Title: Heat Treatment Tensile Strength Laboratory Experiment
Course: Materials of Engineering > Section: MET 2200

MET 2200 HEAT TREAT AND TENSILE STRENGTH EXPERIMENT

INTRODUCTION:

Metal alloys respond differently to thermal treatments.  Some alloys can be strengthened by thermal treatments while others are returned to lower strength levels by exposure to similar temperatures.  Hardening procedures for steels can result in different strength/ductility levels as result of the cooling rates used after heating.  Annealing procedures for many nonferrous alloys also change the strength/ductility levels.  Text references are Sections 10.1, 10.2, 10.3, and 10.5 in Materials Science for Engineers 7th edition.

OBJECTIVE:

It is the objective of this experiment to determine the effects of hardening of AISI 1018 steel and the annealing of CDA 360 free cutting brass on their strength, ductility, and Rockwell hardness

EQUIPMENT & MATERIALS:

Instron tensile test machine, heat treating furnaces, quench tanks, hardness test machine using previously machined tensile test specimens of the following engineering alloys:
1) AISI 1018 cold formed steel
2) CDA 360 free cutting brass

PROCEDURE:

1) Mark each specimen with an identifying mark using a scribe or punch mark.  Care must be taken to not deform the tensile test specimen during the marking process.  Measure the dimensions and Rockwell hardness of the tensile test samples to ensure consistency.  Hardness is to be measured on one of the flat surfaces in the grip area of the sample. Testing hardness in the reduced cross-section area of the test sample will adversely affect the subsequent tensile test.  Record the hardness value and hardness machine scale by specimen number.  SAFETY GLASSES MUST BE WORN BY ALL PERSONS IN THE VICINITY OF THE FURNACES AND THE TENSILE TEST MACHINE!

2) One sample of each material should be reserved to act as a baseline value.

3) Three (3) of the steel samples are to be heated to 1550 degrees Fahrenheit for a time period of 30 minutes.

4) One steel sample is to be water quenched; another is to be oil quenched; and the third is to be air cooled to determine the difference in hardening due to cooling rate.

5) Two brass samples are to be placed in the other furnace at 900 degrees Fahrenheit for a time period of 45 minutes in order to anneal them.

6) One brass sample can then be removed from the furnace and water quenched while the other sample will be air cooled.

7) The samples which were heated must be dried and hardness tested to record the effects of the heating on each sample’s hardness.

8) All samples are then to have a gauge length marked onto them in the event that they might break outside the extensometer while they are being tensile tested in the Instron tensile test machine.  Yield strength, tensile strength and percent elongation will be determined for each of the samples.

9) Each laboratory team is to practice manual load and elongation data collection during the tensile testing of at least one sample.

DATA ANALYSIS:

Make a complete data spreadsheet comparison of the baseline sample values of tensile properties and hardness with those for the samples which were heat treated.  Record raw data in the units used to measure those data and show formulas for all calculations made on that data.  The engineering tensile test properties to be compared in the data tables include max load, yield strength, ultimate tensile strength, fracture strength, % elongation, elastic modulus and relative toughness, all of which can be determined from engineering tensile test data and plots for the samples.  Include handbook reference values in the data table.  DO NOT include hard copies of the complete Instron spreadsheet data files which will be posted on My Course by Dave McCallum.  Make correlations between the fracture appearances and the observed test results.  Visually compare the effects of the heat treatments using plots of engineering stress versus engineering strain strategically chosen to show the trends. (not just individual autoscale plots).  Obtain referenced handbook data for comparisons.

DISCUSSION:

The following are required discussion points.  Discuss how all variations of experimental equipment, material, procedure, and data collection may have changed the results of the experiment and include reasons for these observations.  Discuss the effects of the heat treatments on the properties of both the steel and the brass materials including the mechanisms involved.  Is the cooling method critical for the steel and for the brass?  Discuss how the appearance of the fracture surface relates to the ductility of the specimens.  Compare the toughness of these alloys as estimated from the tensile test curves.  How do the results of this experiment compare to expected theoretical or handbook results?

CONCLUSION:

What conclusion(s) can be drawn from this experiment on these steel and brass materials?