temperature and stress simulation of the hardfacing for … · thermal and stress fields for...

WELDING RESEARCH

AUGUST 2016 / WELDING JOURNAL 309-s

Introduction

A Cr5Mo1V supporting roller is thekey component in steel rolling produc-tion, which plays an important role insupporting the cool-rolling work roller(Refs. 1, 2). During its work process,the Cr5Mo1V supporting roller bearsmechanical, fatigue, and friction loads.After being in service for a period oftime, it may fail due to mechanical fa-tigue and excessive wear (Refs. 3, 4).The failed supporting roller can be re-paired by the hardfacing method to re-store its dimension and shape, and to obtain higher performance (Refs. 5–7). In order to ensure the repaired sup-

porting roller has excellent mechanicalproperties, the composition of the hard-facing alloy should be optimized. Ourteam’s previous research indicated thatby adding an appropriate amount ofrare earth (RE) elements in theCr5Mo1V, the mechanical properties ofthe hardfacing alloy, such as hardness,strength, wear resistance, and tough-ness, are all increased (Refs. 8, 9). However, for the hardfacing alloys,compared with the mechanical proper-ties, the weldability is more important.Excellent weldability is considered to bethe prerequisite for the application ofthe hardfacing alloys (Refs. 10–12).Therefore, before the high-performance

hardfacing alloy (Cr5Mo1V-RE) is usedto replace the traditional Cr5Mo1V alloyfor repair of the failed supporting roller,their weldability should be compared.Moreover, the hardfacing process pa-rameters for the Cr5Mo1V-RE alloyshould be optimized. Simulation of the hardfacingprocess using numerical methods canbe employed to predict welding defor-mation, stress distribution, and otherhardfacing attributes, and thus canpartially replace the expensive, time-consuming experimental-based trial-and-error method of determiningweldability and development of hard-facing process parameters (Ref. 13). Lazić (Ref. 14) researched the tem-perature field during the hardfacingprocess by numerical simulation, andindicated the calculated results areconsistent with the experimental re-sults. Joshi (Ref. 15) adjusted thewelding heat source parameters inGoldak’s double-ellipsoidal model us-ing SysWELD simulation, and showedthat the optimized parameters aremore suitable for hardfacing. The re-sults showed excellent matching withthe experimental ones. Li (Ref. 16) fo-cused on the simulation of processstress of medium-high-carbon steelduring martensite transformation af-ter hardfacing, and indicated that thecompressive stress appeared on thesurface of the specimen during thehardfacing cooling process whenmartensite transformation occurs,while the large tensile stress ap-peared on the surface of the speci-

Temperature and Stress Simulation of theHardfacing for Cr5Mo1VRE Alloy

Various technological parameters and experimental verificationwere used to compare the weldability of two alloys

BY J. YANG, J. HUANG, D. FAN, Z. YE, S. CHEN, AND X. ZHAO

ABSTRACT The temperature field and stress field for hardfacing Cr5Mo1V and Cr5Mo1VRE alloyswere simulated to compare their weldability. Subsequently, those for hardfacing Cr5Mo1VRE alloy using various technological parameters were researched systematically. The resultsindicate that the computational temperature field and stress field agree well with the experimental results, and the errors are smaller than 5%. For Cr5Mo1VRE alloy, the peak stressesare smaller than those for Cr5Mo1V alloy, which indicates the weldability of Cr5Mo1VREalloy is more excellent than that of Cr5Mo1V. The decreasing of y and x can bothcontribute to decreasing of the stress for Cr5Mo1VRE alloy, in which the decline of the longitudinal stress y plays the major role. The hardfacing velocity influences the peak stress atthe hardfacing initial state and the stressinfluenced areas at cold state. The greater thehardfacing velocity, the lesser is the peak stress at the hardfacing initial state and smaller isthe stressinfluenced area at the cold state. The preheating temperature only influences thepeak stress at the hardfacing initial state. When the preheat temperature increases to150C, the peak stress decreases drastically.

J. YANG, J. HUANG ([email protected]), D. FAN, Z. YE, S. CHEN, and X. ZHAO are with the School of Materials Science and Engineering, University of Science and Technology Beijing, China.

KEYWORDS • Temperature and Stress Fields • Simulation • Experimental Verification • Hardfacing • Technological Parameters

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WELDING JOURNAL / AUGUST 2016, VOL. 95310-s

men and was held to room tempera-ture with the increasing of the time.The results are beneficial to improv-ing hardfacing alloy composition andoptimizing the hardfacing technolog-ical parameters. In this work, the temperature fieldand stress field for hardfacing Cr5Mo1Valloy were simulated and the resultswere compared with the experimentalones to verify the reliability of the simulation. Then those for hardfacingCr5Mo1V-RE alloy using various tech-nological parameters were researchedsystematically, which cannot only inves-tigate the weldability of Cr5Mo1V-REalloy but also provide the basis for opti-mizing hardfacing process parameters.

Materials and Methods

Experimental Procedure

A hardfacing experiment was carriedout on Cr5Mo1V alloy thin sheet byCr5Mo1V alloy flux-cored wire using aLincoln 588 hardacing machine. Thethin sheet was in the dimension of 100 40 10 mm with a 100 12 3-mmgroove on its surface, which is shown inFig. 1A. The hardfacing was made usingthe following parameters: 25 V weldingvoltage, 260 A welding current, 5 mm/swelding speed, and 10 L/min flow rateof argon shielding gas. The thermal cy-cles were recorded using K-type thermo-couples spot welded at different loca-tions. The stresses were measured usingan ultrasonic technique described in de-tail by Palanichamy (Ref. 17).

Model Building

The finite element model for hard-facing simulation, which was 100 40

10 mm and consistent with the actu-al sample size, was established bymodeling software Visual-mesh — Fig.1B. In order to reduce the computa-tional work, the hardfacing alloy wasapproximated to a rectangular shapewith the dimensions of 100 12 3mm, which was the actual size of thesingle-pass hardfacing alloy. Besidethat, the meshes in the hardfacing al-loy area were dense, while those in thematrix area were sparse — Fig. 2. Af-ter meshing, 56,041 units and 63,136nodes were in the model. Subsequently, the welding groupswere configured, in which the overallmodel was set to ALL, the matrix areawas set to BASE, the hardfacing alloyarea was set to ADD, and the outersurfaces was set to HEAT. Moreover,welding line WEL, reference line REFL,welding starting node SN, welding endnode EN, and welding starting unit SEwere set according to Fig. 3.

Heat Source Determination

Conical heat source (Ref. 18),Gaussian heat source (Ref. 19), and

double-ellipsoid heat source (Refs. 20,21) are the common heat sources forwelding simulation, in which double-ellipsoid heat source is particularly ap-plicable to the condition that the heatinput distribution range is large (Refs.15, 22). Therefore, in this work, thedouble-ellipsoid heat source was se-lected as the hardfacing heat source.The model uses the following equationto define the volumetric heat flux (q)inside the front and rear regions of theheat source, where these regions aredenoted by the subscripts 1 and 2, respectively:

in which, a, b, and c describe the dimen-sions of the heat source, Q is the powerinput from the welding source, v is thewelding velocity, t is the time, is a lagfactor defining the position of the heatsource at t = 0, and f defines the fractionof the heat deposited in either region.Figure 4 shows the configuration of thedouble-ellipsoid heat source.

q1, 2( x ,y,z,t )

=6 3f1, 2Q

abc1, 2� �e–3x2

a2e–3y2

b2e

–3( z+v(�–t ))2

c1,22

(1)

Fig. 1 — A — Experiment sample; B — calculation model for hardfacing.

Fig. 2 — Profile meshes for the model.

A B

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Material Library Establishment

The parameters of the Cr5Mo1Vand Cr5Mo1V-RE alloys were calculat-ed by experiments, JMat Pro soft-ware, and the differential analyticalmethod. The specific heat, thermal conductivi-ty, and density for simulating the ther-mal field are listed in Table 1, whilethe elasticity modulus, Poisson’s ratio,thermal strain, and yield strength for

simulating the stress field are listed inTable 2. The CCT curves for the two al-loys are shown in Fig. 5.

Initial and Boundary Conditions

Hardfacing simulation was conduct-ed at room temperature. The initialtemperature was noted as 25C. Con-vective and radiation losses on themodel surfaces were taken into ac-count. Given a body temperature T,

surrounded by a fluid or gas, radiationto the surrounding medium followsthe Stefan-Boltzmann law and heatconvection assumes that a thermallayer exists with a heat transfer coeffi-cient, which follows Newton’s law ofcooling. These boundary conditionswere applied to the model by specify-ing the value of combined heat trans-fer coefficient and the surroundingtemperatures to the surface by creat-ing a skin for the model. Force-free

Fig. 4 — Schematic of the doubleellipsoid heat source.

Fig. 5 — CCT curves for the following alloys: A — Cr5Mo1V; B — Cr5Mo1VRE.

Table 1 — Parameters of Cr5Mo1V Alloy and Cr5Mo1VRE Alloy for Simulating the Thermal Field

Temperature (oC) 0 200 900 1100 1400 2500

Specific Heat (J/kgK) 510 530 700 590 630 707

Cr5Mo1V alloy Thermal Conductivity (W/mm) 0.034 0.034 0.026 0.021 0.033 0.033

Density (g/cm3) 7.61 7.48 7.35 7.26 7.03 6.85

Specific Heat (J/kgK) 430 550 565 596 638 707

Cr5Mo1VRE alloy Thermal Conductivity (W/mm) 0.046 0.046 0.022 0.028 0.032 0.032

Density (g/cm3) 7.82 7.63 7.46 7.43 7.34 7.29

A B

Fig. 3 — Configuration of the WEL, REFL, SN, EN, and SEL.

Pearlite(0.1%)

Bainite(0.1%)Pearlite(99.9%)Bainite(99.9%)100.0 C/s10.0 C/s1.0 C/s

0.1 C/s

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clamping was considered at the cor-ners of the weld plate with elastic con-straints of 1 N/mm. It means that theclamping is not rigid.

Results and Discussion

Thermal and Stress Fields forCr5Mo1V Compared withExperimental Results

In order to verify the reliability ofthe calculation, the thermal field andstress field for hardfacing Cr5Mo1V al-loy were researched and comparedwith the experimental results. Duringthe process, the hardfacing heat sourcewas the double-ellipsoid heat source,as determined in Fig. 4, the ambient

temperature and the initial matrixtemperature were 20C, and the hard-facing velocity was 5 mm/s. Moreover,the hardfacing alloy (ADD area) andthe matrix metal (BASE area) wereboth set to the Cr5Mo1V alloy. Before the calculation, the heatsource used under the current condi-tions must be determined. After acomplex parameter correction, the ac-curate heat source parameters can beobtained. The hardfacing bead crosssection obtained by finite elementanalysis was compared with that ob-tained by actual hardfacing, as shownin Fig. 6. It was found that there isgood agreement between the simulat-ed bead cross section and actual hard-facing one. It can be inferred that theheat source parameters are applicable,

in which Q = 4800 W, q1 = 128W/mm3, q2 = 97 W/mm3, c1 = 1.6 mm,c2 = 2.8 mm, a = 2.4 mm, b = 3.6 mm,and v = 5 mm/s. The calculated thermal fields forCr5Mo1V alloy hardfacing models at1.2, 6, 15, 20, 49.5, and 1000 s areshown in Fig. 7. When the hardfacingtime was 1.2 s, the temperature waslow and the peak value was only1570C, as shown in Fig. 7A. With anincrease in the hardfacing time (Fig.7A–D), the peak temperature increasedconsistently at 1892, 1927, and2185C when the hardfacing timeswere 6, 15, and 20 s. Moreover, duringhardfacing (0~20 s), the temperaturegradient before the heat source wassharp while that behind the heat sourcewas gentle. On cooling, as shown in Fig.7D–F, the highest temperature areamoved toward the center gradually.When the hardfacing systems werecooled completely (1000 s, shown inFig. 7F), the temperature of each areawas basically the same. After the thermal fields at differ-ent times were observed, the temper-ature variation tendencies for differ-ent positions on the hardfacing mod-el were investigated. First, five meas-uring points were selected isometri-cally along the centerline of the hard-facing alloy, which are points A, B, C,D, and E, and the nodes are 2992,5260, 7528, 9607, and 11,497. Subse-quently, by determining point A asthe reference point, another fivemeasuring points were selected iso-metrically perpendicular to the cen-

Table 2 — Parameters of Cr5Mo1V Alloy and Cr5Mo1VRE Alloy for Simulating the Stress Field

Temperature (oC) 20 200 500 900 1250 1400

Elasticity Modulus (N/mm2) 210000 200000 140000 94000 3350 1000 Poisson’s Ratio 0.33 0.33 0.33 0.33 0.33 0.33 Thermal Strain (%) 0 0.004 0.008 0.0128 0.0192 0.0208Cr5Mo1V Alloy Thermal Expansion Coefficient 12.2 12.8 14.5 24.3 38.7 47.4 (1E6/K) Tensile Strength (N/mm2) 510 467 237 84 10 10 Yield Strength (N/mm2) 390 258 187 45 5 5

Elasticity Modulus (N/mm2) 210000 210000 135000 3000 1000 1000 Poisson’s Ratio 0.33 0.33 0.33 0.33 0.33 0.33 Thermal Strain (%) 0 0.003 0.009 0.013 0.019 0.021Cr5Mo1VRE Alloy Thermal Expansion Coefficient 12.4 13.2 15.1 26.4 42.3 49.2 (1E6/K) Tensile Strength (N/mm2) 485 384 213 46 10 10 Yield Strength (N/mm2) 340 231 150 13 5 5

Fig. 6 — The hardfacing bead cross sections obtained by the following: A — Finite elementanalysis and B — actual hardfacing.

A

B

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terline of the hardfacing alloy, whichare points A, F, G, H, and I, and thenodes are 2992, 3094, 73, 168, 3150,and 3128, respectively. The measur-ing points on the hardfacing modelfor simulation are given in Fig. 8.

Figure 9 indicates the temperatureson the measuring points along thehardfacing alloy centerline (A, B, C, D,and E) by calculation and experimentat different times. The computationalresults agree well with the experi-mental results, and the errors weresmaller than 5%. The temperaturevariation tendencies of the pointsalong the hardfacing alloy centerlinewere similar, in which the hardfacingheat source moved from far to near,

Fig. 7 — Thermal fields for Cr5Mo1V alloy hardfacing models at different times: A — 1.2 s; B — 6 s; C — 15 s; D — 20 s; E — 49.5 s; F — 1000 s.

Fig. 8 — Measuring points on the hardfacing model for simulation.

A B

C

E

D

F

116.883213.766310.648407.531504.414601.297698.18795.062891.945988.8281085.711182.591279.481376.361473.24

137.011254.022371.033488.044605.055722.065839.076956.0871073.11190.111307.121424.131541.141658.151775.16

CONTOURSTempTime 1.20625Compt. Ref Global

Mn = 20Max = 1570.12


Mn = 20Max = 1892.17

139.812258.998378.183497.369616.555735.741854.927974.1131093.31212.481331.671450.861570.041689.231808.41


Min = 20.6259Max = 1927.6

211.09342.722474354605.986737.618869.251000.881132.511264.151395.781527.411659.041790.671922.312053.94

66.171666.245366.318966.392666.466366.5466.613766.687466.761166.834766.908466.982167.055867.129567.2032

288.331292.093295.855299.617303.378307.14310.902314.664318.426322.188325.95329.712333.474337.236340.998

CONTOURSTempTime 20Compt. Ref Global

Min = 79.4575Max = 2185.57

CONTOURSTempTime 1000Compt. Ref Global

Min = 66.0979Max = 67.2769


Min = 284.569Max = 344.76

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the temperature of the point rosesharply and reached the peak whenthe welding heat source arrived at thepoint. Subsequently, when the hard-facing heat source moved away, thetemperature reduced gradually and

the reduced speedwas far lower thanthe rising speed.What is more, thetemperature ofeach point ulti-mately tended tobe uniform.

Figure 10 illus-trates the temper-atures on themeasuring pointsthat were perpen-dicular to thehardfacing alloycenterline (A, F, G,H, and I) at differ-ent times. Whenthe hardfacingheat source passedby the point on

the hardfacing alloy centerline (pointA), the temperatures of all the pointsrose at first but then reduced, and thetemperatures rose faster than they re-duced. Moreover, the temperature

change on point A was very sharp andthe peak temperature was high,1889C. With increase of the distanceto the hardfacing alloy centerline, thetemperature changes were smoothand the peak temperatures were re-duced gradually, 1260º, 500º, 318º,and 296C for points F, G, H, and I,respectively.

The calculated stress fields forCr5Mo1V alloy hardfacing models at1.2, 6.2, 14.8, 20, 49.5, and 1000 s areshown in Fig. 11. When the hardfacingtime was 1.2 s because the matrix metalwas near the hardfacing alloy (Fig. 11A),which can be considered the heat-affect-ed zone (HAZ), was heated to high tem-perature rapidly with the volume expan-sion (as shown in Fig. 7A), the largestress appeared, and the value was247.8 MPa. Meanwhile, the hardfacingalloy was under the condition of melt-ing, so the stress on it was 0 MPa. Withan increase in the hardfacing time, asshown in Fig. 11B–D, the large stresseswere always focused on the HAZs, andthe peak stresses rose gradually to453.2, 615.8, and 631.2 MPa when thehardfacing times were 6.2, 14.8, and 20s. At the same time, because the hard-facing alloys were cooled gradually, thestresses also appeared on them. In cool-ing, the stresses rose sequentially, andthe peak stress reached 755.1 MPawhen the hardfacing system was cooledcompletely, as shown in Fig. 11F. Computational and experimentallongitudinal stress y distribution alongthe hardfacing alloy centerline after thehardfacing system was cooled complete-ly is given in Fig. 12. The computationalresult agrees well with the experimental

Fig. 9 — Temperatures on the measuring points along the hardfacing alloy centerline for Cr5Mo1V alloy at different times: A — Computational result; B — experimental result.

A B

Fig. 10 — Temperatures on the measurng points perpendicular tothe hardfacing alloy centerline for Ce5Mo1V at different times.

Table 3 — Adjusted Heat Source Parameters for the Models with the Hardfacing Velocitiesof 3 and 7 mm/s

Parameters Value Used

Q (W) 4800 4800 q1 (W/mm3) 141 117 q2 (W/mm3) 104 88 c1 (mm) 1.7 1.2 c2 (mm) 3.5 2.3 a (mm) 2.1 2.8 b (mm) 3.1 3.3 v (mm/s) 3 7

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result. The longitudinal stress y, whichwas caused by the longitudinal shrink-age of the hardfacing alloy, was coupledby tensile stress (y > 0 MPa) and com-pressive stress (y < 0 MPa). Moreover,in most areas, the y was mainly con-tributed by tensile stress, and tended tobe stable in the central zone, which wasnear 0 MPa. While in the hardfacingending zone, because of the applied con-straint, the large compressive stress of192 MPa existed. Figure 13 indicates the computation-al and experimental transverse stress x

distribution along the hardfacing alloycenterline after the hardfacing systemwas cooled completely. The transversestress x is tensile stress (x > 0 MPa)and the stress peak is 158 MPa. More-over, x in the central zone is large whilethat in the fringe area is small, which iscontrary to that of y.

Thermal Field and StressField for Cr5Mo1VRE Alloy

After verifying the accuracy for

simulation, the simulation forCr5Mo1V-RE alloy was conducted tocompare the weldability betweenCr5Mo1V alloy and Cr5Mo1V-RE al-loy. The hardfacing alloy was set toCr5Mo1V-RE, and the heat source pa-rameters were adjusted by comparingthe hardfacing bead cross section fromsimulation with that from actual hard-facing, in which Q = 4800 W, q1 = 112W/mm3, q2 = 84 W/mm3, c1 = 1.8 mm,c2 = 3.1 mm, a = 2.2 mm, b = 4.1 mm,and v = 5 mm/s. The thermal fields for Cr5Mo1V-RE

Fig. 11 — Stress fields for the Cr5Mo1V alloy hardfacing models at different times: A — 1.2 s; B — 6.2 s; C — 14.8 s; D — 20 s; E — 49.5 s;F — 1000 s.

A B

C

E

D

F

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Fig. 12 — Computational and experimental longitudinal stressy distribution along the hardfacing alloy centerline forCr5Mo1V alloy at cold state (1000 s).

Fig. 13 — Computational and experimental transverse stress xdistribution along the hardfacing alloy centerline for Cr5Mo1Valloy at cold state (1000 s).

Fig. 14 — Thermal fields for Cr5Mo1VRE alloy hardfacing models at different times: A — 1.2 s; B — 6 s; C — 15 s; D — 20 s; E — 49.5 s; F — 1000 s.

A B

C

E

D

F

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Fig. 15 — Stress fields for Cr5Mo1VRE alloy hardfacing models at different times: A — 1.2 s; B — 6 s; C — 15 s; D — 20 s; E — 49.5 s; F — 1000 s.

A B

C

E

D

F

alloy hardfacing models at 1.2, 6, 15, 20,49.5, and 1000 s are shown in Fig. 14.Comparing it with Fig. 7, it can be con-cluded that the two temperature changerules are similar. With an increase inhardfacing time, the temperature risesgradually and reaches the peak at 20 s(the moment for the ending of hardfac-ing). Moreover, during hardfacing(0~20 s), the temperature gradient be-fore the heat source was sharp, whilethat behind the heat source was gentle.After hardfacing, the highest tempera-ture area gradually moved toward thecenter, and the temperature of eacharea was basically the same when the

hardfacing systems were completelycooled (1000 s). The temperature dif-ference between Cr5Mo1V alloy andCr5Mo1V-RE alloy at each time wasvery small, which can be ignored. Figure 15 indicates the stress fieldsfor Cr5Mo1V-RE alloy hardfacing mod-els at 1.2, 6.2, 14.8, 20, 49.5, and 1000s. From it, with an increase in hardfac-ing time, the peak stress increased andthe stress area extended constantly.When the hardfacing system wascooled completely, the stresses were al-ways focused on the HAZs. When thetimes were 1.2, 6.2, 14.8, 20, 49.5, and1000 s, the peak stresses were 231.9,

358.0, 389.9, 403.8, 466.7, and 512.5MPa, which are smaller than those forthe Cr5Mo1V alloy hardfacing models. Figure 16 indicates the longitudinalstress y and transverse stress x dis-tribution along the hardfacing alloycenterline for Cr5Mo1V-RE alloy hard-facing models after the hardfacing sys-tem was cooled completely. From it,similar to those for the Cr5Mo1V alloyhardfacing models, the longitudinalstress y is coupled by tensile stress(y > 0 MPa) and compressive stress(y < 0 MPa) and the transverse stressx is tensile stress (x > 0 MPa). Thestress in the central zone is stable

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while that in the fringe areas fluctu-ate. What is more, for Cr5Mo1V-REalloy, the peak values of y and x are96 and 121 MPa, only 0.5 and 0.8 ofthose for Cr5Mo1V alloy, which indi-cates that the weldability ofCr5Mo1V-RE alloy is greater than ofCr5Mo1V. Moreover, the decreasingof y and x can both contribute onthe decrease in the hardfacing stressfor Cr5Mo1V-RE alloy, in which likehere, the decline of the longitudinalstress y plays the major role.

Influence of Hardfacing Velocity on the Thermaland Stress Fields forCr5Mo1VRE Alloy The thermal fields and stress fields

for the Cr5Mo1V-RE alloy hardfacingmodels with hardfacing velocities of 3and 7 mm/s were simulated, and thencompared with those at the hardfacingvelocity of 5 mm/s (as shown in Figs.14 and 15) to investigate the influenceof hardfacing velocity. The adjustedheat source parameters for the modelswith hardfacing velocities of 3 and 7mm/s are listed in Table 3. Figure 17 indicates the thermal fieldsfor Cr5Mo1V-RE alloy hardfacing mod-els with hardfacing velocities of 3 and 7mm/s, when the welding heat sourcesare at the same positions. Comparedwith Fig. 14, it can be concluded thatwith an increase in hardfacing velocity,the peak temperature reduces and theHAZ range obviously decreases. Figure 18 shows the initial stressfields for the hardfacing models with

hardfacing velocities of 3, 5, and 7mm/s, in which the hardfacing timesare 2, 1.2, and 0.86 s to make sure thatthe welding heat sources are at the samepositions. From them, the hardfacing al-loys are under the condition of melting,so the stress is 0 MPa. The large stressesare always focused on HAZs. Moreover,with an increase in the distance to hard-facing alloy centerline, the stress gradu-ally decreased. For the different hardfac-ing velocities, although the distribu-tions of initial stress were similar, therewere large differences between the peakstresses, in which when the hardfacingvelocity was 3 mm/s, the peak stresswas 270.26 MPa, when the hardfacingvelocity increased to 5mm/s, it de-creased to 231.9 MPa, and when thehardfacing velocity was 7 mm/s, thepeak stress was lowest at 190.87 MPa. Figure 19 illustrates the stress fieldsfor the hardfacing models with differenthardfacing velocities after the hardfac-ing systems were cooled completely. Thestresses on the HAZs were large. More-over, when the hardfacing velocity was3 mm/s, the peak stress was 520.8 MPaand the stresses on most zones werelarger than 165.8 MPa. When the hard-facing velocity increased to 5 mm/s, thepeak stress was 512.5 MPa, while onmost zones, the stresses were smallerthan 128.6 MPa. When the hardfacingvelocity further increased to 7 mm/s,the peak stress decreased to 488.6 MPa.Except for the hardfacing alloys andHAZs, the stresses on other zones weresmaller than 89.2 MPa. With an in-crease in hardfacing velocity, the peakstresses at the cold state were not quitedifferent, but the stress-influenced ar-eas were quite discrepant. Therefore, the hardfacing velocity in-fluenced the peak stress at the hardfac-ing initial state and the stress influ-enced-areas at cold state. The larger thehardfacing velocity, the smaller the peakstress at cold state and smaller was thestress-influenced area at the cold state.

Preheating Temperaturefor Cr5Mo1VRE Alloy To investigate the influence of pre-heating temperature on the thermaland stress fields, the Cr5Mo1V-RE al-loy hardfacing models were preheatedto 0, 50, 100, and 150C beforehardfacing, and then the thermalfields and stress fields were compared

WELDING RESEARCH


Fig. 16 — A — Longitudinal stress y and B — transverse stress x distribution along thehardfacing alloy centerline for Cr5Mo1VRE alloy hardfacing models at cold state (1000 s).

A

B

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to each other. The hardfacing velocitywas set to 5 mm/s. Figure 20 indicates the thermalfields for Cr5Mo1V-RE alloy hardfac-ing models with different preheatingtemperatures at the hardfacing initialstate (1.20 s). As the preheating tem-perature was 0C, the peak tempera-ture was 1570.1C. With an increase inpreheating temperature, the peak tem-perature rose slightly to 1598.5,

1647.6, and 1695.2C when the pre-heating temperatures were 50, 100,and 150C. Figure 21 shows the ther-mal fields for the hardfacing modelswith different preheating tempera-tures at the hardfacing middle state(10.2 s). As shown, when the preheat-ing temperature increased from 0 to150C, the peak temperature rosefrom 1927.8 to 2035.1C. Moreover,because the rising temperatures were

not obvious, there were no obviouschanges to the HAZs. The stress fields for Cr5Mo1V-REalloy hardfacing models with differ-ent preheating temperatures at 1.20 sare given in Fig. 22. When the pre-heating temperatures were 0, 50,and 100C, the peak stresses were231.9, 236.4, and 228.2 MPa, respec-tively. The differences among themwere very small. However, when the

Fig. 17 — Thermal fields for Cr5Mo1VRE alloy hardfacing models with different hardfacing velocities: A — 3 mm/s, 2 s; B — 7 mm/s, 0.86 s; C — 3 mm/s, 10 s; D — 7 mm/s, 4.29 s; E — 3 mm/s, 25 s; F — 7 mm/s, 10.7 s; G — 3 mm/s, 34.3 s; H — 7 mm/s, 14.3 s.

A B

C D

F

H

E

G

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preheat temperature increased to150C, the peak stress decreased to152.8 MPa, which is much smallerthan those when the preheat temper-atures were 0, 50, and 100C. It canbe concluded that when the preheattemperature is less than 150C, theinfluence of preheating on the resid-ual stress is very small, while whenthe preheat temperature increases to150C, the residual stress decreasesdrastically. Moreover, when the pre-heating temperature increased, thestress-influenced areas had littlechange. Figure 23 shows the stressfields for Cr5Mo1V-RE alloy hardfac-ing models with different preheatingtemperatures after the hardfacingsystems were cooled completely, inwhich neither the peak stress nor thestress-influenced areas had obviouschange.

Therefore, the preheating tempera-ture only influences the peak stress atthe hardfacing initial state. When thepreheat temperature increased to150C, the residual stress decreaseddrastically. Therefore, in the actualproduction process, the matrix metalscan be preheated (larger than 150C)to decrease the hardfacing initialstress and avoiding cracking.

Conclusion

1. The computa-tional temperaturefield and stressfield agree wellwith the experi-mental results,and the errors aresmaller than 5%.

2. With an increase in hardfacingtime, the temperature increases gradu-ally. Temperature gradient before theheat source is sharp while that behindthe heat source is gentle. On cooling,the highest temperature area movestoward the center. From hardfacing tocooling, the stress increases constant-ly. At the cold state, the large stressesare always focused on the HAZs. 3. For Cr5Mo1V-RE alloy, when thehardfacing times are 1.2, 6.2, 14.8, 20,49.5, and 1000 s, the peak stresses are231.9, 358.0, 389.9, 403.8, 466.7, and512.5 MPa, which are smaller thanthose for Cr5Mo1V alloy, which indi-cates that the weldability of Cr5Mo1V-RE alloy is greater than that ofCr5Mo1V. The decrease of y and x

can contribute to the decrease of thestress for the Cr5Mo1V-RE alloy, inwhich the decline of the longitudinalstress y plays a major role. 4. The hardfacing velocity influ-ences the peak stress at the hardfacinginitial state and the stress-influencedareas at the cold state. The larger thehardfacing velocity, the smaller is thepeak stress at the cold state and thesmaller is the stress-influenced area atthe cold state. 5. The preheating temperature only

influences the peak stress at the hard-facing initial state. When the preheattemperature is less than 150C, the in-fluence of preheating on the residualstress is small; however, when the pre-heat temperature increases to 150C,the residual stress decreases drastically.

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A

C

B

Fig. 18 — Stress fields for Cr5Mo1VRE alloy hardfacing modelswith different hardfacing velocities at hardfacing initial state: A — 3 mm/s; B — 5 mm/s; C — 7 mm/s.

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A

C

B

Fig. 19 — Stress fields for Cr5Mo1VRE alloy hardfacing models withdifferent hardfacing velocities at cold state (1000 s): A — 3 mm/s; B — 5 mm/s; C — 7 mm/s.

A B

C D

Fig. 20 — Thermal fields for Cr5Mo1VRE alloy hardfacing models with different preheating temperatures at hardfacing initial state(1.20 s): A — 0C; B — 50C; C — 100C; D — 150C.

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Fig. 22 — Stress fields for Cr5Mo1VRE alloy hardfacing models with different preheating temperatures at hardfacing initial state (1.20 s):A — 0C; B — 50C; C — 100C; D — 150C.

A B

C D

Fig. 21 — Thermal fields for Cr5Mo1VRE alloy hardfacing models with different preheating temperatures at hardfacing middle state (10.2 s): A — 0C; B — 50C; C — 100C; D — 150C.

A B

C D

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Fig. 23 — Stress fields for Cr5Mo1VRE alloy hardfacing models with different preheating temperatures at cold state (1000 s): A — 0C; B — 50C; C — 100C; D — 150C.

A B

C D

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