EFFECT OF EQUAL–CHANNEL ANGULAR PRESSING ON THE MICROSTRUCTURES AND TENSILE PROPERTIES OF 18Ni(C–250) MARAGING STEEL

An 18Ni (C-250) maraging steel was successfully processed by equal-channel angular pressing (ECAP) for a single pass at room temperature. After ECAP deformation, the peak aging time was cut obviously and the peak strength of the steel was enhanced about 100 MPa. Microstruc- tural observations showed that the martensite laths of 18Ni maraging steel were elongated to more narrow bands with a width of 100—200 nm after ECAP deformation, and the width of martensite lath was not affected by the subsequent aging treatment. ECAP deformation has significant influence on the size of rod-shaped δ-Ni3Mo precipitates. It was observed that the widths (diameters) of pre- cipitates in specimens under treatments of solution+480 , 4 h, solution+ECAP+480 ,4ha nd solution+ECAP+460 , 4 h are 4.92, 12.33 and 3.54 nm, respectively. Additionally, a decomposition of the δ-Ni3Mo precipitates was accelerated after the peak aging time, resulting in a decrease in the strength.