Rockwell hardnes testing

1. Rockwell Hardnes Testing

3. Rockwell Hardness Testing
•Test Principle:
Rockwell hardness Number (RHN) based
on an inverse relationship to the
measurements of the additional depth
Which an indenter is forced by a heavy
(major) load beyond the depth resulting
from a previously applied (minor) load.

5. •Indenter:
•120 degree sphero-conicall diamond
indenter is used for hard material.
• Hardened steel ball indenter with
diameter of 1/16,1/8,1/4.1/2 inch.

6. Types of Test
•Two types of test based on load
Load RockwellSuperfical

Minor 10Kg 3 Kg


Major 60,100,150 Kg 15,30,45 Kg

7. Rockwell Scales
•There are 30 different scales ,depending on the
combination of the indenter and the load.
• 64 HRC means RHN of 64 on C- scale,
(diamond indenter and 150 Kg major load)
• 100 HRB means RHN 100 on B-scale (1/16
inch steel ball and major load 100Kg )
• 81 HR 30 N means SHN 81 on 30 N-scale
(30 N diamond indenter and major load 30 Kg)

8. Dial Gauge
• One revolution of the large pointer equals
1mm
•There are 100 divisions to a revolution
•Therefore ,1 division=0.01 mm
•Dial gauge is connected to a plunger
system in the head of a tester
•By means of the index lever having 5:1
•Therefore depth for 1 division =
0.01x0.2=0.002

9. Indentation depth caused by major load
HRC= 100 - --------------------------------------------------
0.002
indentation depth caused by major load
HRB= 130 - ------------------------------------------------
0.002

10. Rockwell indentation
One dimension on the dial gage - a depth of 0.002mm.
Zero reference line –100 for C scale and-130 for B scale

11. Depth of indentation
•Indentation depth from minor to major load: in
case of Rockwell test
(60HRC).
(100-60)x0.002mm= 0.08mm.
(130-Ball indentation reading)x0.002mm.
Superficial test
(regardless of the indenter used)
80HR30N
(100-80)x0.001mm=0.02mm

12. Factors that control Scale
selection
•-Type of material,
• -Specimen thickness ,
• -Test location ,
• -Scale limitation.

13. Type of Materials
•Hard materials such as steel or tungsten
carbide diamond indenter would be used.
•This limits to one of six Rockwell scale i.e
C,A,D,45N,30N,15N.
•Out of the above scales now determine
which scale will guarantee accuracy,
sensitivity and repeatability.

14. Specimen Thickness
•The material around the indentation is
cold worked.
•The extent of cold work area depends on
the type of material and previous history of
the testing material
•The depth of material affects has been
found by extensive experimentation to be
the order of ten times the depth of
indentation.

15. Test location
•If an indentation is placed with in the cold
worked area (previous indentation).
•The reading usually will be higher than that
obtained had it been placed out side this area.
•As a precaution three diameter from the centre
of one indentation to another is sufficient for
most material.
•The distance from edge should be minimum of
2.5 diameter of indentation.

16. Scale limitation
•No upper limit to the hardness of a
material that can be tested with a diamond
indenter.
•However C scale should not be used on
tungsten carbide (material may fracture or
indenter may damage). A scale is
acceptable in this case.
•Diamond indenter are not calibrated below
values of 20.

17. Anvils
•The work piece must be supported by the
proper anvil so that,
•It can not slide, roll or sag during the test.
•If not supported properly then accurate
reading is obtained.
•Or the indenter may damage.

18. Superficial
hardness
Rockwell
hardness

19. Case hardened and
Decarburization Parts
•Using several different scales case
characteristics can be determined. e.g
•parts shows 91 HR15 N and 62 HRC. This
means same hardness at an appreciable depth .
•91HR15N and 55 HRC. This means indenter
has broken through a relatively thin case.
•Decarburization can be detected by reversing
the techniques described above.

20. Rockwell Testing at Elevated
Temperature
•Tester in a furnace with provision of
controlled atmosphere .
• Facilities to move the specimen in the
furnace.

21. Rockwell testing Machines
•Test load can be applied either dead
weight or through springs.
•Measuring device - a dial or digital meter.
•Microprocessor to control the test process.
•Bench type testing machine.
•Production type.
•Portable type machine