MXPA96003468A - Process to avoid adhesions in the recovery detira f - Google Patents

Process to avoid adhesions in the recovery detira f

Info

Publication number
MXPA96003468A
MXPA96003468A MXPA/A/1996/003468A MX9603468A MXPA96003468A MX PA96003468 A MXPA96003468 A MX PA96003468A MX 9603468 A MX9603468 A MX 9603468A MX PA96003468 A MXPA96003468 A MX PA96003468A
Authority
MX
Mexico
Prior art keywords
protective gas
oxidation
addition
hydrogen
cold
Prior art date
Application number
MXPA/A/1996/003468A
Other languages
Spanish (es)
Other versions
MX9603468A (en
Inventor
Zylla Peter
Original Assignee
Messer Griesheim Gmbh
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Priority claimed from DE19531447A external-priority patent/DE19531447A1/en
Application filed by Messer Griesheim Gmbh filed Critical Messer Griesheim Gmbh
Publication of MX9603468A publication Critical patent/MX9603468A/en
Publication of MXPA96003468A publication Critical patent/MXPA96003468A/en

Links

Abstract

The present invention relates to a process for preventing adhesions in the cold strip annealing in a bell type furnace, preferably using high convection under a protective gas comprising more than 5% to 100% hydrogen, the remainder being nitrogen , which includes the phases of heating, retention and cooling, which comprises the coating of the cold strips during the retention time, with a thin superficial film, by oxidation at temperatures above 600 ° C, by establishing a pressure ratio partial oxidation P (CO2) / P (CO) > 1, by the addition of 0.3 g to 0.6 g of carbon dioxide per m2 of surface area of the protective gas annealing material and the high disorganization of the thermodynamic equilibrium of the homogeneous water gas reactions (K < < 0.0

Description

PROCESS TO AVOID ACCESSIONS IN COLD TIPA RECOVERY. The invention relates to a process for preventing adhesions in cold rage annealing according to the preamble of claim 1. The cold strip is annealed in the form of compact rails in crucible ovens, bell ovens or conveyor ovens. of rollers. In the reclosing operation in closed furnaces, as in example hood furnaces, especially in high convection ovens, diffusion welds 3 are often formed or are known as strip adhesions, between the turns of the strip cold In the tempering mill, these adhesions increase the resistance to unwinding, and as a result, bends or cracks in the material are formed on the strip surface. DE 42 07 394 Cl describes a process for avoiding these strip adhesions. According to this process, the surface of the cold strip rolled to form compact rolls is coated at a temperature higher than 600 degrees C by means of oxidation processes defined with a thin surface film that prevents adhesions in the turns. During the cooling phase, below 600 degrees C, is ß removed again? i surface film by reducing the oxides. This is done by changing the water gas balance. The total process of annealing is carried out in an annealing furnace, especially a hood furnace, in a mixed atmosphere of N2-H2 protective gases, which has a maximum of 5 '/. of H2 and with addition of defined amounts of C02. The entire reaction process is assigned to the water gas reaction H2 + C02 = CO + H20. The reaction between hydrogen and carbon dioxide causes the formation of a large amount of vapor in fune ion of the thermodynamic state of the system. This is favored by means of a high concentration of H2 or CO2 and high temperatures. Table 2 and Fig. 2 show, for example, the temperature-dependent change of the concentration in an initial mixture of 514 H2 and 114 CO2. The curves of H20 and CO coincide. The temperature is indicated in the graph on the x axis and the concentration of the gas components are presented in the graph on the y-axis. The formation of steam increases with the rise in temperature. At 700 degrees C, these values are still below the IV, in volume. Increasing the concentration of C02 in the initial mixture increases steam formation to approximately 2 *? in volume. The amount of C02 is fixed and depends on the surface area of treated annealing material. A proportion ap > The oxidation rate between the partial pressures of C02 and CO is achieved by changing the constant state equilibrium of the water ga reaction. This is achieved by means of a more important protection gas metering. In Table 3, Fig. 3, a protective g is described that has a hydrogen content of 92,614. As shown by the comparison in Table 3 and Table 2, in H2 contents above 514, unreasonable vapor concentrations of up to approximately 6,614 by volume are formed (at 700 grains C). The appropriate ratio of C02-C0 oxidation is not achieved in any temperature range. In high concentrations of CO2, the oxidation is reacted in an uncontrolled manner in the H2-H20 system at low temperatures, therefore not undone, in which case the possibility of a subsequent reduction of the strip surface is not provided. AND-? > The results shown in Table 3 have been clearly confirmed in studies carried out in the laboratory. An addition of 5 to 1014 by volume of C02 to hydrogen at treatment temperatures of 680 degrees C caused the formation of igua to such an extent that these studies had to be completed to avoid the destruction of the analytical instruments. The content of hydrogen in the protective gas in the free adhesion of the cold strip is therefore restricted to a maximum of 514 by volume in DE 42 07 374 Cl. The strip adhesions also occur when the cold strip is treated in a3 convection ovens in an atmosphere of protective gases containing 514 g of hydrogen. Par-co ^ following, a process is desired for the cold strip annealing by which the strip adhesions could be avoided even when the protective gases contain up to lOOtf of H2. The underlying object of the invention is to provide a process for preventing strip adhesions during cold strip annealing in protective gas atmospheres having an oxygen content greater than 514. Starting from the prior art, all in consideration in In the preamble of claim 1, this object is achieved in accordance with the invention by the features specified in the characterizing part of claim 1. Useful developments of the invention are specified in the sub-indications ions. Only by means of the surface film formed by the process of the present invention is it possible to protect against adhesions in the turns of the cold strip in a protective gas atmosphere having a hydrogen content greater than 514 - preferably with a hydrogen content higher than "O * /., especially 10014. The requirement for this is an extremely high balance disorder terrnodin & amp;; mico the homogeneous water gas reaction. This means the suppression of the course of the reaction in accordance with that described by H2 + C02 - = CO + H20. Test operations with approximately 60t harvest batches have surprisingly shown that the cold strips can be coated with a surface layer, and therefore can be treated in such a way that they are free of adhesions, in closed ovens, for example in kilns of the same type. hood, with high convection even in a protective gas atmosphere containing 10014 H2 with a C02 addition. By means of the high capacity of the circulation fans used in the high convection ovens, the flow rates of the protective H2 gas in circulation at temperatures of - < 0 to 750 degrees C are so high that the homogenous water gas reaction can barely still be made and the constant state equilibrium is very different from the thermodynamic equilibrium. In accordance with the present invention, constant state equilibria of I0.0.01 are employed. The constant state equilibrium is understood here as a real state that is calculated mathematically by means of the following formula based on the gas composition analysis: PC0.PH20 • = PH2.PC02 The quotient 1 'becomes .oj only when the divisor is large and the dividend is very small, indicating a virtual suspension of the reaction. In this way, a partial pressure ratio of oxidation (P) of carbon dioxide can be achieved surprisingly. C02) / monoxid carbon dioxide). Steam formation is greatly restricted in this case. The homogenous water gas reaction in this case can not be used to control the process of the invention. It is controlled by means of the dissociation of the aggregate defined amount of C02 as described by means of: C02 = CO + 0.5 02. A partial pressure of oxygen resulting from this reaction is established as required in the protective gas atmosphere . The process of reversing the strip surface with a surface film that prevents adhesion of the turns is carried out under a defined partial pressure of 02. This can be defined as the quotient of the partial pressures (P) of C02 and 00 and should not be less than 1 in the oxidation process above 600 degrees C. Fig. 1 graphically shows the changes in a partial pressure of oxygen (Fig. PQ2). In this figure, P02 is represented as a logarithmic function of temperature and time. The phase of addition of C02 can be clearly observed. Ends at the beginning of the cooling phase. Super fi cial films constructed in this way with an amount of C02 from 0.3 to 0.6 g per m2 of surface of annealing material prevent the adhesion of individual turns in the roll. The high reducing power of the hydrogen in the cooling phase ensures the decomposition of this surface layer at a temperature below 600 degrees 0. During the retention time in pure hydrogen atmospheres, an intense methane formation is observed because H2 reacts with the carbon originating as a distillation product from the volatilization (heating) phase according to the equation H2 + C = CH4. Methane contents greater than about 214 by volume have a negative effect on the establishment of the required partial pressure of oxygen which is critical for coating with a protective surface film. The added C02 then reacts with the methane in accordance with the following reaction: CH4 + C02 = 2H2 + 2C0. The carbon dioxide is consequently decomposed and new CO is formed in an amount such that the proportion of the partial pressures < P) P (C02> / P (C0) is established and as a result of this, a defined coating of the surface of strips with a protective surface film is not possible, or is not economical. proposed coating without interference, the content of methane in the last phase of the retention time, before the addition of CO2, must not exceed a concentration of approximately 214 by volume of the protective gas atmosphere. If steels with low carbon content and sensitive to carbonization are treated by means of the process of the present invention, for example, micron steel IF, steel, titanium (special deep stamping steel), it is necessary to lower the level of C of the atmosphere with protective gas at 0.00314.

Claims (4)

  1. CLAIMS 1. A process to avoid adhesions in the cold strip annealing in a bell type furnace using preferably high convection in a protective gas comprising more than 514 to 10014 hydrogen, the rest of nitrogen, including the phases of heating, retention and cooling, which comprises the coating of the cold strips during the retention time with a thin surface film by oxidation at temperatures higher than 600 degrees C, by establishing a partial pressure ratio of oxidation P C02) / P < C0) > 1 by the addition of 0.3 and 0.6 g of carbon dioxide per m2 of surface area of the protective gas annealing material and the high decomposition of the thermodynamic equilibrium of the homogeneous water gas reactions (yi '0.01)
  2. 2. The process according to claim 3, wherein, during the cooling phase at temperatures below 600 degrees Ct, a partial pressure ratio P (C02) / P (C0) pa is established for the reduction of the surface film.
  3. 3. The process according to claim 1 or 2, wherein the vapor content e > The protective gas is set below 1514 in olum during the addition of C02 and the surface is reduced by hydrogen during the cooling phase.
  4. 4. The process according to any of claims 1 to 3, wherein the methane content in the protective gas is set below 214 by volume before the addition of CO2.
MXPA/A/1996/003468A 1995-08-26 1996-08-16 Process to avoid adhesions in the recovery detira f MXPA96003468A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE19531447A DE19531447A1 (en) 1995-08-26 1995-08-26 Method of avoiding glue when annealing cold rolled strip
DE19531447.6 1995-08-26

Publications (2)

Publication Number Publication Date
MX9603468A MX9603468A (en) 1997-07-31
MXPA96003468A true MXPA96003468A (en) 1997-12-01

Family

ID=

Similar Documents

Publication Publication Date Title
Kim et al. The thermodynamics of volatilization of chromic oxide: Part I. the species CrO 3 and CrO 2 OH
EP0482992B1 (en) Process for the production of a thermic treatment atmosphere
CA1125011A (en) Inert carrier gas heat treating control process
US4208224A (en) Heat treatment processes utilizing H2 O additions
US4236941A (en) Method of producing heat treatment atmosphere
US2231009A (en) Heat treating process
US5772428A (en) Method and apparatus for heat treatment including H2 /H2 O furnace region control
MXPA96003468A (en) Process to avoid adhesions in the recovery detira f
US5785773A (en) Process for avoiding stickers in the annealing of cold strip
US4359351A (en) Protective atmosphere process for annealing and or spheroidizing ferrous metals
US4285742A (en) Heat treatment method
JPS5917168B2 (en) Steel heat treatment method
Allen et al. Internal carbonitriding behavior of Ni-V, Ni-Cr, and Ni-3Nb alloys
EP0804622B1 (en) Method for heat treatment of stainless steel
US2287651A (en) Method of carburizing without deterioration of furnace alloys
JPH0515782B2 (en)
Inouye Interactions of refractory metals with active gases in vacua and inert gas environments
SU800238A1 (en) Method of low-temperature nitrocarburization of steel articles
Rawe et al. The effects of gaseous pretreatment and oxide sintering on oxidation of Ti-4.32 wt.% Nb alloy
JP2803108B2 (en) Heat treatment method for steel
CA1239078A (en) Process for heat treating ferrous material
CA1092496A (en) Method for improving the surface quality of annealed steel strip
JPS5980713A (en) Heat treatment of steel product accompanied by no decarburization
SU604503A3 (en) Method of heat treatment of articles
Bramhoff et al. Effects of Hydrogen Chloride and of Nitrogen in the Oxidation of Fe-20Cr