Nucor has been granted a patent for thin metal strips and methods of making them. The method involves cooling the strip to form bainite and/or martensite, reheating it to form austenite with small grain sizes, and then rapidly recooling it to provide finer martensite. The resulting thin metal strip has specific composition and martensite grain sizes. GlobalData’s report on Nucor gives a 360-degree view of the company including its patenting strategy. Buy the report here.
According to GlobalData’s company profile on Nucor, structure building framework was a key innovation area identified from patents. Nucor's grant share as of June 2023 was 1%. Grant share is based on the ratio of number of grants to total number of patents.
Patent granted for thin metal strip with specific composition and structure
A recently granted patent (Publication Number: US11655519B2) describes a method for producing a thin metal strip with finer martensite from finer prior austenite. The thin metal strip has an as-cast thickness of less than 5 mm and is composed of specific percentages of carbon, chromium, nickel, manganese, silicon, copper, niobium, vanadium, and molybdenum, with aluminum content less than 0.01%.
The method involves several steps. First, a pair of counter-rotatable casting rolls is used to form a gap through which the thin metal strip is cast. The casting rolls are counter-rotated to create metal shells on their surfaces, with a heat flux greater than 10 MW/m2. Molten metal is delivered to the casting pool formed on the casting surfaces, and the thin metal strip is produced with the desired composition.
Next, the thin metal strip is cooled to a temperature equal to or less than the bainite or martensite start transformation temperature to form bainite and/or martensite within the strip. The strip is then reheated to a temperature equal to or greater than the transformation temperature Ac3 and held at this temperature for at least 2 seconds. This process forms austenite within the strip, with at least 75% of the austenite grains having a grain size equal to or less than 10 µm.
Finally, the thin metal strip is rapidly recooled to a temperature equal to or less than the martensite start transformation temperature MS, resulting in finer martensite within the strip from the finer prior austenite. At least 75% of the prior austenite grains have a grain size equal to or less than 10 µm upon the first thermal cycle.
The method also includes specific temperature ranges for reheating and rapid recooling, as well as holding times at the reheat temperature. The temperature to which the thin metal strip is initially cooled is equal to or less than 600°C, and the strip is rapidly recooled to a temperature less than 100°C or equal to or less than 200°C.
This patented method provides a way to produce a thin metal strip with finer martensite from finer prior austenite, offering potential benefits in various applications that require high strength and toughness.