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Formation of phosphides in P-doped 304L stainless steel
Materials Letters 13 (1992) North-Holland
MALETTERS
161-165
Formation of phosphides in P-doped 304L stainless steel Jin Ik Suk, Young Cheol Yoon, Soon Hyung Hong and Soo Woo Nam Department of Materials Science and Engineering, Korea Advanced Institute ofScience and Technology. 3 73. I, Kusung Dong, Yusung Gu, Taejon. South Korea Received
18 October
199
I ; in final form 3 January
1992
The precipitation of phosphide and the orientation relationship with the austenitic matrix in P-doped 304L stainless steel have been studied in detail using transmission electron microscopy and computer-simulated stereographic projection. The M,P phosphide was identified in aged samples and confirmed by computer simulation of selected area diffraction patterns. The needleshaped phosphide is randomly distributed in the austenitic matrix, and grows into thin laths on (00 1) M austenite planes.
1. Introduction
pared with patterns.
The precipitation behavior of carbides of the type M,,C, in austenitic stainless steel has been extensively studied [ l-31. Froes et al. [4] reported that phosphorus was effective in producing fine dispersions of carbides of the M& type. However, little information on the formation of phosphides in phosphorus-containing austenitic stainless steels has been provided [ 5,6 1. Arata et al. [ 5 ] reported that M3Ptype phosphides formed in austenitic-type 3 10 stainless steel. Rowcliffe and Nicholson [ 61 also reported that needle-shaped Cr3P phosphides formed during ageing in a phosphorus-containing austenitic stainless steel. By means of transmission electron microscopy and diffraction techniques, the orientation relationship between M&-type carbides and the austenite phase has been studied [l-3,7]. On the other hand, the orientation relationship between phosphides and the austenitic matrix has not been reported yet. Observation of the morphology of the phosphides suggests that there are strong orientation relationships. The purpose of this study is, therefore, to clarify the orientation relationship between the phosphides and the austenitic matrix in P-doped 304L stainless steel. In order to determine the orientation relationship, both the stereographic projections [ 81 and the simulated diffraction patterns [9-l 11, which were obtained from the computer calculation, were used, and com0167-577x/92/$
05.00 0 1992 Elsevier Science Publishers
experimentally
observed
diffraction
2. Experimental procedures An experimental heat of a P-doped 304L stainless steel was produced in an induction furnace with a composition listed in table 1. This particular composition was chosen because it is known that its high phosphorus content has a strong influence on the precipitation behavior [ 61. The ingot was forged and hot-rolled to a 15 mm thick plate. The plate was solution-treated at 1373 K for 1 h, rapidly quenched into water and then aged at 1033 K for 50 h. The average grain size of the material was measured as 120 pm. Table 1 Chemical
composition
B.V. All rights reserved.
of P-doped
304L stainless steel (wt%)
Material
P-doped
C Si Mn P S Cr MO Ni
0.029 0.30 1.10 0.209 0.020 18.00 0.39 9.20
304L
161
Volume 13, number 2,3
MATERIALS LETTERS
March 1992
Samples were cut from the heat-treated plate, mechanically polished to 50-80 urn thickness and punched so as to make disks of 3 mm in diameter. Thin foils were produced using jet electrolytic polishing in a solution of 5% HClO,, and 95% acetic acid with a current density of 50-60 mA cm-’ at room temperature. The observation of the foils was performed at 160 keV using a JEOL 200CX transmission electron microscope. Both the stereographic projection 181 and the diffraction pattern [9-l 1] were used to identify the phosphide and to compare the orientation relationship with the austenitic matrix.
3. Results and discussion Fig. la shows a typical precipitation-free transmission electron micrograph of the P-doped 304L austenitic stainless steel solution-treated at 1373 K for 1 h. When this steel is aged at 1033 K for 50 h, different mo~hologies of precipitates appear along grain boundaries and within grains, respectively, as shown in fig. lb. Selected area diffraction pattern taken at region A indicated that the precipitates formed along grain boundaries are the M&,-type carbides (fig. 1b), and are identical to those reported by other workers [ l-3,7], whereas the precipitates formed within the grain are the M,P-type phosphides, as shown in fig. 3, which are similar to the Cr3P phosphide observed by Rowcliffe and Nicholson [ 6 ] . The bright-field image for the zone axis B= [0 12 ] M in fig. 2a reveals phosphides with two variants in orientation with respect to the matrix. The dark-field image, fig. 2b, taken using the (002)r reflection, reveals a needle-shaped phosphide of the type M3P. Fig. 2c shows the bright-field image for the zone axis B= [100 f M.This bight-geld image also reveals two variants of phosphide for the given orientation relationship with austenitic matrix. Fig. 2d shows a dark-field image taken using the (03 1) p reflection. The M,P-type phosphide began to grow as needles in ( 00 1)M austenite directions, as shown in fig. 2. The needles grew into thin lath on {OO1)Maustenite planes, and demonstrate a morphology similar to that observed by others [ 61. Complicated diffraction patterns occur in some 162
Fig. 1. Bright-field TEM micrographs of P-doped 304L stainless steel solution-treated at 1373 K for 1h (a) and then aged at 1033 K for 50 h (b). Selected area diffraction pattern taken at region Ain (b).
cases because coexisting, but differently orientated precipitates increase the number of diffraction spots. Furthermore, even if there is only one kind of precipitate morphology present, there may be several variants of the orientation relationship within the selected area, which may also increase the number of diffraction spots, making superimposed electron diffraction patterns difficult to analyse. However, by using computer simulation [ 9- 111, it is possible to analyse the diffraction pattern and stereographic projection. Figs. 3a and 3b illustrate simulated diffraction patterns taken with zone axis B= [1001Mfor the precipitate variants I and II, respectively. Fig. 3c illustrates a simulated diffraction pattern produced by a
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1992
Fig. 2. Electron micrographs of aged P-doped 304L stainless steel. (a) Bright-field image taken with the zone axis B= [012],. (b) Darkfield image taken using (O02)p reflection. (c) Bright-field image taken with the zone axis B= [ 100]w. (d) Dark-tield image taken using (03 I )p reflection.
superimposition of variants I and IX. A [ 100IM diffraction pattern is shown in fig. 3d, the (002)n spots from variants I and II lie along the two associated (001) M directions. In this case, diffraction spots from variants I and II are present in fig. 3d. The simulated pattern, lig. 3c, is in good agreement with the experimental diffraction pattern in fig. 36. The electron diffraction patterns at other orientations could also be similarly simulated. Based on the analysis of both the electron diffraction patterns and the electron micrographs, it is found that the needle-shaped precipitate, M,P-type phosphide, has DO, tetragonal structure with the lattice parameters a=0.9 15 k 0.003 nm and c-O.457 f0.003 nm, which corresponds to that of the Cr,P phosphide [ 12 ] _
The present work has shown that the crystallographic orientation relationship between phosphide and matrix is as follows:
where the subscripts M and P represent the matrix and the phosphide, respectively. The orientation relationship between the phosphide and matrix gives rise to six possible variants of the matrix because of the cubic symmetry in the matrix. These six possible variants are listed in table 2. Using computer simulation, we can describe the stereographic projection [ 8 1. In order to clarify the orientation relationship between M3P phosphide and austenitic matrix, a superimposed M,P/austenite stereogram was used. First, a IO01 ] M stereographic 163
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(cl Fig. 3. Electron diffraction pattern and simulated pattern for the two variants. (a) Simulated pattern for variant I. (b) Simulated pattern for variant II. (c) Simulated pattern includes two possible variants. (d) Electron diffraction pattern taken with the zone axis B= [ 100]M. Open squares denote matrix spots, open circles denote phosphide spots for variant I and filled circles denote phosphide spots for variant II.
Table 2 Notation
of variants
for the orientation Variant
I II III IV V VI
relationship
between phosphide
Plane
Direction
matrix
phosphide
matrix
phosphide
(001) (001) (100) t 100) (010) (010)
(001) (001) (001) (001) (001) (001)
[lOOI
[ too1 [tool [tool [tool [lOOI I1001
projection is constructed for the planes normal to the matrix, based on its lattice parameter, and then [ 00 1 ] p stereographic projection of the phosphide is superimposed on that of the matrix. This projection coincides with one variant of the above orientation
164
and matrix
[OlOl [out1 [utul 1001 I [tool
relationship; that is (OO1)Ml] (OOl),; [ 100]Ml] [ 100]P in a [ 0011 M cube projection. This superimposed projection is shown in fig. 4, the central pole (00 1) M of the matrix coincides with pole (00 1) P of the phosphide (see arrow). Another pole ( 100)M with re-
Volume 13, number
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LETTERS
1992
quenched from 1373 K and aged at 1033 K for 50 h. The needle-shaped phosphide formed within the austenite phase is randomly distributed in austenitic matrix, and grows as thin laths on (00 1 ) M austenite planes. Based on the electron diffraction patterns and stereographic projection, the orientation relationship between M3P phosphide and austenitic matrix is determined as {OOl},~~{OOl},; ( 100)Ml)( loo),,. This orientation relationship gives rise to six possible variants of the matrix.
References
r
[ 1 ] L.K. Singhal and J.W. Martin, Acta Metall. 16 ( 1968) 1159. I
0.2
I
Fig 4. Stereographic representation ship between phosphide and matrix.
[2] D. Vaughan,
Phil. Mag. 8 (1972)
281.
[ 31 F.R. Beckitt and B.R. Clark, Acta Metall. I5 ( 1967) I1 3.
of the orientation
relation-
spect to the matrix coincides with pole (1OO)r with respect to the phosphide (see arrow).
4. Conclusion Both M& carbides and M,P phosphides were observed in a P-doped 304L stainless steel after being
[4] F.H. Froes, M.G.H. Wells and B.R. Banerjee, Metal Sci. J. 2 (1968) 232. [ 51 Y. Arata, F. Matsuda and S. Katayama. Trans. JWRI 5 (1976) 135. [6] A.F. Rowchffe and R.B. Nicholson, Acta Metall. 20 ( 1972) 143. [ 71 T.F. Liu, S.W. Peng, Y.L. Lin and CC. Wu. Metall. Trans. 21A(1990)567. [ 81W. Prantl, Metallography 21 (1988) 33. [ 91 J.C. Li, P.P. Chen and H.C. Eaton. Scripta Metall. 2 I ( 1987) 561. [lo] T.D. Gates, A. Atrens and 1.0. Smith, Scripta Metali. 22 (1988) 1695. [ 1 I ] C.S. Lee, J.W. Kim, C.N. Park and Y.G. Kim. Scripta Metall. Mater. 24 ( 1990) 639. (121 W.B. Pearson in: A handbook of lattice spacings and structures of metals and alloys (Pergamon Press, New York. 1958) p. 169.
16.5
MALETTERS
161-165
Formation of phosphides in P-doped 304L stainless steel Jin Ik Suk, Young Cheol Yoon, Soon Hyung Hong and Soo Woo Nam Department of Materials Science and Engineering, Korea Advanced Institute ofScience and Technology. 3 73. I, Kusung Dong, Yusung Gu, Taejon. South Korea Received
18 October
199
I ; in final form 3 January
1992
The precipitation of phosphide and the orientation relationship with the austenitic matrix in P-doped 304L stainless steel have been studied in detail using transmission electron microscopy and computer-simulated stereographic projection. The M,P phosphide was identified in aged samples and confirmed by computer simulation of selected area diffraction patterns. The needleshaped phosphide is randomly distributed in the austenitic matrix, and grows into thin laths on (00 1) M austenite planes.
1. Introduction
pared with patterns.
The precipitation behavior of carbides of the type M,,C, in austenitic stainless steel has been extensively studied [ l-31. Froes et al. [4] reported that phosphorus was effective in producing fine dispersions of carbides of the M& type. However, little information on the formation of phosphides in phosphorus-containing austenitic stainless steels has been provided [ 5,6 1. Arata et al. [ 5 ] reported that M3Ptype phosphides formed in austenitic-type 3 10 stainless steel. Rowcliffe and Nicholson [ 61 also reported that needle-shaped Cr3P phosphides formed during ageing in a phosphorus-containing austenitic stainless steel. By means of transmission electron microscopy and diffraction techniques, the orientation relationship between M&-type carbides and the austenite phase has been studied [l-3,7]. On the other hand, the orientation relationship between phosphides and the austenitic matrix has not been reported yet. Observation of the morphology of the phosphides suggests that there are strong orientation relationships. The purpose of this study is, therefore, to clarify the orientation relationship between the phosphides and the austenitic matrix in P-doped 304L stainless steel. In order to determine the orientation relationship, both the stereographic projections [ 81 and the simulated diffraction patterns [9-l 11, which were obtained from the computer calculation, were used, and com0167-577x/92/$
05.00 0 1992 Elsevier Science Publishers
experimentally
observed
diffraction
2. Experimental procedures An experimental heat of a P-doped 304L stainless steel was produced in an induction furnace with a composition listed in table 1. This particular composition was chosen because it is known that its high phosphorus content has a strong influence on the precipitation behavior [ 61. The ingot was forged and hot-rolled to a 15 mm thick plate. The plate was solution-treated at 1373 K for 1 h, rapidly quenched into water and then aged at 1033 K for 50 h. The average grain size of the material was measured as 120 pm. Table 1 Chemical
composition
B.V. All rights reserved.
of P-doped
304L stainless steel (wt%)
Material
P-doped
C Si Mn P S Cr MO Ni
0.029 0.30 1.10 0.209 0.020 18.00 0.39 9.20
304L
161
Volume 13, number 2,3
MATERIALS LETTERS
March 1992
Samples were cut from the heat-treated plate, mechanically polished to 50-80 urn thickness and punched so as to make disks of 3 mm in diameter. Thin foils were produced using jet electrolytic polishing in a solution of 5% HClO,, and 95% acetic acid with a current density of 50-60 mA cm-’ at room temperature. The observation of the foils was performed at 160 keV using a JEOL 200CX transmission electron microscope. Both the stereographic projection 181 and the diffraction pattern [9-l 1] were used to identify the phosphide and to compare the orientation relationship with the austenitic matrix.
3. Results and discussion Fig. la shows a typical precipitation-free transmission electron micrograph of the P-doped 304L austenitic stainless steel solution-treated at 1373 K for 1 h. When this steel is aged at 1033 K for 50 h, different mo~hologies of precipitates appear along grain boundaries and within grains, respectively, as shown in fig. lb. Selected area diffraction pattern taken at region A indicated that the precipitates formed along grain boundaries are the M&,-type carbides (fig. 1b), and are identical to those reported by other workers [ l-3,7], whereas the precipitates formed within the grain are the M,P-type phosphides, as shown in fig. 3, which are similar to the Cr3P phosphide observed by Rowcliffe and Nicholson [ 6 ] . The bright-field image for the zone axis B= [0 12 ] M in fig. 2a reveals phosphides with two variants in orientation with respect to the matrix. The dark-field image, fig. 2b, taken using the (002)r reflection, reveals a needle-shaped phosphide of the type M3P. Fig. 2c shows the bright-field image for the zone axis B= [100 f M.This bight-geld image also reveals two variants of phosphide for the given orientation relationship with austenitic matrix. Fig. 2d shows a dark-field image taken using the (03 1) p reflection. The M,P-type phosphide began to grow as needles in ( 00 1)M austenite directions, as shown in fig. 2. The needles grew into thin lath on {OO1)Maustenite planes, and demonstrate a morphology similar to that observed by others [ 61. Complicated diffraction patterns occur in some 162
Fig. 1. Bright-field TEM micrographs of P-doped 304L stainless steel solution-treated at 1373 K for 1h (a) and then aged at 1033 K for 50 h (b). Selected area diffraction pattern taken at region Ain (b).
cases because coexisting, but differently orientated precipitates increase the number of diffraction spots. Furthermore, even if there is only one kind of precipitate morphology present, there may be several variants of the orientation relationship within the selected area, which may also increase the number of diffraction spots, making superimposed electron diffraction patterns difficult to analyse. However, by using computer simulation [ 9- 111, it is possible to analyse the diffraction pattern and stereographic projection. Figs. 3a and 3b illustrate simulated diffraction patterns taken with zone axis B= [1001Mfor the precipitate variants I and II, respectively. Fig. 3c illustrates a simulated diffraction pattern produced by a
Volume
13, number
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LETTERS
March
1992
Fig. 2. Electron micrographs of aged P-doped 304L stainless steel. (a) Bright-field image taken with the zone axis B= [012],. (b) Darkfield image taken using (O02)p reflection. (c) Bright-field image taken with the zone axis B= [ 100]w. (d) Dark-tield image taken using (03 I )p reflection.
superimposition of variants I and IX. A [ 100IM diffraction pattern is shown in fig. 3d, the (002)n spots from variants I and II lie along the two associated (001) M directions. In this case, diffraction spots from variants I and II are present in fig. 3d. The simulated pattern, lig. 3c, is in good agreement with the experimental diffraction pattern in fig. 36. The electron diffraction patterns at other orientations could also be similarly simulated. Based on the analysis of both the electron diffraction patterns and the electron micrographs, it is found that the needle-shaped precipitate, M,P-type phosphide, has DO, tetragonal structure with the lattice parameters a=0.9 15 k 0.003 nm and c-O.457 f0.003 nm, which corresponds to that of the Cr,P phosphide [ 12 ] _
The present work has shown that the crystallographic orientation relationship between phosphide and matrix is as follows:
where the subscripts M and P represent the matrix and the phosphide, respectively. The orientation relationship between the phosphide and matrix gives rise to six possible variants of the matrix because of the cubic symmetry in the matrix. These six possible variants are listed in table 2. Using computer simulation, we can describe the stereographic projection [ 8 1. In order to clarify the orientation relationship between M3P phosphide and austenitic matrix, a superimposed M,P/austenite stereogram was used. First, a IO01 ] M stereographic 163
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(a)
(b)
(cl Fig. 3. Electron diffraction pattern and simulated pattern for the two variants. (a) Simulated pattern for variant I. (b) Simulated pattern for variant II. (c) Simulated pattern includes two possible variants. (d) Electron diffraction pattern taken with the zone axis B= [ 100]M. Open squares denote matrix spots, open circles denote phosphide spots for variant I and filled circles denote phosphide spots for variant II.
Table 2 Notation
of variants
for the orientation Variant
I II III IV V VI
relationship
between phosphide
Plane
Direction
matrix
phosphide
matrix
phosphide
(001) (001) (100) t 100) (010) (010)
(001) (001) (001) (001) (001) (001)
[lOOI
[ too1 [tool [tool [tool [lOOI I1001
projection is constructed for the planes normal to the matrix, based on its lattice parameter, and then [ 00 1 ] p stereographic projection of the phosphide is superimposed on that of the matrix. This projection coincides with one variant of the above orientation
164
and matrix
[OlOl [out1 [utul 1001 I [tool
relationship; that is (OO1)Ml] (OOl),; [ 100]Ml] [ 100]P in a [ 0011 M cube projection. This superimposed projection is shown in fig. 4, the central pole (00 1) M of the matrix coincides with pole (00 1) P of the phosphide (see arrow). Another pole ( 100)M with re-
Volume 13, number
2,3
MATERIALS
ii0
.’ &
210
_ 210
‘?I
. ig?
201 .
iol .. 201 x2
Lil ii0
2io
1 iio
’
ii2
+
I22 a
o T
’ 4:
II0
‘?I
‘A’
o+2k2
-210
210
211 l
00211 io2 001 .o 0 0 101 % To 0 _4
0
y2
. ii
ii0
0;
uooo
km :
II0
121 .
l
ii1
211 .
ioo
021 .
i21
I02
ISI
e_
March
LETTERS
1992
quenched from 1373 K and aged at 1033 K for 50 h. The needle-shaped phosphide formed within the austenite phase is randomly distributed in austenitic matrix, and grows as thin laths on (00 1 ) M austenite planes. Based on the electron diffraction patterns and stereographic projection, the orientation relationship between M3P phosphide and austenitic matrix is determined as {OOl},~~{OOl},; ( 100)Ml)( loo),,. This orientation relationship gives rise to six possible variants of the matrix.
References
r
[ 1 ] L.K. Singhal and J.W. Martin, Acta Metall. 16 ( 1968) 1159. I
0.2
I
Fig 4. Stereographic representation ship between phosphide and matrix.
[2] D. Vaughan,
Phil. Mag. 8 (1972)
281.
[ 31 F.R. Beckitt and B.R. Clark, Acta Metall. I5 ( 1967) I1 3.
of the orientation
relation-
spect to the matrix coincides with pole (1OO)r with respect to the phosphide (see arrow).
4. Conclusion Both M& carbides and M,P phosphides were observed in a P-doped 304L stainless steel after being
[4] F.H. Froes, M.G.H. Wells and B.R. Banerjee, Metal Sci. J. 2 (1968) 232. [ 51 Y. Arata, F. Matsuda and S. Katayama. Trans. JWRI 5 (1976) 135. [6] A.F. Rowchffe and R.B. Nicholson, Acta Metall. 20 ( 1972) 143. [ 71 T.F. Liu, S.W. Peng, Y.L. Lin and CC. Wu. Metall. Trans. 21A(1990)567. [ 81W. Prantl, Metallography 21 (1988) 33. [ 91 J.C. Li, P.P. Chen and H.C. Eaton. Scripta Metall. 2 I ( 1987) 561. [lo] T.D. Gates, A. Atrens and 1.0. Smith, Scripta Metali. 22 (1988) 1695. [ 1 I ] C.S. Lee, J.W. Kim, C.N. Park and Y.G. Kim. Scripta Metall. Mater. 24 ( 1990) 639. (121 W.B. Pearson in: A handbook of lattice spacings and structures of metals and alloys (Pergamon Press, New York. 1958) p. 169.
16.5