DE2443187A1 - PROCESS FOR MANUFACTURING FLAT ROLLED PRODUCTS FROM MECHANICAL ALLOY POWDERS - Google Patents

Description

International Nickel Limited, Thames House, Millbank,
London , S ₀ W. 1, Great Britain

"Process for the manufacture of flat rolled products from mechanically alloyed powders"

The invention relates to a method for producing flat rolled products from mechanically alloyed powders Composite particles based on nickel, iron or cobalt superalloys. ^

A method for producing mechanically alloyed powders is known from the German Offenlegungsschrift 1 909 781,
in which a powder charge is dry-milled with high energy and its particles are mixed with one another, comminuted and mechanically welded together to form composite particles. The powder is ground until work-hardened particles with the composition of the powder and a hardness that corresponds to half the hardness difference between the initial and saturation hardness result small phase spacing are finely dispersed in one another.

From the German Offenlegungsschrift 1 943 062 it is also

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a method for compacting mechanically alloyed powders, for example by extrusion, is already known. The extrusion however, has the disadvantage that it is used on its own for the production of flat material such as blanks, sheet metal or Tape is not suitable. Up to now, the view has also prevailed that roller compaction of mechanically alloyed powders would encounter practical difficulties given the multitude of parameters to be considered.

The invention is therefore based on the object, a method of roll form densifying or ₀ manufacture of flat rolled products from mechanically alloyed powders to create. The solution to this problem is based on the knowledge that flat material can be produced without difficulty if the compaction temperature, the rolling temperature, the deformation rate and the percentage decrease in thickness are carefully coordinated with one another.

In detail, the invention consists in a process in which composite particles in a superalloy based on Nikkei, iron or cobalt are ^{compressed at 927 to 1150 °} C. and below 1120 ^° C., but above the recrystallization temperature of the alloy with a deformation rate of

-1
3 to 40 seconds "is hot-rolled up to a total thickness _{reduction of 75 to 97% o} During compaction, the powder is brought into a suitable preform in the usual way, for example by extrusion using a die seal.

The powder is preferably hot compacted at a temperature of 1010-1093 ⁰ C during the hot rolling preferably at a temperature of 982 or 1010 to 1O93 ° C with a total, that is _e longitudinal and transverse thickness decrease of upstream

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preferably at least 80% takes place. In order to achieve a high creep rupture strength at high temperatures such as 1038 ⁰ C, the alloy should be annealed after hot rolling at a temperature of 1204 ⁰ C, for example, until melting begins, which causes secondary recrystallization and a structure with a coarse and elongated grain essential without fine-grained components. In this way, for example, 0.51 mm dikkes sheet metal can having a high creep rupture strength "at temperatures to 1038 ⁰ C in both the longitudinal manufacture and the transverse direction ,, Such sheet is suitable for the manufacture of gas turbine, combustor and Nachverbrennerteilen.

The particles of the starting powder preferably have approximately the same hardness as saturation in order to ensure a high internal energy. The compaction of the starting powder, for example, by hot pressing, effected presses in an extruder using a closed die and die forging ,, Compaction st emp he ature may however 1150 ⁰ C does not exceed, as higher temperatures, a stress relief annealing, thereby reducing the internal energy of Effect composite particles. Such stress-relieving annealing can lead to an inadmissibly high proportion of fine grains and thus to an impairment of the creep rupture strength. Compaction temperatures below 927 ° C, on the other hand, impair the density and pose the risk of cold cracks. The pressing temperature is advantageously 954 to 1120, better still 982 or 1010 to 1093 ° C.

The hot-pressed body is hot rolled at a temperature above the recrystallization temperature but below 1120 ⁰ C. A hot rolling over 1120 ⁰ C comes due to the dynamic

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Recovery equal in the hot rolling to a strain relief annealing, the rolling temperature and therefore preferably does not exceed 1 076 ⁰ C.

Too strong a dynamic recovery can also occur in the case of rolling at a high temperature, for example above 1093 ^° C. and at the same time a high deformation rate of, for example, over 20 seconds, which at the same time caused adiabatic heating in the rolling stock

Rolling temperatures that are too low, especially at higher deformation speeds, can lead to over-deformation or over-rolling and thus to an impairment of the material properties with an increasing risk of crack formation. Therefore is particularly suitable a roll temperature 996-1080 ⁰ C. on rolled alloys tend namely to a recrystallization structure with the same axes of grains or with a high proportion of fine-grained constituents. In contrast, under-rolled alloys are not subject to any significant secondary recrystallization.

The hot rolling must be carried out at a deformation speed of 3 to 40 seconds. At deformation speeds below 3 see "is the deformation energy given to the material compensated to a certain extent by the dynamic recovery, so that secondary recrystallization is not possible.

—1 is borrowed. Bring deformation speeds over 40 seconds at lower rolling temperatures, however, the risk of a Rolling over or, at the higher rolling temperatures, too strong adiabatic heating and too strong recovery themselves. A deformation speed is particularly suitable

-1 -1

from 15 to 30 sea, better still from a maximum of 20 sea.

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The hot rolling must continue until the decrease in thickness in both the longitudinal and transverse directions reaches 75 to 97%. An insufficient reduction in cross-section or deformation rate adversely affects secondary recrystallization and does not produce any stretched coarse grain, if at all a coarse-grained structure is created. A total cross-section would decrease by more than 97%, on the other hand, would lead to over-deformation. A cross-sectional decrease of 80 to 91% is therefore particularly suitable.

The invention is illustrated below using exemplary embodiments and the drawing of the closer explained. In the drawing show:

1 shows a graphic representation of the relationship between rolling temperature and decrease in thickness when rolling in one direction and

FIG. 2 shows a graphic representation corresponding to the diagram in FIG. 1 for the case of cross rolling.

From the diagram it appears that a roll temperature of 1010 ⁰ C and a thickness reduction of 90.5% results in rolling in a direction of rolling over, while there are no difficulties in cross-rollers. While the aforementioned roll temperature is suitable in both cases, it comes in rolling in a direction toward unacceptably high internal stresses ₀ Accordingly, the rolling temperature, the thickness reduction and the strain rate should preferably be matched so that the rolling conditions in the rolling in one direction a point between the two curves AB and CD of the diagram of FIG. 1 or, in the case of cross-rolling, a point between the curves EF and GH of the diagram of FIG

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Fig. 2 correspond.

In order to improve the high temperature strength, the alloy should be subjected to a coarse grain annealing. However, if the material thickness is less than 2.54 mm, the recrystallization annealing should be carried out before the hot rolling is finished. In this way, a stretched grain can be avoided, which extends over the entire thickness of the material and impairs the strength and ductility. In any case, the compact must be subjected to a total thickness decrease of at least 75%, preferably of at least 80%, during hot forming before coarse-grain or recrystallization annealing . Optionally, the alloy can be heat treated during hot rolling _e

With regard to an optimal creep rupture strength, the coarse fraction and recrystallization annealing should be carried out depending on the alloy composition at a temperature of 1204 ⁰ C to the melting start ,, In general, an annealing temperature is 1288 to 1343 ⁰ C; it results in a coarse grain with an aspect ratio over about 5: 1, for example from 10: 1 to 50: 1-

In tests, mechanically alloyed superalloy powders of the composition shown in Table I below were used, each of which contained nickel as the remainder and was produced by grinding for twenty-two hours in a 455! Ball mill at 75 rpm. The powder of composite particles of the apparent composition of Table I were placed in boxes and after the closing of the cans at 1038 ⁰ C in a closed extruder under comparable

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Twist condensed into sticks,

Table I.

Alloy Cr Al Ti Zr BY ₂ O,

W (%) 00

1 20 0 ₀ 6 1.0 0o07 0.007 1.3

2 20 1.2 2.4 0.07 0.007 1.3

Part of the press stick was initially except for one square cross-section and then rolled out to form blanks or sheet metal. The remaining billets were divided and ground down, to create parallel surfaces on which sheets of mild steel were welded «,

All billets were hot-rolled under the conditions resulting from Examples 1 to 4 below. When producing the thinner sheets, several starting sheets were stacked and placed in a sealed container rolled out of soft steel «, such a container can also made of stainless steel or nickel. To avoid sticking, alumina powder was placed between the sheets as a separating agent sprinkled «, a suspension is also suitable for this purpose of glass or other ceramic materials. With the The finished sheets could easily be separated from one another separate.

The rolled sheets were ^{annealed at 1316 °} C. to form a structure

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to develop with a stretched coarse grain and to achieve an optimal creep strength »The annealing took place for all sheets with a thickness of more than 2.54 mm after hot rolling, otherwise during hot rolling to over the to create transverse grain boundaries throughout the sheet metal thickness.

The creep rupture strength and elongation at break were determined at a temperature of 1038 ⁰ C. The criterion for creep rupture strength at this temperature can be a service life of at least 1000 hours at a load of 68.95 N / mm «,

example 1

The powder 1 in accordance with Table I was compacted at a temperature of 1038 ⁰ C to a 38.1 mm thick billet, which was then rolled under the conditions of Table II to a 3.175 mm thick sheet. During hot rolling, the longitudinal direction of the billet ran parallel to the roll axis and the total cross-sectional reduction was 91%. The roll diameter was 45.7 cm and the rolling speed 41.5 m / min. The mechanical properties of various samples of this sheet are shown in Table III below. The tests A to C fall while under the invention, during the trial D outside the invention is ₀

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thickness Table II - (mm) Deformation
swiftly
speed Sting 38o1 Rolling direction (see " ¹ ) 29.6 • 0 19.1 4th 1 12.7 Cross over 6th 2 9.5 It 7.3 3 6.4 Longitudinal direction 7.3 4th 3.2 ti 10.3 VJl Il 17.6 6th ti

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Table III

Longitudinal samples

Cross samples

Γ Τι Ver
search WaIz-
temp.
( ⁰ C) load
(N / mm ² ) without break was standing
Time
(H) Deh
tion was standing
Time
(N / mm ^) load
(N / mm ² ) was standing
Time
(H) Deh
tion
I OjC. ι
V yO / was standing
Time
1000 h
(N / mm ² ) I.
O i O 9 8 1 1 / A. 982 131 115.2 *
■ 32.8. 2.2 114 131
138 163.8 *
309.8 *
40.5 1.8 128 CD
CO
-J B. 1038 131 235.8 *
262.7 2.2 128 <131
131 145.6
469.8 3.5 128 CO C. 1093 131 168.6 *
61.8 2.7 131 <117
117 47.3 *
9.4 1.8 97 D. 1150 <124
124 163.0 *
15.1 2.7 103 117 189.6 *
24.4 2.7 97 * =

The data of Table III show that a service life of 1OOO hours yields irrespective of the rolling direction ₀ An optimal creep rupture strength in both directions can be achieved at a roll temperature of 1038 ⁰ C, although at a roll temperature of 982 ⁰ C a higher creep rupture strength crosswise to the rolling direction and at a rolling temperature of 1093 ⁰ C results in a better creep rupture strength in the longitudinal direction. On the other hand, the data in Table III show that the creep strength begins to decrease at a rolling temperature of 1150 ° C.

Example 2

From the mechanically alloyed powder 1 of Table I, a 3.175 mm thick sheet was produced in accordance with Example 1. The sheet metal was then ^{annealed at 1316 °} C. for 30 minutes and then freed from the steel sleeve by pickling. Three square sheet metal samples with an edge length of 127 mm were stacked in a container made of mild steel using alumina as a release agent. After closing the container, the stack was rolled out in two stitches and one direction to a thickness of 9.5 mm. The sheet thickness was 1.27 to 1.54 mm. From the following Table IV, the creep rupture strengths of three by the novel process of hot-rolled samples at different temperatures are compiled E to G at 1038 ⁰ C

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Table IV

Longitudinal samples

Cross samples

attempt

WaIter temp.

load

(N / mm ² )

Service life

(H)

strain

Service life
1000 h

(N / mm ² )

load

(N / mm ² )

Stand- elongation

Oi) 00

Standing time
1000 h

(N / mm ² )

cn E. 982 103 306.5 * 1 ,8th 110 103 92.2 * 1 ,8th 97 O 110 121.1 * CD 117 28.0 * 110 23.8 OO 124 51.3 _ _i F. 1038 103 547.7 * 1 ,8th 110 103 42.7 * 0 , 9 93 110 123.2 * O 117 27.9 * 103 25.3 * CO 124 49.9 110 14.4 • <i G 1093 103 69.2 * 1 ,8th 93 103 63.1 1 ,8th 93 (J) 103 154.0

* = without break

The data in Table IV show that the creep rupture strength is greater in the longitudinal direction than in the transverse direction. The difference should decrease as the stack is rolled over. In each case, there was an optimal creep rupture strength at rolling temperatures of 982 to 1038 ⁰ C,

Example 3

According to Example 2, the alloy was made from the powder 1 according to Table I 0.5 to 0.8 mm thick sheets produced and examined with regard to their creep rupture strength using the data shown in the table below.

Rolling temperature
temperature
( ⁰ C) Bela
stung
(N / mm Table V strain
(%) Service life
1000 h
(N / mm ² ) along
across 1038
1038 103
103 0.9
0.9 90
83 attempt was standing
Time
² Kh) H 44.9
4.7

The data in Table V prove the excellent creep behavior of the alloys rolled by the method according to the invention. . ■

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Example 4

A powder of alloy 2 according to Table I was used in accordance with the method according to the invention with an overall thickness decrease of 9096 among those from the tables below VI to VIII apparent conditions 6.35 mm thick sheets are produced.

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WaIz-
temp.
( ⁰ C) Table VI Cross-sectional
acceptance
(%) Walzrich
tion 1066 57 along Sting 1066 Deformation
speed.
(lake") 40 along* 1 1066 6.4 47 along 2 1066 7.1 25th along 3 10.6 4th 8.8

WaIz-
temp.
( ⁰ C) Table VII Cross-sectional
acceptance
00 Walzrich
tion 1066 35
29 along
across Sting 1066 Deformation
speed.
(see " ¹ ) 40 along 1 1066 4.7 47 across 2 1038 7.1 25th along 3 10.6 4th 8.8

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WaIz-
temp.
( ⁰ C) Tabel VIII Rolling mill
t ung Sting 982 Deformation
speed
(see " ¹ ) Cross-sectional
acceptance
(JO along 1 982 4th 35 across 2 982 5.2 37 across 3 982 7th 40 along 4th 982 10.9 50 along 5 8.6 23

The sheets were grobkorngeglüht one hour at 1316 ⁰ C and cured for 24 hours at 704 ⁰ C. Thereafter, the creep rupture strength at 1038 ⁰ C was studied using the models in the following Table IX data.

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Ver Rolling mill Cross-section decrease across Table IX calculator.total Calculator.TimeStand search thing- 00 cross section sab- strength gene 0 total take lengthways 1038 ⁰ C / 1000 h) along across - lengthways across OO 17th sectional 00 (N / mm ² ) (N / mm ² ) I. VI 90 acceptance 85 89 75 62.5 00 cn J VII 90 80 74 75 ο cc K VIII 50 90 78 86 co _ ₅ 92 GC

The method according to the invention is particularly suitable for nickel superalloys with up to 65%, for example 1 to 25 or 35% chromium, up to 30%, for example 5 to 25% cobalt, up to 10%, for example 1 to 9% aluminum, up to 8%, for example 1 to 7% titanium, especially with a total aluminum and titanium content of more than 6% and for nickel superalloys with up to 30%, for example 1 to 8% molybdenum, up to 25%, for example 2 to 20% tungsten, up to 10% niobium and up to 10% tantalum, in particular with a total content of molybdenum, tungsten and niobium and tantalum of at least 4%; up to 2 or 4% zirconium; up to 0.5% boron and up to 5% hafnium; up to 2% vanadium; up to 6% copper, up to 5% manganese and up to 70% iron; until 4% silicon. Cobalt superalloys are also more similar Composition. The superalloys can be effective Amounts, for example up to 10% by volume, of a refractory dispersoid such as oxides, carbides, nitrides and borides contain. The dispersoids can be made from compounds of the elements yttrium, lanthanum, thorium, zirconium, hafnium, titanium, Silicon, aluminum, cerium, uranium, magnesium, calcium and beryllium are made up. The superalloys preferably contain up to 5% by volume of one or more dispersoids.

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Claims (1)

Claims t 1. A method for producing flat rolled products from mechanically alloyed powders made of composite particles based on nickel, iron or cobalt superalloys by compaction, characterized in that the composite ^{particles are hot-compacted at 927 to 1150 0} C and the hot-pressed body at temperatures above the recrystallization temperature and below 1120 ⁰ C with a deformation -1
speed of 3 to 40 seconds as well as a total Thickness decrease from 75 to 97% is hot rolled. 2. The method according to claim 1, characterized in that the hot pressing temperature 1010 to Is 1093 ° C. 3. The method according to claim 1 or 2, characterized in that the rolling temperature is 982 to 1093 ⁰ C. 4. The method according to one or more of claims 1 to 3, characterized in that the rolling temperature is 996 to 1080 ⁰ C. 5. The method according to one or more of claims 1 to 4, characterized in that the rate of deformation 5 to 30 seconds. 509811/0876 ::,: 6. The method according to one or more of claims 1 to 5, characterized in that the Deformation speed is not more than 20 seconds. 7t method according to one or more of claims 1 to 6, characterized in that the total decrease in thickness is 80 to 91%. 8. The method according to one or more of claims 1 to 7, characterized in that the Rolling in one direction under conditions corresponding to a point between curves AB and CD of the diagram of FIG Figure 1 takes place. 9. The method according to one or more of claims 1 to 7, characterized in that rolling in two directions under conditions corresponding to one Point between the curves EF and GH in the diagram of the figure takes place » Process according to one or more of Claims 1 to 9, characterized in that the rolling stock is ^{coarse-grain annealed at a temperature of 1204 0} C up to the start of melting. 509811/0876 Blank page