CS238250B1 - Liquid for the production of controlled atmospheres - Google Patents

Abstract

Liquid for the production of controlled atmospheres intended for heat treatment in a protective atmosphere, or for the production of a supporting atmosphere during cementation and nitro-cementation at temperatures from 70°C to 970°C. The liquid contains a mixture of ethanol and water, with a water content of more than 18% by volume to 40% by volume, or a mixture of isopropanol and water, with a water content of more than 30% by volume to 45% by volume, or a mixture of acetone and water, with a water content of more than 35% by volume to 50% by volume.

Description

The present invention relates to liquids for the production of controlled atmospheres intended for protective annealing without decarburization or for the production of carrier atmospheres during cementation.

During the annealing of the steel under a protective atmosphere, an atmosphere is introduced into the working space of the furnace, which acts neutrally on the treated steel, which means that it does not cause decarburization or carburization of the steel or loss of surface quality, for example by oxidation. The protective atmosphere must therefore be either completely inert to the steel being processed or its carbon level, the carburizing potential, must be equal to the carbon content of the steel. In the case of cementation and nitrocementation of steel in a gas, the basic requirement for a carrier atmosphere suitable for automatic regulation of the effect of the atmosphere is characterized by a low carbon level, which rises easily and quickly with controlled additions of higher carbon or liquid fluids. with the gaseous hydrocarbon additions and decreases easily and quickly when the regulatory additions are reduced or stopped. This property guarantees the required dynamics of carbon level changes in accordance with the required parameters of the cementation or cementing process.

Protective atmospheres and carrier atmospheres for cementation and nitrocementation are usually produced in complex and expensive developing combustion of a hydrocarbon with air or are prepared from liquid or gaseous nitrogen by mixing with hydrocarbons. Both methods require relatively complex operating equipment. Another way of producing protective atmospheres is by thermal decomposition of methanol, which is a highly toxic substance, and therefore its use is associated with a significant operational risk. Other controlled atmospheres, formed by the cleavage of hitherto known liquids on the basis of alcohols, hydrocarbons and water, have a particularly high carbon level in gas-tight furnaces, so that they are highly carburizing. In their control, the low carbon levels required are not guaranteed

- 2,238,250, especially during the diffusion periods of cementation, and furthermore, the dynamics of carbon level changes in terms of its decrease are not guaranteed.

in

These disadvantages are eliminated by the liquid for the production of controlled atmospheres intended for heat treatment in a protective atmosphere or for the production of a carrier atmosphere during cementation and nitroceraentation at temperatures from 780 to 970 ° C. The essence of the liquid according to the invention consists in that it contains a mixture of ethanol with a water content of more than 18% by volume to 40% by volume, or a mixture of isopropanol with a water content of more than 30% by volume to 45% by volume. % to 50% vol.

If the liquid according to the invention, which contains only nontoxic components, is dripped into the furnace workspace, it undergoes thermal cleavage under heat treatment conditions and produces an atmosphere characterized by a very low carbon level which was not known in gas-tight furnaces controlled atmospheres achievable. The gaseous media thus formed can be directly used as a protective atmosphere for low and alternating carbon steels. The choice of liquid composition within the range of the invention depends on the carbon content of the steel being processed. If regulated additions of carbon-rich liquids or gaseous hydrocarbon additions are metered into the carrier atmosphere so formed, the carbon level of the atmosphere can be increased so much that it becomes a cementing atmosphere. A sufficiently low carbon level of the carrier atmospheres of the liquids according to the invention will guarantee excellent dynamics of the desired carbon level changes of the cementing and nitrocementing atmospheres and hence unprecedented precise control of the carbon level even in the low-carbon region. Such precise control over a wide range of carbon levels was not achievable with the known fluids. Extending the range and increasing the accuracy and speed of the control allows the cementation productivity to be increased by about 10%. The liquids according to the invention, in particular the ethanol-water mixture, are also characterized by a very good operating economy.

Examples of liquids according to the invention:

Example 1

Heating before quenching to austenitization temperature of 840 ° C with 200 kg of steel containing 0.45% carbon in a 700 l gas-fired shaft furnace for 2 hours in an atmosphere formed by the cleavage of a liquid consisting of 65% ethanol and 35% water. content of oxide

238 2S0

- 3 carbon dioxide in the atmosphere is automatically regulated by ethanol additions to 1 »0% CO2 · No decarburization is evident on the treated steel.

Example 2

Heating before quenching to an austenitization temperature of 860 ° C 100 kg of steel containing 0.22% carbon, carried out in a 700 l gas-tight shaft furnace for 2 hours, in an atmosphere formed by the cleavage of a liquid consisting of 60% isopropanol and 40% water. the carbon dioxide content is automatically regulated by addition of isopropanol or gaseous hydrocarbon to a value of 1.0% COg. ^There is no decarburization ^{from the racemate} material.

Example 3

Heating before quenching to an austenitization temperature of 890 ° C 20 kg of steel containing 0.55% carbon, carried out in a 700 l gas-tight shaft furnace, lasting for 1 h, in an atmosphere formed by the digestion of a liquid consisting of 55% acetone and 45% water. the carbon dioxide content in the protective atmosphere is automatically regulated by the addition of acetone to a value of 1.1% COg. Decarburization is not apparent on the material being processed.

Example 4

Cementation in a 700 L forced-gas gas-tight shaft furnace with a charge of 400 kg of steel, at a temperature of 930 ° C, at a saturation period of 4 h with a flow rate of 300 ml.h of carrier liquid consisting of 65% ethanol and 35 5¾ of water, with automatically controlled propane additions to maintain the desired carbon dioxide content of 0.24% COg by volume and a subsequent 8 h diffusion period with a flow rate of 700 ml.hh ^ carrier liquid consisting of 65% ethanol and 35% water, with automatically controlled propane additions to maintain the desired constant carbon dioxide content in a cementing atmosphere of 0.38% COg by volume, achieves a layer thickness of 1.5 to 1.6 mm with optimum surface carburization of the cemented layer in the range of 0.7 to 0, 8% by weight of carbon, with automatic regulation meeting the required change dynamics.

Claims (1)

SUBJECT OF THE INVENTION 238 2S0 Liquid for the production of controlled atmospheres intended for heat treatment in a protective atmosphere or for the production of a carrier atmosphere during cementation and nitrocementation at temperatures from 780 to 970 ° C, characterized by containing ethanol mixtures containing more than 18% water by volume to 40% by volume isopropanol having a water content of greater than 30% by volume to 45% by volume, or a mixture of acetone with a water content of greater than 35% by volume to 50% by volume.