AlN precipitate FeCMnAl QP Technology: general issues Zener pinning annealing austempering austenite grain size auto-tempering boiling and quenching heat transfer boiling curve carburization compound layer creep element diffusion elongation to failure flash heating forged steels forging gear steel high silicon steel high speed steel high-Cr steel hole expansion ratio hydrogen embrittlement inoculant kappa carbide low carbon steel low density steels martensite