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

Abstract

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. Microstructural 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-Ni 3 Mo precipitates. It was observed that the widths (diameters) of precipitates in specimens under treatments of solution+480 £, 4 h, solution+ECAP+480 £, 4 h and solution+ECAP+460 £, 4 h are 4.92, 12.33 and 3.54 nm, respectively. Additionally, a decomposition of the δ-Ni 3 Mo precipitates was accelerated after the peak aging time, resulting in a decrease in the strength.

Evolution of Toughening Mechanisms in PH13-8Mo Stainless Steel during Aging Treatment

“…Luo et al [16] proposed that refined martensite sub-grains (packets, blocks or laths) contributed to the improved impact toughness by acquiring finer retained austenite in an ultra-high-strength stainless steel. Han et al [17] revealed that much finer prior austenite subjected to multi-stage forging could increase the impact toughness of 18Ni(250) maraging steel. The above indicates that the synergistic toughening of metastable austenite and a hierarchical maraging matrix can effectively resolve the dilemma of inverse strength-toughness.…”

Development of New Cobalt-Free Maraging Steel with Superior Mechanical Properties via Electro-Pulsing Technology

“…Unfortunately, there exist some problems for traditional austenitic grain (γ) refinement technology of maraging steels. Firstly, some severe plastic deformation technology, such as equal channel angular process (ECAP) [18,19] and high pressure torsion (HPT) can effectively reduce the grain (γ) size. However, a large amount of crystal defects will also be introduced so that the toughening effect is weakened.…”

Microstructural Characterizations of Maraging Steel Processed by Equal-Channel Angular Pressing

“…In our previous work [6][7][8], we reported that equal-channel angular pressing (ECAP) method was very effective in the refinement of the lath size, and lath width could be readily controlled during the multi-pass ECAP process. Accordingly, the yield strength of maraging steel was significantly enhanced by refining lath width down into nano-order via ECAP technique.…”