Nitrogen Enhanced Ferritic Microalloyed Steels

摘要

In many ferritic steels, "free" (uncombined) nitrogen is regarded as a harmful impurity, responsible for aging and embrittlement. In making "clean" steel, nitrogen is expected to be below 20 ×l0~(-4)%. In "enhanced nitrogen" ferritic steels, the amount of nitrogen may be either high residual (e. g. up to 110 ppm in EAF steels) or intentionally added to levels close to the solubility limit. In the presence of nitrogen binding elements (Al, Ti, V), nitrogen is removed from solid solution by forming MN nitrides. The degree of their dispersion affects microstructure and thus properties. The following metallurgical phenomena may be involved: grain coarsening temperature, grain refinement, intragranular ferrite nucleation, optimization of precipitation strengthening, and others. Enhanced nitrogen benefits particularly vanadium steels, contributing to property improvement and cost reduction.