FR2462478A1 - PROCESS FOR THERMALLY TREATING AN IRON-NICKEL-CHROME ALLOY - Google Patents

Abstract

A. THE PROCESS FOR TREATING AN IRON-NICKEL-CHROME ALLOY IS PREFERABLY INTENDED FOR MATERIALS USED IN NUCLEAR REACTORS. B. WE HEAT THE ALLOY BETWEEN 1000 AND 1100C FOR 30S TO 1 HOUR, COOLS IN AN OVEN, COLD FACTORY ON 10 TO 80, HEATS AGAIN BETWEEN 750 AND 825C FOR 4 TO 15 HOURS, COOLES IN THE AIR, AND FINALLY REHEATS BETWEEN 650 AND 700C FOR 2 TO 20 HOURS THEN ALLOW TO AIR COOL. C. THIS PROCESS SIGNIFICANTLY IMPROVES THE TENSILE STRENGTHS OF ALLOYS AND THEIR DUCTILITY AFTER IRRADIATION AND DECREASES THEIR SWELLING UNDER IRRADIATION.

Description

The present invention relates to a method of treating

  thermal effect of an iron-nickel-chromium alloy.

  The present invention is particularly intended for the treatment of certain special nickel-chromium-iron alloys, having very strong mechanical characteristics and at the same time a resistance to swelling under the effect of irradiation, as well as a low absorption of neutrons, such alloys being particularly intended for use as

  coating fast breeder reactors.

  An example of such material is the super-

  gamma-premium reinforced alloy; the properties of this alloy

  can be very strongly modified by modifying the

  thermomechanical treatment to which it is subjected. For applications to nuclear reactors, it is desirable to subject the alloy to a thermomechanical treatment giving the greatest resistance to radiation-induced swelling and / or greater strength, and, more importantly, ductility.

highest post-irradiation.

  To this end, the invention relates to a method of heat treatment of an iron-nickel-chromium alloy, composed mainly of 25% to 45% nickel, 10% to 16% chromium, 1.5% to 3% molybdenum or niobium, from 1% to 3% of titanium, from 0.5% to 3% of aluminum, and the balance being iron, this process being characterized in that the alloy is heated to a temperature of between 1000 ° C. and 1100 ° C. for a period of between 30 seconds and 1 hour, then it is cooled in the oven, the alloy is cold-worked at between 10 and 80%, and the alloy is heated to a temperature of between 750 ° C. and 8250C for 4 to 15 hours, then let it cool in air and heat the alloy to a temperature between 6500C and 7000C

  for 2 to 20 hours, and finally allowed to cool in air.

  According to a preferred characteristic, the initial heat treatment is carried out at a temperature of between 1050 ° C. and 10 ° C. for 2 to 5 minutes for

  minimize the residence time in the oven. This treatment

  The initial thermal process is followed by an oven cooling and a cold machining, preferably a cold rolling on

  at 50%. The alloy is then preferably heated to a temperature of

  7750C for 8 hours and allowed to cool in air before final heating and subsequent cooling to air. The present invention will be described in more detail with the aid of the following examples:

EXAMPLE I

  An alloy whose composition corresponds to Table I below is used, and this alloy is subjected to various thermomechanical treatments: TABLE I Nickel - 45% Chromium - 12% Molybdenum - 3% Silicon - 0.5% Zirconium - 0.05% Titanium - 2.5% Aluminum - 2.5% Carbon - 0.03% Boron - 0.005% Iron - co.mplement The alloy above is a super-alloy gamma-premium reinforced. Table II given below indicates the various thermomechanical treatments to which the alloy, the composition of which is given in Table I above, is subjected; Table III lists the properties of microstructure and

  mechanical properties of this alloy resulting from the treatment

thermal energy.

TABLE II

  Desiccation Thermomechanical treatment AR 1038 C / 1 h / FC + 60% CW IN-1 * 982 C / 1 h / AC + 788 C / 1 h / AC + 720 C / 24 h / AC IN-2 * 890 C / 1 h / AC + 800 C / 11 h / AC + 700 C / 2 h / AC EC * 927 C / 1 h / AC + 800 C / h h / AC + 700O C / 2 h / AC 3O EE * 800 C / 11 h / AC + 700 C / 2 h / AC

after 1038 C / 1 h / FC + 60% CW.

TABLE III

* 6500C

  Designation Observations UTS (MPàP 80 Ma SR (hi AR no gamma-prime, high density of dis- charge 468 IN-1 ganma-prime bimodal, recrystallization at -1044 5.5

above the gamma solvus

premium

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  TABLE III (cont.) 6500C Designation Observations UTS '(MPa) 80 (MPa) SR IN-2 trimodal gamma-prime 974 564 (dislocated) EC trimodal gamma-prime recrystallized below - 446 bimodal EE gamma-prime solvus Table III above shows that the EC-referenced treatment gives breaking properties under higher forces than the IN-1 treatment. EC treatment results in a trimodal distribution of gamma-prime, since the recrystallization annealing was below the gamma-prime solvus and resulted in the precipitation of a low

  volume of gamma-prime precipitates of large size (approximately

600 nm).

  Of the treatments in Tables II and III, three treatments resulted in dislocated structures. These are AR, IN-2 and EE treatments. The information on the breaking stresses according to Table II showed that the EE heat treatment gave a much stronger material. This structure resulted in a dislocated, nested cell structure that was "punched" by a bimodal gamma-prime distribution. This corresponds to the greatest resistance ever tried and was very stable because

  of the punched structure of the dislocation cells.

  The invention will also be described using the

  graphic represented in the single appended figure.

  The graph in the figure shows the swelling behavior of the alloy of Table I under three different thermomechanical conditions namely ST, EC, EE. The swelling curves as a function of temperature are established for radiation doses of 30 dpa, equivalent to 203 MWd / MT

  (that is, greater than the desired creep of 120 MWd / MT).

  The figures show that the ST and EE treatments resulted in the lowest swelling of the alloy of the

  Table II above. EC treatment has given an acceptable level

  swelling table for the desired creep, but the treatment

  was far from optimum for applications within the

of a reactor.

EXAMPLE II

  An alloy having the composition given in the following Table IV is used and subjected to thermomechanical treatments analogous to those of Example I:

TABLE IV

  Nickel 60 - Chrome 15 Molybdenum 5.0 Niobium 1.5 Silicon 0.5 Zirconium 0.03 Titanium 1.5 Aluminum 1.5 Carbon 0.03 Bore 0.01

Iron complement.

  The heat treatments mentioned above and applied to the alloy of Table IV have resulted in mechanical properties and microstructural properties for the resulting alloy, given in Tables V and VI below:

TABLE V

  Designation Thermomechanical treatment BP 1038 C / 1 h / AC + 800 C / il h / AC + 700o C / 2 h / AC BR 927 C / l- h / AC + 8oo0C / 11 h / AC + 700 C / 2 h / AC BT 1038 C / 0, 25 h / AC + 899 C / 1 h / AC + 749 C / 8 h / AC CT 30% WW at 1038 C + 800 C / 1 h / AC + 700o C / 2 h / AC cu 890o C / 1 h / AC + so800o C / 11 h / AC + 700 C / 2 h / AC + 30 BU 800 C / 11 h / AC + 700 C h / AC

* After 1038 C / 1 h / FC + '60% CW.

TABLE VI 650 C-

  Description UTS (MPa) 809 a) SR (h) low range-prime BP 942 no BR bimodal gamma-prime dislocation 1051 503 gamma-prime bimodal gamma-gamma gamma cells

no dislocation 933 -

  CT gamma-prime bimodal non-unifor structure - 1066 me (long cells some subdivisions in grains)

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  TABLE VI (continued) 6500C Description UTS (MPa), 80 (MPa) SR (h)

Bimodal gamma-prime CU 1013 -

  elongated cells BU gamma-prime bimodal cells equiaxes 1078 510

  The gamma-prime solvus and the recrystalline

  For 1 hour, as for the alloy of Table IV was 9150C + 100C and 10000C + 200C. That's why, unlike

  the alloy in Table I, there was no temperature range

  allowing recrystallization by aging. As a result, the BP and BT treatments having an annealing at 103 ° C. and then a subsequent double aging resulted in a non-dislocation austenitic matrix and a bimodal gamma-prime distribution. The structures obtained by CU and BU treatment, which did not induce recrystallization, all exhibited a strongly dislocated cell structure containing various

gamma-premium distributions.

  Table VI is a summary of the structures observed and the corresponding physical properties. It will be noted that the magnitudes of the mechanical properties are grouped into two classes. These are the non-dislocation density, the gamma-prime containing structures at 650C, the final tensile strengths being between 9450 and 9590 bar, the

  dislocated gamma-prime structures that are much more resistant

  tents with ultimate tensile strengths, which are between 10290 and 11000 bars. Because of their greater resistance and because of the interest of the increased incubation time for swelling, it is preferable to have

dislocated structures.

  The CU treatment given in Tables V and VI above began with a dislocated cell structure and trimodal gamma-prime distribution, which was cold-milled to 30%, later. The final cold-machining operation actually decreased the strength as indicated by the extreme tensile strength information at 6500C

  (Table VI) probably coming from the destruction of the

  integrity of the dislocation cell walls.

  The BR and BU treatments of the Table IV alloy

  both resulted in a highly dislocated structure,

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  recrystallized or even to the recovery of a

  cell structure, with a bimodal gamma

  premium dimensions. The BU treatment is preferable since it resulted in properties at break under stress, slightly higher than the BR treatment. The dislocation structures and the gamma-prime structures for the BU treatment resulted in a much more dispersed and nested cell structure than that obtained by the EE treatment of the alloy indicated in Table I. The minimum thickness of the cells according to FIG. the BU treatment was approximately the same

  than the gamma-prime particle spacing.

  To demonstrate the improvement obtained with the aid of the thermomechanical treatment according to the invention, reference will be made to

  Tables VII and VIII show that the heat treatment

  that is very effective to ensure after irradiation a high ductility. In this respect, it should be noted that there is an area in which the ductility of these materials is very

  greatly reduced when tests are conducted at a temperature

  which exceeds the irradiation temperature of the materials by 1100C. Thus, the lowest ductility is found at

  temperature of 8050C for a material irradiated at 6950C.

  This offset at 1100C takes into account all the phenomena

  transients, for example in a fast-acting fast reactor

  nérateur. Thus, the choice of material and the heat treatment or the thermomechanical treatment of the material which, for an irradiation at 6800C, must be tested at 805 ° C., where the lowest ductility post-irradiation is obtained. Tables VII and VIII show very clearly that, for example, the solution state of the alloy D66 irradiated at a temperature of 69 ° C., and then tested

  at a temperature of 8050C, gave a zero ductility. Contrary

  the material that has been subjected to the indi-

  above for the same alloy irradiated at 6950C, then tested at 8050C, allows a uniform elongation of 1.1%. That is

  critically important to maintain superior ductility

  less than 0.3% under these conditions, since this is necessary to maintain the integrity of the fuel rods when the reactor is in divergence; the tables show that these goals are achieved. Tables VII, VIII also show that, in this treatment, the higher ductility obtained is accompanied by a stronger resistance which is very unexpected for

7 2462478

  irradiated materials. These stronger resistances also confirm

  the excellent resistance to swelling shown by

  the alloys subjected to this treatment process.

TABLE VII

  Propo'l: t.t ltl ltriac cioit LI ~ l.:Lligu D -G66 iVuC - ,, O L L: i.UI iz: Tldio6u p "r 'du, IuU t: roL

The chanr-

  he 1 01o Naked | U.U.U.I.I.

Tmp). UI

  ], what is it? a: i q (i,: L 1 'I)

(tl ') I'.

  - i. The Co-ordination of Women (17) (17)

7 1 D66 SA1

I1 I

Lt, I, I.

  I B R -03 __ _ _ _ _ _ __ _ _ _ _ _ __ __ 5_ _i

  BR-03! 695 9232 410 4 81 9.2 905.3 1236. 9 9.0 9.0

  i BR-76 i 735 2 _37 2 _ 4 848. 6__9_ 2 97.3 129 1.4 9.0 9.0!

- II .-- II. 7.6 _ - '' 11- '-1

  _BR __- 2 _ '5500S 4xlO4 899.2 996.4 1152.9.? 07 76 1 1_-2_9 v600 600 4xlo'4 815.5 953.0 i078.5 2.2 33 _ _ _ _ _ _ _ _ _ _ _ __ _ '-1 4i _ _ _ _ _ _ _ _ _ _ __ 1 BR-19; 695 1695 i 4xl0 7756 850.1 879.1 1.3 1.3 3 t - I i 5. '3 BK-32 735 735 4xl04 701 1 746.0 0.15 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ___ ___ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _8, 735, 734 . 682.6 682.5 018 0. - _

| I I I_ _. -__ [--__

  B <- '23 500 610 4x104 7518 d. _ 910.2 0.13 0.13 3_

B1 (-41 695 80 14x104 237.3.3--

TL: istanc: rl i. n. o Li

-TI Fi -

- 1 -

  diaorr _ 01g; i: l: l c; 7L ti f o, ri I j - ',, lug "- /' c 1 o i

1 1-. I

BR-51 4x0l'4 1464.8!

- - - I

  ## STR1 ## l 1 -7-1 448.2 <Ju t: sicuI 104o8.6

161116: 0

1 973.7

_Ij, t .. I_ I-

---- I - .- -

(1. CrI O.01 LA, he

1 - - - - A

  g '> 0% 4c co -r srb1 n 1 1) 2.2 Alr, S 1: fit _9. 2

0.03 (I

I. 0 ']

1 1 (; ..,.;, I w Ln w O rO o tn

TABLE VIII

  Tensile Properties of D 66-EE Alloy Irradiated with Neutron Echan- Irradiation

Temp.

N (C)

________

Time to test

_________.

Rate

deformations

  Elastic proportion 1 imitation (Mpa) |

r ---------------

  Resistance to stresses (MPa) I Terminal resistance

at the trac-

(PMa) I

r -------___-

Elongate-

uni form (%) '

Elongate-

total (%)

D66 EE

  Creep 22 -2 theoretical = 4 x 10 22n-cm-2 (E> 0.1 MeV)

  BT-50! 450 232 4X104 1295.3 1474.0 1721.6 4.5 4.8

  BT-49 695 232 4xlO-4 1108.7 1187.3 1441.01 1 4.8 4.8 BT-30 | 735 232 4xlO4 1035.8 1114.1 1385.8 5.7 5.7 BT-42 450 450 4xlO-4 1134.8 1250.8 1418.4 2.8 3.6 BT-47 500 500 4xlO-4 1052.9 1178.4 1379.1 | 31 | 3.2 BT-61 550 550 1 4x10-4 926.5 1163.3 1369.41 4.1 4.1 BT-41 600 600 4xlO-4 916.5. , 111.5 1312.6 3.4 5.3 BT-26 695 695 | 4xlO-4 672.7 789.4 909.41 2.8 6.3 BT-43 7 35 7 4xlO-4 538.7 616.4 714.31 2.3 3.5 BT-21 450 560 4x10 -4 899 6 1198.3 1297.01 1.15 1.2 BT- 35 500 610 14xlO4 866.5 1122.5 1220.51 1.4 1. 7 BT-00 550 650 4x1r0-4.770.8 963.3 1038.5 1.6 2.8 BT-18 I 600 710 4xlO-4 536.6 _ 704.0 784.71 1.7 2.0 iT49 0 x '39445154011 2.2 o O o Ln 4>. 0% cO 4- Co U1 wn BT-48 4x10-4 339.4 455.1 504.0 1.11 w o

I -------. -----------_

Irradiation

Temp.

  iN o (C) w o Test time Rate of

deformations

  Pn OJ o IUl o TABLE VIII (continued) Proportion Resistance Elastic resistance to terminal

limit constraints to traceability

(MPa) (MPa) tion I '| (a)

Elongate-

  uniform payment () Ln Total elongation (%)

1 I

  Special tests D66-EE Theoretical creep

  BT-31 500 610 4x10 -4 1006.2 1185.2 Sample taken after deformation

  ! 0.56% and cut for microscopic examination BT-58 i 550 232 4x10 1153.0 1242.8.] 452.4 '5.4 5.6

I -I- - _ 4

  BT-07 600 232 4xlO 1165.7 1247.1 1461.8 5.4 5.4 BT-71 | 500 232 4x10 1104. 0. _1201.6 1482.6 6.]. 6.1 BT-74, 600 71 7410 4x10 842 27 5.7 I i A 1 1

iBT-77 600 | 710.

  _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

558.1 I 1637.61 698.4 1.3 2.2

  to ___ ... J __.... ---------- L ..........

Q r1% 0% rN C4O Co

Claims (1)

REVENDICATI 0 NS) Process for the heat treatment of an iron-nickel-chromium alloy comprising essentially between 25% and 45% nickel, 10 to 16% chromium, 1.5 to 3% molybdenum or niobium, between 1 and 3% of titanium, between 0.5 and 3% of aluminum, the balance being iron, process Characterized in that the alloy is heated at a temperature of between 10 000 and 11 000 C for a period of 30 seconds to 1 hour , then cooled in the oven, cold-milled the alloy on 10% to 80% o, heated the alloy has a temperature ranging between 7500C and 8250C for a duration of 4 to 15 hours, cooled in the air and finally the alloy is heated at a temperature of about 6500C-700 ° C for a period of 2 to 20 hours, then allowed to cool in air. 2) Process according to claim 1, characterized in that the alloy is initially heated to a temperature of the order of 10250C to 10750C for 2 to 5 minutes. Process according to one of Claims 1 and 2, characterized in that the alloy is cold-milled by cold rolling for 20 to 50%. Process according to claim 3, characterized in that 30% to 50% cold rolling is carried out on the alloy. A method according to claim 1, characterized in that the alloy is in the form of a tube and is cold-worked by drawing the tube to achieve a reduction of 15% to 35%.   6) Process according to claim 5, characterized in that a reduction is carried out in a range between 20% and 30%.   ) Method according to claim 1, characterized in that after cold machining, the alloy is heated to a temperature of about 7750C for 8 hours, and then left cool in the air.