This document discusses various mechanical properties of metals including strength, ductility, hardness, toughness, fatigue strength, and how they are tested. It provides details on: - Tensile strength and yield strength, which are determined through tensile testing. As temperature increases, strength decreases. - Ductility and how it is measured by elongation and reduction of area. Ductility permits forming without failure and increases with temperature. - Hardness and its relationship to strength. Hardness testing can estimate tensile strength. - Toughness and notch toughness, which refer to energy absorption. Notch toughness is more important for parts with flaws and is tested via impact tests.

1. MODULE – 6
Metal properties and destructive testing Welding inspector may have to review
Documentation related to actual properties of base metal and filler metals. Welding
Inspector must simply compare specifications values with actual numbers to judge
compliance. Metallurgical treatment may alter the properties of a metal. Pre-heating and
post heating technique are applied to maintain certain properties. For quenched and
tempered steel it is essential to monitor welding heat in put to prevent degradation of base
metal properties caused by over heating.
Mechanical properties of metal—STRENGTH, DUCTILITY, HARDNESS,
TOUGHNESS, FATIGUE, STRENGTH.
Strength is the ability of a material to withstand an applied load. Tensile, Shear,
Torsional, Impact and Fatigue strength are 5 types of strength. Tensile strength is the
ability of a metal to resist failure when subjected to a tensile or pulling load. Tensile
strength is expressed in 2 ways 1.Ultimate tensile strength and 2. Yield strength
116/184- UTS refers to maximum load carrying capacity of that metal or the strength of
that metal at the exact point when failure occurs.
Yield strength is that strength level at which material’s response to loading changes from
elastic to plastic.
Elastic behavior refers to the deformation of a metal under load which causes no
permanent deformation when load is removed. When a metal is loaded within its elastic
region it responds with some amount of stretch or elongation.
In the elastic range amount of stretch is directly proportional to the applied load. Hence
the elastic behavior is linear.
If a metal is stretched beyond its elastic limit its behavior is referred as plastic means,
permanent deformation. Here it implies that stress strain relation no longer remains
linear. In plastic deformation the material will exhibit permanent deformation.
Where the material behavior change from elastic to plastic is called YIELD POINT.
A structure becomes useless if stressed beyond its yield point and becomes deformed.
The ultimate tensile strength and yield strength are determined by a tensile test. Once the
tensile strength of a certain metal is known it is easy to find out how large cross section
shall be required to carry a given load. For carbon steel there is a direct relation ship
between tensile strength and hardness. If hardness increases tensile strength also
increases. It is convenient to perform a hardness test on Carbon and low alloy steels to
estimate their equivalent tensile strength. As the temperature increases, the strength of a
metal decreases.
Ductlity – It is ability of a metal to deform or stretch under load without failing. More
ductile a material is, more it shall stretch before it breaks.
High ductile material shall fail gradually. A ductile material shall bend before
failing/breaking; this means that metal’s yield point is being exceeded. Metals having low
ductility fails suddenly in a brittle manner without any warning.
As a metal temperature increases ductility increases. Metals behaving in a ductile manner
at room temperature may fail at sub zero temperature in a brittle manner. Highly ductile
material is called ductile and less ductile material or low ductile material is called
BRITTLE.
Brittle materials do not show any deformation before failure / fracture. Glass and white
C. I. are good example of brittle material.
Ductility is a property which permits several members even of slightly different lengths
to uniformly support some load without one of those members becoming overloaded to
the point of failure.
Ductlity is an essential property for a metal which needs to go some forming operations.

2. Rolling causes crystals/grains to be elongated in the direction of rolling more than
transverse direction.
Hence strength and ductility of a rolled metal is greater in longitudinal direction. In
transverse direction tensile strength decreases by 30% and ductility by 50%. In through
thickness direction these properties are even further less. The ductility of a metal is
normally determined by the tensile strength. Ductility is usually expressed in percent
elongation and percent reduction of area.
Hardness – It is defined as ability of a material to resist indentation or penetration.
Hardness and strength are directly related for carbon steel, hardness increases with the
strength and vice versa. Hence if metal’s hardness is known it is possible to estimate its
tensile strength. This helps us in estimating the strength of a metal without
removing/cutting, preparing and pulling a tensile specimen. Some type of indenter which
is forced into the surface of the metal by an applied load. This hardness is then
determined as a function of either the depth or size of indentation.
By hardness test we can determine hardness of a large area of metal surface or hardness
of an individual grain of the metal.
117/184-- Toughness—It is the ability of a metal to absorb energy. From stress strain
diagram producing during tensile test, the toughness of the metal can be determined by
calculating the area under stress strain curve.
118/184- Notch toughness—This is different from toughness in that it refers to the
material energy absorbing ability when there are surface flaws present, where as
toughness refers to energy absorption capacity of a smooth un notched sample.
Toughness defines material’s behavior when loaded slowly, while notch toughness values
and reflect the energy absorption which occurs at the high rate of loading. Generally
notch toughness is referred as impact strength.
If steady load is applied it takes more time than if string is pulled sharply to break it.
Toughness or notch toughness indicates how much of energy can be absorbed by a
material before it fails. Low toughness values define brittle behavior while toughness
values are related to ductile fracture. Toughness of metal changes with temperature.
Toughness properties of metal are determined at a specific temperature. Without test
temperature information values for toughness has little meaning. Metal with high value of
notch toughness will perform well whether or not there is a notch present. If a metal is
notch sensitive that means it exhibits low notch toughness, then it could more easily fail
during impact or repetitive loading. The metal’s notch toughness decreases as its
hardness increases and its temperature is reduced. While finding out notch toughness of a
metal by testing, it is best to determine that temperature at which the fracture behavior
changes from ductile to brittle. This temperature is referred to as metal’s transition
temperature.
Notch Toughness Test—Impact load is applied when metal is brought to a specified
temperature. Charpy, Drop weight Nil Ductlity, Explosion bulge, Dynamic tear and crack
tip opening displacement tests are various tests conducted to determine notch toughness.
Fatigue Strength.—It is that strength of a metal necessary to resist failure under repeated
load application. S-N curve is a graphic description of how many fatigue cycles are
necessary to produce a failure at various stress level. Steel exhibits a well defined
endurance limit but the curve for Aluminum does not. The endurance limit is the
maximum stress at which no failure occurs, no matter how many cycles the load is
applied. It is observed that aluminum shall fail even at low stress level; however the steel
will last indefinitely as long as stress remains below this endurance limit. Fatigue strength
of steel is roughly equal to half its tensile strength.

3. Fatigue strength like impact strength is extremely dependent upon surface geometry of
members. The presence of notch or stress risers can increase the stress at that point to
above the metal’s endurance limit. Unless ground smooth after welding, the weld itself
creates a surface irregularity. Weld surface irregularity/discontinuity such as Under cut,
over lap, excessive reinforcement or convexity can have an effect on a member’s fatigue
strength. Such conditions create a sharp notch which can act as a fatigue crack initiation
site.
A surface discontinuity will more quickly lead to fatigue failure than will a sub surface
discontinuity. It is established fact that surface stress levels are usually higher than the
internal stress levels.
Discovery and correction of sharp surface irregularities will greatly improve the fatigue
properties of any structure. In many fatigue situations, a small weld with a smooth
contour will perform better than a much larger weld having sharp surface irregularities.
Steel Alloys--- Stainless steel contains at least 12% chromium.
Effects of Chemical Elements in Steel—Most weldable steel have less than 0.5% carbon .
Carbon can exist either dissolved in the iron or in a combined form which such as Iron
carbide (Fe3C) Increased amount of carbon increases hardness and tensile strength as well
as response to heat treatment (Hardenability ). On the other hand increased amount of
carbon reduces weldability.
Sulphur—It is undesirable impurity. It is attempted to eliminate during steel making. If
Sulphur is increasing and exceeds 0.05% it tends to cause brittleness and reduce
weldability. Alloying addition of sulphur in amounts from 0.1% to 0.3% will tend to
improve machinability of steel. Such types may be referred as to a Resulphurised or free
machining. Free machining alloys are not intended for use where welding is required.
Phosphorous – This also is an impurity, it is generally up to 0.4% in steel. In hardened
steel it may tend to cause embrittlement. In low alloy high strength steels phosphorous
may be added in amounts up to 0.10% to improve both strength and corrosion resistance.
Silicon – Usually only small amounts- 0.20% are present in rolled steel When it is used
as deoxidizer. However in steel casting0.35% to 1% is commonly present. Silicon
dissolves in iron and tends to strengthen it. Weld metal usually contains approx. 0.5%
silicone as deoxidizer. Some filler metal may contain up to 1 % to provide enhanced
cleaning and deoxidation for welding on contaminated surfaces.
When these filler metals are used for welding of clean surfaces, the resulting weld
strength will be markedly increased. The resulting decrease in ductility could present
cracking problems in some situation.
Manganese—Steel contains at least 0.3% Mn, It acts as:-
i) Assists in the deoxidation of the steel.
ii) Prevents the formation of iron sulphide inclusion, and
iii) Promotes greater strength by increasing the hardenability of the steel.
Amounts up to 1.5% are found in Carbon steels.
Chromium-- It strongly increases the hardenability of steel and it markedly improves the
corrosion resistance of alloys in oxidizing media. Its presence in some steel can cause
excessive hardness and cracking in and adjacent to the weld. Cr is more than 12% in
steel.
Molybdenum—This is strong carbide former and is usually present in alloy steels in
amounts less than 1 %. It is added to increase hardenability and elevated temperature
strength. It helps to improve pitting corrosion resistance in Austenitic steel.
Nickel—It increases hardenability. It improves toughness and ductility of steel. It
improves steel’s toughness at low temperature.
Aluminum—It is added as de oxidizer. It is also a grain reformer for improved toughness.

4. Vanadium—This increase hardenability and it is added in very small quantity. If more
than 0.05%, there may be tendency for steel to become embrittled during thermal stress
relief treatment.
NIOBIUM—This also increases hardenability. It has strong affinity to carbon. It may
combine with Carbon in steel to result in decrease in hardenability. It is added to SS as a
stabilizer to improve as welded properties.
Dissolved gasses—Hydrogen, Oxygen and Nitrogen can cause porosity if not minimized.
Special fluxes and or shielding gasses are used to prevent solution into molten weld
metal.
Al. Alloys—It is very desirable for application requiring god strength, light weight, high
thermal and electrical conductivity and good corrosion resistance. It has tensile strength
1/5 of stainless steel. Alloying with Copper, Zinc, or Silicon permits heat treating to
increase strength. The heat treatable types get their hardness and strength from
precipitation hardening. The non heat treatable grades are strengthened only by strain
hardening (Cold working).
Nickel—It is a tough silvery metal of about same density as copper. It has excellent
resistance to corrosion and oxidation at high temperature. Many high temperature alloys
have Ni to the range of 60% to 75%.
121/184- Destructive testing –
Tensile Testing This testing gives us many information. UTS, YS, Ductility, %
Elongation, % Reduction in area, Modulus of Elasticity, Proportional Limits, Elastic
Limit and Toughness.
Some tensile test values can be determined through direct reading of a gage. Others can
be quantified only after analysis of stress strain diagram. The value for ductility can be
found out by making comparative measurements of tensile specimen before and after
testing. The percentage of that difference then describes the amount of ductility present.
Slight imperfection in the surface finish can result in significant reduction in the apparent
strength and ductility of the tensile specimen.
The tensile specimen is provided with a reduced section configuration in the middle
centre. This is intended to localize the failure. The reduced section is intended to localize
the failure. The reduced section results in the increased uniformity of the stresses through
out the cross section of the specimen. The reduced section must exhibit following
features:- i) The entire length of the reduced section must be uniform section.
ii) The cross section should be a configuration which can be easily measured so that cross
sectional area can be calculated.
iv) The surface of the reduced section should be free of surface irregularities,
especially if perpendicular to the longitudinal axis of specimen.
The most common gage length is 2” or 8”. The difference of distances provides the
amount of elongation or stretch. Elongation refers to the distance the specimen has
stretched on tension. Percent elongation=The elongation divided by original length
multiplied by 100.
Percent area reduction- When a ductile specimen is subjected to a tensile test a portion of
it exhibits necking. If the final area is measured it shall be less than original area. The
difference of area, divided by the original area multiplied by 100 provides a value for
percent reduction of area.
Extensometer is placed on gage marks and specimen is loaded at steady rate. If load is
applied at non steady rate it can cause inconsistencies in testing.
When load and elongation data are fed into strip chart recorder, this results in a plot of the
variation in the elongation as a function of applied load i. e. Load vs Deflection curve.
Stress is proportional to strength i.e. Load/ Area in Lbs/ in2 PSI.

5. Strain is amount of stretch apparent in a given length, it is a number only without any
unit.
Stress- Strain chart- In the zone of elastic behavior the stress and strain are proportional.
The slope of this line is constant value, i.e. Modulus of Elasticity or Young’s modulus.
The number actually defines stiffness of the metal i.e. higher the modulus of Elasticity.
The stiffer is the metal.
When strain begins to increase faster than stress it indicates that material is stretching
more for a given amount of applied stress. This indicates the end of elastic behavior and
beginning of plastic or permanent deformation. The point on the curve showing the extent
of linear behavior is referred to as elastic. In elastic stage if load is removed the specimen
would return to its original length. In some metals stress increases to some maximum
limit and then drops to some lower limit, these limits are upper yield point and lower
yield point. Upper yield point is that stress at which there is noticeable increase in stress,
or plastic flow, without increase in stress. The stress then drops down and remains
relatively constant at lower YP. While stress continues to increase during what is known
as YP elongation. During yielding plastic flow of metal increases at such a rate that
stresses are relieved faster than they are formed. When this plastic flow occurs at room
temperature it is called COLD WORKING. This action causes metal to become stronger
and harder and is said WORK HARDENNED.
STRUCTURE STEEL IS A TOUGHER MATERIAL THEN SPRING STEEL.
TOUGHNESS—It is a measure of a metal’s ability to absorb energy. In a tensile
specimen % reduction of area will be approx. twice the value for percent elongation.
Hardness-- Brinell is the largest indentation and micro hardness is the smallest. For
metal stock hardness determination because indentation covers a relatively large area.
128/184—TOUGHNESS-- This is metal’s ability to absorb energy. Certain amount of
energy is required to initiate a crack, then additional energy is required to cause that crack
to grow or propagate. The Notch toughness test is measured by Charpy V notch test. The
specimen is generally 55 mm long X 10mm X 10mm square. One of long side of
specimen shall have a carefully machined V shaped notch 2 mm deep. At the base of the
notch there shall be a radius of precisely 0.25mm. The machining of this radius is
extremely critical as small inconsistency shall result in big variation in test result.
Reduced cross section size is used when metal sample is too small, the square cross
section for these are 7.5 mm, 5 mm, 2.5 mm. The sub size sample for test cannot be
compared with full size sample data with corrective factor. The test is conducted at the
required temperature only. The energy reqd to break is expressed in Foot-Pound. Notch
toughness is described in other ways also. These are lateral expression and percent shear.
Lateral expression is a measure of the amount of lateral deformation produced during
fracturing of sample. It is measured in terms of mils or thousandth of an inch. Percent
shear is an expression for an amount of fracture surface which failed in a ductile or
shearing fashion. If various samples are tested at different temperature a graph can be
plotted for values Vs temperature. The graph curve obtained have upper and lower
horizontal shelves with a near vertical zone in between. For each measurement category
there is some temperature at which the value drops rather abruptly. These temperature are
referred as transition temperature, i.e., the behavior of metal changes from ductile to
brittle at that temperature, this indicates that metal should behave satisfactorily above that
temperature. Other tests for measuring notch toughness are :--
Drop weight Nil ductility. 2) Explosion bulge. 3) Dynamic tear. 4) Crack tip opening
displacement. (CTOD)

6. SOUNDNESS TESTING – Destructive soundness test- Bend, Nick break, and fillet
break. There are three types of transverse weld bend specimen testing-
Face, Root, and Side bends.
The weld lies across the longitudinal axis of specimen and its types refers to the side of
the weld which is placed in tension during test. That means- The face of weld is stretched
in a face bend, the root of the weld is stretched in a root bend and side of a cross section
of the weld is stretched in a side bend. Bend tests are performed using some type of bend
jig. 1) Guided bend. 2) Roller equipped guided bend and 3) Wrap around guided bend.
In roller equipped guide the specimen on rollers and does not have friction on the base of
the guide, which allows lower load for bending. In third type specimen is bent around by
being wrapped around a stationary pin.
For some qualification specimen need to be bent around a mandrel having a diameter.
This results in about 20% elongation of the outer surface of the bend specimen. If a
smaller bend mandrel is used amount of elongation shall increase. The bend test
specimen must be carefully prepared to avoid test inaccuracy. Any grinding or sanding
marks on the tension surface should be oriented in the same direction as bending so they
don’t provide transverse notches (Stress risers ) . The corners of specimen should be
radiused or chamfered to relieve stress concentration.
Nick bend test—This is used in pipe line industry as per API 1104. This method judges
soundness of weld by fracturing the specimen through the weld and examining the
fractured surface for presence of any discontinuity like slag inclusion, porosity,
incomplete fusion.
Fillet weld break test--This test is required for qualification of tackers as per AWS D 1.1.
The specimen is broken by hammering to examine LF, Fusion to the joint root, and no
incomplete fusion, or porosity larger than 3/32” in the greatest diameter.
Fatigue testing—Fatigue testing is the cyclic loading of a member . This test helps to
determine how well a metal will resist failure when cyclically loaded in fatigue.
Generally a series of fatigue tests are completed to arrive at the endurance limit for a
metal. Tests are conducted at various stress level until some maximum stress is found
below which metal should exhibit infinite fatigue life. Various types of loadings are
applied for the test.
i) Planar bending, ii) Rotational bending iii) Torsion iv) Axial torsion v) Axial
compression or combination of the above.
Destructive testing for Chemical properties-
Spectrographic, Combustion and Wet chemical analysis.
Metal analysis can be done in the field using X ray fluorescence technique. It is useful in
avoiding material mix up and sorting of alloy types.
There are specific tests designed to determine the corrosion resistance of a metal.
Metallographic test—Macroscopic and Microscopic.
Macroscopic tests are performed at magnification of 10X or lower.
Microscopic tests use magnification greater than 10X, usually 100X or higher.
A weld cross section can provide a macro specimen for determining depth of fusion,
Depth of penetration, Effective throat, weld soundness, degree of fusion, presence of
weld discontinuity, weld configuration number of weld passes etc. macro specimen need
ground finish with an 80 grit finish. Where as Micro specimen requires fine grinding at
600 grit and polishing to produce a micro finish.