Effects of shot peening on material and OSK EffectsEffects ofof shotshot peeningpeening onon materialmaterial andand OOOSKKK EffectsEinflüssepart of shotauf Werkstoff peening on und material Bauteil and OSSK partpart partdurch Verfestigungsstrahlen

S1 S1S1 S1S1

2 Plastically deformed surface lay- [ N/mm[ N/ ] PlastifiziertePlastically deformed Zone surface layer 2 PlastifiziertePlastically deformedZone surface lay- [ N/mm 2] 2 PlasticallyPlastically deformed deformed surface surface lay- lay- [ N/mm[ N/mm] ]

DepthWirktiefe of influence S1 Depth of influence

Zug Zug Depth of influence

Zug Zug Depth of influence

0 0 0 0 0 Residual stress Eigenspannung Residual stress Eigenspannung Residual stress Residual stress Druck Druck Druck Druck Compression Tension

Compression Tension 0 [ mm ] Compression Tension Compression Tension 00 [ mm ] 0 0 Distance from surface [ mm[ mm ] 0 Distance from surface [ mm ] DistanceDistanceRandabstand from from surface surface = machined ungestrahlt= =shot machined peened ungestrahlt= machined= machined = shot peened verfestigungsgestrahlt= shot= shot peened peened In the shot peening process small spherical particles are propelled by air pressure orIn a the centrifugal shot peening acceleration process against small sphericalthe surface particles of a finished are propelled part and by actair likepressure tiny In Inthe the shot shot peening peening process process small small spherical spherical particles particles are are propelled propelled by by air air pressure pressure sledgeBeimor a Verfestigungsstrahlencentrifugal hammers whichacceleration plastically werden against and durch theelastica su gezieltenrfacelly deform of a Beschuss finished the materi part mit al durchand in the act Pressluft surface like tiny or ora centrifugala centrifugal acceleration acceleration against against the the su surfacerface of ofa finisheda finished part part and and act act like like tiny tiny layerodersledge Fliehkraftof components.hammers beschleunigten, which Hertzian plastically Stresskugelförmigen and deform elastica thePartikeln,lly materialdeform die thebelow wie materi winzige theal surface. in Schmiede- the surface Both sledgesledge hammers hammers which which plastically plastically and and elastica elastically llydeform deform the the materi material alin inthe the surface surface effectshämmerlayer ofappear wirken,components. simultaneous begrenzte Hertzian plastische and Stressare influen und deform elastischeced bythe tht material shotVerformungen peening below parameters.the in surface.der Bauteil- Both layerlayer of ofcomponents. components. Hertzian Hertzian Stress Stress deform deform the the material material below below the the surface. surface. Both Both Therandschichteffects elastc appear deformation erzeugt. simultaneous Bei generates der Herz`schen and highare influen compre Pressungcedssive by werden thtresidual shot die peening stress plastische in parameters. the undplastically elasti- effectseffects appear appear simultaneous simultaneous and and are are influen influencedced by by tht tht shot shot peening peening parameters. parameters. deformedscheThe Verformungelastc surface deformation layer. unter dergenerates Oberfläche high erzcompreeugt.ssive Beide residual Wirkungen stress treten in the stetsplastically ne- TheThe elastc elastc deformation deformation generates generates high high compre compressivessive residual residual stress stress in inthe the plastically plastically Thisbeneinanderdeformed surface surface auf layer und islayer. werden relieved durch from die ap liedStrahlkenngrößen tensile stress andbeeinflusst. increases Die the elastische fatigue deformeddeformed surface surface layer. layer. strengthVerformungThis surface and induziert resistancelayer is in relievedder to plastifizier stress from corro aptenliedsion Zone tensile cracking hohe stress Druckeigens and and corrosion increasespannungen. fatigue the of fatigue Das the ThisThis surface surface layer layer is is relieved relieved from from ap apliedlied tensile tensile stress stress and and increases increases the the fatigue fatigue components.Bauteilstrength wird and durch High resistance diecompressive induzierte to stress residualDrucke corroigenspannung stresionss crackingprevents an andalso bzw. corrosionthe unter formation der fatigue Oberfläche and ofpro- the strengthstrength and and resistance resistance to to stress stress corro corrosionsion cracking cracking and and corrosion corrosion fatigue fatigue of of the the pagationvoncomponents. externen of cracks. Zugspannungen High compressive entlastet residual und stre disse Dauerschwingfestigkeitprevents also the formation und dieand Be- pro- components.components. High High compressive compressive residual residual stre stressss prevents prevents also also the the formation formation and and pro- pro- ständigkeitpagation of gegen cracks. Spannungsriss- und Schwingungsrisskorrosion wird gesteigert. pagationpagation of ofcracks. cracks. 8 Gleichzeitig wird die Entstehung und Fortpflanzung von Rissen behindert. 8 8 8 8 8 7 OSK Applications of shot peening

Vehicles and agricultural machines Axle shafts, gear wheels, drive shafts, pinions, cardan shafts, forked axles, cardan joints, universal joint yokes, king pins, shift linkages, rods, clutch facing springs, clutch gears, clutch disks, tow hooks for trailers, turbine blade wheels, leaf springs, rims, etc.

Drive units and gearing Gear wheels, pinions, ring gears, internal geared wheels, worm pinions, worm wheels, hypoid bevel gears, cylindrical lantern gear wheels, input and output shafts, propellers, etc.

Combustion engines Connecting rods, cylinder liners, rocker arms, valve springs, valve tappets, crank- shafts, camshafts, pistons, piston heads, piston pins, chain wheels, link plates, pins, etc.

Steam and gas turbines Turbine disks, turbine blades, turbine rotors, etc.

Compressors and pumps Housings, impellers, distributors, valve glands, valve reeds, valve chambers, valve faces, shafts, crankshafts, pistons, cylinders, screw compressor shafts, etc.

Electrical and pneumatic tools Cylinders, jackets, percussion pistons, anvils, dies, pins, drivers, housings, tappets, percussion drills, boring bits, bore crowns, sleeves, sockets, etc.

Aeronautic and space travel Intricate components, airframes, rims, landing gears, propellers, airfoils, flaps, etc.

Machine parts Extruder shafts, extruding shafts, feed screws, worm casings, threaded spindles, anti fatigue shafts, dowel screws, splines, torsion bars, springs of all kind, membra- nes, dies, bearing housings, ball races, ball retaining rings, etc.

Chemical equipment Centrifuges, mixers, driers, spiral conveyors, oscillating conveyors, heat ex- changers, columns, containers, vessels, compensators, agitators, stirrers, paddles, impellers, fans, etc.

9 8 OSK Applications of shot peening

10 9 OSK Methods to induce compressive residual stress in a surface layer

Surface hardening - case hardening (carburized case hardening) - induction hardening - flame hardening - nitriding (nitrogen case hardening) - quench hardening - etc.

Work hardening and stretching - shot peening - deep rolling - setting - air slip process - autofrettage - coining - etc.

11 10 OSK Shot peening to induce compressive residual stress in a surface layer

Compressive residual stress in a surface layer can be pro- duced by different methods.

Shot peening has some particular advantages:

Shot peening reducing fixture, tooling and start up costs.

Shot peening reducing development and manufacturing time.

Shot peening is unaffected by the size or shape of parts.

Shot peening induces the highest possible compressive residual stress in a surface layer and is extremely valuable for resisting impact and percussive loads.

Shot peening is also most effective when using very hard steel and parts with high stress concentration factors.

Note: Shot peening is not a substitute for heat treatment, but is very effective as an additional process to im- prove many characteristic features of a material.

12 11 OSK Effects and objects of shot peening

Effects of shot peening

- changing residual stress distribution - changing microstructure in the surface layer - changing hardness in the surface layer - changing superficial structure

Objects of shot peening - increasing fatigue life (finite life and extended life) - preventing stress corrosion cracking (stress corrosion and stress corrosion fatigue) - preventing fretting fatigue (fretting and fretting corrosion) - increasing resistance to wear (abrasion and cavitation)

13 12 OSK Advantages of shot peening

The most important objective of shot peening is to increase the fatigue strength and the fatigue life.

Higher fatigue strength leads to

- less weight by the same performance - higher performance by the same weight - smaller dimensions by the same performance - higher performance by the same dimensions - greater material selection by the same performance - higher performance by the same material - lower surface finish by the same performance - higher performance by the same surface finish - higher safety margins on components - reinforcing already designed components without changing materials or dimensions - cost reduction in service and under guarantee - improving the reputation of the products

Shot peening is extremely valuable on parts with a high stress concentration factor, with high notch sensitivity, with high torsional or bending stress, with percussive load, made of brittle material or made of very hard steel.

14 13 OSK SurfaceOberflächenschwächen weakness

A) NotchKerbwirkun sensitivityg A) Kerbwirkung MakrostruktuAfter turningr AfterMikrostruktu grindingr Makrostruktur gedreht Mikrostruktur geschliffen

B) B)SpannungsverteilungSpannung Stress distributionsverteilung Bending Torsion Tensile Compression BiegungBiegung TorsionTorsion ZugZugu und.D Druckruck

C) SpannungskonzentratioSpannungskonzentrationC) Stress concentrationn BruchbeginCrackBruchbeginn start n

D) Corrosion D)Korrosio Korrosionn

E)E) GrainKo Korneinbindungrneinbindung boundaries

AnalysisSchadensanalysen shows that zeigen,crack growth dass, and von cons seltenenequently Ausnahmen failure normally abgesehen, start at die the Schä- sur- face.den an Bauteilen unter Betriebsbedingungen von der Oberfläche ausgehen. TheDie Gründereasons dafür are multifarious: sind vielfältig: - machiningmechanische creates Bearbeitung notches erzeugt Kerben - thedie höchstehighest stressSpannung by nearly bei fast all statesallen Bela of loadstungsarten is close tofindet the sisurfacech an der Oberfläche - maximumKorrosion startetstrain concentrationfast immer an is der most Oberfläche often found at the surface - corrosiondie Korneinbindung starts most ist often an der at theOberfläche surface durch die Bearbeitung geschwächt -Verfestigungsstrahlen grain boundaries are verlagertweakened die by hohenmachining. Eigenspannungen von der Oberfläche in Shotdas Innere peening der transfers Bauteile high (siehe strain Seite from 1176 theund surface 118).7). to the interior (pages 16 and 17). ThisAus diesemis the reason Grund why erhöht shot Verfestigungspeening is verystrahlen effective bei with hochfesten respect undto cycle gehärteten fatigue andWerkstoffen extremely besonders valuable wirkungsvollfor very hard dieand Sc brittlehwingfestigkeit materials. und die Lebensdauer.

15 14 O K Residual stress in the surface layer OOSKK EigenspannungResidual stress undin the Dauerfestigkeit surface layer OSSK and the resultant fatigue limit and the resultant fatigue limit [ N/mm² ] 3232 NiNi CrCr MoMo 88 5,5, (50(50 HRC)HRC) [ N/mm² ] 32 Ni Cr Mo 8 5, (50 HRC) [ N/mm² ] 32 Ni Cr Mo 8 5, (50 HRC) [ N/mm² ] 1000 1000 1000

800800 800 800 600 600600 Fatigue limit 600 Fatigue limit Fatigue limit 600 Dauerfestigkeit Fatigue limit Fatigue limit Fatigue limit 400 Residual400400 stress in the surface layer O K 400 S - 800 - 400 + 400 + 800 [ N/mm² ] and the- 800 resultant- 400 fatigue0 + 400 limit+ 800 [ [N/mm² N/mm² ] ] Compressive- 800 residual- 400stress 0 Tensile+ 400 residual+ 800 stress[ N/mm² ] CompressiveDruckeigenspannung residual stress 0 TensileZugeigenspannung residual stress Compressive residualX 4 Cr Nistress Cu Nb 16 4,Tensile(42 HRC) residual stress [ N/mm² ] 32 Ni Cr Mo 8 5, (50 HRC) [ [N/mm² N/mm² ] ] X 4 Cr Ni Cu Nb 16 4, (42 HRC) [ N/mm² ] X 4 Cr Ni Cu Nb 16 4, (42 HRC) 1000800 800800 800

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F F 200400 200 200 200 - -800 800 - -400 400 ++ 400 400 ++ 800 800 [ [N/mm² N/mm² ] ] - 800 - 400 00 + 400 + 800 [ N/mm² ] Compressive-- 800 800 residual-- 400 400 stress TensileTensile++ 400 400 residual residual++ 800 800 stress stress[ N/mm² ] Compressive- 800 residual- 400 stress 0 Tensile+ 400 residual+ 800 stress[ N/mm² ] Compressive residual stress 0 Tensile residual stress Compressive= groundDruckeigenspannung residual stress TensileZugeigenspannung= electro residual discharge machinedstress [ N/mm²= ] ground X 4 Cr Ni Cu Nb 16 4,= electro(42 HRC) discharge machined =geschliffen groundmilled ( used tool ) =funkenerosiv electroturned discharge abgetragen machined = milled ( used tool ) = turned 800 =gefräst milled ((gebrauchtes usednew tool tool ) ) Werkzeug) =gedreht turnedshot peened = milled ( new tool ) = shot peened =gefräst milledchemical ((neues new milled tool Werkzeug) ) =verfestigungsgestrahlt shot peened

t = chemical milled

i = chemical milled m 600chemisch abgetragen

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The e residual stress in the surface layer has an interrelationship DieThe Eigenspannung residualu stress an der in Oberfläche the surface eines layer Bauteiles has ansteht interrelationship im direkten Zu-

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with i the fatigue life of any component.

The residualt stress in the surface layer has an interrelationship sammenhangThewith residualthe400 fatigue mit stressseiner life ofDauerschwingfestigkeit. in any the component. surface layer has an interrelationship Shot peeninga induces high compressive residual stress in the surface layer. The re- with theF fatigue life of any component. VerfestigungsstrahlenShotsultant peening stress induces distribution induziert high from compressive in residualder Bauteilrandschicht stressresidual and stress load hohein leads the Druckeigenspannun- surface to reduced layer. stress The re- in Shot peening induces high compressive residual stress in the surface layer. The re- gen,sultantthe diesurface sich stress mitlayer. distribution den Even Betriebsspannungen after from loading, residual the stress überlagernsurface and retains load und leads zuunder einer to compressive reduceddeutlichen stress stressEnt- in sultant stress 200 distribution from residual stress and load leads to reduced stress in lastungthewhich surface derprevents Oberfläche layer. the Even formation durch after die andloading, Reduzie growth therung of surface surface der Zugspannungskomponente retains cracks. under compressive führt. stress the surface layer. Even after loading, the surface retains under compressive stress AnwhichDecarburized, der prevents Oberfläche corroded the geschwächte formation or notch and ed Bauteile growth parts ofalso(z. surface B.reach durch cracks. at l Beschichtung,east the strength Entkohlung, they had in Aufkohlung,Decarburized,which prevents Entfestigung, corroded the formation- 800 or Korrosion notch and- 400ed growth parts und meofalso surfacechanische reach+ 400 cracks.at Bearbeitung)least + the 800 strength verlieren[ N/mm² they ] had dra- in the condition they were in before these detrimental0 effects occurred. matischtheDecarburized, condition anCompressive Dauerfestigkeit. they corroded were residual inor beforeVerfestigungsstrahl notch edstress these parts detrimental also enreachTensile ertüchtigt effects at l eastresidual occurred.diese the strength Bstressauteile theyund stellthad in inthe der condition Regel deren they Dauerfestigkeit were in before imthese ungeschädigten detrimental effects Zustand occurred. wieder her. 16 = ground = electro discharge machined 16 = milled ( used tool ) = turned 16 = milled ( new tool ) = shot peened 15 = chemical milled

The residual stress in the surface layer has an interrelationship with the fatigue life of any component. Shot peening induces high compressive residual stress in the surface layer. The re- sultant stress distribution from residual stress and load leads to reduced stress in the surface layer. Even after loading, the surface retains under compressive stress which prevents the formation and growth of surface cracks. Decarburized, corroded or notched parts also reach at least the strength they had in the condition they were in before these detrimental effects occurred.

16 OSK Resultant stress distribution in a shot peened and loaded specimen

A) Stress distribution loaded unpeened 0

F F

B) Residual stress distribution shot peened

C) Resultant stress distribution shot peened and loaded

F F

Compressive stress Tensile stress 0 Shot peening only sligthly changes the physical characteristics of material, such as its strength, hardness and ductility. The important objective of shot peening is to change the stress distribution, i.e. to transfer high tensile stress from the surface to the base material.

17 16 OSK Superficial structure and stress distribution after shot peening and loading

Superficial structure after shot peening

- +

- 0 + 0 - 0 + Bending load Torsional load Compressive Tensile load load

Stress distribution after shot peening and loading

Changes to the superficial structure and the normally slight increase of hardness in the surface layer are additional effects which may be positive or sometimes nega- tive. Insufficient surface finish after shot peening can be improved by shot peening in a DUO process with glass beads, laping, honing or polishing as long as material re- moval does not exceed ca 10 percent of the compressive stressed surface layer.

18 17 OSK Spannungsverlagerung und Ober- OSK ParameterStrahlkenngrößen and effects und in Auswirkungen the shot flächenstruktur durch Verfestigungs- peeningbeim Verfestigungsstrahlen process strahlen DistributionHärteverlauf of hardness DistributionEigenspannungsverlauf of residual stress

S1 S2 MaximumMaximale of compressive E E SEmaxSEmax = = residualDruckeigenspannung stress HVmax

CompressiveDruckeigenspannung residual SE0SE0 = = stressan der at Oberflächesurface SE0 Härte HV HardnessHardnessHärte HV DephtTiefe at des maximum of com- S1S 1 = = ResidualResidual stress stress SEmax pressiveSpannungsmaximums residual stress Eigenspannung S Eigenspannung S DistanceRandabstand from surface RandabstandDistance from surface S2S 2 = = DephtWirktiefe of plastically des Strahlens deformed layer RetainedRestaustenit austenite OberflächentopographieSurface roughness Makrostruktur HVHVmaxmax = = MaximumMaximale of Härte hardness R Rtt

=geschliffen ground RRt t = = MaximumMaximale of Rauhtiefe roughness

RRt t Restaustenit Restaustenit = ungestrahlt= ground =kugelgestrahlt shot peened

AmountAmount retained retained of of austenite austenite DistanceRandabstand from surface = verfestigunsgestrahlt= shot peened

DruckluftstrahlenCompressed-air SchleuderstrahlenCentrifugal-force

VabVab Vab Shot peening system: comressed-airWahl des Strahlsystemes or centrifugal-force - + VelocityStrahlmittel- of impact AngleAuftreffgeschwindigkeit of impact und Strahlauftreffwinkel - 0 + 0 - 0 + DiameterKornklasse of shot peening media Biegung Torsion Druck Zug Densityund Dichte of shot peening media des Strahlmittels Spannungsverlagerung HardnessHärte of shot peening media des Strahlmittels

AmountStrahlmitteltreffer of impacts Die positive Veränderung der Oberflächentopographie und die Steigerung der Härte Peeningwährend timeder Strahldauer StrahlmittelbedeckungsgradCoverage in der Randschicht sind Nebeneffekte, die je nach Einsatz und Anwendung, positiv oder auch negativ sein können. Unzulässige Oberflächenqualitäten können im An- schluss an das Verfestigungsstrahlen durch geeignete Verfahren (z. B. Verfesti- Verfestigungsstrahlen verändert den Spannungszustand, die Oberflächentopogra- gungsstrahlen im “DUO Prozess”, Gleitschleifen, Polieren, Läppen, etc.) nachge- Shotphie, die peening Härte changesund das theGefüge residual in der stress, Rand schicht the superficial von metallischen structure, Bauteilen. the hardness Die bessert werden (siehe Seite 86). andAuswirkungen the microstructure werden in durch the surface das Zwischensp layer. Theiel effects von Strahlkenngr are influencedößen, by the Plastifizie- type of materialrung und and Werkstoffeigenschaften the depth of the plasticized beeinflußt. surface layer.

18 19 18 OSK Distribution of stress and its functions in the shot peening process

Distance from surface

S1 + Tensile stress Tensile 0

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REmax. = maximum compressive residual stress REmax. = f [material, shot peening media, load] RE0 = compressive residual stress at surface RE0 = f [material, shot peening time, shot media, intensity, load] S1 = depth of compressive residual stress S1 = f [material, intensity, shot peening time] S2 = depth of compressive residual stress at the maximum point S2 = f [material, shot peening time, intensity

The distribution of compressive residual stress is the most important variable in the shot peening process for improving fatigue life. The stress on surface, the maximum stress, the depth of plastic deformation and the depth of compressive residual stress at the maximum point can be affected by the parameters in the shot peening process in order to obtain the highest possible fati- gue limit.

20 19 OSK Distribution of residual stress induced OSK Distributionby different of shot residual peening stress parameters induced by different shot peening parameters

[ N/mm² ] Tempered steel, Rm = 1300 N/mm² [ N/mm² ] Tempered steel, Rm = 1300 N/mm² + 400 + 400

+ 200 + 200

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- 800 - 800 0 0.1 0.2 0.3 0.4 0.5 [ mm ] 0 0.1 0.2 0.3 0.4 0.5 [ mm ] Distance from surface Distance from surface Line Intensity Shot size Coverage Line Intensity[mm A] Shot[ mm size Ø ] Coverage [mm A] [ mm Ø ] 0.10 0.3 98 % 0.100.18 0.30.3 982 x % t 98 % 0.180.22 0.30.6 2 x t 98 % 0.22 0.6 98 % 0.30 0.6 2 x t 98 % 0.300.38 0.61.6 2 x t 98 % 0.380.48 1.61.6 982 x % t 98 % 0.48 1.6 2 x t 98 %

Different materials, different heat treatments and different parameters in the shot Differentpeening materials, process result different in different heat treatm distributionsents and of differentresidual stress. parameters in the shot peening process result in different distributions of residual stress.

21 20 21 OOSSKK DistributionDistribution of of residual residual stress stress induced induced byby different different shot shot peening peening parameters parameters

[ N/mm²[ N/mm² ] ] 1616 Mn Mn Cr Cr 5, 5, case case hardened hardened + 200+ 200

0 0

- 200- 200

- 400- 400

- 600- 600 Induced residual stress Induced residual stress

- 800- 800

- 1000- 1000

- 1200- 1200 0 0 0.10.1 0.20.2 0.30.3 0.40.4 0.50.5 [ mm[ mm ] ]

DistanceDistance from from surface surface

LineLine IntensityIntensity CoverageCoverage HardnessHardness of of shot shot [mm[mm A] A] [HRC][HRC]

0.250.25 9898 % % 4646 - 51 - 51 0.550.55 9898 % % 4646 - 51 - 51 0.550.55 9898 % % 5353 - 58 - 58

OnlyOnly shot shot peening peening parameters parameters chosen chosen with with res respectpect to to load, load, material, material, size size and and shape shape ofof parts parts will will lead lead to to the the necessary necessary and and desired desired result. result.

2222 21 OOSSKK DistributionDistribution ofof residualresidual stressstress inducedinduced byby differentdifferent shotshot peeningpeening parametersparameters

[[ N/mm²N/mm² ]] XX 55 CrCr NiNi 1818 9,9, RmRm == 620620 N/mm²N/mm²

++ 200200

00

-- 200200

-- 400400 Induced residual stress Induced residual stress

-- 600600

-- 800800 00 0.10.1 0.20.2 0.30.3 0.40.4 0.50.5 [[ mmmm ]]

DistanceDistance fromfrom surfacesurface

LineLine ShotShot mediamedia ShotShot sizesize IntensityIntensity [mm[mm Ø]Ø] [mm[mm A]A]

GlassGlass beadsbeads 0.2 0.2 0.150.15

CutCut wirewire shotshot 0.60.6 0.300.30

CutCut wirewire shotshot 1.01.0 0.400.40

InIn specialspecial materials,materials, suchsuch asas stainlessstainless ststeels,eels, aluminiumaluminium alloys,alloys, titaniumtitanium alloys,alloys, mag-mag- nesiumnesium alloys, alloys, nickel nickel based based alloys, alloys, powdered powdered metals, metals, shot shot peening peening also also induces induces compressivecompressive residualresidual stressstress withwith aallll thethe aboveabove mentionedmentioned advantages.advantages.

2323 22 OSK Distribution of residual stress induced by different shot peening parameters

Al Zn 5,6 Mg 2,5 Cu 1,6 Cr ( 7075 - T6 ) [ N/mm² ]

+ 400

+ 200

0

- 200 Induced residual stress

- 400

-600 0 0.1 0.2 0.3 0.4 0.5 [mm]

Distance from surface

Line Intensity Shot size Coverage [mm A] [mm Ø]

0.18 0.5 98 %

0.28 0.5 98 %

0.35 0.7 98 %

0.90 1.2 98 %

24 23