heat treatment technology › 2020 › 04 › ...hardening dr. sanjib banerjee 5 heat treatment of...
TRANSCRIPT
HEAT TREATMENT TECHNOLOGY
by
Dr. SANJIB BANERJEE
DEPARTMENT OF MECHANICAL ENGINEERING
TEZPUR UNIVERSITY
2020
Dr. Sanjib Banerjee 1
HEAT TREATMENT OF STEELS
HARDENING
Dr. Sanjib Banerjee 2
Hardening Temperature:
HEAT TREATMENT OF STEELS
HARDENING
Dr. Sanjib Banerjee 3
HEAT TREATMENT OF STEELS
HARDENING
Dr. Sanjib Banerjee 4
Factors Affecting Hardening Process:
Applications and Limitations:
HEAT TREATMENT OF STEELS
HARDENING
Dr. Sanjib Banerjee 5
HEAT TREATMENT OF STEELS
TEMPERING
Dr. Sanjib Banerjee 6
❑ For cylindrical specimens of an oil-quenched 4140 steel, (a) tensile strength,
(b) yield strength, and (c) ductility (percent elongation) versus tempering
temperature for diameters of 12.5 mm, 25 mm, 50 mm, and 100 mm.
HEAT TREATMENT OF STEELS
TEMPERING
Dr. Sanjib Banerjee 7
❑Tensile and yield strengths
and ductility (%RA) (at
room temperature) versus
tempering temperature for
an oil-quenched alloy steel
Tempered Martensite:
IRON CARBON ALLOYS
STRUCTURE - PROPERTY CORELATION
Dr. Sanjib Banerjee 8
❑Hardness (at room temperature) versus tempering time for a water-
quenched eutectoid plain carbon steel.
IRON CARBON ALLOYS
STRUCTURE - PROPERTY CORELATION
Tempered Martensite:
Dr. Sanjib Banerjee 9
✓ The tempering of some steels may result in a reduction of toughness as
measured by impact tests; this is termed temper embrittlement.
✓ The phenomenon occurs when the steel is tempered at a temperature above
about 575 °C followed by slow cooling to room temperature, or when
tempering is carried out at between approximately 375 and 575 °C.
✓ Steel alloys that are susceptible to temper embrittlement have been found to
contain appreciable concentrations of the alloying elements manganese,
nickel, or chromium and, in addition, one or more of antimony, phosphorus,
arsenic, and tin as impurities in relatively low concentrations. The presence
of these alloying elements and impurities shifts the ductile-to-brittle
transition to significantly higher temperatures; the ambient temperature
thus lies below this transition in the brittle regime.
IRON CARBON ALLOYS
STRUCTURE - PROPERTY CORELATION
Temper Embrittlement:
Dr. Sanjib Banerjee 10
➢ It has been observed that crack propagation of these embrittled materials
is intergranular; that is, the fracture path is along the grain boundaries of
the precursor austenite phase. Furthermore, alloy and impurity elements
have been found to preferentially segregate in these regions.
➢ Temper embrittlement may be avoided by:
✓ Compositional control, and/or
✓ Tempering above 575 °C or below 375 °C, followed by quenching to
room temperature.
✓ Furthermore, the toughness of steels that have been embrittled may
be improved significantly by heating to about 600 °C and then
rapidly cooling to below 300 °C.
IRON CARBON ALLOYS
STRUCTURE - PROPERTY CORELATION
Temper Embrittlement:
Dr. Sanjib Banerjee 11