Cold worked steels with packet-lath martensite with / austenite microstructure

摘要

A process for making an alloy carbon steel of high strength and high ductility, said process comprising: (a) forming an alloy carbon steel having a microstructure comprising laths of martensite alternating with films of retained austenite, and (b ) cold working said alloy carbon steel in a series of passes without intermediate heat treatment between passes to a sufficient reduction to achieve a tensile strength of at least 1034 MPa (150 ksi), in which step (a) comprising: (i) forming a composition of alloy carbon steel having a temperature martensite start of at least 300 ° C, (ii) heating said alloy composition carbon steel to a temperature sufficiently high to cause austenitization thereof, to produce a homogeneous austenite phase with all alloying elements in solution, and (iii) cooling said homogeneous austenite phase through d and said transition interval martensite at a rate sufficiently rapid cooling to achieve said microstructure, avoiding carbide formation at interfaces between said martensite laths and said films of retained austenite, wherein said composition of the steel alloy carbon containing 0.004% to 0.12% carbon, from 0% to 11% chromium, 0% to 2.0% manganese and from 0% to 2.0% silicon, all by weight, the remainder iron together with any unavoidable impurities.