Steel sheet and method for manufacturing steel sheet

Patent metadata

Field	Value
Publication number	US-10030280-B2
Application number	US-201113879049-A
Country	US
Kind code	B2
Filing date	Oct 21, 2011
Priority date	Oct 22, 2010
Publication date	Jul 24, 2018
Grant date	Jul 24, 2018

Abstract

The present invention provides a steel sheet with chemical components including, by mass %, 0.18-0.35% of C, 1.0%-3.0% of Mn, 0.01%-1.0% of Si, 0.001%-0.02% of P, 0.0005%-0.01% of S, 0.001%-0.01% of N, 0.01%-1.0% of Al, 0.005%-0.2% of Ti, 0.0002%-0.005% of B, and 0.002%-2.0% of Cr, and the balance of Fe and inevitable impurities, wherein: by volume %, a fraction of the ferrite is 50% or more, and a fraction of a non-recrystallized ferrite is 30% or less; and Cr θ /Cr M is 2 or less, where Cr θ is a concentration of Cr subjected to solid solution in iron carbide and Cr M is a concentration of Cr subjected to solid solution in a base material, or Mn 0 /Mn M is 10 or less, where Mn 0 is a concentration of Mn subjected to solid solution in an iron carbide, and Mn M is a concentration of Mn subjected to solid solution in a base material.

First claim

The invention claimed is:

1. A steel sheet with chemical components which include, by mass %, 0.18% to 0.35% of C, 1.0% to 3.0% of Mn, 0.01% to 1.0% of Si, 0.001% to 0.02% of P, 0.0005% to 0.01% of S, 0.001% to 0.01% of N, 0.01% to 1.0% of Al, 0.005% to 0.2% of Ti, 0.0002% to 0.005% of B, and 0.002% to 2.0% of Cr, and a balance of Fe and inevitable impurities, wherein:
by volume %, a fraction of a ferrite is equal to or more than 50%, and a fraction of a non-recrystallized ferrite is equal to or less than 30%;
a value of a ratio Cr θ /Cr M is equal to or less than 2, where Cr θ is a concentration of Cr subjected to solid solution in an iron carbide and Cr M is a concentration of Cr subjected to solid solution in a base material, or a value of a ratio Mn θ /Mn M is equal to or less than 10, where Mn θ is a concentration of Mn subjected to solid solution in an iron carbide, and Mn M is a concentration of Mn subjected to solid solution in a base material; and
a tensile strength average value is not more than 685 MPa.

2. The steel sheet according to claim 1 , wherein the chemical components further include one or more from 0.002% to 2.0% of Mo, 0.002% to 2.0% of Nb, 0.002% to 2.0% of V, 0.002% to 2.0% of Ni, 0.002% to 2.0% of Cu, 0.002% to 2.0% of Sn, 0.0005% to 0.0050% of Ca, 0.0005% to 0.0050% of Mg, and 0.0005% to 0.0050% of REM.

3. The steel sheet according to claim 1 , wherein a DI inch value which is an index of a hardenability is equal to or more than 3.

4. The steel sheet according to claim 1 , wherein a fraction of a non-segmentalized pearlite is equal to or more than 10%.

5. A method for manufacturing a steel sheet for hot stamping, the method comprising:
hot-rolling a slab containing chemical components according to claim 1 or 2 , to obtain a hot-rolled steel sheet;
coiling the hot-rolled steel sheet which is subjected to hot-rolling;
cold-rolling the coiled hot-rolled steel sheet to obtain a cold-rolled steel sheet; and
continuously annealing the cold-rolled steel sheet which is subjected to cold-rolling, wherein the continuous annealing includes:
heating the cold-rolled steel sheet to a temperature range of equal to or higher than Ac 1 ° C. and lower than Ac 3 ° C.;
cooling the heated cold-rolled steel sheet from a highest heating temperature to 660° C. at a cooling rate of equal to or less than 10° C./s; and
holding the cooled cold-rolled steel sheet in a temperature range of 550° C. to 660° C. for 1 minute to 10 minutes.

6. The method for manufacturing a steel sheet for hot stamping according to claim 5 , the method further comprising performing any one of a hot-dip galvanizing process, a galvannealing process, a molten aluminum plating process, an alloyed molten aluminum plating process, and an electroplating process, after the continuous annealing.

7. A method for manufacturing a steel sheet for hot stamping, the method comprising:
hot-rolling a slab containing chemical components according to claim 1 or 2 , to obtain a hot-rolled steel sheet;
coiling the hot-rolled steel sheet which is subjected to hot-rolling;
cold-rolling the coiled hot-rolled steel sheet to obtain a cold-rolled steel sheet; and
continuously annealing the cold-rolled steel sheet which is subjected to cold-rolling to obtain a steel sheet for hot stamping,
wherein, in the hot-rolling, in finish-hot-rolling configured with a machine with 5 or more consecutive rolling stands, rolling is performed by setting a finish-hot-rolling temperature F i T in a final rolling mill F i in a temperature range of (Ac 3 −80)° C. to (Ac 3 +40)° C., by setting time from start of rolling in a rolling mill F i−3 which is a previous machine to the final rolling mill F i to end of rolling in the final rolling mill F i to be equal to or longer than 2.5 seconds, and by setting a hot-rolling temperature F i−3 T in the rolling mill F i−3 to be equal to or lower than F i T+100° C., and after holding in a temperature range of 600° C. to Ar 3 ° C. for 3 seconds to 40 seconds, coiling is performed, and
the continuous annealing includes:
heating the cold-rolled steel sheet to a temperature range of equal to or higher than (Ac 1 −40)° C. and lower than Ac 3 ° C.;
cooling the heated cold-rolled steel sheet from a highest heating temperature to 660° C. at a cooling rate of equal to or less than 10° C./s; and
holding the cooled cold-rolled steel sheet in a temperature range of 450° C. to 660° C. for 20 seconds to 10 minutes.

8. The method for manufacturing a steel sheet for hot stamping according to claim 7 , the method further comprising performing any one of a hot-dip galvanizing process, a galvannealing process, a molten aluminum plating process, an alloyed molten aluminum plating process, and an electroplating process, after the continuous annealing.

Assignees

• Hayashi Kunio
• Aso Toshimitsu
• Tomokiyo Toshimasa
• Nippon Steel & Sumitomo Metal Corp

Inventors

• Hayashi Kunio
• Aso Toshimitsu
• Tomokiyo Toshimasa

Classifications

• C21D8/00 Primary

  Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment (hardening articles or materials formed by forging or rolling with no further heating beyond that required for the formation C21D1/02) · CPC title

• C21D8/0226 Primary

  Hot rolling · CPC title

• C22C38/06

  containing aluminium · CPC title

• C21D8/0263

  following hot rolling · CPC title

• C22C38/40

  with nickel · CPC title