Heat Treatment Flashcards
heat treatment
is the controlled heating and cooling of metals to alter their physical and mechanical properties without changing the product shapes
uses of heat treatment
- increase the strength of metals
- improve machining
- improve formability
basic steps in heat treatment:
- heat the metal to a specific temperature
- hold the metal at temperature for a specific amount of time
- cool the metal in a specific matter
what are particularly suitable for heat treatment?
steels
steel are good for heat treatment why?
they have alot of carbon
break down carbon content of : low carbon steels, medium carbon steels, high carbon steels
- low carbon steels .2%
- medium carbon steels .2-.4%
- high carbon steels >.4%
Heat treatment provides an efficient way to manipulate the properties of metal by controling
- rate of diffusion
- rate of cooling within the microstructure
in carbon steels fast cooling rates result in____
high degree of hardness
steels are heat treated to accomplish:
softening, hardening, material modification
softening is performed to
- reduce strength or hardness
- remove residual stress
- improve toughness
- restore ductility
- refine grain size
- change the electromagnetic properties of steel
hardening of steel is done to ____
increase the strength and wear properties
one of the pre-requisites for hardening is sufficient ____
carbon content
the basic types of heat treatment include:
annealing, normalizing, quenching, tempering
solubility limit
the maximum amount of solute that can be dissolved in solvent
phases
a homogeneous portion of a system that has uniform physical and chemical characteristics
microstructure
is characterized by the number of phases present, their proportions, and the matter in which they are distributed or arranged
eutectoid reaction
describes the phase transformation of one solid into two different solids
in Fe-C system, there is a eutectoid point at approximately…..
0.8 wt% C, 727°C
name the types of microstrucutures
-pearlite= ferrite+cementite
coarse/fine
-bainite: ferrite+cementite
very fine
-martensite: is formed when autenitized Fe-C alloy is rapidly cool (quenched)… hardest and strongest
define anealing
process for making a material softer while producing uniform material properties…. TEMP SLIGHT ABOVE CRITICAL TEMPERATURE
*RESULTING STRUCTURE coarse pearlite
define normalizing
is a process for making materials softer, but products are strong and less ductile compared to annealed materials….. it is less expensive than annealing….
*Resulting microstructure is fine pearlite or bainite
define quenching
refers to rapid cooling
makes steel harder and strong by creating….
-Martensite
tempering
- heating a martensitic steel to a temperature below eutectoid for a specific period
- resulting structure is martensite
microstructure of tempered martensite consists of…
extremely small and uniformly dispersed cementite particles embedded within a continuous ferrite matrix
fine cementite particles in ferrite matrix provides ____ and ___ to the matrix
high grain boundary area.. and act as reinforcement