27-11-2012, 01:29 PM
Case Hardening
[attachment=41305]
Case – hard , wear resistant.
Core – soft, tough, shock resistant.
0.1% carbon..
0.9% carbon.
Addition of carbon and nitrogen on the surface of the steel.
Carburizing
Nitriding.
Cyaniding.
Carbonitriding.
Carburizing:
Introduce of Carbon, absorption and diffusion.
Heated to 870 to 925 oc, gaseous, solid or liquid carbon containing substance.
case depth is about 1.25mm
Hardness after heat treatment is Rc 65.
Gears, camshafts, bearings..
Pack carburizing,
Gas carburizing,
Liquid Carburizing.
Pack Carburizing:
Wood, charcoal, charred leather,
900 – 995oc, 5 hours, slowly cooled.
Formation of carbon monoxide,
Dissociation of CO with the evolution of carbon
Hardening (Quenching):
Increases hardness by quenching,
Tools and machine parts, heat treatable steels, nodular graphite irons and cast iron. 0.3 to 0.6% C
formation of martensite,
Steel with sufficient carbon ( 0.35 to 0.75%C )
30 to 50oc above A3 line.
15 to 30 min per 25mm of cross section.
Is cooled rapidly or quenched in a suitable medium (brine, water, oil etc)
composition of steel
nature and properties of quenching medium,
quenching temperature.
Interrupted quenching:
Interrupted quenching procedure,
It is two stage process – 1) first quenched in a medium which cools it rapidly past the nose of the TTT diagram,
2) The piece is further quenched in a second medium which cools it rapidly enough to avoid the bainite transformation.
Martempering :
Heated to above the critical range to make it all austenite.
quenched into a salt bath maintained at a temp above Ms and is held at this temp long enough until the temp is uniform, with transformation of the austenite.
subsequent cooling the work piece in air through the martensite range.
[attachment=41305]
Case – hard , wear resistant.
Core – soft, tough, shock resistant.
0.1% carbon..
0.9% carbon.
Addition of carbon and nitrogen on the surface of the steel.
Carburizing
Nitriding.
Cyaniding.
Carbonitriding.
Carburizing:
Introduce of Carbon, absorption and diffusion.
Heated to 870 to 925 oc, gaseous, solid or liquid carbon containing substance.
case depth is about 1.25mm
Hardness after heat treatment is Rc 65.
Gears, camshafts, bearings..
Pack carburizing,
Gas carburizing,
Liquid Carburizing.
Pack Carburizing:
Wood, charcoal, charred leather,
900 – 995oc, 5 hours, slowly cooled.
Formation of carbon monoxide,
Dissociation of CO with the evolution of carbon
Hardening (Quenching):
Increases hardness by quenching,
Tools and machine parts, heat treatable steels, nodular graphite irons and cast iron. 0.3 to 0.6% C
formation of martensite,
Steel with sufficient carbon ( 0.35 to 0.75%C )
30 to 50oc above A3 line.
15 to 30 min per 25mm of cross section.
Is cooled rapidly or quenched in a suitable medium (brine, water, oil etc)
composition of steel
nature and properties of quenching medium,
quenching temperature.
Interrupted quenching:
Interrupted quenching procedure,
It is two stage process – 1) first quenched in a medium which cools it rapidly past the nose of the TTT diagram,
2) The piece is further quenched in a second medium which cools it rapidly enough to avoid the bainite transformation.
Martempering :
Heated to above the critical range to make it all austenite.
quenched into a salt bath maintained at a temp above Ms and is held at this temp long enough until the temp is uniform, with transformation of the austenite.
subsequent cooling the work piece in air through the martensite range.