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Thin strip casting of high speed steels
Joumalof
Materials Processing Technology ELSEVIER
Journal of Materials Processing Teclmology 63 (1997) 792-796
Thin strip casting of high speed steels F. Pan S. Zhou X. Liang P. Ding C. Xu Department of Metallurgy and Materials Engineering, Chongqing University, Chongqing 630044, P. R. China
Abstract The thin strip casting of high speed steels W3Mo2Cr4VSi and W6Mo5Cr4V2 has been investigated. The as-cast strips are of 2.5-4 mm thickness, reduced by hot rolling to 1.8-2 mm thickness. The steel sheets are used to make power hacksaw blades. The experimental results show that the metallurgical quality of the as-cast strips is now at an acceptable level, and the as-cast carbides in the strips are very fIne although the eutectic carbide network still exists. However, most of the eutectic carbide network in the strips can be broken up by post-treatment. Cutting test reveals that the performance of these hacksaw blades is satisfactory, compared with that of hacksaw blades made of conventionally produced steel sheets.
Keywords: near net shape casting, thin strip casting, high speed steels
1. Introduction
The strip casting process, which produces strip sheets directly from molten metal, is drawing much interest as a prospective technique in the steel industry, the reason being that the development of the strip casting process may realise not only the shortening of processes and the saving of energy consumption, but also the near-net shaping of difficultto-form materials. One of the most promising approaches amongst various methods for thin strip casting is the twin-roll method. A lot of experimental and analytical studies have been carried out on this method in the past decade[I-9], most of such work being focused on the strip casting of stainless steels and silicon steels [10-16]. At present, pilot tests for the stainless steels have been carried out in at least fIve countries [2, 17]. Little work, however, has been done on the thin strip casting of high speed steels[17]. High speed steels are very important tool materials, their use including the manufacture of hacksaw blades. The thickness of the strip sheets for the hacksaw blades is normally less than 2 mm. When the conventional technique is used to produce the steel sheets, multirolling and multi-annealing are unavoidable in order to decrease the thickness of the products and to break up the as-cast carbides. As a result, the. production process takes a long time. In this investigation, the twin-roll method is used to produce the strip sheets 0924-0136/97/$15.00 @1997ElsevierScienceSA All rights reserved PII S0924-0136(96)02726-4
in order to shorten substantially the production process, the metallurgical quality of the strips and the microstructure, focusing on the carbides, as well as the cutting performance of the hacksaw blades, being examined.
2. Experimental procedure The high speed steels tested in this study are W6Mo5Cr4V2 and W3Mo2Cr4VSi. The former is most widely used in the world, whilst the latter is a low alloyed high speed steel developed recently in China, which has the almost same properties as the former below 600 °C [18]. The twin-roll caster used in the present investigation is shown in Fig. 1. The caster is composed of a pair of water-cooled rolls and two side-sealing dams. The rolls are made of a stainless steel, with the side-dams being made of a refractory material, which are attached the edges of the rolls. The pouring furnace feeds molten metal into a tundish at a constant flow rate using a sliding nozzle. Then, the melt is poured from a spe.cial nozzle into the nips of the rolls, where it solidifIes immediately as it makes contact with the steel rolls. The rolling force is constant during casting. The gap between the two rolls is controlled to a roughly constant value for uniform solidifIcation. The condition of the thin strip casting process is shown in Table 1.
F. Pan et al. / Journal of Materials Processing Technology 63 (1997) 792-796
melt
been chosen to make the side-dams. The results reveal that when this material is used as the side-dam material and the side-dams are attached to the edges of the roll, the edge quality of the as-cast strips is very satisfactory (Fig. 2). The detailed results on this
rolls
as-cast strips
•
793
sheets
II
I rolling solid solution treatment
Fig. 1. An outline of the twin-roll casting process Table 1. Condition of the strip casting process Roll diameter Roll width Height of molten pool Strip thickness Casting velocity Roll material
250mm 150mm 60 - 85 mm 2.5 - 4mm 8 -20 m/min Stainless steel
Fig. 2. The as-cast strips of high speed steels W3Mo2Cr4VSi and W6Mo5Cr4V2
The as-cast strips were annealed at 870 DC for 4 hours, and the annealed strips were heated to 1100 DC before hot rolling. The rolling temperature is between 720-1050 DC. Following rolling, another annealing heat treatment was earned out. The sheets, of 1.8-2 mm thickness, were then heated to 1130-1230 DC for solid solution treatment, which made the carbides in the steel sheets become finer and broke up the eutectic carbide network. Power hacksaw blades were produced by the conventional process, to enable comparative tests to be carried out. The surface cracks and edge quality of the as-cast strips were examined by both the naked eye and optical microscopy. The carbides in the strips and sheets were investigated by optical and scanning microscopy. The cutting tests were carried out in a factory.
3. Results and discussion
3.1. Surface cracks, microstructure
edge
quality
and
as-cast
Cracks on the surface of the as-cast strip were often observed, running perpendicular or parallel to the direction of casting, during the early stage of the present investigation. The rolling force and casting velocity are found to be the two most important factors which affect the number and size of the surface cracks. Another important factor is the surface quality of the rolls. The experimental result show that these cracks can be avoided when the casting velocity of the as-cast strips is less than 15 m/min. The edge quality of the as-cast strips is poor if ascast iron is used as the side-dam materials. On the basis of many experiments, a refractory material has
Fig. 3. The as-cast microstructure of high speed steel W3Mo2Cr4VSi: (a) as-cast strip; (b) as-cast ingot
794
F. Pan eta/. / Journal of Materials Processing Technology 63 (1997) 792-796
aspect will be reported in a future paper. The as-cast microstructure of the strips of the high speed steels is given in Figs. 3 and 4. It can be seen that the as-cast microstructure is definitely rendered more fine by twin-roll casting. The average thickness of the eutectic carbide network in the as-cast strips after twin-roll casting is only 3.2 jJ1Il and 3.8 jJ1Il for W3Mo2Cr4VSi and W6Mo5Cr4V2, respectively, whilst that in the as-cast ingots is about 13.6 jJ1Il and 23.2 jJ1Il for these two types of high speed steels, respectively. This is because the twin-roll casting process has a high cooling rate of about 10 2 °C/s [2,15].
In order to delete the carbide network in the as-cast strips and to make the as-cast carbide become finer, solid solution treatment was used after very limited hot-rolling. The solid solution temperature was 11301150 °C for W3Mo2Cr4VSi and 1210 -1230 °C for W6Mo5Cr4V2. The results show that when the strips of W3Mo2Cr4VSi were heated to 1130 °C for 6 minutes or 1150 °C for 2 minutes, most of the as-cast carbide network disappeared. When the strips of W6Mo5Cr4V2 were heated to 1210-1230 °C for 4 minutes, only a small amount of carbide network could be observed. The size distribution of the residual carbides in the steel sheets after solid solution treatment is shown in Figs. 5 and 6. It can be seen that for W3Mo2Cr4VSi, the size distribution of the carbides in the steel sheets produced by twin-roll casing is similar to that in the sheets produced by conventional method, and no big carbides, of more than 8 jJ1Il, are observed in the sheets produce by twin-roll casting. For W6Mo5Cr4V2, the size of the carbides in the sheets produced by the conventional method is smaller than that in the sheets produced by
~
>
tIi
150 urn
40
(a) By conventional method (W3Mo2Cr4VSi)
35
8 30 ga < U
25
g,
15
~
~
20
10
5
o """"o
--
1
-
'--
2
3
4
567
8
-9
SIZE OF CARBIDES, pm
40 ~
(b) By twin-roll casting
> 35 [i 30 8 Fig. 4. The as-cast microstructure of high speed steel W6Mo5Cr4V2: (a) as-cast strip; (b) as-cast ingot 3.2. Carbides after solid solution treatment Although the as-cast microstructure of the high speed steels is obviously refined by twin-roll casting, the eutectic carbide network in the as-cast strips still exists, which is very detrimental to the mechanical properties of high speed steels. For the conventional process, these carbide network can be broken up by multi-forging and multi-rolling. For the twin-roll casting process, however, hot working is not sufficient.
~ U ~
0
~0
~
(W3Mo2Cr4VSi)
25 20
15 10 5 0
"---
0
'--
'--
1
2
3
..
4
5
11IIII
6
7
8
9
SIZE OF CARBIDES,llffi
Fig. 5. The size distribution of the residual carbides in the sheets of high speed steel W3Mo2Cr4VSi: (a) by conventional method; (b) by twin-roll casting
F. Pan et aL / Journal of Materials Processing Technology 63 (1997) 792-796
twin-rolling casting, but there is not very significant difference between them. If the thickness of the ascast strips ofW6Mo5Cr4V2 can be increased to up to 5 6 mm, the size of the residual carbides in the steel sheets could be decreased because the amount of hot deformation can be increased 3.3. Tempering hardness and cutting performance Tempering hardness is the most important amongst mechanical properties of high speed steels. The tempering hardness of the steel sheets is shown in Fig. 7. No significant difference between the steel sheets produced by twin-roll casting and by conventional method can be seen. The cutting performance of the power hacksaw blades made ofW6Mo5Cr4V2 is given in Fig. 8. The cut material is type TIO carbon steel with a hardness of HRC 27-29. The results show that the cutting speed of the power hacksaw blades made of the steel sheets
66
~ ~u
25
[5
15
~
~
(a)
u 65
~
cti 64
63
•
62
II
en
~
~
61 1100
1120
1140
1160
By conventional method
By twin-roll casting
1180
1200
1220
1240
TEMPERATURE,·C
66 ()
65
en en
64
a: ::r: ~40 .....- - - - - - - - - - - - - - - - - - , (a) By conventional method ;> 35 (W6Mo5Cr4V2) 30
795
•
UJ
z
Cl 63
a: < ::r: 62
II
61 1160
20
~
~)/
1180
1200
By convevtional method
By twin-roll casting
1220
1240
1260
TEMPERATURE. 'C
10
5
o
o
12345678910
Fig. 7. The tempering hardness of the sheets: (a) W3Mo2Cr4VSi; (b) W6M5Cr4V2
steel
SIZE OF CARBIDES, JlIl1
~
;>
en ~ 8
18 cn 16
40
~
(b) By twin-roll casting
35
(W6Mo5Cr4V2)
30
0" ~ ~
~ 25
cJ
20
0
15
u..
~0
a
14 12
l:l...
cn 10
~
10
U
•
8
a
.
• II
By conventional method
II
By twin-roll casting
6 4
5
~ a
a
a
2
3
4
5
6
7
8
9 10
4
2
6
TEST CODE
SIZE OF CARBIDES, JlIl1 Fig. 8. The cutting performance of the power hacksaw blades made of the steel W6M5Cr4V2 Fig. 6. The size distribution of the residual carbides in the sheets of high speed steel W6Mo5Cr4V2: (a) by conventional method; (b) by twin-roll casting
produced by twin-roll casting is approximately the same as that for the blades produced by the conventional
7%
F. Pan et al./Journal of Materials Processing Technology 63 (1997) 792- 796
method, which reveals that the steel sheets produced by the twin-roll casting process can be used to make the power hacksaw blades. This process would result in a sharp decrease of the cost of the power hacksaw blades.
Zhang, Mr. Q. Gan and Mr. K. Wang of Chongqing University for their assistance in laboratory work.
References 4. Conclusions 1. The metallurgical quality of the as-cast strips of the high speed steels W3Mo2Cr4VSi and W6M05Cr4V2 produced by the twin-roll casting process is at an acceptable level, but has potential for improvement. 2. The as-cast carbides in the steel strips produced by the twin-roll casting process are much finer than those in the conventional ingots, but the eutectic carbide network in the as-cast strips still exists. 3. Most of the eutectic carbide network in the ascast strips can be broken up by hot rolling and solid solution treatment. 4. After solid solution treatment, the size distribution of the residual carbides in the sheets of W3Mo2Cr4VSi produced by twin-roll casting process is similar to that in the conventionally processed products. The retained carbides in the sheets of W6Mo5Cr4V2 by twin-roll casting process, however, is somewhat larger than those by conventional method. 5. The tempering hardness and cutting speed of the power hacksaw blades made of the strip cast sheets is approximately the same as those of conventionally processed products, but the cost of the hacksaw blades can be decreased substantially.
Acknowledgements The present work was supported by both the State Education Commission of China and the Natural Science Foundation of China. Part of the work was carried out in Stuttgart University, Germany. The authors thank Associate Professor Y. Wang, Ms. J.
[1] E. J. Kubel Jr,Advanced Materials & Processes, 134(3XI988)55. [2] F. Pan, S. Zhou and D. V. Edmonds, Materials Review, 10(JXI993)38. [3] F. Pan, P. Ding and X. Liang, Acta Materiae Compositae Sinica, 12(1995)32. [4] F. Pan, S. Zhou and X. Liang, Journal ofChinese Mechanical Engineering, 32(JXI996)45. [5] K. Miyazawa and J. Szekely, Met. Trans., 12A(1981)1047. [6] T. Yamauchi, T. Nakanori, M. Hasegawa, T. Yabuki and N. Ohnishi, Trans. ISIJ, 28(1988)23. [7] T. Saitoh, H. Hojo, H. Yaguchi and C. G. Kang, Met. Trans.,20B(1989)381. [8] Y. Fujita, H. Sato, T. Kitagawa, S. Nishioka, Y. Tsuchida and A. Ozeki, ISIJ Inter., 29(1989)495. [9] H. Takuda, N. Hatto, M. Teramura and J-I Kokado, Steel Res., 61(1990)312. [10] T. Arai, M. Yamada, H. Nakashima, H. Takeuchi, S. Tauaka, Y. Yamakam, K. Sasaki and K. Yamamoto, 77th Steelmaking Conference Proceedings, Steelmaking Division of the Iron and Steel Society, Chicago, Vol. 77, (1994), p.357. [11] J. C. Grosjean, J. L. Jacquot and H. Litterscheidt, Iron and Steelmaker, (8)(1993)27. [12] Y. K. Shin, T. Kang, T. Reynolds and L. Wright, Ironmaking and Steelmaking, 22(JXI995)35. [13] A. R. Buchner and J. W. Schmitz, Steel Res., 63(1992)7. [14] J. W. Schmitz and A. R. Buchner, Stahl u. Eisen, 111(1991)67. [15] H. Takuda, S. Kikuchi, N. Hatta and J-I Kokado, Steel Res., 62(1991)346. [16] H. Takuda, S. Kikuchi, N. Hatta and J-I Kokado, Steel Res., 64(1993)132. [17] X. Liang: Ph.D. Thysis, Chongqing University, Chongqing, P. R. China, 1996 [18] F. Pan, S. Zhou and P. Ding, Materials Science Progress, 4(1990)297.
Materials Processing Technology ELSEVIER
Journal of Materials Processing Teclmology 63 (1997) 792-796
Thin strip casting of high speed steels F. Pan S. Zhou X. Liang P. Ding C. Xu Department of Metallurgy and Materials Engineering, Chongqing University, Chongqing 630044, P. R. China
Abstract The thin strip casting of high speed steels W3Mo2Cr4VSi and W6Mo5Cr4V2 has been investigated. The as-cast strips are of 2.5-4 mm thickness, reduced by hot rolling to 1.8-2 mm thickness. The steel sheets are used to make power hacksaw blades. The experimental results show that the metallurgical quality of the as-cast strips is now at an acceptable level, and the as-cast carbides in the strips are very fIne although the eutectic carbide network still exists. However, most of the eutectic carbide network in the strips can be broken up by post-treatment. Cutting test reveals that the performance of these hacksaw blades is satisfactory, compared with that of hacksaw blades made of conventionally produced steel sheets.
Keywords: near net shape casting, thin strip casting, high speed steels
1. Introduction
The strip casting process, which produces strip sheets directly from molten metal, is drawing much interest as a prospective technique in the steel industry, the reason being that the development of the strip casting process may realise not only the shortening of processes and the saving of energy consumption, but also the near-net shaping of difficultto-form materials. One of the most promising approaches amongst various methods for thin strip casting is the twin-roll method. A lot of experimental and analytical studies have been carried out on this method in the past decade[I-9], most of such work being focused on the strip casting of stainless steels and silicon steels [10-16]. At present, pilot tests for the stainless steels have been carried out in at least fIve countries [2, 17]. Little work, however, has been done on the thin strip casting of high speed steels[17]. High speed steels are very important tool materials, their use including the manufacture of hacksaw blades. The thickness of the strip sheets for the hacksaw blades is normally less than 2 mm. When the conventional technique is used to produce the steel sheets, multirolling and multi-annealing are unavoidable in order to decrease the thickness of the products and to break up the as-cast carbides. As a result, the. production process takes a long time. In this investigation, the twin-roll method is used to produce the strip sheets 0924-0136/97/$15.00 @1997ElsevierScienceSA All rights reserved PII S0924-0136(96)02726-4
in order to shorten substantially the production process, the metallurgical quality of the strips and the microstructure, focusing on the carbides, as well as the cutting performance of the hacksaw blades, being examined.
2. Experimental procedure The high speed steels tested in this study are W6Mo5Cr4V2 and W3Mo2Cr4VSi. The former is most widely used in the world, whilst the latter is a low alloyed high speed steel developed recently in China, which has the almost same properties as the former below 600 °C [18]. The twin-roll caster used in the present investigation is shown in Fig. 1. The caster is composed of a pair of water-cooled rolls and two side-sealing dams. The rolls are made of a stainless steel, with the side-dams being made of a refractory material, which are attached the edges of the rolls. The pouring furnace feeds molten metal into a tundish at a constant flow rate using a sliding nozzle. Then, the melt is poured from a spe.cial nozzle into the nips of the rolls, where it solidifIes immediately as it makes contact with the steel rolls. The rolling force is constant during casting. The gap between the two rolls is controlled to a roughly constant value for uniform solidifIcation. The condition of the thin strip casting process is shown in Table 1.
F. Pan et al. / Journal of Materials Processing Technology 63 (1997) 792-796
melt
been chosen to make the side-dams. The results reveal that when this material is used as the side-dam material and the side-dams are attached to the edges of the roll, the edge quality of the as-cast strips is very satisfactory (Fig. 2). The detailed results on this
rolls
as-cast strips
•
793
sheets
II
I rolling solid solution treatment
Fig. 1. An outline of the twin-roll casting process Table 1. Condition of the strip casting process Roll diameter Roll width Height of molten pool Strip thickness Casting velocity Roll material
250mm 150mm 60 - 85 mm 2.5 - 4mm 8 -20 m/min Stainless steel
Fig. 2. The as-cast strips of high speed steels W3Mo2Cr4VSi and W6Mo5Cr4V2
The as-cast strips were annealed at 870 DC for 4 hours, and the annealed strips were heated to 1100 DC before hot rolling. The rolling temperature is between 720-1050 DC. Following rolling, another annealing heat treatment was earned out. The sheets, of 1.8-2 mm thickness, were then heated to 1130-1230 DC for solid solution treatment, which made the carbides in the steel sheets become finer and broke up the eutectic carbide network. Power hacksaw blades were produced by the conventional process, to enable comparative tests to be carried out. The surface cracks and edge quality of the as-cast strips were examined by both the naked eye and optical microscopy. The carbides in the strips and sheets were investigated by optical and scanning microscopy. The cutting tests were carried out in a factory.
3. Results and discussion
3.1. Surface cracks, microstructure
edge
quality
and
as-cast
Cracks on the surface of the as-cast strip were often observed, running perpendicular or parallel to the direction of casting, during the early stage of the present investigation. The rolling force and casting velocity are found to be the two most important factors which affect the number and size of the surface cracks. Another important factor is the surface quality of the rolls. The experimental result show that these cracks can be avoided when the casting velocity of the as-cast strips is less than 15 m/min. The edge quality of the as-cast strips is poor if ascast iron is used as the side-dam materials. On the basis of many experiments, a refractory material has
Fig. 3. The as-cast microstructure of high speed steel W3Mo2Cr4VSi: (a) as-cast strip; (b) as-cast ingot
794
F. Pan eta/. / Journal of Materials Processing Technology 63 (1997) 792-796
aspect will be reported in a future paper. The as-cast microstructure of the strips of the high speed steels is given in Figs. 3 and 4. It can be seen that the as-cast microstructure is definitely rendered more fine by twin-roll casting. The average thickness of the eutectic carbide network in the as-cast strips after twin-roll casting is only 3.2 jJ1Il and 3.8 jJ1Il for W3Mo2Cr4VSi and W6Mo5Cr4V2, respectively, whilst that in the as-cast ingots is about 13.6 jJ1Il and 23.2 jJ1Il for these two types of high speed steels, respectively. This is because the twin-roll casting process has a high cooling rate of about 10 2 °C/s [2,15].
In order to delete the carbide network in the as-cast strips and to make the as-cast carbide become finer, solid solution treatment was used after very limited hot-rolling. The solid solution temperature was 11301150 °C for W3Mo2Cr4VSi and 1210 -1230 °C for W6Mo5Cr4V2. The results show that when the strips of W3Mo2Cr4VSi were heated to 1130 °C for 6 minutes or 1150 °C for 2 minutes, most of the as-cast carbide network disappeared. When the strips of W6Mo5Cr4V2 were heated to 1210-1230 °C for 4 minutes, only a small amount of carbide network could be observed. The size distribution of the residual carbides in the steel sheets after solid solution treatment is shown in Figs. 5 and 6. It can be seen that for W3Mo2Cr4VSi, the size distribution of the carbides in the steel sheets produced by twin-roll casing is similar to that in the sheets produced by conventional method, and no big carbides, of more than 8 jJ1Il, are observed in the sheets produce by twin-roll casting. For W6Mo5Cr4V2, the size of the carbides in the sheets produced by the conventional method is smaller than that in the sheets produced by
~
>
tIi
150 urn
40
(a) By conventional method (W3Mo2Cr4VSi)
35
8 30 ga < U
25
g,
15
~
~
20
10
5
o """"o
--
1
-
'--
2
3
4
567
8
-9
SIZE OF CARBIDES, pm
40 ~
(b) By twin-roll casting
> 35 [i 30 8 Fig. 4. The as-cast microstructure of high speed steel W6Mo5Cr4V2: (a) as-cast strip; (b) as-cast ingot 3.2. Carbides after solid solution treatment Although the as-cast microstructure of the high speed steels is obviously refined by twin-roll casting, the eutectic carbide network in the as-cast strips still exists, which is very detrimental to the mechanical properties of high speed steels. For the conventional process, these carbide network can be broken up by multi-forging and multi-rolling. For the twin-roll casting process, however, hot working is not sufficient.
~ U ~
0
~0
~
(W3Mo2Cr4VSi)
25 20
15 10 5 0
"---
0
'--
'--
1
2
3
..
4
5
11IIII
6
7
8
9
SIZE OF CARBIDES,llffi
Fig. 5. The size distribution of the residual carbides in the sheets of high speed steel W3Mo2Cr4VSi: (a) by conventional method; (b) by twin-roll casting
F. Pan et aL / Journal of Materials Processing Technology 63 (1997) 792-796
twin-rolling casting, but there is not very significant difference between them. If the thickness of the ascast strips ofW6Mo5Cr4V2 can be increased to up to 5 6 mm, the size of the residual carbides in the steel sheets could be decreased because the amount of hot deformation can be increased 3.3. Tempering hardness and cutting performance Tempering hardness is the most important amongst mechanical properties of high speed steels. The tempering hardness of the steel sheets is shown in Fig. 7. No significant difference between the steel sheets produced by twin-roll casting and by conventional method can be seen. The cutting performance of the power hacksaw blades made ofW6Mo5Cr4V2 is given in Fig. 8. The cut material is type TIO carbon steel with a hardness of HRC 27-29. The results show that the cutting speed of the power hacksaw blades made of the steel sheets
66
~ ~u
25
[5
15
~
~
(a)
u 65
~
cti 64
63
•
62
II
en
~
~
61 1100
1120
1140
1160
By conventional method
By twin-roll casting
1180
1200
1220
1240
TEMPERATURE,·C
66 ()
65
en en
64
a: ::r: ~40 .....- - - - - - - - - - - - - - - - - - , (a) By conventional method ;> 35 (W6Mo5Cr4V2) 30
795
•
UJ
z
Cl 63
a: < ::r: 62
II
61 1160
20
~
~)/
1180
1200
By convevtional method
By twin-roll casting
1220
1240
1260
TEMPERATURE. 'C
10
5
o
o
12345678910
Fig. 7. The tempering hardness of the sheets: (a) W3Mo2Cr4VSi; (b) W6M5Cr4V2
steel
SIZE OF CARBIDES, JlIl1
~
;>
en ~ 8
18 cn 16
40
~
(b) By twin-roll casting
35
(W6Mo5Cr4V2)
30
0" ~ ~
~ 25
cJ
20
0
15
u..
~0
a
14 12
l:l...
cn 10
~
10
U
•
8
a
.
• II
By conventional method
II
By twin-roll casting
6 4
5
~ a
a
a
2
3
4
5
6
7
8
9 10
4
2
6
TEST CODE
SIZE OF CARBIDES, JlIl1 Fig. 8. The cutting performance of the power hacksaw blades made of the steel W6M5Cr4V2 Fig. 6. The size distribution of the residual carbides in the sheets of high speed steel W6Mo5Cr4V2: (a) by conventional method; (b) by twin-roll casting
produced by twin-roll casting is approximately the same as that for the blades produced by the conventional
7%
F. Pan et al./Journal of Materials Processing Technology 63 (1997) 792- 796
method, which reveals that the steel sheets produced by the twin-roll casting process can be used to make the power hacksaw blades. This process would result in a sharp decrease of the cost of the power hacksaw blades.
Zhang, Mr. Q. Gan and Mr. K. Wang of Chongqing University for their assistance in laboratory work.
References 4. Conclusions 1. The metallurgical quality of the as-cast strips of the high speed steels W3Mo2Cr4VSi and W6M05Cr4V2 produced by the twin-roll casting process is at an acceptable level, but has potential for improvement. 2. The as-cast carbides in the steel strips produced by the twin-roll casting process are much finer than those in the conventional ingots, but the eutectic carbide network in the as-cast strips still exists. 3. Most of the eutectic carbide network in the ascast strips can be broken up by hot rolling and solid solution treatment. 4. After solid solution treatment, the size distribution of the residual carbides in the sheets of W3Mo2Cr4VSi produced by twin-roll casting process is similar to that in the conventionally processed products. The retained carbides in the sheets of W6Mo5Cr4V2 by twin-roll casting process, however, is somewhat larger than those by conventional method. 5. The tempering hardness and cutting speed of the power hacksaw blades made of the strip cast sheets is approximately the same as those of conventionally processed products, but the cost of the hacksaw blades can be decreased substantially.
Acknowledgements The present work was supported by both the State Education Commission of China and the Natural Science Foundation of China. Part of the work was carried out in Stuttgart University, Germany. The authors thank Associate Professor Y. Wang, Ms. J.
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