Chai Feng

Effect of Cu And Ni on Corrosion Resistance of Low Alloyed Steels for Cargo Oil Tank

The corrosion behavior of four kinds of low alloyed steels in acid chloride solution (10%NaCl, pH=0.85) was studied on the basis of International Maritime Organization(IMO) standard. Results indicated that, with the increase of Cu and Ni content in steels, the corrosion rate exhibited a law of linear decline, polarization curve moved to positive direction, corrosion potential raised, current density significantly decreased and the interface electric resistance obviously increased. The mechanism of improvement the corrosion resistance of Cu bearing steel can be mainly attributed to the Cu enrichment on the surface of rust layer by means of re-deposition particles(100~500 nm) and keeping high stability. However, Ni was not found in the rust layer but improved the corrosion potential of matrix.

Effects of Heat Treatment on Microstructure and Mechanical Properties of V Microalloyed Bulb Flat Steel

The effects of heat treatment on microstructure and mechanical properties of V microalloyed bulb flat steel were studied. The results showed that a large number of granular bainite was formed in the period of rolling or normalizing continuous cooling. The low-temperature toughness of the steel was decreased obviously with the formation of granular bainite. Akv−40 could be up to 46J by tempering treatment with the granular decomposed. Furthermore Akv−40 could be up to 144J by normalizing and tempering treatment since that the granular bainite decomposed sufficiently.

Microstructure Evolution in the V‐N‐Ti and Nb‐V‐Ti Microalloyed Bulb Flat Steel

Microstructure evolution and impact thoughness of V-N-Ti and Nb-V-Ti microalloyed bulb flat steel in rolling process have been investigated. The results indicate that the V-N-Ti steel has superior impact toughness than Nb-V-Ti steel. Compared with Nb-V-Ti steel, the relatively higher N content increase the amount of undissolved TiN in V-N-Ti steel at 1220 °C, which can effectively inhibit the austenite grain coarsening. Meanwhile, N can also promote the precipitation of V(C,N) in V-N-Ti steel during the rolling process, V(C,N) can be able to promote the intragranular ferrite formation, inhibit the grain boundary ferrite grain coarsen and refine the ferrite grain, which lead to a favourable toughness; While the microstructure of Nb-V-Ti steel is coarsen ferrite and bainite which are detrimental to impact toughness. Compared with Nb-V-Ti steel, the V-N-Ti steel has a more appropriate composition design for bulb flat steel.