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Cracking during cold forming process of rear brake component
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Engineering Failure Analysis 15 (2008) 295–301 www.elsevier.com/locate/engfailanal
Cracking during cold forming process of rear brake component O. Elkoca a, H. Cengizler a
b,*,1
ERDEMIR, Research and Development Department, 67330 Ere gli, Turkey b Celal Bayar University, TMYO, 45410 Turgutlu, Turkey Received 11 February 2007; accepted 24 February 2007 Available online 2 March 2007
Abstract The root cause for cracking of rear brake components occurred during cold forming process was investigated. Optical micrographs showed the abundance of extended inclusions with several rounded ones in the steel. SEM image revealed the fracture surface which contained many extended cavities formed by extended inclusions and dimples all indicating a ductile rupture. EDS analysis confirmed that the extended inclusions were MnS type while the rounded ones were formed as a result of Ca-treatment. The crack propagation along with inclusions was clearly observed on the polished planes and on the fracture surface. It was determined that MnS type inclusions were the root cause for the cracking phenomena. The abundance of extended MnS inclusions indicated insufficient inclusion modification through Ca-treatment and insufficient removal of these inclusions in failed steel. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Failure analysis; Cold forming; Non-metallic inclusions; Calcium treatment; Inclusion modification
1. Introduction The expectations for improved material properties in the automotive industry have been continually striving to affect weight savings, improve fuel efficiency and also allow for cost effective production of the components [1,2]. The production methods also have to be capable of producing components with very high tolerances, in high volumes at as low a cost as possible and with little outage. Considering this combination of requirements on the production method employed, especially with respect to the mechanical property requirements, specially developed high-strength low-alloy steels (HSLA) combine high-strength with good formability. In HSLA steels, the optimal properties for high-strength and cold forming is attained by thermomechanical rolling with appropriate chemical composition to produce a fine grained microstructure [3]. Ensuring optimal cold formability of these steel grades, it is important to limit the levels of trace elements.
*
1
Corresponding author. Tel.: +90 232 244 8125; fax: +90 236 314 4566. E-mail addresses: [email protected] (O. Elkoca), [email protected], [email protected] (H. Cengizler). _ Res.: 223 sok. No: 5/11, 35280 Hatay, Izmir, Turkey. Tel.: +90 232 244 8125; mobile: 0 537 884 9580.
1350-6307/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.engfailanal.2007.02.006
296
O. Elkoca, H. Cengizler / Engineering Failure Analysis 15 (2008) 295–301
In the present work, some cracks were encountered during the cold forming process of rear brake components made of a HSLA steel grade. A metallurgical investigation was carried out on the failed rear brake components. 2. Experimental The rear brake components shown in Fig. 1 were manufactured from 5 mm thick hot-rolled and slit strip of HSLA steel grade S500MC according to DIN EN 10149-2. Some cracks were encountered on the arms of the components during cold forming process as seen in Fig. 2. Chemical composition of the failed components is given in Table 1.
Fig. 1. A failed rear brake component.
Fig. 2. Cracks encountered on the arm of a component during cold forming process.
Table 1 Chemical composition of the failed components (wt%)
Standard (DIN EN 10149-2) Failed component *
C
Mn
Si
P
S
Al (total)
Nb
V
Ti
Ca
Max. 0.120 0.098
Max. 1.700 1.487
Max. 0.500 0.069
Max. 0.025 0.011
Max. 0.015 0.005
Min. 0.015 0.049
Max. 0.090 0.070
Max. 0.200 0.047
Max. 0.150 0.022
*
The manufacturer may add Ca, Ce, Te, etc. to improve cold formability.
0.0025
O. Elkoca, H. Cengizler / Engineering Failure Analysis 15 (2008) 295–301
297
Metallurgical examinations on as-received samples were performed to find out the cause of the cracking problem during cold forming process. Metallographically polished planes which were parallel and normal to the fracture surfaces were examined by Nikon Epiphot-200 optical microscope and Jeol JSM 5600 scanning electron microscope (SEM). Micro-constituents observed on the polished planes were analyzed by Oxford LINK energy-dispersive X-ray spectrometer (EDS) attached to the SEM. The mean linear intercept method was used for the grain size measurement on the sample etched with Nital 3. One of the cracks on the failed part was opened up by a hammer blow in order to examine fracture surface through SEM. 3. Experimental results The chemical composition of the steel used for the failed rear brake component meets the demands defined by the relevant standard DIN EN 10149-2 as shown in Table 1. It also seems that the steel producer added Ca to the steel in order to improve cold formability. It can be seen in Fig. 3 that the microstructure of the failed component was composed of extremely fine grained ferritic–bainitic microstructure (average ferrite grain size being 3.29 lm) which indicated that the steel used was subjected to thermomechanical rolling. Fig. 4 shows crack propagation along with the inclusions on the plane normal to the fracture surface.
Fig. 3. Microstructure of the failed rear brake component.
Fig. 4. Crack propagation along with inclusions.
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O. Elkoca, H. Cengizler / Engineering Failure Analysis 15 (2008) 295–301
Fig. 5. Optical micrograph of the plane parallel to the fracture surface, 100X.
Fig. 6. EDS spectrum of extended inclusions.
Optical micrograph of the plane parallel to the fracture surface which is also parallel to the rolling direction showed the existence of elongated and rounded inclusions in the rolled steel as seen in Fig. 5. EDS analysis performed on these non-metallic inclusions revealed that the elongated ones were sulfide type composed of Mn and S and the rounded ones were Ca-treated type composed of Ca, Al, O and S (Figs. 6 and 7). Examination of the fracture surface emerged during cold forming revealed that the fracture surface abounded in extended and rounded voids formed by inclusions (arrows A and B respectively) which indicated ductile fracture (Figs. 8 and 9). EDS analysis performed on these inclusions also confirmed the existence of the same components of extended and rounded non-metallic inclusions. 4. Discussion Examination of the fracture surface by SEM indicates a ductile mode of fracture. The ductile dimples exhibit a combination of shear and tensile modes of fracture propagation. A ductile fracture generally involves the
Fig. 7. EDS spectrum of rounded inclusions.
O. Elkoca, H. Cengizler / Engineering Failure Analysis 15 (2008) 295–301
Fig. 8. SEM image of the fracture surface (arrows A: elongated sulfide inclusions, arrows B: rounded inclusions).
Fig. 9. Sulphide residuals in extended hallows on the fracture surface.
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nucleation, growth and coalescence of voids in a plastically deforming material. In many structural steels, void nucleation occurs at small strains and failure is controlled by void growth and coalescence. Hot rolled steels may typically contain elongated inclusions with their long axes oriented in the rolling direction. When a tensile specimen is loaded transverse to the rolling direction, the resulting elongated voids grow until coalescence occurs, frequently due to a ‘‘void-sheet’’ mechanism [4–11]. Elongated MnS type inclusions in failed rear brake component nucleate voids at small strains and, at high stress triaxialities, eventually coalesce by the void-sheet mechanism. The presence of non-metallic inclusions is a major cause of incompatibility between the attainable and desirable level of cleanliness in many grades of formable HSLA steel grades such as S500MC. Generally, inclusions degrade the mechanical properties of the steel and thereby reduce the ductility of the steel and increase the risk for mechanical failure of the final product [4–14]. The elongated sulphides have great effects on the fracture properties of steels. During the fracture process, voids are first formed at MnS inclusions which are usually the largest, then at smaller oxide inclusions and finally at small carbides [15]. For a given matrix and inclusion type, there is a minimum particle size below which voids will not form. Reducing the volume fraction of inclusions and control of the inclusion shape will improve the mechanical properties associated with high strain levels, i.e. reduction of area. The number of inclusions per unit area increases with increase in the sulphur content. Through-thickness ductility in plate materials shows improvements with reduced sulphur content and shape control leading to globular rather than elongated inclusions, thus enhancing the resistance to cracking during cold forming. Reducing the content of inclusions increases the resistance to void nucleation and is effective in improving the mechanical properties of steels [16]. High demands on the cleanliness of high-strength steel are also essential to ensure that non-metallic inclusions in the steel do not result in cracking or splitting of the component during forming process. This requirement is met with many grades of steel by ensuring that specific precautions are taken such as non-metallic inclusion reduction techniques [17–19] and modification of residual inclusions with calcium [20–22] or other rare earth elements in steel production processes which have greatly reduced the size and amount of nonmetallic inclusions remaining in molten steels and steel products [23]. Calcium treatment of manganese sulphide inclusions gives species which remain globular during rolling. This treatment is used in the formable HSLA steels for processes such as cold forming where MnS stringers can cause planes of weakness within the steel. In steels not treated with calcium, the sulfur precipitates as finely dispersed manganese sulfide particles in interdendritic liquid that freezes last. During hot rolling the manganese sulfide particles are deformed resulting in stringers in the rolled product [24]. In calcium-treated lowsulfur steels, the grain boundary precipitation of MnS during solidification is suppressed as a result of the precipitation of sulfur as a Ca(Mn)S complex [24]. Depending on the success in the Ca-treatment processes, various modification and cleanliness levels can be attained. In the failed rear brake component, the presence of abundant elongated MnS stringers indicates insufficiency in Ca modification and removal of these inclusions from the liquid steel. 5. Conclusion A metallurgical investigation was carried out on the failed rear brake components in order to find out the root cause for the cracking phenomena occurred during cold forming process. A ductile mode of fracture was found to be related to stringers-type manganese sulfide inclusions. The presence of abundant elongated MnS stringers in the failed steel indicated insufficiency in Ca modification and removal of these inclusions from the steel. References [1] Cho YR, Kim HG, Chin KG, Lee WS, Kwon TW. Application of advanced high strength hot-rolled steels to automotive chassis parts. In: von Hagen I, Wieland, H-J. International conference on steels in cars and trucks – SCT 2005, 5–10 June 2005, Wiesbaden, Germany. Du¨sseldorf: Verlag Stahleisen; 2005. p. 199–206. [2] Flemming GK, Hensger E. Extension of product range and perspectives of CSP technology. MPT Int 2000;1:54–63.
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301
[3] Cohen M, Hansen SS. On the fundamentals of HSLA steels. In: Proceedings of an international conference on HSLA Steels, 4–8 November 1985, Beijing, China. ASM International; 1986. p. 61–71. [4] Tomita Y. Effect of desulphurization and calcium treatments on the inclusion morphology of 0.4C–Cr–Mo–Ni steel. J Mater Sci 1994;29:2873–8. [5] Kiessling R, Clean steel – a debatable concept. In: Proceedings of 2nd international conference on clean steel, June 1981, Balatonfured, Hungary. London: Institute of Metals; 1983. p. 1–9. [6] Gladman T. Developments in inclusion and their effects on steel properties. Ironmaking Steelmaking 1992;19:457–63. [7] Lund T, Akesson J. Effect of steel manufacturing process on the quality of bearing steels. In: Hoo JJC, editor. ASTM STP987. Philadelphia, USA: American Society for Testing and Materials; 1988. p. 308–15. [8] Paul SK, Ray A. Influence of inclusion characteristics on the formability and toughness properties of a hot-rolled deep-drawing quality steel. J Mater Eng Perform 1997;6:27–34. [9] Spitzig WA, Sober RJ. Influence of sulfide inclusions and pearlite content on the mechanical properties of hot-rolled carbon steel. Metall Trans 1981;12A:281–91. [10] Gattelier C, Gaye H, Lehmann J, Bellot J, Moncel M. Inclusion control in low-aluminum steel, La Revue de Metallurgie-CIT 1992, (April): 362. [11] Tomita Y. Improved mechanical properties of ultrahigh strength 0.4C–Cr–Mo–Ni steel through modification of sulphide inclusion shape and microstructural control. Mater Sci Technol 1989;5(11):1084–9. [12] Suito H, Inoue R. Thermodynamics on control of inclusions composition in ultraclean steels. ISIJ Int 1996;36(5):528–36. [13] Jiang LZ, Cui K. Quantitative study of modification of sulphide inclusions by calcium and its effect on the impact toughness of a resulfurised alloy steel. Steel Res 1997;68(4):163–8. [14] Tomita Y. Improved fracture toughness of ultrahigh strength steel through control of non-metallic inclusions. J Mater Sci 1993;28(4):853–9. [15] Leslie WC. Inclusions and mechanical properties. Trans Iron Steel Soc 1983;2:1–24. [16] Hedjazi D, Bennett GHJ, Kondic V. Removal of non-metallic inclusions and their assesment. British Foundryman 1975;68:305–9. [17] Taniguchi S, Brimacombe JKS. Application of pinch force to the separation of inclusion particles from liquid steel. ISIJ Int 1994;34(9):722–31. [18] Singh SB, Chakrabarti AK. Removal of inclusions from steel by halide salt treatment. Ironmaking Steelmaking 1993;20(6):442–4. [19] Uemura K, Takahashi M, Koyama S, Nitta M. Filtration mechanism of non-metallic inclusions in steel by ceramic loop filter. ISIJ Int 1992;32(1):150–6. [20] Imagumbai M, Takeda T. Influence of calcium-treatment on sulfide- and oxide-inclusions in continuous-cast slab of clean steeldendrite structure and inclusions. ISIJ Int 1994;34(7):574–83. [21] Pires JCS, Garcia A. Modification of oxide inclusions present in aluminum-killed low carbon steel by addition of calcium. Revista da Escola de Minas 2004;57(3):183–9. [22] Brinkmeyer L, Melville SD. Factors affecting cleanliness of continuously cast steel. Ironmaking Steelmaking 1995;22(6):502–7. [23] Atkinson HV, Shi G. Characterization of inclusions in clean steels: a review including the statistics of extremes methods. Prog Mater Sci 2003;48(5):457–520. [24] The making, shaping and treating of Steel. In: Fruehan RJ, editor. Steelmaking and refining volume. Pittsburgh, PA, USA: The AISE Steel Foundation; 1998. p. 693 [Chapter 11: Ladle refining and vacuum degassing].
Engineering Failure Analysis 15 (2008) 295–301 www.elsevier.com/locate/engfailanal
Cracking during cold forming process of rear brake component O. Elkoca a, H. Cengizler a
b,*,1
ERDEMIR, Research and Development Department, 67330 Ere gli, Turkey b Celal Bayar University, TMYO, 45410 Turgutlu, Turkey Received 11 February 2007; accepted 24 February 2007 Available online 2 March 2007
Abstract The root cause for cracking of rear brake components occurred during cold forming process was investigated. Optical micrographs showed the abundance of extended inclusions with several rounded ones in the steel. SEM image revealed the fracture surface which contained many extended cavities formed by extended inclusions and dimples all indicating a ductile rupture. EDS analysis confirmed that the extended inclusions were MnS type while the rounded ones were formed as a result of Ca-treatment. The crack propagation along with inclusions was clearly observed on the polished planes and on the fracture surface. It was determined that MnS type inclusions were the root cause for the cracking phenomena. The abundance of extended MnS inclusions indicated insufficient inclusion modification through Ca-treatment and insufficient removal of these inclusions in failed steel. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Failure analysis; Cold forming; Non-metallic inclusions; Calcium treatment; Inclusion modification
1. Introduction The expectations for improved material properties in the automotive industry have been continually striving to affect weight savings, improve fuel efficiency and also allow for cost effective production of the components [1,2]. The production methods also have to be capable of producing components with very high tolerances, in high volumes at as low a cost as possible and with little outage. Considering this combination of requirements on the production method employed, especially with respect to the mechanical property requirements, specially developed high-strength low-alloy steels (HSLA) combine high-strength with good formability. In HSLA steels, the optimal properties for high-strength and cold forming is attained by thermomechanical rolling with appropriate chemical composition to produce a fine grained microstructure [3]. Ensuring optimal cold formability of these steel grades, it is important to limit the levels of trace elements.
*
1
Corresponding author. Tel.: +90 232 244 8125; fax: +90 236 314 4566. E-mail addresses: [email protected] (O. Elkoca), [email protected], [email protected] (H. Cengizler). _ Res.: 223 sok. No: 5/11, 35280 Hatay, Izmir, Turkey. Tel.: +90 232 244 8125; mobile: 0 537 884 9580.
1350-6307/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.engfailanal.2007.02.006
296
O. Elkoca, H. Cengizler / Engineering Failure Analysis 15 (2008) 295–301
In the present work, some cracks were encountered during the cold forming process of rear brake components made of a HSLA steel grade. A metallurgical investigation was carried out on the failed rear brake components. 2. Experimental The rear brake components shown in Fig. 1 were manufactured from 5 mm thick hot-rolled and slit strip of HSLA steel grade S500MC according to DIN EN 10149-2. Some cracks were encountered on the arms of the components during cold forming process as seen in Fig. 2. Chemical composition of the failed components is given in Table 1.
Fig. 1. A failed rear brake component.
Fig. 2. Cracks encountered on the arm of a component during cold forming process.
Table 1 Chemical composition of the failed components (wt%)
Standard (DIN EN 10149-2) Failed component *
C
Mn
Si
P
S
Al (total)
Nb
V
Ti
Ca
Max. 0.120 0.098
Max. 1.700 1.487
Max. 0.500 0.069
Max. 0.025 0.011
Max. 0.015 0.005
Min. 0.015 0.049
Max. 0.090 0.070
Max. 0.200 0.047
Max. 0.150 0.022
*
The manufacturer may add Ca, Ce, Te, etc. to improve cold formability.
0.0025
O. Elkoca, H. Cengizler / Engineering Failure Analysis 15 (2008) 295–301
297
Metallurgical examinations on as-received samples were performed to find out the cause of the cracking problem during cold forming process. Metallographically polished planes which were parallel and normal to the fracture surfaces were examined by Nikon Epiphot-200 optical microscope and Jeol JSM 5600 scanning electron microscope (SEM). Micro-constituents observed on the polished planes were analyzed by Oxford LINK energy-dispersive X-ray spectrometer (EDS) attached to the SEM. The mean linear intercept method was used for the grain size measurement on the sample etched with Nital 3. One of the cracks on the failed part was opened up by a hammer blow in order to examine fracture surface through SEM. 3. Experimental results The chemical composition of the steel used for the failed rear brake component meets the demands defined by the relevant standard DIN EN 10149-2 as shown in Table 1. It also seems that the steel producer added Ca to the steel in order to improve cold formability. It can be seen in Fig. 3 that the microstructure of the failed component was composed of extremely fine grained ferritic–bainitic microstructure (average ferrite grain size being 3.29 lm) which indicated that the steel used was subjected to thermomechanical rolling. Fig. 4 shows crack propagation along with the inclusions on the plane normal to the fracture surface.
Fig. 3. Microstructure of the failed rear brake component.
Fig. 4. Crack propagation along with inclusions.
298
O. Elkoca, H. Cengizler / Engineering Failure Analysis 15 (2008) 295–301
Fig. 5. Optical micrograph of the plane parallel to the fracture surface, 100X.
Fig. 6. EDS spectrum of extended inclusions.
Optical micrograph of the plane parallel to the fracture surface which is also parallel to the rolling direction showed the existence of elongated and rounded inclusions in the rolled steel as seen in Fig. 5. EDS analysis performed on these non-metallic inclusions revealed that the elongated ones were sulfide type composed of Mn and S and the rounded ones were Ca-treated type composed of Ca, Al, O and S (Figs. 6 and 7). Examination of the fracture surface emerged during cold forming revealed that the fracture surface abounded in extended and rounded voids formed by inclusions (arrows A and B respectively) which indicated ductile fracture (Figs. 8 and 9). EDS analysis performed on these inclusions also confirmed the existence of the same components of extended and rounded non-metallic inclusions. 4. Discussion Examination of the fracture surface by SEM indicates a ductile mode of fracture. The ductile dimples exhibit a combination of shear and tensile modes of fracture propagation. A ductile fracture generally involves the
Fig. 7. EDS spectrum of rounded inclusions.
O. Elkoca, H. Cengizler / Engineering Failure Analysis 15 (2008) 295–301
Fig. 8. SEM image of the fracture surface (arrows A: elongated sulfide inclusions, arrows B: rounded inclusions).
Fig. 9. Sulphide residuals in extended hallows on the fracture surface.
299
300
O. Elkoca, H. Cengizler / Engineering Failure Analysis 15 (2008) 295–301
nucleation, growth and coalescence of voids in a plastically deforming material. In many structural steels, void nucleation occurs at small strains and failure is controlled by void growth and coalescence. Hot rolled steels may typically contain elongated inclusions with their long axes oriented in the rolling direction. When a tensile specimen is loaded transverse to the rolling direction, the resulting elongated voids grow until coalescence occurs, frequently due to a ‘‘void-sheet’’ mechanism [4–11]. Elongated MnS type inclusions in failed rear brake component nucleate voids at small strains and, at high stress triaxialities, eventually coalesce by the void-sheet mechanism. The presence of non-metallic inclusions is a major cause of incompatibility between the attainable and desirable level of cleanliness in many grades of formable HSLA steel grades such as S500MC. Generally, inclusions degrade the mechanical properties of the steel and thereby reduce the ductility of the steel and increase the risk for mechanical failure of the final product [4–14]. The elongated sulphides have great effects on the fracture properties of steels. During the fracture process, voids are first formed at MnS inclusions which are usually the largest, then at smaller oxide inclusions and finally at small carbides [15]. For a given matrix and inclusion type, there is a minimum particle size below which voids will not form. Reducing the volume fraction of inclusions and control of the inclusion shape will improve the mechanical properties associated with high strain levels, i.e. reduction of area. The number of inclusions per unit area increases with increase in the sulphur content. Through-thickness ductility in plate materials shows improvements with reduced sulphur content and shape control leading to globular rather than elongated inclusions, thus enhancing the resistance to cracking during cold forming. Reducing the content of inclusions increases the resistance to void nucleation and is effective in improving the mechanical properties of steels [16]. High demands on the cleanliness of high-strength steel are also essential to ensure that non-metallic inclusions in the steel do not result in cracking or splitting of the component during forming process. This requirement is met with many grades of steel by ensuring that specific precautions are taken such as non-metallic inclusion reduction techniques [17–19] and modification of residual inclusions with calcium [20–22] or other rare earth elements in steel production processes which have greatly reduced the size and amount of nonmetallic inclusions remaining in molten steels and steel products [23]. Calcium treatment of manganese sulphide inclusions gives species which remain globular during rolling. This treatment is used in the formable HSLA steels for processes such as cold forming where MnS stringers can cause planes of weakness within the steel. In steels not treated with calcium, the sulfur precipitates as finely dispersed manganese sulfide particles in interdendritic liquid that freezes last. During hot rolling the manganese sulfide particles are deformed resulting in stringers in the rolled product [24]. In calcium-treated lowsulfur steels, the grain boundary precipitation of MnS during solidification is suppressed as a result of the precipitation of sulfur as a Ca(Mn)S complex [24]. Depending on the success in the Ca-treatment processes, various modification and cleanliness levels can be attained. In the failed rear brake component, the presence of abundant elongated MnS stringers indicates insufficiency in Ca modification and removal of these inclusions from the liquid steel. 5. Conclusion A metallurgical investigation was carried out on the failed rear brake components in order to find out the root cause for the cracking phenomena occurred during cold forming process. A ductile mode of fracture was found to be related to stringers-type manganese sulfide inclusions. The presence of abundant elongated MnS stringers in the failed steel indicated insufficiency in Ca modification and removal of these inclusions from the steel. References [1] Cho YR, Kim HG, Chin KG, Lee WS, Kwon TW. Application of advanced high strength hot-rolled steels to automotive chassis parts. In: von Hagen I, Wieland, H-J. International conference on steels in cars and trucks – SCT 2005, 5–10 June 2005, Wiesbaden, Germany. Du¨sseldorf: Verlag Stahleisen; 2005. p. 199–206. [2] Flemming GK, Hensger E. Extension of product range and perspectives of CSP technology. MPT Int 2000;1:54–63.
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301
[3] Cohen M, Hansen SS. On the fundamentals of HSLA steels. In: Proceedings of an international conference on HSLA Steels, 4–8 November 1985, Beijing, China. ASM International; 1986. p. 61–71. [4] Tomita Y. Effect of desulphurization and calcium treatments on the inclusion morphology of 0.4C–Cr–Mo–Ni steel. J Mater Sci 1994;29:2873–8. [5] Kiessling R, Clean steel – a debatable concept. In: Proceedings of 2nd international conference on clean steel, June 1981, Balatonfured, Hungary. London: Institute of Metals; 1983. p. 1–9. [6] Gladman T. Developments in inclusion and their effects on steel properties. Ironmaking Steelmaking 1992;19:457–63. [7] Lund T, Akesson J. Effect of steel manufacturing process on the quality of bearing steels. In: Hoo JJC, editor. ASTM STP987. Philadelphia, USA: American Society for Testing and Materials; 1988. p. 308–15. [8] Paul SK, Ray A. Influence of inclusion characteristics on the formability and toughness properties of a hot-rolled deep-drawing quality steel. J Mater Eng Perform 1997;6:27–34. [9] Spitzig WA, Sober RJ. Influence of sulfide inclusions and pearlite content on the mechanical properties of hot-rolled carbon steel. Metall Trans 1981;12A:281–91. [10] Gattelier C, Gaye H, Lehmann J, Bellot J, Moncel M. Inclusion control in low-aluminum steel, La Revue de Metallurgie-CIT 1992, (April): 362. [11] Tomita Y. Improved mechanical properties of ultrahigh strength 0.4C–Cr–Mo–Ni steel through modification of sulphide inclusion shape and microstructural control. Mater Sci Technol 1989;5(11):1084–9. [12] Suito H, Inoue R. Thermodynamics on control of inclusions composition in ultraclean steels. ISIJ Int 1996;36(5):528–36. [13] Jiang LZ, Cui K. Quantitative study of modification of sulphide inclusions by calcium and its effect on the impact toughness of a resulfurised alloy steel. Steel Res 1997;68(4):163–8. [14] Tomita Y. Improved fracture toughness of ultrahigh strength steel through control of non-metallic inclusions. J Mater Sci 1993;28(4):853–9. [15] Leslie WC. Inclusions and mechanical properties. Trans Iron Steel Soc 1983;2:1–24. [16] Hedjazi D, Bennett GHJ, Kondic V. Removal of non-metallic inclusions and their assesment. British Foundryman 1975;68:305–9. [17] Taniguchi S, Brimacombe JKS. Application of pinch force to the separation of inclusion particles from liquid steel. ISIJ Int 1994;34(9):722–31. [18] Singh SB, Chakrabarti AK. Removal of inclusions from steel by halide salt treatment. Ironmaking Steelmaking 1993;20(6):442–4. [19] Uemura K, Takahashi M, Koyama S, Nitta M. Filtration mechanism of non-metallic inclusions in steel by ceramic loop filter. ISIJ Int 1992;32(1):150–6. [20] Imagumbai M, Takeda T. Influence of calcium-treatment on sulfide- and oxide-inclusions in continuous-cast slab of clean steeldendrite structure and inclusions. ISIJ Int 1994;34(7):574–83. [21] Pires JCS, Garcia A. Modification of oxide inclusions present in aluminum-killed low carbon steel by addition of calcium. Revista da Escola de Minas 2004;57(3):183–9. [22] Brinkmeyer L, Melville SD. Factors affecting cleanliness of continuously cast steel. Ironmaking Steelmaking 1995;22(6):502–7. [23] Atkinson HV, Shi G. Characterization of inclusions in clean steels: a review including the statistics of extremes methods. Prog Mater Sci 2003;48(5):457–520. [24] The making, shaping and treating of Steel. In: Fruehan RJ, editor. Steelmaking and refining volume. Pittsburgh, PA, USA: The AISE Steel Foundation; 1998. p. 693 [Chapter 11: Ladle refining and vacuum degassing].