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US4466842A
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Ferritic steel having ultra-fine grains and a method for producing the same
Assignee: Nippon Steel Corp
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Filing: 1983-04-01
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Granted: 1984-08-21
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Expires: 2003-04-01
Abstract
Abstract A novel hot-rolled ferritic steel composed of 70% or more of equiaxed ferrite grains having an ultra-fine grain size of 4 mu m or less. This steel is produced by a hot working at approximately the Ar3 point and by one or more passes of the hot working having a total reduction ratio of at least 75%. When a plurality of passes is carried out, the time between passes is less than one second. Due to hot working, dynamic transformation of austenite and/or dynamic recrystallization of ferrite takes place. The total reduction ratio may be at least 35% for a high purity steel.
Inventors
- 👤 Hiroshi Yada
- 👤 Yoshikazu Matsumura
- 👤 Koe Nakajima
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-08 20:15
CPC Classifications
C; C21; C21D; C21D8/00; C21D8/02; C21D8/0221; C21D8/0226; C22; C22C; C22C38/00; C22C38/04; C21D2211/00; C21D2211/002; C21D2211/005; C21D2211/008
Claims Analysis
Total Claims: 7
Claim 1
Independent Claim
110 words
A ferritic steel containing from 0.02% to 0.3% of carbon and from 0.1% to 2.0% of manganese, the balance being iron and unavoidable impurities, being essentially free of niobium, tantalum, molybdenum, and tungsten, being composed of 70% or more of ferrite at a hot-worked state, a ferrite structure consisting of equiaxed ferrite crystal grains having an average grain diameter of 4 μm or less, secondary phases other than ferrite phases being composed of at least one phase selected from the group consisting of a pearlite, a martensite, a retained austenite, a carbide, and a bainite, and said ferrite crystal grains having essentially no orientation due to elongation thereof by working.
Claim 2
Dependent Claim
110 words
A ferritic steel containing from 0.02% to 0.3% of carbon and from 0.1% to 2.0% of manganese, the balance being iron and unavoidable impurities, being essentially free of niobium, tantalum, molybdenum, and tungsten, being composed of 70% or more of ferrite at a hot-worked state, a ferrite structure consisting of equiaxed ferrite crystal grains having an average grain diameter of 4 μm or less, secondary phases other than ferrite phases being composed of at least one phase selected from the group consisting of a pearlite, a martensite, a retained austenite, a carbide, and a bainite, and said ferrite crystal grains having essentially no orientation due to elongation thereof by working.
Claim 3
Dependent Claim
43 words
A ferritic steel according to claim 1, wherein said equiaxed ferrite crystal grains are formed, during said working, by a dynamic transformation of an austenite phase or by a dynamic transformation of an austenite phase and a dynamic recrystallization of a ferrite phase.
Claim 4
Dependent Claim
16 words
A ferritic steel according to claim 1, wherein the composition of ferrite is 80% or more.
Claim 5
Dependent Claim
28 words
A ferritic steel according to claim 1, wherein said secondary phases are composed of at least one phase selected from the group consisting of said bainite and martensite.
Claim 6
Dependent Claim
79 words
A method for producing a ferritic steel according to claim 1, wherein hot-working is carried out during cooling from a temperature higher than the Ac 3 point and in that during a final stage of hot-working said steel is subjected at a temperature of from (Ar 1 +50° C.) to (Ar 3 +100° C.) and for less than one second to one or more workings, the total reduction ratio of the one or more workings being at least 50%.
Claim 7
Dependent Claim
41 words
A method according to claim 5, wherein a forced cooling at a cooling rate of 20° C./second or more is carried out during cooling after completion of said hot-working, at least in a high temperature region of 600° C. or more.
References Cited (Backward Citations)
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1987-08-21 | 1988-02-20 | 1988-08-21 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1991-08-21 | 1992-02-20 | 1992-08-21 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1995-08-21 | 1996-02-20 | 1996-08-21 | $7700.00 | Window Closed / Lapsed |