The chemical compossition and macrostructure of the cranksshaft for internal combustion engine with big diameter manufactured by electroslag multistep smelting-casting were investigated.Quaternary slag system

including CaF

2

（20%～30%）

Al

2

O

3

（20%～30%）

CaO（15%～20%）

MgO（15%～20%）

with low melting point and good fluidity was used

in which the hydrogen-removal was pretreated to prevent slag inclusion in welding-zone through improving the purity of slag system.The red copper was used for mould face.Cooling water pressure is more than 0.5 MPa

and flow velocity is more than 4 m/s

and the effluent temperature is less than 50 ℃.Flexible connection was applied for the mould to prevent the crack.The results showed that the crankshaft possesses uniformly composition and soundness microstructure

in which shrinkage porosity and segregation was remarkably decreased

and S content is decreasd by 60% and P content is decreased by 20%.The crankshaft with high toughness and strength can be obtained after annealingat 800 ℃.