Phase transitions in rapidly solidified stainless steels cathodically hydrogen charged
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I.
INTRODUCTION
AUSTENITIC stainless steels are being considered as candidate materials for near-term fusion devices, and among the critical properties are their strength, ductility, and swelling resistance at elevated temperatures. Austenite instability resulting from cathodic charging of conventionally processed commercial Fe-Ni-Cr austenitic stainless steels has been extensively studied during recent years. Austenitic stainless steels are known to transform to a'(bcc) and e(hcp) martensite phases during plastic deformation at temperatures below the critical Me temperature (the temperature at which martensite forms from strained austenite 3'(fcc)). [1-9] Austenite can transform to martensite as a result of strain or subzero cooling. Hydrogen can induce transformation of the 3' phase to e and/or a ' martensite phases, t1~ expanded austenite (3'*) and expanded martensite (e*), t8,16-~81 or metastable hydrid phases. [19.2~ Rapid solidification techniques present one means by which the normal solidification structure can be significantly altered. It has been reported that large degrees of undercooling dramatically altered the structure of type 316 stainless steel, t2~J However, the nature of the different phases following hydrogen charging of RS stainless steels has not been published. Thus, the purpose of the present investigation is to characterize the effects of cathodic hydrogen charging and subsequent aging on the martensitic phase transitions and microstructure of RS austenitic stainless steels and compare the RS product with equivE. MANOR-MINKOVITZ, formerly Research Associate, Department of Materials Engineering, Ben Gurion University of the Negev, is with the Materials Department, University of California, Santa Barbara, CA 93106. D. ELIEZER, Professor and Head, is with the Department of Materials Engineering, Ben Gufion University of the Negev, Beer-Sheva, Israel. Manuscript submitted March 2, 1988. METALLURGICAL TRANSACTIONS A
alent conventionally processed commercial ST austenitic stainless steels following identical charging conditions. II.
EXPERIMENTAL PROCEDURE
Rapidly solidified austenitic stainless steels of types 310, 316, and 316TiM (titanium modified), having compositions shown in Table I, were used for the present study. The RS steel ribbons were prepared by the melt spinning technique.t22] The ribbons produced were typically about 70- to 100-/zm thick and 1- to 2-mm wide. The hydrogen charging was performed in a charging cell at room temperature in the absence of any externally applied stress in IN H2SO4 solution with 0.25 g of NaAsO2 per liter added as hydrogen recombination poison. A platinum counter electrode and a current density of 0.5 A cm -2 were used. The charging time was 6 hours. After the charging process was interrupted, the specimens were studied by a PHILIPS* X-ray diffractometer with Co K~ *PHILIPS is a trademark of Philips Electronic Instruments, Inc., Mahwah, NJ.
radiation. Among other radiations (e.g., Cu K~, Cr K~, and Mo K~), the Co K~ radiation reveals the best combina
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