Microalloyed Ferrite-Pearlite Steels
Composition
•
These steels use
additions of very small amounts of alloying elements such as niobium and
vanadium (<0.10% each) to increase strength (and thereby increase
load-carrying ability) of hot-rolled steel without increasing carbon and/or
manganese contents.
•
Minor alloying
elements refine the grain microstructure and/or facilitate precipitation
hardening.
•
Carbon content
thus could be reduced to improve both weldability and toughness because the
strengthening effects of niobium and vanadium compensated for the reduction in
strength due to the reduction in carbon content.
Properties
•
Along with
microalloying elements, the mechanical properties of microalloyed HSLA steels
depend upon austenite conditioning.
•
Austenite
conditioning depends on the complex effects of alloy design and rolling
techniques.
•
The high yield
strength of 485 MPa (70 ksi) is achieved by the combined effects of fine grain
size developed during controlled hot rolling and precipitation strengthening
that is due to the presence of vanadium, niobium, and titanium.
Classification
The various types of microalloyed ferrite-pearlite
steels include:
Ø Vanadium-microalloyed steels
Ø Niobium-microalloyed steels
Ø Niobium-molybdenum steels
Ø Vanadium-niobium microalloyed steels
Ø Vanadium-nitrogen microalloyed steels
Ø Titanium-microalloyed steels
Ø Niobium-titanium microalloyed steels
Vanadium-titanium microalloyed steels
