US3356493A

US3356493A - Alloys for nitriding steel and method of nitriding steel

Info

Publication number: US3356493A
Application number: US425922A
Authority: US
Inventors: Danis Francois; Cloppet Raymond; Montanteme Jean
Original assignee: Individual
Current assignee: Societe dElectro Chimie dElectro Metallurgie et des Acieries Electriques Dugine SA SECEMAU
Priority date: 1964-01-22
Filing date: 1965-01-15
Publication date: 1967-12-05
Anticipated expiration: 1984-12-05
Also published as: GB1036502A; DE1238221B; FR1391109A; NL6500494A; ES308236A1; BE658099A

Description

United States Patent 5 Claims. (Cl. 75-434 ABSTRACT OF THE DISCLOSURE An alloy for nitriding steel by introducing said alloy into the melting steel, the alloy comprising 40.0-90.0% by weight manganese, 0.50-10.0% by weight aluminum, 0.50-10.0% by weight nitrogen, and about and up to 8%. by weight carbon.

This invention relates to a family of alloys which are introduced into molten steel and impart to the steel a nitrogen content in predictable, given amounts.

It is well-known that during production of mild and dead soft steels, steel is charged with oxygen in an inverse ratio to its carbon content, and that simultaneous presence of oxygen and carbon leads to the formation of carbon monoxide which escapes from the molten steel and thereby generates the elrervescence or rimming action in the molten steel.

It is also wellknown that, if oxygen is fixed by a stronger reducer than carbon, such as silicon or aluminum, the rimming action may be slowed down, even suppressed. Therefore, it is possible to control the rimming action and produce killed or semi-killed steels.

This rimming action occurs irrespective of the steel making employed including the new processes which use pure oxygen. However, while in the prior steel making processes the obtained steels are highly charged with nitrogen, whose excess is sometimes inconvenient, the steels obtained by the pure oxygen processes generally contain a low amount of nitrogen, below 0.005%, even below 0.002% which is not always advantageous.

Certain dead soft steels used in the production of tin plate must be somewhat stifi and accordingly require nitrogen contents higher than 0.010%

It is known to add this nitrogen through different nitrided products. For example, use of calcium cyanamide has been proposed but this compound presents the disadvantage, when hot in the presence of iron, alkaline carbonates and hydrgen (which elements are often present in the slag), to be partly transformed into hydrocyanic acid and cyanide and thereby be dangerous to personnel. Besides, with calcium cyanamide, the nitrogen yield is relatively low: 10% to 40%, and most irregular between different casting operations.

To obviate the disadvantages and risks of calcium cyanamide, it is also known to use nitrided ferroalloys and in particular nitrided ferromanganese-which effect good nitrogen yields in production of nitrogen stainless and special steels.

However, in production of mild and dead soft steels, while nitrogen yields are more predictable or regular with nitrided ferroalloys than with the other nitrogen products previously proposed, the amounts of yields are not always very high, especially in the case of rimmed steels. This phenomenon has been explained by the fact that the oxygen dissolved in steel forms an adsorption layer which slows down dissolution of the nitrogen into the iron.

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The prejudical effect of this gaseous layer might be reduced by introduction of nitrogen combined with a strong reducing agent such as aluminum. However, due to its lightness in weight, aluminum nitride is unsuitable because it floats on top of the metal surface, is not wetted by the steel bath and remains more or less coated with slag. The result is an extremely low and most irregular nitrogen yield in the steel.

We have found that if aluminum is alloyed with manganese, a very good nitrogenation of this alloy is obtained whatever its carbon content. Furthermore, the dissolution speed of such nitrided alloys in molten steel is very high and leads to most regular and predictable nitrogen content in the steel with satisfactory yields.

Our present invention relates to:

1) Complex alloys which contain manganese, aluminum and nitrogen,

(2) A method of nitriding killed, semi-killed and rimmed steels and even for nitriding molten steels obtained during welding or alumino-thermic operations.

These alloys contain:

They may also contain other components or impurities generally found in industrial manganese alloys.

The alloys are relatively dense and they are wetted by liquid steels at normal steel making temperatures and are most soluble therein. Their melting point is definitely lower than that of steel. Significantly, the presence of aluminum renders the nitrogen dissolution in steel easier and reduces the nitrogen losses during the dissolution.

The alloys are made by known industrial processes and they are utilized as homogeneous, crushed or sintered lumps. They are added to the steel either in the furnace before casting, or in the runner, the feeding head sprue, or in the ladle before or during casting.

The nitrogen yield during its introduction into the steel is very high and remarkably regular for similar operating conditions.

Among the alloys, we have found particularly satisfactory those containing:

Percent Mn 70 to A1 2 to 4 N2 4 t0 6 C 0 to 3 Si 0 to 2 Fe Balance The following are non-limitative examples of our in- A rimmed steel was nitrided with this alloy to obtain a steel of the following composition:

Percent C V 0.08 to 0.10 Mn 0.40 to 0.50

N 0.010 to 0.012

For that purpose, 1.7 kg. ofthe alloy per metric ton of liquid steel, was introduced into the liquid steel. The alloy was in a sintered and crushed form, as metallic boxes containing 500 g. of nitrogen, and was added together with the normal complementary additions of ferromanganese.

The steel, before addition of the alloy, had the following composition:

Percent The final composition of the steel was:

Percent C 0.095

The nitrogen yield in the steel was 81%.

Example 2 A killed steel was also nitrided to obtain a steel of the following composition:

Percent C 0.10to 0.13

Mn 1.40 to 1.60

Si 0.30 to 0.50

Al 0.030 to 0.040

N 0.020 to 0.025

Into the steel to be nitrided was introduced 4 kg. of the alloy of the first example, together with the complementary additions of refined ferromanganese, silicon and aluminum.

The molten steel, prior to addition of the-alloy, contained:

4 The final composition of the alloy was:

Percent C 0.13 Mn 1.54

Al 0.035 N 0.022

The nitrogen yield in the steel was 89%.

While we have described preferred embodiments of our invention, it may be otherwise embodied within the scope of the appended claims.

We claim:

1. A metal alloy consisting essentially of about 40.0- 90.0% by weight manganese, about 0.50-10.0% by weight aluminum, about 0.50-10.0% by weight nitrogen and up to 8% by weight carbon.

2. A metal alloy for nitriding steel consisting essentially of about-70.0-90.0% by weight manganese, about 2.04.0% by weight aluminum, about 4.06.0% by weight nitrogen, up to 3% by weight carbon, up to 2% by weight silicon and balance iron.

3. A method of nitriding steel comprising introducing into molten steel an alloy consisting essentially of about 40.0-90.0% by weight manganese, about 0.50-10.0% by weight aluminum, about 0.50-10.0% by weight nitrogen and up to 8% by weight carbon.

4. A method of nitriding steel comprising introducing into molten steel an alloy consisting essentially of 70.0- 90.0% by weight manganese, about 2.04.0% by weight aluminum, about 4.06.0% by weight nitrogen, up to 3% by weight carbon, up to 2% by weight silicon and balance iron.

5. The method of claim 3 characterized by said steel being one of a medium carbon and of a low carbon steel.

References Cited UNITED STATES PATENTS 415,832 11/1889 Cowleset al. -134 2,696,433 12/1954 Tanczyn 75130.5 3,304,175 2/1967 Madsen et al. 75--134 HYLAND BIZOT, Primary Examiner;

DAVID L. RECK, Examiner. RICHARD O, DEAN, Assistant Examiner,

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,356,493 December 5, 1967 Francois Danis et a1.

ror appears in the above numbered pat- It is hereby certified that er the said Letters Patent should read as ent requiring correction and that corrected below.

Column 2, line 25, for "20"1ead 10 Signed and sealed this 17th day of December 1968.

(SEAL) Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer

Claims

1. A METAL ALLOY CONSISTING ESSENTIALLY OF ABOUT 40.090.0% BY WEIGHT MANGANESE, ABOUT 0.50-10.0% BY WEIGHT ALUMINUM, ABOUT 0.50-10.0% BY WEIGHT NITROGEN AND UP TO 8% BY WEIGHT CARBON.