WO1995029270A1

WO1995029270A1 - Method of treating titanium parts

Info

Publication number: WO1995029270A1
Application number: PCT/US1995/004763
Authority: WO
Inventors: Douglas W. Fay, Sr.
Original assignee: Sturm Ruger and Co Inc
Current assignee: Sturm Ruger and Co Inc
Priority date: 1994-04-25
Filing date: 1995-04-18
Publication date: 1995-11-02
Anticipated expiration: 1996-10-25
Also published as: EP0763143A1; JPH10503551A; KR970702386A; CN1151192A; EP0763143A4

Abstract

A method of treating titanium-containing parts and the parts so-treated are disclosed. The treatment includes placing the parts in a furnace chamber (12) having a gaseous atmosphere of 15-25 % carbon dioxide, 30-50 % nitrogen and 30-50 % hydrogen. The atmosphere is at a temperature of between 1450-1850 °F and the treatment lasts for 5-60 minutes. Parts experience improved hardness, strength, and wear resistance.

Description

METHOD OF TREATING TITANIUM PARTS

Background Of The Invention

It has been proposed to heat treat metals in hydrogen and nitrogen atmospheres (U.S. Patent No. 3,211,590) or in an ammonia and methane atmosphere (U.S. Patent No. 3,891,473). The treatment of titanium in a neutral atmosphere of helium has also been suggested (U.S. Patent No. 4,098,623).

No prior method has included titanium parts treatment in an atmosphere of nitrogen, hydrogen and carbon monoxide.

Low carbon steels and iron have been treated in atmospheres of 20% carbon monoxide, 40% hydrogen, and 40% nitrogen and gas. Treatment of titanium alloy specimens using propane-argon mixtures or methane- argon mixtures has been reported for improving resistance to galling (Transactions of the ASM Vol. 46, pp. 257, 267-70 (1953).

Summary Of The Invention

Broadly, the present invention comprises a method of treating titanium-containing parts having the r.teps of creating in a furnace at atmospheric pressure mixture of nitrogen, methanol and optionally natural gas or propane, causing such mixture to obtain an equilibrium; then introducing the titanium parts into the furnace and finally reducing the furnace temperature to a range of 1450°F. to 1850F⁰ for a time period of between five (5) and six hundred (600) minutes. It is a feature of the method that the surface area of the titanium parts so treated are very hard and gall resistant.

It is a feature that a coating caused to form on and at the alloy surface during treatment consists predominantly of titanium oxides with regions of oxynitrides and at times some carbonitrides.

Brief Description Of The Drawings

Fig. 1 is a partially sectioned elevational view of the apparatus used to carry out the present inventive method.

Description Of The Preferred Embodiment

In Fig. 1, apparatus 10 includes furnace 11, furnace chamber box 12 and titanium parts basket 14 supported by blocks 15. Chamber 12 has three gaseous conduit inlets 16, 17, and 18. Conduit 16 supplies methanol from methanol tank 21 to sparger 22 with shaft. Conduit 17 supplies natural gas from gas tank 23 and conduit 18 supplies nitrogen from nitrogen tank 24. Fan 27 with shaft provides for mixing and circulation of gases in chamber 12 and exhaust chimney 29 (not shown) conducts exhaust gases from chamber 12. Sensor 37 measures the temperature, oxygen and gas components in chamber 12. Process monitoring unit 31 controls valves 33, 34, 35 in conduits 16, 17, and 18 respectively to control the mixture in chamber 12.

The combination of the gases in chamber box 12 creates a hydrocarbon inert gas mixture which is varied to achieve the metallurgical layer characteristics of the parts desired and is composed of an atmosphere of carbon dioxide between 15-25%, hydrogen between 30-50% and nitrogen between 30-50% using, as supply, gaseous nitrogen, methanol, and propane or natural gas. Gaseous percentages are by volume. Process control equipment employed may include but is not limited to oxygen measuring and control. Atmosphere characterization equipment may be used but is not necessary.

Parts which are treatable using the present invention are 100% titanium or alloys of titanium including:

Allov A

Component Percent

Titanium 90

Aluminum 6

Vanadium 4

Allov B

Component Percent

Titanium 94.5

Aluminum 3

Vanadium 2.5

Allov C

Component Percent

Titanium 90

Zirconium 4

Tin 2

Molybdenum 6

Aluminum 6

Percentages of the alloys are by weight. Tests run on cast Ti-6AL-4V alloys treated by the present invention and untreated produced the following results: 1. Mechanical Properties

Surface Tensile Strength

Condition Hardness, Hk25 UTS KS1 YS,KS1 %EL

Untreated 350 - 380 132.7 114.3 10.2

Treated 980 - 1300 137.2 . 121.7 12.2

The surface hardness of treated samples was significantly higher than that of the untreated samples with the balance of properties essentially similar.

2. Wear Resistance

Abrasive testing using a #10 grit aluminum oxide media indicated the treated samples wore less than untreated samples.

Condition % Wear Treated .3774 Untreated .4533

Example A batch of firearm triggers made of Alloy A were placed in a furnace in which nitrogen, methanol and natural gas are introduced in proportions of nitrogen: 40% (gas) ; methanol: 58-60% (liquid); and propane: 0-2% (gas) to create in the furnace a gaseous atmosphere of:

Constituent Percent Carbon dioxide 15- -25 Hydrogen 30- -50 Nitrogen 30- -50 The gaseous atmosphere was at or near atmospheric pressure. The treatment atmosphere is a complex mixture of: nitrogen C0₂

CO hydrogen oxygen methane and water.

This mixture should exist in equilibrium in the furnace. Methane dissociates to form hydrogen and carbon dioxide to accomplish the parts treatment including carburizing of the parts surfaces.

Equilibrium is obtained upon completion of reactions of the mixture in the furnace. An equilibrium reaction equation is 2N₂+CH₃OH *+ 2N₂+2H₂+CO. Equilibrium determination is accomplished by indirect means such as the analysis of the implanted or diffused carbon level in the material surface treated. Other methods include the measurement of the carbon potential by the oxygen probe located in the furnace which indicates the carbon potential by an algorithm assuming a consistent level of CO gas in the furnace atmosphere. Carbon potential is largely equivalent to a function of the oxygen content assuming a constant CO content. If the CO content changes, the same oxygen % will yield a different carbon potential. Again, an algorithm is used to put all the variables in perspective. The control of carbon by maintaining a consistent atmosphere and then using oxygen % as a control parameter is very important. A principle of control of the process is controlling the proportions of gases flowing into the furnace.

Claims

I CLAIM :

1. A method for treating titanium-containing parts comprising 1) introducing into the furnace box a mixture of component gases in turn comprising a) 30-50% nitrogen; b) 30-50% hydrogen; and c) 15-25% carbon dioxide

2) introducing titanium parts into a furnace box having air therein;

3) sealing the box from the outside atmosphere; and 4) monitoring and controlling the temperature in the box at between 1450F⁰ and 1850F°.

2. The method of claim 1 in which the introduction of component gases is controlled so that the furnace atmosphere comprises by volume: i) 30-50% nitrogen; ii) 30-50% hydrogen; and iii) 15-25% carbon dioxide.

3. A titanium-containing part treated by the method of claim 1.