Electron microscope helps prevent post-weld strain-age cracking of Rene 41 by identifying in advance microstructures that are detrimental to welding

Hensley, W. E.

English

NASA Technical Reports Server

April 1970	 Brief 70-10081 
- 
	 TECH - BRIEF 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage commercial 
application. Tech Briefs are available on a subscription basis from the Clearinghouse for Federal Scientific and Technical 
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be directed to the Technology Utilization Division, NASA, Code UT, Washington, D.C. 20546. 
Rene 41 Heat Treatment Electron Microscopy 
.
The problem: 
Rene 41 is a high-temperature, precipitation-hard-
ened, weldable alloy. Post-weld strain-age cracking of 
components made from Rene 41 alloy has been a 
serious problem. Variations in raw material or in 
processing may lead to excessive stress, which can 
contribute to post-weld strain-age cracking. The 
welding of 0.250-inch thick Rene 41 plates to a 1-
inch thick forging in a rocket engine manifold gives 
a typical example in which complex heating and cool-
ing cycles during manufacture leave no opportunity 
for conventional strength-developing heat treatments. 
Therefore, it is necessary for each manufacturer to 
find a unique solution to post-weld strain-age crack-
ing problems with Rene 41. 
The solution: 
Because the mechanism of strain-age cracking 
appeared to be related to both Y ' and metal carbide 
precipitates, a program was begun to determine micro-
structural changes resulting from heat treatment vari-
ations. The electron microscope was used as an inspec-
tion tool to identify in advance microstructures that 
are detrimental to welding. 
How it's done: 
Electron microscopy was used in the study of Rene 
41 precipitation reactions because in this alloy, the 'y 
precipitate is so fine that magnification of 10,000X is 
required before it becomes possible to observe phase 
morphology. The electron micrographs produced in 
this study constitute an extensive catalog of the micro-
structure of Rene 41 as influenced by various heat 
treatments. At this stage of the investigation, a number 
of general results may be stated: 1) metal carbide may 
be dissolved given sufficient heat-treatment time at
1975°F; 2) a continuous grain-boundary (carbide) 
film is usually formed during aging following rapid 
cooling from solution heat treatment (exceptions were 
5 and 10 hour solution heat treatment at 2200 and 
2050°F respectively); 3) aging at 1650°F tended to ag-
glomerate matrix (Y) precipitates, and, after low-
temperature solution heat treatment, tended to pro-
duce spheroidal grain boundaries; 4) Y precipitate 
was depleted by aging at 1800°F, and dissolved by 
aging at 1400°F, regardless of solution heattreatment 
temperature; 5) the rate of precipitation in grain 
boundaries and in matrix increased with aging temp-
erature and, to a lesser extent, with solution heat-
treatment temperature; 6) the rate of hardening and 
maximum hardness rise was greater for higher temper-
ature solution heat-treatments; and 7) recovery from 
cold-working under solution heat-treatment is not 
complete at 1975° F, but is complete at 2150* F. 
The photographic data collected forms the basis for 
a better understanding of acceptable fabrication prac-
tices. However, a required further step is to correlate 
the observed microstructural characteristics with 
processing behavior, particularly with respect to the 
problem of strain-age cracking. 
In order to identify more clearly the relationship of 
processing history and heat treatments to the occur-
rence of strain-age cracking, the following steps are 
recommended for further investigation: I) positively 
identify grain boundary (carbide) and matrix (y') pre-
cipitates; 2) quantitatively determine the 'to metal 
carbide ratio and relate this ratio to strain-age cracking 
susceptibility; 3) study hardness and microstructural 
changes during early stages of precipitation (less than 
one-hour aging) and after slow cooling from the solu-
tion heat treatment temperature, 4) determine the ex-
(continued overleaf) 
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tent of matrix shrinkage and the resulting residual 
stress during .Y' precipitation; 5) compare (by means of 
spot check of solution and aging heat treatments) other 
heats of Rene 41 with the present electron microscope 
and hardness data to establish the general validity 
of these results; 6) correlate microstructural and hard-
ness data with the records and processing history of 
incoming material, to deduce the relationship between 
microstructural properties and behavior; 7) establish 
the effect of those solution heat treatments which 
cause discontinuous grain-boundary precipitate aging 
on post-weld strain-age cracking susceptibility and 
other mechanical properties; 8) investigate the nature 
and extent of Y' depletion near grain boundaries in 
weld-heat affected zones of known thermal history; 
and 9) determine the efficacy of welding Rene 41 that 
has been slow cooled from the solution heat treatment 
temperature. 
Notes: 
1. For information on a related investigation, using 
a weld-circle patch test to determine the charac-
teristics of Rene 41 alloy material, refer to Tech 
Brief B69-10605.
2. The following documentation may be obtained 
from:
Clearinghouse for Federal Scientific 
and Technical Information 
Springfield, Virginia 22151 
Single document price $3.00 
(or microfiche $0.65) 
Reference: Rene 41 Heat Treatment Elec-
tron Microscopy (N69-71272) 
Patent status: 
No patent action is contemplated by NASA. 
Source: William E. Hensley of 
North American Rockwell Corporation 
under contract to 
Marshall Space Flight Center 
(MFS-18633) 
Brief 70-10081	 Category 04


Rene 41 heat treatment electron microscopy

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