ASTM Hardness Conversion Table
Mechanics of Materials Lab – Materials Section
Experiment #1: Effect of Heat Treatment on the Strength of Steel
The purpose of this experiment is to introduce the students to the effect of heat treatment on the
mechanical properties of steel.
Steel is the most important commercial metal alloy. Of course, "steel" is not a single alloy, but
instead is a bewildering array of compositions whose common component is iron. The
microstructure of steel is the key to its behavior because the crystal structure, size, carbon content
and arrangement of the microconstituents (BCC ferrite, BCT martensite, FCC austenite,
orthorhombic cementite, etc.) determine its properties.
Relevance of Experimental Design
Hardness can be defined as the resistance of a material to scratching, abrasion, or penetration. Any
hardness index is a manifestation of the combined effects of several related properties, which may
include the yield point, ultimate tensile strength, malleability, work hardening characteristics,
wear-resistance properties and so on. Therefore, hardness measurements must be interpreted with
caution and full consideration of their attendant limitations. In fact, past methods for determining
hardness, like the file hardness test, were not fully reliable because they depended on the skill of
the technician performing the test. It was not until 1900 that Dr. Brinell of Sweden proposed a
new, reliable method whereby the hardness could be indicated by the resistance to indentation.
Nowadays, hardness testing has found extensive industrial applications and is an essential tool in
the quality control of metals, alloys, and metal products. The Most commonly used hardness
testing methods are the Brinell and the Rockwell hardness test.
Worksheet/Informal with Cover Letter
Steel is the term used to describe a large number of alloys containing two key ingredients: iron and
carbon. The most common and least expensive steels contain between 0.05% and 1% C, about
98% Fe and the remainder is made of Mn, Si, and other additions. Steels containing primarily C
and a little Mn fall generally within the 10XX designation of the AISI-SAE. The XX correspond
to the hundredths of percent carbon in the steel. For instance, 1040 steel contains 0.4% C.
Steels of this kind have phase diagrams as the one shown in the Figure 13.1 (1). A 1050 steel heated
to 850 °C will be made of the austenite phase which has a face center cubic structure. If this steel
is slowly cooled to room temperature, maintaining equilibrium conditions, the austenite
decomposes and the microstructure transform into two phases, in accordance with the
corresponding phase diagram, ferrite and cementite. Expressed differently, the microstructure will
be made of two microconstituents: primary ferrite and pearlite. However, if we consider a 1077
steel, the microstructure at room temperature of slow cooled steel will be made of only one
microconstituent: pearlite. Pearlite, the eutectoid microconstituent, is made of alternating plates
or lamellae of ferrite and cementite. It is expected that the 1050 steel will have lower strength than
the 1077 because of its lower pearlite content.
Sometimes, it is desirable to increase steel strength or ductility. Controlling the strength and
ductility of steels can be performed through the chemical composition (carbon content) or through
the cooling process of steel from the austenitic range. If very fast cooling rates are used in cooling
the steel from the austenitic range to room temperature (called quenching), the decomposition of
austenite to cementite and ferrite will not take place. Instead, the austenite still decomposes but
this time a short range, diffusionless rearrangement takes place at the atomic level, which results
in the formation of another phase called martensite. Due to this structure rearrangement, the
dislocation motion becomes more difficult thus resulting in an increase in strength and a decrease
in ductility. Depending on the cooling rate employed, several other microstructures can be obtained
in accordance with the time-temperature curves of the particular steel that is used (1). Martensite is
very strong but quite brittle, which is undesirable. But if the quenched material is furthermore
heated up briefly (a process called tempering) to some intermediate temperature, the martensite
decomposes to a fine dispersion of cementite and ferrite. This tempered martensite will have
properties intermediate between those of the untempered martensite and slowly cooled ferrite plus
eutectoid, retaining still much of the strength of the plain martensite but not nearly as brittle - a
very desirable combination of properties! That is why the martensite is tempered, after quenching,
for most practical applications. The exact properties are determined by the tempering temperature.
If the quenched material is heated again to the temperature where austenite forms, the martensite
microstructure will disappear. If this “re-austenitized” material is cooled down slowly, then the
resulting structure will be softer pearlite/ferrite mixture, just as if the martensite had never formed
These processes can be conducted repeatedly. For example, if the same material is re-heated to
austenite and quenched again, the structure will become martensite and the hardness will be high
In this experiment, hypoeutectoid (meaning XX <77) carbon steel will be heat-treated in different
ways. The effect of heat treatment on mechanical properties will be determined by hardness
measurements using a Rockwell hardness tester.
Table has been created following these instructions for data collection.
0. Make sure all tools, equipment, and machinery are ready to go.
1. Measure the hardness of the sample in as-received condition (three different spots). This
material has been rolled (plastically deformed to its final shape) and contains a large
number of dislocations, so its hardness is higher than that of undeformed slow-cooled
2. The tubular furnace will be pre-heated to about 960 °C. Record the temperature at the
center of the furnace. Tie the metal wire to the steel specimen. Place the steel sample in the
center of the furnace. Leave the specimen in the furnace for at least 10 min and observe the
color changes in the sample as it heats up.
3. Pull the specimen quickly using attached wire (SPECIMEN IS RED HOT; USE
EXTREME CARE PER ASSISTANT INSTRUCTIONS) and allow it to drop in a bucket
filled with water. This is a quenching procedure. Remove sample from bucket and clean
oxide scale using a file.
4. Measure the hardness of the specimen in three different spots. Set the tube furnace to 970
5. Put sample back in furnace; wait 10 minutes. Slide sample away from center of furnace 2
inches every 2 minutes; this results in slow cooling for this experiment. After the sample
is completely out of the furnace, cool in water.
6. File off the oxide layer from the surface and measure the hardness at three different spots.
Change the furnace to 980 ℃.
7. Place the specimen back in the furnace and keep it in for at least 10 minutes.
8. At the end of the heating period, pull out the specimen and drop it into the water until it
cools down. Remove it and file off the oxide layer from the surface of the specimen.
9. Measure the hardness of the quenched specimen on the Rockwell hardness tester at three
10. Calculate the average hardness for each of the conditions tested. Read and record the
estimate tensile strength for each case.
State of Steel
Rockwell Hardness (B or C)
Tensile Strength (ksi)
After 1st Quick
After Slow Cooling
After 2nd Quick
1st Quick Cooling
2nd Quick Cooling
Furnace Temperature (°C)
Time of Cooling Phase (sec)
1. Organize all your data in a table or tables and compute the average tensile strength for each
2. Determine and draw the temperature profile for all cooling procedures. The data can be
presented on top of the corresponding CCT diagram (Figure 12-17).
3. Determine the expected microstructure for both cooling procedures using appropriate CCT
diagram. (e.g. martensite/pearlite/bainite/etc.)
4. Comment on the properties and correlate the properties to the microstructure. (e.g., how is
martensite/pearlite/bainite/etc. related to strength? Did the strength change after the
process? Does martensite/pearlite/bainite/etc. make the steel more ductile/brittle/etc.?)
5. On the Fe-C phase diagram (Figure 11-12), indicate and specify the point at which
austenite starts forming in this particular specimen based on temperature and weight
percent of carbon.
6. Compare measured martensite hardness with that expected for the type of steel used. The
steel that was used is 1060 Steel. Was it higher/lower than expected (Figure 11-24)?
7. Compare slow-cooled hardness with textbook values for the type of steel used. (Figure 1117). The steel used was 1060 Steel. Explain factors that may result in difference. Research
8. Was the second martensite harder/softer/same compared with that obtained the first time?
Include in Lab Report
1. Cover Letter
2. Introduction/Problem Statement (in your own words)
3. Test Procedure (in your own words)
4. Test Data
NOTE: TO RECEIVE FULL CREDIT MAKE SURE TO INCLUDE ALL EQUATIONS,
IMAGES, FIGURES & TABLES USED.
1. D.R. Askeland, “The science and engineering of materials”. PWS-Kent Publishing
Company. Boston. USA. 1994.
State of Steel
After 1st Quick
After Slow Cooling
After 2nd Quick
1st Quick Cooling
Set Temperature of
Time of Cooling
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