Phase transformations at steel/IN626 clad interfaces
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II. EXPERIMENTAL PROCEDURE An approximately 0.635 cm thick IN625 layer was clad onto both AISI 4130 and 2.25Cr-1Mo steels by two wellR A G H A V A N A Y E R , R.R. M U E L L E R , and D.P. L E T A are with the Exxon Research & Engineering Co., Annandale, NJ 08801. W.J. SISAK is with the Exxon Production Research Co., Houston, T X 77001. Manuscript submitted March 7, 1988. METALLURGICAL TRANSACTIONS A
established processes: (1) a weld cladding method in which the IN625 weld is deposited on the steel surface; or (2) Hot Isostatic Pressing (HIP) where IN625 powder is bonded to the steel under an isostatic pressure in an inert environment and elevated temperature. The nominal chemical compositions of the steels and IN625 used by the manufacturers are listed in Table I. Following the cladding process (the exact conditions of cladding being proprietary), the clads were heat treated by the manufacturer(s), and the samples for the present study were provided in the fully heat treated condition. Table II lists the thermal histories of the clad materials provided by the manufacturers which precede and follow the cladding process. Hereafter, these samples shall be referred to as the as-received samples. The heat treatment temperatures were chosen so as to achieve a 413 MPa yield strength for the AISI 4130 steel and a 517 MPa yield for the 2 . 2 5 C r - l M o steel. In order to examine the bulk microstructures of the steel, IN625, and the interface, specimens large enough to include all these regions were sliced from the clad composite. Specimens for optical and scanning electron microscopy (SEM) studies were prepared by conventional mounting, grinding, and polishing methods. As a result of the widely dissimilar compositions across the interface, it was necessary to etch the specimen separately to reveal the microstructures on either side of the interface. The specimens were first etched with a 2 pct nital solution to reveal the microstructure of the steel. Subsequently, the specimen was etched with a solution containing 2 to 5 g C u C I 2 , 60 ml HC1, and 5 ml H20 to reveal the microstructure of the IN625 clad. Specimens for TEM were prepared using conventional thinning and electropolishing with a solution containing 30 ml HC104, 250 ml 2-butoxy-ethanol, and 750 ml methanol at 250 K. As a result of electropolishing differences between the steel and IN625, the steel side of the specimen was thinned preferentially. Therefore, the electropolished specimens were argon ion-milled to provide thin regions on both sides of the interface. Both an VOLUME 20A, APRIL 1989--665
Table I.
4130 2.25Cr-lMo IN625
Nominal Composition of Base Steels and IN625 Clad
Fe
Cr
Mo
Nb
Mn
Si
C
Ti
A1
Ni
Bal Bal 2*
0.9 2.2 21.5
0.2 1 8
--3.3
0.5 0.2 --
0.2 0.2 --
0.3 0.2 0.02
--0.3
--0.2
--Bal
*Composition varies from 1 pct for HIP clad to 4 pct from weld clad.
EM-430 and an EM 400T-FEG electron microscopes were used for the TEM studies; the energy dispersive spectrometer (EDS) system in the former instrument was equipped with an
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