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Industrial Experiment of Reducing Superheat of Steel by Nozzle Cooling
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=Ic ScienceDirect JOURNAL OF IRON AND STEEL RESEARCH, INTERNATIONAL. 2011 18(6) 8 22-25
Industrial Experiment of Reducing Superheat of Steel by Nozzle Cooling YAN Hui-cheng"'
,
QIU Sheng-tao"'
,
WANG Zhong-ying'
TONG Tai-qin3, ZHAO Pei'
,
CAI Yun-teng3,
(1. State Key Laboratory of Advanced Steel Processing and Products, Central Iron and Steel Research Institute, 2. National Engineering Research Center of Continuous Casting Technology, Central Beijing 100081, China; Iron and Steel Research Institute, Beijing 100081, China; 3. Huai Special Steel Co Ltd, Shasteel Group, Huaian, 211600, Jiangsu, China)
Abstract: Nozzle cooling equipment is developed to supervise and control the heat flux by changing water flux. An industrial experiment is held in billet caster in Huaigang The results show that cooling control system works stably and effectively to control the heat fluxes by the temperature of copper tube. The superheat of steel in mould is reduced and the equiaxed crystal ratio, as well as compact degree of steel is raised. Key words: nozzle cooling; low superheat; industrial experiment
.
Low superheat steel is useful to improve the quality of billet. If the temperature of steel in tundish is too low, the inclusion is difficult to float into tundish flux and nozzle clogging often happens. In the 199Os, CRM of Belgium and ARBED of Luxemburg developed a heat exchange shroud and carried out industrial experiment"]. Kenzo AYATA et alCzl of Kobelco designed a shroud with air cooling and electromagnetic stirring for industrial test. Their results indicated that a high equiaxed crystal ratio could be obtained by reducing the superheat of steel. However, the application of the shroud has been not popularized in the steel plants, maybe due to the limits of the controllability and stability of the shroud. Nozzle cooling equipment is developed to cool the liquid steel at the nozzle by adjusting the heat flux via PLC in site. Based on the resultC3-'' in laboratory, the nozzle cooling equipment is set up and experimented in 150 m m X 150 mm billet caster in Huai Special Steel.
1
Experimental Theory and Equipment
1 . 1 Experimental theory In order to reduce superheat of steel and ensure casting stably, the following key points are considered in the equipment design. Cooling media is fog
caused by gas and water, tube temperature can be supervised and cooling water can be changed by PLC timely. T h e experiment equipment is composed of four parts : cooling apparatus, temperature supervising and controlling system, cooling media and emerging nozzle. Cooling apparatus includes copper tube and water sprayer. Cooling media includes transporting tube for water and air, valve and pressure and flow rate meters. Temperature supervising and controlling system includes temperature-measuring and PLC system. T h e working mechanism of four parts is shown in Fig. 1. T h e temperature of immerging nozzle is transported to PLC via copper tube. The water flow rate is adjusted by PLC based temperature. T h e
Vapor
Air Water
.agnletic
I valve TI T, "
Fig. 1
Running mechanism of cooling nozzle
Foundatlon Item: Item Sponsored by State Key Development Program of Basic Research of China (2004CB619107) E-mail: huichengyanCZll63. com; Received Date, June 2 4 , 2010 B1ography:YAN Hui-cheng(l963-), Male, Doctor, Professor;
23
Industrial Experiment of Reducing Superheat of Steel by Nozzle Cooling
Issue 6
water is fogged by high pressed air to cool copper tube and give off as vapor.
Testing equipment 1) Nozzle cooling equipment Nozzle cooling equipment is shown in Fig. 2. It includes input water, input air, output vapor and couple and cooling apparatus. T h e length of copper tube in cooling apparatus is 200 mm, and the outer diameter is $115 mm, inner diameter is $87 mm (upper size) and $84 mm (down size).
1.2
3) Heat flux controlling system online T h e heat flux of emerging nozzle is controlled in a proper zone to ensure low superheat and normal production and not to clog. T, is the temperature value of hot side of copper tube in the middle part. Based on the practical data, the water flow is controlled with the relation of temperature in four ranges (Fig. 3).
TJ v Fig. 3
2
Fig. 2
Nozzle cooling apparatus
2) Improved nozzle T h e carbon content of traditional A1-C nozzle is raised to 50% to improve conductive effect. T h e surface of A1-C nozzle is grounded smoothly to keep good touch with copper tube. Its outer diameter is kept same with the the inner diameter of copper tube and its wall thickness is 15 mm.
Relation between water flow and tube temperature
Result and Analysis
2. 1 Result of industrial experiment T h e industrial experiment is held in 150 m m X 150 mm billet caster in Huaigang. Industrial experiment had been held for five times from 2007 to 2009. Trial steels include No. 45, 60Si2MnA-3, GCrl5. Trial time lasts 1. 5 h to 4 h T h e usage of cooling apparatus made the A1-C nozzle become dimmer, compared with the other nozzles.
.
2.2
Analysis of result of casting No. 45 Parameters of casting No. 45 are listed in Table 1.
Table 1 Testing parameters for No. 45 ~~~~
M-EMS, 320 A, 6 HZ Heat series number Strand number
1104-10503
s1
Temperature of steel in tundish/'C
Casting speed/(m
S6
1104-10504
s1
1531
min-')
-
Air flow rate through nozzle/(m * h-') Water flow rate through nozzle/(L min-') Temperature of inlet water/% Temoerature of outlet water" / %
S6 1518
1529
1523
1528
1520
2.01
2. 0
1.99
2. 0
1. 99
2. 0
1. 99
2. 0
80
/ / / /
80
/ / / /
2-3 22 55-62
2-3 22 56-60
Noter 1) Th e checking point is at the exit of soft metal tube, 5 m away from the cooling equipment.
T h e first strand (S1) is the testing strand with nozzle cooling equipment and the sixth strand (S6) is the contrast strand which is symmetrical to the first strand in position. When the process is stable, the
test is beginning with the second heat. 1) Equipment stability Temperature distribution and variation is collected in Fig. 6. It shows that nozzle cooling equip-
' 24
Vol. 18
Journal of Iron and Steel Research, International
9
ment works stably for a long time and the casting operation can last for several hours. Heat flux can be controlled by PLC timely. 2 ) Temperature supervising and heat conductive analysis Thermocouple is set in copper tube. The points TI and T , is in the middle and at the same height of tube, the distance is I 1 mm between two points of T l and T,. T he point T3 is set at the bottom of tube. In course of testing, the temperature of T I , T z and T, is stable and changed synchronous (shown in Fig. 4). T h e heat flux through the copper tube can be calculated from the temperature distribution in tube.
T h e weight of steel through nozzle is 380 kg/min for casting speed of 2. 2 m/min. T h e c p of steel is 0. 8 kJ/kg 'C 9 0 . 8 X 380 X A T = 4 350 T h e reduced superheat AT is calculated to be 14 'C. 3) Shell solidified in nozzle After casting, the shell tube is formed at the position of cooling equipment along inner wall of nozzle. T h e shell tube is taken out and etched in transversal section (shown in Fig. 5 1. T h e shell has a same length of 180 mm with the cooling tube and a width of 16 mm. Judging from the macro structure, the shell is firstly formed at the position of cooling equipment and then a new layer will cling on it. T h e layers are collected and the appearance show that the shell is in the course of solidification and melting constantly.
I
T3 ,
Fig. 5 Fig. 4 Thermocouple distribution and temperature variation in copper tube
T h e difference between T1and T , is changed in 40- 60 'C and it become a little smaller with the thicker shell during later period. The difference between TI and T z is 45 'C in heat conductive analysis. Heat flux q1 = 360 X 45/0.011= 1. 45MW/m2. Because the temperature of T I , Tz and T , is stable and changed synchronous, the heat flux of whole cooling system is thought t o be uniform and equals to 41. The outer dieter meter of copper tube is 0. 115 m, the inner dieter meter is 0.087 m, the height is 0. 16 m, T h e fact cooling area of copper tube F = 2 X 3.14 X 0.16 X (0.115/2 - 0.087/2 )/In ( 0. 115/0.087 1 = 0.05 mz ,. Q=O. 05X1.45=0.073 MW T h e conductive heat per minute is 4 350 kJ/min.
Macrostructure of shell in nozzle
4 ) Metallurgical effect The sixth strand is symmetrically located in the caster with the experimental strand ( the first strand). The two strands are thought to have the same temperature and distribution. T h e specimen is cut from two strands and to view the macro structure. T h e experimental result of No. 45 steel is shown in Table 2 and Fig. 6. T h e results show that: When superheat of steel in tundish is lower than 40 "C , the equiaxed crystal ratio is raised by 10% and the central porosity is improved greatly with the use of nozzle; T h e metallurgical effect is more remarkable with decrement of the temperature of steel in tundish.
2.3
Analysis of result of cast high carbon steel The cooling nozzle test was held in casting of high
Table 2 Effect of experimental parameters on billet quality Heat number (superheat)
Number of strand
1104-10503 (38 % )
Testing strand Contrastive strand Testing strand Contrastive strand
1104-10504 (30 %)
Experiment condition: No. 45 steel, T L / l 490 C With cooling nozzle and M-EMS With M-EMS With cooling nozzle and M-EMS With M-EMS
Macrostructure of billet Equiaxed crystal ratio/%
Central porosity, grade
45 35 53 40
0 2 0 1
Industrial Experiment of Reducing Superheat of Steel by Nozzle Cooling
Issue 6
(c) , (d) Transversal and longitudinal of contrastive strand.
( a ) , (b) Transversal and longitudinal of testing strand;
Fig. 6
Etched macrostructure of heat No. 1104-10503
carbon steels, including 60SiZMnA-3, LT-BZ. T h e composition of steels is listed in Table 3 and the testing result is shown in Table 4. T h e test of cooling
nozzle is stable and the test time is long enough. T h e usage of cooling nozzle made the billets more solid. (mass percent, % I
Table 3 Composition of high carbon steels Steel
C
Si
Mn
P
S
Cr
60Si~MnA-3 1.T-B2
0. 58-0. 62
1. 75-1. 9
0. 7-0. 8
GO.025
GO. 025
0. 15-0. 25
0.72-0.78
0.2-0.3
0. 7-0. 8
GO. 025
GO. 025
Table 4
3
25
Steels
Billet size/ mm
Heats
Lasting time/h
6OSizMnA-3 LT-B2
150x150 150x150
4 5
3 4
0. 4-0.
5
Testing result of high carbon steels Macrostructure of billet (compared with the contrast strand) The equiaxed crystal ratio is raised by l o % , the central porosity is improved The equiaxed crystal ratio is raised by 8%, the central Dorositv is imDroved
Conclusions
References :
1) T h e cooling- can be adiusted timely based on the hot side of copper tube by PLC. Shell is formed and in inner Of and it is in the dynamic state of solidification. T h e process is stable. 2) T h e usage of nozzle is useful to reduce superheat of steel. T h e equiaxed crystal ratio is raised and strand is more solid. 3) T h e metallurgical effect is remarkable when the temperature of steel in tundish is low.
[2] C31
[4]
Madill J D, Scholes A. Continuous Casting Developments at British Steel [C] // 1998 Steelmaking Conference Proceedings. Warrendale, PA: ISS, 1998. Kenzo Ayata. Low Superheat Teeming With Electromagnetic Stirring [J]. ISIJ International. 1995, 35: 680. QIU Sheng-tao, YAN Hui-cheng. A Kind of Cooling Controlling Equipment of Cesring Nozzle: China, 200720104246. 7 [PI. 2008-03-05. ZHOU Qi, WANG Mei, YAN Hui-cheng. Experimental Research of Casting SUS430 Using Cooling Nommle [J]. Iron and Steel, 2006, 41(10) 29 (in Chinese).
=Ic ScienceDirect JOURNAL OF IRON AND STEEL RESEARCH, INTERNATIONAL. 2011 18(6) 8 22-25
Industrial Experiment of Reducing Superheat of Steel by Nozzle Cooling YAN Hui-cheng"'
,
QIU Sheng-tao"'
,
WANG Zhong-ying'
TONG Tai-qin3, ZHAO Pei'
,
CAI Yun-teng3,
(1. State Key Laboratory of Advanced Steel Processing and Products, Central Iron and Steel Research Institute, 2. National Engineering Research Center of Continuous Casting Technology, Central Beijing 100081, China; Iron and Steel Research Institute, Beijing 100081, China; 3. Huai Special Steel Co Ltd, Shasteel Group, Huaian, 211600, Jiangsu, China)
Abstract: Nozzle cooling equipment is developed to supervise and control the heat flux by changing water flux. An industrial experiment is held in billet caster in Huaigang The results show that cooling control system works stably and effectively to control the heat fluxes by the temperature of copper tube. The superheat of steel in mould is reduced and the equiaxed crystal ratio, as well as compact degree of steel is raised. Key words: nozzle cooling; low superheat; industrial experiment
.
Low superheat steel is useful to improve the quality of billet. If the temperature of steel in tundish is too low, the inclusion is difficult to float into tundish flux and nozzle clogging often happens. In the 199Os, CRM of Belgium and ARBED of Luxemburg developed a heat exchange shroud and carried out industrial experiment"]. Kenzo AYATA et alCzl of Kobelco designed a shroud with air cooling and electromagnetic stirring for industrial test. Their results indicated that a high equiaxed crystal ratio could be obtained by reducing the superheat of steel. However, the application of the shroud has been not popularized in the steel plants, maybe due to the limits of the controllability and stability of the shroud. Nozzle cooling equipment is developed to cool the liquid steel at the nozzle by adjusting the heat flux via PLC in site. Based on the resultC3-'' in laboratory, the nozzle cooling equipment is set up and experimented in 150 m m X 150 mm billet caster in Huai Special Steel.
1
Experimental Theory and Equipment
1 . 1 Experimental theory In order to reduce superheat of steel and ensure casting stably, the following key points are considered in the equipment design. Cooling media is fog
caused by gas and water, tube temperature can be supervised and cooling water can be changed by PLC timely. T h e experiment equipment is composed of four parts : cooling apparatus, temperature supervising and controlling system, cooling media and emerging nozzle. Cooling apparatus includes copper tube and water sprayer. Cooling media includes transporting tube for water and air, valve and pressure and flow rate meters. Temperature supervising and controlling system includes temperature-measuring and PLC system. T h e working mechanism of four parts is shown in Fig. 1. T h e temperature of immerging nozzle is transported to PLC via copper tube. The water flow rate is adjusted by PLC based temperature. T h e
Vapor
Air Water
.agnletic
I valve TI T, "
Fig. 1
Running mechanism of cooling nozzle
Foundatlon Item: Item Sponsored by State Key Development Program of Basic Research of China (2004CB619107) E-mail: huichengyanCZll63. com; Received Date, June 2 4 , 2010 B1ography:YAN Hui-cheng(l963-), Male, Doctor, Professor;
23
Industrial Experiment of Reducing Superheat of Steel by Nozzle Cooling
Issue 6
water is fogged by high pressed air to cool copper tube and give off as vapor.
Testing equipment 1) Nozzle cooling equipment Nozzle cooling equipment is shown in Fig. 2. It includes input water, input air, output vapor and couple and cooling apparatus. T h e length of copper tube in cooling apparatus is 200 mm, and the outer diameter is $115 mm, inner diameter is $87 mm (upper size) and $84 mm (down size).
1.2
3) Heat flux controlling system online T h e heat flux of emerging nozzle is controlled in a proper zone to ensure low superheat and normal production and not to clog. T, is the temperature value of hot side of copper tube in the middle part. Based on the practical data, the water flow is controlled with the relation of temperature in four ranges (Fig. 3).
TJ v Fig. 3
2
Fig. 2
Nozzle cooling apparatus
2) Improved nozzle T h e carbon content of traditional A1-C nozzle is raised to 50% to improve conductive effect. T h e surface of A1-C nozzle is grounded smoothly to keep good touch with copper tube. Its outer diameter is kept same with the the inner diameter of copper tube and its wall thickness is 15 mm.
Relation between water flow and tube temperature
Result and Analysis
2. 1 Result of industrial experiment T h e industrial experiment is held in 150 m m X 150 mm billet caster in Huaigang. Industrial experiment had been held for five times from 2007 to 2009. Trial steels include No. 45, 60Si2MnA-3, GCrl5. Trial time lasts 1. 5 h to 4 h T h e usage of cooling apparatus made the A1-C nozzle become dimmer, compared with the other nozzles.
.
2.2
Analysis of result of casting No. 45 Parameters of casting No. 45 are listed in Table 1.
Table 1 Testing parameters for No. 45 ~~~~
M-EMS, 320 A, 6 HZ Heat series number Strand number
1104-10503
s1
Temperature of steel in tundish/'C
Casting speed/(m
S6
1104-10504
s1
1531
min-')
-
Air flow rate through nozzle/(m * h-') Water flow rate through nozzle/(L min-') Temperature of inlet water/% Temoerature of outlet water" / %
S6 1518
1529
1523
1528
1520
2.01
2. 0
1.99
2. 0
1. 99
2. 0
1. 99
2. 0
80
/ / / /
80
/ / / /
2-3 22 55-62
2-3 22 56-60
Noter 1) Th e checking point is at the exit of soft metal tube, 5 m away from the cooling equipment.
T h e first strand (S1) is the testing strand with nozzle cooling equipment and the sixth strand (S6) is the contrast strand which is symmetrical to the first strand in position. When the process is stable, the
test is beginning with the second heat. 1) Equipment stability Temperature distribution and variation is collected in Fig. 6. It shows that nozzle cooling equip-
' 24
Vol. 18
Journal of Iron and Steel Research, International
9
ment works stably for a long time and the casting operation can last for several hours. Heat flux can be controlled by PLC timely. 2 ) Temperature supervising and heat conductive analysis Thermocouple is set in copper tube. The points TI and T , is in the middle and at the same height of tube, the distance is I 1 mm between two points of T l and T,. T he point T3 is set at the bottom of tube. In course of testing, the temperature of T I , T z and T, is stable and changed synchronous (shown in Fig. 4). T h e heat flux through the copper tube can be calculated from the temperature distribution in tube.
T h e weight of steel through nozzle is 380 kg/min for casting speed of 2. 2 m/min. T h e c p of steel is 0. 8 kJ/kg 'C 9 0 . 8 X 380 X A T = 4 350 T h e reduced superheat AT is calculated to be 14 'C. 3) Shell solidified in nozzle After casting, the shell tube is formed at the position of cooling equipment along inner wall of nozzle. T h e shell tube is taken out and etched in transversal section (shown in Fig. 5 1. T h e shell has a same length of 180 mm with the cooling tube and a width of 16 mm. Judging from the macro structure, the shell is firstly formed at the position of cooling equipment and then a new layer will cling on it. T h e layers are collected and the appearance show that the shell is in the course of solidification and melting constantly.
I
T3 ,
Fig. 5 Fig. 4 Thermocouple distribution and temperature variation in copper tube
T h e difference between T1and T , is changed in 40- 60 'C and it become a little smaller with the thicker shell during later period. The difference between TI and T z is 45 'C in heat conductive analysis. Heat flux q1 = 360 X 45/0.011= 1. 45MW/m2. Because the temperature of T I , Tz and T , is stable and changed synchronous, the heat flux of whole cooling system is thought t o be uniform and equals to 41. The outer dieter meter of copper tube is 0. 115 m, the inner dieter meter is 0.087 m, the height is 0. 16 m, T h e fact cooling area of copper tube F = 2 X 3.14 X 0.16 X (0.115/2 - 0.087/2 )/In ( 0. 115/0.087 1 = 0.05 mz ,. Q=O. 05X1.45=0.073 MW T h e conductive heat per minute is 4 350 kJ/min.
Macrostructure of shell in nozzle
4 ) Metallurgical effect The sixth strand is symmetrically located in the caster with the experimental strand ( the first strand). The two strands are thought to have the same temperature and distribution. T h e specimen is cut from two strands and to view the macro structure. T h e experimental result of No. 45 steel is shown in Table 2 and Fig. 6. T h e results show that: When superheat of steel in tundish is lower than 40 "C , the equiaxed crystal ratio is raised by 10% and the central porosity is improved greatly with the use of nozzle; T h e metallurgical effect is more remarkable with decrement of the temperature of steel in tundish.
2.3
Analysis of result of cast high carbon steel The cooling nozzle test was held in casting of high
Table 2 Effect of experimental parameters on billet quality Heat number (superheat)
Number of strand
1104-10503 (38 % )
Testing strand Contrastive strand Testing strand Contrastive strand
1104-10504 (30 %)
Experiment condition: No. 45 steel, T L / l 490 C With cooling nozzle and M-EMS With M-EMS With cooling nozzle and M-EMS With M-EMS
Macrostructure of billet Equiaxed crystal ratio/%
Central porosity, grade
45 35 53 40
0 2 0 1
Industrial Experiment of Reducing Superheat of Steel by Nozzle Cooling
Issue 6
(c) , (d) Transversal and longitudinal of contrastive strand.
( a ) , (b) Transversal and longitudinal of testing strand;
Fig. 6
Etched macrostructure of heat No. 1104-10503
carbon steels, including 60SiZMnA-3, LT-BZ. T h e composition of steels is listed in Table 3 and the testing result is shown in Table 4. T h e test of cooling
nozzle is stable and the test time is long enough. T h e usage of cooling nozzle made the billets more solid. (mass percent, % I
Table 3 Composition of high carbon steels Steel
C
Si
Mn
P
S
Cr
60Si~MnA-3 1.T-B2
0. 58-0. 62
1. 75-1. 9
0. 7-0. 8
GO.025
GO. 025
0. 15-0. 25
0.72-0.78
0.2-0.3
0. 7-0. 8
GO. 025
GO. 025
Table 4
3
25
Steels
Billet size/ mm
Heats
Lasting time/h
6OSizMnA-3 LT-B2
150x150 150x150
4 5
3 4
0. 4-0.
5
Testing result of high carbon steels Macrostructure of billet (compared with the contrast strand) The equiaxed crystal ratio is raised by l o % , the central porosity is improved The equiaxed crystal ratio is raised by 8%, the central Dorositv is imDroved
Conclusions
References :
1) T h e cooling- can be adiusted timely based on the hot side of copper tube by PLC. Shell is formed and in inner Of and it is in the dynamic state of solidification. T h e process is stable. 2) T h e usage of nozzle is useful to reduce superheat of steel. T h e equiaxed crystal ratio is raised and strand is more solid. 3) T h e metallurgical effect is remarkable when the temperature of steel in tundish is low.
[2] C31
[4]
Madill J D, Scholes A. Continuous Casting Developments at British Steel [C] // 1998 Steelmaking Conference Proceedings. Warrendale, PA: ISS, 1998. Kenzo Ayata. Low Superheat Teeming With Electromagnetic Stirring [J]. ISIJ International. 1995, 35: 680. QIU Sheng-tao, YAN Hui-cheng. A Kind of Cooling Controlling Equipment of Cesring Nozzle: China, 200720104246. 7 [PI. 2008-03-05. ZHOU Qi, WANG Mei, YAN Hui-cheng. Experimental Research of Casting SUS430 Using Cooling Nommle [J]. Iron and Steel, 2006, 41(10) 29 (in Chinese).