Common Metallurgical Defect on Grey Iron

Hydrogen Blowhole

Possible Causes :

1. High moisture content in charging or alloy element (including Rust)

2. High content of Alumunium and Titanium

3. High moisture content of molding sand

4. Buld-up of dead clay in greensand

5. Wet mold or core coating6. Cores have become old and pick up moisture

7. Use of damps refractories

Nitrogen Fissure

Possible Causes :
1. Use of high steel scrap content in cupola melted iron with high coke charges

2. Use of recarburizer with high nitrogen content

3. Use of high nitrogen containing resins or buld-up of nitrogen in the sand

4. Insufficient of Ti or Zr contens to neutralise free nitrogen

Compaction of Graphite Flakes

Possible Causes :

1. Use of steel scrap content in cupola melted iron with high coke charges

2. Use of recarburiser with high nitrogen content

3. Use of high nitrogen containing resins or buld-up of nitrogen in the sand
4. Insufficient of Ti or Zr contens to neutralise free nitrogen

Shringkage

Possible Causes :
1. Soft moulds or not properly cured binder
2. Insufficient clamping or weighting

3. Incorrect carbon content or carbon equivalent

4. Hot spot resulting from poor designed gates and riser system

5. Casting design causing large change in casting section size or sharp radii

6. Incorrect inoculation

Slag Inclusion

Possible Causes :
1. Inadequate slag removal during melting and pouring

2. Cold metal heels in ladles and recievers

3. Lack of slag traps of fitters

4. Low poring temperature

5. Excess addition of slag forming materials

6. Turbulent mould filling

Carbon Monoxida Blowhole

Possible Causes :
1. High sulphur in combination with high manganese content

2. Low pouring temperature

3. Improper slag seperation

4. Slag contaminated ladles and improper leaving a metal heel in the ladle

(Carbon monoxide blowhole is also known as the manganese sulphide blowhole)

Intercellular Carbide

Possible Causes :

1. Excessives of strong carbide promoter elements such as Cr, Ti, V and Mo

2. Low levels of graphite promoter elements such as Si and Ni in base iron

3. Insufficient inoculation

4. Superheating and long holding at base iron

5. Too high amount of steel scrap in the charge

Steadite

Possible Causes :

1. Excessive or high phosphorous content

2. Slow cooling in thicker section casting

(High phosphor content also increase the shringkage tendency and britelness of the iron)

Undercooled Graphite

Possible Causes :

1. Insufficient inoculation

2. Rapid solidification

3. Superheating or long holding of metal prior to pouring

4. High content of Ti

5. low carbon Equivalent

C Type Graphite

Possible Causes :

1. Found in condition of very slow cooling rate and near eutectic compositions

2. Under inoculation

(Also called kish graphite, is mainly found in iron with hyper eutectic composition)

Ferritic Rim

Possible Causes :
1. Too low content of volatiles in greensand moulds

2. Under inoculation

3. Slow pouring rate

4. Low Pouring temperature