Research on heat treatment process of automobile piston pin

Categories:Industry news
Author:
Origin:
Time of issue:2019-11-28
Views:4

(Summary description)Whataretheheattreatmentmethodsofautomobilepistonpin? First,processingroute Differentrawmaterialformscorrespondtodifferentmachiningroutes.Atpresent,therawmaterialssuitableformanufacturingpistonpinaregenerallyhot-rolledroundsteel,cold-rolledroundsteel,hot-rolledseamlesssteelpipe,cold-rolledseamlesssteelpipe,etc.Therefore,accordingtodifferentrawmaterialpistonpinproduction,thefollowingdifferentprocessingroutescanbemade:1)hot-rolledroundsteel→roughturningoutercircle→drillinginnerhole→carburizing→Quenchingandtempering→grinding→finishedproduct;2)coldrollingroundsteel→drillinginnerhole→carburizing→quenchingandtempering→grinding→finishedproduct;3)hotrollingseamlesssteelpipe→roughturningoutercircle→carburizing→quenchingandtempering→grinding→finishedproduct;4)colddrawingseamlesssteelpipe→blanking→carburizing,quenchingandtempering→grinding→finishedproduct. Second,qualitycontrolofcarburizedlayerofpistonpin(20Cr) Thequalityofcarburizedlayerismainlycontrolledbythesizeofcarbides.Generallyspeaking,thesurfaceofchromiumcontainingsteeliseasytoformmassivecarbideswhencarburizing.Theformationconditiondependsonthecarboncontentofcarburizedlayersurface,whichcanalsobesaidtobethecarbonconcentrationduringcarburizing,regardlessofthecoolingmodeaftercarburizing.Thiscarbidecannotbeeliminatedevenifitisdirectlyquenchedaftercarburizing,soitcannotbeeliminatedbynormalizingaftercarburizing.Thiskindofmassivecarbideweakensthecombinationofcarburizedlayerandmatrixstructure,andalsoeasilycausesstressconcentrationandmakescarburizedlayerbrittle.Sothewaytosolvethisproblem:first,limitthecarbideintherangeofgrindingamount,increasegrindingallowance,soastoremoveitinthesubsequentgrindingprocess.Secondly,thecarburizingpotentialiscontrolledbyamicrocomputercontrolledatmospherecarburizingfurnace.Themaximumcarburizingpotentialoffurnacegasis1.25%,themaximumsurfacecarbonpotentialis1.15%,thefinalsurfacecarbonconcentrationis0.85%,andthediffusioncoefficientis1.60.Atthesametime,thecarburizingtimeisshortened,thediffusiontimeisprolonged,andthecarbonconcentrationinthesurfacelayerisdecreased,whichcaneffectivelycontrolandreducethedepthofmassivecarbide.SeeFig.1forcarburizingprocessofpistonpinwithcarburizingdepthof1.2mm. Third,twotimesquenchingprocessofpistonpin(20Cr) Theimprovementofthequalityandservicelifeofautomobilepistonpindependsonthereasonableheattreatmentprocess.Theheattreatmentprocessofpistonpinismainlycarburizingandquenchingprocess.Carburizingsteel(20Cr)isgenerallyquenchedandtemperedatlowtemperatureaftercarburizing.However,forthepistonpinwithhighperformancerequirements,theheattreatmentprocessoftwicequenchingandtemperingcanbeadopted.Becausethepistonpiniscarburizedunderhightemperatureforalongtime,thegrainsizeissignificantlycoarsened,andthesurfacelayeriseasytoformanetworkcementite.Suchabadstructurewillreducethestrengthofthepistonpin,reducethewearresistanceandincreasethebrittleness,especiallytheimpacttoughness.TherearetwowaystoeliminateitSecondaryquenching.ThefirsttimethequenchedpartsareheatedtoaboveAC3,three-phaserecrystallizationoccursabovethistemperature,thecoreisrefinedaftercooling,andthesurfacenetworkcementitedissolvedinausteniteiseliminated,soastoimprovethecorestrengthofpistonpin.ThesecondtimequenchedpartsareheatedtoacertaintemperatureaboveACCM.Duetothefirsttimeheating,thecorestructureisfullyaustenitizedtoavoidtheappearanceofundissolvedferrite.However,thehighcarbonpartofthesurfaceinevitablytendstooverheatandthestructureisrelativelycoarse.Inordertoimprovethesurfacestructure,thesecondtimeofheatingquenchingforhypereutectoidsteelisconducted.Thesecondtimeofheatingislowerthantheprevioustemperature,sothesurfacestructureisnotAsforthecorestructure,thesecondheatingistoreheatinthequenchedmartensitestate,refinethecarburizedlayerstructure,improvethesurfacehardnessofthepistonpin,andenhancethesurfacewearresistance.Aftercarburizingandquenching,thepistonpinwithhighcontentofalloyelementsshouldbecooledtoreducetheamountofretainedausteniteinthecarburizedlayerandimprovetheuniformityandstabilityofthesurfacehardnessofthepistonpin.SeeFig.2fortwicequenchingandtemperingprocess. Fourth,theinfluenceofcarburizationofpistonpininnerholeonfatiguelife Accordingtothetestresultsofphotoelasticstressanalysis,asshowninFigure3,thereisalargeplanetensilestressbetweenpointCandpointDintheinnerholeofpistonpin.Inmanycases,inordertoimprovethebendingandcontactfatiguestrengthoftheparts,thesurfaceofthepartsoftenproducesresidualcompressivestressthroughcarburizingandquenchingandlowtemperaturetempering.Therefore,forthepistonpinwhichisnotcarburizedandhardenedontheinnerholesurface,becausethereisnoresidualcompressivestressontheinnerholesurfaceofthepistonpin,thepointbetweenpointCandpointDoftheinnerholewillbepronetofatiguedamageatfirst,makingthepartsinvalid.However,forthepistonpinwithcarburizedandhardenedinnerholesurface,theresidualcompressivestressontheinnersurfaceofthepistonpinreducesthepossibilityoffatiguecrackontheinnerholesurface,andthefatiguecrackofthepartsusuallyoccursontheoutersurfacefirst,sothecarburizedandhardene

0





Research on heat treatment process of automobile piston pin

(Summary description)Whataretheheattreatmentmethodsofautomobilepistonpin? First,processingroute Differentrawmaterialformscorrespondtodifferentmachiningroutes.Atpresent,therawmaterialssuitableformanufacturingpistonpinaregenerallyhot-rolledroundsteel,cold-rolledroundsteel,hot-rolledseamlesssteelpipe,cold-rolledseamlesssteelpipe,etc.Therefore,accordingtodifferentrawmaterialpistonpinproduction,thefollowingdifferentprocessingroutescanbemade:1)hot-rolledroundsteel→roughturningoutercircle→drillinginnerhole→carburizing→Quenchingandtempering→grinding→finishedproduct;2)coldrollingroundsteel→drillinginnerhole→carburizing→quenchingandtempering→grinding→finishedproduct;3)hotrollingseamlesssteelpipe→roughturningoutercircle→carburizing→quenchingandtempering→grinding→finishedproduct;4)colddrawingseamlesssteelpipe→blanking→carburizing,quenchingandtempering→grinding→finishedproduct. Second,qualitycontrolofcarburizedlayerofpistonpin(20Cr) Thequalityofcarburizedlayerismainlycontrolledbythesizeofcarbides.Generallyspeaking,thesurfaceofchromiumcontainingsteeliseasytoformmassivecarbideswhencarburizing.Theformationconditiondependsonthecarboncontentofcarburizedlayersurface,whichcanalsobesaidtobethecarbonconcentrationduringcarburizing,regardlessofthecoolingmodeaftercarburizing.Thiscarbidecannotbeeliminatedevenifitisdirectlyquenchedaftercarburizing,soitcannotbeeliminatedbynormalizingaftercarburizing.Thiskindofmassivecarbideweakensthecombinationofcarburizedlayerandmatrixstructure,andalsoeasilycausesstressconcentrationandmakescarburizedlayerbrittle.Sothewaytosolvethisproblem:first,limitthecarbideintherangeofgrindingamount,increasegrindingallowance,soastoremoveitinthesubsequentgrindingprocess.Secondly,thecarburizingpotentialiscontrolledbyamicrocomputercontrolledatmospherecarburizingfurnace.Themaximumcarburizingpotentialoffurnacegasis1.25%,themaximumsurfacecarbonpotentialis1.15%,thefinalsurfacecarbonconcentrationis0.85%,andthediffusioncoefficientis1.60.Atthesametime,thecarburizingtimeisshortened,thediffusiontimeisprolonged,andthecarbonconcentrationinthesurfacelayerisdecreased,whichcaneffectivelycontrolandreducethedepthofmassivecarbide.SeeFig.1forcarburizingprocessofpistonpinwithcarburizingdepthof1.2mm. Third,twotimesquenchingprocessofpistonpin(20Cr) Theimprovementofthequalityandservicelifeofautomobilepistonpindependsonthereasonableheattreatmentprocess.Theheattreatmentprocessofpistonpinismainlycarburizingandquenchingprocess.Carburizingsteel(20Cr)isgenerallyquenchedandtemperedatlowtemperatureaftercarburizing.However,forthepistonpinwithhighperformancerequirements,theheattreatmentprocessoftwicequenchingandtemperingcanbeadopted.Becausethepistonpiniscarburizedunderhightemperatureforalongtime,thegrainsizeissignificantlycoarsened,andthesurfacelayeriseasytoformanetworkcementite.Suchabadstructurewillreducethestrengthofthepistonpin,reducethewearresistanceandincreasethebrittleness,especiallytheimpacttoughness.TherearetwowaystoeliminateitSecondaryquenching.ThefirsttimethequenchedpartsareheatedtoaboveAC3,three-phaserecrystallizationoccursabovethistemperature,thecoreisrefinedaftercooling,andthesurfacenetworkcementitedissolvedinausteniteiseliminated,soastoimprovethecorestrengthofpistonpin.ThesecondtimequenchedpartsareheatedtoacertaintemperatureaboveACCM.Duetothefirsttimeheating,thecorestructureisfullyaustenitizedtoavoidtheappearanceofundissolvedferrite.However,thehighcarbonpartofthesurfaceinevitablytendstooverheatandthestructureisrelativelycoarse.Inordertoimprovethesurfacestructure,thesecondtimeofheatingquenchingforhypereutectoidsteelisconducted.Thesecondtimeofheatingislowerthantheprevioustemperature,sothesurfacestructureisnotAsforthecorestructure,thesecondheatingistoreheatinthequenchedmartensitestate,refinethecarburizedlayerstructure,improvethesurfacehardnessofthepistonpin,andenhancethesurfacewearresistance.Aftercarburizingandquenching,thepistonpinwithhighcontentofalloyelementsshouldbecooledtoreducetheamountofretainedausteniteinthecarburizedlayerandimprovetheuniformityandstabilityofthesurfacehardnessofthepistonpin.SeeFig.2fortwicequenchingandtemperingprocess. Fourth,theinfluenceofcarburizationofpistonpininnerholeonfatiguelife Accordingtothetestresultsofphotoelasticstressanalysis,asshowninFigure3,thereisalargeplanetensilestressbetweenpointCandpointDintheinnerholeofpistonpin.Inmanycases,inordertoimprovethebendingandcontactfatiguestrengthoftheparts,thesurfaceofthepartsoftenproducesresidualcompressivestressthroughcarburizingandquenchingandlowtemperaturetempering.Therefore,forthepistonpinwhichisnotcarburizedandhardenedontheinnerholesurface,becausethereisnoresidualcompressivestressontheinnerholesurfaceofthepistonpin,thepointbetweenpointCandpointDoftheinnerholewillbepronetofatiguedamageatfirst,makingthepartsinvalid.However,forthepistonpinwithcarburizedandhardenedinnerholesurface,theresidualcompressivestressontheinnersurfaceofthepistonpinreducesthepossibilityoffatiguecrackontheinnerholesurface,andthefatiguecrackofthepartsusuallyoccursontheoutersurfacefirst,sothecarburizedandhardene

Categories:Industry news
Author:
Origin:
Time of issue:2019-11-28
Views:4

What are the heat treatment methods of automobile piston pin?

First, processing route

Different raw material forms correspond to different machining routes. At present, the raw materials suitable for manufacturing piston pin are generally hot-rolled round steel, cold-rolled round steel, hot-rolled seamless steel pipe, cold-rolled seamless steel pipe, etc. Therefore, according to different raw material piston pin production, the following different processing routes can be made: 1) hot-rolled round steel → rough turning outer circle → drilling inner hole → carburizing → Quenching and tempering → grinding → finished product; 2) cold rolling round steel → drilling inner hole → carburizing → quenching and tempering → grinding → finished product; 3) hot rolling seamless steel pipe → rough turning outer circle → carburizing → quenching and tempering → grinding → finished product; 4) cold drawing seamless steel pipe → blanking → carburizing, quenching and tempering → grinding → finished product.

Second, quality control of carburized layer of piston pin (20Cr)

The quality of carburized layer is mainly controlled by the size of carbides. Generally speaking, the surface of chromium containing steel is easy to form massive carbides when carburizing. The formation condition depends on the carbon content of carburized layer surface, which can also be said to be the carbon concentration during carburizing, regardless of the cooling mode after carburizing. This carbide can not be eliminated even if it is directly quenched after carburizing, so it can not be eliminated by normalizing after carburizing. This kind of massive carbide weakens the combination of carburized layer and matrix structure, and also easily causes stress concentration and makes carburized layer brittle. So the way to solve this problem: first, limit the carbide in the range of grinding amount, increase grinding allowance, so as to remove it in the subsequent grinding process. Secondly, the carburizing potential is controlled by a microcomputer controlled atmosphere carburizing furnace. The maximum carburizing potential of furnace gas is 1.25%, the maximum surface carbon potential is 1.15%, the final surface carbon concentration is 0.85%, and the diffusion coefficient is 1.60. At the same time, the carburizing time is shortened, the diffusion time is prolonged, and the carbon concentration in the surface layer is decreased, which can effectively control and reduce the depth of massive carbide. See Fig. 1 for carburizing process of piston pin with carburizing depth of 1.2mm.

Third, two times quenching process of piston pin (20Cr)

The improvement of the quality and service life of automobile piston pin depends on the reasonable heat treatment process. The heat treatment process of piston pin is mainly carburizing and quenching process. Carburizing steel (20Cr) is generally quenched and tempered at low temperature after carburizing. However, for the piston pin with high performance requirements, the heat treatment process of twice quenching and tempering can be adopted. Because the piston pin is carburized under high temperature for a long time, the grain size is significantly coarsened, and the surface layer is easy to form a network cementite. Such a bad structure will reduce the strength of the piston pin, reduce the wear resistance and increase the brittleness, especially the impact toughness. There are two ways to eliminate it Secondary quenching. The first time the quenched parts are heated to above AC3, three-phase recrystallization occurs above this temperature, the core is refined after cooling, and the surface network cementite dissolved in austenite is eliminated, so as to improve the core strength of piston pin. The second time quenched parts are heated to a certain temperature above ACCM. Due to the first time heating, the core structure is fully austenitized to avoid the appearance of undissolved ferrite. However, the high carbon part of the surface inevitably tends to overheat and the structure is relatively coarse. In order to improve the surface structure, the second time of heating quenching for hypereutectoid steel is conducted. The second time of heating is lower than the previous temperature, so the surface structure is not As for the core structure, the second heating is to reheat in the quenched martensite state, refine the carburized layer structure, improve the surface hardness of the piston pin, and enhance the surface wear resistance. After carburizing and quenching, the piston pin with high content of alloy elements should be cooled to reduce the amount of retained austenite in the carburized layer and improve the uniformity and stability of the surface hardness of the piston pin. See Fig. 2 for twice quenching and tempering process.

Fourth, the influence of carburization of piston pin inner hole on fatigue life

According to the test results of photoelastic stress analysis, as shown in Figure 3, there is a large plane tensile stress between point C and point D in the inner hole of piston pin. In many cases, in order to improve the bending and contact fatigue strength of the parts, the surface of the parts often produces residual compressive stress through carburizing and quenching and low temperature tempering. Therefore, for the piston pin which is not carburized and hardened on the inner hole surface, because there is no residual compressive stress on the inner hole surface of the piston pin, the point between point C and point D of the inner hole will be prone to fatigue damage at first, making the parts invalid. However, for the piston pin with carburized and hardened inner hole surface, the residual compressive stress on the inner surface of the piston pin reduces the possibility of fatigue crack on the inner hole surface, and the fatigue crack of the parts usually occurs on the outer surface first, so the carburized and hardened inner surface of the piston pin will greatly improve the fatigue life of the piston pin. For the comparison of the fatigue life of the piston pin hardened by carburizing the inner hole and the piston pin hardened by non carburizing the inner hole, see Fig. 4. The fatigue life of the piston pin hardened by carburizing the inner hole is significantly improved, and the process is simple, and the production cost is reduced.

Scan the QR code to read on your phone

Previous: How to repair and replace crank pin of motorcycle?

Next: How to repair the broken crankshaft of motorcycle engine?

Previous: How to repair and replace crank pin of motorcycle?

Next: How to repair the broken crankshaft of motorcycle engine?