DD298950A5 - FERRITIC STEEL ALLOY - Google Patents

Abstract

A heat-formable, ferritic steel alloy having 20 to 25% of chromium, 5 to 8% of aluminium, not more than 0.01% of phosphorus, not more than 0.01% of magnesium, not more than 0.5% of manganese and not more than 0.005% of sulphur, the remainder being iron, including unavoidable impurities, is proposed, according to the invention the said alloy furthermore containing 0.03 to 0.08% of yttrium, 0.004 to 0.008% of nitrogen, 0.02 to 0.040% of carbon and about equal amounts of 0.035 to 0.07% of titanium and 0.035 to 0.07% of zirconium, with the proviso that the sum of the contents of titanium and zirconium in percent is 1.75 to 3.5 times as large as the sum of the contents of carbon and nitrogen in percent. The alloy has substantially better properties in use than the base alloy.

Description

including unavoidable impurities, characterized in that the distortion is still

0.03 to 0.08% yttrium 0.004 to 0.008% nitrogen 0.020 to 0.040% carbon

and about equally

0.035 to 0.07% titanium 0.035 to 0.07% zirconium

and with the proviso that the sum of the contents of Ti and Zr in percent from 1.75 to 3.5 times as large as the sum of the contents of C and N in percent.

2. An alloy according to claim 1, characterized in that the ratio of the addition amounts of titanium and zirconium in the range of 0.6 to 1.4.

3. Alloy according to claim 1 or 2, characterized in that titanium and zirconium are completely or partially replaced by hafnium and / or tantalum or vanadium.

4. An alloy according to claim 3, characterized in that in each case at least two of the elements Ti, Zr, Hf, Ta and V have been added.

5. An alloy according to claim 4, characterized in that in each case at least three of said elements are used.

For this 5 pages drawing

The invention relates to a wamiverformbare, ferritic steel alloy

20 to 25% chromium

5 to 8% aluminum

Max. 0.01% phosphorus

Max. 0.01% magnesium

Max. 0.5% manganese

Max. 0.005% sulfur residue Eison,

including unavoidable impurities.

Such alloys are used to make electrical heating elements and high temperature catalyst supports. They form adherent oxide layer and therefore have a very good Zunderboständigkeit on.

Of course, it has not been foiled to seek to further improve base-ion buildup by adding additional elements or reducing unavoidable manufacturing-induced contaminants.

For example, it is proposed in GB-A-2070642 to add up to 2% yttrium, hafnium, zirconium, cerium or lanthanum and 0.1 to 2% titanium to make the cast fine-grained and to improve hot ductility. The additions of yttrium, hafnium, zirconium and misch metal (CE + La) should preferably each be up to 1% (Ansprücho 7,8,10 and 11). Diebesten Result 0.34% Ti and 0.46% Nb achieved ^(r Boi iiol B). However, it has been found that the teaching of GB-A-2070642 is still associated with disadvantages.

If you look davoi once; that some of the proposed additions are very expensive and 'in shares ' ; 1% significantly affect the economic efficiency of the steel alloy, it can be stated that although titanium causes an improvement of the mechanical properties in the prescribed quantity, it simultaneously effects the behavior under cyclically changing conditions

Oxidation condition deteriorated. Dio Loboiudauor SanV in the VIW-T "sf of 5000 changes for djo titonlroio Probo to 2800 changes for 0.25% Titanium Dioxide propos." Oios is often attributed to the amoichlorination of titanium oxide in the outer oxide layer, which causes oint chipping of the oxide layer (see Corrosion Scionco, Vol.24, No.7, 1984, pp 013 027.) External root boi oinor Probo with 0.47% Ti In the formative step strongo, unfortunate vortoilto Titanium carbide precipitation bootedot, dio very different mochnischo properties bowirkon and olno oinhoitlicho Knltformgobung orschworon odor impossible.

Dio Zugnbo of Niob bow in forritischon Fo-Cr-Loglorungon not only oonon loichton Anstiog dor 475 ° C-Vorödung (see Boron, Calcium, Columbium and Zirconium in Iron and Stool, pogo 199, John Wiloy & Sons, Now York, 196G ), and also the boron ozone and the cyclic wochsolndon oxidation state. With r.toigondor tomporotur, the protohodone niobium oxide (Nb, NbOj, Nb ₂ O ₆ ) decomposes, which is vorbunclon with volumonzunohmo, growth pacemaker, and resulting chipped oxide. Außordom dio dos Hochtomporaturvorsion niobium oxide is not very stable, since their melting point comparatively niodrig, ie boi about 1BOO ⁰ C (see P. Kofstud. High Temperature Oxidation of Metals, pago 215 JohnWiloy & Sons, New York, 1966).

According to EP-BO 091 526, the basic filtration contains, in addition to 0.002 to 0.06% Soltonon Erdon and most 0.04% phosphorus and 0.03% sulfur, zirconium and niobium to stabilize and improve the stability of the dauorite. Depending on the content of Kohlons " H (max 0.05%) and nitrogen (max 0.05%), Zr and NL should be added up to 1.068 and 1.928%, respectively, and still up to 0.364 or 1.209% Nb, if carbon and nitrogen are completely cloudy (see claim 1).

Even after this Lohro horgostollto steellogiortingnn woison still Nachtoilo on. Sowoit Soltono Erdon zugosotzt must, with the formation of relatively low melted or Oxido porochnot wordon, so that the steel alloy is only up to certain maximum temperatures anwondbar. Phosphorus contents up to 0.04% and sulfur content up to 0.03% are also not tolerable, according to the comments of the applicant. In particular, boron zirconia to about 1% and niobium to about 2% orhoblicho cons to be taken into account. For niobium, the boroite results from the comments on GB-A-2070642. At higher Zirkongohalton the Vorbossorung dor oxidation resistance decreases rapidly and even anticipates the opposite (H. Pfeiffer and H. Thomas: Zundorfosto alloys, p.260, Springer-Verlag, 1963). Outside boi zirconia, which lie far above the dissolving power of the forritic Fe matrix, coarsely disperse precipitates of zirconium nitride, carbide and -carbonitridone occur, · no sustained inhibition of grain growth and no appreciable strength enhancement bowirkon.

The invention is based on the object of further improving the long bokannto base alloy while avoiding the ncchtoilo found in the prior art. In particular, dos grain growth is clearly limited and the life in the cyclic Oxidationstost naming word vorbessert wordon. To solve this problem it is proposed that the alloy with

20 to 25% chrome 5 to 8% aluminum Max. 0.01% phosphorus Max. 0.01% Magnosium Max. 0.5% manganese Max. 0.005% Schwofol rust Iron,

including unavoidable impurities, yet

0.03 to 0.08% yttrium 0.004 to 0.008% nitrogen 0.020 to 0.040% carbon

and to otwa equal parts

0.035 to 0.07% titanium 0.035 to 0.07 zirconium

and with the proviso that the sum of the contents of Ti and Zr as a percentage is 1.75 to 3.5 times that of the content of C and N in percent.

Advantageous developments of the inventive concept are described in the dependent claims boschrieben.

Further details and advantages of the inventive concept will be explained in connection with FIGS. 1 to 5 close.

Fig. 1 a u. 1 b: show greatly simplified the test equipment used,

FIG. 2 shows the sound of life words,

3 shows the achieved Wärmefostigkeitswerto,

4 shows the achieved lifetime values under tension,

Fig. 5a u. 5 b: show values for the co-growth or for the bending numbers.

In the VIW test, small test coils of 0.4 mm thick Daht were heated by direct current passage in air. The power supply is switched on and off in constant change for every 2 minutes. The rr.aximal temperature achieved thereby is optically measured and constant gohalton at the same Schauffrequenz by Ändotung the applied tone voltage during the entire test period (K. E. people: nickel and nickel alloys, p. 145, Springer-Verlag, 1970).

Flg. 1 α shows strongly inferiority means for examining the dorsal lobulus olnos horizontal angoordnoton, schrnubonformig gowickolton hoizloitors (1), which is odeosponded in oino HaHoruny (2) and is vorbundon with oinor voltage quollo (3). In the pre-London case bostand dor Hoizloitor from oinor 50mm longon Wondol with 12 Wirulungon and oinom Innondurchmussor of 3 mm. Dor wire penetrator botrug 0.4 mm. Dor Hoizloitor became oin and ausgoschnltot in the Wocltsol of jo, with the help of the radiator pyromotor ilio wrthrond dor Hoizphaso orreichto Tomporatur controlled contactless gomosson and by modifying the voltage applied to a constant word.

Dorartigo has been carried out in normal atmospheric air until it reaches the peak of the Hoizlo- ritor, the number of which is the cyclone or diroctos measure of the lobone dauor. Dio boi allon work material unvormoidbaro, mohr odor wonigor strong precornering causes that for the Loitung dos oloktrischon current available stohondo metallic cross section in the course of Zoit is always kloinor woboi dor oloktrischo Widorstand ontsprochond vorgrößort and oino vorgogobono Prüftomperatur boi unvorändortom switching rhythm only has been maintained, wherein the voltage is increased. Dio vorwondoto test apparatus was equipped automatically with a tomporature control device, so that it could be oingohalton for dio Hoizphaso before {ogobono test tablature during the gosamton test period until Durchbmnnon irrespective of the progress of the UK Hoizloitor

Fig. 1 b shows - if strongly strongly inferred - oino device for testing the Lobonsdauor olnos sonkrocht hanging Heizloitordrahtos (4) of oinom engine length, which oingospannt with soinom oboron endo in oino Haltorung (5), with oinom variablon Gowicht (6) bulastot and with oinor tension swell (7) vorbundon is.

With this device, a 0.4mm thick Hoizloitordraht in ooo minutes oy minutes ogo and ausgoschaltot. Also, in the case of the Hoiz phase, wio boi dor the device according to Fig. 1 a, the dioal temperature was contactless gomosson and gorogelled to oonon constant word.

The results obtained in FIGS. 2 to 5 indicate that oino precursor alignment (Probo 1) and oino are modified according to the invention according to the invention (sample?), According to the following equation:

Sample 1

Probo 2

Cr 20.10 20.45 al 4.91 5.05 P 0.009 0,007 mg <0.01 5 0.01 Mn 0.22 0.15 S 0,003 0,002 Y - 0.04 N 0,010 0,007 C 0,045 0.037 Ti - 0.07 Zr 0.16 0.06 Fe rust rest

FIG. 2 shows the lifespan words achieved in a device according to FIG. 1 a, expressed by the cyclone number reached until burnout. The samples were switched on and off in each case for 2 minutes and the temperature reached during the heating phase was reached without contact and by altering the applied voltage ensured that a constant test temperature of 1200 ° C. was maintained during the entire test period in the iodine cycle. Dio Probe 1 has sustained 5343 cycles, while the dio Probo 2 has blown only at 6213 cycles. This corresponds to an increase of over 15%.

In Fig. 3, the determined heat resistance values are plotted and it can be seen that the alloy modified according to the invention has higher heat resistance values in the entire temperature test range.

Fig. 4 shows the achieved cycle number boi a test gomöß Fig. 1b in response to the applied voltage again. The modified alloy is characterized by a significantly longer service life under all loads. At a voltage of 2N / mm ', the 6 times, boi 3N / mm ² approximately dio 5 times and boi 4N / mm ² at least still achieved a 3.5 times life.

The dueling of a material after long-term use of high temperatures is an important design feature. The decrease in ductility in ferritic Fe-Cr-Al-Legiorungon is due to the strong grain growth at high temperatures. In Fig. 5a, the grain size words for the Probo 1 after 6.5 days outsourcing boi 950 to 1050 ⁰ C in pm indicated (upper Kurabzug). In addition, the grain size values for the modified alloy are given at 1350.1050 and 1150 ° C after a storage time of 13 days (lower cure). L ^ is readily apparent that the modified alloy is significantly finer grained than the comparative alloy even at twice as high a shelf life. It is therefore not surprising that the bending numbers (number of bends by 180 ° to break) according to Figure 5b in the modified alloy according to the invention because of their foinkörnigoron microstructure are significantly higher than those of the comparison prioritization for at 13 or 6, r. Days at 950,1075 and 1175 ° C outsourced Probon. The comparison shows that the modified alloy has a much higher ductility than the comparative alloy.

Claims (1)

claims: 1. W'imvor malleable, forritischo steal logiorting with 20 to 2Ü
8th Max. 0.01
Max. 0.01
Max. 0.5 % Chromium
% Aluminum
% Phosphorus
% Magnosium
% Manganese Max. 0.005% Schwofol
Rust Eison,