铸造铁水的电化学变质处理

ELECTROCHEMICAL MODIFICATION IN CAST IRON

球墨或蠕墨铸铁的生产,国内外大多采用纯镁或稀土镁中间合金作为变质剂。本工作证实在铸造铁水电渣精炼工艺中采用直流供电制度,选用含镁、钙、稀土等元素氧化物的 CaF_2基渣系,可以使铁水直接球化或蠕化.本文探讨了铸造铁水电化学变质处理的热力学条件及变质处理机制,给出了控制铸铁中球化元素含量的部分工艺参数。

Modifiers,such as magnesium or magnesium cerium interalloy are used to produce spheroidal-graphite or vermicular-graphite cast iron in many commercial foundries of the world.This paper presents the testmony of making spheroidel-graphite cast iron directly in ESM under D.C.condi- tion by molten CaF_2-based slag systems containing MgO,CaO and ReOx. Thermodynamic calculation of electrochemical modification shows that the applied decomposition voltages E_(Ca),E_(Mg),E_(Ce),E_(Al) and 0.71V,0.14V, 0.077V,0.030V,respectively for CaO,MgO,Ce_2O_3,and Al_2O_3,forming 0.1 wt.% nodulizing element in base iron containing 4.0 wt.% C and 1.0 wt.% Si.The mixing ratio of oxides in the moltent slag is essential to the control of the relative content of nodulizing elements in cast iron under D.C.voltage adapted to ESM process.Graphite morphology of cast iron changes from flake or undercooled graphite to vermicular or spherulitic gra- phite with treatment time.Reduction of carbon content in base iron during ESM under D.C.condition probably owes to the formation of carbon anion or carbide of alkaline earth and rare earth in liquid iron as negative of elec- trochemical modification.