Steel with ultrafine grains is produced by altering the transformation from one which normally proceeds with grain boundary nucleation followed by intragranular nucleation at deformation bands and other defects, to one which induces a substantially instantaneous transformation homogeneously over the austenite grain. This is favoured by a reduction or minimisation of grain boundary nucleation, (for example by enlargement of the austenite grain size), prior to or during the transformation. In an embodiment, a partially cooled austenite phase steel is deformed in a single pass at a temperature in the range of 700-950° C. to obtain ferrite grain size of 5 μm or less.

Strain-induced transformation to ultrafine microstructure in steel

The strength of interstitial free steels is increased by up to 100% and the ductile to brittle transition temperature is decreased by up to 100° C. by warm finish rolling in the single phase ferrite region below A rl to effect ferrite dynamic recrystallization of the steel microstructure to a ferrite structure of grain size having a grain size of up to 5 μm, and especially an ultra fine grain size of 1 to 2 μm; the method may be employed in various hot working methods including strip and rod mills, planetary hot rolling and extrusion.

Interstitial free steels and method thereof

In accordance with the invention, nanostructured metallic materials having high tensile strength and increased ductility are prepared by providing a metallic material, deforming the metallic material to form a plurality of dislocation cell structures, annealing the material at a temperature from about 0.3 to about 0.7 of its absolute melting temperature, and cooling the annealed metallic material. The result is a nanostructured metal or alloy having increased tensile strength as compared with the corresponding coarse-grained material and substantially greater ductility as compared with nanostructured material made by conventional processes. Using this process applicants have made nanostructured alloys with tensile strengths in excess of 1.5 Gpa and ductility greater than 1 per cent strain-to-failure. They have also made nanostructured metals with tensile strength in excess of 400 MPa and ductility in excess of 50% strain-to-failure. The new materials are useful in a variety of applications such as rotors, electric generators, magnetic bearings, microelectromechanical devices and biomedical systems.

High performance nanostructured materials and methods of making the same

Illustrative embodiments provide systems, methods, apparatuses, and applications related to annealing nuclear fission reactor materials.

System and method for annealing nuclear fission reactor materials

Ferrous articles are austenitized, then converted to at least 60% bainite, and the balance substantially converted to martensite by quenching; the articles are then cold worked, preferably by both compression and tensile deformation to at least 60% yield strength. The articles have improved serviceability, particularly fatigue life.

High-hardness, highly ductile ferrous articles

Ferrous alloys containing up to about 25 percent Ni, 15 percent Mn, 1.2 percent C, 0.5 percent N are cooled to form a martensitic or bainitic structure. The material is then worked to an extent sufficient to remove the principal nucleating effect of the prior austenite boundaries and other microstructural interfaces, so that when subsequently heated into the multiphase region, recrystallization occurs by random nucleation of extremely fine austenite crystals thoughout the material. Exceptionally fine equiaxed grains in the micron and submicron range are achieved, thereby providing unique combinations of both increased strength along with increased ductility and increased notch toughness.

Miller Robert Lewis

Papers

Method for producing ultra fine-grained microstructure in ferrous alloys