US2004836A - Process for the production of chromium steel alloys by the basic process - Google Patents

Description

Patented June 11, 1935 UNITED STATES PATENT OFFICE PROCESS FOR THE PRODUCTION OF CHRO- MIUM STEEL ALLOYS BY THE BASIC PROCESS Ernst Hermann Schulz, Dortmund, Germany, assignor to firm Vereinigte Stahlwerke Aktiengesellschaft, Dusseldorf, Germany No Drawing. Application January 3, 1934, Serial No. 705,159. In Germany December 18, 1930 The production of chromium steels by the basic process is usually an extremely difficult matter.

The addition of solid ferro-chromium in the ladle is unfavourable because, owing to the high melting point of this alloy, it cannot be expected to dissolve in the steel bath with absolute certainty and suflicent uniformity. Adding the alloy in the basic converter prior to the termina-' tion of the blow is precluded because, in consequence of the great affinity of chromium for oxygen, most of the added chromium would slag during even ashort final stage of blowing. Again, no satisfactory results can be obtained by adding chromium (or ferro-chromium) in the converter after the end of the blow, followed by an uptilting and very short blowing that is merely sufficient for the thorough mixing and melting of the chromium. The reason is that, as is well known, the production of a usable steel necessitates the blowing in the basic converter to be continued until the phosphorus content has been reduced to a very low value-usually below 0.07%. This extensive blowing of the steel, however, results in the formation of relatively high quantities of ferrous oxide, because, in accordance with the law of mass action, considerable amounts of iron must be oxidized along with the final traces of the phosphorus. In consequence of the great aflinity of chromium for oxygen, the result of adding chromium (or ferro-chromium) to the basic converter after a normal blow, is that the chromium acts as a powerful reducing agent which extracts oxygen from the ferrous oxide and is itself transformed into oxide. In other words, it plays the part of the usual reducing agents, such as manganese and silicon, which are added to the steel at this stage, either in the converter or in the ladle, with the drawback that, owing to the high melting pooint of chromium oxides, the amount of non-metallic inclusions left in the steel is larger than with the ordinary method of operating. Moreover, this oxidized and slagged chromium can no longer exert its alloying action on the steel, whilst the addition of chromium in such quantities as would leave suficient chromium as an alloying component, after the aforesaid reduction process, is precluded for reasons of economy.

Now since I have discovered that the action of a somewhat higher content of phosphorus in increasing the brittleness of steel can be counteracted by the addition of a certain amount of chromium as described and claimed in my prior patent specification Serial Number 589,525, filed Jan. 28, 1932, there is no need, in the production of chromium-steel alloys by the basic process to carry the refining process, or blowing until the phosphorus content has reached such a low amount, which has hitherto been necessary, but

the blowing treatment is already finished, when the phosphorus content is higher than 0.08%. As a result, the formation of ferrous oxide during the final stage of blowing is, naturally, considerably diminished. A higher phosphorus content, of at least 0.08%, remains in the bath, and therefore the amount of ferrous oxide is also considerably decreased. To the steel blown in this manner there is added chromium in sufficient quantities in order to obtain a chromium steel alloy of the desired composition. The chromium may be added for instance in the form of ferro-chromium or of any suitable pre-alloy. After the addition of chromium care must be taken for causing an intimate mixture between the steel bath and the chromium. For this purpose the bath is either blown over for a short time or it is left to stand for a short time of for instance one quarter of one hour. In this manner the bulk of the added chromium is alloyed with the steel whereas only a relatively small proportion of the chromium will be slagged by the reaction with ferrous oxide. Experiments made by the inventor gave a loss of 25%, in the most unfavourable case, whilst the remainder of the chromium is retained as alloying component. The aforesaid action of the chromium then removes the brittleness which would otherwise be manifested by steels containing such amounts of phosphorus.

In this manner steel alloys can be produced containing besides more than 0.08% of phosphorus chromium contents of between about 0.2 and 1.0%. The carbon content of the alloys thus produced may amount from traces up to about 0.2%. The remaining composition is the usual one. It may be mentioned that though it is of importance to terminate the blowing treatment when the steel has a phosphorus content above 0.08%, there is no necessity to continue the blowing treatment until the phosphorus content is 0.08 or about 0.08%, but also higher phosphorus contents can be used without dangerous efiect if care is taken for an increased chromium content as stated above. But for other reasons it will be suitable to maintain a certain upper limit for the phosphorus content. Thus it is suggested to finish the blowing treatment at a phosphorus content between 0.08 and 0.2%. For instance steel alloys of the following compositions were produced in the described manner:

Said alloys had qualities much superior to that of steel alloys produced in the basic open hearth furnace in the hitherto used manner.

The process may, for example, be carried out as follows:

An 18 ton charge found, by testing a sample, to contain 0.090%' of phosphorus, was treated with an addition of kg. of ferro-chromium containing 63% of chromium, the chromium content, referred to the weight of the charge, being therefore 0.59%. After a short final blow, the analysis of the finished product gave: phosphorus 0.096%, chromium 0.46%, the loss of chromium by burning-off being therefore 22%.

Further experiments have shown that chromium can be favourably alloyed, without any substantial loss by burning, if, after stopping the blow while the phosphorus content is over 0.08%, the bath be deoxidized in a known mannerpreferably with ferromanganesethe chromium, or pre-alloy, being then added to the bath and the melt left, if necessary, to stand for up to a quarter of an hour, and poured under normal conditions. In this method of operating, renewed blowing is superfluous, and consequently theloss of chromium by burning is also lessened.

- A third embodiment of the process consists in employing-a chromiferous pigiron for the basic process, instead of adding chromium or ferrochromium alloys. For example, if the blast furnace be charged with a chromiferous mixture, with a mean chromium content of about 5%, then the pig iron blown from such charge will contain about 0.6% of chromium, the composition being otherwise normal. If, when this pig iron is employed, the blow in the converter be arrested when the phosphorus content is about .1%, the basic steel will contain about .3-.4% of chromium. After the usual deoxidation, the mechanical properties of such -a basic steel will be considerably superior to those of basic steel produced in the ordinary way. A special addition of chromium may be omitted in this case, or if it is desired to produce an alloy containing still more chromium, such further amounts may be added, whereupon the bath is treated in the described manner in order to cause an intimate mixing.

As already stated the mixing of the chromium and the steel bath may be effected either by a short after-blowing or by leaving the bathto stand after the addition of chromium. The last mentioned .embodiment of the invention may be illustrated by the following example.- 1 A An 18-ton charge which had been blown in the basic converter until an example taken therefrom had a phosphorus content of .097% was treated with an addition of kg. of ferro- -chromium containing 63% of chromium, the

chromium content, referred to the weight of the charge, being therefore .63%. After the addition the bath was left to stand during about fifteen minutes, whereupon the finished steel had a phosphorus content of .102% and a'chromium content of 59%; the loss of chromium by buming-off being therefore about 6.5%.

This application is a continuation in part of application Serial No. 592,185, filed Feb. 10, 1932.

What I claim and desire to secure by Letters Patent of the United States is:

- 1. A process for the production of chromium steel alloys of all kinds by the basic process, which comprises subjecting a steel which contains phosphorus to a blowing treatment in a converter and interrupting said blowing before the elimination of phosphorus has reached the normal extent from .08%, then introducing sufiicient chromium into the converter to give a content of between .2 and 1% of chromium in the final steel, thereupon intimately mixing the chromium with the steel bath by subjecting the bath to a very short blow.

2. A process for the p'roduction'of chromium steel alloys of all kinds by the basic process, which comprises subjecting a steel which contains phosphorus to a blowing treatment in a converter and interrupting said blowing when the phosphorus content amounts to between .08 and .2%, then introducing sufficient chromium into the converter to give a content of between .2 and 1% of chromium in the final steel, and thereupon intimately mixing the chromium with the steel bath by subjecting the bath to a very short blow.

3. A process for the production of chromium steel alloys of all kinds by the basic process, which comprises subjecting a steel which contains phosphorus to a blowing treatment in a converter and interrupting said blowing when the phosphorus content amounts to between .08 and .2%, then introducing sufficient chromium into the converter in the form of a prealloy to give a contentof between .2 and 1% of chromium in the final steel, and thereupon intimately mixing the chromium with the steel bath by subjecting the bath to a very short blow.

4. A process for the production of chromium steel alloys of all kinds by the basic process, which comprises blowing in theconverter pig iron containing phosphorus and already containing a part at least of the chromium, interrupting the blowing in the converter before the elimination of phosphorus has reached the normal extent from then introducing the balance of th cient chromium into the converter to give a content of between .3 and .4% of chromium in the a phorus to a blowing treatment in a converter and interrupting said blowing before the elimination of phosphorus has reached the normal extent from .08'% to about .10%, then introducing sum-- final steel, and the bath being afterwards subjected to a very short blow.

6. A process for the production of chromiumsteel alloys of -all kinds by the basic process,

which comprises subjecting a steel which com tains phosphorusto a blowing treatment infa converter and interrupting saidblowing before the elimination of phosphorus has reached the normal extent from .08% to about .10%', then introducing sufficient chromium into the converter in the form of a pre-alloy, to give a content of between .3 and .4% of chromium in the final steel, the bath being afterwards subjected to a very short blow.

7. A process for the production 'of chromiumsteel alloys of-all kinds by the basic process, which comprises subjecting a steel which contains phosphorus to a blowing treatment in a converter and interrupting said blowing when the phosphorus content remains at about .08%, then introducing sufiicient chromium into the converter to give a content of between .3 and .4% of chromium in the final steel, the bath being afterwards subjected 10 to a very short blow.

8. A process for the production of chromium steel alloys of all kinds by the basic process,

which comprises blowing in the converter pig iron containing phosphorus and already containing a part at least of the chromium, interrupting the blowing in the converter before the elimination of phosphorus has reached the normal extent from .08% to about .10%, then introducing the balance of the chromium into the converter to give a content of between .3 and .4% of chromium in the final steel, the bath being afterwards subjected to a very short blow. K

ERNST HERMANN SCHULZ.