A steel sheet for the manufacture of a press hardened part is provided, having a composition of: 0.15%≤C≤0.22%, 3.5%≤Mn<4.2%, 0.001%≤Si≤1.5%, 0.020%≤Al≤0.9%, 0.001%≤Cr≤1%, 0.001%≤Mo≤0.3%, 0.001%≤Ti≤0.040%, 0.0003%≤B≤0.004%, 0.001%≤Nb≤0.060%, 0.001%≤N≤0.009%, 0.0005%≤S≤0.003%, 0.001%≤P≤0.020%. A microstructure has less than 50% ferrite, 1% to 20% retained austenite, cementite, such that the surface density of cementite particles larger than 60 nm is lower than 10{circumflex over ( )}7/mm.sup.2, and a complement of bainite and/or martensite, the retained austenite having an average Mn content of at least 1.1*Mn %. Press-hardened steel part obtained by hot forming the steel sheet, and manufacturing methods thereof.

The present invention relates to an ultra-high strength, hot-dip galvanized steel sheet having excellent surface quality and coating adherence and to a method for manufacturing thereof, the ultra-high strength, hot-dip galvanized steel sheet comprising: 0.1-0.3% by weight carbon (C); 0.1-2.0% by weight silicon (Si); 0.005-1.5% by weight aluminum (Al); 1.5-3.5% by weight manganese (Mn); 0.04% by weight or less phosphorus (P) (excluding 0% by weight); 0.015% by weight or less sulphur (S) (excluding 0% by weight); 0.02% by weight or less nitrogen (N) (excluding 0% by weight); the balance being Fe; and other inevitable impurities, and further comprising 0.01 wt.% to 0.07 wt.% of at least one kind of element selected from the group consisting of bismuth (Bi), tin (Sn) and antimony (Sb).

A method for manufacturing a high-strength cold-rolled steel sheet includes a temperature distribution forming step of forming a temperature distribution in a width direction of a steel sheet such that a temperature of the steel sheet increases from an end of the steel sheet in the width direction toward a center part of the steel sheet in the width direction, and a water quenching step of performing water quenching treatment on the steel sheet by immersing, in cooling water, the steel sheet on which the temperature distribution is formed in the width direction.

A method for producing a steel sheet for packaging includes: cold-rolling a hot-rolled steel sheet made from a steel having a carbon content of 10 to 1000 ppm by weight, the steel of the hot-rolled steel sheet having a predetermined recrystallization temperature (T.sub.R); heating the cold-rolled steel sheet to a predetermined heating temperature (T.sub.E), where T.sub.R≤T.sub.E, the heating performed at least partially in the presence of a nitrogen donor at least until T.sub.R is reached such that when the cold-rolled steel sheet is heated, nitrogen from the nitrogen donor is diffused at least into a near-surface region of the cold-rolled sheet steel and incorporated in the near-surface region, as a result of which the T.sub.R in the near-surface region is increased by a value ΔT, where T.sub.E<T.sub.R+ΔT. Using this method, high-strength steel sheets having a multilayer microstructure can be produced.

A steel sheet for a crown cap has sufficient strength and formability even when the thickness thereof is reduced for use, and has a composition containing, in percent by mass, C: 0.010% to 0.025%, Si: 0.10% or less, Mn: 0.05% to 0.50%, P: 0.050% or less, S: 0.005% to 0.050%, Al: 0.020% to 0.070%, N: less than 0.0040%, and the balance being Fe and inevitable impurities, wherein yield strength after heat treatment at 210° C. for 15 minutes is as follows: the yield strength is 550 MPa or more in a rolling direction, and the yield strength in a direction 45° from the rolling direction in a rolling plane is equal to or less than the average of the yield strength in the rolling direction and the yield strength in a direction 90° from the rolling direction in the rolling plane.

Provided is a metal gasket including, expressed in mass%, C: 0.10% or less, Si: 1.0% or less, Mn: 2.0% or less, P: 0.04% or less (including 0%), S: 0.01% or less (including 0%), Ni: 25.0-60.0%, Cr: 10.0-20.0%, either Mo or W alone, or both Mo + W/2: 0.05-5.0%, Al: more than 0.8% to 3.0% or less, Ti: 1.5-4.0%, Nb: 0.05-2.5%, V: 1.0% or less (including 0%), B: 0.001-0.015%, Mg: 0.0005-0.01%, S/Mg: 1.0 or less, N: 0.01% or less (including 0%), and O: 0.005% or less (including 0%), with the remainder being Fe and unavoidable impurities. The metal gasket has a metal structure in which a precipitate γ′ phase having an average equivalent circle diameter of 25 nm or larger is not present within the austenite base.

Manufacturing a steel sheet for a steel belt includes hot rolling a steel slab containing, in mass %, 0.60 to 0.80% of C, 1.0% or less of Si, 0.10 to 1.0% of Mn, 0.020% or less P, 0.010% or less S, 0.1 to 1.0% of Cr, 0 to 0.5% of V, 0 to 0.1% of Ti, 0 to 0.1% of Nb, and 0 to 0.01% of B, the balance Fe and unavoidable impurities, under a finish hot rolling temperature of 800 to 900° C. An average cooling rate from finish rolling to coiling is 20° C. per second or more. A coiling temperature is 450 to 650° C. The hot-rolled slab is cold rolled with a total rolling reduction ratio of 40% or more and a reduction ratio per one pass of less than 12%, without performing a heat treatment. The cold-rolled slab is aged at 200 to 500° C. for 0.5 to 30 hours.

A steel sheet for cans has a chemical composition containing, by mass %, C: 0.015% or more and 0.150% or less, Si: 0.04% or less, Mn: 1.0% or more and 2.0% or less, P: 0.025% or less, S: 0.015% or less, Al: 0.01% or more and 0.10% or less, N: 0.0005% or more and less than 0.0050%, Ti: 0.003% or more and 0.015% or less, B: 0.0010% or more and 0.0040% or less, and the balance being Fe and inevitable impurities. The steel sheet has a microstructure including a ferrite phase as a main phase and at least one of a martensite phase and a retained austenite phase as a second phase, the total area fraction of the second phase being 1.0% or more, and the sheet has a tensile strength of 480 MPa or more, a total elongation of 12% or more, and a yield elongation of 2.0% or less.

A steel sheet having a specified chemical composition and a tensile strength of 1,320 MPa or more, and methods for producing the steel sheet. The steel sheet has a specified microstructure including martensite and bainite, the total area fraction of the martensite and the bainite being 95% or more and 100% or less, the balance being one or more selected from ferrite and retained austenite. The forumulae [% Ti]+[% Nb]>0.007 and [% Ti]×[% Nb].sup.2≤7.5×10.sup.−6 are satisfied in the chemical composition.

A high strength cold rolled steel sheet having excellent burring properties includes: by weight %, 0.13-0.25% of carbon (C), 1.0-2.0% of silicon (Si), 1.5-3.0% of manganese (Mn), 0.08-1.5% of aluminum (Al)+chrome (Cr)+molybdenum (Mo), 0.1% or less of phosphorus (P), 0.01% or less of sulfur (S), 0.01% or less of nitrogen (N), and the balance of Fe and inevitable impurities; and, by area fraction, 3-25% of ferrite, 20-40% of martensite, 5-20% of residual austenite. The ferrite has an average grain size of 2 μm or less at the reference point of 4/t (wherein t refers to a steel sheet thickness), with the average ratio between lengths in the thickness direction and in the rolling direction being 1.5 or less.