Interphase Precipitation and Application to Practical Steels

Abstract

Interphase precipitation is a phenomenon in which precipitates are generated on interphase boundaries during phase transformation, creating carbides having a form like bands or fibers in micro-alloyed steels. In isothermal transformation, a lower transformation temperature reduces the carbide diameter and band spacing, and a higher cooling rate reduces them in the continuous cooling process. Various interphase precipitation mechanisms have been suggested, and some models for the ledge mechanism attempted to explain the regular band spacing in steels containing carbide-forming elements quantitatively. Recently, as the orientation relationship in the grains of the interphase boundary is not consistent with the ledge mechanism, three-dimensional interface structures have been suggested to explain the experimental results of observation by transmission electron microscopy in low carbon steel. The newly-proposed interphase structure model may explain both the ledge and quasi-ledge mechanisms. Steels with tensile strength of more than 590 MPa, which are manufactured by using interphase precipitated carbides, have been developed and used practically not only in plate and sheet products but also in forged products to improve formability. In steels consisting of ferrite and a second hard phase, interphase precipitated carbides are used to realize high local ductility and to reduce the difference of hardness between the two phases. Ferritic steels strengthened by nanometer-sized carbides are developed to achieve excellent formability, realizing precipitationstrengthening of more than 300 MPa.

On the role of transmission electron microscopy for precipitation analysis in metallic materials

“…Precipitation crystallography is crucial for understanding orientation, morphology, habit plane, etc., of precipitates in crystalline matrices. [240][241][242][243] However, in comparison to the well-developed thermodynamic [244] and kinetic [245] theories of precipitation, the knowledge of precipitation crystallography is rather rudimentary. [246] A complete understanding of precipitation thermodynamics, kinetics and crystallography is necessary to reveal the full picture of precipitation reactions in metallic materials, before controlling precipitation hardening.…”

Strengthening of Low Carbon Steel by Nano-sized Vanadium Carbide in Ferrite and Tempered Martensite

“…3) In that case, the magnitude of precipitation strengthening is predicted to be larger with the refinement in size under a certain volume fraction of the precipitates, 4) and the strategy to utilize the nano-sized alloy carbides formed by microalloying of strong carbide-forming elements has already been widely applied in steel industry. 5,6) The precipitation of nano-sized alloy carbides in microalloyed steels can be obtained in two different ways. One is the precipitation by aging in the conventional quenching…”

Modeling Dissolution of Vanadium Carbide and Carbonitride in Fe–C–V(–N) Austenite

“…2,3) In particular, V is an important element because it prevents martensitic steel from softening during tempering, 4) and it is used for alloy design and texture control of various highstrength steels. [5][6][7][8][9] For V steels (steels to which V has been added as a hardening element), numerous studies have been made on the relationships of mechanical properties with heat treatment conditions and microstructure. [10][11][12][13][14][15] It is known that there are two modes of precipitation of V carbide.…”

“…............ (8). (iii) The concentration of V x V B is related to the concentration of C and N on the solubility surface as, ................ (9). …”