Title of Invention | A NON-DESTRUCTIVE ULTRASONIC TESTING METHOD FOR DETERMINING MACROSTRUCTURE IN CONTINUOUSLY CAST BILLETS |
---|---|
Abstract | A non-destructive ultrasonic testing method for determining macro structure in continuously cast billets for studying the effects of electromagnetic stirring, comprising the steps of selecting the continuously cast billets from different grades of steel like low carbon (WR3), high carbon (PC 115 and 75/ 80); saw cutting samples in desired sections from the selected billets, keeping transverse faces parallel; grinding and finishing said parallel transverse faces for ultrasonic test; identifying equiaxed / columnar transition by changing in ultrasonic backwall echo amplitude using a single crystal normal probe; and evaluating flaws indicated by number of back scattered signals using a twin crystal normal probe. |
Full Text | The present invention relates to a non-destructive ultrasonic testing method for determining macrostructure in continuously cast billets. More particularly the invention relates to an off line non-destructive method of ultrasonic testing to determine macrostructure (columnar and equiaxed zone as well as flaws) in continuously cast billets by scanning through one face of the continuously cast billet samples using ultrasonic 10 MHz single crystal and 6 MHz twin crystal normal probe. This determination is very important for determining the quality of continuously cast billets. BACKGROUND OF THE INVENTION Determining the macro-cast billets assist in modifying the process parameters for improving the billet quality. At present there is no off-line non-destructive testing technique (NOT), which could accurately determine the macro-structure in continuously cast steel products. Assessment of macro-structure of continuously cast steel products (billets / slabs / blooms) are generally done by visual inspection of macro-etch, or by sulphur print evaluation methods on transverse / longitudinal cut slices. With the use of electromagnetic stirring (ENS) in continuous casting of steel, the steel melt is homogenized for obtaining a solid structure upon solidification. The effect of electro-magnetic stirring on continuously cast billets and slabs can be assessed by the above-mentioned methods. But macro-etching and sulphur print methods provide information in one plane only. For more realistic assessment these methods require large number of test samples and hot acids, which is hazardous and pollute the atmosphere also. Ultrasonic assessment provides through thickness information of the test samples. Ultrasonic method is pollution free and eco-friendly method, non-destructive, and may require less number of samples also. SUMMARY OF THE INVENTION Because of the problems associated with macro-etching and sulphur print methods, there was a need to find out the possibility of assessment of such macro-structures (including columnar / equiaxed grain, flaws / macro-inclusions, central looseness, porosity etc.) by non-destructive technique. Due to heterogeneous cast structure and presence of flaws, ultrasonic losses are significant when it is scanned from edges to the center of the transverse cut slices of continuously cast steel products. The variation of ultrasonic losses depends on the severity of change in macro- structure. For indicating ultrasonic losses, drop in back-wall echo can be measured wharaas for finding tha severity of flaws, the ultrasonic internal reflections can be counted. Tha pattern of echo drop can be studied and it is possible to predict aquiaxad zona in continuously cast steal billets. Tha effect of electro-magnetic stirring on the macro-structure of low carbon as well as high carbon billets, could be assassad by this unique technique. Tha operating cost of this method is very low and the assessment of macro- structure is fast. Hence quick corrective / preventive actions can be taken. Large volume of tha test specimen can be inspected by this method when compared with other techniques (e.g. macro-etching / sulphur print etc.). Thus, the present invention provides a non destructive ultrasonic testing method for determining macro structure in continuously cast billets for studying the effects of electromagnetic stirring, comprising the steps of selecting the continuously cast billets from different grades of steal like low carbon (Witt), high carbon (PC 115 and 75 / 80); saw cutting samples in desired sections from the selected billets, keeping transverse faces parallel; grinding and finishing said parallel transverse faces for ultrasonic test; identifying equiaxed / columnar transition by changing in ultrasonic backwall echo amplitude using a single crystal normal probe; and evaluating flaws indicated by number of back scattered signals using a twin crystal normal probe. This determination will assist in modifying the process parameters to improve the billet quality. The conclusions derived from the ultrasonic results art given below: LOW CARSON GRADES WR-3: ? Due to the electro magnetic stirring (EMS) system, the billet portion towards the inner and outer radius becomes cleaner. The cleaning effect was more towards the inner radius than that towards outer radius. Ultrasonic investigation reveals more number of flaws in the central region when compared with rest portion of the sample. ? Electro magnetic stirring (EMS) system was found less effective during the process of equiaxed zone formation in low carbon samples. HIGH CARBON GRADES PC-115: ? Electro magnetic stirring (EMS) is quite effective towards the surface. It seems that high carbon grade is much cleaner than the low carbon grades. ? It seems that due to electro magnetic stirring (EMS) practice, there is 2 times increase in the equiaxed zone if compared with Non-EMS sample. HIGH CARBON GRAPES 75/80: ? Electro magnetic stirring (EMS) is quite effective towards the surface. It seems that high carbon grade continuously cast billets are much cleaner than the low carbon grade continuously cast billets. ? It seems that due to electro magnetic stirring (EMS) practice, there is 4 times increase in the equiaxed zone if compared with non- electro magnetic stirring (EMS) sample. BRIEF DESCRIPTION OF ACCOMPANYING DRAWING The invention can now be described in detail with the help of the figures of the drawings, where Figure 1 shows a sketch of continuously cast billet structure showing chill zone, columnar zone an equiaxed zone. Figure 2 shows a cross section of 130 x 130 mm continuously cast billet showing different zones in which ultrasonic evaluation was done using 6 MHz, 15 mm die., twin crystal normal probe. Figure 3 shows a schematic diagram showing location of 15 x 130 mm band on which back-wall echo amplitudes wtrt measured using 10 MHz, 15 mm dia., single crystal normal probe. Figure 4 shows a number of ultrasonic indications, coming from the flaws, in different zones on the transverse section of electro magnetic stirring continuously cast billets samples of WR-3 grade. Figure 5 shows ultrasonic back wall echo drop vs. distance from inner radius to outer radius of the strand showing the equiaxed / columnar transition in electro magnetic stirring continuously cast billets samples of WR-3 grade. Figure 6 shows macro-etched photograph of one of electro magnetic stirring continuously cast billets samples of WR-3 grade the results obtained during ultrasonic assessment. Figure 7 shows a number of ultrasonic indications, coming from the flaws, in different zones on the transverse section of non-electro magnetic stirring continuously cast billets samples of WR-3 grade. Figure 8 shows ultrasonic back wall echo drop vs. distance from inner radius to outer radius of the strand showing the equiaxed / columnar transition in non-electro magnetic stirring continuously cast billets samples of WR-3 grade. Figure 9 shows a macro-etcbed photograph of ont of non-electro magnetic stirring continuously cast billets samples of WR-3 grade the results obtained during ultrasonic assessment. Figure 10 shows a number of ultrasonic indications, coming from the flaws, in different zones on the transverse section of electro magnetic stirring continuously cast billets samples of PC-115 grade. Figure 11 shows an ultrasonic back wall echo drop vs. distance from inner radius to outer radius of the strand showing the equiaxed / columnar transition in electro magnetic stirring continuously cast billets samples of PC-115 grade. Figure 12 shows a macro-etched photograph of one of electro magnetic stirring continuously cast billets samples of PC-115 grade the results obtained during ultrasonic assessment. Figure 13 shows a number of ultrasonic indications, coming from the flaws, in different zones on the transverse section on non- electro magnetic stirring continuously cast billets samples of PC-115 grade. Figure 14 shows an ultrasonic back wall echo drip vs. distance from inner radius to outer radius of the strand showing the equiaxed / columnar transition in non- electro magnetic stirring continuously cast billets samples of PC-115 grade. Figure 15 shows a macro-etched photograph of one of non- electro magnetic stirring continuously cast billets samples of PC-115 grade the results obtained during ultrasonic assessment Figure 16 shows a number of ultrasonic indications, coming from the flaws, in different zones on the transverse section of electro magnetic stirring continuously cast billets samples of 75/80 grade. Figure 17 shows an ultrasonic back wall echo drop vs. distance from inner radius to outer radius of the strand showing the equtaxed / columnar transition in electro magnetic stirring continuously cast billets samples of 75/80 grade. Figure 18 shows a macro-etched photograph of one of electro magnetic stirring continuously cast billets samples of 75/80 grade the results obtained during ultrasonic assessment. Figure 19 shows a number of ultrasonic indications, coming from the flaws, in different zones on the transverse section of non- electro magnetic stirring continuously cast billets samples of 75/80 grade. Figure 20 shows an ultrasonic back wall echo drop vs. distance from inner radius to outer radius of the strand showing the equiaxed / columnar transition in non electro magnetic stirring continuously cast billets samples of 75/80 grade. Figure 21 shows a macro-etched photograph of one of non-electro magnetic stirring continuously cast billets samples of 75/80 grade the results obtained during ultrasonic assessment. DETAILED DECEPTION Ultrasonic waves when pass through a continuously cast billet / slab test piece which has a heterogeneous structure (dendritic, columnar, equiexed with pin / blow holes, non-metallic Inclusions, cracks etc.), it interacts with all these reflectors / scatterers. The ultrasonic signal observed on the oscilloscope Is resultant amplitudes of the reflections, diffraction and scattering of ultrasound with ail the above structures. When the macro-structure changes from columnar to equiaxed, there are a lot of ultrasonic losses, which is shown as a sudden reduction in back-wall echo of ultrasound. On this basis columnar / equiaxed transition is identified in the test samples. Other flaws in the sample are equiaxd as backscattered signals on the oscilloscope. P.C. Glaws(5) studied in detail the influence of electro magnetic stirring (EMS) on inclusion distribution as measured by ultrasonic inspection. He preferred ultrasonic method in comparison to other methods due to the possibility of larger volume of inspection. Determination of columnar / equiaxed zone transition is a tedious and laborious job using macro etching / sulphur printing and by metallography. The ultrasonic method can be considered a better way of understanding the variation of such structure in continuously cast steel products due to it simplicity in use and getting quantitative results. The sensitivity of ultrasonic losses with the microstructure has been reported by the authors (6-7). The difficulty in ultrasonic inspection due to high ultrasonic losses and changes in ultrasonic velocity had been recognized earlier and pretence of coarse dendrites. In the inspection of cast stainless steel a difference in ultrasonic velocity in chill / columnar / equiaxed zone were reported by J. L Rose et. al. (8) and corrections were recommended in locating the defects. Depending upon the cooling conditions a chill zone is first formed at the region in contact with mould followed by columnar and then equiaxed zone at the core (Figure 1). A large equiaxed lone is desired to reduce inter -columnar segregation, axial segregation and central looseness. There has been continuous change in the steel making process in enter to reduce these delects. The following corrective actions may be incorporated: • Steps to reduce slag carry over • Nozzle design to improve fluid flow in the mould • Tundish design to improve inclusion floatation • Argon shrouding to reduce oxidation of metal stream by air • improvement in deoxidanon practice • Changes in the Strand radius • Reduction in superheat • Application of electro-magnetic stirring (EMS) system etc. These corrective actions cause increase in equiaxed zone as well as to reduction in the flaws. The use of electro magnetic stirring (EMS) to improve the quality of strand cast steel has continued to grow over the last fifteen years. As a more thorough understanding of electro magnetic stirring (EMS) is achieved, improvement and refinements to the process continue to be made. The original awareness of the influence of a magnetic field on the motion of an electrically conducting fluid through induced currents was achieved in the early nineteenth century. The first proposal to exploit this effect for stirring of solidifying metal was made in 1917. Although the results were promising, only sporadic interest in electro magnet stirring (EMS) was generated until the viable commercialization of the continuous casting process for steel, when Junghans and Schaaber designed an electro magnetic stirring (EMS) system specifically for continuous casting of steel. Still the use of electro magnetic stirring (EMS) in continuous casting of steel, like continuous casting itself, was slow in developing. Despite of the early awareness of the influence of time varying magnetic fields on the motion of conducting fluids and the resulting improvement in the cast structure, the first commercial electro magnetic stirring (EMS) installation was not started until 1973. However, since that time, the benefits of electro magnetic stirring (EMS) have been recognized and over a hundred stirrers have been installed. The primary benefits obtained with electro magnetic stirring (EMS) have been thoroughly treated in the literature. Simply put, the purpose of electro magnetic stirring (EMS) is to homogenize the steel melt in order to obtain a favourable solid structure upon solidification. The specific benefits are as follows: 1. Improvement in cast structure through increased volume of equiexed grains, 2. Reduced degree of macro-inclusions, specifically in the central portion of cross sections, 3. Improved surface quality and 4. Reduced shrinkage porosity. In addition, inclusion re-distribution and removal is an often mentioned, but seldom unambiguously demonstrates benefits of electro magnetic stirring (EMS) of continuous casting steel(1). Electro magnetic stirring (EMS) facility is installed at a high capital investment in order to improve the continuous casting bilIet quality. It is highly desirable to assess the effectiveness of this system in improving the billet quality particularly by non-destructive evaluation techniques. Due to ever increasing demand of cleaner and cleaner steel from customer, steel producers are facing too much constraint in always changing and optimizing their process parameters in order to attain the product leadership in the market. The effectiveness of the change in the process parameters should be carefully measured in order to exactly know the extent of improvement in equiaxed zone and reduction in flaws. THEORETICAL ASPECTS: Dendrite Selidification(9): Solidification may be of plane front or dendrite front, but in steel dendrite solidification exists. Any solidification step will be as a plane front, but later either continues that way or change into cellular or dendrite type. Dendrite means 'tree-like' and it has stem, branches, sub-branches (known as primary, secondary and tertiary arms). According to Flemings, dendrite may be said to form when secondary arms appear. Dendrite arm spacing is an important parameter in the morphology of cast structure. Chill Zone This consists of equiaxtd crystal and randomly oritnted dendrites (Fig. 1). As soon as the molten metal comes in contact with mould wall, there is rapid chilling of the outer layer. This under cools liquid, below its equilibrium liquidous temperature, from the theory of nucleation(10), Around a critical T', 'I' becomes so larger that the corresponding temperature is called nucleation temperature. Columnar Zone: When the under cooling is low i.e. the temperature of the liquid is above the nucleation temperature, further nucleation almost ceases and growth starts from the existing crystal at solid liquid interlace. Such growth preferentially takes place along the heat flow direction which gives rise to the columnar zone. Since, the number of crystal becomes fewer as we move inwards, the grain size also increase. Dendrites located near the outer chill zone have more random orientation than these further inward in the columnar zone. Columnar zone also contains some equiaxed crystals (10). A conventional and widely used measure of the effects of solidification conditions on dendrite structure is 'Dendrite Arm Spacing (?). Measurements are more conveniently done on secondary arms(11). For low alloy carbon steel with solidification, where, a in mm, R in mm / h and G in ° C / cm. For steel containing 0.6% C, ?2 = 0.0158 Qf044 and for 1.5 % C, ?2 = 0.0072 Qf0.50 Equiaxed Zone : In this zone, the equiaxed crystal as well as the dendrites are oriented at random. Chalmers have reviewed the findings up to early sixties. Two theories have been proposed till then. 1. The first theory by Winegard and Chalmers says the nucleation of the crystal in the equiaxed zone occurs when the liquid reaches its nucleation temperature, as a result of constitutional super cooling. The subsequent rapid growth of these prevents further advancement of columnar zone. 2. According to second theory, nucleation occurs in the outer chili zone. Some of crystal thus formed break, survive and float in the remaining liquid and later on provide the necessary nuclei for growth in the equiaxed zone when constitutional super cooling ceases. Chalmers presented several evidences in favour of the latter mechanism such as presence of small equiaxed crystal in columnar zone. In his experience he exhibits unusually large grain size pointing out to nucleation difficulties. W R frying et. al.(12) presented correlation of % equiaxed with degree of super heat and chemical composition in continuously cast steel as given below. Equiaxed structure (%) = 1.21 ?T (° K) + 109 % C - 21 % Si - 32 % Mn - 95 % P-186 % S + 25.8 for the composition within the range of 0.25 % C. Detectabillity of colummar / Equiaxed Transition Zone in Steel(13): Changes in wave propagation speed and energy losses from interaction with material microstructure are two key factors in ultrasonic determination of material microstructure and material properties. Ultrasonic velocity and attenuation measurement are bask. Relatively small variation of velocity and attenuation are often associated with significant variation in microstructural characteristics and mechanical properties. Scattering and absorption are the energy loss mechanism that governs ultrasonic attenuation in the frequency ranges of interest of characterizing most engineering solid. Diffusion, Rayleigh and Stochastic (Phase) scattering losses are extrinsic to individual grains such as crystallites. Extrinsic Mechanism Scattering usually accounts for the great portion of losses in engineering solids. The scatter attenuation coefficient a is function of frequency 'f' and usually expressed in the term of the intensity 'I' of sound after traversing a distance X though a material: In poly crystalline aggregates (metals and ceramics), there are three scatter attenuation processes defined by the ratio of mean grain size D to the dominant wavelength a. For the Raleigh Kettering process where ? > >nD ; In this case, excessive scattering may cause drop in back-wall echo. In this case, scattering may cause slightly lest drop in back-wall echo % if compare with the same in case of Raleigh scattering process. In this case, there is a small fraction of scattering, which may causa incraasa in back-wall echo. The constant Cr, Cp and Cd contain geometric factors, longitudinal and transverse velocities, density and elastic anisotropy factors. The above grain scattering formulae are not valid for the columnar / dendritic structure. However the morphology of such structure will affect the ultrasonic losses. A dendritic structure will scatter more ultrasonic energy than columnar. Large equiaxed grains will scatter more than small equiaxed grains as per the grain scattering formula as mentioned in above equations. EXPERIMENTAL DETRAILS: Equipment Details: Model EPOCH 4, Penametries, USA make Probe 1. 10 MHz, 15 mm dia., single crystal normal probe (for identification of equiaxed / columnar transition). 2. 6 MHz, 15 mm dia., twin crystal normal probe (overall ultrasonic evaluation of flaws). Couplant SAE 40 Machine Oil Scanning - Pulse Echo 'A' Scan Gain 1. 60 dB (for identification of equiaxed/columnar tansition). 2. 65.1 d8 (overall ultrasonic evaluation of flaws) Calibration - In order to achieve reproducible result during ultrasonic evaluation of macro level flaw counts, the amplitude Calibretion block; was sat to 80% FSH on oscilloscope of tha ultrasonic equipment. Materials Investigation: Low carbon grade (WR-3) and high carbon grades (PC-US and 75/80) of non- alactro magnetic stirring (EMS) and electro magnetic stirring (EMS) continuously cast bidets of section 130 mm x 130 mm, (from the strand # 3 of billet caster#l at LD#1) ware selected for study the effect of electro-magnetic stirring (EMS) on macro-structure of continuously cast billats by ultrasonic technique. Table 1 shows their EMS details whereas Table 2 shows their chemical compositions. Test samples of length 300 mm were gas cut from the head end of the non- electro magnetic stirring stirng and electro magnetic stirring (EMS) continuously cast billets of section 130 mm x 130 mm for each grades (WR-3, PC-115 and 75/80) from the strand no. 3 of bidet caster #1 at LO# 1. Billet samples were then saw-cut to make total 48 numbers of test samples of size 130 mm x 130 mm x 40 mm. The transverse faces were made parallel and ground finished for ultrasonic and macro-etch testing. Table 3 shows the investigated sample details of different grades of continuously cast billet. Methodology: Identification of equiaxed / columnar transition by subsequent change in ultrasonic back-wall echo amplitude using 10 MHz, 15 mm dia., single crystal normal probe arid verification of ultrasonic results was done by macro-etch test Overall ultrasonic evaluation of flaws indicated by number of back-saattered signals was done using 6 MHi, 15 mm die., and twin crystal normal probe. Ultrasonic evalumtion: For ultrasonic evaluation of macro level flaw counts, ultrasonic scanning was done as shown in Figure 2, whereas for locating equiaxed / columnar transition, ultrasonic scanning was done as shown in Figure 3. The details of test procedure ere as follows: Overall evaluation of flaws: The overall ultrasonic evaluation of flaws indicated by number of back scattered signals was performed on each and every band as shown in Figure 2 by using 6 MHz, 15 mm dia., twin crystal normal probe. On each band (A, B, C, D, E & F) of the sample, the total numbers of flaw echoes were noted. For each sample, the total number of flaws (Ntotal) was calculated as given below : (Ntotal) - (NA + NB + NC + ND + NE + NF) The total flaws for each sample, were tabulated and reported. Increase in value of Ntotal indicates increase in dirtiness of the steel. Identification of equtexed / columnar transition: The equiaxed / columnar zone in test samples was assessed by subsequent change in ultrasonic back-wall echo amplitude using 10 MHz, 15 mm dia., single crystal normal probe as shown in the Figure 3. After every 5 mm increment on the shown band (Figure 3), the amplitude of the back-wall indications were noted. The noted results, for each sample, were tabulated and reported. The verification of ultrasonic results was done by macro-etch test. RESULTS AND DISCUSSION: Evaluation af WR-3 grade af continuausly cast billets: Total flaws: Zones A and B towards the inner radius (top surface) and E and F towards the outer radius (bottom surface) of the strand showed less flaws in electro magnetic stirring (EMS) billet when compared with non-electro magnetic stirring (Non- EMS) billet. The scanned zone C and D towards the central portion of the strand show more flaws in EMS billet when compared with non-electro magnetic stirring (Non-EMS) billet (Figs. 4,6,8 & 9). Equiaxed zone: There was no clear indication of equiaxed zone in non-electro magnetic stirring (Non-EMS) sample whereas in electro magnetic stirring (EMS) sample, there was an indication of a small equiaxed zone (15 x 10 mm) which was found away from the center and towards the radius (Figures 5,6,8 & 9), evaluation of PC-118 grade of continuously cast billets: Total flaws: Zones A and E of the billets sample were found to contain lass flaws in electro magnetic stirring (EMS) billet when compared with non-electro magnetic stirring (Non-EMS) billet. The scanned zone C and D towards the central portion of the strand showed no flaw (Figures 10,12,13 & 15). Equiaxed zone : There is an indication of a small equiaxed zone (approx. 25mm x 25 mm) in non-electro magnetic stirring (Non-EMS) sample whereas in electro magnetic stirring (EMS) sample, there is an indication of a comparatively larger equiaxed zone (approx. 50 mm x 50 mm ) (Figures 11,12,14 & 15). Evaluation of 7S/80 Grades of Continuously Cat IHIets: Total flaws : Zones A and E of the billet samples were found to contain less flaws in electro magnetic stirring (EMS) billet when compared with non-electro magnetic stirring (Non-EMS) billet. The scanned zone C and D towards the central portion of the strand showed no flaw (Figures 22,24,25 & 27). Equiaxed lone: There is an indication of a small (approx. 20 mm x 20 mm) equiaxed zone in non-electro magnetic stirring (Non-EMS) sample whereas in electro magnetic stirring (EMS) sample, there is an indication of a comparatively larger (approx. 40 mm x 40 mm) equiaxed zone (Figures 23,24,26 & 27). A non-destructive ultrasonic technique has been developed for study the effect of electro magnetic-stirring (EMS) on macro-structure of continuously cast billets, which will assist in modifying the process parameters to improve the billet quality. REFERENCES: 1. R. Albany et aI., A First Rtport on IRISDs & Magnetorotative continuous casting process for Rounds & Squart Sections, Industrial Applications in EBVs Steelworks in EschweHer, Steel making Proceedings, Vol. 61, ISS - AIME1978,p.37-59. 2. J. Chone et. al., Development of the magnetogyr process for the continuous casting of Blooms & Billets - application to aluminum killed steels, steel making proceedings, Vol. 63, ISS - AIME 1980, p. 261-272. 3. M. Gary et al., electro-magnetic staring in the mould - During continuous casting, Iron & Steelmaker, Vol. 4,1982, p. 20 - 26. 4. K. Ayata et. Al., Improvement of the distribution of large inclusion by electro-magnetic stirring in bending type continuous casting machine. Trans. ISD, 1980, Vol. 20(6), p.8 - 211. 5. P.C. Glaws et. Al., the influence of electro-magnetic stirring on inclusion distribution as Measured by Ultrasonic Inspection, Steelmaking Conference Proceedings, 1991, p. 247-264. 6. J.C. Pandey, R. Jha, M.P. Singh & O.N. Mohanty, Ultrasonic Attenuation Technique and Quality of Steel Products, Proceedings, 14th WCNDT, New Delhi, Dec. 8 - 13,1996, p. 2247 - 2251. 7. J.C. Pandey, A.S. Prasad and O.N. Mohanty, some application of ultrasonic attenuation and velocity techniques in assessing mkrostructural variation in steel and cast Iron, Journal of NDE, 1995,15, (l),pp 10-16. 8. R.L Rose and Tverdokhlebov, ultrasonic testing considerations for metal with mild Anisotropy, British Journal of NOT, Vol. 31 (2), 1989, p. 71-76. 9. M.C. Flemings, solidification proceedings, R.E. Keiger publishing Co. Huntington, New York, 1964. 10. B. Chalmers, principle of solidification, R E Keiger publishing Co., Huntigton, New York, 1964. 11. F. Oethers, K. Ruttiger and H.J. Selenz, Information Symposium on casting and solidification of steel proceedings, commission of the European Communities, IPC Science & Technology Press Ltd., Guildford, UK, Vol. 1,1977. 12. W.R. Irving, A. Perkins and M.G. Brooks, effects of chemical, operational and engineering factors on segregation in continuously cast slabs, continous casting, 1995, Vol. 7, p. 256 - 269. 13. Material properties characterization, ASNT Hand Book, p. 405 - 407. WE CLAIM 1. A nondestructive ultrasonic testing method for determining macro structure in continuously cast billets for studying the effects of electromagnetic stirring, comprising the steps of : - selecting the continuously cast billets from different grades of steel like low carbon (WR3), high carbon (PC 115 and 75 / 80); - saw cutting samples in desired sections from the selected billets, keeping transverse faces parallel; - grinding and finishing said parallel transverse faces for ultrasonic test; identifying equiaxed / columnar transition by changing in ultrasonic backwall echo amplitude using a single crystal normal probe; and - evaluating flaws indicated by number of back scattered signals using a twin crystal normal probe. 2. The method as claimed in claim 1, wherein said single crystal normal crome is of 10 MHz and 15 mm in diameter. 3. The method as claimed in claim 1 or 2, wherein said twin crystal normal probe is of 6 MHz and 15 mm in diameter. 4. The method as claimed in claims 1 to 3, wherein said billet samples are saw-cut to make a total of 48 numbers test samples of sites 130 mm x 130 mm x 40 mm. 5. The method as claimed in claim 1, wherein for said ultrasonic evaluation of macro level flaw counts, ultrasonic scanning is carried out in different zones, comprising a central looseness zone and one pin holed zone and two macro inclusion zones on either side of said central zone (Fig. 2). 6. The method as claimed in claim 1, wherein for ultrasonic evaluation for beating equiaxed / columnar ultrasonic scanning is carried out by measuring back wall echo amplitudes (Fig. 3). 7. A non-destructive ultrasonic testing method for determining macro structure in continuously cast billets for studying the effects of electromagnetic stirring, substantially herein described and illustrated in the accompanying drawings. A non-destructive ultrasonic testing method for determining macro structure in continuously cast billets for studying the effects of electromagnetic stirring, comprising the steps of selecting the continuously cast billets from different grades of steel like low carbon (WR3), high carbon (PC 115 and 75/ 80); saw cutting samples in desired sections from the selected billets, keeping transverse faces parallel; grinding and finishing said parallel transverse faces for ultrasonic test; identifying equiaxed / columnar transition by changing in ultrasonic backwall echo amplitude using a single crystal normal probe; and evaluating flaws indicated by number of back scattered signals using a twin crystal normal probe. |
---|
839-kol-2004-granted-abstract.pdf
839-kol-2004-granted-claims.pdf
839-kol-2004-granted-correspondence.pdf
839-kol-2004-granted-description (complete).pdf
839-kol-2004-granted-drawings.pdf
839-kol-2004-granted-examination report.pdf
839-kol-2004-granted-form 1.pdf
839-kol-2004-granted-form 13.pdf
839-kol-2004-granted-form 18.pdf
839-kol-2004-granted-form 2.pdf
839-kol-2004-granted-form 3.pdf
839-kol-2004-granted-form 5.pdf
839-kol-2004-granted-reply to examination report.pdf
839-kol-2004-granted-specification.pdf
Patent Number | 234002 | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Indian Patent Application Number | 839/KOL/2004 | ||||||||||||
PG Journal Number | 18/2009 | ||||||||||||
Publication Date | 01-May-2009 | ||||||||||||
Grant Date | 29-Apr-2009 | ||||||||||||
Date of Filing | 21-Dec-2004 | ||||||||||||
Name of Patentee | TATA STEEL LIMITED | ||||||||||||
Applicant Address | RESEARCH AND DEVELOPMENT DIVISION, JAMSHEDPUR | ||||||||||||
Inventors:
|
|||||||||||||
PCT International Classification Number | B21C 51/00,B21J 1/02 | ||||||||||||
PCT International Application Number | N/A | ||||||||||||
PCT International Filing date | |||||||||||||
PCT Conventions:
|