Research of microalloy elements to induce intragranular acicular ferrite in shipbuilding steel

Based on the minimum degree of disregistry mechanism in oxide metallurgy, laboratory and industrial research have been conducted on intragranular acicular ferrite (IAF) induced by microalloying elements in austenite. Based on the chemical compositions of DH36 steel and Mg, Al, Ti, V, Nb microalloyed steel, experimental results show that in ingots' organization, both V and Nb can induce IAF, but when the adding sequence was Al-Mg-Ti, smaller and dispersion inclusions were formed in austenite. When the Mg content was 0.005 wt%, the inclusion structure induced IAF in austenite is as follows: MgO and Al2O3 forms the core and TixOy adheres to the Al-Mg complex inclusions to produce smaller particle size and dispersions of Al, Mg, Ti complex inclusions. Finally, upon lowering the temperature, carbonitrides of Ti, V, and Nb were precipitated on the outermost layer of the inclusions. These carbonitrides with small disregistry contribute to induce intragranular acicular ferrite.