some manifestations of antioxidation coating for hot

Research ArticleSome Manifestations of Antioxidation Coating for Hot PrecisionForging Gears

Dongcheng Li 12 Nana Han1 Luca Quagliato3 Naksoo Kim3 and Ge Yu2

1Roll Forging Institute Jilin University Changchun China2School of Materials Science and Engineering Jilin University Changchun China3Department of Mechanical Engineering Sogang University Seoul Republic of Korea

Correspondence should be addressed to Dongcheng Li dclijlueducn

Received 21 November 2018 Revised 17 January 2019 Accepted 29 January 2019 Published 17 February 2019

Academic Editor Michael J Schu tze

Copyright copy 2019 Dongcheng Li et al+is is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

A high temperature protective coating was prepared onto the surface of 20CrMnTi steel by brushing technique and the heatedbillet was subjected to hot forging Compared with an uncoated sample the effect of coating on high-temperature oxidationbehavior of steel was investigated by scanning electron microscopy-energy dispersive spectroscopy and X-ray diffraction Beforehot forging an oxide layer of 153 μm was formed on the surface of the uncoated sample however no oxide layer was formed onthe surface of the coated sample After hot forging the thickness of scale on the surface of uncoated gear forging is 89 μmwhile thethickness of coating on the surface of coated gear forging is 39 μm It is concluded that such a coating material not only enhancesthe dimensional accuracy but also improves the surface quality of the gear

1 Introduction

Gears are the most important transmission parts used totransmit motion and power between two space shafts +eyhave some advantages of stable transmission wide appli-cation range etc With the rapid development of modernmanufacturing high precision gears are required +e coldprecision plastic forming as one of the methods processinggear has several advantages such as excellent surface qualitywithout subsequent mechanical machining of the toothsurface At present the small modulus gear is usually fab-ricated through cold precision plastic forming Howeverthere still exists a challenge in achieving gears with modulushigher than 10 processed by the cold precision plasticforming due to its large deformation resistance and non-available large tonnage forming equipment Although thedeformation resistance of the gear can be reduced by hotforging it is inevitable that the accuracy and surface qualityof gears are poor which are caused by accuracy of toolingthermal expansion and high-temperature oxidation

In a process of hot forging resistance of deformation andfriction could lead to elastic deformation which results in

dimensional deviation of the forming product In view offorming defects in dimensional accuracy Balendra [1] putsforward a method to improve the accuracy of forgings by acalculation or simulation to analyze the elastic deformationof a die and the die cavity size was compensated In order toreduce the forging defects caused by thermal expansion offorging and die Tian et al [2 3] established a formula ofequivalent linear expansion rate and a theorem of linearcompensation of the involute tooth profile which provided atheoretical basis for tooth profile design of the gear with aprecision forging die However the effect of severe oxidationon the surface of the billet at high-temperature condition hasnot been significantly investigated in relation to the surfacequality and precision of the gear

With the aim of protecting metals from oxidation at hightemperature coating has been widely used in hot stampingIn hot stamping in order to achieve the best protection effectat high temperature composition of a coating used in dif-ferent steel grades is different Al2O3-MgO-TiO2-CaO ce-ramic coating was applied to Q235B for reducing oxidationloss [4] MgO-CaO-Al2O3-SiC coatings which could beapplied on high-carbon steel [5 6] have shown a good

HindawiAdvances in Materials Science and EngineeringVolume 2019 Article ID 3864765 9 pageshttpsdoiorg10115520193864765

ability of preventing steel from oxidation and de-carburization A ceramic coating was applied on low alloysteel by the slurry spraying technique [7ndash11] +e coatinghad achieved very good antioxidation effects at 1250degC +eAl2O3-SiO2-Na2O protective coating was applied to stainlesssteel [12 13] Effect of the thickness of coating on the high-temperature oxidation was investigated When the coatingthickness is 15mm protective effect is best and the burningrate of oxidation decreased by 95 +erefore the formingquality of low carbon steel high carbon steel low alloy steeland stainless steel in the hot stamping process can be ef-fectively improved by protection coating+e stress state hasa certain effect on the oxidation layer behavior Metal flow isrelatively simple in the stamping process However forgingis mostly used for bulk forming of bar or billet In a processof bulk forming the metal flow in the three-dimensionaldirections and the stress state is complicated +e de-formation load of forging is much larger than that of sheetstamping At present research studies in hot forging underthe protection of antioxidation coating have not beenreported

So far precision forging at a temperature of more than1000degC is impossible due to intense oxidation Aims of thispaper are to achieve precision forging of gear at a tem-perature of more than 1000degC without additional machiningof the teeth In this paper a high-temperature protectivecoating suitable for hot forging of gear is prepared andinvestigated according to material properties of the blank inorder to prevent the high-temperature oxidation and toimprove the dimensional accuracy of forgings After holdingthe sample at 1100degC for 30min the surface layer structureof a sample was observed by scanning electron microscopeand high-temperature oxidation resistance of the coatingwas analyzed +e elements distribution and phase on thesurface of the sample were studied by EDX and XRD +esection structure and surface morphology of gear forgingswere analyzed by scanning electron microscope With theresults of metal flow velocity and normal pressure inDEFORM-3D simulation the predicted loads on the coatingare shown

2 Experimental

21 Preparation of Steel Sample +e chemical compositionof 20CrMnTi used in the present study is 023 C 097 Cr030 Si 097Mn 0057 Ti 0059 S 0009 P in weightpercent and Fe balanced Samples with diameter of 10mmheight of 15mm and diameter of 30mm height of 47mmwere prepared by a wire cutting machine respectivelySubsequently the samples were abraded and polished onpapers of SiC from 100 to 1000 meshes After that thesamples were cleaned and rinsed in an ultrasonic alcoholbath and dried

22 Preparation of the Coating +e coating powder consistsof the following analytical reagents Al2O3 MgO Al CaOand C +e purity of the coating powder is greater than 98An electron balance with an accuracy of 00001 grams was

used for weighing the content of mixed powder +ecomposition of the mixed powder is 1 g Al2O3 1 g MgO04 g Al 02 g C and 003 g CaO +e particle size of thecoating was nanoscale to ensure high-temperature activity+e size of the powder is about 100 nm for Al2O3 500 nm forMgO 10 μm for Al 500 nm for C and 500 nm for CaOSodium silicate was used as a binding agent in which silicaaccounts for 26 Sodium silicate with a density of 135 gcm3 is used as 8ml +e mass ratio of the coating powders tosodium silicate in the coating slurry is 1 4106 Mixture ofthe coating raw materials (coating power and binding agent)was stirred at 500 rpm for 3 hours by a magnetic stirrer tomake sure the slurry is homogeneous A method of brushcoating was adopted to obtain a uniform film on the steel+e thickness of coating was about 01mm+en the coatedsample was dried at 60degC for 2 hours

23 Experimental and Analytical Methods To evaluate aprotecting effect of coating on 20CrMnTi at high temper-atures coated and uncoated samples with a diameter of10mm and a height of 15mm were heated at 1100degC for30min in a muffle furnace +e heated sample was air-cooled and then the sample was rough ground along theradial direction with 200 mesh sandpaper+e specimen wasrotated 90 degrees and the finer sandpaper was replacedwhen the abrasion marks were uniform +e grinding paperwas used in turn with 500 and 1000 meshes +en thesample was cleaned with anhydrous ethanol and then thesurface of the sample was observed +e structure and theelement distribution of the steel specimen were analyzed byscanning electron microscopy (SEM) equipped with anenergy dispersive spectroscopy Changes of phases in thecoating and the oxide layer were analyzed by X-ray dif-fraction results

In the gear hot forging experiment the samples with adiameter of 30mm and a height of 47mm were heated to1150degC in a muffle furnace and then formed into bevel gearsin a friction press+e structure and the surface morphologyof the cross section of gear forgings were characterized bySEM

In order to verify the conditions related to the materialflow velocity and forming pressure acting on the materialsurface during the forming operation a numerical model hasbeen implemented in DEFORM-3D (deformation and heattransfer simulation) In the numerical simulation the sameprocess conditions utilized in the experiments have beenutilized and are hereafter summarized

To the top die a boundary condition resulting in amoving speed of 750mms has been applied whereas a fullconstraint has been applied to its bottom surface to thebottom dies Considering the initial position of the top die atotal of 320 steps of 01mm each have been utilized tosubdivide the total simulation step In order to avoid anymesh volume loss during the simulation the volumecompensation option has been utilized both during thecalculation as well as during the remeshing phase

Dies have been considered as rigid without heat transferdue to the small duration of the forging process and to limit

2 Advances in Materials Science and Engineering

the computational time whereas the billet has been meshedutilizing tetrahedron elements with the size ratio 2 for a totalcount of 100000 elements

For the solution of the numerical model a conjugategradient solver with the direct iteration method has beenemployed considering a Lagrangian incremental integrationAn initial temperature equal to 350degC has been applied to thedies whereas the initial billet temperature has been set to1150degC Friction has been modeled by utilizing the shearfriction formulation by setting the friction factor m 03

Moreover the convective heat transfer coefficient betweenworkpiece and environment has been set to 002NsmiddotmmmiddotdegCwhereas the conductive heat transfer coefficient between diesand billet to 5NsmiddotmmmiddotdegC Concerning the material prop-erties for the 20CrMnTi steel alloy Wei and Fu [14] char-acterized its high-temperature behavior by means oflaboratory experiments carried out at in the temperaturerange between 950degC and 1150degC and for strain rates equal to001s 01s 1s and 5s +e flow stress model [14] used inthis simulation is

σ 1

001135sinhminus1 exp

ln _εminus ln 2987 middot 1014 1113857 + 38899 middot 105 1113857(8314 middot T) 1113857

539141113890 1113891 (1)

where T is the temperature and _ε is the strain rate

3 Results and Discussion

31 Change of Sample Surface after Heating without Stress

311 Coating Layer Structure of Sample after High Tem-perature Heating Figure 1 shows the SEM picture of thecross section of uncoated and coated samples after holding1100degC for 30min in a furnace As shown in Figure 1(a) thetotal thickness of the oxide scale is 153 μm Basic structure ofthe oxide layer consists of a dense outer layer and a loose innerlayer +e outer layer is dense and thin with thickness about123 μm 8 of the total thickness of the oxide scale+e innerlayer is loose and thick with thickness about 1407 μm 92 ofthe total thickness of the oxide scale After holding at hightemperature the loose layer has good bonding strength+ereare obvious cracks between the loose layer and the dense layer+e dense layer is easily detached from the loose layer

Coated samples were held at 1100degC for 30min +ecoating was sintered and the thickness was about 105 μmwhich was tightly bonded to the substrate and there was nooxide structure between the coating and the substrate in-dicating that the coating was able to play a good oxidationprotection effect during heating Compared with the oxidestructure the coating structure is relatively so dense that theamount of the oxygen diffused to the substrate decreases+e carbon powder and aluminum powder in the coatingsurface reacts with oxygen thus reducing the oxidationatmosphere surrounding the steel surface +e coating re-duces the oxidation of the substrate

312 Influence of Coating on the Distribution of Elements ofSubstrate Figures 2 and 3 show the results of EDS mappingof the cross section of the coated and uncoated samplesheld at 1100degC for 30min As shown in Figure 2 a Si-richregion existed at the interface of the scale and the sub-strate on the uncoated sample Si in steel might react withO to form SiO2 which reacts with FeO in the scale toproduce Fe2SiO4 or eutectic products of FeO-Fe2SiO4[6 10ndash12] +erefore fayalite might be formed at theinterface of the scale and the substrate on the uncoated

sample +e compact structure of fayalite can improve theoxidation resistance of steel Meanwhile the fayaliteproducts strengthen the bonding strength between thescale and the steel substrate make scale residue on thesurface of substrate in subsequent processing and reducethe surface quality of products As the coating ingredientscontain sodium silicate the coating material contains acertain amount of Si It can be seen from Figure 3 that Sievenly distributed in the coating and no enrichment isobserved +e results show that the coating effectivelycontrols the enrichment of the Si element at the interfaceof coating and substrate while fayalite may be formed inthe coating to improve the oxidation resistance of steel+e protective effect of fayalite in the coating makes nooxide scale structure on the surface of the substrate whichreduces the oxide residue on the substrate surface andimproves the surface quality of products Fayalite alsomakes the coating better bonded to the substrate surface

As shown in Figure 3 Cr is enriched at the interface ofthe substrate and coating on the coated sample +e ox-idation of Cr will form a dense Cr2O3 protective oxidefilm which can effectively reduce the diffusion of oxygeninto the substrate Fe element appears in the enrichmentlayer of Cr which might form an Fe-Cr spinel layerAlthough the oxygen diffusion resistance in the Fe-Crspinel is much lower than that in Cr2O3 [7] there is stillsome resistance to the diffusion of oxygen to the substrateIn the uncoated sample no enrichment layer of Cr wasfound It is impossible to form a Cr2O3 protective film or adense Fe-Cr spinel layer that resists to the diffusion ofoxygen to the substrate +e above results show that thecoating can effectively improve the oxidation resistance ofthe metal

As shown in Figure 2 the content of Fe in the oxide layerof the uncoated sample is about 81 of the Fe content in thesubstrate With increasing distance from the interface ofcoating and substrate the content of Fe in the coating de-creases as shown in Figure 3 At a distance of 73 μm near tothe interface of coating and substrate the content of Feelement in the coating is about 55 of the substrate +econtent of Fe element dramatically declined far away fromthe interface more than 73 μm +ese phenomena indicated

Advances in Materials Science and Engineering 3

that the coating creates a substance being able to resist to thediffusion of Fe during heating Zhou et al [11] believed acoating of MgO will react with Fe oxides to produce the Fe-Mg spinel structure when temperature rises to 820degC +eFe-Mg spinel might be formed at a high temperature and canresist to the diffusion of Fe into the coating +e Fe-Mgspinel structure can also reduce the diffusion speed of ox-ygen hinder the diffusion of oxygen into the substrate andimprove the oxidation resistance of the substance

313 Phase Analysis of Coating Material +e XRD resultsof samples are shown in Figure 4 All samples were held at1100degC for 30min +e oxide scale of the uncoated samplewas mainly composed of Fe2O3 Fe3O4 and Fe245Si055O4 inFigure 4(a) However in Figure 4(b) it indicates that newphases are formed on the coated sample at 1100degC includingseveral spinels (MgFe2O4 MgAl2O4 and Fe(CrAl)2O4) and(Fe245Si055O4 and Fe2O3)

At high temperature an element of Si in the uncoatedsample enriched at the interface of scale and substrate wasoxidized to amorphous SiO2 Fe2SiO4 was formed when thenewly formed SiO2 reacts with iron oxides according toreaction (2) [15] Fe2SiO4 is unstable and Fe3+ substitutes apart of Fe2+ and Si4+ in Fe2SiO4 through the substitutionmechanism as shown in (3) [16] getting the compositionFe245Si055O4 From Figure 4(b) it is evident that fayalite isformed in the coating +erefore the section structure ofXRD and EDS indicated the formation of dense fayalite andspinel in the coating which prevents the formation of theoxide scale structure on the steel surface reduces the residualamount of oxide scale on the steel surface and improves thesurface quality of the forgings

2FeO + SiO2⟶ Fe2SiO4 (2)

2Fe3+⟶ Si4+ + Fe2+ (3)

At a lower temperature the aluminum powder reactswith oxygen to form a dense alumina film which can preventthe diffusion of oxygen into the metal substrate As thetemperature rises to 600degC carbon powder in the coatingreacts with oxygen ie C +O2 CO2 Oxygen content on

the surface of the sample is reduced and the oxidation ofoxygen to the substrate is relieved When the temperaturerises to 800degC the system of Na2O-SiO2 in sodium silicateappears in the liquid phase [17] which bonds various re-fractory materials (MgO Al2O3 and CaO) together It willform a dense protective film to prevent the diffusion ofoxygen to the substrate When the temperature rises to820degC MgO in the coating reacts with iron oxides andaluminum oxides to form a spinel structure [11] +e resultsof XRD and the distribution of Fe indicate that in addition tothe Fe-Mg spinel structure of the MgFe2O4 component thespinel structure of MgAl2O4 is also formed +e spinelstructure increases density of the coating and effectivelyreduces the diffusion speed of oxygen In EDS analysis of thecoated sample Fe was contained in the enrichment layer ofCr indicating that Cr2O3 was not formed in the coating It isfurther proved by XRD results that chromium reacts withiron oxides and aluminum oxides to form the Fe(CrAl)2O4spinel structure above 1100degC [6] which further enhancesdensity of the coating inhibits the diffusion of oxygen andimproves the oxidation resistance of the sample

32 Effect of Coating on Forgings

321 Effect of Coating on the Surface of Gear Forgings+e billet was heated to 1150degC and then subjected to forgein a friction press to form a certain size of bevel gear asshown in Figures 5(a) and 5(b) After forging a layer ofmaterial adheres to the surfaces of both coated gear forgingsand uncoated gear forgings +e teeth of gears are cut out asshown in Figures 5(b) and 5(e) In Figure 5(c) after hotforging the thickness of the scale on the surface of theuncoated gear is 89 μm and the oxide structure is dense InFigure 5(f) the thickness of coating on the surface of thecoated gear is 39 μm and there is no oxide structure betweenthe coating and the substrate +e thickness of the surfaceresidue of coated forgings is reduced by 562 comparedwith the uncoated forgings

Figure 6 shows the gear surface after removing thecoating or the scale It can be noted that the surface of theuncoated gear is very rough meanwhile the surface of the

Substrate

Subs

trat

e

Coat

ing

Air

(a) (c)

Looselayer

Denselayer

(b)

153μm

100μm 10μm

123μm

100μm

105μm

Figure 1 Cross section of the 20CrMnTi uncoated and coated samples after reheating (a) Uncoated sample (b) magnification of the denselayer (c) coated sample


coated gear is very smooth +e coating can enhance thesurface quality of gears Main reason for this phenomenonis that oxidation at high temperature corrodes the surface

of forging resulting the gear surface to be rough How-ever the coating reduces oxidation of the gear surface toobtain a smooth surface gear at a high temperature When

Air

Scale

100μm

Subs

trat

e

(a)

Air

Scale

Si

Subs

trat

e

(b)

Subs

trat

e

Air

Cr

Scale

(c)

Air

Fe

ScaleSu

bstr

ate

(d)

00 50

Chromium kal (μm)100 150

1

2

3

4

5

6

7

8

(e)

Iron kal (μm)0 50 100 150

0

100

50

(f )

Figure 2 Element distribution on the cross section of the 20CrMnTi uncoated sample


the coating material is applied on steel in a process of hotforging it can not only enhance the dimensional accuracybut also improve the surface quality of gears

322 Loads on the Surface of the Gear during ForgingAfter hot forging the thickness of the scale on the surface ofthe uncoated gear is 89 μm and the thickness of coating on

Substrate Coating

Air

(a)

Substrate Coating

Si

Air

(b)

Substrate Coating

Air

Cr

(c)

Air

Fe

Substrate Coating

(d)

00 50

Chromium kal (μm)100

10

20

(e)

Iron kal (μm)

0

50

100

0 50 100

(f)

Figure 3 Element distribution on the cross section of the 20CrMnTi coated sample


the surface of the coated gear is 39 μm +e hot forgingprocess of the bevel gear was simulated by means ofDEFORM-3D +rough an analysis of the normal pressureand the flow velocity in a forming process of a bevel gear theloads on the coating were shown

Figure 7 shows a time curve of the normal pressure andvelocity at top and side of a gear tooth When running to00026 s the tooth side is in contact with die +e flowvelocity of the metal at the tooth side is 723mms and theflow direction of the metal is consistent with the normal

direction of the mold surface When running to 00393 s thetooth top is in contact with the die +e flow velocity of themetal at the tooth top is 627mms and the flow directionbegins to change from the normal direction to the parallel tothe mold surface However the material at the tooth sideflows into the free surface

From the simulation results we can see that the flowvelocity of the metal is not zero In the forging process thereexits the relative movement and the friction created bycontact of the billet with the mold At 1150degC the oxide scale

Inte

nsity

(au

)

10 20

32

3 1 Fe3O42 Fe2O33 Fe245Si055O4

2

32

2 2 2

2

11

31

31

1

3

321

11

30 402θ (deg)

50 60 70 80 90

32

(a)

Inte

nsity

(au

)

1 Fe2O32 MgFe2O43 MgAl2O44 Fe(Cr Al)2O45 Fe245Si055O4

54

51

111

1

2

521

2

32 2

54

55

241

41

4

4

1

333

2

2

10 20 30 402θ (deg)

50 60 70 80 90

2

(b)

Figure 4 XRD patterns of (a) uncoated sample and (b) coated sample

(a) (b) (c)

89μm

50μm

39μm

Coating

50μm

Substrate

Substrate Scale

(f)(e)(d)

Figure 5 Bevel gears showing the (a) uncoated gear (b) uncoated teeth (c) cross section of uncoated gear forgings (d) coated gear (e)coated teeth and (f) cross section of coated gear forgings


is solid and the coating is semisolid +e relationship be-tween coating viscosity and temperature can be expressed asfollows [13]

ln η minus00065T + 1447 (4)

+e oxide scale cracks by friction and leads to oxidation ofthe exposed metal Under the action of friction the coatingthickness is reduced and the coating can be uniformly coated

on the surface of the billet to prevent further oxidation of themetal

+e size of the billet isΦ30mmtimes 47mm Before forgingthe surface area of the billet is 58434mm2 After forging thesurface area of gear forgings is 76453mm2 Gear forgingincreased the surface area of the billet by 31 Under actionof the forging stress the oxide scale cracks because of in-creasing surface area and exposes the nonoxidation metalleading to further oxidation of the billet and increasing the

(a) Gear surface Gear surface

20μm 20μm

(b)

Figure 6 +e gear surface after removing (a) the scale of the uncoated gear surface and (b) the coating of the coated gear surface

P1 tooth topP2 tooth side

0

ndash200

ndash400

ndash600

ndash800

ndash1000

ndash1200

ndash1400

ndash1600

ndash2500Velocity direction

Before contact

Nor

mal

pre

ssur

e (M

Pa)

Vel

ocity

(mm

sec

)

After contact

Afte

r con

tact

Befo

re co

ntac

t

ndash2000

ndash1500

ndash1000745723627522

213131

340000 000500026 0010 0015 0020

Time (sec)0025 0030 0035 004000415

00393

Figure 7 Time curves of the normal pressure and the velocity in tooth top and tooth side


thickness of the oxide scale Under the same forging stress theslurry of coating flows and a layer of coating covered on thesurface of forgings prevent further oxidation of the forgings+e coating thickness is only 438 of the scale thickness on thesurface of noncoating forgings and the quality of the gearsurface is improved thus the dimensional accuracy and surfacequality of gear forgings are efficiently improved

4 Conclusions

(1) To solve the problem of high-temperature oxidation aprotective coating was prepared onto the surface of20CrMnTi steel by the brushing technique Holding at1100degC for 30min an oxide layer of 153μm wasformed on the surface of the uncoated sample how-ever no oxide layer was formed on the surface of thecoated sample+e coating enhanced the antioxidationability of 20CrMnTi steel

(2) X-ray diffraction analyses revealed that MgFe2O4MgAl2O4 Fe(CrAl)2O4 and Fe245Si055O4 wereformed on the coated sample at 1100degC which in-creases the density of coating and effectively reducesthe diffusion speed of oxygen

(3) +e billet was heated to 1150degC and then subjected tobe forged in a friction press to form a certain size ofbevel gear After hot forging the thickness of the scaleon the uncoated surface is 89μmwhile the thickness offilm on the coating surface is 39μm After removingthe oxide scale or coating film the surface of theuncoated gear is rough and the surface of the coatedgear is very smoothWhen applied on the surface of thesteel such a coating material can not only enhance thedimensional accuracy but also improve the surfacequality of forged gears

(4) In the forging process there is friction on the surfacebetween billet and die and the surface area of billet willincrease +e oxide scale will crack and lead to furtheroxidation of the metal of the uncoated billet But forthe coating billet the coating thickness is reduced andthe coating slurry can be uniformly adhered on thesurface of the billet to prevent further oxidation of themetal So the coating can effectively improve thedimensional accuracy and the surface quality of gearforgings

Data Availability

+e data used to support the findings of this study areavailable from Nana Han upon request

Conflicts of Interest

+e authors declare that there are no conflicts of interestregarding the publication of this paper

References

[1] R Balendra ldquoEconomic considerations in die-form com-pensation for nett-formingrdquo Journal of Materials ProcessingTechnology vol 115 no 2 pp 260ndash263 2001

[2] Z B He G N Chu J Zhang et al ldquoDevelopment of forgingtechnologyrdquo Journal of Plasticity Engineering vol 15 no 4pp 13ndash18 2008

[3] F X Tian ldquoDesign of tooth form of die for precision forgingspur gearrdquo Forging and Stamping Technology vol 2 pp 57ndash59 1998

[4] XM Xia M J SunWWang et al ldquoIndustry experiment andeffect of oxidation resistance coating for steel slabrdquo BaosteelTechnical Research vol 6 no 4 pp 11ndash15 2012

[5] M Kitayama and H Odashima ldquoMethod for preventingdecarburization of steel materialsrdquo US Patent 4227945 1980

[6] X Wang L Wei X Zhou X Zhang S Ye and Y Chen ldquoAsuperficial coating to improve oxidation and decarburizationresistance of bearing steel at high temperaturerdquo AppliedSurface Science vol 258 no 11 pp 4977ndash4982 2012

[7] X Shan L Q Wei X M Zhang et al ldquoA protective ceramiccoating to improve oxidation and thermal shock resistance onCrMn alloy at elevated temperaturesrdquo Ceramics Internationalvol 41 no 3 pp 4706ndash4713 2015

[8] M H Chen W B Li M L Shen S Zhu and F Wang ldquoGlasscoatings on stainless steels for high-temperature oxidationprotection mechanismsrdquo Corrosion Science vol 82pp 316ndash327 2016

[9] X H Yang X Zhou S T Wang et al ldquoStudy on mechanismof Mg-Al-O high temperature protective coating for Ni-containing alloy steelrdquo Paint and Coatings Industry vol 46no 1 pp 1ndash7 2016

[10] G Fu L Wei X Shan et al ldquoInfluence of a Cr2O3 glasscoating on enhancing the oxidation resistance of 20MnSiNbstructural steelrdquo Surface and Coatings Technology vol 294pp 8ndash14 2016

[11] X Zhou S F Ye H W Xu P Liu X J Wang and L Q WeildquoInfluence of ceramic coating of MgO on oxidation behaviorand descaling ability of low alloy steelrdquo Surface and CoatingsTechnology vol 206 no 17 pp 3619ndash3625 2012

[12] X Shan L Q Wei P Liu et al ldquoInfluence of CoO glass-ceramic coating on the anti-oxidation behavior and ther-mal shock resistance of 200 stainless steel at elevatedtemperaturerdquo Ceramics International vol 40 no 8pp 12327ndash12335 2014

[13] J X Zhu S L Liu and L Q Zhang ldquoHigh-temperatureresistant coating for stainless steelrdquo Materials Protectionvol 30 no 9 pp 38ndash42 2000

[14] F Wei and Y Fu ldquoHigh temperature deformation behaviorand constitutive modeling for 20CrMnTiH steelrdquoMaterials ampDesign vol 57 pp 465ndash471 2014

[15] A Chattopadhyay and T Chanda ldquoRole of silicon on oxidemorphology and pickling behaviour of automotive steelsrdquoScripta Materialia vol 58 no 10 pp 882ndash885 2008

[16] A B Woodland and R J Angel ldquoCrystal structure of a newspinelloid with the wadsleyite structure in the systemFe2SiO4-Fe3O4 and implications for the Earthrsquos mantlerdquoAmerican Mineralogist vol 83 no 3-4 pp 404ndash408 1998

[17] Y Q Liu Phase Diagrams in Silicate Ceramics ChemicalIndustry Press Beijing China 1st edition 2011


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ability of preventing steel from oxidation and de-carburization A ceramic coating was applied on low alloysteel by the slurry spraying technique [7ndash11] +e coatinghad achieved very good antioxidation effects at 1250degC +eAl2O3-SiO2-Na2O protective coating was applied to stainlesssteel [12 13] Effect of the thickness of coating on the high-temperature oxidation was investigated When the coatingthickness is 15mm protective effect is best and the burningrate of oxidation decreased by 95 +erefore the formingquality of low carbon steel high carbon steel low alloy steeland stainless steel in the hot stamping process can be ef-fectively improved by protection coating+e stress state hasa certain effect on the oxidation layer behavior Metal flow isrelatively simple in the stamping process However forgingis mostly used for bulk forming of bar or billet In a processof bulk forming the metal flow in the three-dimensionaldirections and the stress state is complicated +e de-formation load of forging is much larger than that of sheetstamping At present research studies in hot forging underthe protection of antioxidation coating have not beenreported

So far precision forging at a temperature of more than1000degC is impossible due to intense oxidation Aims of thispaper are to achieve precision forging of gear at a tem-perature of more than 1000degC without additional machiningof the teeth In this paper a high-temperature protectivecoating suitable for hot forging of gear is prepared andinvestigated according to material properties of the blank inorder to prevent the high-temperature oxidation and toimprove the dimensional accuracy of forgings After holdingthe sample at 1100degC for 30min the surface layer structureof a sample was observed by scanning electron microscopeand high-temperature oxidation resistance of the coatingwas analyzed +e elements distribution and phase on thesurface of the sample were studied by EDX and XRD +esection structure and surface morphology of gear forgingswere analyzed by scanning electron microscope With theresults of metal flow velocity and normal pressure inDEFORM-3D simulation the predicted loads on the coatingare shown

2 Experimental

21 Preparation of Steel Sample +e chemical compositionof 20CrMnTi used in the present study is 023 C 097 Cr030 Si 097Mn 0057 Ti 0059 S 0009 P in weightpercent and Fe balanced Samples with diameter of 10mmheight of 15mm and diameter of 30mm height of 47mmwere prepared by a wire cutting machine respectivelySubsequently the samples were abraded and polished onpapers of SiC from 100 to 1000 meshes After that thesamples were cleaned and rinsed in an ultrasonic alcoholbath and dried

22 Preparation of the Coating +e coating powder consistsof the following analytical reagents Al2O3 MgO Al CaOand C +e purity of the coating powder is greater than 98An electron balance with an accuracy of 00001 grams was

used for weighing the content of mixed powder +ecomposition of the mixed powder is 1 g Al2O3 1 g MgO04 g Al 02 g C and 003 g CaO +e particle size of thecoating was nanoscale to ensure high-temperature activity+e size of the powder is about 100 nm for Al2O3 500 nm forMgO 10 μm for Al 500 nm for C and 500 nm for CaOSodium silicate was used as a binding agent in which silicaaccounts for 26 Sodium silicate with a density of 135 gcm3 is used as 8ml +e mass ratio of the coating powders tosodium silicate in the coating slurry is 1 4106 Mixture ofthe coating raw materials (coating power and binding agent)was stirred at 500 rpm for 3 hours by a magnetic stirrer tomake sure the slurry is homogeneous A method of brushcoating was adopted to obtain a uniform film on the steel+e thickness of coating was about 01mm+en the coatedsample was dried at 60degC for 2 hours

23 Experimental and Analytical Methods To evaluate aprotecting effect of coating on 20CrMnTi at high temper-atures coated and uncoated samples with a diameter of10mm and a height of 15mm were heated at 1100degC for30min in a muffle furnace +e heated sample was air-cooled and then the sample was rough ground along theradial direction with 200 mesh sandpaper+e specimen wasrotated 90 degrees and the finer sandpaper was replacedwhen the abrasion marks were uniform +e grinding paperwas used in turn with 500 and 1000 meshes +en thesample was cleaned with anhydrous ethanol and then thesurface of the sample was observed +e structure and theelement distribution of the steel specimen were analyzed byscanning electron microscopy (SEM) equipped with anenergy dispersive spectroscopy Changes of phases in thecoating and the oxide layer were analyzed by X-ray dif-fraction results

In the gear hot forging experiment the samples with adiameter of 30mm and a height of 47mm were heated to1150degC in a muffle furnace and then formed into bevel gearsin a friction press+e structure and the surface morphologyof the cross section of gear forgings were characterized bySEM

In order to verify the conditions related to the materialflow velocity and forming pressure acting on the materialsurface during the forming operation a numerical model hasbeen implemented in DEFORM-3D (deformation and heattransfer simulation) In the numerical simulation the sameprocess conditions utilized in the experiments have beenutilized and are hereafter summarized

To the top die a boundary condition resulting in amoving speed of 750mms has been applied whereas a fullconstraint has been applied to its bottom surface to thebottom dies Considering the initial position of the top die atotal of 320 steps of 01mm each have been utilized tosubdivide the total simulation step In order to avoid anymesh volume loss during the simulation the volumecompensation option has been utilized both during thecalculation as well as during the remeshing phase

Dies have been considered as rigid without heat transferdue to the small duration of the forging process and to limit





σ 1



539141113890 1113891 (1)















2Fe3+⟶ Si4+ + Fe2+ (3)






Substrate

Subs

trat

e

Coat

ing

Air

(a) (c)

Looselayer

Denselayer

(b)

153μm

100μm 10μm

123μm

100μm

105μm





Air

Scale

100μm

Subs

trat

e

(a)

Air

Scale

Si

Subs

trat

e

(b)

Subs

trat

e

Air

Cr

Scale

(c)

Air

Fe

ScaleSu

bstr

ate

(d)

00 50


1

2

3

4

5

6

7

8

(e)

Iron kal (μm)0 50 100 150

0

100

50

(f )





Substrate Coating

Air

(a)

Substrate Coating

Si

Air

(b)

Substrate Coating

Air

Cr

(c)

Air

Fe

Substrate Coating

(d)

00 50


10

20

(e)

Iron kal (μm)

0

50

100

0 50 100

(f)







Inte

nsity

(au

)

10 20

32

3 1 Fe3O42 Fe2O33 Fe245Si055O4

2

32

2 2 2

2

11

31

31

1

3

321

11

30 402θ (deg)

50 60 70 80 90

32

(a)

Inte

nsity

(au

)


54

51

111

1

2

521

2

32 2

54

55

241

41

4

4

1

333

2

2

10 20 30 402θ (deg)

50 60 70 80 90

2

(b)


(a) (b) (c)

89μm

50μm

39μm

Coating

50μm

Substrate

Substrate Scale

(f)(e)(d)




ln η minus00065T + 1447 (4)





20μm 20μm

(b)



0

ndash200

ndash400

ndash600

ndash800

ndash1000

ndash1200

ndash1400

ndash1600


Before contact

Nor

mal

pre

ssur

e (M

Pa)

Vel

ocity

(mm

sec

)

After contact

Afte

r con

tact

Befo

re co

ntac

t

ndash2000

ndash1500

ndash1000745723627522

213131

340000 000500026 0010 0015 0020

Time (sec)0025 0030 0035 004000415

00393




4 Conclusions





Data Availability




References





















Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls







σ 1



539141113890 1113891 (1)















2Fe3+⟶ Si4+ + Fe2+ (3)






Substrate

Subs

trat

e

Coat

ing

Air

(a) (c)

Looselayer

Denselayer

(b)

153μm

100μm 10μm

123μm

100μm

105μm





Air

Scale

100μm

Subs

trat

e

(a)

Air

Scale

Si

Subs

trat

e

(b)

Subs

trat

e

Air

Cr

Scale

(c)

Air

Fe

ScaleSu

bstr

ate

(d)

00 50


1

2

3

4

5

6

7

8

(e)

Iron kal (μm)0 50 100 150

0

100

50

(f )





Substrate Coating

Air

(a)

Substrate Coating

Si

Air

(b)

Substrate Coating

Air

Cr

(c)

Air

Fe

Substrate Coating

(d)

00 50


10

20

(e)

Iron kal (μm)

0

50

100

0 50 100

(f)







Inte

nsity

(au

)

10 20

32

3 1 Fe3O42 Fe2O33 Fe245Si055O4

2

32

2 2 2

2

11

31

31

1

3

321

11

30 402θ (deg)

50 60 70 80 90

32

(a)

Inte

nsity

(au

)


54

51

111

1

2

521

2

32 2

54

55

241

41

4

4

1

333

2

2

10 20 30 402θ (deg)

50 60 70 80 90

2

(b)


(a) (b) (c)

89μm

50μm

39μm

Coating

50μm

Substrate

Substrate Scale

(f)(e)(d)




ln η minus00065T + 1447 (4)





20μm 20μm

(b)



0

ndash200

ndash400

ndash600

ndash800

ndash1000

ndash1200

ndash1400

ndash1600


Before contact

Nor

mal

pre

ssur

e (M

Pa)

Vel

ocity

(mm

sec

)

After contact

Afte

r con

tact

Befo

re co

ntac

t

ndash2000

ndash1500

ndash1000745723627522

213131

340000 000500026 0010 0015 0020

Time (sec)0025 0030 0035 004000415

00393




4 Conclusions





Data Availability




References





















Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls








2Fe3+⟶ Si4+ + Fe2+ (3)






Substrate

Subs

trat

e

Coat

ing

Air

(a) (c)

Looselayer

Denselayer

(b)

153μm

100μm 10μm

123μm

100μm

105μm





Air

Scale

100μm

Subs

trat

e

(a)

Air

Scale

Si

Subs

trat

e

(b)

Subs

trat

e

Air

Cr

Scale

(c)

Air

Fe

ScaleSu

bstr

ate

(d)

00 50


1

2

3

4

5

6

7

8

(e)

Iron kal (μm)0 50 100 150

0

100

50

(f )





Substrate Coating

Air

(a)

Substrate Coating

Si

Air

(b)

Substrate Coating

Air

Cr

(c)

Air

Fe

Substrate Coating

(d)

00 50


10

20

(e)

Iron kal (μm)

0

50

100

0 50 100

(f)







Inte

nsity

(au

)

10 20

32

3 1 Fe3O42 Fe2O33 Fe245Si055O4

2

32

2 2 2

2

11

31

31

1

3

321

11

30 402θ (deg)

50 60 70 80 90

32

(a)

Inte

nsity

(au

)


54

51

111

1

2

521

2

32 2

54

55

241

41

4

4

1

333

2

2

10 20 30 402θ (deg)

50 60 70 80 90

2

(b)


(a) (b) (c)

89μm

50μm

39μm

Coating

50μm

Substrate

Substrate Scale

(f)(e)(d)




ln η minus00065T + 1447 (4)





20μm 20μm

(b)



0

ndash200

ndash400

ndash600

ndash800

ndash1000

ndash1200

ndash1400

ndash1600


Before contact

Nor

mal

pre

ssur

e (M

Pa)

Vel

ocity

(mm

sec

)

After contact

Afte

r con

tact

Befo

re co

ntac

t

ndash2000

ndash1500

ndash1000745723627522

213131

340000 000500026 0010 0015 0020

Time (sec)0025 0030 0035 004000415

00393




4 Conclusions





Data Availability




References





















Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls






Air

Scale

100μm

Subs

trat

e

(a)

Air

Scale

Si

Subs

trat

e

(b)

Subs

trat

e

Air

Cr

Scale

(c)

Air

Fe

ScaleSu

bstr

ate

(d)

00 50


1

2

3

4

5

6

7

8

(e)

Iron kal (μm)0 50 100 150

0

100

50

(f )





Substrate Coating

Air

(a)

Substrate Coating

Si

Air

(b)

Substrate Coating

Air

Cr

(c)

Air

Fe

Substrate Coating

(d)

00 50


10

20

(e)

Iron kal (μm)

0

50

100

0 50 100

(f)







Inte

nsity

(au

)

10 20

32

3 1 Fe3O42 Fe2O33 Fe245Si055O4

2

32

2 2 2

2

11

31

31

1

3

321

11

30 402θ (deg)

50 60 70 80 90

32

(a)

Inte

nsity

(au

)


54

51

111

1

2

521

2

32 2

54

55

241

41

4

4

1

333

2

2

10 20 30 402θ (deg)

50 60 70 80 90

2

(b)


(a) (b) (c)

89μm

50μm

39μm

Coating

50μm

Substrate

Substrate Scale

(f)(e)(d)




ln η minus00065T + 1447 (4)





20μm 20μm

(b)



0

ndash200

ndash400

ndash600

ndash800

ndash1000

ndash1200

ndash1400

ndash1600


Before contact

Nor

mal

pre

ssur

e (M

Pa)

Vel

ocity

(mm

sec

)

After contact

Afte

r con

tact

Befo

re co

ntac

t

ndash2000

ndash1500

ndash1000745723627522

213131

340000 000500026 0010 0015 0020

Time (sec)0025 0030 0035 004000415

00393




4 Conclusions





Data Availability




References





















Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls






Substrate Coating

Air

(a)

Substrate Coating

Si

Air

(b)

Substrate Coating

Air

Cr

(c)

Air

Fe

Substrate Coating

(d)

00 50


10

20

(e)

Iron kal (μm)

0

50

100

0 50 100

(f)







Inte

nsity

(au

)

10 20

32

3 1 Fe3O42 Fe2O33 Fe245Si055O4

2

32

2 2 2

2

11

31

31

1

3

321

11

30 402θ (deg)

50 60 70 80 90

32

(a)

Inte

nsity

(au

)


54

51

111

1

2

521

2

32 2

54

55

241

41

4

4

1

333

2

2

10 20 30 402θ (deg)

50 60 70 80 90

2

(b)


(a) (b) (c)

89μm

50μm

39μm

Coating

50μm

Substrate

Substrate Scale

(f)(e)(d)




ln η minus00065T + 1447 (4)





20μm 20μm

(b)



0

ndash200

ndash400

ndash600

ndash800

ndash1000

ndash1200

ndash1400

ndash1600


Before contact

Nor

mal

pre

ssur

e (M

Pa)

Vel

ocity

(mm

sec

)

After contact

Afte

r con

tact

Befo

re co

ntac

t

ndash2000

ndash1500

ndash1000745723627522

213131

340000 000500026 0010 0015 0020

Time (sec)0025 0030 0035 004000415

00393




4 Conclusions





Data Availability




References





















Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls








Inte

nsity

(au

)

10 20

32

3 1 Fe3O42 Fe2O33 Fe245Si055O4

2

32

2 2 2

2

11

31

31

1

3

321

11

30 402θ (deg)

50 60 70 80 90

32

(a)

Inte

nsity

(au

)


54

51

111

1

2

521

2

32 2

54

55

241

41

4

4

1

333

2

2

10 20 30 402θ (deg)

50 60 70 80 90

2

(b)


(a) (b) (c)

89μm

50μm

39μm

Coating

50μm

Substrate

Substrate Scale

(f)(e)(d)




ln η minus00065T + 1447 (4)





20μm 20μm

(b)



0

ndash200

ndash400

ndash600

ndash800

ndash1000

ndash1200

ndash1400

ndash1600


Before contact

Nor

mal

pre

ssur

e (M

Pa)

Vel

ocity

(mm

sec

)

After contact

Afte

r con

tact

Befo

re co

ntac

t

ndash2000

ndash1500

ndash1000745723627522

213131

340000 000500026 0010 0015 0020

Time (sec)0025 0030 0035 004000415

00393




4 Conclusions





Data Availability




References





















Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls





ln η minus00065T + 1447 (4)





20μm 20μm

(b)



0

ndash200

ndash400

ndash600

ndash800

ndash1000

ndash1200

ndash1400

ndash1600


Before contact

Nor

mal

pre

ssur

e (M

Pa)

Vel

ocity

(mm

sec

)

After contact

Afte

r con

tact

Befo

re co

ntac

t

ndash2000

ndash1500

ndash1000745723627522

213131

340000 000500026 0010 0015 0020

Time (sec)0025 0030 0035 004000415

00393




4 Conclusions





Data Availability




References





















Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls





4 Conclusions





Data Availability




References





















Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls






Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls




some manifestations of antioxidation coating for hot

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