PROPERTIES OF HIGH DENSITY FERROUS P/M MATERIALSA STUDY OF VARIOUS PROCESSES

S. H. LUK, H. G. RUTZ, AND M. A. LUTZHOEGANAES CORPORATIONRIVERTON, NJ 08077

PRESENTED AT 1994 INTERNATIONAL CONFERENCE &EXHIBITION ON POWDER METALLURGY & PARTICULATE MATERIALS

MAY 8-11,1994- TORONTO, CANADA

ABSTRACT

Several methods of achieving higher density in ferrous P/M partsare possible. Double press/double sinter allows densities inexcess of 7.3 g/cm3 but is limited by cost and geometryconsiderations. A new method of single processing highperformance materials is evaluated and compared to other methodsof processing. The comparison is performed utilizing Ancorsteel85HP and Distaloy 4800A base materials. Various green andsintered properties are evaluated including; green strength,transverse rupture strength, tensile properties and impactvalues.

The data clearly demonstrates that the patented (1) ANCORDENSE™*process offers performance comparable to double press/doublesinter processing. Green density values of approximately 98.5% ofthe pore free density limit are achieved with a single compactionstep.

INTRODUCTION

The ANCORDENSE process is a patented powder premixing andcompaction technology that enables the production of powdermetallurgy parts by single press and single sinter operations todensities of approximately 7.4 g/cm3. The ANCORDENSE premixes area derivative of the ANCORBOND®** process (2), thus insuring goodflowability and segregation resistance. The ANCORDENSE processutilizes traditional powder metallurgy compaction equipment butrequires that the powder and tooling be heated to moderatetemperatures in order to achieve high as-compacted densities. TheANCORDENSE process is represented schematically in Figure 1. Thepress ready powder is heated to a temperature in the range of265°F to 310°F prior to compaction. It is recommended that thepowder temperature be controlled to a maximum variation of +/-5°F to insure minimum part to part variability. The ANCORDENSEprocess utilizes a highly engineered lubricant system to optimize

performance within this temperature range.

Figure 1: The ANCORDENSE Process

Following heating, the powder is held in a storage container t atprovides powder to the shuttle. The die, top punch and any largecore rod assemblies are heated to the same temperature as thepowder. The warm powder is fed into the heated die and compactionproceeds as in normal powder metallurgy processing to providehigh density/high performance components. Rutz and Hanejko (3)offer a more detailed description of the compaction process. TheANCORDENSE process has been proven to be capable of commercialproduction of high performance powder metallurgy parts.

This paper will document various properties obtained by theANCORDENSE process and compare these results to conventionalsingle and double compaction processes. Two high performanceAncorsteel®*** based premix compositions were chosen forevaluation. Test specimens were prepared and evaluated accordingto standard procedures (4) for green density, green strength,sintered TRS, sintered tensile and sintered Charpy impactproperties. Additionally, data was collected to evaluate theeffect of the ANCORDENSE process on dimensional change andejection characteristics.

PROCEDURE

Two premix compositions were prepared using both the ANCORDENSEprocess and conventional premix methods. The ANCORDENSE processutilized the newly developed lubricant system while theconventional premix utilized Acrawax as the lubricant. Typicalbase material chemistries and specific premix additions arelisted in Table I.

Table I. Premix Compositions EvaluatedBase Material Premix Additions

BasePowder

Ni(Wt.%)

Cu(Wt.%)

Mo(Wt.%)

Ni(Wt.%)

Graphite(Wt.%)

Lubricant(Wt.%)

Distaloy4800A

4 1.5 0.50 -- 0.5 0.6

Ancorsteel

85HP

-- -- 0.85 2 0.4 0.6

Test specimens were compacted at 30, 40 and 50 tsi. In all cases,between 5 and 10 test specimens were evaluated for each testcondition. The green strength, transverse rupture strength, andtensile test specimens were compacted on a 10-ton hydraulic presswhile the Charpy impact specimens were compacted on a 22-tonCincinnati press. On both presses, the conventional mixes werecompacted at ambient temperature and specimens were onlycollected after the die had reached steady state temperatureconditions. The ANCORDENSE processed samples were compacted at apowder and die temperature of 290°F.

In addition to the single press/single sinter samples, both TRSand tensile specimens were also prepared using doublepress/double sinter techniques. Following the first compaction,both the ANCORDENSE and conventionally processed materials werepre-sintered at 1400°F for 30 minutes at temperature in a 25%N2/75% H2 atmosphere. These specimens were then repressed at thesame pressure used in the first compaction step. The secondcompaction step was performed at ambient temperature for both theANCORDENSE and the conventionally prepared materials.

Once compaction was completed, sintering was done in a productionsintering furnace. The Distaloy 4800A-based specimens weresintered at 2050°F and the Ancorsteel 85HP-based specimens weresintered at 2300°F. In both cases, a 10% H2/90% N2 atmosphere wasused.

Green density, green expansion from die size, and green strengthwere determined from the green strength bars. Density was

determined by immersion techniques for all sintered specimens.Additionally, TRS, sintered hardness and sintered dimensionalchange from die were determined on the TRS specimens. Values for0.2% offset yield strength, ultimate tensile strength and tensileelongation were determined from flat unmachined tensile specimenswith a 1” gauge length and at a strain rate of 0.1” per minute.Un-notched Charpy impact values were measured on the Charpy bars.

RESULTS AND DISCUSSION

Green Properties

The green properties for the two mixes are listed in Table 2. Forboth materials, the ANCORDENSE process achieved higher greendensity than the conventionally processed samples (Figure 2). Theincreases in green density ranged from 0.08 g/cm3 to over 0.14g/cm3 for a given compaction pressure.

Table II: Green PropertiesBase

MaterialProcessingTechnique

CompactionPressure(tsi)

GreenDensity(g/cm3)

GreenStrength(psi)

GreenExpansion

(%)

PeakEjection(tsi)

Ancorsteel

ANCORDENSE 304050

7.147.317.37

337036853580

0.190.260.29

2.152.432.32

85HP Conventional

304050

7.007.197.29

143017701950

0.170.230.27

2.703.683.90

Distaloy ANCORDENSE 304050

7.077.297.36

410044454515

0.170.230.29

1.992.302.37

4800A Conventional

304050

6.937.157.26

177021702450

0.190.240.28

2.703.523.77

Figure 2: Green Density versus Compaction Pressure for TwoMaterials (Ancorsteel 85HP+2% Ni+0.4% Graphite +0.6% Lubricantand Distaloy 4800A+0.5% Graphite+0.6% Lubricant) Compacted byANCORDENSE and Conventional Techniques

Figure 3: Green Strength versus Green Density ComparingANCORDENSE and Conventional Processing

For both materials, the ANCORDENSE process achieved higherdensities at 40 tsi then the corresponding conventional premixdid at 50 tsi. At 50 tsi, both ANCORDENSE premixes attaineddensities of over 7.35 g/cm3. This density level corresponds toapproximately 98.5% of the por-free density for those mixcompositions. Past experience with the ANCORDENSE process hasindicated that obtaining this high percentage of pore freedensity is typical for these two base materials.

The ANCORDENSE process shows significantly higher green strengththan the conventionally processed materials (Figure 3).Dramatically higher green strengths were achieved relative to theconventionally compacted samples, both at a given pressure and ata given density. For both materials, the green strengths obtainedat approximately 7.2 g/cm3 with the ANCORDENSE process were 85%higher than the conventional premix strengths. The ANCORDENSEDistaloy 4800A achieved the highest green strength of the group,reaching over 4500 psi at 50 tsi.

Green expansion from die size is presented in Figure 4. At a

given density, the ANCORDENSE processed materials exhibitslightly lower green expansion than the conventionally processedmaterials. This may be an indication of the mechanism by whichthe ANCORDENSE process achieves higher density compared toconventional compaction.

While compacting the green density samples, the peak force duringejection was recorded. This measurement should be an indicationof lubricant performance. The data is presented in Figure 5. Atall compaction pressures and green densities, the ANCORDENSEprocess exhibited significantly lower ejection forces than theconventionally compacted materials. This result confirmspreviously observed results (3) and may provide significantbenefits to the powder metallurgy part producer.

Sintered Density and Transverse Rupture Strength

TRS bars were prepared from both compositions utilizing fourdifferent processing techniques:ANCORDENSE single press/single sinter (SP/SS), ConventionalSP/SS, ANCORDENSE double press/double sinter (DP/DS),Conventional DP/DS. Sintered density, dimensional change fromdie, TRS and sintered hardness results from these tests arelisted in Table III.

Figure 6 presents the sintered densities achieved for theAncorsteel 85HP composition utilizing all four compactionprocesses (sintered at 2300°F). The densities achieved throughANCORDENSE SP/SS were very similar to those reached byconventional DP/DS. Over the compaction range, these densitieswere on average ~0.15 g/cm3 higher than the standard single pressresults. Double processing the ANCORDENSE samples increased thedensity even further, reaching over 7.6 g/cm3 at 50 tsi.

Figure 4: The Effect of Process and Chemistry on Green Expansionfrom Die Size

Figure 5: The Effect of Compaction Technique on Peak EjectionPressure

Figure 6: Sintered Density of Ancorsteel 85HP+2% Ni+0.4%Graphite+0.6% Lubricant Utilizing Various Compaction Processes(Sintered at 2300°F for 30 minutes in 10% H2/90% N2)

Figure 7: Sintered Density of Distaloy 4800A+0.5% Graphite+0.6%Lubricant Utilizing Various Compaction Processes (Sintered at2050°F for 30 minutes in 10% H2/90% N2)

The sintered densities (2050°F sinter) achieved with the Distaloy4800A composition are shown in Figure 7. These results indicatethat the ANCORDENSE SP/SS densities are once again about 0.15g/cm3 higher than conventional SP/SS processing. ConventionalDP/DS obtains densities of about 0.1 g/cm3 higher than theANCORDENSE SP/SS for a given compaction pressure. By utilizingANCORDENSE DP/DS, the sintered density is increased, about 0.06g/cm3 to 0.12 g/cm3 higher than the density achieved byconventional DP/DS.

Table III: TRS PropertiesBase

MaterialProcessingTechnique

CompactionPressure(tsi)

SinteredDensity(g/cm3)

TRS(103 psi)

Dim.Chg.(%)

Hard.(HRB)

Ancorsteel ANCORDENSESP/SS

304050

7.187.367.47

159.5192.1194.6

-0.25-0.13-0.07

838891

85HP ANCORDENSEDP/DS

3040

7.367.54

194.6216.7

8992

50 7.63 221.7 94(2300°FSinter)

ConventionalSP/SS

304050

7.017.227.32

144.3166.0185.7

-0.27-0.16-0.09

798588

DP/DS 304050

7.227.427.50

180.2212.0221.9

879294

Distaloy ANCORDENSESP/SS

304050

7.047.277.35

174.8199.6210.1

0.170.250.30

909497

4800A ANCORDENSEDP/DS

304050

7.207.407.49

218.5245.4246.0

9497100

(2050°FSinter)

ConventionalSP/SS

304050

6.907.087.20

141.4183.5194.1

0.110.240.28

818791

ConventionalDP/DS

304050

7.127.347.46

199.4238.8261.1

909496

Dimensional change from die size is presented in Figure 8 forboth materials. For a given density, the ANCORDENSE processedmaterials exhibited slightly more shrinkage (Ancorsteel 85HP) orless growth (Distaloy 4800A) from die size than theconventionally processed materials. The difference in dimensionalchange between the two processes can be correlated back to thedifference in green expansion (Figure 4). The results indicatethat the two processes obtained the same degree of sintering.

Figure 8: Sintered Dimensional Change from Die (Sintered at1200°F (Ancorsteel 85HP) and 2050°F (Distaloy 4800A) for 30minutes in 10% H2/90%N2)

Figure 9: Transverse Rupture Strength for the Ancorsteel 85HPMaterial Compacted Utilizing ANCORDENSE and ConventionalProcesses

Figure 10: Transverse Rupture Strength for the Distaloy 4800AMaterial Compacted Utilizing ANCORDENSE and ConventionalProcesses

Figure 11: Hardness Values for the Ancorsteel 85HP and theDistaloy 4800A materials Compacted Utilizing ANCORDENSE andConventional Processes

Transverse rupture values for each of the four processes areshown in Figure 9 for the Ancorsteel 85HP material and in Figure10 for the Distaloy 4800A material. Both graphs clearly show theimportance of density on strength. For both materials, theANCORDENSE SP/SS process provides approximately a 12% strengthincrease over the conventionally processed premixes for each ofthe compaction pressures. It is important to note that at thehigh density levels achieved, the TRS specimen deflectssignificantly during the test. This suggests that tensile testresults are a better measure of material performance. Hardnessvalues generated on the TRS specimens are shown in Figure 11.These results generally follow the TRS values and again indicatethe dependency of physical properties on density.

Tensile Properties

Tensile properties, including 0.2% offset yield strength,

ultimate tensile strength, elongation and hardness, weredetermined for both mixes. Both SP/SS and DP/DS data werecollected for each material and compaction method with theexception of the ANCORDENSE processed Distaloy 4800A, where onlySP/SS data were determined. The results are listed in Table IV.The data for ultimate strength, 0.2% offset yield strength andelongation for the Ancorsteel 85HP composition are shown inFigures 12 through 14, respectively, and for the Distaloy 4800Acomposition in Figures 15 through 17, respectively. In a similarfashion to the TRS results, the strength and elongation valuesall show a significant dependence on density.

For the Ancorsteel 85HP composition, the yield and ultimatestrength obtained with the ANCORDENSE process are improved for agiven density level relative to the conventional premix.Evaluating the SP/SS processes for a given compaction pressure,the ANCORDENSE process provided an average increase in yieldstrength of 11% and an average increase in ultimate strength of13.5% over conventional processing. In reviewing the DP/DSprocesses, the ANCORDENSE prepared samples achieved an increaseof 8.3% and 8.8% for yield and tensile strength, respectively,over the conventional process. Even though the conventional DP/DSprocess provided marginally higher sintered density than theSP/SS ANCORDENSE process, the strength values are nearlyidentical at equivalent compaction pressures. Elongation values(Figure 14) indicate a very strong dependence on sintereddensity. Noteworthy among the data is the nearly 6% elongationobtained by the DP/DS ANCORDENSE process.

Similar trends were obtained when the Distaloy 4800A chemistrywas evaluated (Figures 15-17). The yield and ultimate strengthsincreased an average of 11.3% and 17.3%, respectively, for theANCORDENSE 5P/SS sintered samples over the conventionallyprocessed SP/SS samples. The SP/SS ANCORDENSE samples indicateonly slightly lower yield and tensile strengths compared to theconventional DP/DS samples for a given compaction pressure.However, the ANCORDENSE SP/SS samples do indicate much higherelongation values.

Figure 12: Ultimate Tensile Strength of the Ancorsteel 85HPMaterial Compacted Utilizing ANCORDENSE and ConventionalProcesses

Figure 13: 0.2% Offset Yield Strength of the Ancorsteel 85HPMaterial Compacted Utilizing ANCORDENSE and ConventionalProcesses

Figure 14: Tensile Elongation of the Ancorsteel 85HP MaterialCompacted Utilizing ANCORDENSE and Conventional Processes

Figure 15: Ultimate Tensile Strength of the Distaloy 4800AMaterial Compacted Utilizing ANCORDENSE and ConventionalProcesses

Figure 16: 0.2% Offset Yield Strength of Distaloy 4800A MaterialCompacted Utilizing ANCORDENSE and Conventional Processes

Figure 17: Tensile Elongation of the Distaloy 4800A MaterialCompacted Utilizing ANCORDENSE and Conventional Processes

Table IV: Tensile PropertiesBase

MaterialProcessingTechnique

CompPress(tsi)

SinterTemp(°F)

SinterDen

(g/cm3

)

0.2%YieldStrg(103

psi)

UTS(103

psi)

Elong(%)

Hard(HRB)

Ancorsteel ANCORDENSESP/SS

304050

2300 7.177.397.46

61.367.770.3

82.092.997.4

1.912.763.27

848890

85HP ANCORDENSEDP/DS

304050

2300 7.337.517.60

68.972.676.9

92.4101.6

105.5

2.494.175.81

879295

ConventionalSP/SS

304050

2300 7.027.267.36

56.260.662.6

70.882.187.2

1.502.302.70

798788

ConventionalDP/DS

304050

2300 7.237.447.55

61.769.071.8

82.594.598.8

2.203.204.10

859192

Distaloy ANCORDENSESP/SS

304050

2050 7.077.277.34

53.455.857.7

92.0102.2

106.9

2.242.792.95

899293

4800A ConventionalSP/SS

304050

2050 6.917.127.24

45.950.853.8

76.887.492.8

1.982.362.42

838990

ConventionalDP/DS

304050

2050 7.137.347.45

55.562.365.3

91.1105.9

115.0

2.052.492.65

919597

Impact Properties

Impact testing was performed on SP/SS samples only and theresults are listed in Table V. The results are plotted versussintered density in Figure 18 for the Ancorsteel 85HP basematerial and in Figure 19 for the Distaloy 4800A base material.As expected, both figures indicate that the impact energy is afunction of density for each chemistry and not a function ofcompaction technique. The higher density achieved for theANCORDENSE processed materials allow significantly higher impactproperties to be realized. The highest value achieved by theAncorsteel 85HP mix processed by the ANCORDENSE technique was 39ft-lbf at a sintered density of 7.42 g/cm3 This value is over 33%higher than the highest value achieved by conventional compactiontechniques.

Figure 18: Charpy Impact Values for the Ancorsteel 85HP MaterialSP/SS by ANCORDENSE and Conventional Processes

Figure 19: Charpy Impact Values for the Distaloy 4800A MaterialSP/SS by ANCORDENSE and Conventional Processes

Table V: Impact PropertiesBase

MaterialProcessingTechnique

Compacting

Pressure(tsi)

SinteringTemp(°F)

SinteredDensity(g/cm3)

ImpactEnergy

(ft-lbf)

Hard(HRB)

Ancorsteel ANCORDENSESP/SS

304050

2300 7.097.347.45

13.827.839.3

798690

85HP Conventional

SP/SS

304050

2300 6.907.237.37

12.621.029.6

778286

Distaloy ANCORDENSESP/SS

304050

2050 7.047.257.34

17.420.020.0

848992

4800A Conventional

SP/SS

304050

2050 6.907.107.24

13.616.619.8

818587

CONCLUSIONS

A comparison was made between ANCORDENSE processing andconventional compaction techniques utilizing two premixes(Ancorsteel 85HP+2% Nickel+0.4% Graphite+0.6% Lubricant sinteredat 2300°F and Distaloy 4800A+0.5% Graphite+0.6% Lubricantsintered at 2050°F). Both single press/single sinter and doublepress/double sinter techniques were performed. The following canbe concluded from the study:

1) Green density increases of up to 0.14 g/cm3 were obtainedfrom the ANCORDENSE process. The single press/single sinterdensity increase realized by the ANCORDENSE process ranged from0.14 to 0.19 g/cm3. Single press/single sintered density valuesof over 7.45 g/cm3 were obtained from the ANCORDENSE processingof the Ancorsteel 85HP chemistry.

2) Sintered density improvements on the double press/doublesinter samples utilizing the ANCORDENSE process ranged from 0.03to 0.14 g/cm3 over conventional processing for a given compactionpressure. Sintered density values in excess of 7.6 g/cm3 wereobtained for the Ancorsteel 85HP material utilizing theANCORDENSE process.

3) The ANCORDENSE process produced green strength enhancementsof over 85% when compared to the conventionally processed premix.Green strengths in excess of over 4500 psi were obtained from theDistaloy material utilizing the ANCORDENSE process.

4) All physical properties showed a strong dependence onsintered density. For a given compaction pressure, the ANCORDENSEprocessed materials consistently achieved higher density and thushigher physical properties, than the conventionally processedmaterials. Of particular note are the impact values of nearly 40ft-lbf for the ANCORDENSE SP/SS processed Ancorsteel 85HPmaterial and the elongation values of nearly 6% for theANCORDENSE DP/DS processed Ancorsteel 85HP material.

ACKNOWLEDGMENTS

The authors would like to thank the Hoeganaes Corporation forsupporting the preparation of this paper. They would like toparticularly thank W. Bentdiff, S. Clisby, P. Kremus, P. Muetz,C. Oliver, H. Phan, A. Lawrence, and A. Rawiings for theirsupport in the development of the ANCORDENSE process and thepreparation and testing of the materials in this paper. S.Tworzydlo is to be thanked for professional preparation of thefinished manuscript. The staff of the Cincinnati IncorporatedTechnical Center were most helpful in the compaction of testspecimens. The authors are indebted to John Kosco and the staff

of Keystone Carbon Company for providing the productionsintering.

REFERENCES

1. Rutz, H.G., Luk, S.H., “Method of Making a Sintered MetalComponent”, U.S. Patent 5,154,881.

2. Luk, S.H., Hamill, J.A.,Jr., “Dust and Segregation-FreePowders For Flexible P/M Processing”, Advances in PowderMetallurgy & Particulate Materials-1993, Vol. 1, pp 153-169,Metal Powder Industries Federation, Princeton, NJ.

3. Rutz, H.G., Hanejko, F.G., “High Density Processing of HighPerformance Ferrous Materials”, To be Published, Advances inPowder Metallurgy & Particulate Materials-1994, Metal PowderIndustries Federation, Princeton, NJ.

4. “Standard Test Methods for Metal Powders and PowderMetallurgy Products”, Metal Powder Industries Federation,Princeton, NJ, 1993.

Notes

•ANCORDENSE is a trademark of the Hoeganaes Corporation.**ANCORBOND is a registered trademark of the HoeganaesCorporation.***Ancorsteel is a registered trademark of the HoeganaesCorporation.