Iron and Steel and their Alloys

1. Iron and Steel and their Alloys Metals and Welding

2. Four Raw Products • Coke (Coking Coal) • Iron Ore • Limestone • Oxygen

3. Coke • Made from bituminous coal (soft) • Baked at 2100º F for 17-18 hours in air tight ovens then quenched with water • 90% carbon • Rapid burning (helps to heat) • Carbon combines with Oxygen to act as a reducing agent for the Iron Oxide

5. Limestone • Calcium carbonate • Removes impurities • Ends up in slag

6. Limestone Quarry

7. Iron Ore

8. Iron Ore • Iron Oxides (up to 50% iron) • Also held in compounds with Oxygen, Silicon, Sulfur, and other impurities • Low grade ore is upgraded (beneficiation)to form a pellet type material (up to 66% iron) • Fine grains combined to for sinter

9. An Ore Mine

11. Oxygen • Oxygen supports combustion • Combines with carbon and other impurities • Carried out in slag or gasses

12. Blast Furnace • Limestone, Iron Ore, and Coke are “charged” in alternate layers in the furnace. • Coke is burned and Oxygen is forced through the base of the furnace (3500 degrees F) • Slag is drawn off of the high notch • Molten iron is drawn off of the lower notch • Molten iron (Pig Iron) is poured into molds or sent directly to refining

13. Blast Furnace

14. Production of 1 ton of Pig Iron Iron Ore + Coke + Limestone + Air  (1.93) (0.96) (0.48) (3.93) Pig Iron + Slag + Gases + Flue Dust (1.0) (0.55) (5.68) (0.09)

15. Pig Iron

16. Refining of Pig Iron • While Pig Iron is still molten, it must be refined using one of four processes: • Open Hearth Process • Bessemer • Electric Furnace • Basic Oxygen Process

17. Open Hearth Furnace • 200-400 tons per “heat” • Charge consists of pig iron, scrap iron, limestone and some iron ore • 1 “Heat” requires 8-10 hours • Hearth heated by a gas flame sweeping across • Was once the major process used in steel production • Can use up to 50% scrap iron

18. Open Hearth Furnace

19. Bessemer Converter • Early production of steel • Now obsolete in U.S. – method used to develop modern processes • 25 tons of pig iron and scrap per heat • Heat requires only 20 minutes • Could use up to 10% scrap iron • A jet of air causes impurities to be burned out

20. Bessemer Converter

21. Electric Furnace • Electric Arc used to heat and remove impurities • 35% of total production in the U.S. • Used for making stainless steel, carbon tool steel, and high alloy steels and for recycling scrap • Up to 100 tons per heat • Time for each heat determined by the amount of scrap included in the charge

22. Electric Furnace

23. Electric Arc Furnace

24. Basic Oxygen Process • Source of most of the steel produced today • Uses oxygen blown into the furnace through a water cooled lance • Exothermic reaction – no heating required • Up to 200 tons per heat • Heat requires 45-60 minutes • Scrap iron can be added to the charge • Automatic process controlled by a computer • Results in clean product with very tight specifications

25. Basic Oxygen Process

27. Steel Casting – Rimmed Steel • Molten steel poured into cast iron ingot molds • Oxygen during cooling process combines with carbon to become carbon monoxide • Escapes to atmosphere or moves to the core • Outer 3 inches (rim) is almost pure steel and is not as hard as the core • Carbon content of the core is higher (harder) • Rim used for wire, plate, sheet, electrodes

28. Steel Casting – Killed Steel • Molten steel is deoxidized in the ladle or ingot by adding aluminum, silicon, titanium, calcium or zirconium in various combinations and quantities • Produces a uniform premium grade steel • Majority of steel produced

29. Steel Casting – Continuous • Relatively new – becoming more common • More efficient • No need to reheat for shaping/finishing • Reduced waste • Molten metal flows into mold and water cooled • Metal rolled and cut to desired length

30. Continuous Casting

31. Shaping of Steel • Cast – continuous or ingot molds • Forged – pressed or pounded • Rolled – hot or cold (most common)

32. Hot Rolled • Rolled in hot condition • Surface is scale covered • Grain structure is elongated and fiber like • Size tolerance is wide

33. SlabMill

34. BilletMill Billet - Cross sectional area 36 square inches maximum with 1.5 inch minimum thickness and width at least twice thickness.

35. BloomMill Bloom - Cross sectional area 36 square inches minimum, usually square or rectangular.

36. Other Hot Rolled Mill Products • Structural Shapes – Channel, I-beams, angle • Bars – Rounds, squares, hexagons, flat • Rods – 3/8 in. diameter round and smaller • Plate – 3/16 in. thickness and higher; substantial width • Sheet – thickness less than 3/16 in. (gauge) with substantial width • Strip – up to ¼ in. thick and 12 in. wide

37. Cold Rolled • Rolled cold • Increased strength and hardness • Smooth, shiny surface with no scales • Close size tolerance

38. Steel Classification • Numerical Index • Society of Automotive Engineers (SAE) • American Iron and Steel Institute (AISI) • First two digits are the type of steel • 2nd digit generally gives approximate amount of predominate alloying element • The last two digits generally indicate the approximate middle of the carbon range

39. Steel Classification • Prefix Letter – Production process used to make steel (or the quality of the steel) • Suffix Letter – Specific use or restrictions of the steel

40. Wrought Iron • Low Carbon Steel (practically pure iron) from Bessemer converter or Byers process • Ductile and corrosion resistant • Mixed with slag and rolled into long strands • Weldable, but not strong

41. Metal Identification AG 221 – Metals and Welding

42. Metal Identification - Rationale • Metal ID is important for all metal workers • Machinists, welders, etc. • Imagine starting a welding job without knowing what metal you are working with. What problems might result?

43. Useful methods for ID • 1st step – Separate known’s from unknown’s • What color is it? • (i.e., Aluminum, Copper, Brass, Stainless) • How heavy/dense is it? • (i.e., aluminum vs. stainless) • What is the surface appearance? • (i.e., roughness, from molds, part numbers)

44. Useful methods for ID • How was the part used? • Mechanical and physical requirements of the job • (i.e., drill bit – hard enough to last but not brittle) • How was the part made? • Forge marks, cast marks, rolling, stamping, etc. • Fracture appearance • Texture of grain structure, color of new and old break, uniformity of grain structure, degree of bending before break

45. Useful methods for ID • Magnetic Test • Some alloys are non-magnetic • Chip Test • Observe how chip separates • File Test • Observe relative ease of filing • Oxy-acetylene test • With neutral welding flame – test heat conductivity, speed of melting, color change

46. Spark Testing • Observe sparks at grinding wheel under subdued light • Grinding wheel should be clean • Pressure of metal should be medium and uniform • Compare known samples to unknown samples

47. Spark Testing Lines: Length and color Sparklers: Number Appendages: Present or not

48. Spark Testing (cont’d) • Accurate method of identification • Sparks occur relative to oxidation of the heated metal particles • Iron does not oxidize rapidly therefore the spark lines are long and fade out with cooling • High carbon steels have a spark with short lines and many explosions

49. Spark Testing (cont’d) • Observe: • Color • Length of spark lines • Number of explosions • Explosion shape • Refer to text (pages 65-71) for specific characteristics of each metal type

50. Spark Testing