Defects in Metallurgy

Prepared by:

Raghavendra P. Joshi

Submitted to:

Dr. V.J.Rao

Defects in Metallurgy

Outline of seminar

• Defination of “defect”

• Classification of defects

• Defects forms during different processes

• Reference

Defianation of defect

• Defect : “any local variation in material continuity such as change in

• geometry,

• structure,

• composition

• Properties

• presence of holes , cavities or cracks”

• A mistake in process is called “error”

• Error found by tester is called “defect”

• Component does not meet the requirements then it is “failure”

Classification of defects

Defects can be classified according to process during it forms

Defects formed during manufacturingo Casting defectso Forming defectso Welding defectso Heat treatment defects o Grinding defects

Defects introduce during service

1. Casting defects

Classification of Casting defects as per their origin

1.Shaping faults arising in pouring2.Inclusion and sand defects3.Gas defects4.Shrinkage defects5.Contraction defects6.Dimensional errors7.Compositional errors

1. Shaping faults arising in pouring

2.Inclusion and sand defects

Inclusion

Sand expansion defects

Scabbing

3.Gas defects

• It can be classified in 2 types

• Entrapment defects: air may be entrapped within a casting

• Precipitation defects : precipitation of gases from the metal on cooling

4. Shrinkage defects

5. Contraction defects

Hot Tearing: This defect, also called hot cracking. The defect is manifested as a separation of the metal(hence the terms tearing or cracking) at a point of high tensile stress caused by metal's inability to shrink naturally

6.Dimensional errors

1. alignment faults

2. Mould distortion

7. Compositional errors

1. melting losses of reactive elements

2. segregation

2. Forming defects

it can be classified into

1.Forging defects

2.Rolling defects

3.Extrusion defects

4.Drawing defects

Forging defects

Rolling defects

Extrusion defects

Drawing defects

Center burst:

the most common type of drawing defect is the “center burst ” or chevron cracking. center burst is caused due to drawing at too low temperature

3. Welding defects

3. Welding defects

• Spatter

• Cracks Longitudinal Transverse Crater Throat Toe Root Under-bead and Heat-

affected zone Hot Cold or delayed

• Misalignment• Undercut• Underfill• Concavity or Convexity• Excessive reinforcement• Improper reinforcement• Overlap• Burn-through• Incomplete or Insufficient

Penetration• Incomplete Fusion• Surface irregularity

– Overlap

• Porosity– Uniformly Scattered– Cluster– Linear

Definitions of weld defects

• Undercut Groove melted in base metal adjacent

to weld edge and left unfilled• Slag Inclusion

Nonmetallic solid entrapped in weld• Porosity

Gas cavity trapped during solidification• Overlap

Weld metal protrusion beyond toe, face or root

• Tungsten inclusion Tungsten electrode particles entrapped

in weld• Spatter

Metal particles expelled during welding that do not become part of the weld.

• Shrinkage voids Cavities formed by shrinkage at

solidification• Lack of Penetration

Less than the specified penetration• Craters

Depressions at the termination of the weld bead

• Arc strikes Localized re-melted or heat affected

metal resulting from an errant arc• Under fill

A depression of the weld below the intended profile

Misalignment

• Definition: Amount a joint is out of alignment at the root

Undercut

UNDERFILL

Excessive Concavity or Convexity

• Definition: Concavity or convexity of a fillet weld exceeding specified limits

• Cause: travel speed

EXCESSIVE CONCAVITY

Convexity

EXCESSIVE CONVEXITY

UNACCEPTABLEWELD PROFILES

Overlap

• Definition: When the face of the weld extends beyond the weld toe

OVERLAP

INCOMPLETE & EXCESSIVE PENETRATION

SPATTER

Cracks

• Longitudinal : in direction of weld axis

• Transverse : perpendicular to weld axis

• Crater : generally in shape of “X” found in crater

• Throat: longitudinal crack located in weld throat area

• Toe : crack in base metal begining at the toe

• Root : crack in the weld at the weld root

• Underbead and Heat-affected zone : A crack in the un-melted parent metal of the HAZ.

• Hot crack : A crack in the weld that occurs during solidification.

• Cold or delayed : A crack that occurs after the metal has completely solidified

Porosity

• Single Pore

• Uniformly Scattered

• Cluster

• Linear

porosity

4. Heat treatment defects

Defects Due to Causes

1. Overheating Heating for long periods at temperature exceeding normal values

Causes coarse grained microstructure

2. Burning Heating for long duration at high temp. under oxidizing condition

Poor ductility

3. Oxidation Oxidizing atmosphere in heating furnace

Thick layer is seen on the surface of component

4. Decarburization Oxidizing atmosphere in heating furnace

Carbon content decreases in surface layer of steel component

Defects Due to Causes

5. Black fracture Excessive heating time and slow cooling after annealing

Free carbon inclusions are seen in the steel

6. Warping Non uniform heating or cooling of component

Asymmetrical deformation of component occurs during quenching

7. Soft spots Localized decarburization Certain portions on the surface of component with lower hardness

8. Corrosion High content of sulphuric salts (0.7-0.8%) in molten salt bath

pitting

9. Quench crack Internal stresses External or internal cracks and zig-zag in appearance

5. Grinding defects

• Grinding cracks are caused by stresses which are built up from excessive heat generated between the grinding wheel and material.

• These cracks occur on the surface of the material at right angles to the direction of rotation of the grinding wheel

Defects introduced during service condition

• Types of material failure during service conditions are

1.Excessive plastic deformation

2.Fracture

3.Fatigue

4.Corrosion

References

1. Practical non-destructive testing by Baldevraj

2. Foundry technology by peter beeley

3. Welding engineering and technology by R.S.Parmar

4. Mechanical metallurgy by G.E.Dieter

5. Heat-treatment by rajan and sharma

6. Google search

• Thank you

1. Excessive plastic deformation:Yielding followed by excessive plastic

deformation occurs when the elastic limit of the material has been exceeded

2. Fracture:Brittle fracture occurs far below the yield

strength. It is associated with flaws and are often catastrophic in nature.

High strain rates,triaxial stresses or low temperatures can make a normally ductile material to behave in a brittle manner

3. Fatigue:

Failures occurring under condition of dynamic loading are called “fatigue failure”

4. Corrosion:

In general corrosion is a deterioration of metals by the chemical action of some of the surrounding or contacting medium which may be liquid, gas or some combination of two.