Objective:
To determine the difference in hardness of various metals as a result of heat treating them.
To view the microstructures of various metals that were quenched in various ways.
Procedure:
Part A
Three bars of steel (1045, 4140, and unknown), are to be heat treated in an oven to their austenite temperature. The ends are then end quenched with a water flow for 10 minutes, after which they are cooled to room temperature. Flats are then milled along two sides of each specimen, so that we can perform a Rockwell Hardness Test on them.
Part B
Eight buttons will be polished by grinding them with various grit tooling. The specimens can then be viewed under the microscope. There are two groups of specimens, 1045 or 4140 steel. Within each group one specimen will remain untreated, one will be air cooled, one will be water quenched, and one will be annealed.
Results:
Part A
The unknown sample behaves in hardness over its length much like the 1045 steel sample. Another noticeable characteristic from the graph is the sharper decrease in d(RCH)/dx of 1045 steel versus 4140 steel. The RCH of 4140 decreases more linearly with distance form the quenched end. Data for the graph is found here.
Part B
Pictures of the microstructures pictures #1, #2, #3, and #4
Descriptions of views
Specimen #1 - 1045 steel, air cooled
-Fine microstructures tightly fit together.
Specimen #2 - 1045 steel, water
quenched
-Larger grain boundaries than the first specimen.
Specimen #3 - 1045 steel, annealed
-Surface is smoother than the rest.
Specimen #4 - 1045 steel, untempered
-Many strands of pearlite are visible.
Specimen #5 - 4140 steel, air cooled
-Very unlike 1045 steel in microstructure. Consists of large microstructures mixed with smaller structures.
Specimen #6 - 4140 steel, water quenched
-Much larger grain boundaries with many visible imperfections in the surface.
Specimen #7 - 4140 steel, annealed
-Smaller grain boundaries than #6 and much more consistency in structures.
Specimen #8 - 4140 steel, untreated
-Large microstructures and very similar to #5.
