Engineering 45 (Material Science)
We observed how the properties of 4140 steel vary with the heat treatment to investigate the impact they would have on a design project. We prepared six specimens with three different heat treatments, Annealed (O), quenched and tempered (QT), and Normalized/ As-Received
(Norm/AR) and each were tensile tested using the universal testing machine (UTM) along with a
Rockwell hardness test. From the data collected stress strain curves were created for each specimen and % elongation (EL), % reduction in area(RA), ultimate tensile strength(UTS), and
0.2% offset yield strength(YS) were computed. 4140 O and 4140 O old values are 25.26% and
26.5%, 18.45% and, 42.19%, 28,991,474.20psi and, 28,508,137.50psi, 55,000psi for both. For
4140 QT A and B 13.71% and 12.56%, 52.51% and 47.5%, 29,977,578.79psi and
27,120,022.94psi, 188,082.39psi and 193,841.0712psi, 179,700psi and 186,000psi. For 4140
(AR/Norm) 12.3% and 12.46%, 43.9 % and 25.7%, 28,231,239.03psi and 27,750,052.85psi,
113,889.2psi and 159,705.4psi, 94,800psi and 105,100psi.The significance of these tests is to determine the properties of each heat treatment which in turn could help with future design applications. Introduction
We experimented with the effects of heat treatment on the 4140 Steel on a macroscopic scale. We used three different heat treatments, as-received, fully annealed, and quenched and tempered. We did a tensile test and hardness test on each of the specimens.Fully annealed steel is created by heating the steel into the austenite region which is an FCC phase, and then slow cooling it in a furnace to room temperature. Slow cooling allows enough time for pearlite to form which gives the steel a high ductility but low strength. Whereas the quenched and tempered specimen is acquired by quenching, this is to rapidly cool the steel, preventing the pearlite from forming.
Instead of perlite forming martensite is formed, an extremely strong but brittle phase of steel which is metastable. After quenching steel it is tempered, which is reheating the steel to a temperature below the eutectoid temperature for a specific period of time. This puts the steel into a higher energy state to allow the carbon atoms inside the martensite to precipitate, forming tempered martensite, which reduces the strength, but increases ductility. Since the properties can vary by simply manipulating the structure of steel, it is important to take into consideration when an engineer designs a project based on what conditions the steel will be under and evaluate how large the safety factor must be.
1. Quenched and tempered (QT)
a. Put an As- received (AR) specimen in carbon rich environment
b. Heat to 1600°F (austenite region) for 1 hour in a carbon rich environment
c. Remove from oven and immediately quench in oil to room temperature to create martensite d. Perform a Rockwell hardness test on the c scale
e. Reheat (temper) to 1000°F for 1 hour
f. Return to room temperature
g. Perform a Rockwell hardness test on the c scale
2. Annealed (O)
a. Heat to 1600°F (austenite region) for 1 hour
b. turn off furnace and let the specimen cool overnight
c. Perform a Rockwell hardness test on the b scale
a. Record initial specimen diameter with a caliper
b. Create indents for the axial length 2” apart and record the actual distance between the markings using a caliper.
c. Insert specimen into UTM and connect the extensometer
d. Start the tensile test
e. Remove extensometer at 0.2 strain for O samples, and at 0.1 strain for AR and QT samples. f. Continue testing until the specimen fails
g. Record final diameter
h. Record final axial length
a. download emailed data from instructor (excel format)
b. Plot stress vs. engineering strain up to the removal of extensometer.