Strengthening Mechanisms and Microstructure of Vanadium and Nitrogen Microalloyed High Strength Seismic Rebar

Abstract

Using metallographic test, physicochemical phase analysis, X-ray diffraction and transmission electron microscope, the microstructure of seismic rebars with yield strength of 500MPa, which were fabricated by vanadium and nitrogen microalloying and controlled rolling and controlled cooling, were investigated. The results of metallographic test show that the microstructure in centre and interlayer of tested rebar samples are made up of ferrite, pearlite and a small amount of bainite, but tempered sorbite with thickness of 0.9mm on the edge of the rebars. Physicochemical phase analysis indicates that vanadium in the rebars had precipitated by VN mainly, and the precipitation rates of V and N are 60% and 70%, respectively. The result of strengthening mechanisms analysis shows that fine grain strengthening and transformation strengthening are the dominated contributions to strength and strengthening increments of them are 184.4 MPa and 111.6 MPa, respectively.

Galvanic corrosion behaviour and mechanism of skin effect heat tracing pipes

“…However, Fe 3 C, as a component of the carbon-rich layer of acicular ferrite, has higher electrode potential than ferrite in the crystal, so the grain boundary is protected as a cathode and is hard to be corroded. In addition, although the M-A island structure in X52 steel is a brittle composition, its structure is fine and uniform, but it can play a second phase strengthening effect, enhance the toughness of the material, delay the crack growth rate, and reduce the corrosion rate of the metal [32,33]. Therefore, the corrosion rate of X52 steel is lower than the corrosion rate of 20# steel.…”