Cold-rolled steel sheet, method of manufacturing cold-rolled steel sheet, automobile member and facility for manufacturing cold-rolled steel sheet

Patent metadata

Field	Value
Publication number	US-2017306507-A1
Application number	US-201515507601-A
Country	US
Kind code	A1
Filing date	Aug 12, 2015
Priority date	Sep 2, 2014
Publication date	Oct 26, 2017
Grant date	—

Abstract

A cold-rolled steel sheet has excellent chemical convertibility and excellent corrosion resistance after coating. A method of manufacturing a cold-rolled steel sheet includes first pickling applied to a steel sheet which is continuously annealed after cold rolling, second pickling applied to the steel sheet subsequently and, thereafter, neutralizing treatment applied to the steel sheet using an alkaline solution.

First claim

1 .- 19 . (canceled)

20 . A method of manufacturing a cold-rolled steel sheet, wherein first pickling is applied to a steel sheet which is continuously annealed after cold rolling, second pickling is applied to the steel sheet subsequently and, thereafter, neutralizing treatment is applied to the steel sheet using an alkaline solution.

21 . The method according to claim 20 , wherein the alkaline solution has pH of 9.5 or more, and one or two or more selected from a group consisting of sodium hydroxide, sodium carbonate, sodium hydrogen carbonate, orthophosphate and condensed phosphate are mixed into the alkaline solution.

22 . The method according to claim 20 , wherein the neutralizing treatment is performed in a state that a temperature of the alkaline solution is set to 20 to 70° C., and a treatment time is set to 1 to 30 seconds.

23 . The method according to claim 20 , wherein the first pickling is performed using any one of a nitric acid, a hydrochloric acid, a hydrofluoric acid, a sulfuric acid and a mixture of two or more thereof.

24 . The method according to claim 20 , wherein the first pickling is performed using either one of the following acidic solutions (a) and (b):
(a) the acidic solution containing a nitric acid and a hydrochloric acid, wherein concentration of the nitric acid is more than 50 g/L and 200 g/L or less, a ratio R1 of the concentration of the hydrochloric acid to a concentration of the nitric acid (hydrochloric acid/nitric acid) is set to 0.01 to 0.25, and a concentration of Fe ion is set to 3 to 50 g/L. (b) the acidic solution containing a nitric acid and hydrofluoric acid, wherein concentration of the nitric acid is more than 50 g/L and 200 g/L or less, a ratio R2 of the concentration of the hydrofluoric acid to a concentration of the nitric acid (hydrofluoric acid/nitric acid) is set to 0.01 to 0.25, and a concentration of Fe ion is set to 3 to 50 g/L.

25 . The method according to claim 20 , wherein a non-oxidizing acid is used in the second pickling.

26 . The method according to claim 25 , wherein the non-oxidizing acid is any one of a hydrochloric acid, a sulfuric acid, a phosphoric acid, a pyrophosphoric acid, a formic acid, an acetic acid, a citric acid, a hydrofluoric acid, an oxalic acid, and an acid which is a mixture of two or more of the acids.

27 . The method according to claim 25 , wherein the non-oxidizing acid is any one of hydrochloric acid having a concentration of 0.1 to 50 g/L, a sulfuric acid having a concentration of 0.1 to 150 g/L and an acid which is a mixture of a hydrochloric acid having a concentration of 0.1 to 20 g/L and a sulfuric acid having a concentration of 0.1 to 60 g/L.

28 . The method according to claim 20 , wherein the second pickling is performed in a state that a temperature of the acidic solution is set to 20° C. to 70° C., and a pickling time is set to 1 to 30 seconds.

29 . The method according to claim 20 , wherein the steel sheet contains, as a component of the composition thereof, 0.5 to 3.0 mass % Si.

30 . The method according to claim 29 , wherein the steel sheet further contains, as components of the composition thereof: 0.01 to 0.30 mass % C, 1.0 to 7.5 mass % Mn, 0.05 mass % or less P, 0.01 mass % or less S, 0.06 mass % or less Al, and Fe and unavoidable impurities as a balance.

31 . The method according to claim 30 , wherein the steel sheet further contains, as components of the composition thereof, one or two or more of elements selected from a group consisting of 0.3 mass % or less Nb, 0.3 mass % or less Ti, 0.3 mass % or less V, 1.0 mass % or less Mo, 1.0 mass % or less Cr, 0.006 mass % or less B and 0.008 mass % or less N.

32 . The method according to claim 30 , wherein the steel sheet further contains, as components of the composition thereof, one or two or more of elements selected from a group consisting of 2.0 mass % or less Ni, 2.0 mass % or less Cu, 0.1 mass % or less Ca, and 0.1 mass % or less REM.

33 . A cold-rolled steel sheet manufactured by the method of manufacturing a cold-rolled steel sheet described in claim 20 , wherein an Si containing oxide layer formed on a surface layer of the steel sheet is removed, and a surface coverage of an iron-based oxide existing on a surface of the steel sheet is 40% or less.

34 . The cold-rolled steel sheet according to claim 33 , wherein a maximum thickness of the iron-based oxide existing on the surface of the steel sheet is 150 nm or less.

35 . An automobile member formed by using the cold-rolled steel sheet described in claim 33 .

36 . A facility for manufacturing a cold-rolled steel sheet, wherein a first pickling device, a second pickling device, an acid neutralizing treatment device, and a drying device are arranged in this order on a rear stage of a continuous annealing device.

37 . The facility according to claim 36 , further comprising a water cleaning device arranged on a rear stage of the first pickling device, the second pickling device, and the acid neutralizing treatment device.

38 . The facility according to claim 36 , further comprising a water cleaning spray device arranged on an inlet side and/or an outlet side of one or more devices selected from a group consisting of the first pickling device, the second pickling device, the acid neutralizing treatment device and the water cleaning device.

Assignees

• Jfe Steel Corp

Inventors

• Masuoka Hiroyuki
• Taira Shoichiro
• Furuya Shinichi

Classifications

• C22C38/005

  containing rare earths, i.e. Sc, Y, Lanthanides · CPC title

• C22C38/14

  containing titanium or zirconium · CPC title

• C22C38/04

  containing manganese · CPC title

• C22C38/02

  containing silicon · CPC title

• C23G1/085

  solutions containing HNO3 · CPC title