Analysis of Surface cracks in CHQ grades
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2012-Summer Internship Project Report

2012-Summer Internship Project Report

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Analysis of Surface cracks in CHQ grades Document Transcript

  • 1. 1 Summer Industrial Training Report-2012 Analysis of longitudinal Surface Discontinuous Cracks in Cold Headed Quality steel grade as-rolled coils at Sunflag Iron & Steel Company Limited, Bhandara Road, Maharashtra 7th May-6th July. (Submitted in partial fulfillment of the Summer Internship-2012)Guided by Submitted byMr Avinash Pansi Piyush VermaGeneral Manager, 09MT3018Quality Assurance and Customer Services Metallurgical & Materials EngineeringSunflag Iron & Steel Plant IIT, KharagpurCo-guided byMr Nitin Raut ManagerQuality Assurance and Customer ServicesSunflag Iron & Steel Plant
  • 2. 2Acknowledgement I would like to thank my Guide, Mr Avinash Pansi (General Manger) and Co-Guide, Mr Nitin Raut (Manager),Quality Assurance & Customer Services department, Sunflag Iron & Steel Plant, Bhandara Road) for their immensesupport and guidance throughout my Internship at Sunflag. I would specially like to thank Mr Nitin Raut for alwaysgiving time out of his busy schedule, whenever I approached. I would like to thank Sunflag Steel Plant’s HR Management Department for providing me an opportunity to getan exposure of working in an industrial environment, the problems related to manufacturing and an opportunity for 2continuous months to meet the metallurgists working in industry. I am thankful to Mr Sandeep Nadagouda (Assistant General Manager, Industrial Engineering & Training), forproviding me an opportunity to deliver a short lecture on “Iron-Iron carbide phase diagram” to GETs from non-metallurgical background on 15th June, which I believe added some value to the Sunflag Organization. Piyush Verma 28th August, 2012
  • 3. 3Contents Page 1. About the Company 4 2. About the Internship 4 3. Plant Visit 4 4. Following a CHQ Grade production process 6 5. Project 7 6. Analysis 8 7. Final Conclusion 16 8. At the End of Training 17
  • 4. 4About the Company Sunflag Iron & Steel Company Limited is a part of Sunflag Group of Industries. It’s an Integrated SteelPlant, situated at Bhandara Road, Maharashtra & is in the business of manufacturing special steel and power for22 years. The plant is located on 2.3 Sq. Km of land. Sunflag Steel has strength of around 2000 people. Theplant has present installed capacity of making 400,000 metric tonnes per year of quality special steels. SunflagSteel is the leading producer of Special Carbon, Alloy Steels, Micro Alloy and Stainless steels. Sunflag Steel’scustomers include all major Original Equipment Manufacturers in India, Americas, Europe, South East / FarEast / Middle East Asia.About the Internship  Observed the steel production process and got an overview of a steel plant, from its Sinter plant, Mini Blast Furnace, Refining Furnaces to Rolling mills and testing.  Worked on the Analysis of Longitudinal Discontinuous Surface cracks in Cold Headed Quality Steel grade coils in Bar & Section Mill.Plant Visit 1. EAF-Electric Arc Furnace-Mannesmann Demag (55 MT)  Continuous feeding of sponge iron  Decarburization & Dephosphorization.  Eccentric Bottom Tapping. Raw materials:- Scrap – 6 Tonne Hot Metal from MBF (Mini Blast Furnace) – 30-32 Tonne DRI (Direct Reduced Iron)- 28-30 Tonne. Reactions:- C+O₂ = CO ₂ Si+O ₂ =SiO ₂ Mn+O ₂ =MnO ₂ P+O ₂ =P ₂ O5 2. LRF-1 Ladle Refining Furnace1 (55 MT)-  Deoxidation and Desulphurization (Continuous Arcing)  Ferro Alloys, Lime etc additions for controlling the chemistry like  FeMn, FeSi, FeCr, FeMo, SiMn, CPC (Coke Calcined Petroleum).  Sulphur is mainly reduced to 100-150 ppm (0.010%-0.015%) Al+ [O] = Al ₂ O3 Si+ [O] =SiO ₂ Mn+ [O] =MnO ₂ S+ [O] =SO ₂ 3. LRF-2 Ladle Refining Furnace2 (55 MT)-  Reheating of the heat if necessary for maintaining the temperature (Continuous Arcing)
  • 5. 54. Vacuum Degassing –Danieli (VD)  To reduce dissolved gases levels like H₂ , N₂, O₂ by creating vacuum (1milliBar)  Addition of wire rods Al (for fixing O₂) Ti (for fixing N₂), CaSi (for modifying the  Al₂O3 inclusion into spherical C₁₂A7 (12CaO.7Al₂O3) and B wire (to achieve Hardenability in CHQ grades)  CHQ GRADE- 10 min VD holding time at 1mbar5. Continuous Casting Machine (CCM)  Laddle from VD is put in a turret (can contain at a time 2 laddle containing hot metal), from which through shroud (made of graphite) liquid metal is poured in a T-type(to avoid turbulence) tundish (all closed to avoid oxidation of liquid steel), from tundish, steel is passed through already heated (to avoid thermal shock) SEN( Sub-Entry Nozzle-made of Zr+Graphite-3 numbers per tundish).  Casting of the liquid steel continuously in 2 X 3 stand billet caster.  Electro Magnetic Stirrer (EMS)(600 mm from the top of the mould which is also 300 mm from the bottom- total mould length 900 mm) to avoid dendritic structure during solidification(Avoids macro-segregation of Pb and S).  Hydraulic Mould (Water cooled Copper) Oscillator to avoid sticking (can produce Oscillation hook marks later in the billets).  Addition of Mould Flux (REDx here) to avoid friction between cast and the mould (can result in entrapments later in rods).6. Billet Yard  Hot-Billet is gas-cut and air-cooled, for 2 days, then the Billet-Grinding (must for CHQ Grades for better surface finish) takes place either manually or in Billet Grinding Machine.  Billet-Grinding done upto 1-3mm depth removes surface oxides.7. Reheating Furnace  Billet is reheated upto1200˚C (Top Heating), fuel used: gases from MBF.  For 2-3 hrs depending upon the cross-section of the billet (160X160, 130X130, 320X230).  Discharge temperature around 1150˚C.8. Rolling Mill  From reheating furnace, billets are rolled in either 20 stand WRD (Wire RoD mill) (For sizes >12mm) or 20+10 stand WRB (Wire Rod Block mill)(for sizes 5.5-12mm).  -Morgardshammer Garret coiler (made of nodular cast iron to avoid friction between drum and rod) used to coiling the wire rods.9. Testing and Sampling  In SMS (EAF+LRFs+VD) using lollypop samples (for chemistry).  Billet cross-section chemistry, Shear-cutting at stand-8 of rolling mill and finishing stands.  Front and back ends of each coil goes following testings /observations  MPI (Magnetic Particle Separation method for locating defects if any)  Under Magnifying glass for identifying various surface defects and measuring crack length.  Under Optical Microscope  For differentiating between continuous and discontinuous cracks.  For measuring the decarburization depths near the cracks and concluding whether crack formed before or during rolling.  For locating any entrapments near cracks.  For identifying the type of inclusion(if any near the cracks)  For measuring the crack depth. Crack depth (in mm) Crack length (in mm) 0.1(20mm)
  • 6. 6Following a CHQ Grade production process  Heat Number-74101 (15B25) (Continuous Arcing)  EAF Tapping temperature-1630˚C Additions made:- -SiMn-600 kg -Cao (lime)-300 kg.  LRF-1 Starting Temperature-1561˚C (Refractory Lining- MgO -C, Magnesia-Carbon) Additions made:- -Al bar – 2 X 22 kg, after 3 minutes of arcing. -CaO – 100 kg -SiMn-250 kg -Fe-Si-36 kg -CPC (Coke Calcined Petroleum)-50 kg -Al cored wires-120 meter -FeCr HC (High Carbon)-50 kg -Al dros (major content Al₂O3, added to refine the slag, contains SiO₂ too) -Electrode (Length-2100 mm and diameter-500mm) (Electrode length decreases due to erosion) -HC FeMn 120 kg -HC FeCr 10 kg -CaO-50 kg  VD (Vacuum Degassing) P-1 millibar For CHQ Grade-10 min holding time at 1 millibar CaSi-strand1-61 m Al-strand1-64 m B-strand1-16 m Ti-strand1-125 m Laddle In Temperature-1669˚C Laddle out Temperature-1600˚C  CCM -EMS 600mm below top surface (300 mm from bottom) of the oscillating mould (vertically), total length of the mould-900 mm -REDx added to avoid oxidation of liquid steel in the tundish.
  • 7. 7Project  Problem: In Sunflag, significant rejections in coils are coming from CHQ grades, most of which comprise of Boron CHQ grades (10B21, 15B25, 15B41). Samples sent by Sunflag Customer Micro Turner Rejected Cold Forged  About CHQ grades:  Cold Forged- Mainly for fasteners and similar components.  Starting material-Wire Rods.  Metallurgical specification:- - Surface defect depth less than 0.5% of wire rod diameter. - Decarburization depth less than 0.5% of wire rod diameter. - Cold-upsetting to 85% minimum of wire rod.  Benefits of Cold-Forging:- - High As-forged strength. - No trimming and scaling loss. - Good surface finish (required for automotive components)  Approach: Work in the project mainly included  1st-Data Collection from the Record registers of CHQ grades for discontinuous cracks between January-May & arranging it.  2nd-Data Analysis of January-May-To find out which grade among Boron CHQ grades is most problematic, and further which size(cross-section) and to look if there’s any trend.  3rd-Identification of the “NOT OK” Heat and observing its cracks under Optical Microscope (if available i.e. sample not thrown) and to look for any inclusion.)  4th-Comparison of various processing parameters responsible for inclusion occurrence of the Good Heats and the Bad Heats.
  • 8. 8Analysis  January-April NUMBER O F NTFRO NT BAC K BAC K TO TAL C O ILS C O ILS Sr HEAT GRAD SIZ FRO %AGE %AGE REMARK No. NO . E E SAMPLES O K NO T O K O K NO T O KC O ILS O K NO T O K O K REJEC TIO N C HEC KED 1 72665 10B21 5.5 44 22 0 22 0 22 22 0 OK 100 0 3 71590 10B21 6 10 5 0 4 1 5 4 1 80 20 4 71590 10B21 6 10 5 0 4 1 5 4 1 NOT OK 80 20 46 72866 10B21 7 36 18 0 18 0 18 18 0 OK 100 0 49 71806 10B21 8 10 4 1 4 1 5 3 2 NOT OK 60 40 51 71937 10B21 8 50 20 5 20 5 25 17 8 NOT OK 68 32 84 72847 10B21 9 64 0 32 0 32 32 0 32 NOT OK 0 100 85 72847 10B21 9 64 20 12 11 21 32 4 28 NOT OK 12.5 87.5 86 71590 10B21 10 14 7 0 4 3 32 4 3 NOT OK 90.7 9.3 91 72861 10B21 10 56 26 2 24 4 28 22 6 NOT OK 78.57 21.42 92 72860 10B21 12 70 35 0 35 0 35 35 0 OK 100 0 205 72670 15B25 5.5 40 18 2 20 0 20 18 2 NOT OK 90 10 206 71569 15B25 6 6 3 0 3 0 3 3 0 OK 100 0 255 72754 15B25 8 8 3 1 3 1 4 2 2 NOT OK 50 50 256 73338 15B25 8 16 4 4 5 3 8 2 6 NOT OK 25 75 257 73339 15B25 8 46 15 8 5 10 23 9 14 NOT OK 39.14 60.86 258 71597 15B25 9 4 2 0 2 0 2 2 0 OK 100 0 259 71628 15B25 9 4 1 1 2 0 23 1 1 NOT OK 95.66 4.34 260 71664 15B25 9 22 9 2 11 0 2 9 2 NOT OK 0 100 262 71569 15B25 10 16 8 0 3 5 8 3 5 NOT OK 37.5 62.5 369 72863 15B25 16 4 2 0 2 0 2 2 0 OK 100 0 370 72900 15B25 16 16 8 0 8 0 8 8 0 OK 100 0 371 72911 15B25 16 22 8 3 10 1 11 7 4 NOT OK 63.64 36.36 372 71628 15B25 17 4 1 1 2 0 8 1 1 NOT OK 87.5 12.5 373 72900 15B25 17 16 7 1 7 1 8 6 2 NOT OK 75 25 374 72827 15B25 18 30 12 3 13 2 15 12 3 NOT OK 80 20 386 71596 15B41 16 12 0 6 0 6 6 0 6 NOT OK 0 100 387 72214 15B41 16 4 1 1 2 0 2 1 1 NOT OK 50 50 388 72215 15B41 16 6 0 3 0 3 3 0 3 NOT OK 0 100 389 72215 15B41 16 6 3 0 3 0 3 3 0 OK 100 0 390 72215 15B41 16 28 11 3 14 0 14 11 3 NOT OK 78.58 21.42 391 72757 15B41 19 14 7 0 7 0 7 7 0 OK 100 0 406 71776 15B41 24 14 7 0 5 2 7 5 2 NOT OK 71.43 28.57 407 71776 15B41 25 42 12 9 11 10 7 4 3 NOT OK 57.15 42.85 408 73280 15B41 25 40 18 2 15 5 20 13 7 OK 65 35 409 73280 15B41 25 6 0 3 0 3 3 0 3 NOT OK 0 100 410 73279 15B41 26 20 8 2 7 3 10 6 4 NOT OK 60 40 411 73279 15B41 26 2 1 0 1 0 1 1 0 OK 100 0 (Total Data for January-April includes observation of 411 entries-All not shown)
  • 9. 9 Population Grade Vs Size Vs Rejection (January-April) GRADE SIZE Total Coils Coils % Rejection Coils Checked OK NOT OK 10B21 5.5 70 70 0 0 6 479 446 33 6.88 6.5 40 39 1 2.5 6.7 167 163 4 2.39 7 107 104 3 2.8 8 82 58 24 29.26 13.3 7 5 2 28.57 15 9 6 3 33.33 16 7 7 0 0 16.3 3 3 0 0 17 11 11 0 0 18 4 2 2 50 19 11 11 0 0 20 7 5 2 28.57 21 75 45 30 40 23 22 10 12 54.54 24 79 25 54 68.35 26 30 21 9 30 28.5 84 29 55 65.47 15B25 5.5 87 65 22 25.28 6 80 61 19 23.75 6.7 76 75 1 1.31 8 219 154 65 29.68 9 12 5 7 58.33 10 114 85 29 25.43 11 130 112 18 13.84 12 47 43 4 8.51 13 672 531 141 20.98 14 37 1 36 97.29 15 216 162 54 25 16 26 21 5 19.23 16.3 265 205 60 22.64 17.3 10 7 3 30 18 22 19 3 13.63 18.3 33 27 6 18.18 23 7 3 4 57.14 15B35 18.3 1 0 1 100 15B41 14 7 6 1 14.28 16.3 49 34 15 30.61 19 7 7 0 0 20 48 42 6 12.5 23 47 37 10 21.27 24 24 19 5 20.83 25 20 3 17 85
  • 10. 10 Population Curves 500 10B21, Coils Checked Vs Rejected 6 450 400 Number of Coils Coils Checked 350 300 8.5 250 200 150 6.7 9 9 100 7 10 5.5 8 21 24 28.5 50 6.5 24 28.5 6 8 12 21 23 26 0 5.56.5 8.5 10 6.77 13.3 13.3 15 16 17 18 19 20 12 16.3 16.3 23 15 16 17 18 19 20 26 0 5 10 15 20 25 30 Size (in mm) 700 15B25, Coils Checked Vs Rejected 13 Coils Checked 600Number of Coils 500 Coils Not OK 400 300 16.3 200 8 15 13 100 10 11 5.5 6.7 8 6 16.3 14 15 16 0 5.5 6.7 6 9 10 11 12 12 18.3 18 16 17.318.3 18 23 0 5 10 15 20 25 Size (in mm) 15B41, Coils Checked Vs Rejected 60 50 Numbe of Coils 16.3 20 23 40 30 Coils Checked 24 20 25 Coils Not OK 16.3 25 10 23 Полиномиальная (Coils Not OK) 14 1920 24 0 14 19 26 0 5 10 15 20 25 30 Size (in mm)
  • 11. 11 Grade-Size-Rejection Trend Higher Rejection Trend in 10B21 % Coils Rejection Cross-section around 23mm 100 9 80 % Rejection 24 28.5 60 18 23 40 21 8 13.3 15 20 26 20 0 6 6.7 7 5.56.5 8.5 10 12 16 17 16.3 19 0 5 10 15 20 25 30 Size (in mm) 15B25 % Coils Rejection 100 14 90 80 70 % Rejection 60 9 23 50 40 30 8 17.3 5.5 6 10 13 15 16.3 20 16 18.3 10 11 18 12 0 6.7 0 5 10 15 20 25 Size (in mm) 15B41 % Coils Rejection 100 90 25 80 70 % Rejection 60 50 40 30 16.3 20 23 24 14 20 10 0 19 26 0 5 10 15 20 25 30 Size (in mm)
  • 12. 12 All Grade Vs Size Analysis Grade-wise Rejection in coils in different sizes Common 100 Rejection of around 60% for 90 14-15B25 10B21,15B25,15B4 Higher Rejection in 80 10B21, 15B25 around size at 9-10 mm 70 15B25 60% Rejection 50 15B41 40 30 Полин 20 омиал ьная 10 (10B21 ) 0 0 5 10 15 20 25 30 Size (in mm)  May GRADE SIZE TOTAL COILS COILS REJECTED %REJECTED 10B21 5.5 217 7 3.22 10B21 6 39 18 46.15 10B21 6.5 58 24 41.37 10B21 6.7 45 16 35.55 10B21 8 148 54 36.48 10B21 8.5 160 8 5 10B21 10 145 9 6.2 10B21 12 8 0 0 10B21 13.3 7 2 28.57 10B21 15 15 2 13.33 10B21 18.4 4 0 0 10B21 20 29 8 27.58 10B21 21 11 4 36.36 10B21 23 35 3 8.57 10B21 23.5 35 2 5.71 10B21 24 38 16 42.1 10B21 26 13 7 53.84 10B21 27.5 7 5 71.42 10B21 28.5 52 38 73.07
  • 13. 13 GRADE SIZE TOTAL COILS COILS REJECTED %REJECTED 15B25 5.5 22 3 13.63 15B25 6.7 14 6 42.85 15B25 8 49 35 71.42 15B25 8.5 126 5 3.96 15B25 10 218 3 1.37 15B25 12 179 52 29.05 15B25 20 23 0 0 15B25 21 2 0 0 15B25 23 29 16 55.17 15B41 10 12 2 16.67 15B41 12 14 0 0 15B41 13 108 12 11.11 15B41 14 3 1 33.33 15B41 15 6 1 16.67 15B41 17 36 0 0 15B41 17.3 5 3 60 15B41 20 9 3 33.33 15B41 21 58 3 5.17 15B41 23 48 1 2.08 15B41 24 19 10 52.63 10B21 % Coils Rejection 100 Again in MAY month, high 90 rejection trend in Higher 80 70 28.5 27.5% Rejection 60 50 6 6.5 26 40 24 6.7 8 21 30 13.3 20 20 10 15 8.5 10 23 23.5 0 5.5 12 18.4 0 5 10 15 20 25 30 Size (in mm)
  • 14. 14 15B25 % Coils Rejection 100 14 90 80 70 8% Rejection 60 23 50 40 6.7 30 12 20 18.3 10 5.5 13 8.5 10 0 17.3 18 20 21 0 5 10 15 20 25 Size (in mm) 15B41 % Coils Rejection 100 90 80 70% Rejection 60 17.3 50 24 40 30 14 20 20 10 15 10 13 40 21 23 0 12 17 0 5 10 15 20 25 30 35 40 45 Size (in mm)
  • 15. 15  Observations  Observed, measured and compared the depth of discontinuous surface cracks between samples from stand 8 and the finishing stand 18th, of grade 10B21 (Heat Number-74313), using magnifier. -Crack depth decreased between stands 8th & 18th.Left: Discontinuous crack (depth 0.8mm)Right: Continuous crack (depth 0.7mm)  Observed the distribution of discontinuous cracks on both the samples under MPI (Magnetic Particle Inspection). -Discontinuous cracks formed, along with few continuous cracks, all over the surface (Not on any specific side).  Observed the surface cracks under Optical Microscope (100x) for the inclusion pattern, by polishing the sample along the crack. -Of the few samples which were observed, most of the cracks where regular shaped, indicating rolling problem. -One of the cracks showed Alumina pattern. Heat number-72828 Grade-15B25 Diameter- 11mm Rejection-(rejected coils/total coils)-(2/14) Rejection-14.28% Crack type-Discontinuous Crack depth-0.1mm Crack pattern resembles Alumina pattern
  • 16. 16 Heat Number-72911 Grade-15B25 Diameter-15mm Rejection-(rejected coils/total coils)-(7/24) Rejection-29.16 % Crack type-Discontinuous Crack shape is regular, (Rolling-Crack) No inclusion found Heat Number-72846 Grade-10B21 Diameter-9 mm Rejection-(rejected coils/total coils)- (66/66) Rejection- 100% Crack type-Discontinuous Crack shape is regular, (Rolling-Crack) No inclusion foundFinal Conclusion  High rejection around 23-26mm, significantly that of 10B21  10B21 most sensitive to surface cracks, next 15B25 & lastly 15B41. (Increasing rejection trend with cross-section clearly seen for 10B21, from the data.)  Higher Cross Section gets rejected more because “Crack-Depth” is larger in larger cross-section as compared to lower cross-section, as depth gets decreased during plastic deformation, so the acceptability depth of cracks in lower cross-section is mostly not crossed.(Generally for Rolling Mill-Cracks, without inclusions)  Cracks in lower-cross-section can occur by inclusions(or entrapments), as crack depths don’t get reduced even after plastic deformation ( Alumina inclusion found in 15B25, 11mm)  Some coils with good surface finish may get rejected if crack opens in UPSETTING, due to more hardenability.  Problems may be coming from rolling mill largely, as per the metallurgists at QC told, “Full- Decarb” is generally not found around observed cracks.  Almost every billet of CHQ was billet-grinded, and data from auto & manual mode of billet- grinding, showed no-effect.
  • 17. 17At the End of Training  Got the necessary steel industry exposure for 2 continuous months.  Got the opportunity to closely observe the steel manufacturing processes and to relate it to the theories studied.  Met with different metallurgists of different departments ( from Mini Blast Furnace-MBF, SMS , CCM to Rolling and lastly the Quality Department), which highly enriched our experience.  Realized the importance and role of the “Demand-Quality-Plan-Production-Supply” chain in connection to Industry & its Customers, as from my daily visit in the “Quality Assurance & Customer Services Department-(QA-CS)”.  As the training period was of just 2 months, coupled with no prior industrial experience & lack of research facilities at Sunflag and related provisions, an “EXTENSIVE PRACTICAL STUDY” could not be met, which would have definitely put some more light over the CHQ problem.