Classification of testing Importance of testing Destructive testing Mechanical testing(hardness, tensile and impact)

1. Metallurgical Testing
By - K.Sevugarajan
Contact details
Metz Lab Pvt.Ltd.
First floor, Thangavel Nagar
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Mannivakkam-600048
Cell: +91-8190810222
Mail: sevugarajan@metzlab.org
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• Classification of testing
• Importance of testing
• Destructive testing
• Mechanical testing(hardness, tensile and impact)
• Metallographic testing(microstructure, case
depth etc,.)
• Chemical testing(spectro,edax etc)
• Other testing
Metallurgical testing-Course content

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Destructive Examination
• Destructive Examination renders the material
unfit for further service.

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Common methods used in Destructive
Examination
• Tensile testing
• Impact testing
• Bend testing
• Hardness testing
• Chemical analysis
• Metallography
• Peel testing
• Spark testing

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Tensile Strength Testing
• “Tensile” is a test in which a prepared sample
is pulled until the sample breaks.
• Test Measurements are recorded in PSI (Pounds
per Square Inch) E7018 = 70,000 PSI Tensile
• Test samples called “Tensile Bolts” can reveal a
welds Tensile strength, Elastic limit, Yield
point, and Ductility.

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Tensile Strength Testing
• The Elastic Limit of metal is the stress (load) it
can withstand and still return to the original
length after the load is released.
• Yield Strength occurs when the test sample
stretches however will not return to its
original length.
• Ductility is the ability of a metal to stretch or
elongate before it breaks.

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Properties Obtained from the Tensile Test
 Elastic limit
 Tensile strength, Necking
 Poisson’s ratio
 Modulus of resilience (Er)
 Tensile toughness
 Ductility

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(c)2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.
Figure 6.11 (a) Determining the 0.2% offset yield strength in gray cast ion, and (b)
upper and lower yield point behavior in a low-carbon steel

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(c)2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.
Figure 6.12 Localized deformation of a ductile material during a tensile test
produces a necked region. The micrograph shows necked region in a
fractured sample

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Figure 6.13 Typical yield strength values for different engineered materials. (Source: Reprinted from Engineering
Materials I, Second Edition, M.F. Ashby and D.R.H. Jones, 1996, Fig. 8-12, p. 85. Copyright © Butterworth-Heinemann.
Reprinted with permission from Elsevier Science.)

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Tensile Testing Strength Graph

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Strain Rate Effects and Impact Behavior
 Impact test - Measures the ability of a material to absorb the sudden
application of a load without breaking.
 Impact energy - The energy required to fracture a standard specimen
when the load is applied suddenly.
 Impact toughness - Energy absorbed by a material, usually notched,
during fracture, under the conditions of impact test.
 Fracture toughness - The resistance of a material to failure in the
presence of a flaw.

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(c)2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.
The impact test: (a) The Charpy and Izod tests, and (b) dimensions of typical
specimens

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Impact Testing
• An Impact tester uses a heavy pendulum that
is able to measure the amount of force
required to shear or fracture a test sample
taken from welds “Heat Affected Zone” (HAZ)
• Impact testing may be performed using either
the Izod or Charpy method. (Both methods are
similar)

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Impact Testing
• A Charpy or Izod test measures the welds
ability to withstand an Impact force.
• Low Charpy test readings indicate brittle weld
metal
• Higher Charpy readings indicate the samples
toughness.

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Bend Testing
• Bend test samples are referred to as
“Test Coupons”
• The most common bend tests are
– Guided face and root bend testing
– Guided side bend testing
– Longitudinal root and side bend testing
– Fillet weld bend testing
– Unguided bend testing

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Bend Testing Sample Removal

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Bend Testing Sample Preparation

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Face Bend Testing

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Root Bend Testing

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Side Bend Testing

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Longitudinal Face Bend Testing

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Longitudinal Root Bend Testing

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Fillet Bend Testing

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Pipe Fillet Bend Testing

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Hardness testing
• Hardness may be defined as the
resistance to permanent indentation.
• Three common hardness measuring
tests are
– Rockwell test
– Scleroscope test
– Brinell
– Microhardness test

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Hardness of Materials
 Hardness test - Measures the resistance of a material to penetration
by a sharp object.
 Macrohardness - Overall bulk hardness of materials measured using
loads >2 N.
 Microhardness Hardness of materials typically measured using loads
less than 2 N using such test as Knoop (HK).
 Nano-hardness - Hardness of materials measured at 1–10 nm length
scale using extremely small (~100 µN) forces.

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(c)2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under
license.
Figure 6.23 Indentors for the Brinell and Rockwell hardness tests

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Hardness testing
• The Rockwell testing machine operates
somewhat like a press, using a indenter to
penetrate the surface of the test sample.
• The depth of the indentation determines
the materials hardness on a scale of 0-100

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Hardness testing
• The Sceleroscpoe testing machine measures
the amount “bounce” that a diamond tip
hammer rebounds off the test sample after
being dropped.
• The Brinell method presses the “indenter”
into a sample for a given period of time.
• The ability for the sample to resist
indentation determines hardness.

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Hardness testing
• Microhardness testers allow you to
measure a materials hardness while leaving
the least amount of damage possible on
the metals surface.
• After the indenter is used a powerful
microscope is used to determine the the
amount of indentation into the
components surface.

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Chemical Analysis
• Chemical analysis is used in metallurgical
laboratories to determine the metals grain
and crystalline structures.
• Samples are then place under a high power
microscope to view the results.
• This is referred to as “Metalography”

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Metallography

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Objective
• To prepare the specimens surfaces to be examined
for their microstructure study by the microscope .
• To learn and to gain experience in the preparation of
metallographic specimens.
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Introduction
• Metallography is basically the study of the structures and
constitution of metals and alloys, using metallurgical
microscopes and magnifications, so that the physical and
mechanical properties of an alloy can be related to its
observed microstructure.
• It provides information about the specimen under
investigation, including the size and shape of the grains
(crystallites), the presence of micro defects (such as
segregation, hair cracks, and nonmetallic inclusions), and
the nature and distribution of secondary phases.
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Metallography
• Cutting
• Grounding – emery paper (240, 300, 400, 600)
• Polishing (0.5, 0.1, 0.05μ)
• Etching –Nitol/ Kellers Solution
• Microscopy

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• Soft non-ferrous metals - Initial grinding is recommended with 320 grit SiC
• abrasive paper followed by 320 400, 600 and , 800 grit SiC paper. because
These materials are relatively soft they do not easily break down the SiC
paper.
• The initial grinding with 320 grit is generally sufficient for minimizing initial
deformation and yet maintaining adequate removal rates.
•
• For extremely soft materials such as tin, lead and zinc it is also
recommended that the abrasive paper be lightly coated with a paraffin wax.
The wax reduces
• the tendency of the SiC abrasive to embed into the soft specimen.
Grinding Soft non-ferrous metals

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• Ferrous metals - are relatively easy to grind with the depth of
deformation being a major consideration.
120 grit SiC abrasives provide a good initial start with subsequent use
of 240 or 320, 400, 600 and 800 grit SiC.
• Super alloys - are generally of moderate hardness but have extremely
stable elevated temperature characteristics and corrosion resistance.
• the procedures for preparing super alloys is very similar to that for
most non-ferrous metals.
Grinding Ferrous metals

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• Polishing is the process of creating a smooth
and shiny surface by rubbing it or using a
chemical action, leaving a surface with a
significant reflection
• Aluminum Oxide(0.5, 0.1, 0.05μ)
Polishing

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Grain
• The micro structure of many metallic or ceramic materials consists of many grains.
• A grain
• is portion of the materials within which the arrangement of the atoms is nearly
identical but the orientation or crystal structure of atoms
are different.
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Etching:
Sample
material
Etchant Composition Remarks
Carbon steel (usually 2%)
(nitric acid)
HNO3 1-5 ml
Ethyl alcohol 100ml
Few seconds (15
Sec)
Carbon steel Picric Acid Picric acid 4g
Ethyl alcohol 100ml
Few seconds (15
Sec)
Aluminum Hydrofluoric acid HF (conc.) 0.5ml
H2O 99.5ml
Swab for 15 sec.
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Hydrostatic Testing to Destruction
• Pressure testing or leak testing can be
performed with either gasses or liquids.
• When this pressure exceeds the limitations of
the structures design it will rupture under
force.
• This rupture will allow engineers to
understand the welds weakest areas.

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Peel testing
• Lap joints may be tested to destruction using a
Peel test.
• Peel testing is most commonly used to check
the strength of resistance spot welds or stud
weld
• Spot weld peel tests are considered successful
when the spot weld nugget is torn out of the
test sample pieces in tact.

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Spark Testing
• The shape and
characteristic of
sparks created when
metal is ground will
help determine its
properties.
• IE: carbon steel ,
mild steel.

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