Arcelormittal France

Arcelormittal Investigacion Y Desarrollo, S.l.

Arcelormittal

Olivier Bouaziz

Kangying Zhu

Jean-Claude Chevallot

Astrid Perlade

Frédéric Bonnet

Xavier Garat

Jean-Louis Uriarte

Josee Drillet

Josée Drillet

David Barbier

Coralie Jung

Jean-Claude (decede) Chevallot

The present invention provides a method for the fabrication of a steel sheet with a completely martensitic structure which has an average lath size of less than 1 micrometer and an average elongation factor of the laths is between 2 and 5. The elongation factor of a lath is defined as a maximum dimension ldivided by and a minimum dimension l. The steel sheet has a yield stress greater than 1300 MPa and a mechanical strength greater than (3220(C)+958) megapascals. A composition of a semi-finished steel product includes, expressed in percent by weight, is, 0.15%&#x2264;C&#x2264;0.40%, 1.5%&#x2264;Mn&#x2264;3%, 0.005%&#x2264;Si&#x2264;2%, 0.005%&#x2264;Al&#x2264;0.1%, 1.8%&#x2264;Cr&#x2264;4%, 0%&#x2264;Mo&#x2264;2%, whereby: 2.7% 0.5 (Mn)+(Cr)+3(Mo)&#x2264;5.7%, S&#x2264;0.05%, P&#x2264;0.1%, optionally: 0%&#x2264;Nb&#x2264;0.050%, 0.01%&#x2264;Ti&#x2264;0.1%, 0.0005%&#x2264;B&#x2264;0.005%, 0.0005%&#x2264;Ca&#x2264;0.005%. The semi-finished product is reheated to a temperature Tin the range between 1050&#xb0; C. and 1250&#xb0; C., then subjected to a roughing rolling at a temperature Tin the range between 1000 and 880&#xb0; C., with a cumulative rate of reduction &#x3b5;greater than 30%, to obtain a sheet with a completely recrystallized austenitic structure with an average grain size less than 40 micrometers and preferably less than 5 micrometers. The sheet is then partially cooled to prevent a transformation of the austenite at a rate Vgreater than 2&#xb0; C./s to a temperature Tbetween 600&#xb0; C. and 400&#xb0; C. in the metastable austenitic range, and subjected to a finishing hot rolling at the temperature Tof the partially cooled sheet, with a cumulative rate of reduction &#x3b5;greater than 30% to obtain a sheet that is then cooled at a rate Vwhich is greater than the critical martensitic quenching rate.

Very high strength martensitic steel or part and method of fabrication

A steel plate, the chemical composition of which includes, the contents being expressed by weight: 0.010%&#x2264;C&#x2264;0.20%, 0.06%&#x2264;Mn&#x2264;3%, Si&#x2264;1.5%, 0.005%&#x2264;Al&#x2264;1.5%, S&#x2264;0.030%, P&#x2264;0.040%, 2.5%&#x2264;Ti&#x2264;7.2%, (0.45&#xd7;Ti)&#x2212;0.35%&#x2264;B&#x2264;(0.45&#xd7;Ti)+0.70%, and optionally one or more elements chosen from: Ni&#x2264;1%, Mo&#x2264;1%, Cr&#x2264;31, Nb&#x2264;0.1%, V&#x2264;0.1%, the balance of the composition consisting of iron and inevitable impurities resulting from the smelting.

Steel plate for producing light structures and method for producing said plate

The present invention provides a method for the fabrication of a steel sheet with a completely martensitic structure which has an average lath size of less than 1 micrometer and an average elongation factor of the laths is between 2 and 5. The elongation factor of a lath is defined as a maximum dimension 1divided by and a minimum dimension 1. The steel sheet has a yield stress greater than 1300 MPa and a mechanical strength greater than (3220(C)+958) megapascals. A composition of a semi-finished steel product includes, expressed in percent by weight, is, 0.15%&#x2264;C&#x2264;0.40%, 1.5%&#x2264;Mn&#x2264;3%, 0.005%&#x2264;Si&#x2264;2%, 0.005%&#x2264;Al&#x2264;0.1%, 1.8%&#x2264;Cr&#x2264;4%, 0%&#x2264;Mo&#x2264;2%, whereby: 2.7%&#x2264;0.5 (Mn)+(Cr)+3(Mo)&#x2264;5.7%, S&#x2264;0.05%, P&#x2264;0.1%, optionally: 0%&#x2264;Nb&#x2264;0.050%, 0.01%&#x2264;Ti&#x2264;0.1%, 0.0005%&#x2264;B&#x2264;0.005%, 0.0005%&#x2264;Ca&#x2264;0.005%. The semi-finished product is reheated to a temperature Tin the range between 1050&#xb0; C. and 1250&#xb0; C., then subjected to a roughing rolling at a temperature Tin the range between 1000 and 880&#xb0; C., with a cumulative rate of reduction &#x3b5;greater than 30%, to obtain a sheet with a completely recrystallized austenitic structure with an average grain size less than 40 micrometers and preferably less than 5 micrometers. The sheet is then partially cooled to prevent a transformation of the austenite at a rate Vgreater than 2&#xb0; C./s to a temperature Tbetween 600&#xb0; C. and 400&#xb0; C. in the metastable austenitic range, and subjected to a finishing hot rolling at the temperature Tof the partially cooled sheet, with a cumulative rate of reduction &#x3b5;greater than 30% to obtain a sheet that is then cooled at a rate Vwhich is greater than the critical martensitic quenching rate.

Method for the production of very high strength martensitic steel and sheet or part thus obtained

The present invention provides a method for the fabrication of a martensitic steel sheet with a yield stress greater than 1300 MPa. The method includes the steps of obtaining a semi-finished steel product, the composition of which includes, whereby the contents are expressed in percent by weight: 0.15%&#x2264;C&#x2264;0.40%, 1.5%&#x2264;Mn&#x2264;3%, 0.005%&#x2264;Si&#x2264;2%, 0.005%&#x2264;Al&#x2264;0.1%, S&#x2264;0.05%, P&#x2264;0.1%, 0.025%&#x2264;Nb&#x2264;0.1%, and optionally: 0.01%&#x2264;Ti&#x2264;0.1%, 0%&#x2264;Cr&#x2264;4%, 0%&#x2264;Mo&#x2264;2%, 0.0005%&#x2264;B&#x2264;0.005%, 0.0005%&#x2264;Ca&#x2264;0.005%. The remainder of the composition is iron and the inevitable impurities resulting from processing. The semi-finished product is reheated to a temperature Tin the range between 1050&#xb0; C. and 1250&#xb0; C., then the reheated semi-finished product is subjected to a roughing rolling at a temperature Tin the range between 1050 and 1150&#xb0; C., with a cumulative rate of reduction &#x3f5;greater than 100%, to obtain a sheet with a not totally recrystallized austenitic structure with an average grain size less than 40 micrometers and preferably less than 5 micrometers. The sheet is then cooled to prevent a transformation of the austenite at a rate Vgreater than 2&#xb0; C./s to a temperature Tin the range between 970&#xb0; C. and Ar3+30&#xb0; C., is then subjected to a finishing hot rolling at the temperature Tof the cooled sheet, with a cumulative rate off reduction &#x3f5;greater than 50% to obtain a sheet, then the sheet is cooled at a rate Vwhich is greater than the critical martensitic quenching rate. Steel sheets are also provided.

Method for production of martensitic steel having a very high yield point and sheet or part thus obtained

A cold-rolled and annealed ferritic steel sheet is provided. The steel has a composition comprising, expressed by weight: &#x3a3;di denotes the total length of grain boundaries containing &#x3ba; precipitates relative to an area (A) and &#x3a3;Li denotes the total length of the grain boundaries relative to the area (A). A content of carbon in solid solution is less than 0.005% by weight, and the cold-rolled and annealed ferritic steel sheet has a thickness between 0.6 mm and 1.5 mm. A skin part or structural part for the automotive field is also provided.

Low density steel having good drawability

The invention relates to a steel plate, the chemical composition of which comprises, the contents being expressed by weight: 0.010%&#x2266;C&#x2266;0.20%, 0.06%&#x2266;Mn&#x2266;3%, Si&#x2266;1.5%, 0.005%&#x2266;Al&#x2266;1.5%, S&#x2266;0.030%, P&#x2266;0.040%, 2.5%&#x2266;Ti&#x2266;7.2%, (0.45&#xd7;Ti)&#x2212;0.35%&#x2266;B&#x2266;(0.45&#xd7;Ti)+0.70%, and optionally one or more elements chosen from: Ni&#x2266;1%, Mo&#x2266;1%, Cr&#x2266;3%, Nb&#x2266;0.1%, V&#x2266;0.1%, the balance of the composition consisting of iron and inevitable impurities resulting from the smelting.

A rolled steel sheet or blank is provided, the composition of which comprises the elements listed below in percent by weight: C&#x2266;0.1%; 0.5%&#x2266;Mn&#x2266;7%; 0.5%&#x2266;Si&#x2266;3.5%; 0.5%&#x3c;Ti&#x2266;2%; 2%&#x3c;Ni&#x2266;7%; Al&#x2266;0.10%; Cr&#x2266;2%; Cu&#x2266;2%; Co&#x2266;2%; Mo&#x2266;2%; S&#x2266;0.005%; P&#x2266;0.03%; Nb&#x2266;0.1%; V&#x2266;0.1%; B&#x3c;0.005%; N&#x2266;0.008%, and the silicon and titanium contents are such that: the remainder of the composition consisting of iron and unavoidable impurities resulting from processing. A method for the fabrication of a part for a land motor vehicle from the sheet or blank by hot stamping is also provided. The microstructure of the part consisting essentially of martensite and intermetallic precipitates of type FeTiSi with an area percentage between 1 and 5% intermetallic precipitates.

Rolled steel that hardens by means of precipitation after hot-forming and/or quenching with a tool having very high strength and ductility, and method for manufacturing same

The invention relates to a hot-rolled ferritic steel sheet, the composition of the steel of which comprises, the contents being expressed by weight: 0.001&#x2266;C&#x2266;0.15%, Mn&#x2266;1%, Si&#x2266;1.5%, 6%&#x2266;Al&#x2266;10%, 0.020%&#x2266;Ti&#x2266;0.5%, S&#x2266;0.050%, P&#x2266;0.1%, and, optionally, one or more elements chosen from: Cr&#x2266;1%, Mo&#x2266;1%, Ni&#x2266;1%, Nb&#x2266;0.1%, V&#x2266;0.2%, B&#x2266;0.010%, the balance of the composition consisting of iron and inevitable impurities resulting from the smelting, the average ferrite grain size dmeasured on a surface perpendicular to the transverse direction with respect to the rolling being less than 100 microns.

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Metz, France

Olivier Bouaziz