DE1508454A1 - Method of dehulling steal - Google Patents

Description

The invention relates to a method for softening of carbon-containing, high-alloy steels, but especially steels containing carbon, nickel and other alloying elements contain.

Recently, a group of alloy steels has made it because of their

high tensile strength, which is, for example, 126 to 147kp / mm, has received a lot of attention. These steels get their strength through a combined carbide precipitation and tempering process. Such steels contain a large amount of nickel, ie at least 4 % and other alloy elements such as chromium, molybdenum, cobalt and vanadium, but also considerable amounts of carbon, ie about 0.06 % or more. Because of the

Patent attorneys Dipl.-Ing. Martin Licht, ÄpL-Wimch.-Yng.MeYrftniftTiann, Dipl.-Phys. Sebastian Herrmann

8 MÖNCHEN 2, THERESIENSTRASSE 33 ■ Telephone: 2 »21 02 · Telearamm-Adre« ·: Upatli / Munich

Oppenau office: PATENT ADVOCATE DR. REINHOLD SCHMIDT

Relatively high in carbon and alloying elements, these steels are quite "as rolled" hard and make cold deformation very difficult. Furthermore These steels speak because of their hardenability, which prevents the formation of transition products at high temperatures and due to their low-lying lower critical temperature, which prevents effective supercritical annealing, does not rely on the well-known softening treatments. The mechanical properties of such steels are tempting

in addition, they are used as filler metal when welding for weld seams

high strength (126 to 147 kgf / mm). If so

However, if this is to happen, these steels must be soft enough so that welding wire can be produced from them which can be processed with the known welding processes. The drawing of such welding wires can best be carried out when the hardness of the blank is in the range between 10 and 20 R-, (Rockwell). However, wire can also be produced from blanks by cold drawing, the hardness of which is 29 R _ß . The initial hardness of the above-described carbon-containing, high-alloy steels is so large that a softening of such steel compositions is very desirable to values between 20 R "for wire drawing, would wherein a reduction of the hardness to less than 30 R sufficient _ß.

The invention provides a method for softening alloyed, carbon-containing steels of the type described, which have high strength. This procedure exists

909843/0742

from a series of temperature changes within the intercritical range followed by a subcritical glow. This is achieved in that such steels are subjected to at least two Brwärmungs- and Abkühlrungzyklen within which the steel is heated to the ranging from about 621 ° C to 76o ⁰ C interkritiechen temperature range and is then cooled down to the martensite transition region. Thereafter, the steel in the subcritical range of from about 566 is annealed for a period up to about 635 C, the λ to greater reductions tion sufficient hardness. After the annealing process, the steel is cooled down from the annealing temperature to such an extent that it can be processed further. The method is particularly useful for softening carbonaceous high alloy steels containing at least 0.06 % carbon, at least 4% nickel and other alloying elements (usually at least two) from the group consisting of chromium, molybdenum, vanadium and cobalt.

Further advantages and details of the subject of the invention I The current status results from the following description and the examples contained therein.

As explained in the above, the are alloy steels high tensile strength to which the invention relates, the Softening by the known annealing processes is not accessible.

009843/0742

To demonstrate this, a number of the compounds shown in Table I were subjected to five different known softening treatments, the results of which are given in Table II. It is pointed out that among the compounds there are three that do not contain chromium or molybdenum and one that does not contain only one of the two elements. Those steels which either do not contain chromium or molybdenum or do not contain either element can be softened using the known methods. The other steels of this type, however, which contain chromium and molybdenum, cannot be significantly softened with the known annealing treatments.

909843/07

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009843/0742

• TABLE II of 927 ° < Austenitic blank 621 and 677 C Same as before Intermediate critical cn Rockwell C hardness hr 593 C / 24 hr Oven cooling ι to do this, glow cyclic annealing CD 13.7 20.6 at 621 C / 48 . 704 ° C, 4 times. OD Z of 927 ° C 24.8 41.4 Warming up and CONVENTIONAL TREATMENTS 26.7 40.5 18.5 hr cool designation Subcritical glow cyclic annealing 27.7 44.1 32.5 593 C / 16 hr 760 ° C, 4 times. 25.4 42.3 32.9 20.4 Hot rolled quenched quenched cycle between 28.1 44.2 30.8 '25.5 blank blank 28.7 41.2 29.8 25.2 ' A. 621 C / 24 hr 621 C / 48 25.7 34.6 33.1 23.6 "" B. 21.2 22.6 37.1 33.1 22.9 ' O 22.0 28.6 25.8 42.4 31.9 24.9 ° » (O " 36.8 29.1 29.9 42.8 28.8 24.7 i- • ο Ε 35.1 28.5 27.3 45.1 34.2 25.9 ν. ** F 36.6 27.8 29.3 46.7 33.0 22.2 ^: to G 34.7 28.6 30.4 44.2 32.2 20.0 · *"" H 33.7 30.0 30.1 43.9 32.6 25.0 38.2 29.8 29.4 48.2 34.4 23.1 36.3 24.5 23.7 43.9 34.0 26.8 to ^ 29.6 29.7 29.6 44.9 33.6 30.4 L. 36.8 30.7 : ⁺ Blank removed hot-rolled, hardness for the composition 30.1 28.4 M. 38.1 29.6 29.0 23.3 N 36.0 28.6 P -48.0 R ₀ 20.2 « O 35.6 33.4 Hardness after normalization (1038 ° C, oven cooling) Composition P -42.0 R _c 22.6 P ⁺ 37.0 31.9 Q 38.2 30.9 R. 35.5 26.9 annotation 33.4 28.8 33.5

The softening methods shown in Table II contain three subcritical annealing processes and two austenitic cyclic annealing processes as well as a normalization treatment. The first subcritical glow is that the hot rolled blanks as received are heated to 621 C for 24 hours. The second subcritical glow became a heated one, from a typical one Hot rolling temperature (927 C) quenched blank 48 hours warmed up to 621 C for a long time. The third subcritical Annealing treatment became a blank quenched from 927 C ' Heated to 593 C for 24 hours. At the first austenitic cyclic annealing process, a blank, as it was removed, was heated to 76O ° C. and then, after cooling, to 621 ° C with four heating and cooling cycles subject, within which the steel to temperatures

ο heated between 621 C and 677 C and after the cycle im

Oven has cooled down. The second austenitic cyclic Annealing treatment was carried out under the same conditions as

the first austenitic cyclic annealing treatment, however λ

the blank was additionally at 621 C for 48 hours at the end glows for a long time. The typical hardness of the steel delivered and the steel after normalization is in the footnote

mentioned in Table II.

To the effect of the known hardening or softening treatments with the effect of the invention

909843/0742

To compare processes for the softening of high-strength alloy steels, steels with the same composition were subjected to the treatment process according to the invention and the resulting hardnesses are shown in the last column of Table II. In the latter treatment, the steels in the cycle were four times heated to 704 ⁰ C and "deterred it water, after siedann finally at 593 C for 16 h were annealed country. As can be seen, the steel assemblies after the treatment according to the invention are generally considerably softer than after treatment with the known annealing processes. It can also be seen from the values in Table II that the hot-rolled blanks are quite hard in the as-delivered condition, as shown by the hardness of 48 R _{c of} a typical steel P (see footnote). If the blanks are subjected to a subcritical annealing process in the as-delivered condition, that is, if they are heated to a temperature below the lower transformation temperature of 621 ° C

the steels do not _{soften below 29 R n} , with the exception of the

I ^C

Steel A because, as mentioned above, neither chrome

still contained molybdenum. It can also be seen that the doubling of the annealing time to 48 hours does not result in any significant Reducing hardness leads. By doubling the annealing time for those blanks that were heated at 1,038 C with Water have been quenched, a certain decrease in hardness has been achieved, but as can be seen from the table most steels are still too hard to allow efficient drawing of wire. As in the following-

»09843/0742

BATH ORIGINAL

which is discussed, it was found that annealing temperatures below 593 C make the steels harder because of the aging hardening effect of chromium and molybdenum obtained hardnesses were higher than those of the blanks in the delivery state.

The novel softening makes calibrating the ER-% weichungseffekt large amounts of stable, transformed austenite to benefit This structure occurs in high nickel steels in appearance, which are subjected within the between critical temperature range a cyclic heat treatment in which spots produced by alloy-enriched austenite, which at the Cooling to room temperature remains stable. Thus, as a result of the successive temperature changes within the intercritical area according to the method, a considerable amount of alloyed λ- enriched, transformed austenite is produced. The final subcritical anneal ages the transformed martensite and any fresh martensite created by quenching the unstable transformed austenite.

Ö09843 / 0742

As can be seen from the following description, optimal results can be achieved by cyclical temperature changes between the temperature range of 621 ° C to 760 ° C and the martensite transformation range as well as by annealing at a temperature in the range of 566 ° C to 635 ° C. Although some softening, which may be sufficient in many cases, can not be achieved than two hours by an annealing over a period of, it is advantageous that ψ final annealing to at least about 10 hours, but preferably extend at least 16 hours. Quite generally, the longer the annealing time, the lower the hardness.

The effect of the variation in the inter-critical cycle temperature is shown in Table IV Results based on the compositions given in Table III. As can be seen, occurs in the temperature range from about 649 to about 732 ° C a greater decrease in hardness, while the hardness increases in the range above 732 ° C slightly increased.

909843/0742

C. 11 Mn O P. TABBLLE IH ⁺ Ni 1 1 Cr Mon Co V Al designation O. 105 O.OlO O .0016 S. Si 10. Oil O .02 0.99 7.57 TFTT 0.006 S. 0. 0.78 .007 0.006 0.090 5. .55 0.55 0.052 0.014 τ 0.004 0.23 ⁺ Test analyzes

TABBLLB IV

Hardness. Rockwell C

Intermediate critique After furnace designation Cycle temperature cooling from
1038 ° C S. 621 ° C 37.0 3 649 ° C 37.0 S. 677 ° C 37.0 S. 704 ° C 37.0 S. 732 ° C 37.0 S. 760 ° C 37.0 T 621 ° C 27.5 T - ⁶⁴⁹ o ^r 27.5 T «77 ° C 27.5 T 704 ^e C 27.5 T - 732 ° C 27.5 T 760 ° C 27.5

After 1 cycle *

.5 35 .0 38 .0 40 .0 43 .0 44 .0 30th .0 31 .0 38 .0 42 .0 43

To

Cycles

32.0 30.5 33.5 38.5 43.0 42.5

28.5 27.0 29.5 36.5 37.5 42.0

Cycle - 1 hour at temperature and water quenching to room temperature annealing - 16 Standen at 593 C and water quenching to room temperature.

To

Cycles

and glow

29.0 31.0 23.0 28% 29.5 33.5

27.5 26.0 26.5 25.5 28.5 32.0

- 12 -

In Table V further results are given that
should show that the original condition of the steel does not significantly affect the final hardness. In these examples
Various initial treatments have been carried out on the samples of composition S. Bs is also closed
recognize that the initial treatments do not achieve a satisfactory reduction in throat thickness, but only after the steel has undergone the cyclic heat treatment according to the invention
and is subjected to glow; only then occurs like that
last column of Table V can be seen, a
substantial reduction in hardness.

TABBLLB V

ι lignin iiiaiiiiiM imbmnmi · ^

Hardness, Rockwell C

To

originally heat after originally after after ^{y θη u} *

Designation heat treatment. 1 cycle 4 cycles of annealing

S 1 43.5 43.0 34.0 28.5

S 2 37.5 45.5 35.0 29.5

S 3 40.5 42.5 34.0 28.5

S 4 37.0 42.5 28.5 27.5

S 5 38.5 40.0 33.0 27.5

T rolled condition 39.5 34.0 24.0

1 - quenched with water at 816 C.

.O.

° 2 - furnace cooled from 816 ° C ⁰⁰ 3 - quenched with water from 1 O38 ° C

<*> 4 - Oven-cooled from 1 038 C

■ * "■» ο

O 5 - Oven-cooled from 1,038 C to room temperature and with ^ quenched liquid nitrogen.

• "° ⁺⁺ cycle - 1 hour at 704 ° C and with water to room temperature

deterred.

Annealing - 16 hours at 593 ° _{r 11nH m4 r Ua} _ _

O and quenched with water to room temperature.

15084 * 4

The effect of the various final annealing temperatures is shown in Table VI. In these examples, samples were subjected to the compositions Sj ^ T and a four-fold cycle at 677 ° C (heated to 677 ⁰ C and then cooled to below the Martensitumwandlungsbereich) and then annealed at various temperatures between 566 C and 649 C. As can be seen from the table, optimal results are obtained in the temperature range between 566 C to about 635 C. At 649 C the hardness begins to increase.

Annealing temp.
⁰ C TABBLLB VI Rockwell C
Hardness after
48 hours
glow designation 566 Rockwell C
Follow up
16 hours
glow 26.0 S. 593 27.5 25.5 S. 621 26.5 27.5 S. 649 26.5 32.5 S. 566 28.5 22.5 T 593 25.0 21.5 T 621 24.0 22.0 T 649 24.0 '28.5 T 25.5

Original Treatment - Oven Cooled at 1,038 C,

cycle four times at 677 ° C.

If the steel is not heated and cooled cyclically, but only cooled and annealed in the oven, then calibrated

909843/0742

unsatisfactory results. This can be seen from Table VII, which shows the results of the treatments on the samples of compositions SS and T. How one
As can be seen, the hardness has not decreased significantly after annealing for 16 hours or even 48 hours after furnace cooling from 1,038 C. However, if the samples are cycled prior to annealing in accordance with the invention, so is
the resulting hardness is much lower.

909843/0742

TABLE VII

Hockwell C Harte after

Rockwell C hardness according to

Rockwell C hardness according to

Rockwell C Hardness after

Oven cooling 16-hour glow. 48-hour glow four cycles

Λ / * NTO / ** W _I V Λ * 9 ** f * »_ i P * Λ * ψ ^ •>« _ i ^ "M ^ V * ^^

Designation of 1 038 C at 593 C

at 593 C

at 677 C and after 16 hours Annealing at 593 ° C

Rockwell C Hardness after four cycles at 677 ° C and after 48 hours, Annealing at 593 ° C

O QD CD

37.0

27.5

32.0

30.5

31.5

29.0

26.5

24.0

25.5

21.5

cn O CX)

The significance of the subsequent annealing treatment in the softening of these steels is based on the information given in Table VIII values reported. In these examples, the samples of the steel compositions were tested on the intermediate critical Area heated, held in this temperature range for one hour and quenched with water. With additional cyclical Treatment (twice more, middle column), the hardness was generally lowered. In almost every case, however, was the harshness of the steel after the final annealing at 593 C for 16 hours.

TABLE VIII

designation Warming up
704 ° C / l hr
removed with water
frightens (2 x) Warming up
+704 C / l hr
removed with water
frightens (2
additional times) .1 Warming up
+593 C / 16 hr,
removed with water
frightens .4 A. 30.9 34 .4 20th • ⁵ B. 31.3 29 .9 25th .2 C. 32.0 30th .5 25th .6 D. 25.3 25th .2 · 23 .9 E. 31.9 29 .6 22nd .9 F. 33.8 31 .6 24 .7 G 34.0 32 .2 24 .9 H 21.3 19 .2 25th .2 I. 32.1 31, .3 22nd .0 J 33.7 33, .6 20th .0 K 33.2 34, .1 25th .1 to
O L. 33.3 33, .6 23 .8th CD M. 31.1 30, , 7 26th .4 CO
■ Γ » N 36.5 38 « 4th 30th .4 CO O 37.2 34. , 0 28 .3 O P. 36.9 33. , 0
, 4 23 .2
.6 Q
R. 31.7
25.2 30th
25, 20th
22nd

1 50845 A

By quenching after every temperature increase up to the intercritical range, the unstable, transformed austenite fresh martensite, whereupon in the following intercritical cycle of martensite is transformed into overaged martensite and reverse austenite. The annealing at 566 to 635 C brings due to the aging of the fresh one formed in the last intercritical cycle Martensites further soften the steels. The glow time at the intermediate critical temperature is not decisive, rather, satisfactory results can also be achieved with annealing times of just a few seconds. Longer Times than 1 hour per cycle are not required. Basically, all steels can be considered Soften drawn alloy systems using the annealing conditions described above.

From the above it can be seen that the original condition has no noticeable influence on the final hardness. Although some of the softening occurs in these steels through the agglomeration of the carbides, it is assumed that that the formation of the stable, transformed austenite contributes most to the softening. It is believed that in the presence of significant amounts of stable transformed austenite, i.e., at least 10%, a softer steel results because the austenite is softer than ferrite and because of the

$ 09843/0742

Austenite, the secondary hardening elements absorbs and holds characterized in solution. It has been found that a maximum amount of stable transformed austenite gives the softest structure, and that the cyclic heating and cooling refines the grain size and increases the grain surface area. It is possible that the smaller grains create more imperfections and greatly increase the nucleation sites for the austenite. This leads to an acceleration of the austenite nucleation rate and the time for the formation of the amount of austenite for the thermodynamic equilibrium, since more crystal nuclei of the austenite and austenite are formed with each cycle until an equilibrium amount is present. It appears that the inertia of the reaction at the temperatures in question results in less austenite formation after a single relatively long cycle than after many shorter cycles. During the annealing process, the martensite is transformed into ferrite and carbide and forms an austenite with a higher alloy content. Relatively long annealing sets in a slow transformation and sufficient diffusion to form a certain amount of high-alloy austenite. The high-alloy austenite formed during quenching, if any, very little martensite, the final microstructure consisting of ferrite, stable, converted Auetenit and carbides,

SO98A3 / O742

Claims (1)

UNITED STATBS STBBL CORPORATION Munich, the PITTSBURGH / PBNNSYLVANIBN yourz.ioSen WILLIAM PBNN PLACB 525, V. St. A. ₂ October 8 , 1966 iw sign / HM Patent application; Process for softening steels * ¹ PATBNT CLAIMB O (O 1. A method for softening high-alloy steels with at least 0.06 % carbon, at least 4 % nickel and other alloy elements from the group consisting of chromium, molybdenum, vanadium and cobalt, characterized in that the steel is subjected to at least two heating and cooling cycles, within which it is heated to the intercritical temperature range of about 621 C to about 760 ° C and then cooled to the martensitic transformation range, and that the steel is then annealed in the subcritical temperature range of about 566 ° C to about 635 C and cooled to room temperature. _ω 2. The method according to claim 1, characterized in that the O zwiechenkritische temperature is in the range of about ** 649 ° C to about 732 ⁰ C. Patent attorneys Dipl.-Ing. Martin Licht, Dipl.-Wirtsch.-Ing. Axel Hansmann, Dipl.-Phys. Sebastian Herrmann 8 MÖNCHEN 2. TH E RES 1 ENSTRASSE 33 ■ Telephone: 292102 ■ Telegram address: Lipatli / Munich 3. The method according to claim 1, characterized in that the steel has four heating and cooling · cycles. 4. The method according to claim I _1, characterized in that the annealing takes place over at least IO hours. 5. The method according to claim 1, characterized in that the annealing takes place for at least 16 hours. 909843/0742