US3788836A - Method of making low nitrogen alloys - Google Patents
Method of making low nitrogen alloys Download PDFInfo
- Publication number
- US3788836A US3788836A US00128531A US3788836DA US3788836A US 3788836 A US3788836 A US 3788836A US 00128531 A US00128531 A US 00128531A US 3788836D A US3788836D A US 3788836DA US 3788836 A US3788836 A US 3788836A
- Authority
- US
- United States
- Prior art keywords
- steel
- nitrogen
- nitrogen content
- porous mass
- vacuum
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D3/00—Diffusion processes for extraction of non-metals; Furnaces therefor
- C21D3/02—Extraction of non-metals
- C21D3/08—Extraction of nitrogen
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
- C21C7/10—Handling in a vacuum
Definitions
- the present invention relates to an improvement in the manufacture of steel of low nitrogen content and more particularly to an improvement in the manufacture of steel of low nitrogen content wherein nitrogen is removed from solid steel having a high nitrogen content,
- the mechanical, physical, corrosion and/ or magnetic properties are dependent upon the amount of nitrogen present therein.
- control of the nitrogen content is especially significant, as corrosion resistance is generally greater at lower nitrogen levels.
- the present invention teaches an improvement in the manufacture of steel of low nitrogen content. More specifically, it teaches an improvement in the manufacture of steel of low nitrogen content wherein nitrogen is removed from solid steel having a high nitrogen content, in an amount of at least 70% of the original content thereof.
- the method of the present invention comprises the steps of: compacting steel having an average thickness of less than 0.25 inch, preferably less than 0.065 inch, into a porous mass; heating the porous mass at a temperature between about 2000 F. and the melting point of the steel, preferably at a temperature between 2200 F. and 2500 F., in a vacuum at a pressure below one mm. Hg, preferably below 10 mm. Hg, for a period of time, generally at least one hour, to remove at least 70%, preferably at least of the nitrogen therefrom; melting the porous mass in a furnace having a controlled atmosphere, generally a vacuum or inert gas; and casting the melt.
- the steel has an average nitrogen content of at least 150 p.p.m., generally at least 250 p.p.m., prior to nitrogen removal, and is quite often present in amounts of at least 1000 lbs. and generally in amounts of at least one ton, and can take various object forms such as machine tool turnings, edge trim and powder. Although it is preferable to compact the steel into one porous mass, it can be compacted into several.
- the final nitrogen content is generally below 50 p.p.m. and preferably below 30.
- the machined chips were compacted into a porous mass using a 400 ton load and subsequently denitrided. Denitridation involved the steps of transferring the porous mass into a vacuum furnace which was pumped down to the best of its capabilities, and heating the mass at a temperature of 2400 F. for 2 hours.
- the steel After denitriding, the steel had a nitrogen content of 45 p.p.m.; a decrease from the original value of 250 p.p.m. which is in excess of 80%.
- the denitrided steel was subsequently: melted under vacuum and brought to a temperature of 2800 R; analyzed; adjusted with vacuum grade additions of silicon, chromium and nickel; subjected to higher pressures as the vacuum furnace was back filled with argon to mm. Hg; adjusted with carbon; and cast.
- the nitrogen content was as high as 197 p.p.m.; a decrease from the original value of 250 p.p.m. of only about 20%. Moreover, a decrease which indicates that substantial nitrogen removal is not present with the diffusional resistance imposed by the 0.25 inch thick plates.
- EXAMPLE III Additional compacted chips from Example I were treated as were the plates of Example II, with the exception that the chips were melted at a faster rate. The chips were present in an amount suflicient for a heat of approximately 7 pounds. After meltdown the nitrogen content was 141 p.p.m. and after casting it was 45 p.p.m. Time from meltdown to casting was approximately 30 minutes.
- the nitrogen content of this example was lower after meltdown than was the nitrogen content of Example II after casting, as the chips did not offer the same resistance to difiusion as did the plates. Furthermore, the high loss in nitrogen from meltdown to casting for this example is attributable to the small laboratory size of the heat. Larger melts offer considerably more resistance to diffusion than do smaller heats as they are accompanied by a smaller melt surface to melt volume ratio, as is shown in the following example.
- EXAMPLE IV Two 12,000 pound melts of stainless steel having a nitrogen content of 290 p.p.m. were vacuum refined at different pressures of 8x10" mm. Hg and 10" mm. Hg.
- the composition of the heats was as follows, in wt percent: 0.035% C., 0.66% Mn, 0.013% P, 0.020% S, 0.36% Si, 18.46% Cr, 8.67% Ni, 0.029% N and balance essentially Fe.
- the first heat was maintained at 8X10 mm. Hg for approximately 50 minutes while the second heat was maintained at 10- mm. Hg for approximately 34 minutes. Neither heat had a nitrogen content much below 250 p.p.m. after treatment.
- Example III A comparison of the results of this example with the results of Example III clearly shows that larger melts offer considerably more resistance to diffusion than do smaller melts.
- the nitrogen level of Example III dropped over 60% between meltdown and casting whereas it was less than in this example, despite the fact that the original melt nitrogen level was considerably higher in this example than in Example III.
- EXAMPLE V Solid stainless steel having a nitrogen content of 340 p.p.m. and a thickness of 0.25 inch was denitrided in a vacuum of from 3 to 10 10- mm. Hg at a temperature of 2300" F. for 12 hours.
- the composition of the steel is as follows, in wt. percent: 0.053% C, 1,80% Mn, 0.017% P, 0.012% S, 0.46% Si, 18.59% Cr, 8.74% Ni, 0.034% N and balance essentially iron.
- the nitrogen content of the steel was 196 p.p.m. on the outer surface and 274 p.p.m. in the center; a decrease from the original value of 340 p.p.m. which is less than 50% of the original value at the surface and less than 20% in the center. Moreover, a decrease does not compare favorably with Example I.
- a process of removing nitrogen form solid steel which comprises the steps of: compacting steel having an average thickness of less than 0.25 inch and an average nitrogen content of at least 150 p.p.m. into a porous mass; heating said porous mass at a temperature between about 2000 F. and the melting point of said steel, in a vacuum at a pressure below one mm. Hg, for a period of time sufiicient to remove at least of the nitrogen from said solid steel, said period of time being at least one hour; subsequently melting said porous mass in a furnace having a controlled atmosphere; and casting the melt.
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- Mechanical Engineering (AREA)
- Treatment Of Steel In Its Molten State (AREA)
Abstract
Description
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US12853171A | 1971-03-26 | 1971-03-26 |
Publications (1)
Publication Number | Publication Date |
---|---|
US3788836A true US3788836A (en) | 1974-01-29 |
Family
ID=22435784
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US00128531A Expired - Lifetime US3788836A (en) | 1971-03-26 | 1971-03-26 | Method of making low nitrogen alloys |
Country Status (1)
Country | Link |
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US (1) | US3788836A (en) |
Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPS5129313A (en) * | 1974-09-06 | 1976-03-12 | Nippon Steel Corp | Nanshitsudekakosei taishokuseinosuguretaoosutenaitogatasutenresuko |
US4154602A (en) * | 1977-01-31 | 1979-05-15 | Kawasaki Steel Corporation | Method of denitriding a high chromium molten steel with a minimum chromium loss |
US4170467A (en) * | 1977-01-31 | 1979-10-09 | Kawasaki Steel Corporation | Method for producing high chromium steels having extremely low carbon and nitrogen contents |
-
1971
- 1971-03-26 US US00128531A patent/US3788836A/en not_active Expired - Lifetime
Cited By (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPS5129313A (en) * | 1974-09-06 | 1976-03-12 | Nippon Steel Corp | Nanshitsudekakosei taishokuseinosuguretaoosutenaitogatasutenresuko |
JPS552465B2 (en) * | 1974-09-06 | 1980-01-21 | ||
US4154602A (en) * | 1977-01-31 | 1979-05-15 | Kawasaki Steel Corporation | Method of denitriding a high chromium molten steel with a minimum chromium loss |
US4170467A (en) * | 1977-01-31 | 1979-10-09 | Kawasaki Steel Corporation | Method for producing high chromium steels having extremely low carbon and nitrogen contents |
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Legal Events
Date | Code | Title | Description |
---|---|---|---|
AS | Assignment |
Owner name: ALLEGHENY LUDLUM CORPORATION Free format text: CHANGE OF NAME;ASSIGNOR:ALLEGHENY LUDLUM STEEL CORPORATION;REEL/FRAME:004779/0642 Effective date: 19860805 |
|
AS | Assignment |
Owner name: PITTSBURGH NATIONAL BANK Free format text: SECURITY INTEREST;ASSIGNOR:ALLEGHENY LUDLUM CORPORATION;REEL/FRAME:004855/0400 Effective date: 19861226 |
|
AS | Assignment |
Owner name: PITTSBURGH NATIONAL BANK Free format text: ASSIGNMENT OF ASSIGNORS INTEREST. RECORDED ON REEL 4855 FRAME 0400;ASSIGNOR:PITTSBURGH NATIONAL BANK;REEL/FRAME:005018/0050 Effective date: 19881129 |