JPH03166343A - Heat treatment of metal - Google Patents

Abstract

PURPOSE: To enable economically advantageous annealing by bringing impure oxygen into nitrogen contact reaction with excessive hydrogen, when producing an annealing atmosphere of a metal harder to be oxidized than iron at a site from non extra low temp. produced nitrogen.

CONSTITUTION: For example, when nitrogen is separated from air by pressure self absorption at a plant 2, the nitrogen containing 5-3vol% oxygen impurity is generally produced. This nitrogen flow is passed in a catalyst reactor 4, and oxygen impurity in nitrogen flow is reacted with the hydrogen stoichiometrically a little excessive at a reaction temp. by using a Pd or Pt catalyst. The produced gas mixture consists of nitrogen, hydrogen and water vapor. This produced gas mixture is introduced into a heat treatment furnace 6 to anneal a metal product of copper, bronze, etc., harder to be oxidized than iron. By this method, gloss annealing is made possible.

COPYRIGHT: (C)1991,JPO

Description

[Detailed description of the invention] The present invention relates to heat treatment of metals.

In particular, it relates to heat treatment of metals that are more difficult to oxidize than iron. Such metals include cobalt, nickel, lead, copper, palladium, silver, gold, alloys of these metals, and alloys of mercury.

When manufacturing articles made of metals that are less susceptible to oxidation than iron, it is generally desirable to subject the articles to an annealing process. Although the product is relatively resistant to oxidation, it is nevertheless necessary to maintain a reducing or non-oxidizing atmosphere in the furnace used to perform the annealing operation. It is known that nitrogen can theoretically be used to form an inert atmosphere for annealing. Generally, nitrogen can be supplied from a nitrogen source that is separated from air by distillation at cryogenic temperatures and must contain only parts per million of reactive impurities such as oxygen. The nitrogen can be used in a heat treatment shop as an atmosphere for different heat treatment ranges.

In recent years, although it is possible to produce nitrogen off-site using cryogenic distillation methods and transport it to the work site, there are certain economic advantages to producing nitrogen on-site using non-cryogenic methods. I came to understand that.

There are two main room temperature methods that can be used to separate nitrogen from air. The first method involves absorbing oxygen from the air with an absorbent to produce a nitrogen product and periodically regenerating the absorbent by subjecting the absorbent to a very low pressure when the absorption occurs. This is due to free absorption.

The second method is to separate air using a semipermeable membrane. Known semipermeable membranes suitable for separating air allow oxygen to diffuse through the membrane at a much faster rate than nitrogen, so that the non-permeable gas is enriched in nitrogen.

If you take into account the cost of transporting nitrogen produced at cryogenic temperatures to the work site, it is cheaper to separate nitrogen from air using cryogenic methods, but it is cheaper to use non-cryogenic methods.
Nitrogen products can be produced that contain more or less oxygen. For many industrial processes, it is not a disadvantage that nitrogen produced at non-cryogenic temperatures contains about 1 by volume of oxygen as an impurity. However, it has been found that such an oxygen concentration is certainly a drawback when annealing metals that are difficult to oxidize, such as iron. Although it is readily conceivable that a suitable annealing atmosphere could be produced by mixing non-cryogenically produced nitrogen and hydrogen, for example in copper annealing carried out at temperatures between 400 and 800 °C, hydrogen The reaction between hydrogen and oxygen is slow enough to occur even at temperatures in at least the cold part of the critical temperature range, where copper oxidation still occurs, even with the addition of a stoichiometric excess of hydrogen to the atmosphere. proceed.

It is known to purify nitrogen containing about one bullet of oxygen by volume by first reacting oxygen with hydrogen using a catalyst and then absorbing the resulting water vapor by absorbers or getters. Considering the reliability of the absorption process to purify nitrogen, it is recommended to have two parallel absorption stages so that purified gas can be produced continuously, one of which is regenerated while the other is used. A device that can do this is needed. The need for an absorption stage significantly increases the capital and operating costs of the equipment and tends to eliminate the economic benefits derived from on-site nitrogen production by non-cryogenic methods.

Therefore, from an economic point of view, there is a need for a method and apparatus for annealing products made of metals that are less oxidizable than iron, making the use of non-cryogenically produced nitrogen containing measurable amounts of oxygen impurities attractive. There is (need).

In accordance with the method of the invention, the product is exposed to an annealing temperature in a heat treatment furnace, and nitrogen is separated from the air in situ in the annealing furnace to produce a gas mixture containing at least 95 parts by volume of nitrogen and a small amount of oxygen impurity; Oxygen impurities are catalytically reacted with a stoichiometric excess of hydrogen to produce water vapor, and the product gas mixture of nitrogen, water vapor, and unreacted hydrogen is passed through a furnace to create an annealing atmosphere. To provide a method for annealing metal products that are more difficult to oxidize than iron and are produced in a process.

Instead of using a stoichiometric excess of hydrogen: 2H2+0
2--)2H20 The exact stoichiometric amount of hydrogen required for the above reaction can be used. Therefore, the product gas mixture is then free of oxygen and hydrogen.

The invention also includes an annealing furnace, means for separating from air a gas mixture containing at least 95 volumes of nitrogen and oxygen impurities, and catalytically reacting the oxygen impurities with a stoichiometric excess of hydrogen, A catalytic reactor having an outlet communicating with an annealing furnace and capable of creating a suitable annealing atmosphere in the furnace, which produces a gas mixture consisting of water vapor, water vapor, and unreacted hydrogen, can The Company also provides equipment for annealing products made of difficult metals.

The method and apparatus according to the invention are particularly suitable for brightly annealing metals that are less susceptible to oxidation than iron.

Preferably the nitrogen product contains between 0.5 and 3 volumes of oxygen upstream of the catalytic reaction with hydrogen. Generally, only a small amount, if any, of stoichiometric excess of hydrogen is required.

For example, when copper is brightly annealed at a temperature of about 600° C., appropriate annealing conditions can be maintained as long as the partial pressure ratio of hydrogen to water vapor in the annealing atmosphere does not fall below 1×10.

The catalytic reaction preferably takes place with a platinum or palladium catalyst. Alternatively, copper or nickel catalysts can be used. The catalyst is generally heated to a temperature of 200° C. by reaction of hydrogen and oxygen.

The method and apparatus according to the invention will now be described by way of example with the aid of the accompanying drawings. 1 is a schematic diagram of an apparatus for bright annealing of copper; FIG. 2 is a schematic diagram illustrating an apparatus according to the present blasting including a continuous mesh belt furnace; FIG.

FIG. 1 shows a plant 2 for separating nitrogen from air by pressure free absorption.

Plants and equipment suitable for this purpose are described, for example, in British patent specifications 2073043A and 2195097A. The produced nitrogen generally contains 0.5 to 3 volumes of oxygen impurity. A nitrogen stream is passed through the catalytic reactor 4 and the impurities in the nitrogen stream are reacted with a small stoichiometric excess of hydrogen using a palladium or platinum catalyst at the reaction temperature. The product gas mixture consists of nitrogen, hydrogen, and water vapor. The produced gas mixture is made of copper or bronze, copper-nickel,
or products made of brass containing up to 15% zinc by weight, generally at 400°C to 800°C for a period of 10 minutes to 2 hours.
The sample is annealed by being immersed in an annealing atmosphere at a temperature of 100 mL and placed in a heat treatment furnace 6 for batchwise or continuous processing. Maintaining the conditions in the atmosphere for reducing copper by maintaining the partial pressure ratio of hydrogen to water vapor in the atmosphere, i.e. in the nitrogen supplied from the catalytic reactor 4 at a value greater than or equal to I x IO-6. Can be done. Therefore, the shiny surface of the product is maintained during annealing.

FIG. 2 shows an inlet zone 712 with a length of 1 m, a length of 5.67 m
A conventional continuous mesh belt furnace 10 is shown having a heating zone 714 of m and a cooling zone 16 of 6.86 m in length. The furnace IO is equipped with baffles 18 or the like to prevent air from entering the inside of the furnace from outside the furnace. Heating zone 714 and cooling zone 716 each have an inlet and a base for gas.

The inlet and the base can each be placed in communication with a separate source of a gas mixture consisting of hydrogen, water vapor, and nitrogen. The source section consists of a plant 26 for separating nitrogen from air by pressure free absorption and a catalytic reactor line for reacting oxygen impurities in the nitrogen with hydrogen.

A commercially available catalyst consisting of palladium supported on aluminum is used. Typically, the catalyst is heated by the reaction of hydrogen and oxygen, and the gas mixture exits reactor 28 at a temperature in the range of 50-150°C.

In operation, a gas mixture of nitrogen, steam, and hydrogen from the catalytic reactor is admitted into the furnace 10 through either or both of the inlet ports 22. heating zone 14,
Heat to a selected temperature, generally in the range of 500-800<0>C. The copper workpiece to be brightly annealed is placed on the furnace belt (not shown) and then the workpiece is typically
The belt is slowly advanced through the oven at a speed such that it remains in the oven for 0 minutes to 1 hour. As the workpiece advances through heating zone 14, its temperature increases approximately to the temperature of heating zone 14. Upon exiting heating zone 14, the workpiece enters cooling zone 716 and is cooled by contact with the relatively cold atmosphere therein. Generally, the furnace 10
The temperature of the workpiece on exit is between room temperature and 50°C.

Using the atmosphere according to the invention ensures that a bright annealed workpiece emerges from the furnace 10.

A number of experimental tests were performed on the apparatus shown in FIG. The results of the tests are shown in Tables 1-4 below.

Table 1 shows how hydrogen is added to the PSA plant (
The results of a comparative experiment are shown in which the mixture was mixed with nitrogen from 0.5% oxygen (oxygen impurity) and the resulting mixture was passed through a furnace without catalytic reaction between hydrogen and oxygen. Matsufuru (made of a nickel- and chromium-rich alloy with the property of acting as a jetter for free oxygen to enter the heating zone)
The characteristic of the furnace used was that it entered via a muffle. Therefore, all oxygen that enters the furnace with the gas mixture is substantially removed from the gas mixture. As a result, glossy workpieces could be obtained at 750° C. even when the oxygen level was slightly in excess of the required stoichiometric adjustment for reaction with hydrogen. Experimental results for oxygen concentration, hydrogen concentration, and dew point in both heating zone 14 and cooling zone 16 of furnace 10 at different hydrogen levels are shown in Table 1.

The results shown in Table 2 are for a series of experiments similar to Table 1, except that the mixture of nitrogen, oxygen, and hydrogen was reacted in the catalytic reactor swamp upstream before entering the heating zone of the furnace through the inlet gas. It is something.

The experiments shown in Tables 3 and 4 show that heating zone 7 is
Comparisons can be made with the experiments shown in Tables 1 and 2, respectively, except that no gas mixture was introduced directly into 14. Rather, it is introduced directly into the cooling zone 16 through the inlet cage. Table 3 shows the experiments in which the gas mixture bypassed the catalytic reactor, while Table 4 shows the experiments with the catalytic reactor. The experimentally obtained low dew points shown by Table 3 are
If the gas mixture is fed directly to the cooling zone, even if the heating zone is operated at a temperature of 750 °C, a lack of reaction between oxygen and at least the stoichiometric amount of hydrogen in the catalytic reactor path will result in a lackluster appearance. Indicates that it tends to produce artifacts.

If we use a furnace 10 that does not have a jetter to act as a jetter for oxygen, and if substantially 75
It should further be noted that if the heating zone 14 is operated at temperatures lower than 0° C., the copper workpiece will not have a bright finish.

Table 1 - H2/02/N2 mixture introduced directly into the heating zone Table 2 - H2/o2/N2 mixture reacted with a catalyst upstream before entering the heating zone C 860 mV 0.2 superior + 12 2. 6 910mV 0.95% +14 920mV 1.2% +10 3.15 950mV 1.9 +11 950mV 2.05% +12 3.9 965mV 2.5 +12 960mV 2.6% +12 4,25 970mV 3. 15% +12 970mV 3.1% +11'7 Table 3 - H2/0 introduced directly into the cooling zone. /N2C 4000ppm O 31% Table 4 - Addition of H2/02/N2 mixture catalyzed upstream before entering the cooling zone Zone atmosphere composition C 4500ppm -36 0.7 815mV O% +6 950 ppm O% -32 sleeve 1.45 825mV O +13μ880mV
0.24 0 2.05 895mV 0.55% +11 poles 920mV
0.7% +72.6 935mV 1.5% +10%945mV
1.65 yen +8 3.15 960mV 2.3% +10960mV
2.2q6+8 3.9 970mV 3.14 +10970mV
Section 3.2 +8 4.25 980mV 3.65% +8μ980mV
3.7% +8 Oxygen concentration is measured using an oxygen probe.
Measured using The gas temperature from the heating zone at the sampling point was 750°C; the gas temperature from the cooling zone at the sampling point was 200'C.

Most results are given in millivolts (mV). The effective oxygen concentration is determined by the formula E = 0.0215. T. loge (20.95
/ %O2) (where E is the oxygen probe value in mV,
T is the Kelvin temperature at the point where the oxygen probe is located,
is the oxygen concentration expressed in terms of volume).

[Brief explanation of the drawing]

1 is a schematic diagram of an apparatus for bright annealing of copper, and FIG. 2 is a schematic diagram Z'' showing an apparatus according to the invention comprising a continuous mesh belt furnace. Engraving of the drawings (no changes in content) FIG.1

Claims (1)

[Claims] 1. The product is exposed to an annealing temperature in a heat treatment furnace, and nitrogen is separated from the air at the site of the annealing furnace to form a gas mixture containing at least 95% by volume of nitrogen and a small amount of oxygen impurity. the oxygen impurity is catalytically reacted with a stoichiometric excess of hydrogen to produce water vapor, and the product gas mixture containing nitrogen, water vapor, and unreacted hydrogen is passed through a furnace to anneal. A method of annealing products made of metals that are less susceptible to oxidation than iron, which involves creating an atmosphere. 2.Exposing the product to annealing temperature in a heat treatment furnace, separating nitrogen from air at the site of the annealing furnace to produce a gas mixture containing at least 95% by volume nitrogen and a small amount of oxygen impurity; is made of a metal that is less oxidizable than iron, and involves reacting with a stoichiometric amount of hydrogen using a catalyst to produce water vapor, and then passing the resulting gas mixture containing nitrogen and water vapor through a furnace to create an annealing atmosphere. How to anneal the product. 3. Claim 1: The nitrogen product contains 0.5 to 3% by volume of oxygen upstream before reacting with hydrogen using a catalyst.
Or the method described in 2. 4. A method according to any one of the preceding claims, wherein the catalytic reaction takes place with a platinum or palladium catalyst. 5. According to any one of the preceding claims, the metal is cobalt, nickel, lead, copper, palladium, silver or gold, or an alloy of at least one of such metals, or an alloy of mercury. Method described. 6. A method according to any one of the preceding claims, wherein the metal is brightly annealed. 7. Process according to any one of the preceding claims, characterized in that the product gas mixture is introduced directly into the cooling zone of a continuous furnace. 8. an annealing furnace, a means for separating from air a gas mixture containing at least 95% by volume of nitrogen and small amounts of oxygen impurities;
and a suitable annealing atmosphere having an outlet in communication with an annealing furnace for catalytically reacting the oxygen impurity with a stoichiometric excess of hydrogen to produce a gas mixture consisting of nitrogen, water vapor, and unreacted hydrogen. A device for annealing products made of metals that are less susceptible to oxidation than iron, including a catalytic reactor, which can be made in a furnace. 9. The apparatus of claim 8, wherein the catalytic reactor comprises a platinum or palladium catalyst.