Slide 1

Lab. ExperimentsMT-306Experiment -1

Determination of Phase Diagram of lead tin system by Direct Cooling Curves

Cooling curvesSingle-component systemBinary system

Single-component system exhibiting supercooling PROCEDURE

Plot the direct cooling curve for an unknown sampleThe molten alloy is kept in a crucible in the center of the furnace.Immerse a Chromel-Alumel thermocouple with a protective sheath into the molten metalAllow it to cool the alloy to room temperatureStir the molten specimen frequently to reduce the temperature gradient and improve chemical homogeneity. Temperature readings by PID controller. Be sure that you make any necessary reference junction corrections.

Specimenwt% of pbwt% of Sn1955285153703045545538.161.9625757158581.598.5OBSERVATIONS

Plot Time temperature curve (direct cooling curve) using Excel software and note the arrest points (change of slope).

After standard polishing and etching procedure measure the volume/weight fraction of different phases in your sample.

Compare the measured fraction with the calculated one for your composition from the phase diagram (Fig.3).

To measure volume fraction use point counting methodQUESTIONS

From the Pb--Sn phase diagram, estimate the composition of your sampleCompare, calculated and measured weight fractions. Discuss difference between them.Discuss the arrest point in Pb-61.9 percent Sn alloyWhat type of binary system is represented by the Pb-Sn diagram?Would you expect a difference in the arrest points obtained by heating curves and cooling curves?

Volume fraction by point counting method

Rationale

If a point is placed at random within a volume, the probability that it will fall within a given constituent is equal to the volume fraction of that constituent

Basic equation for equality

GridExperiment 2Determination of Hardenability of steel by Jominy End Quench Test

Schematic of Jominy end quench test

Cooling rate as a function of distance from the endHardness profile as a function of distance

Procedure:

Normalize steel sample to eliminate differences in microstructure.Heat it at 8500C for at least 2 hrs.Transfer the specimen to test machine held vertically and spray with a controlled flow of water onto one end of sample. Ground flat the specimen along its length so that the face width is 10mm.Then measure hardness (VHN) at intervals of 2 mm.Plot Vickers hardness values versus distance from quenched end. Cut the sample into 4 pieces and examine each piece for its microstructure.Use NITAL as an etching reagent.Also calculate the percentage carbon (by weight)Discussion

Submit microstructure (print out) of your sample, identify different constituent, plot hardness as a function of distance (collect data from all your group members).How do your hardness measurements correlate with your microstructural observations.Give five applications for quench-hardened steels.What will be the difference in hardness profile of a steel part quenched in water and in oil at the same temperature?

Experiment 3CarburizingAim : To measure diffusion coefficient of carbon in steel2CO (g)= CO2 (g) + C (steel)Carburization of steel involves a heat treatment of the metallic surface using a gaseous, liquid, solid or plasma source of carbon. The process of carburization works via the implantation of carbon atoms in to the surface layers of a metalCalculation of diffusion coefficientUsing Ficks second law

Solution of this equation is

Cs - Surface carbon concentrationC(x,t) - Carbon concentration at depth x after time tCo - Initial carbon concentration of steel sampleProcedure

After carburizing quench the sampleFrom hardness measurement and metallography find out the distance where 50% martensite is present (x)Concentration at this point will be 0.4% C (c(x,t) )Cs is carbon concentration at the surfacet time of carburization is known

So one can calculate D (at the temperature of carburizing)Experiment -4 Determination of grain growth exponent in a given material and activation energy of grain growthWhereDt is the average grain diameter after time tn is grain growth exponent (slope of the straight line)K is a constantTheoretically the value of n=0.5, experimentally observed to be