engleski

Properties of Low-Alloyed Ni-Mo-Cu Ausferritic Nodular Graphite Cast Iron

Motivation for this paper was the developing of high quality castings from grade GJS-800-10 in accordance with the EN 1564: 2011 standard. For these purpose nodular cast iron of appropriate composition was manufactured in foundry “Kovis Livarna”, Štore, Slovenija, which will provide high quality as-cast microstructure as well as hardenability, and that during subsequent austempering the preferred mechanical properties will be obtained The purpose of these work is to report on tensile properties determined in differentially processed heavy-section casting in as-cast and commercially austempered conditions and to related those properties to microstructure observed within the casting as function of position. During the developing of the specific casting from grade GJS 800-10, the influence the casting mass effect, different inoculation agents and procedures as well as global chemical composition on microstructures, mechanical properties and general soundness of the investigated castings were determined. Specimens for tensile testing were cut and machined from differentially processed as-cast castings, fully commercially austempered castings and cast on samples, diameter 20 mm. Metallographic samples were cut from the broken helves of the tensile test specimens in order to conduct optical microscopy for microstructural analysis. The microstructures in as-cast condition were predominantly pearlitic regardless of the section thickness and cooling conditions of casting. These can be attributed to relatively high amount of Ni and Cu in ally composition. The nodularity and number of nodule per mm2 were varied by casting section size and of course by art and manner of inoculation procedure. The combination of late inoculation in melt stream by using the inoculation agent on the base of Ce (Ressed ®) and insert of agent on base of Bi in mould were resulted by high nodule count and nodularity (more than 500 nodule per mm2 in cast on samples and more than 100 nodule per mm2 in the most thicker section size of the casting). As-cast tensile strengths were relatively high, a result consistent with the properties of a pearlitic matrix. The elongations values were varied by position in the casting. Cast on samples were generally showed the highest values of elongation. As- expected, austemperd tensile strengths were much higher in compared with as-cast samples. Tensile properties ware also varied by position in casting. The difference in strength and elongation between the cast on samples and the samples which were cut from fully austempered casting can be attributed different primary microstructure (nodule count, nodularity, segregation and phase precipitation) an simply reflect the fact that austempering of entire casting result in a much slower cooling rate between astenitization and austempering temperature, thereby resulting in coarse structure with lower strengths. By developing the specific casting with asferritic structure according to EN 1563: 2011 it should be taken into account the degradation of graphite with casting section thickness and with these related decreasing of nucleation sites and nucleation potential of melt in thermal center of the casting. It is usually associated with effective inoculation of the melt. Another fact is that appropriate charged material decrease the possibility of unwanted segregation and precipitation of the phases in last to freeze zone of the casting. Also, the change of the feeding system an introduction the chills will help in developing sound casting.

Ausferitic Cast Iron ; ADI ; Tensile properties ;

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