RU2428488C1 - Procedure for thermo-treated metal items non-oxidation heating in air medium in muffle and device for its implementation - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: procedure consists in thermo-treated metal items non-oxidation heating in air medium in muffle with gap relative to wall of muffle determined by formula:

where δ is value of gap, B is diametre of circle, area of which is equal to area of cross section of thermo-treated item, and K is biggest internal diametre of muffle, (mm). Further, the procedure consists in placement of the muffle into a heating surface and in items heating above 670°C. Also, the items are set into a preliminary heated muffle where upon an end of the muffle connected with air medium is left open or closed. The muffle is made of material with less potential, than potential of item metal, which form galvanic pair at heating in air medium. The device consists of the heating furnace and the muffle made of material with potential less, than potential of treated metal. The end of the muffle connected with environment is open or is made with a door. According to one version of the group of inventions the muffle can be made of metal with an external layer of oxide or of oxides - quartz or porcelain, or ceramics, or metal ceramics with a substrate of material of potential less, than potential of metal of a thermo-treated item.

EFFECT: thermal treatment of metal without oxidation with reduction of oxides without application of protective mediums and coating.

5 cl, 4 dwg, 5 tbl

Description

The invention relates to the field of heat treatment and can be used for non-oxidative heating of metal products with the reduction of oxides during heat treatment, heating under plastic deformation of ferrous and non-ferrous metals and alloys. Known and widely used methods of protection against oxidation of products during heat treatment using reducing and inert media, vacuum and coatings. Thus, the method of heat treatment of metal parts includes heating, holding and cooling the parts in a sealed furnace muffle, which is evacuated and filled with a protective atmosphere (application for invention 99126303 C21D 1/74, F28B 5/04, F27d 1/18. Method of heat treatment of metal parts , steels and alloys). In this case, the muffle is sealed with a shutter filled with the corresponding activators. The impact of factors such as the tightness of the muffle, evacuation, the use of protective reducing media and activators increases the protection against oxidation during heat treatment. However, due to the many technological operations, the method is complicated in execution and expensive.

A known method of heat treatment of products, which allows to exclude oxidation of the surface of the copper tape and destroy the oxide film (patent 2352646, C21D, F27B. The method of annealing of products in a protective environment and an oven for its implementation). The method includes laying products in a sealed container, pumping air out of it, filling it with protective gas, heating the products in an oven, cooling the products together with the container. After laying the products in a container, a reducing agent is additionally introduced. The method is also complicated and expensive because of the need to ensure the tightness of the container, its evacuation, filling with protective gas and the use of a reducing agent.

где δ - величина зазора, В - диаметр круга, площадь которого равна площади поперечного сечения изделий, К - наибольший внутренний диаметр муфеля (мм), при котором возможен безокислительный нагрев изделий с любыми размерами, который устанавливается опытным путем. Величина К зависит от материала муфеля и нагреваемого металла изделия, температуры и формы муфеля. Так, при 900°С в муфелях круглого сечения, когда муфели выполнены из углеродистой стали и Х18Н10Т, при нагреве материалов из углеродистой стали и меди К=16-19, тогда как при нагреве меди в медном муфеле К=8. Способ прост в исполнении и нашел применение при нормализации мелких изделий. Данный способ не позволяет обоснованно подбирать материал муфеля и обрабатываемого изделия, так как в одних случаях изделие окисляется, в других нет, что сдерживает применение. То же самое связано со скоростью охлаждения нагретого изделия в муфеле. В одних случаях изделие получается окисленным, в других нет.To implement this method, a furnace is known that contains a sealed container, where it is provided to pump out atmospheric air and fill it with protective gas. A pocket is made near the side surface of the container to place a reducing agent in it. This device is difficult to manufacture and expensive due to the tightness of the container, pumping air out of it, filling it with protective gas and introducing a reducing agent. The closest in technical solution and the achieved result is the "Method of heating products, and.with. 619529, class C21D 9/00, F27D 5/00 ”, which we took as a prototype. To ensure non-oxidative heating and reduction of oxides, the products are positioned with a gap relative to the muffle, which is determined from the formula:

where δ is the size of the gap, B is the diameter of the circle, the area of which is equal to the cross-sectional area of the products, K is the largest inner diameter of the muffle (mm), at which non-oxidative heating of products with any sizes is possible, which is established experimentally. The value of K depends on the material of the muffle and the heated metal of the product, the temperature and shape of the muffle. So, at 900 ° C in round muffles, when the muffles are made of carbon steel and X18H10T, when heating materials from carbon steel and copper, K = 16-19, while when heating copper in a copper muffle, K = 8. The method is simple to implement and has found application in the normalization of small products. This method does not allow to reasonably select the material of the muffle and the workpiece, since in some cases the product is oxidized, in others there is not, which inhibits the use. The same is connected with the cooling rate of the heated product in the muffle. In some cases, the product is oxidized, in others not.

For the proposed device, the closest in technical solution and the achieved result is the device used in the "Method of heating products, and.with. 619529 ”, which is also taken by us as a prototype. It contains a heating furnace and an open end tubular muffle in air. Products for heat treatment are placed inside the muffle in the heating zone with a certain clearance relative to the wall of the muffle. This device is easy to manufacture and operate, but has a significant drawback. When heated, some products are not oxidized, while others are oxidized, which does not allow more widely and reasonably use this device. The technical task to be solved is the expansion of the technological capabilities of non-oxidative heating of heat-treatable metal products in air in a muffle - namely, the sound use of muffle materials and heated heat-treatable metal products.

где δ - величина зазора, В - диаметр круга, площадь которого равна площади поперечного сечения металла, К - внутренний диаметр муфеля, (мм), помещение муфеля в нагревательную печь и нагрев изделий выше 670°С достигается тем, что изделия размещают в предварительно нагретый муфель, после размещения изделий торец муфеля, связанный с воздушной средой, оставляют открытым или закрывают, при этом муфель выполняют из материала, имеющего меньший потенциал, чем потенциал металла изделия, которые при нагреве в воздушной среде образуют гальваническую пару. При этом муфель выполняют металлическим с оксидным наружным слоем или муфель выполняют из оксидов - кварца, или фарфора, или керамики, или металлокерамики, с подложкой из материала, имеющего меньший потенциал, чем потенциал металла изделия.The technical problem to be solved is a method for non-oxidative heating of heat-treatable metal products in air in a muffle, including placing products in a muffle with a gap relative to the wall of the muffle, determined by the formula

where δ is the size of the gap, B is the diameter of the circle, the area of which is equal to the cross-sectional area of the metal, K is the inner diameter of the muffle, (mm), the placement of the muffle in a heating furnace and heating of products above 670 ° C is achieved by placing the products in a preheated muffle, after placing the products, the end of the muffle associated with the air is left open or closed, while the muffle is made of a material having a lower potential than the potential of the metal of the product, which when heated in air creates galvanic vapor at. In this case, the muffle is made of metal with an oxide outer layer or the muffle is made of oxides - quartz, or porcelain, or ceramics, or cermets, with a substrate of a material having a lower potential than the potential of the metal of the product.

где - δ величина зазора, В - диаметр круга, площадь которого равна площади поперечного сечения изделия, К - наибольший внутренний диаметр муфеля, (мм), достигается тем, что муфель выполнен из материала, имеющего меньший потенциал, чем потенциал металла изделия, которые при нагреве в воздушной среде образуют гальваническую пару, при этом торец муфеля, связанный с воздушной средой, выполнен открытым или с дверцей. Муфель выполнен металлическим с наружным слоем из оксида или муфель выполнен из оксидов - кварца, или фарфора, или керамики, или металлокерамики и с подложкой из материала, имеющего меньший потенциал, чем потенциал металла изделия, являющегося элементом муфеля.The technical problem to be solved in a device for non-oxidative heating of heat-treatable metal products in air in a muffle, comprising a heating furnace, a muffle placed in it in which the products are placed with a gap relative to the muffle wall, determined by the formula

where - δ is the gap, B is the diameter of the circle, the area of which is equal to the cross-sectional area of the product, K is the largest internal diameter of the muffle, (mm), is achieved by the fact that the muffle is made of a material having a lower potential than the potential of the metal of the product, which at heating in air form a galvanic pair, while the end of the muffle associated with the air is open or with a door. The muffle is made of metal with an outer layer of oxide or the muffle is made of oxides - quartz, or porcelain, or ceramics, or cermets, and with a substrate of material having a lower potential than the potential of the metal of the product, which is an element of the muffle.

Figure 1 shows a device for implementing the proposed method; figure 2, 3 - options for implementing the method; figure 4 - a device for non-oxidative heating of metal products with a quartz muffle. The device shown in figures 1, 4, contains a heating furnace 1 and placed in it a metal muffle with an oxide outer layer, where 2 is the metal base of the muffle, 3 is the oxide outer layer of the muffle. The end of the muffle associated with the external environment is provided with a door 4 for closing. The muffle is made of a material having a lower potential than the heat-treating metal product 5. In the muffle 6, made of oxides - quartz, or porcelain, or ceramic, or cermets, a substrate 7 is located under its outer surface, the material of which has a lower potential than the potential metal products.

Consider the implementation of the method using the proposed device. To implement the method, the maximum allowable gap is determined by the formula and the product is placed in the muffle so that the gap between the product and the muffle does not exceed the obtained value. Some values of K for determining δ are given above. The muffle, consisting of a metal base 2 and an oxide outer layer 3, which is obtained by preliminary heat treatment of the muffle at a temperature of 900 ° C or entirely from oxides: quartz, porcelain, ceramic or cermet (figure 4). The muffle is heated to the required temperature and then the product is loaded 5. This allows to reduce the oxidation of the metal until it enters the oxidative and reduction processes at a temperature above 670 ° C. The product can withstand the required heat treatment time and the muffle with the product is removed from the furnace 1.

With the rapid cooling of small metal products outside the furnace in the muffle, they turn out to be light. Upon slow cooling of bulk samples, they oxidize upon cooling. You can cool them in a liquid medium (water, oil, etc.).

The method of non-oxidative heating of metals with the reduction of oxides is implemented as follows. The material of the metal muffle with an oxide outer layer should have a potential less than the metal of the product. As a measure of the potential, the electron work function can be used. During non-oxidative heating of metal products in muffles made of quartz, porcelain, ceramics and cermets, their outer surface in contact with the substrate 7 during heating process, the material of which also has a lower electron work function than the processed metal of the product. Tables 1, 2, 3 show the results of experimental studies that determine the pattern of redox processes from the materials of the muffle and the processed metal of the product in the proposed method.

Table 1. Muffle material The electron work function of the sample material, eV. iron titanium 4.14-4.5 nickel 4.91-5.01 copper 4.36 iron 4.4-4.71 FeO TiO ₂ , 96-3.1 NiO 5.55 CuO 4.35-5.34 FeO 3.85 surface state of samples after heat treatment oxidized bright bright bright

Table 2. Muffle material Sample Material Surface condition copper iron bright titanium oxidized nickel copper oxidized titanium oxidized

Table 3. Muffle material Backing material The surface state of the sample material after heat treatment * iron titanium iron nickel Copper quartz oxidized bright bright bright china oxidized bright bright * The experiments were carried out in muffles with a diameter of 10 mm with a heating time of 15 min at 900 ° C for samples with sizes 20 × 7 × 1 mm.

From table 1 it can be seen that a metal muffle with an oxide outer layer has a lower electron work function than nickel, copper, and the samples are light, non-oxidized. When titanium undergoes heating in the muffle, it forms TiO oxide (up to 15 oxides) with an electron work function of 2.96-3.1 eV, which is significantly lower than the electron work function of FeO - 3.85 eV, therefore it is oxidized. In nickel and copper muffles, titanium also has a lower electron work function than nickel and copper, and the samples are oxidized (Table 2). Electrons rush from a metal with a lower electron work function (RVE) into a metal with a higher RVE value.

Metal with lesser R.V.E. positively charged, and with greater R.V.E. Charges negatively. So, when heating an iron muffle to 900 ° C, the potential difference between the outer and inner walls in the heating zone is 4 × 10 ^-5 V. The iron muffle inside also turns out to be light, non-oxidized. This happens when the muffle is made of the same material as the sample, and a potential gradient is realized along its length due to differences in temperature, or when the muffle contacts the elements of the furnace from a more active metal.

When metals are heated in quartz and porcelain muffles at high temperatures, the heat treatments go into the class of semiconductors and conductors, which ensures interaction with a material (substrate) having a lower electron work function (Table 3).

The iron substrate material with oxides is R.V.E. 3.85 eV, i.e. less than that of nickel, copper and iron, which ensures oxidation-free heating of the latter with the reduction of oxides. As in the prototype, the samples are oxidized when heated, and then restored at temperatures above 670 ° C.

Titanium is oxidized in quartz and porcelain muffles. Similar results were obtained for muffles made of ceramics and cermets.

Using the example of st.20, the state of the surface of the sample after heating in a steel muffle is studied. Spectral analysis found that when the samples were heated to reduction temperatures of oxides of 830 ° C and 950 ° C, the content of oxygen, hydrogen, and nitrogen was the same as their content in the initial samples (Table 4). When heated, the carbon content also does not change (20%). When heated at 550 ° C, the surface layer contains a significant amount of iron oxides, and at 700 ° C no oxides are observed by X-ray phase analysis (Table 5).

In the proposed method, between the muffle and the metal being heated, which differ in the electron work function, a potential gradient is created during heating, i.e. a galvanic cell is formed in the air, which provides non-oxidative heating of metals.

A galvanic cell is formed both at contact and at small distances between them. If there is contact between the muffle and the product metal being heated, the galvanic cell works more efficiently. The recovery process begins at lower temperatures.

Table 4. The gas content (in%) in the samples of st.20 in the initial state and after heating in the muffle and under ordinary conditions Heat treatment mode In the surface layer At a depth of 0.01 mm About ₂ N ₂ H ₂ About ₂ N ₂ H ₂ Raw material 0.010 0.010 2.0 · 10 ^-4 0.006 0.010 2.0 · 10 ^-4 830 ° C, muffle 30 minutes 0.008 0.014 1.0 · 10 ^-4 0.004 0.010 1.3 · 10 ^-4 120 min 0.008 0.010 1.0 · 10 ^-4 0.006 0.012 2.0 · 10 ^-4 950 ° C, muffle 30 minutes 0.008 0.010 1.0 · 10 ^-4 0.006 0.010 1.8 · 10 ^-4 120 min 0.005 0.012 1.4 · 10 ^-4 0.006 0.012 1.6 · 10 ^-4 950 ° C, normal conditions 30 minutes lots of no 1.910 ^-4 a lot ^a 0.011 ^a 2.0 · 10 ^{-4a and} after descaling

Table 5. Phase composition of the surface layer of the initial sample st.20 and after heat treatment in a steel muffle Temperature ° C Phase composition the initial state α-Fe 900 α-Fe 700 α-Fe 600 α-Fe, a small amount of Fe ₂ O ₃ , FeO 550 α-Fe, a significant amount of Fe ₂ O ₃ , Fe ₂ O ₃ , FeO

During heat treatment at reduction temperatures, the number of defects on the surface decreases and very thin, but sufficiently dense, low-defective oxide films are formed that impede the process of further oxidation of metals. The method can be implemented in a muffle, where the end associated with the air can be either open or closed.

The proposed method of non-oxidative heating of metals with the reduction of oxides in air in a muffle and the device expand the technological capabilities of its substantiated use without protective environments, vacuum and coatings. The method is simple to implement and does not require expensive equipment and can be used for heat treatment of metal products, welding, heating under deformation, obtaining metals from oxides, metallurgical and other processes.

Claims (5)

1. The method of non-oxidative heating of heat-treatable metal products in air in a muffle, comprising placing the products in a muffle with a gap relative to the wall of the muffle, determined by the formula:

where δ is the size of the gap, B is the diameter of the circle, the area of which is equal to the cross-sectional area of the heat-treated product, K is the largest internal diameter of the muffle, (mm), placing the muffle in a heating furnace and heating the products above 670 ° C, characterized in that the products are placed in a preheated muffle, after placing the products, the end of the muffle associated with the air is left open or closed, while the muffle is made of a material having a lower potential than the potential of the metal of the product, which when heated in air medium to form a galvanic couple. 2. The method according to claim 1, characterized in that the muffle is made of metal with an oxide outer layer. 3. The method according to claim 1, characterized in that the muffle is made of oxides - quartz or porcelain, or ceramics, or cermets with a substrate of a material having a lower potential than the metal potential of a heat-treated product. 4. A device for non-oxidative heating of heat-treatable metal products in air in a muffle, comprising a heating furnace, a muffle located in it, in which the products are placed with a gap relative to the muffle wall, determined by the formula:

where δ is the size of the gap, B is the diameter of the circle, the area of which is equal to the cross-sectional area of the product, K is the largest internal diameter of the muffle, (mm), characterized in that the muffle is made of a material having a lower potential than the potential of the metal of the product, which when heating in air form a galvanic pair, while the end of the muffle associated with the air is open or with a door. 5. The device according to claim 4, characterized in that the muffle is made of metal with an outer layer of oxide or the muffle is made of oxides of quartz or porcelain, or ceramic, or cermets with a substrate of a material having a lower potential than the metal potential of a heat-treated product.

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