DE941487C - Manufacture of a low-nitrogen and low-phosphorus Thomas steel - Google Patents

Description

Production of a low-nitrogen and low-phosphorus Thomasstahl In more recent A Thomasstahl has time with less than o, oiz ° / o nitrogen and at the same time less when o, o5% phosphorus became more important. Such a steel shows after cold deformation slight increase in hardness and is still used for parts that are at their manufacture is heated with subsequent accelerated cooling, particularly suitable.

In - further development of the processes that lead to such a steel, it has now been found that, surprisingly, the water vapor of the forced air a not inconsiderable influence on the nitrogen content in the finished blown Steel, namely the nitrogen content of the finished steel is otherwise equal Much lower in certain circumstances if the forced air has only low water vapor content having.

The invention therefore relates to the use of predried, d. H. blower completely or partially freed from water vapor and hydrogen, vind for the production of Thomasstah.l with less than o, oia ° / o nitrogen and less as 0.05% phosphorus.

This influence of air drying was in no way to be expected, otherwise the oxygen in the water vapor also contributes to the freshness effect and . Now the bubble time corresponds to the reduction in the water vapor content in the Forced air must be extended. It is well known that the bubble time is prolonged an increase in the nitrogen content as a result: attempts were made decades ago were made in which steel was blaxed with a pre-dried wind. One. Influencing however, the nitrogen content in the steel was not determined.

The influence of a reduction in the water vapor content of the fan air can be seen from the following example: In a steel with o, io% C and 0.004% N2 Various gases in dried and moisture-saturated gas for ten minutes State initiated. The steel had a temperature of 160o °. For drying The gases were passed through a vessel with calcium chloride, the accumulation of moisture happened by passing through 70 ° warm water. While now blowing in moist air increased the nitrogen content of the steel from 0.00q. ° / 0 to o, oo6%, blowing in the same amount of dried air caused practically no noticeable effect Nitrogen increase. Passing wet nitrogen through it caused a doubling the original content to o; oo8%, while dry nitrogen only an increase on o, oo6%.

That the nitrogen content per se in these experiments is not very great are high is due to the test temperature chosen for test reasons of the steel of 160o °. At higher temperatures, such as those in practical steelworks are present, is the nitrogen uptake and thus the difference in nitrogen content significantly higher when blowing dry and moist gases through. On the other hand Every reduction in the nitrogen content in the Thonia pre-cast steel by o, ooi% means one noticeable improvement in steel properties, especially its use even with high deformation stresses and for particularly difficult parts that during their production a heating with subsequent accelerated cooling experienced, made possible.

It remains to be seen what this surprising effect of Predrying of the blower wind is due to. It would be conceivable that the water vapor or the hydrogen content of the water vapor catalyzes the nitrogen uptake of steel increased. In any case, by more or less extensive distance the water vapor and hydrogen content from the blower wind the nitrogen content of the finished Thomass.tahles lower in a noticeable way, so that when used completely or partially dried wind the production of a Thomas steel with less than 0.02% nitrogen and less than 0.05% phosphorus is made much easier.

The increase in the nitrogen content when the Thomas stole was blown is known to occur essentially during the last few minutes and in particular during the phosphorus combustion. You can therefore for economic reasons according to the invention also work in such a way that one initially, for. B. -to - about the end of carbon combustion, works with a wind of normal moisture content and only in the last minutes, especially during the phosphorus combustion, switches to pre-dried wind.

In the method according to the invention, the other known or already proposed measures to achieve low nitrogen contents can be used individually or in groups in the Thomasstahl. For this purpose are z. B. The following can be expected: Cooling with scrap or ore during decarburization or during Beginning of phosphorus combustion, low manganese content of pig iron (preferably below 0.5'10,), relatively low bath height., Since when blowing with predried Wind the endothermic effect of the water vapor decomposition ceases to exist the lowest possible finished temperature with a correspondingly larger proportion to work on coolants. But you can also use pre-dried wind do without part of the coolant and thereby a better and lighter one Castable steel is preserved, but it still has the conditions of a maximum nitrogen content of o, oi2% and at the same time one of 0, o5% is fulfilled.

Claims (3)

PATENT CLAIMS: i. The use of pre-dried, i. H. from Steam and hydrogen wholly or partially freed blower wind for production from Thomasstahl with less than 0.01% nitrogen and less than 0.05% phosphorus. 2. The method according to claim i, characterized in that only during the last Minutes, especially during the Pho @ spho @ rburning, with predried wind is blown away. 3. The method according to claim i and 2, characterized in that the blowing with pre-dried wind is used in conjunction with one or more known or already proposed measures to achieve low nitrogen content in Thomas pig iron, such. B. cooling with scrap or ore during decarburization or at the beginning of the phosphorus combustion, low manganese content - of the pig iron (preferably 'below 0.5%), relatively low bath height. Referred publications: "Stahl u. Eisen", 19o8 p. Ii5o; 1909 p. 132; 1923. pp. 1476/77; 1940 pp. 905 to 91o.