FERRITIC STAINLESS STEEL AND PROCESS FOR PRODUCING SAME

• US 20170349995A1
• Filed: 11/17/2015
• Published: 12/07/2017
• Est. Priority Date: 12/24/2014
• Status: Active Grant

• Current Assignee: JFE Steel Corporation (JFE Holdings Incorporated)
• Original Assignee: JFE Steel Corporation (JFE Holdings Incorporated)
• Inventors: FUKUDA, Kunio, ISHIKAWA, Shin, FUJISAWA, Mitsuyuki, YAMAUCHI, Katsuhisa, KAMI, Chikara
• Granted Patent: US 10,458,013 B2
• Time in Patent Office: Days
• CPC Class Codes: C21D 1/06 Surface hardening
• CPC Class Codes: C21D 1/76 Adjusting the composition of the atmosphere
• CPC Class Codes: C21D 9/46 for sheet metals
• CPC Class Codes: C22C 38/00 Ferrous alloys, e.g. steel alloys cast-iron alloys C22C37/00
• CPC Class Codes: C22C 38/001 containing N
• CPC Class Codes: C22C 38/002 containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
• CPC Class Codes: C22C 38/02 containing silicon
• CPC Class Codes: C22C 38/04 containing manganese
• CPC Class Codes: C22C 38/06 containing aluminium
• CPC Class Codes: C22C 38/42 with copper
• CPC Class Codes: C22C 38/44 with molybdenum or tungsten
• CPC Class Codes: C22C 38/46 with vanadium
• CPC Class Codes: C22C 38/48 with niobium or tantalum
• CPC Class Codes: C22C 38/50 with titanium or zirconium
• CPC Class Codes: C22C 38/54 with boron
• CPC Class Codes: C23C 8/26 of ferrous surfaces

Abstract

Provided is a ferritic stainless steel having a chemical composition containing, in mass %: 0.003% to 0.025% of C; 0.05% to 1.00% of Si; 0.05% to 1.00% of Mn; 0.04% or less of P; 0.01% or less of S; 16.0% to 23.0% of Cr; 0.20% to 0.80% of Cu; 0.05% to 0.60% of Ni; 0.20% to 0.70% of Nb; 0.005% to 0.020% of N; and the balance being Fe and incidental impurities, in which a nitrogen-enriched layer is present that has a nitrogen concentration peak value of 0.03 mass % to 0.30 mass % at a depth of within 0.05 μm of a surface of the steel.

Claims

1. A ferritic stainless steel comprising

a chemical composition containing, in mass %:

0.003% to 0.025% of C;

0.05% to 1.00% of Si;

0.05% to 1.00% of Mn;

0.04% or less of P;

0.01% or less of S;

16.0% to 23.0% of Cr;

0.20% to 0.80% of Cu;

0.05% to 0.60% of Ni;

0.20% to 0.70% of Nb;

0.005% to 0.020% of N; and

the balance being Fe and incidental impurities, wherein

a nitrogen-enriched layer is present that has a nitrogen concentration peak value of 0.03 mass % to 0.30 mass % at a depth of within 0.05 μ

m of a surface of the steel.

2. The ferritic stainless steel of claim 1, wherein

the chemical composition further contains, in mass %, one or more of:

0.05% to 0.20% of Mo;

0.01% to 0.15% of Al;

0.01% to 0.15% of Ti;

0.01% to 0.20% of V;

0.0003% to 0.0030% of Ca; and

0.0003% to 0.0030% of B.

3. A process for producing the ferritic stainless steel of claim 1, the process comprising:

hot rolling a slab having the chemical composition of claim 1 to form a hot-rolled sheet;

optionally performing hot-rolled sheet annealing on the hot-rolled sheet; and

performing a combination of cold rolling and annealing on the hot-rolled sheet one or more times,

wherein a cold-rolled sheet after subjection to final cold rolling is heated in final annealing with a dew point of an atmosphere in a temperature range of 600°

C. to 800°

C. being −

20°

C. or lower, and subjected to a nitrogen-enriched layer forming treatment at a temperature of 900°

C. or higher in an atmosphere of −

20°

C. or lower in dew point and 5 vol % or more in nitrogen concentration.

4. A process for producing the ferritic stainless steel of claim 2, the process comprising:

hot rolling a slab having the chemical composition of claim 2 to form a hot-rolled sheet;

optionally performing hot-rolled sheet annealing on the hot-rolled sheet; and

performing a combination of cold rolling and annealing on the hot-rolled sheet one or more times,

wherein a cold-rolled sheet after subjection to final cold rolling is heated in final annealing with a dew point of an atmosphere in a temperature range of 600°

C. to 800°

C. being −

20°

C. or lower, and subjected to a nitrogen-enriched layer forming treatment at a temperature of 900°

C. or higher in an atmosphere of −

20°

C. or lower in dew point and 5 vol % or more in nitrogen concentration.