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ISOTHERMAL TRANSFORMATION OF 4140 STEEL

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by

Meagan Wey

on 6 May 2014

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Transcript of ISOTHERMAL TRANSFORMATION OF 4140 STEEL

Austenite

Ferrite

Pearlite

Bainite

Martensite
Tensile Test
ISOTHERMAL TRANSFORMATION OF 4140 STEEL
Group Members
Christine Munda
Christanto Oil
Juan Pineda
Meagan Wey
TA: Ye Shi
TA Asst.: Lele Peng
Technical Background
The transformation of Austenite to different microstructures.
Depends on Temperature and cooling rate of time
Pearlite, Bainite, and Martensite
Determines the hardness, ductility, and strength of the material
4140 Steels contains: 0.4 wt% C, 1.0 wt% Cr, 0.2 wt% Mo
Product of austentic transformation
Moderate Cooling
Elongated Cementite particles in a Ferrite matrix
Forms as needles or plates depending on the temperature
Diffusional process
Formed when austentized iron-carbon alloys are rapidly cooled (quenched) to a low temperature
Diffusionless transformation occurs instanteously
Plate-like/needle-like apperance
Slow Cooling
Layers of Cementite and Ferrite
Coarse Pearlite
higher ductility
greater toughness
Fine Pearlite
greater strength
a) Coarse Pearlite
b) Fine Pearlite
Iron - Iron Carbide Phase Diagram
TTT Diagram
11.8
Bainite
Martensite
Experimental Techniques
Quenching
700°C
Tensile Test
Conclusion
Pearlite
Young's Modulus

Tensile Test
Tensile Test
Tensile Test
Tensile Test
660°C
620°C
460°C
360°C

Quenched in oil
Formation of Martensite expected
Six 4140 tensile specimen and six Charpy V-notch impact specimens have been austenitized in the furnace set at 850°C.
Transfer a tensile specimen and one impact specimen from the 850°C austentizing furnace to each of the following furnaces and hold for the time specified:
Box furnace
700°C for 2 hours
660°C for 1 hour
620°C for 1.5 hours
Crucible furnace
460°C for 1 hour
360°C for 1 hour
Remove one tensile specimen from the 850°C austentizeing furnace and quench it in oil. Repeat the quenching process with one impact specimen.

Wash the specimens with soap and water. Remove oxide scale using the wire wheel.

Use the 120-grit or 180-grit SiC paper grinder to grind parallel faces.
Perform a Rockwell Hardness Test with the 0.5 inch shallow "V" anvil on the quenched tensile specimen.

Perform a Rockwell Hardness Test with the 2.5 inch diameter anvil on the quenched impact specimen.
When each isothermal transformation is completed, cool the tensile and impact specimen in running water.

Remove oxide scale by using the wire wheel.

Use the 120-grit or 180-grit SiC paper grinder to grind parallel faces on the unnotched sides of each impact specimen.

Perform a Rockwell Hardness Test with the 0.5 inch shallow "V" anvil on each tensile specimen.

Perform a Rockwell Hardness Test with the 2.5 inch diameter anvil on each impact specimen.
Perform impact tests using the Tinius Olsen Impact Testing Machine to find the impact energy.
Perform tension tests using the Instron 5800 Series Materials Testing System with the 25 mm gauge length extensometer.
Step 3
Step 2
Pre-lab
Step 1
Duration : 2 hours
Expected : Austenite and Pearlite (Cementite and Ferrite).
Step 4
Step 5
Step 6
Step 7
Duration : 1 hour
Image look very similar to isothermal transformation of 700°C.
Expected : Austenite and Pearlite (Cementite and Ferrite).
Hardness Testing
Impact Test
Impact Specimen
Tensile Specimen
Impact Testing
Microstructures: Expectation vs. Reality
Yield and Tensile Strength
Elongation at Fracture and Reduction in Area
Duration : 1 hour
Expected: Austenite, Lower Bainite and Pearlite (Cementite and Ferrite).
Duration : 1.5 hours
Expected: Austenite and Pearlite (Cementite and Ferrite).
Duration : 1 hour
Expected: Austenite, Pearlite (Cementite and Ferrite) and Bainite.
Increase with Temperature:
Impact Energy
Young's Modulus
Elongation and Reduction of Area
Decrease with temperature:
Hardness
Yield and Tensile Strength
Full transcript