EFFECT OF ACCELERATED SPHEROIDISATION AND LONG ANNEALING OF 100CRMNSI6-4 STEEL ON STRUCTURE AND PROPERTIES AFTER HARDENING

Accelerated carbide spheroidisation enables significant shortening of time necessary for formation of steel microstructure consisting of ferritic matrix and globular carbides. Conventional way to obtain such structure is long duration soft annealing after semiproduct hot forming. Research of accelerated carbide spheroidisation showed that it is possible to spheroidise lamellar pearlite in minutes. Accelerated carbide spheroidisation produces very similar microstructure like conventional soft annealing in morphological point of view, but carbide particles and grain size of the matrix is significantly smaller. Finer microstructure results in higher hardness in comparison with conventionally annealed steel. Finer microstructure also ensures more homogeneous and finer structure after final heat treatment, after hardening. This fact indicates, that properties of final product differ according to previous structure after soft annealing. Finer carbides in structure enhance hardness and facilitates carbide dissolution during austenitisation. This effect enables quenching temperature lowering. Steel 100CrMnSi6-4 microstructure and properties are compared in view of various kind of spheroidisation and quenching temperature.