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An Atom Probe Investigation of Addition of Nitrogen in Hot Work Tool Steel

Rehan, Arbab LU (2012) FYSM31 20112
Department of Physics
Abstract
Two different hot work tool steels, QRO 90 and QRO 80N were investigated using atom probe tomography. QRO 90 is a commercial alloy while the other QRO 80N is an experimental test alloy. The main composition of QRO 90 is 0.38C-2.6Cr-2.3Mo-0.9V-0.75Mn (wt%) whereas QRO 80N has the composition 0.38C-1.7Cr-2.7Mo-1.2V-1.1Mn-0.044N (wt%). Hence the main difference between both materials is the nitrogen addition, but there is also an increase in the concentrations of Mo, V and Mn, and a decrease in Cr in QRO 80N. The alloys were investigated after tempering for 1h and 30h, respectively. Previous work has shown an increased tempering resistance of QRO 80N.

Atom probe analysis showed that the QRO 80N and QRO 90 have MC type carbides with mix... (More)
Two different hot work tool steels, QRO 90 and QRO 80N were investigated using atom probe tomography. QRO 90 is a commercial alloy while the other QRO 80N is an experimental test alloy. The main composition of QRO 90 is 0.38C-2.6Cr-2.3Mo-0.9V-0.75Mn (wt%) whereas QRO 80N has the composition 0.38C-1.7Cr-2.7Mo-1.2V-1.1Mn-0.044N (wt%). Hence the main difference between both materials is the nitrogen addition, but there is also an increase in the concentrations of Mo, V and Mn, and a decrease in Cr in QRO 80N. The alloys were investigated after tempering for 1h and 30h, respectively. Previous work has shown an increased tempering resistance of QRO 80N.

Atom probe analysis showed that the QRO 80N and QRO 90 have MC type carbides with mix composition of Mo and V. The number density of the carbides decreases with tempering suggesting that the small precipitates dissolves during the tempering providing more vanadium to big carbides. Mo, V and C are strongly depleted in the matrix due to carbide precipitation. After 30 hours of tempering the carbides in both materials are still MC type. However, they become more V-rich, at the expense of Mo. The Mo/V ratio in the carbides changes from 1.4 to 1.1 in QRO 80N while it changes form 2.2 to 1.0 in QRO 90. The only difference between the materials is that the carbides in QRO 90 have a homogenous distribution of V and Mo; in contrast QRO 80N has an inhomogeneous distribution of Mo and V in the carbides. It is also seen that N is strongly enriched in the V-rich areas inside the carbides. However, the average N content of the carbides is only slightly higher in QRO 80N than in QRO 90.

The difference between the secondary carbides in the two steels is not very large and thus it is difficult to determine the reason for the improved tempering resistance. The separation into V-rich (and N-rich) and Mo-rich regions of the carbide could be due to the addition of nitrogen in the QRO 80 N or it could be a consequence of the increase in V and Mo and the decrease in Cr.

Further investigations on materials tempered for different periods of time can provide a good insight about the material. It could be beneficial in understanding the evolution from early stage precipitation to thermally stable carbides. (Less)
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author
Rehan, Arbab LU
supervisor
organization
course
FYSM31 20112
year
type
H2 - Master's Degree (Two Years)
subject
keywords
atom probe tomography, hot work tool steel, carbides, proxigram, iso-surface
language
English
id
2438384
date added to LUP
2012-06-28 10:14:50
date last changed
2012-06-28 10:14:50
@misc{2438384,
  abstract     = {Two different hot work tool steels, QRO 90 and QRO 80N were investigated using atom probe tomography. QRO 90 is a commercial alloy while the other QRO 80N is an experimental test alloy. The main composition of QRO 90 is 0.38C-2.6Cr-2.3Mo-0.9V-0.75Mn (wt%) whereas QRO 80N has the composition 0.38C-1.7Cr-2.7Mo-1.2V-1.1Mn-0.044N (wt%). Hence the main difference between both materials is the nitrogen addition, but there is also an increase in the concentrations of Mo, V and Mn, and a decrease in Cr in QRO 80N. The alloys were investigated after tempering for 1h and 30h, respectively. Previous work has shown an increased tempering resistance of QRO 80N.

Atom probe analysis showed that the QRO 80N and QRO 90 have MC type carbides with mix composition of Mo and V. The number density of the carbides decreases with tempering suggesting that the small precipitates dissolves during the tempering providing more vanadium to big carbides. Mo, V and C are strongly depleted in the matrix due to carbide precipitation. After 30 hours of tempering the carbides in both materials are still MC type. However, they become more V-rich, at the expense of Mo. The Mo/V ratio in the carbides changes from 1.4 to 1.1 in QRO 80N while it changes form 2.2 to 1.0 in QRO 90. The only difference between the materials is that the carbides in QRO 90 have a homogenous distribution of V and Mo; in contrast QRO 80N has an inhomogeneous distribution of Mo and V in the carbides. It is also seen that N is strongly enriched in the V-rich areas inside the carbides. However, the average N content of the carbides is only slightly higher in QRO 80N than in QRO 90.

The difference between the secondary carbides in the two steels is not very large and thus it is difficult to determine the reason for the improved tempering resistance. The separation into V-rich (and N-rich) and Mo-rich regions of the carbide could be due to the addition of nitrogen in the QRO 80 N or it could be a consequence of the increase in V and Mo and the decrease in Cr.

Further investigations on materials tempered for different periods of time can provide a good insight about the material. It could be beneficial in understanding the evolution from early stage precipitation to thermally stable carbides.},
  author       = {Rehan, Arbab},
  keyword      = {atom probe tomography,hot work tool steel,carbides,proxigram,iso-surface},
  language     = {eng},
  note         = {Student Paper},
  title        = {An Atom Probe Investigation of Addition of Nitrogen in Hot Work Tool Steel},
  year         = {2012},
}