Production method for grain-oriented electrical steel sheet and primary recrystallized steel sheet for production of grain-oriented electrical steel sheet

Patent metadata

Field	Value
Publication number	US-9953752-B2
Application number	US-201314650378-A
Country	US
Kind code	B2
Filing date	Dec 25, 2013
Priority date	Dec 28, 2012
Publication date	Apr 24, 2018
Grant date	Apr 24, 2018

Abstract

A method for producing grain-oriented electrical steel sheets includes subjecting a steel slab to hot rolling to obtain a hot rolled sheet, the steel slab having a composition consisting of, by mass % or mass ppm, C: 0.08% or less, Si: 2.0% to 4.5% and Mn: 0.5% or less, S, Se, and O: less than 50 ppm each, sol.Al: less than 100 ppm, N: 80 ppm or less, and the balance being Fe and incidental impurities, and satisfying the relation of sol.Al (ppm)−N (ppm)×(26.98/14.00)≤30 ppm; then subjecting the hot rolled sheet to annealing and rolling to obtain a cold rolled sheet; then subjecting the cold rolled sheet to nitriding treatment, under specific condition, before, during or after primary recrystallization annealing; then applying an annealing separator on the cold rolled sheet; and subjecting the cold rolled sheet to secondary recrystallization annealing.

First claim

The invention claimed is:

1. A production method for a grain-oriented electrical steel sheet, the method comprising:
subjecting a steel slab to hot rolling, without re-heating or after re-heating, to obtain a hot rolled sheet, the steel slab having a composition comprising, by mass % or mass ppm:
C: 0.08% or less,
Si: 2.0% to 4.5%,
Mn: 0.5% or less,
S: less than 50 ppm,
Se: less than 50 ppm,
O: less than 50 ppm,
sol.Al: less than 100 ppm,
N: 80 ppm or less, and
the balance being Fe and incidental impurities,
where the relationship sol.Al (ppm)−N (ppm)×(26.98/14.00)≤30 ppm is satisfied;

then subjecting the hot rolled sheet to annealing and rolling to obtain a cold rolled sheet of final sheet thickness;
then subjecting the cold rolled sheet to nitriding treatment, with a nitrogen increase (ΔN) being specified by the following formula (1) or (2), before, during or after primary recrystallization annealing:
when sol.Al−N×(26.98/14.00)≤0, 50 ppm≤ΔN≤1000 ppm  (1),

when 0<sol.Al−N×(26.98/14.00)≤30,

(N−sol.Al×14.00/26.98+100)≤ΔN≤(N−sol.Al×14.00/26.98+1000)  (2);

then applying an annealing separator on the cold rolled sheet; and
allowing N to diffuse into a steel substrate during a heating process of a secondary recrystallization, so as to precipitate silicon nitride at grain boundaries with a precipitate size of 100 nm or more without containing Al, in order to provide an inhibiting force for normal grain growth,
wherein a staying time in a temperature range of 300° C. to 800° C. in the heating process is 5 hours or more,
the nitriding treatment is performed at a temperature of 800° C. or lower, and
86% or more of the nitrogen introduced into the cold rolled steel sheet localizes in a surface region of 3 μm thick in the nitriding treatment.

2. The production method for a grain-oriented electrical steel sheet according to claim 1 , wherein the steel slab further comprises, by mass %, one or more of Ni: 0.005% to 1.50%, Sn: 0.01% to 0.50%, Sb: 0.005% to 0.50%, Cu: 0.01% to 0.50%, Cr: 0.01% 1.50%, P: 0.0050% to 0.50%, Mo: 0.01% to 0.50% and Nb: 0.0005% to 0.0100%.

Assignees

• Jfe Steel Corp

Inventors

• Shingaki Yukihiro
• Yamaguchi Hiroi
• WAKISAKA Yuiko
• Matsuda Hiroshi
• Terashima Takashi

Classifications

• H01F1/16

  in the form of sheets (H01F1/147 takes precedence) · CPC title

• C21D6/008

  containing Si · CPC title

• C22C38/12

  containing tungsten, tantalum, molybdenum, vanadium, or niobium · CPC title

• C21D8/1272

  Final recrystallisation annealing · CPC title

• C22C38/22

  with molybdenum or tungsten · CPC title