1. Final Project:
Effects of Super Cooling on Free Cut Brass, Hardness, Impact Energy, and Ductility.
ENGR 2322 – Material Science
Advisor: Dr. Magesh Thiyagarajan
Date Submitted : May 13, 2013
Shawn Robinson

2. Abstract
The objective of thislabisto observe the effectof supercool heattreatmentonfree cutBrass (Alloy
360) material properties.The material propertieswe willbe payingattentiontowill be hardness,impact
energy,andductility.The brasswill be heat treatedandquenchedindryice (-78.5C),andliquidnitrogen
(-275C). Thena hardnesstestandimpact testwill be performedonthe posttreatedsamples.
Materials
- Oven
- Dog bone Brass sample (152mm*12.7mm*3.4mm)
- Face shield
- Thermal shieldinggloves
- Safety goggles
- Rockwell Hardnesstester
- CharpyImpact tester
- End mill,
- Ban saw
- Sandingwheel
- LiquidNitrogen
- Dry Ice
- 2 StyrofoamCoolers
Introduction
Heat treating is a methodology to increase hardness, toughness, relieves
stress or ductility of a material. In general, heat treatment is a process
used to alter physical or sometimes chemical properties of a material. To
combine, hardenability of any metal alloy is its capability to be hardened
by heat treatment. Hardness is the resistance of the material to
indentation or scratch. It is a qualitative indication of the materials
strength. The higher the hardness of a material, the more it is difficult to
make an indentation or a scratch, and vice versa.
Annealing temperatures for this brass are 795-1100°F. In this lab the
effects of extreme cooling rates will be investigated by quenching in liquid
nitrogen and dry ice. Super cooling sends the brass into extreme
temperature shock, thus forcing out impurities and making it more
ductile. The first test that will be done is the Rockwell hardness test, to
Fig.1.Brass sample
Fig.2.Rockwell hardnesstester

3. find the hardness of brass before heat treating. Hardness is a materials ability to resist surface
wear by indentation or scratching. These hardness tests are used throughout the field of
material science to help determine the surface properties of a
material to facilitate the requests of the engineers desires for certain
surface properties for a part or job. These tests are also used to help
determine the effectiveness of a manufacturing process such as
quenching and other heat treating methods. Rockwell hardness test
has different scales for different materials based on their degree of
resistance to wear. These scales differ mainly by the amount of load
applied to the material, the indenter used to make the indention in
the material and the formula used to calculate the resulting hardness
reading. For this experiment we used the HRB scale with the
Diamond Cone indenter and a major load of 100 kg to identify the
effects of heat treating on hardness. The last test that will be
conducted is the Charpy Test. The Charpy test is “a standardized high
strain-rate test which determines the Yield Strength, amount of
energy absorbed by a material during fracture”. The energy
absorbed is measured by the toughness or the ability of the material
to absorb this energy and resist lateral fracture. The Charpy apparatus that was used in this
experiment is the Universal Pendulum Impact Test machine. The pendulum acts as a hammer
that is used in order to break the material. This apparatus will be used to test the toughness
and ductility of the dry Ice quenched brass, and compare it to the liquid nitrogen quenched
brass. This will give a good indication of how the ductility of brass is comparatively affected by
the different cooling rates.
Material Characteristics
Brass is a binary alloy composed mainly copper and zinc, with copper being the majority of the
mixture, and the zinc content being anywhere form a few percent to 40%. Most brass alloys
have a tiny bit of lead in their composition to help improve machinability. Free-Cutting Brass is
a common alloy. It is one of the most widely used of the copper metals, with hundreds of
millions of pounds of it are consumed annually in the USA. It is commonly used as a substitute
for leaded steel in screw machine parts because of its higher strength and cheaper cost. Brass
has a density of 8.49 g/cc, a melting point of 1652-1724 °F (900-940 °C), and a crystal structure
of face centered cubic. It is commonly used in, condenser plate, marine hardware, valve stems,
balls, nuts, bolts, and rivets fittings.
Free-Cutting Brass, UNS C36000
COMPONENT WT. %
C 60 - 63
Fe Max 0.35
Other Max 0.5
Fig.3.Charpy Impacttest

4. Pb 2.5 - 3.7
Zn 35.5
PHYSICAL
PROPERTIES
METRIC ENGLISH COMMENTS
Density 8.49 g/cc 0.307 lb/in³ at 20°C (68°F)
MECHANICAL
PROPERTIES
METRIC ENGLISH COMMENTS
Tensile Strength,
Ultimate
338 -
469 MPa
49000 -
68000 psi
Tensile Strength,
Yield
124 -
310 MPa
18000 -
45000 psi
Depending on temper
Elongation at Break 53% 53% in 457.2 mm
Modulus of
Elasticity
97 GPa 14100 ksi
Bulk Modulus 140 GPa 20300 ksi Typical for Steel
Poisson's Ratio 0.31 0.31 Calculated
Machinability 100% 100% UNS C36000 (free-cutting
brass) = 100%
Shear Modulus 37 GPa 5370 ksi
THERMAL
PROPERTIES
METRIC ENGLISH COMMENTS
CTE, linear 250°C 20.5 µm/m-
°C
11.4 µin/in-
°F
from 20-300°C (68-
570°F)
Thermal
Conductivity
115 W/m-K 798 BTU-in
/hr-ft²-°F
at 20°C (68°F)
Melting Point 885 - 900 °C 1630 -
1650 °F
Solidus 885 °C 1630 °F
Liquidus 900 °C 1650 °F
Experimental Procedure
Step1. Test the hardnessusingHRB scale before heattreatment.
1. Mount the Anvil onthe Rockwell Hardnesstester
2. Turn the powerON switchlocatedonthe lowerrearside.
Table.1Material Propertiesof brass[3]

5. 3. Clearthe memoryof previousdatasetbyclickingthe delete button.
4. Identifythe sample tobe testedandchoose the correspondingindenter.Mountthe diamond
cone intenderonthe Rockwell Hardnesstester.
5. Set the scale to HRC.
6. If the “major load”isflashingonthe screen,itindicatesincorrectloadposition.Setthe
correct majorload byturningthe knobon the right side.
7. Once the indenter,scale andloadisset,youcan proceedtothe testbyraisingthe specimen
on the anvil byturningthe wheel.
8. When the sample makescontactwiththe indenterthe initial preloadwill be appliedasyour
raise furtherandyou can see the increase initialloadandyoumuststop whenitreachesa SET
value followedbyaclickingsound.
9. Then the machine will automaticallyapplythe majorloadandcalculate the harnessnumber
inthe correspondingscale
10. Recordthe resultsandlowerthe anvil andmove the specimentotestona differentspot.
11. Thenrepeatthe procedurestodetermine 10data points.
Step 2. Brass dog bone sample needs to be machined into two charpy impact samples with the
following dimensions: 3"x.5"x.03" with 60 degree notch angle.
1. Use the ban sawto cut the sample in two,at half of the length.
2. Grindoff the faresof the samplestogive a uniformwidth &length.Note thata cup of water
shouldbe usedtoperiodicallydipthe sampleinbecause itgetshot.
Fig.4.Cuttingsample onban saw
Fig.5.Cut sample

6. 3. Use the endmill tomanuallycutthe 60 degree notchangle inthe middle of the lengthside
of the samples,makingeachpassat3-5 tenthousandthsof an inch.
Fig.6.Grindingthe samples
Fig.7.Sample aftergrinding

7. Step3. Put the two sample in the oven at 1000F for 30mins
Step 4. While the samples are in the over, prepare the two Styrofoam coolers, one with 10lbs of
dry ice, and the other with 1L of liquid nitrogen.
Step 5. Retrieve each sample from the oven, safely quenching them in their respective
containers. Note: the sample that is lowered into the liquid nitrogen should be done slowly to
ensure the sample does not burn through the container. Let samples sit in their respective
containers for 15mins
Fig.8.Cutting60 degree notchangle
Fig.9.Preparingthe “baths”

8. Step 6. Remove samples form containers and let them sit for 15mins to reach room temp.
Fig.10 quenchingthe sample

9. Step 7. Repeat step 1 for the heat treated samples.
Step 8. Perform the Charpy impact test for the heat treated Samples.
1. Raise the pendulum arm to the right until it is firmly supported by the latching mechanism.
Caution: Make sure the safety latch is in the clear when raising the pendulum arm into this
test position.
2. Place the Charpy specimen horizontally across supports with the notch away from the
hammer. Make sure the specimen is centered within the anvil jaws (see Figure 1).
3. Slide the indicator pointer to the left until it indicates the maximum energy range on the
upper Charpy Tension scale.
4. Ensure all participants are clear and behind the caution stripe. The test conductor shall then
release the pendulum by pushing up on the release knob. The hammer will drop and attain a
striking velocity of 16.8 ft/s, striking the specimen, with a swing through dependent on the
amount of energy absorbed by the test specimen. The indicator will move and stop when
peak swing through is registered, providing a direct reading of the energy absorbed by the
specimen. Read the indicated value from the Charpy scale and record.
5. Apply manual brake until the pendulum has returned to its stable hanging vertical position.
6. Record the scale and readings.
Fig.11 samplesleftincontainers
Fig.12. SamplespostquenchingDry
Ice (top) &liquidnitrogen(bottom)

10. 7. Remove the specimen from the testing area and observe the failure surface.
8. Take pictures of your broken samples for analysis. Microscopes can be used to study the
broken surfaces.
Leave pendulum in the down hanging vertical position until another test is to be performed.
Experimental Data
Unheattreated Heat Treated
Dry Ice
Heat Treated
Liquid Nitrogen
Material
Type: Brass
Indenter:
1/16 dial
steel sphere
Scale: HRB
Scale
Major Load:
100 kg
Test
Number
HRB HRB HRB
1 73.0 *-10.3 -14.4
2 72.7 *0.9 -17.4
3 73.4 4.6 -13.6
4 72.7 4.5 -12.7
5 72.7 6.5 -12.4
6 72.6 7 *-6.3
7 72.8 7 *-2.8
8 73.0 6.2 *2.9
9 72.9 6 *2.7
10 72.9 3.8 *3.4
Mean 72.9 5.7 -14.1
Standard
Deviation
0.219317122 1.152171862 1.793320942
Min 72.6 3.8 -17.4
Max 73.4 7 -12.4
Table.2.Hardnesstestdata

11. Sample Test Result – Images
-30
-20
-10
0
10
20
30
40
50
60
70
80
h
a
r
d
n
e
s
s
(
H
R
B
)
Test number
Rockwell Hardness for differentheat treatment
processes
Unheattreated
Heat Treated Dry Ice
Heat Treated Liquid Nitrogen
Graph.1. Hardnessgraph forall samples
Fig.13. PostquenchingDryIce sample
Leechingonleftend

12. Data Analysis
The acquireddata showsthat the hardnessforthe stock sample (pre-heattreated),hadanaverage HRB
value of 72.9 [table.2].Itisimportantto note thatthe HRB scale isdimensionlessandisjustusedto
expressthe relativehardnessof amaterial. Most sourcesshow thatthisis an accurate hardness with
mostbeingaround75-78 [5]. Whenthe dry ice sample wasquenched,the sample made a loudvibrating
soundfor a fewsecondsandstopped.Thishappenedbecause of the rapidcoolingof the material,
causedthe excessenergystoredinthe momentumof the particles, tobe releasedinthe formof sound
energy [6].The average hardnessof the dry ice quenched sample was5.7on the HRB scale,witha
standarddeviationof 1.15 [table.2]. Thisdatashowsthat whenbrassisquenched,It becomessofter.
Thisis due to the grainstructuresbecominglarger,andmakingthe material softer[7].Itisimportantto
note that the endof the sample thatwas quenchedfirst experienced leechingonone end [fig.13].
Leechingiswhere the zincisforcedoutof the alloy[4] leavingbehindthe spongysoftcopper.This
wouldexplainthe softerdatapointstoone endand the higherstandarddeviation.The liquidnitrogen
quenchedsample hadanaverage hardnessof -14.2 on the HRB scale and had a standard deviationof
1.79. The data showsthatthe liquidnitrogenquenchingprocesscausesthe brasstobecome evensofter
than the dry ice quenchedsample.Thisisdue tothe grain structuresas discussedearlier,aswell as
forcesfromtemperature shock.Since the coolingrate forliquidnitrogeninmuchhigherthandryice,
the compressive force fromtemperature shockcausedmore impuritiestobe squeezedoutandthe
grainstructure larger [7] makingthe brass evensofter.Itwasalsonotedthat the endwhich the sample
was grippedwiththe irontongsandloweredintothe liquidnitrogen,hadhigherhardnessvaluesthan
the rest of the material [fig.14].Since liquidnitrogenisclose to0K, meaningnoenergy,the slightest
Fig.14. PostquenchedLiquidNitrogensample;
suface texture gradientonrightend
Fig.15. Postimpacttest(dry Ice sample) Fig.16. Postimpacttest(LiquidNitrogensample)

13. momentumtransferbetweenthe moleculesof the tongsandbrasssample cause a raise inenergy,
almostcreatinga jominyendquenchresult.Thisgivesreasontothe higherstandarddeviation.During
the experimentthe Charpyimpacttestwasperformedonthe postheat-treatmentsamples,yielding
impactenergies138ftxlbsand120ftxlbs,forthe dry ice and liquidnitrogensamplesrespectively.I
believemycharpytestyieldedinvalidresultsdue toseveral reasons.The firstreasonisdue tothe fact
that bothsamples didnotbreak,and simplybentaroundthe hammer[fig.15& 16]. Thishappened
because the effectsof supercoolingbrassleftitextremelysoftandductile.Alsoanotherreasonisthat
the sample shouldhave beencutintosmallerpieces,tobe able torun multipletrials, create control
data, andto ensure thatthe sampleswouldbreakdue tothembeingsosoft.Ialsofeel thatthe notch
shouldhave beencutdeepertocompensate forthe softness. However,aquickcomparative analysis
can be done onthese twovalues.Since the impact energyforthe liquidnitrogenwaslowerthanthatof
the dry ice,itsupportsour data of the liquidnitrogenbeingsofterandmore ductile thanthatof the dry
ice,because itgave lessresistance toimpactandmoldedmore easilyaroundthe hammer.Inthe end,
the highercoolingrate didhave a higherimpacton the hard andductilityof brass,whichiswhat we
were lookingfor[graph.1].Smallertestsamplesshouldbe usednexttime toachieve more controlled
and consistentresults.
Conclusion
The effectsof supercoolinghada drasticeffectonthe material propertiesof brass.Itbecame much
softerandductile asthe coolingrate wasincreased [graph1].This iscausedby the massive compressive
force due to temperature shockcoupledwiththe conductive material propertiesof brass.Itis important
to note fromthislab that whenworkingwithextremelylow temperatures,thatanyminute variations
on the macro alongthe sample have drasticvariationsonmicrostructure of the material andwhat
happens.To improve thislab,smallersamplesizesshouldbe usedtodecrease variationsineachsample
and the effectsof erroron the macro level,aswell asgetmore normalizeddataandreliable datafrom
the charpy impacttest.
References
1 James F. Shackelford, “Introduction to Material Science For Engineers”, 7th Ed, Prentice
hall. pp. 153-155
2 http://www.copper.org/applications/rodbar/alloy360/alloy360.html
3 http://www.ezlok.com/TechnicalInfo/MPBrass.html
4 Heat Treater's Guide: Practices and Procedures for Nonferrous Alloys
5 http://www.speedymetals.com/information/Material13.html
6 CRACKINGPERCEPTION BY EMITTED SOUNDDURING QUENCHING Franc RAVNIK 1, Janez
GRUM* 2 Universityof Ljubljana,Facultyof Mechanical Engineering,
7 Science of Conflict Metallurgy-Iron Quenching