Microstructurally Patterned Blanks
Most all present advanced high strength steels (AHSS) rely on a martensitic phase that encompasses the entire coil, sheet, or die quenched part. Difficulties with the primary and/or secondary stamping operations are often encountered. Metal springback, even in non-critical areas, is a notorious problem. If a part is not brought to the proper shape on the first hit, it is often scrapped as no further work can be performed. Prototype and sometimes even production dies are designed and machined multiple times just to achieve the desired shape.
The present embodiment of this invention can be used to create a pattern of different microstructures in the steel sheet to allow easier formability, while maintaining strength where needed. It is now possible to "flash" form bainite or other austenite daughter phases only in areas of the blank where those characteristic properties are desired. Transportation industry structural engineers will now be able to design individual steel members with built in "crumple zones" by varying the localized microstructure of the member itself.
By regulating the heat, and subsequent quench, applied in certain areas of the steel being processed, the resultant microstructure in those areas can be controlled. Applying this theory, one can envision a piece of sheet metal to be used in the stamping of the bodyside panel of an automobile. The A, B, and C pillars, as well as the roof line and rocker areas, could be heated to yield bainite, or martensite, as the panel is processed. The other areas could be left unheated, and therefore unchanged to maintain all of the properties originally in the sheet of steel. Imagine a sheet of cold rolled, high strength, dual phase, or TRIP steel that has an 80 to 90 % bainitic microstructure added only where desired for strength and formability.