Computer-aided design of transformation toughened blast resistant naval hull steels: Part I

Abstract

A systematic approach to computer-aided materials design has formulated a new class of ultratough, weldable secondary hardened plate steels combining new levels of strength and toughness while meeting processability requirements. A theoretical design concept integrated the mechanism of precipitated nickel-stabilized dispersed austenite for transformation toughening in an alloy strengthened by combined precipitation of M 2 C carbides and BCC copper both at an optimal ∼3 nm particle size for efficient strengthening. This concept was adapted to plate steel design by employing a mixed bainitic/martensitic matrix microstructure produced by air-cooling after solution-treatment and constraining the composition to low carbon content for weldability. With optimized levels of copper and M 2 C carbide formers based on a quantitative strength model, a required alloy nickel content of 6.5 wt% was predicted for optimal austenite stability for transformation toughening at the desired strength level of 160 ksi (1,100 MPa) yield strength. A relatively high Cu level of 3.65 wt% was employed to allow a carbon limit of 0.05 wt% for good weldability, without causing excessive solidification microsegregation.

Strength Recovery in a High-Strength Steel During Multiple Weld Thermal Simulations

“…[1,2] BA160 is a low carbon martensitic steel additionally strengthened primarily by nanometersized Cu-rich precipitates and M 2 C precipitates (where M = Cr, Mo, and V). The yield strength of BA160 is 160 ksi (1104 MPa).…”

“…[5] For steels, there are four distinct HAZ regions depending upon the peak temperature in a given weld thermal cycle. (1) In subcritical HAZ regions (SCHAZ; T P < A c1 ), no detectable transformation of ferrite to austenite occurs. (2) In the intercritical HAZ (ICHAZ), partial transformation of ferrite to austenite occurs because the peak temperature is between A c1 and A c3 .…”

“…[6] On the other hand, the strengthening contribution on yield strength from Cu precipitates and martensite block and packet boundaries could be several hundred mega-Pascals. [1,22] As a result, in the present study, only precipitation and grain boundary strengthening are considered in the overall strengthening.…”

Computational design of advanced steels

“…Cementite particles then become the prime fracture initiators. A goal in the computational design of blast-resistant steel [1] was therefore to eliminate cementite by controlled alloy-carbide precipitation which leads to finer dispersions by virtue of the need for substitutional solutes to diffuse [1,2]. The intended matrix would then be based on a secondary-hardened bainite and martensite mixture, containing dispersed austenite, the stability of which is designed to exploit transformation plasticity.…”

Multiscale Modeling of Phase Transformations in Steels

“…Computational materials science now offers tremendous opportunities to formulate models containing fundamental information on the basic atomic mechanisms of microstructure evolution that can be implemented across different length and time scales. [7][8][9] This approach essentially embraces the concept of integrated computational materials engineering (ICME) as a transformational discipline to efficiently develop advanced materials and their incorporation into the design of new products. 10 ICME is considered to be a promising tool to accelerate innovation in the engineering of materials and manufactured products; i.e., it is critical for the steel industry to remain at the forefront of related research and development activities.…”