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Wear 263 (2007) 301–308

Erosion wear in heat treated tool steels used in core boxesat automotive foundries

J. Rodrıguez a, D. Martinez a,∗, A. Perez a, R. Gonzalez a,E. Rodrıguez a, S. Valtierra b

a Universidad Autonoma de Nuevo Leon, Facultad de Ingenierıa Mecanica y Electrica, Ave. Pedro de Alba s/n, Cd. Universitaria,San Nicolas de los Garza, C.P. 66450 Nuevo Leon, Mexico

b Nemak S.A., de C.V. Libramiento Arco Vial Km 3.8. Garcia, Nuevo Leon, Mexico

Received 15 August 2006; received in revised form 16 December 2006; accepted 18 December 2006Available online 23 May 2007

bstract

Sand cores are extensively used on automotives foundries, if a core box is used as core making pattern; erosive wear damage is caused by theilica sand blown. Multiple sand impacts affect the dimensional profile of the core box when the sand is blown causing core rejection. The objectivef the present study is to determine the erosion wear rate and the erosive wear mechanism on two tool steel grades, AISI H13 and AISI P20. Bothhe steels were heat treated, quenched and tempered, to obtain certain hardness values similar to those are used in core boxes. In addition studies onnnealed AISI H13 and carburized AISI P20 were proposed to get broader hardness values. The tests were developed in a sand blast type machinepecially designed to impact the blown sand in six different angles between 20◦ and 90◦, the blown pressure was same as that utilized in coreaking machines. The erosion rate is defined as loss of weight caused by the mass of the erosive particles impacted. When the steels are under

aximum hardness condition the higher erosion rate is found for angles greater than 60◦. The erosive mechanism was characterized using optical

nd electronic microscopy techniques on the worn layer. When, the hardness is maximum the loss of weight is due to shear adiabatic bands wheres in the annealed samples these bands were not observed.

2007 Published by Elsevier B.V.

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eywords: Erosion wear; Tool steel; Core box; Shear adiabatic bands

. Introduction

The wear phenomenon is a problem that affects certain engi-eering systems. This present study is about erosive wear in twoypes of specific tool steels utilized in die molds to blow sil-ca sand cores at an automotive foundry plant [1,2]. The sandores are used on semipermanent molding or in all completeilica sand molds. Sand cores are essential in the foundry pro-esses and these generate complex geometries or cavities thathey would be difficult to obtain by machining. Sand cores fab-ication is a relatively simple process where a silica sand and

henolic resin mixture are blown into the mold by high pres-ure dry air, and then a catalytic gas is injected to promote theesin reaction giving enough strength to sand cores to be eas-

∗ Corresponding author. Tel.: +52 8111589965; fax: +52 8183320904.E-mail address: dorairma@gama.fime.uanl.mx (D. Martinez).

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043-1648/$ – see front matter © 2007 Published by Elsevier B.V.oi:10.1016/j.wear.2006.12.051

ly removed from core box [3,4]. Filling the core boxes cavitiesuring blown step; silica sand particles impact the internal coreox surface producing erosive wear damage. The erosive wears caused when particles in a fluid strike a solid surface resulting

aterial loss by deformation and cutting processes. Erosive wearnvolves various factors. Some of these factors are particle char-cteristics such as size, shape and hardness, material propertiesuch as hardness and microstructure, and fluid flow conditionsuch as impact angle, particle velocity and fluid type [5,6]. Allhese factors directly influence wear mechanism and modify therocess of the material loss from the eroded surface. Two mainifferent erosion mechanisms named ductile and brittle behaviorre reported. In the ductile behavior the higher material loss isbserved at the impact angle between 20◦ and 30◦ while in the

rittle behavior the higher material loss is at 90◦. Both mecha-isms can be presented in the same material according to testingonditions [5,7,8]. One of the main concerns in an automotiveoundry is the maintenance of the cores boxes. When a core box

302 J. Rodrıguez et al. / Wear 263 (2007) 301–308

Table 1Chemical composition of AISI H13 y AISI P20 steel (wt%)

Steel C Si Mn P Cr Mo Ni Fe

AISI H13 0.383 1.05 0.38 0.008 5.2 1.16 0.18 BalanceAISI P20 0.417 0.29 1.7 0.004 1.98 0.24 0.15 Balance

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Table 2Sample classification and heat treatment used

Materials Hardness (HV) Heat treatment

H13-1A 196 SpheroidizedH13-1B 313 Quenched and temperedH13-1C 381 Quenched and temperedH13-1D 458 Quenched and temperedH13-1E 530 Quenched and temperedH13-1F 581 Quenched and tempered

ig. 1. Silica sand particles of subangular shape and size range of 150–425 �m.

s worn certain procedures can be applied to reuse the core boxesowever, the better knowledge of the wear process that occurs inhe core box surface will enhance core box life. The main objec-ive of the present study is to determine the erosion wear rate andhe erosive wear mechanism on two types of heat treated toolteel grades. The sand blast type equipment designed to test theaterials is based on the parameters used in the foundry plant

nd some literature data [9–12].

. Experimental procedure

.1. Materials

The methodology followed to evaluate the erosive wearechanism in AISI H13 and P20 steel grades consisted of test-

ng at different impact angles in the sand blast type equipment.sand rate of 2.5 g/s was used in all the tests and each test

as performed with 1000 g of silica sand. The test couponsimensions were 100 mm × 50 mm × 5 mm. Table 1 shows the

P20-1A 303 Quenched and temperedP20-1B 398 Quenched and temperedP20-1C 640 Carburized and quenched

Fig. 3. Samples H13-1F, eroded with 150–425 �m, SiO2 particles at 1.38 bar pressure. The impact angle were 20◦, 30◦, 40◦, 60◦, 75◦ and 90◦ from left to right.

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hemical composition of both the steels. The coupons wereeat treated, quenched and tempered, in order to obtain dif-erent hardness values (Table 2). In addition, a H13 coupon

et was spheroidized and a P20 was surface hardened by car-urizing. The surface finishing was done by electroerosionachining condition on H13 samples. The P20 steel samples

ig. 4. AISI H13 steel eroded with 150–425 �m, SiO2 particles at 0.69 barressure: (a) hardness effect vs. erosion rate and (b) impact angle effect vs.rosion rate.

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63 (2007) 301–308 303

ere grinded with 120, 320, 400, 600 and 800 paper grit.he initial roughness was measured using a digital rough-ess meter (Taylor Hobson) and the scan distance was 10 mm

long the impacted particle direction. Subangular morphologyand having grain sizes between 150 and 425 �m was utilizedFig. 1).

ig. 5. AISI H13 steel eroded with 150–425 �m SiO2 particles at 1.38 bar pres-ure: (a) hardness effect vs. erosion rate and (b) impact angle effect vs. erosionate.

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.2. Erosion test

The erosion machine was designed to have two chambers andsystem to set different angles between 10◦ and 90◦ (Fig. 2).

n the upper chamber a specific quantity of sand is depositedor each erosion test, and the chamber is sealed to increase their pressure. The sand is blown through a nozzle localized athe bottom chamber of the machine and the sand is directly

ig. 6. Impact angle effect vs. erosion rate in the AISI P20 steel eroded with50–425 �m SiO2 particles at: (a) 0.69 bar and (b) 1.38 bar pressure.

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63 (2007) 301–308

truck on the sample that was previously attached to the angleeflector. The nozzle dimensions are of 100 mm long and ofmm inner diameter to allow a uniform impact erodent particle

tream according to Stevenson and Hutchings [11]. The nozzleas fabricated using quenched H13 steel type and was replaced

fter a cycle of 20 tests. The impact distance between the nozzlend the sample was 50 mm. The samples were tested at anglesf 20◦, 30◦, 40◦, 60◦, 75◦ and 90◦ with reference to the angle

ig. 7. Roughness measurements in samples tested at 30◦, 60◦ and 90◦: (a) AISI13 and (b) AISI P20 (20 is a pressure of 1.38 bar and 10 is 0.69 bar).

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etween the nozzle axis and the specimen surface. Three testsere carried out for each hardness value and the average of the

esults was used to plot erosion charts.The tests were done with 0.69 and 1.38 bar pressure, of dry

ir maintaining constant pressure during the testing time; pres-ure sensors were located inside the chamber to monitor testingressure. The erosion rate was calculated as the loss of materialy erodent particle mass [8] using formula (1),

= mr

Mp(1)

here mr is the removed mass, and Mp is the erodent particleass.Optical and electronic microscopy techniques were utilized

o determine the erosion wear mechanism on steel surfaces.

. Results and discussion

.1. Visual inspection

When the erodent particle impact angle increases from 20◦ to0◦ the damaged area is diminished. The worn area gets localizedhen impact angles are between 60◦ and 90◦ due to stream

pread reduction. On the other hand stream divergence causes

ig. 8. AISI H13 and AISI P20 microstructures steels: (a) H13-1A quenched andempered and (b) P20-1C carburized and quenched. The samples were etchedith nital (97 ml ethylic alcohol and 3 ml nitric acid) and Picral (100 ml ethylic

lcohol and 4 g picric acid) rate 1:1.

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63 (2007) 301–308 305

cattered damage between 20◦ and 40◦ impact angles, as shownn Fig. 3. These results confirm that the entire sand mass utilizedn the erosion test was completely impacted on the samples.

.2. Erosion rate

When a 0.69 bar pressure was used to perform tests on H13,ardness does not have significant effect on the erosion resis-ance, if the impact angle is between 20◦ and 40◦ (Fig. 4a) aseported by Finnie [13] in which a heat treated steel was collidedy Al2O3 particles at 20◦ impact angle showing same erosionesistance while the steel tested was harder. The average erosionate was 1.4 × 10−4 g/g at 20◦ impact angle and this value didot change significantly when the same steel grade was testedith different hardness. When the sand particles impact on the

ample surface it becomes strain hardened as a consequencef plastic deformation [8,13,14]. Nevertheless, if the hardnessncreases the ductility diminishes. Low ductility reduces plas-ic deformation and thus the materials are easily removed. Thetrain hardening produced in softer materials keep constant ero-ion rate at 20◦, 30◦ and 40◦ impact angles because sand particlenteract only with the hardened layer, even at the spherodizedondition in which the strain hardening achieved should benough at stable state and equivalent to the hardness conditionsound for H13-1F (581 HV). Moreover, when hardness increaseshe erosion rate increases while the tests are performed between0◦ and 90◦ impact angles. Fig. 4b shows the impact angle effectgainst erosion rate. The erosion rates tested at 90◦ impact anglesre 0.8 × 10−4 and 1.4 × 10−4 g/g, respectively, of samples hav-ng hardness values 196 HV at 581 HV. At low hardness valuesuctile behavior is observed where as at higher hardness val-es, the ductile–fragile transition is presented [8,13,15]. Thisransition is not clearly shown in H13 steels samples. P20 steelrade shows the ductile–fragile transition between P20-1A (303V) and P20-1C (640 HV). The erosion rate is maximum when

he particles impinged on H13 samples at 40◦ impact angle ashown in Figs. 4b and 5b. In the case of P20, erosion rate againstmpact angle is shown in Fig. 6a and b. A ductile mechanismccurs when a tempered martensite microstructure is present.he brittle erosion mechanism arises when the carburized sur-

ace microstructure is present. The sample P20-1C case depthas approximately 250 �m which was completely removed due

o erosion exposing as-quench martensite microstructure. Theigher the hardness the clearer the impact angle influence on ero-ion rate in both the steel grades. The spherodized microstructuren H13 steel shows a ductile behavior. The maximum erosion rateas at 40◦ and the minimum material loss at 90◦ at spherodized

ondition. When the steel is quenched and tempered (581 HV)he erosion rate becomes maximum at 60◦ impact angle and thenecreases slightly as the impact angle is increased, as shown inig. 5b. In the case of P20-1C, the larger erosion at 90◦ impactngle is due to brittle erosion behavior (Fig. 6b).

.3. Roughness

In the semipermanent casting process core box surface rough-ess is an important characteristic. In this process casting pieces

306 J. Rodrıguez et al. / Wear 263 (2007) 301–308

Fig. 9. AISI H13 and P20 steels surfaces eroded with 150–425 �m SiO2 particles at 1.38 bar pressure at 30◦: (a) H13-1A, 500× at inset picture, (b) H13-1F, 1000×at inset picture and (c) P20-1C, 1500× at inset picture. All the samples were eroded with 1000 g of silica sand.

Fig. 10. AISI H13 and P20 steels surfaces eroded with 150–425 �m SiO2 particles at 1.38 bar pressure at 90◦: (a) H13-1A, 1000× at inset picture, (b) H13-1F,1000× at inset picture and (c) P20-1C, 1500× at inset picture. All the samples were eroded with 1000 g of silica sand.

J. Rodrıguez et al. / Wear 263 (2007) 301–308 307

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ig. 11. AISI H13 and P20 subsurface steels eroded with 150–425 �m SiO2 pands are observed only in (b) and (c). All the samples were eroded with 1000 g

re solidified in a mold that contains some sand cores. The cast-ng roughness profile depends on the sand core texture, and asonforming corebox is getting worn, this texture could change.he initial average roughness in H13 samples is due to elec-

roerosion process and, when the hardness is above 313 HV, theverage roughness, Ra is decreased due to the surface smoothen-ng by the erodent particles at 30◦ impact angle.

The impact angle with the greater Ra is at 30◦ which isbserved at the lowest hardness conditions in H13 and P20 sam-les, as shown in Fig. 7. When low hardness conditions areresent in the samples large grooves are observed (Fig. 9a) dueo particle striking effect. In the P20 samples the initial rough-ess is increased in all impact angles tested and the lower initialoughness is due to grit surface preparation. If we compare H13-B (313 HV) and P20-1A (303 HV) the final Ra is similar at allmpact angles and at 90◦ the difference is less than 1.00 �mhen the steel hardness is between 196 and 381 HV.

.4. Microstructural analysis

Fig. 8a shows the annealed microstructure with globular car-ides shape for sample H13-1A; Fig. 8b shows the untempered

artensite microstructure of P20-1C sample. The damage sur-

ace of H13 samples with 196 HV, 581 HV and P20 with 640 HVre shown in Fig. 9 (30◦ impact angle at 1.38 bar). In these casesrosion grooves are present all over the impacted area by the

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s at 1.38 bar at 90◦: (a) H13-1A, (b) H13-1F and (c) P20-1C. Adiabatic shearlica sand.

articles and large chips remain on the damaged surface. Sam-le surfaces at 90◦ are subjected to direct impingement causingaterial deformation. The material is indented by the subangu-

ar particles and is displaced forming a lip that can be removedy later impacts during the erosion test (Fig. 10). A subsur-ace profile of H13-1F (581 HV) tested at 30◦ and 90◦ impactngle is shown in Fig. 11. From the figure, the shear adiabaticands are evident at angles above 60◦ and these promote theaterial loss mechanism by micro cracks. The shear adiabatic

ands are not observed at low impact angles due to the largerivergence area. Also, the shear adiabatic bands are localized onhe P20-1C (640 HV) subsurface profile tested at impact anglesbove 60◦.

.5. Material selection

The erosion resistance is larger in H13-1B and P20-1A andt is more evident at impact angles between 60◦ and 90◦, as ishown in Fig. 12. The most of the blow tubes are located at 90◦ith reference to the core box. Steel samples with hardness of03 and 313 HV have twice erosion resistance at 90◦ impact

ence air pressure must be maintained as low as possible tomprove tooling life. On the basis of better templability proper-ies of AISI H13 steel grade than AISI P20 steel grade, leadingo less distortion risks in core boxes during core making [16].

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ig. 12. Erosion resistance on P20-1A, P20-1C, H13-1B and H13-1F (20 is aressure of 1.38 bar and 10 is 0.69 bar).

. Conclusions

In the case of steel AISI H13 tested at 20–40◦ impact angles,he average erosion rates for the range of hardness used in theresent work (196–581 HV) were approximately 1.4 × 10−4 and.3 × 10−4 g/g at 0.69 and 1.38 bar, respectively. The H13 steelear mechanism was ductile when the spherodized microstruc-

ure was obtained by heat treatment. The ductile–brittle wearechanism transition was observed above 581 HV hardness

alue, when the microstructure was composed by temperedartensite. In the case of P20 samples, the ductile–brittle

ransition wear mechanism occurred when as-quench marten-ite microstructure is carburized and the case depth is totallyemoved even at low impact testing due to silica sand impacts.

The low impact angle mechanism is characterized by theresence of large grooves and some remained chips, whilempact angles above 60◦ are featured by craters surroundinghe deformed material or lips.

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63 (2007) 301–308

Shear adiabatic bands were found near subsurface edge atigh hardness (581 HV with H13 and 640 HV in P20) conditionshen the impact angle above 60◦ was utilized to perform tests.icrocracks located at adiabatic shear bands were more evident

t maximum hardness condition.

cknowledgements

The authors acknowledge the support provided by Nemak.A. de C.V. and Industria Meccanica Bassi Luigi & Co., during

his work.

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