Rare earth powder metallurgy natural gas engine valve guide pipe and preparation method thereof
阅读说明：本技术 一种含稀土粉末冶金天然气发动机气门导管及其制备方法 (Rare earth powder metallurgy natural gas engine valve guide pipe and preparation method thereof ) 是由 戴泽玉 王厚发 戴泽厚 于 2018-07-23 设计创作，主要内容包括：本发明公开了一种含稀土粉末冶金天然气发动机气门导管,由以下化学原料按照如下质量百分比制成：碳0.8-1.5%、铬1.7-4.5%、铜1.5-3.0%、铝3.0-4.5%、钴1.0-1.5%、镍1.0-1.5%、锰2.0-4.0%、钨0.5-1.2%、稀土元素0.1-0.3%,余量为铁,制造时加入合金粉末质量0.5-1.2％的硬脂酸锌。经过混合、压制、多段温区烧结、数控机床精加工、精磨外圆、浸油处理后,所得的天然气发动机气门导管具有高的硬度、强度、耐磨性、耐高温性和耐腐蚀性等优良性能,可在950℃以下正常工作,完全可以满足天然气发动机在高温、干摩擦和含硫气氛等服役环境中的工况要求。(The invention discloses a rare earth powder metallurgy natural gas engine valve guide pipe which is prepared from the following chemical raw materials in percentage by mass: 0.8 to 1.5 percent of carbon, 1.7 to 4.5 percent of chromium, 1.5 to 3.0 percent of copper, 3.0 to 4.5 percent of aluminum, 1.0 to 1.5 percent of cobalt, 1.0 to 1.5 percent of nickel, 2.0 to 4.0 percent of manganese, 0.5 to 1.2 percent of tungsten, 0.1 to 0.3 percent of rare earth element and the balance of iron, and zinc stearate accounting for 0.5 to 1.2 percent of the mass of the alloy powder is added during the preparation. After mixing, pressing, multi-section temperature zone sintering, finish machining of a numerical control machine tool, accurate grinding of an excircle and oil immersion treatment, the obtained natural gas engine valve guide pipe has high hardness, strength, wear resistance, high temperature resistance, corrosion resistance and other excellent performances, can normally work below 950 ℃, and can completely meet the working condition requirements of a natural gas engine in service environments such as high temperature, dry friction, sulfur-containing atmosphere and the like.)
1. The rare earth-containing powder metallurgy natural gas engine valve guide pipe is characterized by being prepared from the following chemical raw materials in percentage by mass: 0.8 to 1.5 percent of carbon, 1.7 to 4.5 percent of chromium, 1.5 to 3.0 percent of copper, 3.0 to 4.5 percent of aluminum, 1.0 to 1.5 percent of cobalt, 1.0 to 1.5 percent of nickel, 2.0 to 4.0 percent of manganese, 0.5 to 1.2 percent of tungsten, 0.1 to 0.3 percent of rare earth element and the balance of iron.
2. The natural gas engine valve guide of claim 1, wherein the rare earth element is one of cerium, lanthanum or yttrium.
3. The natural gas engine valve guide pipe containing rare earth powder metallurgy as claimed in claim 1 and claim 2, wherein the preparation method comprises the steps of powder mixing, pressing, multi-temperature zone sintering and the like, and comprises the following specific steps:
(1) sieving the alloy powder by a sieve of 100 meshes respectively, and then mixing the sieved alloy powder with the mesh number larger than 100 meshes with a proper amount of zinc stearate for 30-120 minutes;
(2) filling the raw material components uniformly mixed in the step (1) into a floating female model cavity of the valve guide for compression molding, and controlling the pressure to be 350-600MPa to obtain a valve guide green compact;
(3) placing the molded valve guide green body into a push rod furnace, manufacturing the valve guide green body by adopting a method of 4-section presintering and 3-section sintering under the protection of hydrogen, respectively controlling the presintering temperature and time and the sintering temperature and time, and naturally cooling after the presintering temperature and time and obtaining a sintered product;
(4) and carrying out finish machining, fine grinding and oil immersion treatment on the sintered product by a numerical control machine tool, and obtaining a finished product after the inspection is qualified.
4. The method for preparing the natural gas engine valve guide pipe containing the rare earth powder metallurgy according to the claim 3, wherein the zinc stearate in the step (1) is added in an amount of 0.5-1.2% of the total mass of the alloy powder.
5. The method for preparing the rare earth-containing powder metallurgy natural gas engine valve guide pipe as claimed in claim 3, wherein the pre-sintering temperature and time and the sintering temperature and time in step (3) are respectively controlled, specifically the pre-sintering temperature is controlled to be 600 ℃ and 800 ℃, and the time is 1-2 h; the sintering temperature is 950 ℃ and 1150 ℃ and the time is 1.5-2.5 h.
Technical Field
The invention relates to the technical field of powder metallurgy manufacturing of key parts of an engine, in particular to a rare earth-containing powder metallurgy natural gas engine valve guide pipe and a preparation method thereof.
Background
In recent years, non-renewable petroleum resources commonly used by people are gradually exhausted. Meanwhile, a large amount of harmful gases such as nitrogen, oxygen and sulfide emitted when petroleum fuel is used worsen the living environment pollution of human beings and aggravate the global greenhouse effect. Therefore, high-quality Gas fuels such as Compressed Natural Gas (CNG), Liquefied Natural Gas (LNG), and Liquefied Petroleum Gas (LPG) have been remarkably developed as alternative fuels for Petroleum, and have advantages of low emission pollution, low operating cost, high safety, and good social benefits, and thus have been gradually paid attention by people. At present, the development of clean fuels of this type is very rapid and the clean fuels are widely used in engines of automobiles, ships and aircrafts.
The valve guide pipe is a guide device of the engine valve, and can transfer heat on the valve rod to the cylinder cover in addition to having a guide effect on the valve, so that the purpose of heat dissipation is achieved. When the working temperature of the engine rises, the valve guide pipe needs to bear high-temperature friction and wear, and the inner hole and the valve ejector rod of the valve guide pipe deform to a certain degree, so that the sliding resistance of the valve ejector rod in the valve guide pipe is increased, and the normal work of the engine is influenced. Meanwhile, the valve guide pipe is influenced by the lateral force of the valve, the thermal load of a cylinder cover and high-temperature waste gas in an air passage in the running process of the engine, and eccentric wear is easily caused, and the phenomenon is particularly obvious in a natural gas engine. The eccentric wear of the valve guide tube causes a series of problems, such as eccentric wear of the valve seat ring, breakage of the valve, which in turn affects the supply of fuel gas, the normal operation of the ignition system, and the reliability of the natural gas engine.
Compared with diesel engines, natural gas engines have a slower combustion rate and higher exhaust gas temperatures. Because the valve guide pipe does not contain the lubricating component of fuel oil, the valve guide pipe easily generates the problems of large friction resistance, serious abrasion, large thermal load, high exhaust temperature and the like, and the valve guide pipe and the like made of traditional materials and structures are difficult to meet the use requirements of a natural gas engine. Meanwhile, natural gas containing high content of oxygen and sulfur can be oxidized and vulcanized at high temperature, so that the valve guide pipe is corroded and damaged, and the mechanical property and the service life of the valve guide pipe are further reduced. Therefore, the working condition of the natural gas engine is worse than that of gasoline and diesel engines, and the valve guide pipe which can meet the service performance requirements of the gasoline and diesel engines is seriously worn on the natural gas engine and cannot be qualified as the normal service condition. Therefore, in service, the valve guide pipe is subjected to high-temperature impact and corrosion of exhaust gas, abrasion, deformation, burning loss and even fracture failure. Generally, the service life and reliability of the valves and valve guides determine to a large extent the operating performance, service life and output power of the engine.
In summary, after the natural gas engine is used, the working condition of the valve guide is remarkably deteriorated due to the change of the fuel property and the like, and the development of a novel engine valve guide which can adapt to natural gas (CNG, LNG, LPG) and oil-gas mixed fuel is urgent.
The invention patent 1 (application publication No. CN107099754A) discloses a natural gas engine valve guide tube material, which comprises 0.5-1.2% of graphite, 1.0-4.0% of copper, 0.2-3.0% of molybdenum disulfide, 0.2-3.0% of calcium fluoride, 0.2-1.0% of manganese sulfide, 1-10% of aluminum bronze and the balance of chromium iron powder. The valve guide prepared from the material through a powder metallurgy process meets the working condition requirements of natural gas engines of national V emission standards, has the performances of high temperature resistance, wear resistance, self lubrication, easy cutting and the like, can meet the use requirements of natural gas engines with the working temperature below 500 ℃, replaces imported products, and reduces the installation cost.
Invention patent 2 (granted publication No. CN102102161B) provides a sintered valve guide and a method for manufacturing the same, the chemical composition of which comprises P0.07-0.525%, cu 3.0-10.0%, C1.0-3.0%, and the balance of Fe and inevitable impurities. The microstructure is composed of pearlite, a Fe-P-C ternary eutectic phase, a ferrite phase, a copper phase, pores, and a hard phase dispersed in the mixed structure in a mass ratio of 2 to 15%.
Invention patent 3 (application publication No. CN 102189262 a) discloses a valve guide made of a powder metal material, which is composed of: 0.6 to 1.2 percent of C, 1.0 to 3.0 percent of Cu1, 0.4 to 1.5 percent of MnSs, 0.1 to 0.2 percent of P, 0.01 to 0.05 percent of S, less than or equal to 3 percent of others, and the balance of Fe. The valve guide pipe can store lubricating oil, ensures the oil content of the guide pipe, has good self-lubricating property and good wear resistance, is beneficial to cutting, and can ensure that the dimensional precision and the surface roughness of subsequent processing are controlled within 0.01 mm.
The invention patent uses powder metallurgy method to make engine valve guide, the invention patent 1 clearly indicates that it can only be used in natural gas engine working below 500 deg.C, the invention patent 2 and invention patent 3 are for gasoline engine valve guide, they are difficult to bear the damage of high temperature dry abrasion and cavitation caused by natural gas to valve guide.
Disclosure of Invention
Aiming at the defects of the prior valve guide pipe technology and the special requirements of the valve guide pipe of the natural gas engine, the invention provides the valve guide pipe of the powder metallurgy natural gas engine containing multiple alloy elements such as chromium, cobalt, nickel, tungsten and the like, and the rare earth element (RE) is added for modification, thereby greatly reducing the abrasion and corrosion of the valve and the valve guide pipe caused by high-speed, high-temperature and repeated impact in a high-temperature and high-pressure gas environment. The valve guide pipe has excellent performances of high temperature resistance, wear resistance, oxidation resistance and the like, and can meet the discharge standards of China V and China VI.
Different from the valve guide pipe containing rare earth multicomponent alloy, the valve guide pipes 1 to 3 of the invention do not contain rare earth elements in chemical composition, and have no content of rare earth for modifying the valve guide pipe of the natural gas engine, and the density, hardness, strength, crushing strength, corrosion resistance, working temperature and the like of the valve guide pipes are not ideal, so that the valve guide pipes can not be used for a long time at high temperature. The invention patent of the application contains various alloy elements such as chromium, cobalt, nickel, tungsten and the like, and rare earth elements with obvious modification effect.
The invention is realized by the following technical scheme:
a rare earth-containing powder metallurgy natural gas engine valve guide pipe is prepared from the following chemical raw materials in percentage by mass: 0.8 to 1.5 percent of carbon, 1.7 to 4.5 percent of chromium, 1.5 to 3.0 percent of copper, 3.0 to 4.5 percent of aluminum, 1.0 to 1.5 percent of cobalt, 1.0 to 1.5 percent of nickel, 2.0 to 4.0 percent of manganese, 0.5 to 1.2 percent of tungsten, 0.1 to 0.3 percent of rare earth element and the balance of iron.
A natural gas engine valve guide tube containing rare earth powder metallurgy, wherein the rare earth element is one of cerium, lanthanum or yttrium.
A rare earth-containing powder metallurgy natural gas engine valve guide pipe is prepared by the steps of mixing powder, pressing, sintering in a multi-section temperature zone and the like, and comprises the following specific steps:
(1) sieving the alloy powder by a sieve of 100 meshes respectively, and then mixing the sieved alloy powder with the mesh number larger than 100 meshes with a proper amount of zinc stearate for 30-120 minutes;
(2) filling the raw material components uniformly mixed in the step (1) into a floating female model cavity of the valve guide for compression molding, and controlling the pressure to be 350-600MPa to obtain a valve guide green compact;
(3) placing the molded valve guide green body into a push rod furnace, manufacturing the valve guide green body by adopting a method of 4-section presintering and 3-section sintering under the protection of hydrogen, respectively controlling the presintering temperature and time and the sintering temperature and time, and naturally cooling after the presintering temperature and time and obtaining a sintered product;
(4) and carrying out finish machining, fine grinding and oil immersion treatment on the sintered product by a numerical control machine tool, and obtaining a finished product after the inspection is qualified.
A preparation method of a rare earth-containing powder metallurgy natural gas engine valve guide pipe comprises the step (1) that zinc stearate is added in an amount of 0.5-1.2% of the total mass of alloy powder.
A preparation method of a rare earth powder metallurgy natural gas engine valve guide pipe comprises the steps of respectively controlling the temperature and time of pre-sintering and the temperature and time of sintering in the step (3), specifically controlling the pre-sintering temperature to be 600-; the sintering temperature is 950 ℃ and 1150 ℃ and the time is 1.5-2.5 h.
The natural gas engine valve guide pipe contains alloy elements such as chromium, cobalt, nickel, tungsten and the like, is modified by rare earth elements, can normally work below 950 ℃, can be used under the working conditions of high temperature, dry friction and sulfur-containing atmosphere, and ensures the normal work of the natural gas engine.
The purpose of adding chromium in the present invention is to form finely dispersed Cr of high melting point and high hardness7C3The carbides are added, so that the high-temperature hardness, the strength, the thermal fatigue resistance and the corrosion resistance of the valve guide pipe are improved; in addition, chromium has a greater affinity for oxygen and can form dense Cr2O3The oxidation resistance is effectively improved by the passivation film; chromium can also form CrS and Cr7S8、Cr2S3、Cr5S8Reducing the cavitation of sulfur by various sulfides; the chromium can also act with elements such as aluminum and the like to improve the heat strength of the valve guide pipe.
The main function of cobalt in the alloy is to improve the high-temperature strength, the thermal fatigue resistance, the high-temperature sulfur corrosion resistance and the oxidation resistance, and the cobalt can increase M2The nucleation rate of carbides such as C and the like is reduced, the growth speed of the carbides is reduced, the carbides can be separated out in a fine and dispersed state and can stably exist at high temperature, and the heat strength of the matrix is improved; cobalt may also form dispersion strengthening phases (CoCrW) with other alloying elements6C-type carbide and the like, and further improves the high-temperature performance; the cobalt can reduce the diffusion rate of sulfur and improve the high-temperature sulfur corrosion resistance of the valve guide pipe; the cobalt can also improve the form and distribution of the second phases of chromium and tungsten, and improve the wear resistance.
The nickel can obviously improve the mechanical property, corrosion resistance and oxidation resistance, and can interact with chromium, tungsten and the like to form NiO & Cr2O3And the corrosion resistance, the high-temperature oxidation resistance and the heat strength of the valve guide pipe are further improved.
Tungsten can be alloyed by methods such as solid solution strengthening, precipitation strengthening, dispersion strengthening and the like, so that the high-temperature strength and plasticity of the valve guide pipe are improved; tungsten can also block MC type, M2Type C, M6The aggregation of C-type carbide is long, so that the WC can still keep higher hardness at the high temperature of more than 1000 ℃; tungsten can improve the bonding strength of metal bonds and generate carbides WC and W with high melting point and high hardness2C, and the like, can obviously improve the high-temperature strength of the valve guide pipe.
At high temperature, the aluminum, the iron and the chromium act to form a complex spinel type oxide solid solution m (FeO. Cr)2O3)+n(FeO·Al2O3) And the high-temperature oxidation resistance is obviously improved.
The rare earth elements of cerium, lanthanum and yttrium have high activity, are easy to combine with elements of oxygen, sulfur and the like to generate rare earth oxygen sulfur compounds RE2O2S and the like can simultaneously play roles in deoxidation and desulfurization, and reduce the adverse effect of sulfur and oxygen on the valve guide pipe at high temperature; one of the main damage modes of the valve guide pipe at high temperature is the preferential oxidation of grain boundaries, and trace rare earth elements can effectively inhibit the damage. The rare earth is surface active element, has high affinity with oxygen, and is favorable for forming dense rare earth compound, such as CeO2The formation of a surface oxide reaction film can be promoted in the friction process, so that the adhesion among friction pairs is favorably reduced, the abrasion is reduced, and the abrasion resistance is improved. The rare earth can form a stable compound with a high melting point to become a tiny heterogeneous crystal nucleus, and the effect of refining crystal grains is achieved; in addition, the rare earth can form W (1-3) -RE (La, Y)2O3、Al2RE、CeFe5、Fe2Ce2C3And (Fe, Ce)3C, and compounds of rare earth, nickel and cobalt and the like, so that the activity of the rare earth, nickel, iron and other elements is reduced, the solubility is increased, the alloying is accelerated, and the fatigue strength is improved; the rare earth also blocks the grain boundary migration in the sintering process, can obviously refine grains, provides more alloy element diffusion channels and is beneficial to obtaining a uniform and compact sintered body. The rare earth also reduces the sintering power, promotes the spheroidization and shrinkage of pores in a sintered body, and makes the rearrangement of particles more favorable, thereby obviously changing the morphology and distribution of the pores and leading the pores to tend to spheroidization and homogenization; the rare earth also has microalloy strengthening; improving the shape, size and distribution of harmful impurities; refining and rounding carbide; the rare earth element can also purify and strengthen crystal boundary, prevent intergranular cracks from growing and growing, and obviously improve the toughness, the shaping, the wear resistance, the corrosion resistance and the high-temperature strength of the valve guide pipe.
Compared with the powder metallurgy natural gas valve guide pipe without rare earth, the invention has the advantages that:
1. the rare earth has the effects of promoting sintering, strengthening microalloy, strengthening fine grains, changing carbide morphology, improving high-temperature strength of crystal boundary, inhibiting crack propagation, improving hardness, strength, wear resistance, corrosion resistance, high-temperature performance and the like; and the rare earth compound can be formed with oxygen and sulfur, so that the adverse effect of inclusions on the mechanical properties, particularly the impact toughness of the valve guide of the natural gas engine is reduced.
2. The invention designs the chemical composition of the natural gas engine valve guide pipe containing rare earth and alloy elements such as chromium, cobalt, nickel, tungsten and the like, and the valve guide pipe has high performance: the density is 6.7-7.0g/cm3The hardness is 80-105HRB, and the crushing strength is more than or equal to 550 MPa.
3. Under the combined action of rare earth and alloy elements of chromium, cobalt, nickel and tungsten, the valve guide tube of the powder metallurgy natural gas engine has excellent high-temperature wear resistance, oxidation resistance and sulfur corrosion resistance, and 5 multiplied by 106The abrasion loss of the secondary strengthening impact test is less than or equal to 0.1mm, and the vulcanization weight gain rate is less than 1.00 percent. The maximum working temperature of the valve guide pipe can reach 950 ℃, and the working condition requirements of the natural gas engine in high-temperature, dry friction, sulfur-containing atmosphere and other service environments can be completely met.
4. The invention designs a method for manufacturing the valve guide pipe by adopting 4-section pre-sintering and 3-section sintering under the protection of hydrogen, improves the process performance, reduces the porosity, improves the compactness and the tissue uniformity of a pressed compact and a sintered body, and ensures that the valve guide pipe of the powder metallurgy natural gas engine with high density, hardness, strength, high-temperature abrasion resistance and corrosion resistance is obtained.
Detailed Description