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RAIL SPECIFICATIONS AND RAIL CORROSION

RAIL SPECIFICATIONS AND RAIL CORROSION. RAIL SPECIFICATION. Standard Specifications for Flat Bottom Rails initially adopted in 1934 Revised in 1939, 1955, 1958, 1960 1964, 1988,1996 Latest version : T-12 (2009)

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RAIL SPECIFICATIONS AND RAIL CORROSION

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  1. RAIL SPECIFICATIONS AND RAIL CORROSION

  2. RAIL SPECIFICATION • Standard Specifications for Flat Bottom Rails initially adopted in 1934 • Revised in 1939, 1955, 1958, 1960 1964, 1988,1996 • Latest version : T-12 (2009) • Provides specifications for rails having UTS of 880 MPa, 1080 MPa CR and 1080 MPa HH • Specifies Niobium (NB), Vanadium (VN), Copper Molybdenum (CM), Nickel Chromium Copper (NC) rails

  3. Rail Sections • IRS 52 kg/m • UIC 60kg/m • ZU 1-60 Profile (73kg/m) • 136 RE 14 (68kg/m)

  4. Iron from Iron Ore.. • Iron ore mixed with carbon (coke) & a flux (lime-stone) and mixture heated in a blast furnace. • Carbon (Coke) burns to produce carbon monoxide (CO) & heat. • CO :highly reducing gas which reduces iron oxide to iron. • Other impurities are absorbed by flux to form slag which being lighter than iron floats on the surface. Slag also protects iron from further re-oxidation. • Molten iron is tapped from blast furnace & cast into pigs. • This called Pig Iron & process called smelting of iron ore.

  5. MANUFACTURING PROCESS • To convert pig iron into steel, various methods: • Bessemer Process, • Open Hearth Process, • Basic oxygen method & • Electric Arc Furnace Method • Steel to be manufactured using Basic oxygen method or Electric Arc Furnace Method (with secondary ladle refining & vacuum degassing) • Basic Oxygen Method is being used in Bhilai Steel Plant for manufacture of rails.

  6. CASTING • INGOT CASTING: liquid steel poured in ingot moulds of Cast Iron. Defects viz piping, blow-holes, segregation, columnar structure & internal fissures present in Ingots.not used now. • CONTINUOUS CASTING process :to be adopted – no interruption to flow of liquid steel into the moulds and strands – inter-mixing of some liquid steel from the two successive casts is ensured • Cleaner steel • Small and more uniformly distributed inclusion • No Reheating is required. • Economical

  7. CONTINUOUS CASTING • This process comprises the direct solidification of liquid steel into a solid bloom which is continuously extracted from the casting machine and cut into the required length • The cross sectional area of bloom should not be less than ten times the rail section to be produced

  8. Bloom

  9. Structures of Steel • Austenite: As liquid metal from blast furnace solidifies, it takes up Gamma format (temp of 910 deg, crystalline structure transformed into Gamma iron) it can take upto 1.7% solid carbon into solution. Iron form called Austenite. • Perlite: On further, cooling, Austenite itself transforms into Alpha Iron, a low carbon content phase. (Pure iron exists at room temp in crystalline form known as Alpha Iron) & a lameller structure called as Perlite. (Desired in Rail manufacturing) • Martensite: when hot metal is rapidly quenched, carbon atoms do not have sufficient time to combine with iron atoms hence formation of Perlite is not possible. Surplus Carbon atoms becomes trapped in crystalline structure & distort it. Resultant structure is extremely hard/brittle material known as Martensite.

  10. Classification of Rails • Prime Quality Rails • Class ‘A’ Rails • Class ‘B’ Rails • The classification is based on the tolerance in end straightness • Industrial Use (IU) Quality Rails • Based on tolerances in sectional dimensions and end straightness

  11. CHEMICAL COMPOSITION OF RAIL STEELS

  12. MECHANICAL PROPERTIES OF RAIL STEELS The Chemical composition of NB, VN, CM & NC rails has also been given in the specs.

  13. EFFECT OF DIFFERENT ELEMENTS CARBON (C) • INCREASES • UTS • YIELD POINT • HARDNESS BUT • DECREASES • DUCTILITY

  14. EFFECT OF DIFFERENT ELEMENTS CHROMIUM (Cr) • INCREASES UTS/hardness • If more than 2% difficult to weld. SILICON (Si) • USED AS DEOXIDISING AGENT (removes extra oxygen=killing) • INCREASES THE DEPTH OF HEAT TREATMENT • EXCESS LEADS TO BRITTLENESS, • Preferred deoxidizing agent compared to AL, as oxides of SI which solidify as inclusions in solidified steel are less harmful than AL during subsequent service life.

  15. EFFECT OF DIFFERENT ELEMENTS ALUMINIUM (AL) (max 0.015%) • USED AS DEOXIDISING AGENT (removes extra oxygen=killing) • But SI is preferred deoxidizing agent compared to AL, as oxides of SI which solidify as inclusions in solidified steel are less harmful than AL during subsequent service life.

  16. EFFECT OF DIFFERENT ELEMENTS • PHOSPHORUS (P): 0.030% (MAX) • LEADS TO COLD SHORTNESS i.e. liable to crack when cold worked • INCREASES UTS, YIELD POINT, HARDNESS • INCREASES BRITTLENESS • REDUCES IMPACT STRENTH DUE TO INCREASED GRAIN SIZE • Its basically a impurity from naturally occurring iron ore. Difficult to eliminate altogether in smelting/refining process.

  17. EFFECT OF DIFFERENT ELEMENTS • SULPHUR (S) (0.30% max) :CAUSES • SEGREGATION • HOT SHORTNESS i.e. liable to crack when hot • EXCESS CAUSES POROSITY DURING WELDING • Highly injurious impurity (from naturally occurring iron ore), Manganese is added to form Manganese Sulfide (MnS), which floats off in slag.

  18. EFFECT OF DIFFERENT ELEMENTS • HYDROGEN (H2) 1.6ppm Max. • Basically a impurity. • H2 atoms are smallest, move freely by diffusion within cavities of liquid & solidified steel in micro/submicro-scopic level. H2 molecules exert increasing pressure on metal surrounding cavities. • CAUSES hydrogen FLAKES/SHATTER CRACKS • Makes steel brittle • Higher strength steels more prone for hydrogen embrittrilment than low strength steels. • Higher strength wear resistance steel requires more careful control procedure to reduce risk of fractures. • CONTROLLED COOLING ALLOWS HYDROGEN TO DIFFUSE OUT

  19. EFFECT OF DIFFERENT ELEMENTS MANGANESE • USE AS DEOXIDANT • PREVENTS IRON SULPHIDE FORMATION THUS REDUCES HOT SHORTNESS. • IF >0.8% INCREASES UTS WITHOUT LOSS OF DUCTILITY • INCREASES WELDABILITY • IF BEYOND 2% : BAINITIC & MERTENSITIC STEELS ARE FORMED • Advantageous as it increases hardness of steel thereby improving its strength and toughness.

  20. EFFECT OF DIFFERENT ELEMENTS • OXYGEN • DECREASES • DUCTILITY • IMPACT RESISTANCE • INCREASES HARDNESS SLIGHTLY • NITROGEN • Basically a impurity. • Nitrogen dissolves in liquid steel & due to its small atomic size, atoms are located between iron & carbon atoms making bulk of steel. • INCREASES strength &HARDNESS but reduces ductility. • LEADS TO AGE HARDENING

  21. BRAND MARK • The brand mark shall be rolled in relief at least every 3 m, and shall include • The rail section • The grade of steel • Grade 880 - 880 • Grade 1080 HH - 1080 HH • Grade 1080 Cr - 1080 CR • Grade 880 Cu-MO - 880 CM • Grade 880 Ni Cr Cu - 880 NC • Grade 880 Vanadium - 880 VN • Grade 880 Niobium - 880 NB

  22. BRAND MARK • Identification mark of the manufacturer • Month (using roman numbers) and last two digits of year of manufacture • Process of steel making • Basic oxygen – O • Electric - E

  23. MARKING ON RAIL • Hot stamping at least every 4.0 m on web • Cast No. with letter ‘C’ • Number of the strand. • For rails from change over bloom, cast number should be the preceding cast number with prefix letter ‘B’ • Cold punching on one of the end faces • Inspecting Agency Id and Group ID • Shift No in which product inspected • Date of Inspection

  24. MARKING ON RAIL • For IU rail, the letter ‘IU’ to be stamped on both end faces of each rail • Rails shall be painted as per colour code given in Appendix-IV of the Specifications to distinguish grade, class, length and other special requirements

  25. COLOUR CODING Prime 13 m Prime 12 m Prime 11 m Prime 10 m IU 13 M IU 11 M REJECTED

  26. SECTIONS AND DIMENSIONS Tolerances in sectional Dimensions Length End Squareness End Straightness Surface defects

  27. MEASUREMENTS DIMENSIONAL ACCURACY – PRIME QUALITY RAIL ACTUAL WEIGHT WITHIN +1.5%/ – 0.5% 0F CALCULATED WEIGHT (SAMPLE PIECE SHOULD BE ATLEAST 300 MM IN LENGTH) OVERALL HEIGHT +0.8 MM AND – 0.4 MM WIDTH OF HEAD ± 0.5 MM(MEASURED 14 MM BELOW THE RAIL HEAD)

  28. DIMENSIONAL ACCURACY – PRIME QUALITY RAIL WIDTH OF FLANGE ±1.0 MM FOR SECTION LESS THAN 60 KG./M. +1.2 MM/-1.0 MM FOR SECTIONS 60KG/M AND ABOVE WEB THICKNESS +1.0MM/ -0.5 MM – measured at the point of min thickness VERTICALITY/ASYMMETRY +1.2 MM/-1.2 MM BOTTOM OF THE RAILS SHOULD BE FLAT BUT CONCAVITY OF 0.4 MM IS PERMITTED. MEASUREMENTS

  29. MEASUREMENTS DIMENSIONAL ACCURACY – PRIME QUALITY RAIL STRAIGHNESS CHECKED ON 1.5 M. STRAIGHT EDGE SHALL BE LIMITED TO 0.7 MM, entire length END STRAIGHTNESS CHECKED BY 2.0 M. STRAIGHT EDGE FOR CLASS A RAILS TO BE LIMITED TO 0.4MM VERTICAL ( UP SWEEP), DN SWEEP NIL AND 0.5MM HORIZONTAL BY 1.5 M STRAIGHT EDGE FOR CLASS B RAILS TO BE LIMITED TO 0.5MM VERTICAL ( UP SWEEP), DN SWEEP NIL AND 0.7MM HORIZONTAL

  30. Online Top Flatness Measurement

  31. Online Straightness Measurement

  32. TESTING OF RAILS • QUALIFYING TESTS • Residual Stress Measurement – residual tensile stress anywhere < 190 MPa • Fracture Toughness Measurement • Fatigue Test – sample should endure 10 million cycle at specified strain level • THESE WILL BE CARRIED OUT FOR EACH SECTION, GRADE AND CLASS OF RAIL WHENEVER THERE IS A CHANGE IN MANUFACTURING PROCESS OR AT STIPULATED FREQUENCY

  33. TESTING OF RAILS FREEDOM FROM DEFECTS FREE FROM DEFECTS, CRACKS, PIPING ETC. ULTRASONIC TESING EDDY CURRENT TESTING

  34. ULTRA SONIC TESTING MACHINE • FOR DETECTING INTERNAL DEFECTS • 13 PIEZO-ELECTRIC PROBES • DIFFERENT LOCATIONS OF DEFECTS MARKED BY DIFFERENT COLOUR

  35. RAIL MANUFACTURING 850 MM FINISHING STAND 950 MM ROUGHING STAND 800 MM 3 HI INTERMEDIATE STANDS 3*75T/Hr BLOOM REHEATING FURNACES RAIL STRAIGHTENING MACHINE PRECAMBERING & WALKING BEAM COOLING BED AUTOMATIC STAMPING MACHINE HOT SAWS ULTRASONIC TESTING MACHINE EDDY CURRENT TESTING MACHINE LASER STRAIGHTNESS MEASUREMENT SYSTEM ONLINE ULTRASONIC TESTING MACHINE

  36. EDDY CURRENT TESTING • FOR DETECTING SURFACE DEFECTS AT FOOT, RAIL TOP AND SIDES OF RAIL HEAD • USES EDDY CURRENT LOOPS GENERATED ON RAIL SURFACE BY PROBE WINDINGS

  37. RAIL MANUFACTURING 850 MM FINISHING STAND 950 MM ROUGHING STAND 800 MM 3 HI INTERMEDIATE STANDS 3*75T/Hr BLOOM REHEATING FURNACES RAIL STRAIGHTENING MACHINE PRECAMBERING & WALKING BEAM COOLING BED AUTOMATIC STAMPING MACHINE HOT SAWS EDDY CURRENT TESTING MACHINE LASER STRAIGHTNESS MEASUREMENT SYSTEM ONLINE EDDY CURRENT TESTING MACHINE

  38. Testing of rails ACCEPTANCE TESTS • Chemical Analysis • Tensile Tests • Sulphur Print – macrographic defect • Hardness Test • Falling Weight Test – fracture under std fall • Hydrogen content • Inclusion Rating Level

  39. RAIL STRESSES

  40. Stresses in Rail Residual Stress Flexural stress Thermal stress Contact stress

  41. Typical Values Adopted on IR

  42. HANDLING OF RAILS

  43. HANDLING OF RAILS:MAIN CONSIDERATIONS • 90 UTS RAIL ARE HARDER AND MORE BRITTLE COMPARED TO 72 UTS RAIL, DUE TO HIGH CARBON CONTENT • Min elongation - 90 UTS – 10%, 72 UTS – 14% • 90 UTS RAIL ARE HIGHLY NOTCH SENSITIVE • Notch of even 0.25 mm may cause fracture • RAIL SHOULD BE HANDLED AS PER ‘GUIDELINE FOR HANDLING OF RAIL – NOV,2006’ issued vide Railway Board’s letter No.Track/21/98/0908/7 dated 30-10-2006

  44. HANDLING OF RAILS:MAIN CONSIDERATIONS PROTECTION OF STRAIGHTNESS AVOIDING POINT LINE LOADING PROTECTION OF RAIL SURFACE PREVENTION OF METALLURGICAL DAMAGE PROTECTION FROM CONTACT WITH INJURIOUS SUBSTANCES MINIMISING DANGER TO PERSONNEL

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