| The aim of this work was to investigate the ductile iron for di-esel, the gray iron and ductile iron for crankshaft. Firstly, melting and spheroidizing crafts were improved, moreover, the research of the micro-structure and mechanical properties after isothermal treatment and carbo-nitriding surface hardening were also carried out. The main conclusions of this paper are as follows:(1)To study the effects of nodulizer on the microstructure and mech-anical properties of austempered ductile iron, Three types of commerc-ial nodulizers were used. It was proved under VNA-60P, for suitable size, better nodularity and distribution of graphite nodule, the austempe-red ductile iron can achieve well mechanical properties, which are bett-er than materials under VNCR-70and HQ8-3nodulizer.(2)By a special isothermal treatment on the as-cast QT400-15ductile iron, ADI were obtained and of which the microstructure were made of upper-lower bainite and retained austenite. which gre-atly improved the mechanical properties of the ductile iron.(3)Four types of sand molds were used, one were applied vibration, the other two were reinforced one and three cold iron to reducing the cooling rate, the rest one was done nothing. The mechanical properties of casting and austempered ductile iron obtained by the four types of sand molds were compared. The results showed that the faster the cooling rate, the better the mechanical properties; one were applied vibration treatment can improve organizational density, but had little effect on the mechanical properties of ADI.(4)Carbonitriding for ductile iron and gray iron were done at570℃for6hours on Ion carbonitriding furnace. The microstructure showed a bright layer, nitriding thickness of120～210μm. What’s more, the experiments about wear were done and the results showed that after carbonitriding, HV could be increased firmly, greatly improved wear re-sistance, in addition, the tests showed that ductile iron can get better wear resistance than gray cast iron. |
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