The influence of carbon content on austenite-ferrite morphology in Fe-Mn-Al weld metals
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Communications The Influence of Carbon Content on Austenite-Ferrite Morphology in Fe-Mn-AI Weld Metals C H A N G - P I N CHOU and C H I E N - H S U N LEE Recently, Fe-Mn-A1 alloys have attracted considerable attention as promising candidates to substitute for the traditional Cr-Ni stainless steels. Accordingly, many basic characteristics and possible uses were studied and evaluated by many researchers. For the past few years, a series of Fe-30Mn-9A1 alloys with various carbon contents was examined to evaluate the weldability using the Varestraint test. tq However, only little attention has been paid to the studies of the microstructural characteristic and solidification process of the Fe-Mn-A1 welds. ]2~ In contrast, there has been much effort to elucidate the relationships solidification process, ferrite content, and characteristic solidification morphology in the austenitic and duplex weld metal of Cr-Ni stainless steels. I3,4,51 It is well known that carbon is a strong austenite former; thus, a small amount of carbon addition would affect the ferrite content of Fe-Mn-A1 alloy pronouncedly. In this communication, the influence of carbon content on the ferrite-austenite morphology in the welds of Fe30Mn-9A1 alloys was studied through optical microscopy analysis. In this study, the base metal was produced through air induction melting, casting, hot forging at 1200 ~ homogenization at 1050 ~ for 12 hours, cold rolling, then annealing at 950 ~ for 1 hour. The final thickness of the test specimen was controlled to be 1/8 of an inch. The autogenous gas-tungsten arc-welding (GTAW) process was employed to make a weld. The welding parameters used were 10 V, 150 A, and a travel speed of 5 m m / s . The chemical compositions of the base and weld metals were analyzed by inductively coupled plasma atomic emission spectroscopy (ICP-AES) and are presented in Table I. The metallographic specimens were etched in 8 pct nital solution (8 pct HNO3, 92 pct alcohol) for various etching times (1 to 3 minutes). Ferrite content below 40 pct was measured by ferritescope,
Fig. 1 - - T h e weld morphology of Fe-30Mn-9Al-l.29C alloy showing dendritic structure of austenite (ferrite content < 0.9 pct).
CHANG-PIN CHOU, Associate Professor, and CHIEN-HSUN LEE, Graduate Student, are with the Department of Mechanical Engineering, National Chiao Tung University, Hsinchu, Taiwan, Republic of China. Manuscript submitted November 7, 1988.
Table I.
Fig. 2 - - T h e weld morphology of Fe-30Mn-9AI-1.0C alloy (ferrite content < 10 pct).
Chemical Compositions and Ferrite Contents of Fe-Mn-AI-C Alloys
Wt Pct
Ferrite Content (Pct)
Alloy
Fe
Mn
A1
C
Si
Base Metal
Weld Metal
M1 M2 M3 M4 M5 M6
bal. bal. bal. bal. bal. bal.
30.04 29.00 29.76 29.73 28.91 29.44
8.882 9.010 9.169 9.085 9.995 10.02
1.29 1.00 0.68 0.43 0.311 0.116
0.0192 0.0175 0.0165 0.0180 0.0481 0.0419
0.0 0.0 8.1 23.4 35.0 52.0
0.9 10.2 23.0 35 to 40 45 to 65 65 to 80
METALLURGICAL TRANSACTIONS A
VOLUME 20A, NOVEMBER 1989--2559
Fig. 3---The weld morphology of Fe-30Mn-9A
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