LU80006A1 - PROCESS FOR THE PREPARATION OF CHROMED ALLOY STEELS, ESPECIALLY STAINLESS STEELS - Google Patents

Description

r A 525

8 — f \ Λ — rr7J GRAND-DUCHY OF LUXEMBOURG

DD U ...... U D

du. — M.Ji (Lî9Z8, ............. £ §fe Monsieur the Minister of National Economy

Title issued ................; ................. Industrial Property Service,

_ LUXEMBOURG

U'iiß · —— Patent Application

Siufo ................................................

I. Request ARBED SA- ............................................ .................................................. ...................: .............................. ....... Cl) LUXEMBOURG. ................ .................................. .................................................. ....

'' represented by Mr. René NEYEN, engineer .......................................... .................. (2) ki deposits this ... twenty July 1900 seventy-eight ............... ................... ®) at ../ (/ [................. hours, at the Ministry of National Economy, in Luxembourg: 1. this request for obtaining a patent for an invention concerning: (4) Φ .................... .................................................. ................. "................................ .........................

Process for the production of bare alloy steels. chromium./...................................

.......................... in particular of 1 stainless steels .................... .................................................. ..................................

declares, assuming responsibility for this declaration, that the inventor (s) is (are): M, ..... Jean. GOEDERT ................................................. ..................... M * - -Robert J ^ OUSEL ..................... ............................. {5) ipjênieur ................. .................................................. ...........................engineer...................... .................................................. ....

131y rue de Luxembourg ............................................ 45, rue Dominique Lang .............................

ESCH / AL ZETTE .............................................. ..................................... DUDELANGE ............ .................................................. .....................

2. the delegation of power, dated ......................... on 3. the description in language .... French .... ........ of the invention in two copies; 4. ............. / ............ drawing boards, in two copies; 5. the receipt of the taxes paid to the Luxembourg Registration Office on ..... July 20 ... 1978 ...................... .................................................. .................................................. ..................................................

claims for the above patent application the priority of one (s) request (s) of (6) ........................... .................................................. .... filed in (7) ...................................... .................................................. ....................

the ..................../............................ .................................................. .................................................. .................................................. ........................ (8) on behalf of .................... .................................................. .................................................. .................................................. ......................................... (9) takes up residence for him (she ) and, if appointed, for its representative, in Luxembourg .................................

.Aclminis.tr.atiQn .... CentralÊ-.de .... l.îARBED., .... Case .... postal ... J, 802 ........... ................ uo) requests the grant of a patent for the invention for the subject described and represented in the abovementioned appendices, - with postponement of this grant to ... ...18 months.

The agent...........................

IT Minutes of Filing

The above patent application has been filed with the Ministry of National Economy, Industrial Property Service in Luxembourg, on: 2 D Jllll. 1978 | i Pr. the Minister of National Economy, at _______ iî / l .......... fs /? · d · / d ’% Ve Head of Service / Industrial Property,

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A 68007. / 1 i A 525 Descriptive memorandum filed in support of an invention patent application in the Grand Duchy of Luxembourg 2iE2Sâ2i = arbed s.a.

Avenue de la Liberté, Luxembourg

Process for the production of chromium alloyed steels, in particular stainless steels

The present invention relates to a process for the production of steels alloyed with chromium, in particular stainless steels.

It is known that decarburization of steel baths containing Cr can be carried out without significant loss of chromium in the slag, even at low carbon contents, by using one or the other of the following two devices or two at a time: 1. decarburization at elevated temperature, 2. decarburization under reduced CO (carbon monoxide) pressure.

Decarburization at high temperature is well known in the practice of electric furnaces. Its main drawback * "- 2 - however lies in the excessive attack of refractories at high temperatures, therefore in a reduced availability of ovens due to more frequent repairs.

Decarburization under reduced CO partial pressure can be done by vacuum or partial vacuum treatments, which requires the use of special and expensive equipment.

Another means of reducing the partial pressure of CO during decarburization in retort consists in injecting oxygen in admixture with a gas capable of diluting the carbon monoxide and of reducing the partial pressure. Among the variants of this technique, a distinction is made: 1. processes with oxygen and gas retort insufflation diluting carbon monoxide below the level of the bath by means of single, double or triple nozzles . In practice, there is a poor behavior of the nozzles in the absence of protection of the latter by the joint injection of a liquid or gaseous hydrocarbon. But it is mainly because of the costly complexity of regulating fluids (oxygen, diluent gas, protective hydrocarbon) that this process lacks appeal.

2. processes for blowing gas mixtures (oxygen + carbon monoxide diluent) from above on the free surface of the retort bath. For the known variants of these processes, the major drawback lies in the fact that below a certain carbon content (<0.2%) the agitation of the bath ceases following a rapid fall. > decarburization speed and that therefore, even with reduced partial pressure of CO, the low carbon contents (<0.03%) required for stainless steels can no longer be achieved without excessive oxidation of the chromium contained in the bath.

To remedy this drawback we have hitherto resorted to the creation of an artificial movement of the bath by the injection - 3 - of a non-oxidizing gas through one or more nozzles situated below the level of the bath, in to accelerate the transport of carbon to the reaction zones at the point of impact of oxygen on the surface of the bath. However, by this measure, the refractory lining below the level of the bath is weakened by the presence of one or more nozzles. On the other hand, to avoid clogging of the nozzles, the injection of neutral gas must continue at least at a minimum flow rate throughout the refining operation, even during periods when this artificial agitation of the bath is not required. , which is expensive.

The object of the present invention is therefore to propose, with a view to the production of chromium-alloyed steels, in particular stainless steels from cast irons or carburetted steels containing Cr, a process making it possible to obtain, without vacuum treatment, directly by converting the desired reduced carbon contents to the converter.

This object is achieved by the method according to the invention which is characterized in that one blows on the surface of a bath of carburetted steel or cast iron containing chromium through a lance which comprises a primary circuit and a secondary circuit in a first phase of pure oxygen through the two circuits, in a second phase a neutral or oxidizing fluid, generator of an agent diluting carbon monoxide through the primary circuit and of pure oxygen through the circuit secondary and in a third phase an oxidizing fluid generating an agent diluting carbon monoxide through the primary circuit and a neutral gas through a bubbling brick located in the converter below the level of the bath.

The process according to the invention therefore consists of a combination of a refining specially designed to reduce the carbon content of the bath without appreciable reduction of that of chromium, and of an adjustable stirring at will of the bath allowing precisely lead to very low carbon contents without the costs of implementing the process making the latter prohibitive.

For the implementation of the method according to the invention

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- 4 - “preferably a blowing lance with adjustable turbulence and a double fluid supply circuit is used. In this way the flow rates of the fluids in each circuit can be adjusted from 0 up to a critical value independently of one another and without risk of blockage of the circuit at zero flow rate by splashes of metal or slag, given that each circuit is protected by the fluid injected by the other circuit. In addition the impact force of the jets of this lance is adjustable at will by the relative gas flow rates in the primary (central) and secondary (peripheral) circuits and by the height of the lance.

It is therefore possible to create a movement of the bath varying from weak to very intense, as is demonstrated during the application of such lances in the LD-AC process for refining phosphorous cast irons. This adjustable bath movement is sufficient for the production of alloy steels containing chromium and in particular stainless steels, up to a carbon content of 0.030%. For carbon contents of less than 0.030%, the equilibrium approach is carried out according to the invention by creating an additional bath movement by injecting a neutral gas, at low flow rate, by a bubbling brick located below the bath level. Such a bubbling brick with a low gas flow rate (100 Nm / hour for example) presents against submerged nozzles neither the risk of clogging at zero flow nor the risk of premature wear, given the low flow for a short time. By this measurement it is possible to achieve sufficient homogenization of the bath to obtain the very low carbon contents (less than 0.030%) required for certain grades of steel.

According to the invention the neutral fluid introduced into the bath through the bubbling brick can be any neutral gas.

"·

Indeed, the role of this gas being limited to dynamic purposes, it is preferable to choose gases which are not capable of reacting with the components of the bath, in particular nitrogen or argon.

According to the invention the duration of introduction of the fluid

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- 5 - c neutral through the bubbling brick can be limited to the third phase of the development.

A nonlimiting example of execution will make it easier to understand the principle of the process: when refining a steel bath containing 2% C and 17% Cr, the blowing is started by injecting only O 2 by the primary and secondary circuits of the lance and by adjusting the respective flow rates of the two circuits so as to have a calm bath movement without projections of metal or slag. This blowing is continued until a C content of 0.8%, that is to say until the lower limit in C where the protection of Cr against oxidation is still ensured by C. For the blowing between 0.8 and 0.2% of * C, where the partial pressure of CO must already be reduced to prevent the oxidation of Cr, the oxygen in the primary circuit is replaced by a gas which can dilute the CO, by example of water vapor, blown at a critical flow allowing an increasing bath movement according to the relative gas flow rates to continuously homogenize the C content of the bath. Below 0.2% of C, where the partial pressure of CO must be even lower, we cut off the supply of O2 in the secondary circuit and we only blow water vapor at a critical flow allowing maximum bath movement. It is only at the end of decarburization, if necessary, to drop below 0.030% of C, that neutral gas is blown in through the submerged bubbling brick to create the complementary bath movement necessary for the approach to balance.

By comparison of the method described with the methods of blowing by submerged nozzles or the methods of blowing combined from above and by submerged nozzles, it is understood that a * major advantage of the method according to the invention lies in the fact that it can be implemented on any type of existing converter.

Claims (3)

1. Process for the production of chromium alloyed steels, in particular stainless steels, characterized in that one blows on the surface of a bath of carburetted steel or of cast iron comprising. '' of chromium through a lance which comprises a primary circuit and a secondary circuit in a first phase of pure oxygen through the two circuits, in a second phase a neutral or oxidizing fluid, generator of an agent diluting the monoxide of carbon, through the secondary circuit and in a third phase an oxidizing fluid generating an agent diluting carbon monoxide through the primary circuit and a neutral gas through at least one bubbling brick located in the converter below of the bath level. 2. Method according to claim 1, characterized in that the neutral fluid which is introduced into the bath by bubbling bricks is in particular nitrogen or argon. 3. Method according to claims 1-2, characterized in that the neutral fluid is introduced into the bath by bricks housed in the bottom and / or in the side wall of the retort.