To quantify the effects of heating and cooling on the properties of steel.
Before the lab there was a mini-trip up to the lab where the class saw how the heat treatments were accomplished. The heat treatments were done in accordance with the ASTM A255-85 Standard. During the heating of the samples the lower time limit of 30 minutes was adhered to. The upper limit of not greater than 35 minutes was not mentioned, or the what the slight effects might have been. After the hardness test sample was heated the sample was quenched in a cooling fixture. The oven should have been set up closer to the sink. Because of the number of students and setting the sample into the fixture the 5 seconds transportation time was compromised.
During the lab on the following day the sample was further prepared for testing. The flats were cut using a mill instead of water cooled grinding wheel may have slightly altered the heat properties of the sample. Before the sample was milled a steel brush was used to remove scale indicating that a atmospheric contaminant may have been present during heating. During the milling process sparks were produced in the harder sections of the sample resulting in lower than expected hardness values. The sanding procedure called for a figure eight to be used, and to avoid straight lines. By using a 45 degree rotation and straight lines the objective was achieved which was a finished surface for inspection of the metal microstructure
The unmarked sample appears to 1045 steel. The 4140 steel stays harder for longer cooling time. The hardness of the 1045 steel rod decreases rapidly until approximately one half inch from the end. The sample 4140 stayed hard for approximately an inch from the end.
1 Air cooled - Dark gray scaling and decarbonization - Course pearlite and fine pearlite
2 Water cooled - Greenish tint to the scaling - Fine pearlite and cementite
Larger more defined grain boundaries
3 Annealing - Darker and more scaling than button 1 - Pearlite and ferrite
4 Nothing - Reference button - Pearlite and ferrite
looks like #3 (Raw stock must have been annealed)
5 Air cooled - Dark gray scaling and decarbonization - Martensite and austenite
6 Water cooled - Greenish tint to the scaling - Fine pearlite and cementite
7 Annealing - More scaling than button any other button - Pearlite and ferrite
8 Nothing - Reference button - Martensite and austenite
looks like #5 (Raw stock must have been air cooled)
Microscopic inspection of the finished buttons.
More bounadry pictures B1 , B2 , B3 , B4
Graph of the metal phase boundaries of time vs temperture.
