Civil Engineering Reference
In-Depth Information
CVN impact energy absorbed at a given test temperature (e.g., designations 50T2
indicating non-FCM Zone 2 and 50WF3 indicating FCM Zone 3 toughness criteria).
Further increases in strength, ductility, toughness, and weathering resistance
through steel chemistry alteration have been made in recent years. HSLA steels
with 70 ksi yield stress have been manufactured with niobium, vanadium, nickel,
copper, and molybdenum alloy elements. These alloys stabilize either austenite or
ferrite so that martensite formation and hardening does not occur, as it would for
higher-strength steel attained by heat treatment. A concise description of the effects
ofvariousalloyanddeleteriouselementsonsteelpropertiesisgiveninBrockenbrough
(2006).
2.3.3 H
EAT
-T
REATED
L
OW
-A
LLOY
S
TEELS
Higher-strength steel plate (with yield stress in excess of 70 ksi) is produced by
heat treating HSLA steels. A disadvantage of higher-strength steels is a decrease in
ductility. Heat treatment restores loss of ductility through quenching and tempering
processes. The quenching of steel increases strength and hardness with the forma-
tion of martensite. Tempering improves ductility and toughness through temperature
relief of the high internal stresses caused by martensite formation. Even HPS steel
with 100 ksi yield stress has been quench and temper heat treated to provide good
ductility, weldability, and CVN toughness (Chatterjee, 1991). However, after quench-
ing,tempering,andcontrolledcoolingthesesteelswillnotexhibitawell-definedyield
stress (Steel 3 in
Figure 2.1)
.
In such cases, the yield stress is determined at the 0.2%
offset from the elastic stress-strain relation.
Use of these steels may result in considerable weight reductions and precipitate
fabrication, shipping, handling, and erection cost savings. High-strength steel can also
allow for design of shallower superstructures. ASTM A514, A852, and A709 Grade
70W and 100W are quench and tempered low-alloy steel plates. However, none of
these steels are typically used in ordinary railway bridges.
2.3.4 H
IGH
-P
ERFORMANCE
S
TEELS
HPSplateshavebeendevelopedinresponsetotheneedforenhancedtoughness,weld-
ability, and weathering resistance of high-strength steels. HPS 70W and 100W steels
are produced by a combination of chemistry manipulation and quench and temper
operations or, for longer plates, thermo-mechanical controlled processing (TMCP).
The first HPS steels were produced with a yield stress of 70 ksi. However, HPS with
50 ksi yield stress soon followed due to the weldability, toughness, and atmospheric
corrosion resistance property improvements of HPS. HPS 50W is produced with the
same chemistry as HPS 70W using conventional hot or controlled rolling techniques.
HPS plates with 100 ksi yield stress are also available. HPS 100W is considered an
improvement of A514 steel plates (Lwin et al., 2005).
Weldability is increased by lowering the carbon content (e.g., below 0.11% for
HPS 70W), therefore, benefiting the CE (Equation 2.6). This weldability increase
results in the elimination of preheat requirements for thin members and limited pre-
heat requirements for thicker members. Also, postweld treatments are reduced and
