Hyundai Steel has filed a patent for an ultra-high strength cold rolled steel sheet that offers excellent spot weldability and formability. The steel sheet contains specific percentages of carbon, silicon, manganese, aluminum, chromium, molybdenum, titanium, boron, antimony, phosphorus, sulfur, and nitrogen, along with iron and other impurities. The sheet’s microstructure consists of ferrite and low hardness martensite. GlobalData’s report on Hyundai Steel gives a 360-degree view of the company including its patenting strategy. Buy the report here.
According to GlobalData’s company profile on Hyundai Steel, Hydrogen fuel cells was a key innovation area identified from patents. Hyundai Steel's grant share as of September 2023 was 27%. Grant share is based on the ratio of number of grants to total number of patents.
Ultra-high strength cold rolled steel sheet with specific composition
A recently filed patent (Publication Number: US20230265536A1) describes an ultra-high strength cold rolled steel sheet with specific composition and properties. The steel sheet consists of carbon, silicon, manganese, aluminum, chromium, molybdenum, titanium, boron, antimony, phosphorus, sulfur, nitrogen, and iron, along with other impurities. The microstructure of the steel sheet is composed of ferrite and low hardness martensite. The average interphase hardness difference between ferrite and low hardness martensite is between more than 0 GPa to 1.0 GPa. The ferrite fraction ranges from 50% to 60%, while the low hardness martensite fraction ranges from 40% to 50%. The crystal grain size of ferrite or low hardness martensite is between 1 µm to 5 µm. The low hardness martensite has an average hardness between 3.5 GPa to 4.5 GPa. The ratio of the average hardness of ferrite to the average hardness of low hardness martensite is between 70% to less than 100%. The steel sheet also includes a mesh structure formed by a first and second low hardness martensite, with the second low hardness martensite connecting the first low hardness martensite at the crystal grain boundary of ferrite. The second low hardness martensite has a ratio of minor axis length to major axis length between 0.5 to 1.0. The steel sheet satisfies various mechanical properties, including a yield strength of 480 MPa or more, a tensile strength of 820 MPa or more, an elongation of 5% or more, and a bendability at an angle of 60 degrees of 2.5 or less. The steel sheet can be manufactured by a method that involves hot rolling, cold rolling, annealing heat treatment, multistage cooling, and over-aging heat treatment.
Additionally, the patent also describes an ultra-high strength plated steel sheet. The plated steel sheet consists of a base steel sheet with a hot-dip galvanized layer or alloyed hot-dip galvanized layer formed on its surface. The manufacturing method for this plated steel sheet involves similar steps as the cold rolled steel sheet, including hot rolling, cold rolling, annealing heat treatment, multistage cooling, and hot-dip galvanizing. The plated steel sheet can also undergo alloying heat treatment after the hot-dip galvanizing step.
Overall, this patent presents a novel composition and manufacturing method for ultra-high strength cold rolled steel sheets and plated steel sheets. The steel sheets exhibit specific microstructures and mechanical properties, making them suitable for various applications that require high strength and durability.