The present application provides a hot-work die steel and a preparation method thereof, wherein the chemical constituents of the hot-work die steel in mass percentage are as follows: C: 0.20-0.32 wt %, Si: ≤0.5 wt %, Mn: ≤0.5 wt %, Cr: 1.5-2.8 wt %, Mo: 1.5-2.5 wt %, W: 0.5-1.2 wt %, Ni: 0.5-1.6 wt %, V: 0.15-0.7 wt %, Nb: 0.01-0.1 wt %, and a balance of iron, wherein an alloying degree is 5-7%; a tensile strength of the hot-work die steel at 700° C. is 560-700 MPa; a value of hardness of the hot-work die steel at room temperature is 32-38 HRC after holding at 700° C. for 3-5 h; and the hot-work die steel has an elongation of 14% to 16% at room temperature, a percentage reduction of area of 48% to 65%, and an impact toughness of 52-63 J at room temperature. The hot-work die steel of the present application has an excellent thermal stability as well as a good plasticity and a toughness at room temperature.

A method for producing a cold rolled steel sheet having a tensile strength≥1470 MPa and a total elongation TE≥19%, the method comprising the steps of annealing at an annealing temperature AT≥Ac3 a non-treated steel sheet whose chemical composition contains in weight %: 0.34%≤C≤0.40%, 1.50%≤Mn≤2.30%, 1.50≤Si≤2.40%, 0%<Cr≤0.5%, 0%<Mo≤0.3%, 0.01%≤Al≤0.07%, the remainder being Fe and unavoidable impurities, quenching the annealed steel sheet by cooling it to a quenching temperature QT<Ms transformation point and between 150° C. and 250° C., and making a partitioning treatment by reheating the quenched steel sheet to a partitioning temperature PT between 350° C. and 420° C. and maintaining the steel sheet at this temperature during a partitioning time Pt between 15 seconds and 120 seconds.

A method for producing a cold rolled steel sheet having a tensile strength ≥1470 MPa and a total elongation TE≥19%, the method comprising the steps of annealing at an annealing temperature AT≥Ac3 a non-treated steel sheet whose chemical composition contains in weight %: 0.34%≤C≤0.40%, 1.50%≤Mn≤2.30%, 1.50≤Si≤2.40%, 0<Cr≤0.5%, 0<Mo≤0.3%, 0.01%≤Al≤0.07%, the remainder being Fe and unavoidable impurities, quenching the annealed steel sheet by cooling it to a quenching temperature QT<Ms transformation point and between 150° C. and 250° C., and making a partitioning treatment by reheating the quenched steel sheet to a partitioning temperature PT between 350° C. and 420° C. and maintaining the steel sheet at this temperature during a partitioning time Pt between 15 seconds and 120 seconds.

A method IS for producing a cold rolled steel sheet having a tensile strength ≥1470 MPa and a total elongation TE≥19%. The method includes the steps of annealing at an annealing temperature AT≥Ac3 a non-treated steel sheet whose chemical composition contains in weight %: 0.34%≤C≤0.40%, 1.50%≤Mn≤2.30%, 1.50≤Si≤2.40%, 0%<Cr≤0.7%, 0%≤Mo≤0.3%, 0.01%≤Al≤0.07%, the remainder being Fe and unavoidable impurities, quenching the annealed steel sheet by cooling it to a quenching temperature QT<Ms transformation point and between 150° C. and 250° C., and making a partitioning treatment by reheating the quenched steel sheet to a partitioning temperature PT between 350° C. and 420° C. and maintaining the steel sheet at this temperature during a partitioning time Pt between 15 seconds and 250 seconds.

The steel material according to the present disclosure has a chemical composition consisting of, in mass %, C: 0.20 to 0.35%, Si: 0.05 to 1.00%, Mn: 0.01 to 1.00%, P: 0.025% or less, S: 0.0100% or less, Al: 0.005 to 0.100%, Cr 0.25 to 0.80%, Mo: 0.20 to 2.00%, Ti: 0.002 to 0.050%, B: 0.0001 to 0.0050%, N: 0.0020 to 0.0100% and O: 0.0100% or less, with the balance being Fe and impurities, and satisfying Formula (1). A number density of precipitates having an equivalent circular diameter of 400 nm or more is 0.150 particles/μm.sup.2 or less. The yield strength is within a range of 655 to 965 MPa. A dislocation density ρ is 7.0×10.sup.14 m.sup.−2 or less.

5×Cr—Mo-2×(V+Ti)≤3.00  (1)

A steel alloy having very high strength in combination with good ductility, impact toughness, and fracture toughness is disclosed. The alloy has the following weight percent composition. C 0.30-0.46 Mn 0.04 max. Si 0.03 max. P 0.003 max S 0.0010 max. Cr 1.65-2.90 Ni 10.5-13.0 Mo 1.2-3.4 Co 15.4-18.6 Al 0.01 max Ti 0.02 max. O 0.0010 max. N 0.0010 max.
The balance is iron and usual impurities.

A method for producing a cold rolled steel sheet having a tensile strength≥1470 MPa and a total elongation TE≥19%, the method comprising the steps of annealing at an annealing temperature AT≥Ac3 a non-treated steel sheet whose chemical composition contains in weight %: 0.34%≤C≤0.40%, 1.50%≤Mn≤2.30%, 1.50≤Si≤2.40%, 0%<Cr≤0.7%, 0%≤Mo≤0.3%, 0.01%≤Al≤0.07%, the remainder being Fe and unavoidable impurities, quenching the annealed steel sheet by cooling it to a quenching temperature QT<Ms transformation point and between 150° C. and 250° C., and making a partitioning treatment by re-heating the quenched steel sheet to a partitioning temperature PT between 350° C. and 420° C. and maintaining the steel sheet at this temperature during a partitioning time Pt between 15 seconds and 250 seconds.

The present disclosure discloses a method for heat treating an iron-carbon alloy. The method comprises acts of heating the iron-carbon alloy to a first pre-determined temperature at a pre-determined heating rate, holding the iron-carbon alloy at the first pre-determined temperature for a pre-set period of time. The method further comprises acts of cooling the iron-carbon alloy to a second pre-determined temperature at a pre-determined cooling rate and inducing magnetic field on the iron-carbon alloy selectively during at least one of heating and cooling of the iron-carbon alloy. The induction of magnetic field on the iron-carbon alloy results in microstructural changes to improve formation of pearlitic structure in the iron-carbon alloy.

The present disclosure discloses a method for heat treating an iron-carbon alloy. The method comprises acts of heating the iron-carbon alloy to a first pre-determined temperature at a pre-determined heating rate, holding the iron-carbon alloy at the first pre-determined temperature for a pre-set period of time. The method further comprises acts of cooling the iron-carbon alloy to a second pre-determined temperature at a pre-determined cooling rate and inducing magnetic field on the iron-carbon alloy selectively during at least one of heating and cooling of the iron-carbon alloy. The induction of magnetic field on the iron-carbon alloy results in microstructural changes to improve formation of pearlitic structure in the iron-carbon alloy.

The present invention discloses a method for processing a highly alloyed aluminum alloy sheet with a high rolling yield, including the steps of cold rolling and hot rolling of an alloy sheet followed by heat treatment. The highly alloyed Al—Cu—Mg—Ag alloy sheet is subjected to short-time solution treatment and quenching at high temperature for multiple times by increasing the solution treatment temperature and shortening the solution treatment time. In this way, the mechanical properties of the alloy at room temperature and high temperature match with or even exceed those of a conventional alloy subjected to long-time solution treatment at high temperature. The present invention implements multiple times of short-time continuous solution treatment and quenching of a highly-alloyed coiled aluminum alloy sheet. This prevents a large amount of scraps caused by the conventional processes of segmented solution treatment and quenching of the coiled material and stretching straightening treatment.