the cast iron piston is preferably obtained by friction welding a separately machined piston skirt blank and a separately machined piston head blank.
In the invention, the bottom of the piston head is provided with a part of cooling oil channel. Specifically, the volume proportion of the partial cooling oil passage in the cooling oil passage cavity is preferably 20% to 80%, more preferably 30% to 70%, and more preferably 40% to 60%.
In the invention, the diameter of the cooling oil duct cavity is preferably 4-15 mm, more preferably 6-13 mm, and more preferably 8-11 mm. It should be noted that, in the present invention, the diameter of the cooling oil-passage cavity preferably refers to the diameter of the cooling oil-passage cavity in the height direction. Wherein the height direction is the same as the height direction of the piston.
In the invention, the bottom of the cooling oil duct cavity is preferably provided with an oil inlet and an oil outlet. Specifically, the oil inlet and/or the oil outlet are/is preferably obtained by electrochemical corrosion machining.
Specifically, the cooling oil passage cavity and the cooling oil passage in the invention can be processed in advance before the welding of the piston head and the skirt part, so that the shapes of the cooling oil passage cavity and the cooling oil passage can be adjusted according to actual needs or design requirements, and the cooling oil passage cavity and the cooling oil passage can be designed into more complicated shapes.
In the present invention, the shape of the cooling gallery cavity and/or the cooling gallery is preferably adjustable. The cross-sectional shape of the cooling oil passage can be circular, oval or the like.
Referring to fig. 1, fig. 1 is a schematic diagram of a cross-sectional structure of a cooling oil passage of a piston of a high-performance friction-welded cast iron piston according to the present invention.
In the present invention, the material of the cast iron piston, i.e., the material of the piston skirt portion and the material of the piston head portion, preferably includes, by mass:
C：3.70wt％～3.95wt％；
Si：2.0wt％～2.5wt％；
P：0～0.01wt％；
S：0～0.02wt％；
Mn：0～0.1wt％；
Cu：0.2wt％～0.5wt％；
Ni：0.5wt％～1.0wt％；
Nb：0.02wt％～0.06wt％；
Mo：0.1wt％～0.2wt％；
Mg：0.03wt％～0.06wt％；
Ce：0.01wt％～0.03wt％；
the balance being Fe.
Wherein, the content of C is preferably 3.70 wt% to 3.95 wt%, more preferably 3.75 wt% to 3.90 wt%, more preferably 3.80 wt% to 3.85 wt%. The content of Si is preferably 2.0 wt% to 2.5 wt%, more preferably 2.1 wt% to 2.4 wt%, and still more preferably 2.2 wt% to 2.3 wt%. The content of P is preferably 0 to 0.01 wt%, more preferably 0.002 to 0.008 wt%, and still more preferably 0.004 to 0.006 wt%. The content of S is preferably 0 to 0.02 wt%, more preferably 0.01 wt% to 0.015 wt%. The content of Mn is preferably 0 to 0.1 wt%, more preferably 0.02 wt% to 0.08 wt%, and still more preferably 0.04 wt% to 0.06 wt%. The Cu content is preferably 0.2 to 0.5 wt%, more preferably 0.25 to 0.45 wt%, and still more preferably 0.3 to 0.4 wt%. The Ni content is preferably 0.5 to 1.0 wt%, more preferably 0.6 to 0.9 wt%, and still more preferably 0.7 to 0.8 wt%. The Nb content is preferably 0.02 to 0.06 wt%, more preferably 0.03 to 0.05 wt%. The content of Mo is preferably 0.1 to 0.2 wt%, more preferably 0.12 to 0.18 wt%, and still more preferably 0.14 to 0.16 wt%. The Mg content is preferably 0.03 to 0.06 wt%, more preferably 0.04 to 0.05 wt%. The content of Ce is preferably 0.01 wt% to 0.03 wt%, more preferably 0.015 wt% to 0.025 wt%.
In the invention, the skirt part of the piston and the head part of the piston can be made of the same material, and both adopt nodular cast iron and are controlled according to the mass percentage. The material of the skirt part can also be non-quenched and tempered steel 38MnVS6Ti, the specific material is shown in Table 1, and the material of the skirt part is shown in Table 1 in percentage by mass (wt%).
TABLE 1
Figure BDA0003074348850000101
In the present invention, the cast iron piston preferably comprises a ferritic spheroidal graphite cast iron piston.
In the present invention, the ferrite content of the cast iron piston is preferably 90% or more, more preferably 93% or more, and still more preferably 95% or more. Specifically, the content of the organic solvent can be 90% -99.9%, or 92% -98%, or 94% -97%.
In the present invention, the spheroidization rate of the cast iron piston is preferably 95% or more, more preferably 97% or more, and still more preferably 99% or more. Specifically, the concentration may be 95% to 99.9%, or 96% to 99%, or 97% to 98%.
In the invention, the graphite sphere diameter of the cast iron piston is less than or equal to 0.06mm (sphere diameter size is 6-8 grade), more preferably less than or equal to 0.04mm, and still more preferably less than or equal to 0.02 mm. Specifically, the thickness of the film can be 0.01-0.06 mm, or 0.02-0.05 mm, or 0.03-0.04 mm.
In the invention, the as-cast hardness of the cast iron piston is preferably 160-200HBW, more preferably 170-195 HBW, and more preferably 180-190 HBW.
In the present invention, the as-cast strength of the cast iron piston is preferably 500MPa or more, more preferably 530MPa or more, and still more preferably 550MPa or more.
In the present invention, the elongation of the cast iron piston is preferably 7% or more, more preferably 8% or more, and still more preferably 9% or more.
In the present invention, the cast iron piston preferably has a metallographic structure including acicular ferrite and a copper-rich austenite composition, and more preferably has a metallographic structure including acicular ferrite and a copper-rich austenite composition. Specifically, the copper-rich austenite can also be a niobium-rich and copper-rich austenite structure.
In the present invention, the cast iron piston preferably further includes a manganese-based phosphate coating layer compounded on the surface of the cast iron piston.
In the present invention, the thickness of the manganese-based phosphating coating is preferably 2 to 10 μm, more preferably 3 to 9 μm, more preferably 4 to 8 μm, and more preferably 5 to 7 μm.
In the present invention, the cast iron piston preferably further includes a nanocoating layer compounded on the manganese-based phosphate coating layer. In particular, the nanocoating preferably comprises a graphite nanocoating comprising titanium dioxide.
In the invention, the thickness of the nano coating is preferably 6-16 μm, more preferably 8-14 μm, and more preferably 10-12 μm.
In the invention, the height of the cast iron piston, namely the compression height, is preferably 40-100 mm, more preferably 50-90 mm, and even more preferably 60-80 mm. In the present invention, the high compression means a distance from the center of the pin hole to the top surface of the piston.
The novel high-performance friction welding cast iron piston provided by the steps comprises the following chemical components in percentage by weight: c: 3.70-3.95 wt%, Si: 2.0-2.5 wt%, P: 0-0.01 wt%, S: 0-0.02 wt%, Mn: 0 to 0.1 wt%, Cu: 0.2 to 0.5 wt%, Ni: 0.5 to 1.0 wt%, Nb: 0.02 to 0.06 wt%, Mo: 0.1-0.2 wt%, Mg: 0.03-0.06 wt%, Ce: 0.01-0.03, the balance being Fe, the piston being made of ferrite nodular cast iron, the ferrite content being more than 90%, the spheroidization rate being more than 95%, the graphite sphere diameter being less than 0.06mm (sphere diameter size of 6-8 grade), the as-cast hardness being 160-200HBW, the as-cast strength being more than or equal to 500MPa, and the elongation being more than 7%; and carrying out integral isothermal quenching and low-temperature tempering after friction welding, wherein the hardness of a finished product is 250-300 HBW, the tensile strength is more than or equal to 850MPa, and the yield strength is more than or equal to 600 MPa.
Referring to fig. 2, fig. 2 is a schematic cross-sectional view of the appearance of a high-performance friction-welded cast iron piston according to the present invention.
The invention provides a preparation method of a cast iron piston, which comprises the following steps:
1) mixing and smelting cast iron piston raw materials to obtain molten iron, then sending the molten iron into a mold for cooling, then carrying out hot rolling to obtain a ferrite ball-milling cast iron bar, and carrying out rough machining to obtain a cast iron piston skirt blank;
mixing and smelting cast iron piston raw materials to obtain molten iron, then carrying out centrifugal casting to obtain a ferrite ball-milling cast iron pipe, and carrying out rough machining to obtain a cast iron piston head blank;
2) friction welding the cast iron piston skirt blank and the cast iron piston head blank obtained in the step to obtain a cast iron piston semi-finished product;
3) and (3) carrying out isothermal quenching treatment on the cast iron piston semi-finished product obtained in the step, then carrying out electrochemical corrosion, processing an oil inlet and outlet hole of the cast iron piston, and then carrying out heat treatment and finish machining to obtain the cast iron piston.
Firstly, mixing and smelting cast iron piston raw materials to obtain molten iron, then sending the molten iron into a mold for cooling, then carrying out hot rolling to obtain a ferrite ball-milling cast iron bar, and carrying out rough machining to obtain a cast iron piston skirt blank;
mixing and smelting cast iron piston raw materials to obtain molten iron, then carrying out centrifugal casting to obtain a ferrite ball-milling cast iron pipe, and carrying out rough machining to obtain a cast iron piston head blank.
In the invention, the smelting mode preferably comprises medium-frequency induction furnace smelting.
In the invention, the smelting temperature is preferably 1550-1650 ℃, more preferably 1570-1630 ℃ and more preferably 1590-1610 ℃.
In the present invention, the cooling manner of the mold preferably includes copper mold water cooling.
In the invention, the diameter of the ferrite ball-milling cast iron bar is preferably 100-160 mm, more preferably 120-150 mm, and more preferably 130-140 mm.
In the invention, the diameter of the ferrite ball-milling cast iron pipe is preferably 100-160 mm, more preferably 120-150 mm, and more preferably 130-140 mm.
In the invention, the wall thickness of the ferrite ball-milling cast iron pipe is preferably 15-40 mm, more preferably 20-35 mm, and more preferably 25-30 mm.
In the present invention, the welding surface roughness Rz of the rough-machined skirt blank and/or the rough-machined head blank is 100 or more, more preferably 110 or more, and still more preferably 130 or more.
In the present invention, the edge of the welding surface of the rough-machined skirt blank and/or the rough-machined head blank is provided with an arc chamfer of R1.5 to R2.0mm, more preferably an arc chamfer of R1.6 to R1.9mm, and still more preferably an arc chamfer of R1.7 to R1.8mm.
In the present invention, the bottom of the roughly machined head blank is preferably also machined with a partial cooling oil passage. And the roughly machined skirt blank is preferably further machined with a cooling oil channel matched with the piston head blank.
In the present invention, the welding surface roughness Rz of the part of the cooling oil passage of the rough machined head blank and/or the cooling oil passage of the rough machined skirt blank fitted to the piston head blank is preferably equal to or greater than 100, more preferably equal to or greater than 110, and more preferably equal to or greater than 130.
In the present invention, the welding surfaces of the partial cooling oil passage of the rough machined head blank and/or the cooling oil passage of the rough machined skirt blank fitted to the piston head blank are preferably set to be circular arcs or flat surfaces of R18 to R25 mm. Among them, the arc is more preferably R19 to R24mm, and more preferably R20 to R23 mm.
The invention is a complete and refined integral preparation process, which better ensures the structure, the appearance, the parameters and the performance of the cast iron piston, and the process can specifically comprise the following steps:
smelting a skirt blank:
accurately weighing each raw material, weighing each component according to a proportion, and smelting by adopting a medium-frequency induction furnace at the smelting temperature of 1550-1650 ℃; standing the smelted molten iron for 10-20 minutes; and then, water cooling is carried out by adopting a copper die, and then hot rolling, air cooling and finishing are carried out to form a ferrite ball-milling cast iron bar with the diameter of 100-160 mm.
More specifically, a piston skirt blank is smelted by a medium-frequency induction furnace, when a bar raw material is produced by hot rolling and air cooling, the smelting temperature is 1650-1800 ℃, and the smelted molten iron is kept stand for 10-20 minutes; pouring to form a skirt bar by adopting a copper mold water cooling technology, and then conveying an iron blank to a rolling machine for hot rolling and air cooling, wherein the rolling temperature is 1100-1250 ℃; and air cooling and finishing after rolling to form a bar with the diameter of 100-160 mm. Wherein the preheating temperature of the die is 300-500 ℃, the water supply time is 1-3 seconds, the water exciting time is 80-100 seconds, the reduction time is 100-120 seconds, and the temperature of the blank is controlled to be 1000-1100 ℃.
Smelting of a head blank:
accurately weighing each raw material, weighing each component according to the proportion, and smelting by adopting a medium-frequency induction furnace at the smelting temperature of 1550-; standing the smelted molten iron for 10-20 minutes; and then, centrifugally casting to form the ferrite ball-milling cast iron pipe with the diameter of 100-160 mm and the wall thickness of 15-40 mm.
More specifically, a piston head blank is smelted by adopting a medium-frequency induction furnace at the smelting temperature of 1500-1650, the smelted molten iron is kept stand for 10-20 minutes, then a water-cooled metal mold centrifugal casting machine is adopted to produce the piston head blank, the preheating temperature of a mold is 300-400 ℃, the water supply time is 1-3 seconds, the water injection time is 90-120 seconds, the reduction time is 110-150 seconds, and the temperature of the blank discharged from the mold is controlled to be 100-200 ℃.
Half of cooling oil passages are machined in the head portion and the skirt portion of the piston in advance, the welding surface roughness Rz is larger than 100, the welding surface is set to be an arc or a plane of R18-R25 mm, and the dimensional tolerance of the welding surface reaches +/-0.05 mm.
The semi-finished products of the piston head and the skirt formed by the method can reach the ferrite content of more than 90 percent, the spheroidization rate of more than 95 percent, the graphite sphere diameter of less than 0.06mm (the sphere diameter size is 6-8 grade), the as-cast hardness of 160-200HBW, the as-cast strength of more than or equal to 500Mpa and the elongation of more than 7 percent.
Referring to fig. 3, fig. 3 is a schematic diagram of the structure of the piston head before welding according to the present invention.
Referring to fig. 4, fig. 4 is a schematic diagram of the structure of the piston skirt prior to welding as provided by the present invention.
And then, friction welding the cast iron piston skirt blank and the cast iron piston head blank obtained in the step to obtain a cast iron piston semi-finished product.
In the present invention, the friction welding is particularly preferably performed by second-order friction welding under nitrogen protection.
In the invention, the flow rate of the nitrogen is preferably 8-10L/m3More preferably 8.5 to 9.5L/m3。
In the present invention, the pressure of the nitrogen gas is preferably 0.8 to 1MPa, and more preferably 0.85 to 0.95 MPa.
In the invention, the rotation speed of the friction welding is preferably 800-1800 r/min, more preferably 1000-1600 r/min, and more preferably 1200-1400 r/min.
In the invention, the pressure of the first-stage friction welding of the two-stage friction welding is preferably 250-270 Bar, more preferably 253-268 Bar, and more preferably 255-265 Bar.
In the present invention, the dwell time of the first-stage friction welding of the second-stage friction welding is preferably 1 to 6 seconds, more preferably 2 to 5 seconds, and still more preferably 3 to 4 seconds.
In the invention, the pressure of the second-stage friction welding is preferably 85-95 Bar, more preferably 87-93 Bar, and more preferably 89-91 Bar.
In the invention, the second-stage friction welding of the second-stage friction welding preferably has a dwell time of 3-8 seconds, more preferably 4-7 seconds, and even more preferably 5-6 seconds.
In the present invention, the inner welding surface of the second order friction welding is preferably a circular arc surface or a flat surface of R18 to R25. Among them, the arc is more preferably R19 to R24mm, and more preferably R20 to R23 mm.
The invention is a complete and refined integral preparation process, which better ensures the structure, the appearance, the parameters and the performance of the cast iron piston, and the process can specifically comprise the following steps:
firstly, cleaning semi-finished products of the head part and the skirt part of the piston to ensure cleanliness, wherein the maximum particle of impurities is less than 850 microns, and the weight of the impurities is less than 15 milligrams;
secondly, friction welding is carried out under the protection of nitrogen, wherein the flow rate of the nitrogen is 8-10L/m3The pressure is 0.8-1 MPa, and the technological parameters of the two-stage friction welding technology are special, wherein the first-stage pressure is 260 +/-10 Bar, the second-stage pressure is 90 +/-5 Bar, the rotating speed is 1000-2000 RPM, the pressure maintaining time is 5-8 seconds, and the welding shortening is 2.5 +/-0.3 mm.
According to the invention, the piston head and the skirt part are connected by adopting a nitrogen protection special second-order friction welding technology, the width of the pre-upset supporting shoulder is 3-6 mm, the thickness of the supporting shoulder is 2-3 mm, the designed width of the welding surface is 6-12 mm, and the height of the welding surface from the end surface is controlled to be 25-35 mm. The inner welding surface is an arc surface of R18-R25 +/-5 mm, or a plane inner welding surface, the welding amount is 2.0 +/-0.4 mm, and the welding amount of the outer welding surface is 3.5 +/-0.4 mm.
More specifically, after the forging pieces of the head and the skirt of the piston are roughly machined, the roughness Rz of the welding surface is larger than 100, an arc chamfer of R1.5-R2.0 mm is added to the edge of the welding surface, and the dimensional tolerance of the welding surface can reach within 0.05 mm.
After the head and the skirt of the piston are machined, a second-order friction welding technology is adopted. Wherein, the parameters of the second-order friction welding process are shown in table 2. Table 2 is a parameter table of the second order friction welding process provided by the present invention.
TABLE 2
Parameter(s) Rotational speed RPM First order pressure Second order pressure Dwell time
Require that 1500±10U/min 260±10bar 90±5bar 3～8s
The first step of the welding process: the head part and the skirt part of the piston are arranged in a tool and clamped, the head part is fixed, and the skirt part and the sliding table approach the head part at a certain speed and are separated by about 3mm after collision;
the second step is that: accelerating the head and the flywheel to a set rotating speed, and then disconnecting the driving source;
the third step: the skirt part is contacted with the head part under the preset first-stage pressure and rubs to generate heat, so that the temperature of the welding surface part of the head part and the skirt part of the piston reaches about 1200 ℃; under the action of high temperature and extrusion force, the total height of the piston is continuously reduced;
the fourth step: and the rotating speed of the flywheel is reduced to 0, the height of the piston is reduced to about 3.5 +/-0.4 mm, at the moment, preset pressure in the second stage is applied to upset forging, the pressure is kept for 3-8 seconds, then the pressure is reduced to 0, the clamp is loosened, the piston is taken down to be welded, the subsequent integral isothermal quenching treatment is carried out after welding, and nitrate remained on the surface is cleaned after discharging.
And finally, carrying out isothermal quenching treatment on the cast iron piston semi-finished product obtained in the step, carrying out electrochemical corrosion on the cast iron piston semi-finished product to machine an oil inlet and outlet hole of the cast iron piston, and carrying out heat treatment and finish machining to obtain the cast iron piston.
In the present invention, the austempering treatment preferably includes a quenching treatment step and an isothermal treatment step. Specifically, the steps of quenching treatment and isothermal treatment are carried out.
In the invention, the quenching temperature of the isothermal quenching treatment is preferably 890-910 ℃, and more preferably 895-905 ℃.
In the invention, the quenching time of the austempering treatment is preferably 30 to 180 minutes, more preferably 60 to 150 minutes, and even more preferably 90 to 120 minutes.
In the invention, the isothermal temperature of the isothermal quenching treatment is preferably 355-375 ℃, more preferably 357-373 ℃, and more preferably 360-370 ℃.
In the invention, the isothermal time of the austempering treatment is preferably 30 to 180 minutes, more preferably 60 to 150 minutes, and even more preferably 90 to 120 minutes.
In the present invention, the heat treatment is preferably a low-temperature stabilization treatment (low-temperature tempering treatment). The temperature of the heat treatment is preferably 340-380 ℃, and more preferably 350-370 ℃.
In the present invention, the heat treatment time is 2.5 to 3.5 hours, more preferably 2.7 to 3.3 hours, and still more preferably 2.9 to 3.1 hours.
In the invention, the heating rate of the heat treatment is preferably 150-300 ℃/h, more preferably 180-270 ℃/h, and more preferably 200-250 ℃/h.
After friction welding, integral isothermal quenching and low-temperature tempering are carried out, and the hardness of the obtained cast iron piston is 250-300 HBW, the tensile strength is larger than or equal to 850MPa, and the yield strength is larger than or equal to 600 MPa.
In the present invention, the finishing preferably further comprises a manganese-based phosphating step and a composite nanocoating step.
The invention is a complete and refined integral preparation process, which better ensures the structure, the appearance, the parameters and the performance of the cast iron piston, and the process can specifically comprise the following steps:
the isothermal quenching treatment adopts a quenching treatment technology of atmosphere protection.
Wherein the nitrogen flow of the protective atmosphere is 8-10 m3H, the pressure is 0.25-0.5 MPa, the purity is more than 99.999%, the quenching temperature rise speed is more than 180 ℃/h, the quenching temperature is 900 +/-10 ℃, the quenching heat preservation time is 3min/mm according to the effective wall thickness of the semi-finished product, the isothermal temperature is 365 +/-10 ℃, the isothermal time is 90 minutes, and residual salt on the surface of the semi-finished product is cleaned after isothermal quenching.
And (3) carrying out primary finish machining on the semi-finished product subjected to the isothermal quenching treatment, and then carrying out electrochemical corrosion machining on the oil inlet and outlet holes of the piston (so as to prevent the oxidation of a cold oil duct in the piston in the isothermal quenching process after the friction welding).
And then carrying out low-temperature heat treatment (low-temperature tempering treatment) on the piston semi-finished product at 360 +/-20 ℃ for 3 +/-0.5 hours at the heating speed of 150-300 ℃/h, and cooling along with the furnace. The low-temperature tempering treatment can improve the stability of the surface structure of the piston and reduce the residual stress, thereby improving the cutting performance of the final finish machining excircle and improving the stability of the final molded line of the piston.
And performing final finish machining after low-temperature tempering treatment to form a semi-finished product of the pin hole and the excircle with special molded lines. And after finish machining, forming a finished product of the novel high-performance friction welding cast iron piston through phosphorization and a novel nano coating.
The manganese series phosphating treatment step and the composite nano coating step:
the piston skirt surface with the roughness RZ larger than 100 is formed by adopting a high-temperature manganese-phosphorus co-permeation technology, the thickness of a manganese-phosphorus co-permeation layer is 6 +/-4 microns, and then a novel nano coating technology is carried out, wherein the thickness of the coating is 11 +/-5 microns.
The novel high-performance friction welding cast iron piston and the preparation method thereof provided by the invention are a novel cast iron material suitable for friction welding, namely nodular cast iron with ferrite as cast state. The welding carbon equivalent is low, the welding performance is good, the elongation is high, the limit of sulfur and phosphorus elements is strictly required, strengthening elements such as copper, nickel, niobium and molybdenum are added, and the secondary strengthening is carried out by controlling the heat treatment process of the welded piston, so that the strength and the hardness of the material are obviously improved; meanwhile, welding stress can be eliminated, a weld heat affected zone is eliminated, welding flash hardness is reduced, and the cutting performance of the friction welding piston is greatly improved through heat treatment.
The invention carries out key technical research aiming at the friction welding of ferrite ball-milling cast iron materials, the internal cooling oil passages of cast iron pistons at the present stage are all formed by lost foam casting, the casting process is complex, the casting cost is high, the casting rejection rate is high, the batch automatic production is difficult to realize, impurities are easy to remain in the internal cooling oil passages during casting, the diameter of the internal cooling oil passages which can be cast is limited, the compression height of the piston is high (the height is large), the cooling oil passages of the head part and the skirt part of the piston are processed in advance, and then the head part and the skirt part are connected in a welding mode to form a closed cooling oil passage so as to cool the piston.
The invention also carries out corresponding technical research aiming at the non-oxidation friction welding and the post-welding heat treatment of the cooling oil duct of the cast iron piston, and the cooling oil duct in the cast iron piston at the present stage is formed by lost foam casting, the surface of the cooling oil duct is not processed, the residual oxidation layer is more, and the loose oxidation layer can fall off in the running process of the piston, thereby causing serious consequences such as cylinder pulling, occlusion and the like; the invention processes the cooling oil duct of the piston head and skirt part in advance by adjusting the processing procedure, without drilling the oil outlet, so the inner cooling oil duct is equivalent to the sealing environment in the friction welding of the piston head and skirt part and the heat treatment process after welding, the surface of the inner cooling oil duct can not form an oxide layer in the welding and heat treatment process after welding, and can also avoid scrap iron entering the blind hole of the inner cooling oil duct in the finish machining process.
The invention provides a high-strength high-temperature-resistant wear-resistant piston material. As the explosion pressure and the power per liter of the diesel engine are continuously improved, the working temperature and the working environment of the piston are more and more severe, and therefore the piston is required to have good high temperature resistance and wear resistance.
Referring to fig. 5, fig. 5 is a schematic view of the production process flow of the high-performance friction-welded cast iron piston provided by the invention.
The invention provides a novel high-performance friction welding cast iron piston and a preparation method thereof, the ferrite nodular cast iron piston can be used for forming a closed cooling oil duct by pre-processing the cooling oil ducts of the head part and the skirt part of the piston and then connecting the head part and the skirt part in a welding mode; the required shape of the cooling oil channel can be processed according to the design requirement, and the surface quality of the oil channel is good. The cast iron piston prepared by the invention can reduce the height (compression height) of the traditional cast iron piston by more than 20 percent, is a novel high-performance ultralow-compression high-friction welding cast iron piston, fills the technical blank in the cast iron piston industry, can greatly reduce the piston cost, improves the service performance, can meet the severe technical requirements of the current internal combustion engine such as large explosion pressure, direct injection in a cylinder and the like, and further prolongs the service life of the piston, a cylinder sleeve, a piston ring and even an engine.
The novel high-performance friction welding cast iron piston obtained by the invention through the cast iron piston formula and the production process has high welding strength, low width of a heat affected zone, ultralow welding quantity, low oxidation, low stress and good cutting processability, the throat of the combustion chamber of the piston has good high temperature resistance and oxidation resistance, and the working face has good wear resistance, wear reduction and thermal fatigue resistance, can effectively prolong the service life of the piston, obviously reduce the frequency of replacement of the piston due to failure such as abrasion, corrosion, thermal fatigue and the like, but also can further reduce the weight of the diesel engine (the density of the nodular cast iron is less than that of steel), improve the effective power and the heat efficiency of the engine, play a good role in energy conservation and emission reduction, meanwhile, the preparation process is simple and stable, is easy for industrial automation popularization and use, and has better market prospect.
The experimental result shows that the cast iron piston prepared by the invention has low stress and good cutting processability relative to a steel piston, the throat of a combustion chamber of the piston has good high temperature resistance and oxidation resistance, the working face has good wear resistance, wear reduction and thermal fatigue resistance, the service life of the piston can be effectively prolonged, the frequency of replacement of the piston due to failure such as wear, corrosion and thermal fatigue can be obviously reduced, the weight of a diesel engine (the density of nodular cast iron is less than that of steel) can be further reduced, the effective power and the thermal efficiency of the engine can be improved, good effects of energy conservation and emission reduction can be achieved, and meanwhile, the preparation process is simple and stable, the industrial automation popularization and use are easy, and the market prospect is good.
For further illustration of the present invention, a cast iron piston and a method for manufacturing the same will be described in detail with reference to the following examples, but it should be understood that the examples are carried out on the premise of the technical solution of the present invention, and the detailed embodiments and specific operation procedures are given only for further illustration of the features and advantages of the present invention, not for limitation of the claims of the present invention, and the scope of protection of the present invention is not limited to the following examples.
Example 1
The chemical composition of the high-performance friction welding cast iron piston is calculated by the following weight percentage (%): c: 3.70-3.95 wt%, Si: 2.0-2.5 wt%, P: 0-0.01 wt%, S: 0-0.02 wt%, Mn: 0 to 0.1 wt%, Cu: 0.2 to 0.5 wt%, Ni: 0.5 to 1.0 wt%, Nb: 0.02 to 0.06 wt%, Mo: 0.1-0.2 wt%, Mg: 0.03-0.06 wt%, Ce: 0.01 to 0.03, and the balance being Fe.
The specific smelting process comprises the following steps: smelting a piston skirt blank by adopting a medium-frequency induction furnace, and standing the smelted molten iron for 10-20 minutes at a smelting temperature of 1650-1800 ℃ when a bar raw material is produced by hot rolling and air cooling; pouring to form a skirt bar by adopting a copper mold water cooling technology, and then conveying the cast iron blank to a rolling machine for hot rolling and air cooling, wherein the rolling temperature is 1100-1250 ℃; air cooling and finishing after rolling to form a bar stock with the diameter of 100-160 mm; the preheating temperature of the die is 300-500 ℃, the water supply time is 1-3 seconds, the water exciting time is 80-100 seconds, the reduction time is 100-120 seconds, and the temperature of the blank is controlled to be 1000-1100 ℃.
Smelting a head blank, accurately weighing each raw material, weighing each component according to a proportion, and smelting by adopting a medium-frequency induction furnace at the smelting temperature of 1550-1650 ℃; standing the smelted molten iron for 15 minutes; then, the ferrite ball-milling cast iron pipe with the diameter of 160-100 mm and the wall thickness of 15-40 mm is formed by centrifugal casting.
The performance of the semi-finished products of the piston head and the skirt prepared in the embodiment 1 of the invention is tested.
The result shows that the ferrite content is more than 90 percent, the spheroidization rate is more than 95 percent, the graphite sphere diameter is less than 0.06mm (the sphere diameter size is 6-8 grade), the as-cast hardness is 160-200HBW, the as-cast strength is more than or equal to 500Mpa, and the elongation is more than 7 percent.
The semi-finished products of the piston head and the skirt prepared in the example 1 of the invention are characterized.
Referring to fig. 6, fig. 6 is a graphite photograph (100 times) of a semi-finished product before friction welding of the ball-milled cast iron head skirt prepared by the present invention.
Referring to fig. 7, fig. 7 is a photograph (100 times) of a matrix structure of a semi-finished product before friction welding of the ball-milling cast iron head skirt prepared by the present invention.
Referring to fig. 8, fig. 8 is a photograph (500 times) of the matrix structure of a semi-finished product before friction welding of the ball-milled cast iron head skirt prepared by the present invention.
Friction welding of semi-finished products and heat treatment thereof
After the forging pieces of the head and the skirt of the piston are roughly processed, the roughness Rz of the welding surface is more than 100, the edge of the welding surface is added with an arc chamfer of R1.5-R2.0 mm, and the dimensional tolerance of the welding surface is within 0.05 mm; after the head and the skirt of the piston are machined, a second-order friction welding technology is adopted, and the second-order friction welding technology is adopted, wherein the parameters of the second-order friction welding process are shown in table 3.
Referring to table 3, table 3 shows the parameters of the second order friction welding process in example 1 of the present invention.
TABLE 3
Parameter(s) Rotational speed RPM First order pressure Second order pressure Dwell time
Require that 1490U/min 270bar 90bar 8s
The first step of the welding process is that the head part and the skirt part of the piston are assembled into a tool and clamped, the head part is fixed, and the skirt part and the sliding table are close to the head part at a certain speed and separated by about 3mm after collision; secondly, accelerating the head and the flywheel to a set rotating speed, and then disconnecting the driving source; thirdly, the skirt part is contacted with the head part under the preset first-stage pressure and is rubbed to generate heat, so that the temperature of the welding surface part of the head part and the skirt part of the piston reaches about 1200 ℃; under the action of high temperature and extrusion force, the total height of the piston is continuously reduced; fourthly, reducing the rotating speed of the flywheel to 0, reducing the height of the piston to 3.5 +/-0.4 mm, applying preset pressure of the second stage to upset, keeping the pressure for 4 seconds, reducing the pressure to 0, loosening the clamp, taking down the piston and welding; carrying out integral isothermal quenching treatment after welding, and cleaning the residual nitrate on the surface after discharging; and carrying out integral isothermal quenching and low-temperature tempering after friction welding.
Wherein the quenching temperature rise speed is 190 ℃/h, the quenching temperature is 900 ℃, the quenching heat preservation time is 30min, the isothermal temperature is 365 ℃, and the isothermal time is 90 min.
The semi-finished product prepared in example 1 of the present invention was subjected to performance testing.
The results show that the hardness is 280HBW, the tensile strength is 865MPa, and the yield strength is 610 MPa.
The friction welding bending strength detection result shows that the welding line is broken from the outside of the welding area by adopting bending test detection, and the welding line strength is larger than the strength of the base material.
Finishing and surface treatment of semi-finished products
After the semi-finished product is subjected to primary finish machining, the oil inlet and outlet holes of the piston are machined through electrochemical corrosion (the oxidation of a cold oil duct in the piston in the isothermal quenching process after friction welding can be prevented).
And then carrying out low-temperature tempering treatment (improving the stability of the surface structure of the piston, reducing residual stress, further improving the cutting performance of the final finish machining excircle and improving the stability of the final profile of the piston) on the piston semi-finished product at 360 +/-20 ℃ for 3 +/-0.5 hours at the heating rate of 150-300 ℃/h, cooling along with the furnace, and carrying out finish machining after the low-temperature tempering treatment to form a semi-finished product with a pin hole and an excircle of a special profile.
After phosphorization is carried out on the semi-finished product after finish machining, a manganese series phosphorization coating is compounded, and then a graphite nano coating with titanium dioxide is compounded, so that the high-performance friction welding cast iron piston finished product is formed.
The friction welded cast iron piston finished product prepared in example 1 of the present invention was characterized.
Referring to fig. 9, fig. 9 is a metallographic photograph (500 times) of a friction-welded cast iron piston finished product prepared according to the present invention.
The performance of the friction welded cast iron piston finished product prepared in the embodiment 1 of the invention is detected.
Because the wall thickness of the final product after processing is thin, and sampling detection cannot be carried out, the performance of the upper semi-finished product represents the final product (the upper semi-finished product is only processed and is not subjected to other treatment, and the mechanical property is the same as that of the finished product): the hardness is 280HBW, the tensile strength is 865MPa, and the yield strength is 610 MPa.
The friction welding bending strength detection result shows that the welding line is broken from the outside of the welding area by adopting bending test detection, and the welding line strength is larger than the strength of the base material.
While the present invention has been described in detail with respect to a novel high performance friction welded cast iron piston and method of making the same, the principles and embodiments of the present invention are described herein using specific examples, which are included to facilitate an understanding of the method and its core concepts, including the best mode, and to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. It should be noted that, for those skilled in the art, it is possible to make various improvements and modifications to the present invention without departing from the principle of the present invention, and those improvements and modifications also fall within the scope of the claims of the present invention. The scope of the invention is defined by the claims and may include other embodiments that occur to those skilled in the art. Such other embodiments are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.

Claims (10)

1. A cast iron piston is characterized by comprising a piston skirt part and a piston head part which is friction welded at the upper end of the piston skirt part;
the bottom of the piston head is provided with a part of cooling oil duct;
the top of the piston skirt part is provided with a cooling oil channel matched with the piston head part;
and a closed cooling oil passage cavity is formed between the piston head and the piston skirt through friction welding.
2. The cast iron piston of claim 1, wherein the friction weld comprises a second order friction weld;
the cast iron piston is obtained by friction welding of a piston skirt blank which is processed independently and a piston head blank which is processed independently;
the volume proportion of the partial cooling oil passage in the cooling oil passage cavity is 20-80%;
the bottom of the cooling oil duct cavity is provided with an oil inlet and an oil outlet;
the oil inlet and/or the oil outlet are/is obtained by electrochemical corrosion processing;
the shape of the cooling oil channel cavity and/or the cooling oil channel can be adjusted;
the diameter of the cooling oil duct cavity is 4-15 mm.
3. The cast iron piston according to claim 1, comprising, in mass percent:
C：3.70wt％～3.95wt％；
Si：2.0wt％～2.5wt％；
P：0～0.01wt％；
S：0～0.02wt％；
Mn：0～0.1wt％；
Cu：0.2wt％～0.5wt％；
Ni：0.5wt％～1.0wt％；
Nb：0.02wt％～0.06wt％；
Mo：0.1wt％～0.2wt％；
Mg：0.03wt％～0.06wt％；
Ce：0.01wt％～0.03wt％；
the balance being Fe.
4. The cast iron piston of claim 1, wherein the cast iron piston comprises a ferritic spheroidal graphite cast iron piston;
the ferrite content of the cast iron piston is more than or equal to 90 percent;
the spheroidization rate of the cast iron piston is more than or equal to 95 percent;
the graphite sphere diameter of the cast iron piston is less than or equal to 0.06 mm;
the as-cast hardness of the cast iron piston is 160-200 HBW;
the cast strength of the cast iron piston is more than or equal to 500 Mpa;
the elongation of the cast iron piston is more than or equal to 7 percent;
the cast iron piston has a metallographic structure composed of acicular ferrite and copper-rich austenite.
5. The cast iron piston according to claim 1, further comprising a manganese-based phosphate coating layer compounded on a surface of the cast iron piston;
the thickness of the manganese series phosphating coating is 2-10 mu m;
the cast iron piston also comprises a nano coating compounded on the manganese series phosphating coating;
the nanocoating comprises a graphite nanocoating comprising titanium dioxide;
the thickness of the nano coating is 6-16 mu m;
the compression height of the cast iron piston is 40-100 mm.
6. The preparation method of the cast iron piston is characterized by comprising the following steps of:
1) mixing and smelting cast iron piston raw materials to obtain molten iron, then sending the molten iron into a mold for cooling, then carrying out hot rolling to obtain a ferrite ball-milling cast iron bar, and carrying out rough machining to obtain a cast iron piston skirt blank;
mixing and smelting cast iron piston raw materials to obtain molten iron, then carrying out centrifugal casting to obtain a ferrite ball-milling cast iron pipe, and carrying out rough machining to obtain a cast iron piston head blank;
2) friction welding the cast iron piston skirt blank and the cast iron piston head blank obtained in the step to obtain a cast iron piston semi-finished product;
3) and (3) carrying out isothermal quenching treatment on the cast iron piston semi-finished product obtained in the step, then carrying out electrochemical corrosion, processing an oil inlet and outlet hole of the cast iron piston, and then carrying out heat treatment and finish machining to obtain the cast iron piston.
7. The preparation method according to claim 6, wherein the smelting mode comprises medium-frequency induction furnace smelting;
the smelting temperature is 1550-1650 ℃;
the cooling mode of the die comprises copper die water cooling;
the diameter of the ferrite ball-milling cast iron bar is 100-160 mm;
the diameter of the ferrite ball-milling cast iron pipe is 100-160 mm;
the wall thickness of the ferrite ball-milling cast iron pipe is 15-40 mm.
8. The method of manufacturing according to claim 6, wherein the weld surface roughness Rz of the rough-machined skirt blank and/or rough-machined head blank is 100 or greater;
the edge of the welding surface of the rough machined skirt blank and/or the rough machined head blank is added with an arc chamfer of R1.5-R2.0 mm;
a part of cooling oil duct is processed at the bottom of the head blank after rough machining;
the roughly machined skirt blank is also provided with a cooling oil duct matched with the piston head blank;
the welding surface roughness Rz of a part of the cooling oil channel of the roughly machined head blank and/or the cooling oil channel of the roughly machined skirt blank, which is matched with the piston head blank, is more than or equal to 100;
and the welding surface of the part of the cooling oil channel of the roughly machined head blank and/or the cooling oil channel matched with the piston head blank of the roughly machined skirt blank is set to be an arc or a plane of R18-R25 mm.
9. The method for manufacturing according to claim 6, wherein the friction welding is particularly a second order friction welding under nitrogen protection;
the flow rate of the nitrogen is 8-10L/m3；
The pressure of the nitrogen is 0.8-1 MPa;
the rotating speed of the friction welding is 800-1800 r/min;
the pressure of the first-order friction welding of the second-order friction welding is 250-270 Bar;
the pressure maintaining time of the first-stage friction welding of the second-stage friction welding is 1-6 seconds;
the pressure of second-order friction welding of the second-order friction welding is 85-95 Bar;
the second-order friction welding of the second-order friction welding has the pressure maintaining time of 3-8 seconds;
the inner welding surface of the second-order friction welding is an arc surface or a plane from R18 to R25.
10. The production method according to claim 6, wherein the quenching temperature of the austempering treatment is 890 to 910 ℃;
the quenching time of the isothermal quenching treatment is 30-180 minutes;
the isothermal temperature of the isothermal quenching treatment is 355-375 ℃;
the isothermal time of the isothermal quenching treatment is 30-180 minutes;
the temperature of the heat treatment is 340-380 ℃;
the heat treatment time is 2.5-3.5 hours;
the heating rate of the heat treatment is 150-300 ℃/h;
the fine finishing also comprises a manganese series phosphating treatment step and a composite nano coating step.
CN202110548352.0A 2021-05-19 2021-05-19 High-performance friction welding cast iron piston and preparation method thereof Active CN113236435B (en)

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