Lecture 35
The Lecture Contai ns:
Objectives
Structure-property relation
Property of t he pha ses
What are t he fina l finishing operations?
Surf ace ha rdening
Steel types a nd hardening method s
Obje ctiv es:
The final finishing operation s are perform ed to produce a pro duct fo r a given applic ation, which ranges
from structural to space applications. In this connection it is important to note the role of steelmaking to
produce st eels o f desir ed chem istry and cle anline ss. Imp uritie s like sulphur and p hosphrous are
detrimental to most of the steel grades for all finishing operations. In aluminum killed steels, alumina
incl usions must be s uitabl y modif ied prior to deformatio n proc essing. Ot her types of inclusions m ust b e
suit ably d istributed within t he matrix. The o bjecti ves of these operations ar e to generate the mechani cal
properties in th e steel produc t requ ired fo r a given applic ation. The im portan t prope rties are:
Streng th : Measure of the resistance of material to perm anent deformatio n
Duct il ity : Measure of the degree of plastic deformation
Hardness : Resistance to localized deformat ion
Creep : Resista nce to time d ependent defo rmation under load
Fatigue: Resistance of a material against fluctuating stresses.
Fractu re tou ghness : Resistance to brittle failure
The above properties depen d stro ngly on th e number , size and size d istribution of phases and the
impurities.
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