Research On Mechanism And Application Of Cast Steel With Spheroidal Graphites

Cast steel with spheroidal graphites is a new kind of engineering material. The carbon content of it is between plain carbon steel and grey iron. In use of spheroidizing agency treatment, some spheroidal graphites and carbide on the matrix of lamellar or sorbitic pearlite can be achieved in as-cast state. By means of alloying and heat treatment, the amount and shape of the graphite, carbide and pearlite can be changed objectively. The material is of wide application because of the excellent properties of wear resistant, thermal fatigue and so on. At present, the research on spheroidal梘raphite cast steel at home and abord, many aspects are studied little. For example, technology property and the spheroidal mechanism of graphite. The work of this thesis involved in the content above. During the study, spheroidal pearlite of spheroidal-graphit cast steel has been achieved after hot-forging or normalizing first. And in this thesis, the spheroidal mechanism of carbide was researched in detail.The main work of this thesis is as follows:(1) Technology properties: Cast steel with spheroidal graphites has excellent castability such as fluidity. Also it has good ductility and machineability.(2) Heat treatment: Through annealing, spheroidal pearlite can be achieved ,and toughness rises, and on the other hand strength decreases. In range of 860-950℃ normalizing, ideal spheroidal pearlite can be achieved after normalizing.(3) Spheroidal mechanism of graphite: The point of this thesis is that the nucleution of spheroidal graphites come from the inclusion or bubble in the melt steel.(4) Spheroidal mechanism of carbide: The study of this thesis shows that, the first, the non-dissolution carbide at high temperature is the main nuclei of forming spheroidal carbide; the second, the existing of graphites make the austenite become non-uniformly highly, which is advantageous to the formation of spheroidal pearlite; at last, the density of dislocation of the material increases greatly after hot forging, then segregation of carbon occurs, which also result in non-uniformly austenite and then spheroidal pearlite.