Process for manufacturing a galvannealed steel sheet by DFF regulation
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A steel sheet and coating technology, which is applied in the direction of manufacturing tools, coatings, hot-dip galvanizing, etc., can solve problems such as the cost impact of steel sheets
Active Publication Date: 2010-08-18
ARCELORMITTAL INVESTIGACION Y DESARROLLO SL +1
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However, this has the major drawback that high levels of tensile strength, i.e. around 800 MPa, can only be achieved when the carbon content is increased
However, this has an impact on the cost of the steel sheet
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[0054] The invention will now be illustrated by way of an example provided in a non-limiting manner and with reference to FIGS. 1 and 2 .
[0055] Tests were carried out using samples A and B from 0.8 mm thick sheets made of steel sheets with the composition shown in Table I.
[0056] Samples A and B were preheated from ambient temperature (20°C) to 750°C in a direct-fired furnace, and they were subsequently and continuously annealed in a radiant tube furnace in which they were heated from 750°C to 800°C, then soak them at 800°C for 60s, and finally cool them down to 460°C. The atmosphere in the radiant tube furnace contains 30% by volume of hydrogen, the balance being nitrogen and unavoidable impurities.
[0057] After cooling, samples A and B were hot-dip galvanized in a molten zinc-based bath containing 0.12% by weight of aluminum, the balance being zinc and unavoidable impurities. The temperature of the bath was 460°C. After sweeping with nitrogen and cooling the zinc-b...
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Abstract
The invention deals with a process for manufacturing a hot-dip galvannealed steel sheet having a TRIP microstructure, and comprising, by % by weight, 0.01 <= C <= 0.22%, 0.50 <= Mn <= 2.0%, 0.5 < Si <= 2.0%, 0.005 <= Al <= 2.0%, Mo < 0.01 %, Cr <=1.0%, P < 0.02%, Ti <= 0.20%, V <= 0.40%, Ni <= 1.0%, Nb <= 0.20%, the balance of the composition being iron and unavoidable impurities resulting from the smelting, said process comprising the steps consisting in: - oxidizing said steel sheet in order to form a layer of iron oxide on the surface of the steel sheet, and to form an. internal oxide of at least one type of oxide selected from the group consisting of Si oxide, Mn oxide, Al oxide, complex oxide comprising Si and Mn, complex oxide comprising Si and Al complex oxide comprising Al and Mn, and complex comprising Si, Mn and Al, - reducing said oxidized steel sheet in order to reduce the layer of iron oxide, - hot-dip galvanising said reduced steel sheet to form a zinc-based coated steel sheet, and - subjecting said zinc-based coated steel sheet to an alloying treatment to form a galvannealed steel sheet.
Description
technical field [0001] The present invention relates to a method of manufacturing a hot-dip galvanized annealed steel sheet having a TRIP microstructure. Background technique [0002] In order to meet the need to lighten the structure of powered land vehicles, it is known to use TRIP steels (the term TRIP stands for Transformation Induced Plasticity), which combine high mechanical strength with the possibility of very high deformation levels. TRIP steels have a microstructure comprising ferrite, retained austenite and optionally martensite and / or bainite, which allows them to achieve tensile strengths of 600-1000 MPa. This type of steel is widely used in the production of energy absorbing parts such as structural and safety parts such as longitudinal members and reinforcements. [0003] Steel sheets are usually coated with a zinc-based coating by hot-dip galvanizing before being sent to the car manufacturer in order to improve corrosion resistance. After leaving the zinc b...
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