Aim
“Understand the material hardness and effect of carbon content and heat treatment on hardness”
Aim of this lab work is to understand the material hardness of different materials and effect of carbon content present in material on material hardness and effect of heat treatment of material on material hardness.
Objectives
In order to achieve the aim of this lab work the following mention objectives have to be completed in said sequence
1. Develop a comprehensive understanding of methods used for measuring material hardness
2. Develop a comprehensive understanding of effect of carbon percentage on material hardness
3. Develop a comprehensive understanding of effect of heat treatment on material hardness
4. Perform hardness test to measure material hardness
5. Perform hardness test after increasing carbon content
6. Perform hardness test after heat treatment of material
7. Develop a comprehensive conclusion about work
Theory
Hardness
Material hardness can be defined as the material ability to resist indentation. In more details it can be define as the material ability to resist the localized plastic deformation which is in the shape of indention and scratch. Material hardness is also a great way to understand the material wear resistance as it is observed that greater the material hardness greater is the material wear resistance. Another important relation of hardness with material is that the material hardness is roughly proportional material strength.
Hardness testing
Material hardness tests are very simple, easy and straight forward to perform as the only thing needed to be done in material hardness test is to produce a dent in material and then the force or load needed to product dent in material is used to measure the material, hardness. Hardness measure during the experiment is usually a dimension less number only that defines the level of hardness of material means hardness is a unit less quantity. Hardness test are destructive test by their nature of testing material but in some case these tests can be considered as non-destructive test as they only create a small dent on material surface and material can be used in any way possible after the test.
There are three different hardness testing methods namely as Brinell hardness test, Rockwell hardness test, and Vicker hardness test. Difference in type of hardness test tis based on the type indenter used in the experiments, load applied during the experiments and manner in which load is applied during the experiment. There are three different types of indenters used for the hardness test. First is the ball indenter made from the steel and has the diameter of 10 mm in most of the cases. Second the diamond cone and third is diamond pyramid.
Material Sample
In order to check the effect of carbon content and heat treatment on the material, different samples of material are provided as per below mention details
For checking carbon content
Plain Carbon Steel Sample No |
Carbon content |
1 |
0.18 |
2 |
0.35 |
3 |
0.60 |
4 |
0.90 |
5 |
1.20 |
For
heat treatment
·
As-received sample
·
Sample hardened at 1300oC and
quenched
·
Samples quenched and tempered for 1 hour
at various temperatures from 200oC to 750oC.
Sample No for Tempering |
Tempering Temperature, oC |
01 |
As-received |
02 |
As-hardened (Room temp. tempering, 25oC) |
03 |
200 |
04 |
400 |
05 |
450 |
06 |
500 |
07 |
550 |
08 |
600 |
09 |
700 |
Results
Table
1 Carbon content and Material Hardness
|
Rockwell Hardness |
Vickers Hardness |
|||||
% Carbon |
Hardness Readings, HRC |
Ocular Readings (mm) |
Hardness |
||||
|
1 |
2 |
Mean |
X |
Y |
Mean |
HV |
0.18 |
21.7 |
24.1 |
22.9 |
0.464 |
0.47 |
0.467 |
255 |
0.35 |
30.5 |
31 |
30.75 |
0.4195 |
0.4165 |
0.418 |
321 |
0.6 |
36.7 |
36.1 |
36.4 |
0.375 |
0.363 |
0.369 |
387 |
0.9 |
36.5 |
36.6 |
36.55 |
0.373 |
0.377 |
0.375 |
396 |
1.2 |
31 |
27.4 |
29.2 |
0.399 |
0.402 |
0.4005 |
346 |
Table
2 Tempering Temperature and Material Hardness
|
Rockwell Hardness |
Vickers Hardness |
|||||
Tempering |
|||||||
Temperature, oC |
Hardness Readings, HRC |
Ocular Readings (mm) |
Hardness |
||||
|
1 |
2 |
Mean |
X |
Y |
Mean |
HV |
As-received |
66.6 |
66 |
66.3 |
0.239 |
0.24 |
0.24 |
966 |
(for reference only) |
|||||||
As-hardened |
67.1 |
67 |
67.05 |
0.234 |
0.244 |
0.239 |
990 |
(Room temp. tempering, 25oC) |
|||||||
200 |
65 |
64.2 |
64.6 |
0.244 |
0.244 |
0.244 |
934 |
400 |
63.3 |
63.8 |
63.55 |
0.244 |
0.244 |
0.244 |
934 |
450 |
63.7 |
64.1 |
63.9 |
0.238 |
0.241 |
0.24 |
960 |
500 |
64.8 |
5.2 |
35 |
0.225 |
0.23 |
0.228 |
1070 |
550 |
66.6 |
66.7 |
66.65 |
0.214 |
0.215 |
0.215 |
1203 |
600 |
61.4 |
60.7 |
61.05 |
0.258 |
0.259 |
0.259 |
829 |
700 |
46.6 |
46.6 |
46.6 |
0.329 |
0.336 |
0.333 |
502 |
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