INCREASING OF DUCTILE CAST IRON PLASTICITY VIA IN-MOLD MODIFYING OF MELT WITH LOWERED SILICON CONTENT

Procesi littâ, 2023, Vol 3 (153), 3-11

Abstract

Ductile cast irons with increased plasticity are widely used in production of machine parts that work under shock-cyclic and dynamic loads as well as at low temperatures. The plasticity of ductile cast iron is determined mainly by its chemical composition, modification method, casting method and type of heat treatment. In the world ductile cast irons with a twice higher minimum relative elongation as stipulated by the Ukrainian state standard are common and the manufacturing technologies of such cast irons are based on the use of expensive refined cast irons in the charge and energy-intensive heat treatment. The article presents the results of influence of silicon content reducing in ductile cast iron composition on changes in its structure and mechanical properties. The research was carried out using cheap charge materials and highly effective ferrosilicon-magnesium modifiers with low energy consumption on castings heat treatment. Experimentally shown that during ladle modifying chill begins to form in the casting metal at silicon content of 2.2–2.3 %wt., while at in-mold modifying using up to 7 % of cementite is formed during the crystallization of ductile cast iron with a Si content of 0.9–1.1 %wt. The mechanical properties of in-mold ductile cast iron with 1.2–1.3 %wt. Si (which guarantees a metal base obtaining without cementite inclusions) in the cast state correspond to the GJS480-15 grade at Brinell hardness of 156-163 НВ. After graphitizing
annealing this ductile cast iron has a ferritic metal base and a corresponding for it combination of tensile strength Rm = 400–450 MPa with a higher relative elongation A = 22–26 %, impact toughness KS = 100–120 J/cm² and with low hardness of 134–156 HB. The results of the research show a significant increase in the plasticity of ductile cast iron with nodular graphite modified in a foundry mold due to silicon content reducing and create preconditions for the development of new cast parts designs for modern technic with given high mechanical properties and performance characteristics and of high-efficiency economic technologies for their production.