DD220845A1 - METHOD FOR DELAYING THE AGING EXPERIENCE OF NICKEL ALLOYS AND THEIR USE - Google Patents

Abstract

The invention relates to a process for the thermal treatment of austenitic FeNi or Ni alloys with titanium and / or niobium / tantalum and aluminum and their use as components which are subjected in the temperature range of 800 to 950 K high stresses. In this critical temperature range, it comes after the previously known heat treatments after relatively short periods for aging Verversung and thus premature failure of the components. According to the invention, a delay in this aging prevention has been achieved by following a solution annealing period followed by a period of slowly controlled cooling down to a carbide precipitation annealing of the intermetallic and carbide precipitation phase followed by air cooling and tempering.

Description

field of use

The invention relates to a method for heat treatment of curable Ni. or FeNi base alloys with titanium and / or niobium / tantalum and aluminum contents and their prewonding, which are used as components in the temperature range from 800 to; 950K high stresses or are exposed to this critical temperature range very often. In addition to the more or less stationary operated reactors in the chemical process engineering applies the above stress even with preferential cyclic temperature changes for the hot parts of gas turbines.

Characteristic of the known technical solutions

In order to achieve high creep resistances, preliminary anneals are carried out at FeNiCr and NiCr alloys with intermetallic coherent hardness phase Ni ₃ (TiAl) or Ni ₃ (NbAl) at a sufficiently high temperature and sufficient time to produce a more or less complete solution of all curing. and solidification phases. After cooling from this solution annealing treatment in air, further annealing follows at a lower temperature and for a sufficiently long time during which the solidification phases precipitate (precipitation aging). Other heat treatment methods have been proposed to improve the creep resistance of these thermosetting FeNiCr or NiCr alloys for use temperatures above 950K. For example, the introduction of a carbide precipitation anneal to solidify the grain boundaries separately or following a period of slower controlled cooling from the solution anneal temperature. All these known methods of heat treatment do not take into account the aging embrittlement in the temperature range from 800 to 950 K, which manifests itself, for example, in the low ductility and toughness properties critical for the application. '

Object of the invention. ,

, The aim of the invention is to delay in the temperature range of 800 to 950K unavoidable aging embrittlement compared to the known methods of heat treatment at approximately comparable creep resistances in order to significantly extend the status of the correspondingly claimed reactors, components of gas turbines, etc.

Explanation of the essence of the invention

It is an object of the present invention to provide a method for retarding the aging embrittlement of nickel and iron-nickel alloys of the face centered cubic lattice type within the following basic composition:

Fe O to 50 Wt .-% Cr 12 to 30 Wt .-% Co O to 25 Wt .-% W O to 12 Wt .-% Mo O to 10 Wt .-% Ti 0.30 to 5 Wt .-% Nb / Ta 0 to 5 Wt .-% al 0.10 to 4 Wt .-% Mn 0 to 2 Wt .-% Si 0 to 1 Wt .-% ν: 0 to 0.5 Wt .-% C 0 to 0.3 Wt .-% Ni rest

and other deoxidizing additives such as Mg, Ce, Zr, B, Ca, etc. and alloy impurities up to 0.5% by weight, characterized in that a solution annealing in the range of 1500 to 1300K within 2 to '8 hours with a Cooling rate <5 K / minute, a carbide precipitation annealing of 1300 to 1200K within 2 to 8 hours with a cooling rate <3 K / minute precalcination annealing of the intermetallic and carbide precipitation phases at 1050 to 1150K within 8 to 16 hours followed by air cooling and this annealing by quenching on 900 to 10OOK for a period of 8 to 24 hours with cooling in air is terminated. ^x

The task continued to be to use this alloy for highly stressed parts.

This was achieved for reactor parts in cracking furnaces for EDC pyrolysis and in styrene gas generators and as a material for gas turbine and turbocharger systems.

The creep behavior is governed by the formation and movement of the dislocations as well as the cracking due to the condensation of vacancies. Here, the processes in the interior of the crystals, near the grain boundary and in the grain boundaries themselves play a different role. By thermal treatment of the curable FeNiCrTi (Nb) Al or NiCrTi (Nb) Al alloys, it is possible to achieve a desired arrangement and to fix the dislocations to a certain extent and thus to increase the creep resistance. As a result of preferential removal of chromium carbides at the grain boundaries by a period of slower controlled cooling from the solution annealing temperature followed by a longer carbide precipitation anneal, the steady creep, life, and creep rupture elongation were possible at test temperatures above 950K as compared to air cooling from the solution anneal temperature to increase two to three times. This kprngrenzenstabilisierender effect is achieved by low-excretion grain boundary seams due to carbon and chromium diffusion. As a result of chromium depletion at grain boundary a substantially lower density of excretion ^r intermetallic y 'phase of Ni ₃ (TiAl) or Ni ₃ (NBAI) occurs here. Surprisingly, it has now been found that increased by a further controlled slow cooling to just above the precipitation temperature of the intermetallic γ'-phase with a longer holding time and subsequent cooling in air, the creep rupture even in the critical temperature range of application of these curable alloys from 800 to 950K by more than three times can be. In this connection, no reduction in the creep rupture strength was detected compared to the two-stage standard heat treatment (solution annealing + aging annealing). At the same time, tensile tests on stress-aged four-stage heat-treated specimens had lower 0.2-yield strength ratios to tensile strength and higher elongation at break values over standard heat-treated specimens.

embodiment

The invention will be explained in more detail with reference to an Alisführungsbeispieles.

The Ni-based alloy comprising 74% by weight of Ni, 20% by weight of Cr2.8% by weight of Ti and 1% by weight of Al and 2.2% by weight of deoxidation additives

and alloy-related impurities were thermally treated in four stages as follows: -

1400K / 8h / 4K per minute regulated cooling on; 1275K / 4h / 2.5K per minute regulated cooling on

1125K / 16hrs. / Air cooling

+ 975K / 16h / air cooling

in comparison, the three-stage took place

14OK / 8h / 4K per minute controlled cooling on

1275K / 4h / air cooling ·

+ 975K / 16h / air cooling

and the two-stage thermal treatment (standard heat treatment)

1350K / 8h / air cooling; + 975K / 16h / air cooling; ^f

The creep rupture test results are shown in Table 1 below:

Table 1 two-step     , A5 three-stage four-stage Rm; T; t   t test ,% thermal treatment MPA tempera door 12 BOOStd.-Zeitstandfestigkeitseigehschaften 630 Rm; T; t , '.5 Rm; T; t A5 460 o-c ·, · .. MPA 10 MPA% 380 A5 '' ι 620 20 580 10 270 •% 600 480 25 500 4 180 22 650 350 340 12 18 700 240 230 25 29 750 170 160 30 35 800 38

FeNiCrTiAl alloy containing 32 wt% Ni, 21 wt% Cr; 1.5% by weight of Mn; 0.5% by weight of Ti, 0.25% by weight of Al and 1% by weight

Deoxidation additives, including alloying impurities and iron as the remainder, became four-stage as follows. · Thermally treated:

1400k / 2h / 2.5K per minute controlled cooling on

1275k / 4h / 1,5k per minute controlled cooling to ¹ ^ ^

1O75k / 8h. / Air cooling

+ 925k / 8h / air cooling

In comparison, the single-stage AS treatment

J 400k / 2h / water cooling

In the following comparison Table 2, the strength properties in the thermally treated and aged state are <0.15% bl. Elongation at 875k and 90MPA load after 3000'h. and- <0.25% bl. Elongation at 975k and

7MPA load after 3000h listed:,

Table 2/, '', '', . ' '·'. '-'. ^x ''" . '

State

Prüftemp.

stage

Rp 0.2

MPA

thermal treatment Rm A5 Z Rp

0.2

MPA

rm

four stage

A5

a-or

 yierstuf

 th. Nimbly).

20 600 650

246 185 173

532 412 386

42 37 43

73 66 69

193 160 156

545 398 359

46 44 49

State

test

temp.

⁰ C

stage

Rp 0.2

MPA

thermal treatment Rm _λ A5 Z Rp

0.2% MPA

rm

four-stage A5 Z

aged

875K /

3000Std./

9ÖMPA

Beiast.

20 600

370,297

630 482

33 24

61 51

275 203

592 427

38 32 '

925K / j, 20 314 612 32 61 1.95 526 42 59 aooostd./ 70 MPa 650 230 416 35 57 120 350 38 58 Beiast.

Claims (5)

-1- Zt> »634 ö Invention claims: 1 .. A method for delaying the aging brittleness of face-centered cubic lattice type nickel alloys within the following basic composition:  ; and further deoxidizing additives such as Mg, Ce, Zr, B, Ca etc. and alloying impurities up to 0.5% by weight, characterized in that a solution annealing in the range of 1500 to 1800K within 2 to 8 hours with a cooling rate < 5K / minute, a carbide precipitation annealing of 1300 to 1200K within 2 to 8 hours at a cooling rate of £ 3K / minute, precombustion annealing of the intermetallic and carbide precipitation phases at 1050 to 1150K within 8 to 16 hours followed by air cooling and annealing by annealing is terminated at 900 to 1000 K for a period of 8 to 24 hours with cooling in air. 2. The method according to item 1, characterized in that for a nickel alloy with 74Gew .-% Ni, 20Gew .-% Cr, 2.8Gew .-% Ti and 1.2Gew .-% Al and 2Gew .-% deoxidizer and alloy-related Impurities is subjected to the following heat treatment:   Solution annealing 1400K / 8h. Hold and 4K / minute Cooling time to 1275K / 4h Holding and 2.5K / minute Cooling time to 1 ^ oK / ieh. Hold time / air cooling
, followed by tempering at 975K / 16h. Holding time with air cooling. 3. The method according to item 1, characterized in that for an iron-nickel-chromium alloy with 32Gew .-% Ni, 21 wt .-%; Cr, 1.5% by weight of Mn, 0.5% by weight of Ti, 0.25% by weight of Al and 1% by weight of deoxidizer including alloy-related impurities and Fe as the remainder of the following heat treatment: Solution annealing 1400K / 2h, holding and 2.5K / minute Cooling time to 1275K / 4h Holding and 1.5K / minute Cooling time to 1075K / 8h. Holding time / air cooling - with subsequent tempering on 925K / 8h Holding time with air cooling. 4. Use of a heat-treated alloy according to the method of the points 1 to 3 as a material for chemical plants, which elevate as reactor parts in cracking furnaces of EDC pyrolysis and in Stolygenzeugungsanlagen : Heat stress loads in the temperature range of preferred aging embrittlement are exposed, Use according to item 4 of an alloy heat-treated according to the method of items 1 to 3 as a material for gas turbine and exhaust gas turbines, which are used as hot components in the form of turbine runner rotor and guide vane in high creep rupture in the temperature range of preferred aging embrittlement.