DE931772C - Warming salt bath for carbonaceous, alloyed steels - Google Patents

Description

Heating salt bath for carbonaceous alloy steels The invention refers to a heating salt bath for carbonaceous alloy steels, such as high-speed turning and tool steels, in which an inert base salt is metal oxides are attached.

It is known per se that such steels, such as tool steels and high-speed steels, to be heated in the weld pool. The main salt used in the salt bath is barium chloride or barium chloride in conjunction with sodium chloride, potassium chloride, sodium carbonate and potassium carbonate are used.

It is known that such salt baths during the heating process remove carbon from the workpiece.

Such simple chloride salt baths have the disadvantage that the steel when quenching on the surface, especially at the edge points serrated and deformed parts, often remains soft. It has therefore already been suggested to prevent the formation of soft skin by adding metal oxides and the Effect of the metal oxides on the surface of the goods used by additional Addition of borax, pyrophosphates, fluorine compounds to favor.

Such baths have significant advantages over previous ones, however, they have the disadvantage that they melt slowly. The additives could so far have only been melted in pure barium chloride. The salt forms as well a lot of slag, which in turn has a relatively unfavorable effect on the bath lining acts and, in the case of electrode salt baths, also on the electrodes.

In the case of these known salt mixtures, the one in the hardening bath has a particular effect Oxygen released between the melting point and the service temperature is disadvantageous the end. It has already been suggested in another context that to use oxygen-binding substances such as nitrites in salt baths. Such So far, however, additives have only been used appropriately for quenching baths in order to obtain a Reaction between a cyanide-containing heating bath and a nitric one To prevent quenching bath. However, these additives could not be in the actual Hardening processes, in which it is important to prevent decarburization, intervene.

The quenching bath containing nitrite according to previous proposals is only at temperatures between 15o to 5oo °, advantageously at about 2oo °, effective during When treating carbon-containing alloyed steels, it is essential to rely on oxygen binding arrives at temperatures above 700 to 75o ° and nitrites lose their effectiveness here.

For heating salt baths in which an inert base salt contains metal oxides are attached, experiments have shown that prevents the development of a soft skin can be, if according to the invention in connection with the addition known per se of substances that promote the dissolution of the metal oxides, small additions of oxygen-inhibiting substances Sulphites are added to the salt bath. These additives are particularly effective at Baths that use borax, fluorine compounds or pyrophosphates as the solution of the metal oxides favoring substances are included.

It has surprisingly been found that in the connection with the metal oxides and the oxide-dissolving salt additives, the sulphites also at those temperatures in the sense the oxygen binding remain effective, in which sulfite already disintegrates as an individual substance.

This is also proven by the fact that at the use temperatures no sulfur dioxide to be expected from the sulphite fall from the baths is being developed.

The amount of sulfite added is small and only a few percent of the total pool mix; it depends on the metal oxide content of the bath and oxide-dissolving compounds. The higher the addition of metal oxides and oxide-dissolving agents Compounds, the higher the addition of sulfites can be, but the increases Sulphite addition not to the same extent as the other two additives.

Depending on the proportion of metal oxides and oxide-dissolving substances it is advantageous to use oxygen-binding substances such as barium sulfites, sodium sulfites - to be added in the amount of o, oi to 100 / o of the total amount. Example i Contains a Melt of barium chloride or barium chloride in connection with sodium chloride, Potassium chloride, sodium carbonate and potassium carbonate 0.6% metal oxides, e.g. B. Alumina or magnesium oxide and 0.8% fluorine compounds, or pyrophosphates or borax, @so no more than 0.2% sulfites need to be added to the melt.

Example 2 If the content of metal oxide and oxide-dissolving compound increases on 3% metal oxide and 61% oxide-dissolving compound, it is advisable to add 0.4% Add sulphites. In this case, however, the sulphite content can be increased up to i% will.

The effect of the sulfites is so great that actually only small additives to a heating bath are necessary to the treated in the bath and subsequently to give hardened workpiece a surface that is otherwise only possible through nitriding is to achieve.

One of the most important advantages is that also from the. Warming bath Hardened steels of inferior quality assume great hardnesses.

However, it has been found to be particularly advantageous from one To harden bath with sulfite addition, in which the amount of metal oxides below z ° / o and that of the oxide-dissolving additives is around 11/0.

Experiments have shown that in connection with metal oxides and oxide-dissolving Substances the one-time low addition of sulphite for the normal usage time of a Warming bath is sufficient. The bathrooms only need to be reloaded in the usual way to become. It is not necessary for the good effects of this bath to be constant to keep the bath more often than usual new, unmelted salt or even sulfites to be added as a single addition.

In order to keep the composition of the bath according to the invention constant it is advisable to do the same with an appropriately neutral preheating bath to let work together, so that it is prevented that by the introduction of strangers, harmful salts impair the effectiveness of the bath. The preheating bath sets together: 6o, o 1 / o barium chloride, 33.6% sodium chloride, 6, o '/ o, borax, 0., 490 Magnesia.

The preheating bath is suitable for temperatures, from 68o bns iioo °. The bathroom; is also to be used for decarburization-free heating of tool steels.

Of course, similar preheating baths can also be used in conjunction can be used with the heating main bath according to the invention without the frame the invention is abandoned.

Claims (5)

PATENT CLAIMS: i. Heating salt bath for carbonaceous, alloyed Steels, such as high-speed turning and tool steels, in which an inert base salt is metal oxides and substances that promote the dissolution of the metal oxides - such as boron compounds, in particular Borax, fluorine compounds or pyrophosphates - are included, marked by adding small amounts of oxygen-binding sulphites. 2. salt bath according to claim i, characterized characterized in that depending on the proportion of metal oxides and oxide-dissolving Substances o, oi to io% of the total amount of oxygen-binding sulfites, such as barium sulfite, Sodium sulfite, are added. 3. Salt bath according to claim i, characterized in that that the inherent principle at less than i%, lying proportion of metal oxide - for example 0.6%, aluminum oxide or magnesium oxide - and about 10 / a proportion of oxide-dissolving Additives - for example, 0.88 / 9 borax, about up to 0.50 / 0 - preferably 0.2 'IM -Sulfites are added. q .. Salt bath according to claim i, characterized in that the inert principle with a proportion of metal oxide above i 0% - for example 3% aluminum oxide - and more than 1% proportion of oxide-dissolving additives - for example 6% borax - about up to 1% - preferably 0.4% - sulfites are added ;are. 5. Use of a salt bath according to one of claims i to q., Characterized characterized in that it is kept at temperatures between 68o to 10o ° C Preheating bath made of 6.0% barium chloride, 33.6% sodium chloride, 6.0% borax, 0.4 "/ @ Magnesium oxide, for hardening heating between 110 and 135o ° is connected downstream. Attached publications: Swiss patent specification No. 219 2i9.