Microstructure and Properties of Fine Grained Supersaturated FE-C Alloys
- PDF / 811,892 Bytes
- 5 Pages / 417.6 x 639 pts Page_size
- 86 Downloads / 238 Views
423
MICROSTRUCTURE AND PROPERTIES OF FINE GRAINED SUPERSATURATED FE-C ALLOYS B. L. MORDIKE AND H. W. BERGMANN Institut fLirWerkstoffkunde und Werkstofftechnik, W. Germany
University of Clausthal,
ABSTRACT Rapidly quenched tapes of Fe-C-X alloys (X=Cr, Mn, Ni, Co, Al, Si) were produced by melt spinning. The hardness, ductility, grain size and micro and lattice structure were determined. The system Fe 2.1C 13 Cr was chosen for further study. The transformation (isothermal and continious) characteristics were determined for the as quenched and reaustinitized states. The results can be presented in the form of TTT diagrams and hardness measurements INTRODUCTION Rapid quenching of liquid Fe-C-X alloys with high C content produces a microcrystalline, supersaturated structure. Depending on the alloy element and composition the structure is austenitic,austenitic with carbide precipitation or ferrite with carbide precipitation. The fine grain size and the supersaturated phase causes changes in the mechanical properties and transformation behaviour compared with conventionally cooled alloys. The alloying elements were chosen as they have different effects on graphitisation, carbide formation and austenite stability. To avoid oxidation effects the tapes were produced by melt spinning in a helium atmosphere RESULTS Hardness values were measured in a conventionel microhardness tester on the broad race of polished specimens with a load of 0,1 Kp. A copper support was used.l. A simple reverse bend test was used to characterize the ductility. A bending radius of 0,1 mm was used and the ductility defined as follows: - very 0 brittle less than 1800, brittle >0 1800 < 3600, ductile > 3600 < 7200, very 0 ductile > 720 . The transformation behaviour was investigated in a modified Perkin-Elmer DSC 2 scanning calorimeter, capable of working up to - 10000C.
Fig. 1 shows the influence of composition of austenite stabilisers (Ni,Mn,Co) on the one hand and, on the other, austenite restricters (Cr,Al,Si) on the hardness and ductility of as quenched tapes.
424
1000.
4/%C
.. OC
- 8o •>
S•
•
• 2%
d400.2/C-
2000 0
6
1b T."
1
6 6 16 1oý-Fe-C-M -aLtoys
Fe-C-{r-altoys
12
Wt % Co
Wt%Mn
Wt% Ni
1200
4%C
/.C+2%Si
rA
S
Z -a . , LOL~ • ,•
N,*
-24
•
tdvery ctil ductile
ductile
LINa~
0
odutl
6 Wt% Cr
10 f2
14 f6
01
m
brittle
234 Wt%C
Fig. 1 Influence of composition on the hardness, ductility and structure of as quenched Fe-C-X alloys The symbols employed for the hardness indicate the ductility and crystal structure of the tapes. In all systems increasing the carbon concentration increases the hardness. On the other hand increasing the nickel and manganese concentration reduces the hardness and improves the ductility. This is probably associated with the change from a martensitic to an austenitic structure. Cobalt although it extends the y range is known to raise the martensite start temperature. Consequently only martensitic structures are observed with corresponding high hardness and lack of ductility. Of the a
Data Loading...
