engleski

Microstructural Characteristics of Nodular Cast Iron Grade EN-GJS-350-22LT

Ductile iron is increasingly being used for engineering application due to its excellent mechanical properties that can be obtained either by altering certain processing variables or through various heat treatments. The purpose of the present study is to provide the basis for understanding the mechanical behavior of ductile iron for predominantly ferritic, heat treated microstructures and to get generally valid microstructure-properties correlation for investigated ductile iron grade. Investigation of ductile iron grade EN-1563-GJS-350-22-LT was performed on the shop floor in real foundry conditions. Samples were separately cast in sand moulds. Each heat was poured into three moulds to produce specimens for evaluation of microstructural and mechanical properties. The dimensions and the form of the poured Y-blocks were specified according to EN 1563. The cast Y-blocks were subjected to full anneal treatment procedure. The details of this procedure and sample preparation procedure will not be included in this paper. The test paces were subsequently machined from these heat treated coupons. Tensile strength, yield strength and elongation were examined in accordance with EN 10002-1 at ambient temperature. Impact toughness of ductile iron samples was examined by Charpy method at – 40 °C according to EN 10045-1. Microstructure examination was curried out by means of an optical microscope on test pieces of impact toughness samples. Quantitative metallographic analysis was performed by "Soft Imaging System – Materials Lab". The microstructure features was quantitatively determined by assessment of nodularity, number of nodules per mm2 and ferrite/pearlite share. It was established that nodularity in the range from 0, 67 to 0, 77 and number of nodules in the range of 70 to 160 nodules/mm2 have no significant affect on tensile properties and impact toughness of investigated samples of cast iron grade. Increase of pearlite share (in the range of 2 to 16 %), in the matrix of investigated samples of fully heat treated ductile irons reduced elongation and impact toughness values.

ductile iron; microstructural features; impact toughness; tensile properties

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