ArcelorMittal has been granted a patent for a press hardening method that involves coating a carbon steel sheet with a barrier pre-coating containing nickel and chromium. The method includes cutting the sheet, thermally treating it in an oxidizing atmosphere, transferring it to a press tool, hot-forming it, and cooling it to obtain a specific microstructure in the steel. The microstructure can be martensitic, martensito-bainitic, or primarily equiaxed ferrite with small amounts of martensite and bainite. GlobalData’s report on ArcelorMittal gives a 360-degree view of the company including its patenting strategy. Buy the report here.
According to GlobalData’s company profile on ArcelorMittal, photovoltaic roof tiles was a key innovation area identified from patents. ArcelorMittal's grant share as of September 2023 was 64%. Grant share is based on the ratio of number of grants to total number of patents.
A recently granted patent (Publication Number: US11773464B2) describes a press hardening method for carbon steel sheets coated with a barrier pre-coating. The method involves several steps to achieve a desired microstructure in the steel.
In the first step, a carbon steel sheet is provided, which is coated with a barrier pre-coating comprising nickel and chromium. The weight ratio of nickel to chromium in the pre-coating is between 1.5 and 9, preferably between 2.3 and 9. The pre-coating may also include other elements such as rare gases, carbon dioxide, and methane.
Next, the coated carbon steel sheet is cut to obtain a blank, which is then thermally treated in an atmosphere with an oxidizing power equal to or higher than 1% oxygen and equal to or smaller than 50% oxygen by volume. The atmosphere should have a dew point between -30 and +30°C, preferably between -20 and +20°C. The preferred atmosphere for the thermal treatment is air, consisting of about 78% nitrogen, 21% oxygen, and other gases.
After the thermal treatment, the blank is transferred into a press tool and hot-formed to obtain a part. The part is then cooled to achieve a desired microstructure in the steel. The microstructure can be martensitic, martensito-bainitic, or made of at least 75% equiaxed ferrite, with 5 to 20% martensite and bainite in an amount less than or equal to 10%.
The patent also describes variations in the composition and thickness of the barrier pre-coating, as well as the use of an anticorrosion pre-coating layer on top of the carbon steel sheet. The thermal treatment temperature ranges from 800 to 950°C, with a dwell time between 1 to 12 minutes. The hot-forming temperature ranges from 600 to 830°C.
The patent claims that this press hardening method can be used in the manufacturing of vehicles. By following the steps outlined in the patent, manufacturers can achieve the desired microstructure in carbon steel sheets, which can enhance the strength and durability of vehicle components.
Overall, this granted patent provides a detailed method for press hardening carbon steel sheets, offering potential benefits for the automotive industry in terms of improved material properties and manufacturing processes.