Materials for engineering, 3rd Edition - (Malestrom)

Metals and alloys 109
400
Pearlitic
Yield strength (N mm –2 )
200
Ferrite grain size
Mn + pearlitic steels
Steels
0
50 100
Pearlite (wt%)
3.26 Showing the contribution to the strength of pearlitic steels.
Experimental points are shown •.
very high strengths with good fracture toughness, but at a cost greatly exceeding
that of conventional quenched and tempered low-alloy steels.
They generally contain about 18% nickel, but their carbon content does
not exceed 0.03%. On air-cooling, they transform martensitically to a finegrained
α of high dislocation density. They are then age-hardened at around
500°C when a high density of intermetallic phase precipitates, due to the
presence of Co, Mo and Ti in the alloy. They owe their high strength, therefore,
to a combination of strengthening mechanisms.
Machinable steels
Machinability cannot be defined by means of a single parameter: important