Physical and Numerical Analysis of Extrusion Process for Production of Bimetallic Tubes Page: 95 of 108
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+ 102 304
A A A A A
t=2hr, t=0,T=25 C,
t = 2 hr,
T= 1100C, E= 1.2
t >> 2 hr, T = 25 C,
Fig. 4.71. Microstructural development schematic for the co-extruded
stainless and plain carbon steel. P-pearlite, A-austenite,
F-ferrite, MxCy-Cr-rich carbides.
4.3.7 Conclusions from Interface Study of Co-extruded Tubes
1. Simulation of interface microstructural development show that the majority of carbide
precipitation in the stainless steel and decarburization of the plain carbon steel occurs after
extrusion during the cool down to room temperature. At higher cooling rates, such as those seen
in the Gleeble bonding experiment, a layer of martensite develops at the interface. The effect of
strain and strain rate is minimal on the formation of these features other than changing the
thickness of the layer after the preheat treatment due to bond surface extension/layer thickness
compression. The preheat TT was not long enough to remove all porosity at the interface under
normal shrink-fit pressures.
2. Chromium carbides precipitate on the austenite grain boundaries in the stainless steel, and iron
carbides precipitate in the ferrite matrix in the plain carbon steel side of the interface.
3. Accurate simulation of bond microstructural development can be performed via a combination of
FEM modeling to determine state variables and thermomechanical means, provided that the
proper TT profile is followed, including the anticipated cool down to room temperature during
4. Sensitization of the stainless steel can be minimized by using higher cooling rates after extrusion,
but subsequent heat treatments will be needed to temper the martensite layer that may develop.
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Misiolek, W. Z. & Sikka, V. K. Physical and Numerical Analysis of Extrusion Process for Production of Bimetallic Tubes, report, August 10, 2006; United States. (digital.library.unt.edu/ark:/67531/metadc884646/m1/95/: accessed September 23, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.