Materials for engineering, 3rd Edition - (Malestrom)

Metals and alloys 105
Structural steels
Structural steels are predominantly C–Mn steels with ferrite–pearlite
microstructures, used in buildings, bridges and ships, as well as off-shore rigs
and pipelines. A number of the general strengthening mechanisms we have
reviewed at the beginning of this chapter are applicable to this family of steels.
Figure 3.22 illustrates this approach in accounting for the effect of increasing
manganese content upon the yield strength of 0.15%C steel: the contributions
to the observed yield stress are shown, which are made by solution-hardening
of the ferrite by Mn, by grain-size hardening (equation [3.2]), and by increasing
the volume fraction of the hard eutectoid pearlite phase. The properties of
particular importance in these materials include weldability and resistance to
brittle fracture under the service temperature conditions.
Engineering steels
High-strength steels may be classed as those with tensile strengths in
excess of 750 MPa and they embrace a wide range of composition and
microstructure.
500
Tensile strength (MPa)
400
Pearlite
Grain size
Mn in SS
300
0 0.5 1.0 1.5 2.0
Mn (wt%)
3.22 Showing the effect of Mn, grain size and pearlite on the strength
of a 0.15%C steel. (SS = solid solution.)