DE1433107A1 - Nitride-containing, low-carbon, ductile steels and processes for their manufacture - Google Patents

Description

PATINTANVfXLTI

dr. LorrmHos-dr.-ing. lottirhos

PRAHKPlRT (MAIM) 1/0 O 1 Π

UCHTINtTIlN-STRAlU 1 _limK - ^ IHJO IU /

rtlNSHICHIIi (0 * 11) 55 * 041 TIlieiAMMIi LANSiSZtNTi • RESDNEtIA

POSTAL CHECK PllANKFURT CMAIN), 1o. Harz 1961

ISHIKAIAJIMA-HAEIMA JUKOGYO KaBTJSHIKI KAISHA 4ι Ohtemaoni 2-ohome, Ohiyoda-ku, Tokyo (Japan)

Low carbon, ductile steels containing nitride and process for their production «

The invention relates to new nitride-containing, low-carbon, ductile steels and processes for their production and heat treatment.

In particular, the invention relates to new nitride containing, low carbon, ductile steels such as 0.013 to about 0.090% by weight of stable nitrides which, at elevated temperatures, have a certain solubility in steel, which sioh in the solid state, such as beryllium nitride and / or niobium nitride and / or aluminum nitride, and / or about 0.01 to about 0.10 wt% of another Kind of nitrides that have practically no solubility in either solid or molten steel, such as B. Titanium nitride and / or zirconium nitride "and furthermore less than 1 weight ^ of an alloy element" such as "B * Viok" l, Chromium, molybdenum, vanadium, manganese, silicon, etc. contains.

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It has been found that steel that contains at least one nitride that is partially dissolved in the matrix and is partially present as free nitride, the nitride at its grain boundaries and within its crystals "at shape-forming Machining, which is carried out at elevated temperatures, has continued to precipitate in dispersed form found that steel with the structure described has mechanical properties which are those of a steel of the same composition is far superior, and in particular its strength at low temperature is markedly improved and the transition temperature is shifted noticeably towards lower temperatures.

In the following, using the attached figures and photos, the production of a low-carbon, ductile steel according to Invention will be described and explained with excellent properties.

In Fig. 1, the impact values and the Tr15 values are one settled commercial steel at various low temperatures, in Fig. 2 the shear stress ratio and the Tr values of the same steel shown; with Fig. 3 A, B, G and D the impact values, the shear stress ratio, the Tr15- and illustrates Tr values of ductile steel according to the invention; with Fig. 4, the relationships between the transition temperatures. (Tr15- and Tr values) of a low-carbon steel and its nitrogen and aluminum content; Fig. shows the relationships between the impact values of said

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low carbon steel and its total content of nitrides, while Photos Nos. 1 to 6 are electron micrographs relate to structures of ductile steel according to the invention.

Image no. 1 Btellt an electron micrograph in 1o ooo times magnification of low-carbon cast steel B having a content of 0.08 i * carbon and 0.090 # aluminum nitride is in which long and large crystals of free aluminum nitride, which are excreted at a grain boundary, are shown «

If a steel of the structure shown undergoes plastic deformation at a temperature above the A * transformation * point through machining processes such as forging, rolling, etc. is subjected, the crystallites break this in the as-cast state existing steel as well as the nitrides present at the grain boundaries. On the other hand, the former tend to be Crystallites generally tend to become coarser, counter to the fracture effect, as the temperature is increased.

However, the growth of the crystallites is during the described The recrystallization process is extremely hindered by the fine, hard nitride particles in the steel structure be in a finely dispersed form, creating a fine-grain structure of the steel. It follows that at constant constriction of the steel, i.e. when the rolling or forging ratio is increased by repeated plastic Deformations at such elevated temperature as mentioned above,

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the metal nitrides are even more finely divided and thus at the same time the crystallites of the steel also become finer. It also follows that when the final temperature is lowered (finishing temperature) during rolling or forging, especially if these allowances in a temperature range between 110 and 600 ° G, which is the maximum separation area corresponds to the above-mentioned nitrides, the growth of the recrystallized grains is more inhibited, which is expressed in an even finer grain structure

Photo Mr. 2 is a micro diagram magnified 100 times of the ductile steel B already mentioned, which is made by ~ a

Temperature of 95o ^u G in air after forging had been "cooled down" in order to illustrate its grain fineness, which corresponds to the 9 of ASTM -Korn-Wr.

In fine-grained steel, as described above, there are indeed more crystals per unit volume, all of which are crystallographically oriented differently from one another. Therefore, if a compressive or shear stress is exerted on such a steel, a certain grain begins to slide. However, the adjacent grains can also slide against one another before a large accumulation of dislocations occurs at the oxen boundaries, since in this way the local concentration of the shear or compressive stress is waived before it becomes too great a fine-grained üefü _c e a less jjruch "becomes" caused by the cracks that due to accumulation of displacements eind which vorkomiuen easily in a coarse-Gefii above.

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Such a steel therefore has a high tensile strength when there is severe constriction.

These kinds of nitrides, which dissolve to a certain extent in solid steel, if they are sufficiently precipitated, have a size of 0.1 micron or less or less. (The size of the nitride precipitate is in the same order of magnitude as measurements made with the electron microscope or by means of X-ray technology, which were carried out on chemically obtained samples.) If pressure is exerted on a structure containing such nitride precipitates ? then the Ver s e tzuji £ en_jcuÄ & - UJ & ^^
movement against the xiorn limits. As a result, there is no pink accumulation of dislocations, which reduces fracture formation.

Therefore, the strength is both normal and high temperature, so does the breakdown at low temperature, and the transition temperature becomes high postponed to lower temperatures.

The i'otos Kr. 3 and 4 represent electron micro diagrams in 1o,000 or 5o,000-fold thickening of structures of ductile steel B, which has been heated to 95o ° O after forging in order to precipitate the fine nitrides to achieve in full. In the ib'otos, the fine Particles that appear in the bulk, aluminum nitride and other nitrides.

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In steels that have been killed with titanium and zirconium are to reduce the free nitrogen by converting it into very stable compounds, the definition becomes of the dislocations weakened by the free nitrogen, the pressure necessary to remove the dislocations reduced, thereby facilitating the guiding and as a result that noticeably improves elongation and constriction, and eliminates the phenomenon of hardening with aging Photos 5 and 6 represent electron micrographs of the Structures of a ductile släale D with a 1o ooo or 50,000 times magnification. The precipitated particles in the figure are beryllium nitride, ffitride of this type on steel have a similar effect as the one described above and can also affect the mechanical properties of the To improve steel noticeably · The following table summarizes the results, through which the actual and actual improvements in the mechanical properties of steels treated according to the invention are to be proven in comparison with those of a calmed steel of the trade.

For this purpose, 5 types of steels were made, such as Table 1 shows, of which steels A and E are only aluminum nitride, steel B aluminum nitride and zirconium nitride and steels 0 and D contain beryllium nitride.

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Table 1

stole A. O, σ O, Chemical O, Mn 0 AlN Component "/> S. Al ₀ O, O, N ₂ O Al Έ O, 10 0, Si 0, 59 0 P. , 023 2 3 ο, 023 O , 096 Ductile steel C. O, 08 ο, 32 O, 57 , 071 0.016 O , 021 0.019 ο, 032 O , 085 ti It I. O, 09 ο, 23 O, 6o , 084 0.016 O , 025 0.021 O, Oo 9 O , 006 IN THE I. O, 07 ο, 34 O, 65 0 0.013 O , 022 - ο, 017 O , 006 η - η 0, 09 0, 31 O, 55 0 0.015 O , 023 021 O , 038 η it 13th 27 79 , 052 0.014 O , 031 0.020 , 023 calmed down " 18th , 009 0.035 O -----— "■ —_ Chemical Component% stole Be Zr Be N sol ZrN A. 3 έ Al B. 0 0.087 Ductile steel C. O, , 06 0.074 0.02 Il It D. 0, 119 0.016 'It Il E. 120 0.024 H ^; ZH 0.027 ti Il calmed down "

The mechanical properties of these steels, which were treated at 95 ° C and then cooled in air to precipitate the nitrides, are listed in Table 2.

ORIGINAL INSPECTED

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Tensile strength 8th Table 2 5 Fließver .5 strain .4-37 .5 A- 67 speed 2 5 ratio .1 .2-4o .7. stoking._ 77 kg / mm 9 Flow 9 .9 .8-4o .0 ί
i 69 stole 5 border 3 .7 .o-4o .5 69 45.7.-46, kg / mm .0 73 • 0 35 .5-39 .0 71. more ductile 41.9 -42. 72 39 Steel A ' 46.5 -46. 53.3-54. 68, 37 "B. 46.5 -47. 51.5-33, 76 35 .5-71.9 "G 45.1-47.5 32.5-36. 7ο., 37 .4-78.4_ “D 36.5τ59. .8-73.0- "" E 55.75.52 .8-73.0 .0-73 .0-73.5 .6-79 .7-78 , 5-82 5-74

1 to 5, the notch impact values ^f fr15- and the Tr-Y / erte of ductile steels according to the invention, which are below the value 0, are compared with those of killed steels in trade both in the normal and in the oil-quenched condition.

The impact values at O ⁰ G are the Tr-15 and Tr values. of ductile steels, as can be read from these curves, are summarized in Table 3.

+) (yield point)
++) (yield ratio)

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Table 3

stole Impact values (1) Warmth (3)
treated Tr15 ° C I. behan
delt He values ⁰ O kg-m / cm Normalized
(2) 32.0 normal -12o normal behan
delt aanctile 38.0 -125 Steel A 30.0 33.0 -95 -11o -65 -90 “B 36.0 37.0 -100 -110 -80 -95 * O 33.0 37.0 -95 -75 -80 -90 "D 31.0 16.0 -100 -70 -7o -90 η j « 32.0 -70 -4o -45 calmer
stole 8.8 -47 -40

(1) Charpy V-notch, at O ⁰ G

(2) cooled in air

(3) quenched in oil

4 and 5 illustrate the relationship between total nitride content and impact values Tr15 and Tr values.

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It can be stated that a larger total amount of nitrides corresponds to higher and higher impact values and lower Tr15 and Tr values. It can also be observed that the properties of a steel whose total amount of nitrides is more than 0.03 # up to 0.1o io are markedly improved at low temperature.

The result of the breaking test, which was ^{carried out on ductile steel A at 45o 0} G, gives a duration of 88 to 125 hours at a load of 20 kg / mm with an elongation at break of 70 " ^A to 80 $, while steels have a comparable composition, which, however, do not contain any i-nitride, after assessment by ASTM standard values, tear for about 50 hours at an elongation at break of 35 to 40 γο. This result can be seen as proof of the excellent properties at high temperature of a ductile ¹ according to the invention. " * '"""

This extraordinarily good strength at full temperature can be attributed to the nitride particles, -Säag. in finely dispersed Shape of 0.1 u or less atif ^ the ^ ü -leitplanen the crystallites are present and "the ^ 'free mobility of the dislocations by limiting the latter to fix oneself under stress ... and accumulate

- r ■ ■ · ...._ "'' ären

changes of dislocations at the KorngrehzenV which there to ?. Disaster of cracking would lead, _r can be prevented.

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From the experimental result described it can be seen that the nitrides at the grain boundaries and excreted within the grains in dispersed form and steels with such a structure both at normal and at elevated temperatures show mechanical properties that of steels of comparable composition, but that do not contain nitrides, are far superior, in particular the improvement in properties at lower Temperature is remarkable in such citride-containing steels is.

The present invention also relates to a method for Heat treatment of steels which contain at least one ketal nitride and comprises heating of such Nitride-containing, low-carbon steel on a Temperature above the A3 transformation point. The invention also provides a method for heating the steel in such a temperature range in which the precipitation of nitrides is greatly increased, namely for a sufficiently long time so that the precipitation of a large part of the nitrides is achieved. Finally concerns the invention a rapid cooling of the steel using Laßnahiuen, such. Air cooling, oil cooling or water cooling, or following this cooling heating the steel again to a temperature below the Uniwandlun ^ point for tempering, with which a '' heat treatment intended for nitride-containing, ductile steels becomes, with welclier not only the mechanical iS

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shafts of steel at Eaum ^ unrl; _.....:: "on: higher Temperaturν improved due to the Verfeinerung- its grain size ,."., but also its strength, increased especially at low temperature "and" dieί Uniwändiungstemperätu'r according hied- "challenging temperatures is shifted.

The term steels, the size and mechanical properties of which can be refined or improved according to the invention, also includes pure iron, low-carbon steels, for example those containing 0.55 to 0.055 % carbon, less than $ 1.00 manganese, less than 0, 5 $ 'silicon and a few * fo than 0.055 sulfur and less than 0.055 1 ° phosphorus and kohlenst'offarme special steels .55 to .055 ia carbon and less than 1.00% nickel, chromium, molybdenum, manganese, vanadium and / or silicon or the like ^1, as well as less than 0.5 i> contain at least one x ^ etallniiirid. as such u-etallnitride the nitrides of aluminum, beryllium, niobium, titanium and zirconium, may be mentioned.

The heating temperature and iialtezeit may vary depending on the composition of the be varied steel to be treated, but it has been found in general to be advantageous to a temperature above the A ~ transformation point, between 8oo and iioo ⁰ G for a period when more than · Maintained 5o min. "The slowdown may be one of kethodeh, air cooling, the ülabsehreckung, the 'V / be carried out by any asserabschreökung. The annealing is pre-" · su ^ sweise at a temperature between 15o and 7oo ⁰ C. : -. ■■ ■ ν -;.,: .-. ■■ -. 8ADOFUGiNAL ■ - ■ -:

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The heat treatment according to the invention is described in more detail below with reference to the pigments and photos.

In Pig * 6 is the solubility curve of AM in a nitride-containing, low-carbon ductile steel shown according to the invention.

Pig. 7 (A), (B), (C) and (D) are graphs showing the impact value at low temperature and the Tr15 value of the ductile steel heat-treated according to the invention. Pig. 8 $ A), (B), (C) and (D) concern Diagrams showing the shear fracture ratio and the Tr values of the same steel already mentioned. Pig. 9 shows a diagram showing the change in tensile strength, the yield point, the elongation, the necking and the impact values of the same steel mentioned above.

Potos 7 to 26 relate to microphotographs of the structure of the above-mentioned heat-treated steel.

For example, pure iron, low carbon steel, or special low carbon steel containing 0.020 to 0.045 # nitrogen, 0.040 to 0.5 ^ aluminum, 0.05 to 0.3 # zirconium, or 0.030 to 0.1 $ titanium, or both Procedures are applied with success. The metal is 3o min. HEATER to a temperature between 8oo and 1ooo ⁰ C, and after the largest possible part of the iat l.letallnitride excreted, the lüetall from a temperature above

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Wirde the transformation point A * quenched in iiuft, in Ul or in ./asset and optionally then annealed at a temperature within a range between 15o and 7oo ⁰ G

The procedure can take the measures purely for a steel containing 0.005-0.045 "Ä nitrogen, 0.01-0.20 * 6 .beryllium, and 0.05-0.20 % zirconium or 0.03-0.20 # titanium include heating the steel to a temperature between 8oo and 11oo ⁰ C for less than an hour, then quenching it from a temperature above the A ~ transformation point in air, in oil or in water and if desired with a χ ^ lupe rat ur to be tempered between 15o and 7oo ⁰ O.

The fact that the mechanical properties are improved by the heat treatment, which comprises quenching the nitride-containing ductile steel from a temperature range with a greatly increased nitride precipitation above the A ^ transformation point, according to the invention, is obtained from the solubility studies of nitrides in solid steel Results and the examples can be seen which relate to the heat treatment of common, nitride-containing, ductile steels. Namely, a Kitrid-containing, ductile steel .0,032 yö nitrogen contained, for two hours at 12oo ⁰ O heated to the nitrides to dissolve completely in the ⁰ matrix. The nitrides were then precipitated again by heating the steel to various temperatures between 200 and 1100 C for one hour.

■ - ■ "■■■ ':' BADORfGiMAL

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The length of nitrides which had separated chemically from the matrix was then measured. The value thus obtained is to be interpreted as a sum of coarse nitrides, which have been eliminated already in the solid state, namely those which are insoluble in 12oo ⁰ C and the finer nitrides, which were newly excreted in the grains. Therefore, a larger value indicates a greater amount of nitrides that have been newly precipitated in the crystals »Pig. 6 illustrates experimental results obtained on a steel with AlN. Oaraus it can be seen that the Nitridausscheidung at about 7oo ⁰ C reaches a maximum that is maintained for up to 11oo ⁰ C and quite rapidly decreases at higher temperatures, which is on the Ί / iederauflösung of the precipitated nitrides in the matrix due.

Similar conditions are also found for steels with beryllium nitride observed.

Hence the improvement of the mechanical properties of steels is to be achieved through the precipitation of nitrides alone, this goal can just as well be achieved through a sufficiently long heating of the steels to a temperature below the transition point can be achieved. However, since that Grain structure of the steel through rapid cooling from a temperature just above the A3 transformation point can be refined, it follows that it is cheaper to use fine-grained steel with excellent mechanical properties ji properties if one has both of the mentioned

9 0 9903/02 37

Method Applied as One The invention relates to So a method of heat treatment for nitride-containing steels, in which a simultaneous application of the provided for both procedures submitted

In the following, the application of the described methods to 4 typical ductile steels is described in detail with practical examples to show how a nitride-containing, low-carbon steel is changed by its structure (size of the ferrite crystals) its mechanical properties Room temperature, (tensile strength, peel strength, elongation, constriction, hardness, inheritance values or the like) its notched impact ^{values below 0} ° C., Tr15 and Tr values are improved. "" In the following table 4 the previous composition of these steels is given.

Table 4

stole A. C. Si Mn 0 P. S. O, Al more ductile Il B. 0.10 0.52 0.59 0 , 016 0.025 O, 096 Il H C. 0.08 0.25 0.57 O , 016 0.021 0, 085 Il η D. 0.09 0.54 0.60 0 , 015 0.025 0, 006 It 0.07 0.51 0.65 , 015 0.022 006 (calmed down
Stole)

9 0 9 SM /

H33.107

Table 4

B. O, Be Zr 0.023 0 AlN 0 Be ₃ N _{2 e.g.} G O, 0.032 0 , 071 0 ductile steel A D. 0.06 0.009 , 087 . 0.02 π η killed steel 119 0.017 , 016 η η 120 , 024 It N

The photos 7 to 26 show ffiikrodiagramnie these Steels after air cooling, oil quenching and water quenching, which shows for all these steels that when the cooling rate is increased the perrit grain size becomes smaller in the following order:! air cooling, oil removal and water quenching

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In the following labeile 5 is the crystal size these steels in the ASiCM grain no. specified. From it is to see that extremely fine grain sizes are achieved what was previously not possible with a mild steel ·.

Tabel 5

stole

ASTM Ferrite Grain Mummer

normalized

Oil-quenched Water-quenched

ductile steel A ductile steel B ductile steel C 'ductile steel D

10 10.5

10.5 11.0 11.5 11.0

It should be pointed out that in all these steels the perrit grain number is in the following order: air cooling, oil quenching and water restriction becomes bigger

In the following table 6 the tensile strength, the yield point, the elongation, the constriction and the Charpy V-notch impact values at -4o ⁰ C, which have been obtained on these air-cooled steels, are compiled.

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Table 6

Steel - '■' - '■ ■ Tensile strength- ile- elongation Constriction KerbbTanj. speed limit impact

kg / mm ² kg / mm ² * "' * values- +)

kg-m / em

more ductile stole A. 45.7-
46.Θ 33.3-
34.3 37.5-
35.5 71.9-
69.5 25.5 more ductile stole B. 42.2-
41.9 31.5-
33.5 39.2-
40.7 78.4-
79.4 33.1 more ductile stole C. 46.5-
46.9 36.5-
37.0 39.0-
4o.O. 7o.0-
74.0 33.0 more ductile stole D. 46.3-
47.5 56.5-
39.3 38.5-
4o.O. 69.8-
73.0 30.7

+) Charpy V-notch at -4o ⁰ G

Of these steels, those with less than 0.01 io carbon, namely very low-carbon river steels, undergo almost no change at all due to the air cooling or cooling and it is not necessary to temper them.

However, even such a steel can drive through the Vex be made ductile according to the invention, so that it is a structural steel that can be used even at low temperatures 'is usable

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Liit]? Ig. 7. » 8 and 9 ,. will the. _; & er / bs; cMagw.er.te below, - -,. ^ -. from O ⁰ G,, .die _; ϊγ-1; 5-and Ir-fourth ^^; zw ^ scJä.eA ^ yp ^ is, chen> · duk · ^ - .:
tilen steels ,, how, they are above),, beachriebeii -has-, -in -.-, " . / f>-;■; air-cooled and .olafrgee eeche state together y © r- -, ;; ··. ' and, it is shown that in all cases the oil-drained steels _: .better properties than the air-cooled steel
· It should not be emphasized, doeh "fes-t -, .. ··. put, that these steels only. in the. -air-cooled. · --state. ■ Those who. in. tempered, rolled or forged state .. present !!., are superior. Tuck 3rgab.nis.pe. are in .der-naoh-v
following 'fabeile compiled., -.,: _; ·; ■. · .- ·. ■ ■ - ■ "- ■ -. ■

table '7 "

stole Steel ■■ '-: ·': - ■ Notched
value. n- - "" ^! ΐϊ · 1'5 O.A. Tr O.A. '"■ · ■ u · -"'' kg-m / em ⁰ G -120 ⁰ C -90 • _; - _r II, "; .-- SC ²⁾ O. A. ^ L.K. -125 L.K. ~ '-95 more ductile Il A. 30.0 32 .0 0-95 -110- -65 " • '■ --90 "■ / '- ■ , - ·: - ·. ^: - B ^{! I} '■■' ■ - ■ .o ■ '"-1CKT"' "■ ' '"-8O ^- G. -: ...- ■ 30 * 0 33 '- ^ 80- Il P, ,, - 31.0 37 -, -1.00,. _; . ., r7P _; .

1) max.value, Charpy V-notch, at 2), -.! Lu-f-t ^^ l ^ hl / b.fQder ... normalized ~ 3) olal? Startled

O "C

_; iAp.

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Steels containing more than 0.10 i "contain carbon, tend the Absehrecken something to cure with the result that the tensile strength, the three left border?, Hardness, slightly increased, while the elongation, the constriction and impact values are reduced . As a result, tempering becomes necessary for such steels after water quenching. Pig. 9 shows the change in tensile strength, yield strength, hardness, elongation, the constriction and the impact values of ductile steel A when it is annealed at various temperatures above 200 ° 0 after quenching of 1100 ⁰ C *

It is found that the tensile strength and the yield strength at 400 ⁰ C decrease rather sharply, the elongation is fairly obtained again at about 300 ⁰ C and a little more improved by further increasing the annealing temperature, while the constriction and the impact value at about 300 G can be completely recovered and no noticeable further benefit is observed at a higher temperature

With reference to these experimental results it can be established that the mechanical properties of ductile steel can be improved if this steel is removed from a Temperature quickly cools within the range of maximum nitride precipitation and above the A ^ transformation point. A such steel with its Tr15 and Tr values, both of which closely related to brittleness at low temperature,

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which noticeably towards the side of the lower temperature ■ is shifted, makes excellent structural steel.

Nitride-containing, low-carbon steels according to the invention are produced by one of the following three processes. Namely, the process of the invention also relates to production of nitride-containing, low-carbon steels, after which first nitrogen or a mixed gas of nitrogen and a hot gas is blown into molten steel or at least one nitride is added to molten steel, which dissociates therein to form gaseous nitrogen, or the slag, calcium cyanamide is added to the molten one during the reduction period of steelmaking To incorporate nitrogen into steel. The steel obtained is then at least one of the metals, such as aluminum, Beryllium, Jfiob- or the like, with nitrogen to form able to react from metal nitrides, which have a certain degree of solubility in solid steel, added to by to convert the nitrogen contained in the molten steel into mitride. Finally, the steel will be zirconium and / or titanium, which form even more stable nitrides, can be added to the excess nitrogen in these nitrides To convert metals, and, if desired, the steel produced in this way according to a precise specification of a heat treatment. is subjected to precipitate part of the mitride and then subjected to plastic deformation at an elevated temperature subjugate by measures such as rolling or forging.

. BAD ORiGINAL

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According to ^ rf ^^ ung. This method, can be applied to pure iron, using low carbon steels. nearly $ 0.35>. or less carbon or low-carbon special steels which, in addition to carbon, also contain alloying elements in a narrow range of less than 1.0 56 individual alloying elements.

It has been found that "in the presence of 0.010% to 0.10% of at least one nitride of the lethal, such as aluminum, beryllium, mob or the like, the steel receives better mechanical properties" at normal and elevated temperatures and, in particular, its notched impact strength at low temperatures The temperature is greatly improved ¹ and the transition temperature is shifted noticeably towards the lower temperature than is to be expected for those steels which, with the exception of the citrides, have identical components.

The nitride-containing steel can be used with success any of the devices such as Bessemer converter (overblowing; converter), Sieniens- ^ artin furnace, electric arc furnace., electric high frequency furnace, and the like. manufactured The process can be divided into three categories, be classified as described below lsi; ·,

The first method is in molten steel ..; ■■: ■: · .. nitrogen or a mixture of ^ as. made of state material and one or:. - _; ;> several.-inert Gau- (e.g. a GasiRisciiun ^ of .., nitrogen.off ^; .. ·,; / and Ar ^ on ouer iielium etc.) and then

BAD ORlGIMAL 9 0 9 8 0 3 / D 2 3 7: ■ ■

Add at least one of the metals to nitrogen react to form a hard Mtride which has some degree of solubility in solid steel, such as ζ.Β, Aluminum, beryllium, niobium, and these metals with nitrogen to react, being a nitride-containing ductile steel forms. Next, in one example, is the manufacture of ductile steel in an electric arc furnace describe in detail according to one of the methods mentioned.

example 1

First, scrap steel is melted in an electric arc furnace and refined under oxidizing conditions. Then, 0.35% and 0.70 Perrosilizium fo ferromanganese to Des oxidation are added to this stage through a nitrogen conduction

The tube was blown into the molten steel for about 6 minutes at a pressure of about 5 kg / cm and finally 0.20 ° fo aluminum or in the anaeric pail 0.10 $ beryllium were added to blocks before casting. Table 8 shows the chemical composition of the typical steels produced by the process described.

Table 8 ■

Steel 0 Si IVIn PSF ₀ Al AlN Al ₀ O, Be

ΒβH ^{2 2}

. 0.07 0.25 0.61 0.015 0.022 0.035 0.15 0.088 0.020 0.02 * 0.07 0.31 0.65 0.015 0.022 0.015 0.006 - - 0.120

As can be seen from this table, a part of the

'903803/0237. ^iÄD

added aluminum reacted with the oxygen present in the molten steel to aluminum oxide, while which forms aluminum nitride. The beryllium nitride Be-zNp is also clearly recorded by the chemical analysis.

The cluss blocks produced in this way were then brought to a temperature of 1150 and 1250.degree. It was then allowed to cool to normal temperature and then the steel was ^{heated again for one hour to 950,000 in the air} commercial, high-killed mild steel with comparable, chemical composition compared.

Table 9

$ 0.15 Tensile strength
speed
p
kg / mm I. Flow
border
p
kg / mm 9098 Deh
tion
t> A
lacing Notched Tr15
blow
values (2)
■ kgp-m / ⁰ C
cm TEs
⁰ O at..·· 42.0 52.0 40.0 79.0 55.5 -105 -85 46.7 58.0 59.0 79.0 51.0 -100 -7o stole 44 50 28 57 8.0 - 47 -5o B. G, calm down D. ⁰ C 03/0 237 E'luss
Steel (1) (D (2)

1433197

It is then found that the process of the invention is the manufacture of nitrogen-containing ductile steel enables. The method of the invention is not only by means of an electric arc furnace, but also in use a Bessemer converter, Siemens Lartin furnace, electrical High frequency furnace or the like. feasible with the same result «

The measure of blowing in nitrogen is also associated with the further advantage that a cleaner steel is obtained. The stirring action by this, in the molten;, etal introduced nitrogen gas is generated .. has to IPojLge, dajfc different Desoxydationsprodukte which coagulate therein duktionsperiode of the Re forth are available.

If so, a citride-containing steel alone according to the above Process is produced, the Cfußblock is not stabilized or calmed down, but represents a so-called "unaffected" ingot (rimmed ingot) containing bubbles, there a. Part of the unreacted nitrogen gas when solidifying of the metal tries to escape.

However, even this type of ingot shows no disadvantages in terms of the quality of the steel, since these bubbles in can be easily welded together during forging and folding »

However, killed steels are often preferred when higher quality ingots are desired. To achieve this goal must generally reach aluminum when it is alone

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is applied, an amount of about 1 ⁰ Jo can be used to cause a change in the properties of the steel, so that. it not only gives the impression of being ductile.

It has been found that it is possible to stabilize or calm nitride-containing, ductile steels, the excess nitrogen gas, which wants to escape during solidification, with at least one metal which is capable of forming more stable nitrides than those of aluminum or beryllium, and which do not dissociate at the solidification temperature of the steel. Among the metals that have these properties, titanium and zirconium have proven to be particularly suitable and an addition of about 0.03 to 0.3 $ is sufficient for this purpose to reach. The resulting titanium and zirconium nitrides are insoluble in the molten steel. A part of them is eliminated therefrom, while the rest remains floating in it and is suspended in it in a finely dispersed state while the steel solidifies. The particles of these metal nitrides in the form described above exert a normal effect on the steel in any case, and even a favorable influence on the steel can be expected.

Table 1o contains information on the chemical composition and the mechanical properties of a steel that has been manufactured according to the process described

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Table to

stole 0 Si Mn P SN ₂ Al Zr AlN Al ₂ O ₃ ZrN B ⁺ ) 0.08 0.23 0. 57 0.016 0 .021 0.032 0. 085 0.06 0.084 0.021 0 .02 Tensile strength
speed
ρ
kg / mm Stretch
border
ρ
kg / mm Stretching
■ * "" A lacing Notched bar
worth ₊₊₎
kg-m / sq.cm Tr15
⁰ C Trs
⁰ C 41.0-42.2 31.5-35 .5 39.2-40 .7 77.4-78.4 36.0 -100 -80

+) ductile steel
++) at 0 ⁰ C

It can be seen from this that the concentration of free nitrogen due to the addition of metallic elements such as zirconium or sitan, for the production of killed steel it is extraordinary is effective

The second method is to get in melted Steel has at least one unstable nitride that dissociates into its components nitrogen and metal, e.g. Iviangane nitride, lithium nitride, molybdenum nitride, ^ hromnitrid or the like. or Iron alloys ^ this he nitride components, in a length that the desired nitrogen content, as derived from the nitrogen content the nitride is calculated, added and then a

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metallic element such as aluminum or beryllium or the like. Adds to the nitrogen formed therein into a nitride of transferring the latter elements and thus nitride-containing produce ductile steel as desired. This method was also tested by a Yersuehsan approach, which follows described in detail in an example.

Example 2

First, scrap steel is melted in an electric arc furnace and after the oxidation refining process $ 0.35> ferrosilicon and 0.60 > ferromanganese for deoxidization, as well as manganese nitride with 14 56 nitrogen, which was previously obtained by heating metallic manganese in an ammonia atmosphere was prepared, added in an amount up to 0.20 i », whereupon in a Pail 0.20% aluminum, and in another case 0.1 9 & beryllium, which combines with the nitrogen to form stable nitrides added.

O ₀ Table 11 shows the chemical composition of the

o ■

ω ten ductile steels specified. Then ingots became these J ^ steels in a manner similar to that described above,

CO O

^ ₄ forges and then heated to 950 G. The mechanical properties of these steels are summarized in Table 12

Table 11

Si Mn P S Np Al AlN Al ₂ O ₃ Be ₃ N ₂ Be

0.10 0.32 0.59 0.016 0.023 0.023 0.096 0.071 0.019 pjtyß

0.09 0.34 0.60 0.013 0.025 0.0o9 O.OO6 Θ— - 0.016 0.119

Table 12

Tensile strength elongation constriction notch- "TrI5 Trs; steel ρ limit impact-

kg / mm kg / mm # # value ρ ^ ^C

45.7—46.8 53.3—34.3 35.4—37-5 67.5—71.9 30 -95 -65 46.5—46.9 32.3..36.9 37.8—4o.O-69.8—73.0 33 -95 -80

It can be seen from Tables 11 and 12 that the process described can be used to produce nitride-containing, ductile steels can get.

The steel described can contain a small amount of titanium and / or Zirconium was added to obtain the killed steel mentioned above noted above, not only with an electric arc furnace, but also with a ^ m Bessemer converter, high frequency electric furnace, Siemens Ii artin furnace or the like. be performed"

The (L. tte i-ethode concerns the addition of calcium cyanamide to slag during the reduction period in the steel making process, so that the nitrogen in the molten steel with it the decomposition of this agent is introduced, or the blowing of calcium cyanamide into the molten steel along with an inert gas (e.g. argon) or nitrogen or a mixed gas of nitrogen and inert gas so that the introduced nitrogen from the decomposition of this agent and / or the direct Supply of gaseous nitrogen comes from and in the jüischluß it the addition of at least one metallic clement that the is able to form the desired nitrides, in such a way that the

Steel contains nitride and becomes ductile

When using Bessemer converters, electric arc furnaces, Siemens-luartin-üfen, electric high-frequency furnace etc. nitride-containing, ductile steels can be produced in a simple manner can be produced without great effort of the methods described.

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Claims (1)

Claims 1 · Low-carbon, ductile, alloyed or unalloyed steels "or iron, such as simple steel, special steels with less than 1 Gw # nickel, 1 Gw # Ohrom, 1 Gw # molybdenum, 1 Gw # vanadium, 1 Gw # manganese, 1 gw? S silicon udgl., or steel with less than 1 manganese, less than 5 O ₉ Gw # silicon, less than 0.035 Gw # sulfur and phosphorus and less than about $ 0.35, preferably 0.035 to about 0.35 Gw carbon # , characterized by a content of less than 0.5 Gw # of metal nitrides that are stable in solid steel and soluble to a certain extent, such as aluminum nitride, beryllium nitride and / or niobium nitride, and possibly other nitrides that are more stable in solid steel, like ζ · Β · titanium nitride and / or zirconium nitride. 2 · Steel according to claim 1, characterized in that its content in solid steel up to a certain Degree of soluble metal nitrides, about 0.015 to about 0.090 Gw # is * 909803/0237 U33107 3 · Steel according to claim 1 · or 2, characterized) that its content of further in solid steel, even more stable nitrides, is about 0.01 to 0.10 wt. #. 4. Process for the production of low carbon, Nitride-containing, ductile governed or unalloyed Steels or · iron according to claims 1 to 3, characterized in that initially nitrogen f-containing molten steel resp. Iron is made, then the steel one or more metals that are capable of using to react with nitrogen to form metal nitrides, which in solid steel or iron, have a certain solubility, such as aluminum, beryllium and / or niobium and the like added and optionally by adding other metals with nitrogen under Formation of nitrides react, which are even more stable in solid steel, such as zirconium and / or excess titanium present in the steel «? Nitrogen is bound. 909803/0237 5. The method according to claim 4, characterized in that for the production of a nitrogen-containing steel or iron molten steel, decomposable nitrides, such as manganese nitride, lithium nitride,
Molybdenum nitride, chromium nitride j can be added. 6. The method according to claim 4, characterized in that for the production of a nitrogen-containing steel or iron in molten steel gaseous nitrogen, optionally mixed with inert gases such as argon, helium and / or a ^ replaceable, nitrogen-evolving compound ,
such as calcium cyanamide ^ is introduced. 7 »The method according to claim 4, characterized in that that for the production of a nitrogen-containing steel or iron, the slag on the molten Calcium cyanamide is added to the steel during the reduction stage in the steel production process. 8. The method according to claim 4, characterized in that the nitride-containing steel or iron is subjected to a heat treatment, whereby some of the nitrides precipitate in the solid phase and the steel obtained is then subjected to deforming processing, such as rolling, at an elevated temperature ,
Forging and the like is subjected. 9Q9SÖ3 / 0237 9. The method according to claim 8, characterized in that the nitride-containing steel or iron is heated to a temperature above the Αχ-transformation point, in particular between about 400 and about 11,000 ⁰ O, preferably between about 800 and 1000 ⁰ O, for a sufficiently long time , then quickly.zB cooled in air, oil or water and, if necessary, then tempered below the A ^ transformation point, in particular in a temperature range between about 150 and 700 ° C. 909803/0237