How Steel Is Made. 2.5 tons of raw material and a nearly equal amount of air is required to produce 1 ton of pig iron.

Transcription

1 Steel

2 How Steel Is Made It starts with the production of Pig Iron in a Blast Furnace There are three (3) primary components of Pig Iron: 1. Iron Ore = Primary source of iron 2. Limestone = Flux used to remove impurities 3. Coal (Coke) = A fuel and reducing agent 2.5 tons of raw material and a nearly equal amount of air is required to produce 1 ton of pig iron. Generic diagram of a blast furnace BlueScope Steel Blast Furnace #5 Port Kembla, Australia 2

3 How Steel Is Made Pig Iron, or molten iron, is transferred from the Blast Furnace to either a Basic Oxygen Furnace (BOF) or Electric Arc Furnace (EAF) for final conversion to steel. The majority of Steelscape material is produced by the BOF method. Oxygen is blown through the molten pig iron which lowers the carbon content and removes impurities. Alloying additives are added which typically include carbon, manganese, silicon, phosphorus, and sulfur. The alloy mixture is determined by specific end use and customer requirement. The BOF method is an extremely dynamic process involving extreme pressures, temperatures and chemical reactions. 3

4 BOF/EAF to Steel Coil (Continuous Casting Method) After the BOF/EAF process, steel is tapped into a ladle and taken to the continuous caster. The ladle is raised onto a turret that rotates the ladle into the casting position above the tundish (broad, open container with holes in the bottom) where the liquid steel flows out of the ladle into the tundish, and then into a water-cooled copper mold. Solidification begins in the mold, and continues until the strand is straightened, torch-cut, then discharged for intermediate storage or charging into hot rolling mill. To create coil, the slabs are heated and rolled on a Hot Mill. Slabs are reheated to a temperature exceeding 2300º F, which then pass through a scale breaker/roughing mill. Slabs continue through additional roughing mills where a substantial portion of the thickness is reduced. Slabs are passed through a finishing mill where final thickness and surface quality are achieved. The cooling rate of the strip is controlled to approximately ºF, exiting the finishing mill. Strip is quenched to ºF to control the microstructure (grain), mechanical properties and formation of scale (oxide). 4

5 Hot Band Starting Point for Steelscape Steelscape s processing begins with Hot Band and is sourced primarily from BlueScope Steel (Australia), NSSMC (Japan), and NorthStar (Ohio). Hot Band is not necessarily the finished width when received, and is never the final thickness. It is however, a specific chemistry. The most common chemistries utilized are listed below: %C %Mn %Al 01 Chemistry % % % 02 Chemistry % % % 03 Chemistry % % % The steel chemistry plays a significant role in determining the final grade of steel and impacts formability. The lower the carbon content, the softer and more ductile the steel. All steel produced by Steelscape is considered low carbon steel. Hot Band Coils at Steelscape Kalama, WA 5

6 Pickle Line and Cold Mill The Hot Band has to be cleaned & trimmed before it is reduced in thickness then annealed, metallic coated or painted. Primary Functions of the Pickle Line: Eliminate hot mill oxides from the surface Trim the edges for improved width control Fulfill the inspection requirements (i.e. surface, width, edge quality) of finished Hot Rolled Pickled product Prepare the strip for further processing (cold reduction). Primary Functions of the Cold Mill: Reduce strip to ordered (BMT) thickness Apply a surface texture to the strip Maintain strip thickness & shape control Steelscape Reversing Cold Mill 6

7 Metallic Coating Line / Galvanizing Process The majority of coil used in the roofing and siding industry is metallic-coated as either Hot Dip Galvanized (Zinc) or Hot Dip Galvalume (55% Alum / 45% Zinc). TruZinc is the Steelscape trade name for Hot Dip Galvanized and ZINCALUME is the trade name for Galvalume. Why Apply a Metallic Coating? Steel is prone to rusting which as we know causes the surface to become unsightly and, over time, may even contribute to product failure. Some metals, such as zinc and aluminum, can be applied as a metallic coating over steel to prevent, or limit corrosion, through the formation of a barrier coat or galvanic protection. Barrier Protection the metallic coating reacts with air and water to create a thin, impervious, stable layer that protects the metallic coating from further exposure therefore greatly limiting any corrosion. Galvanic Protection the metallic coating is more reactive than the base steel, thus corrodes first when both are exposed to air and water. The base steel will not rust until the surrounding metallic coating has been consumed. The Galvanic Series list on the left shows this relationship. Galvalume is registered trademark of BIEC International, Inc. 7

8 Metallic Coating/Galvanizing Process The metallic coating line does a lot more than just apply a metal alloy surface: Cleans the incoming strip of any residual rolling oil, iron fines and/or oxides Heat treats the strip to achieve desired mechanical properties (ordered grade) Reduces any oxides on steel surface and further provides a wetable surface for the molten coating metal Levels the strip to an acceptable shape Conditions the surface of the metallic coating in preparation for painting Ability to apply protective oil, chemicals or resins 8

9 Typical Metallic Coatings Available at Steelscape TruZinc ZINCALUME G30 =.0005 AZ50 =.0016 G40 =.0007 AZ55 =.0018 G60 =.0010 G90 =

10 Mechanical Property Requirements by Steel Strength Levels Steel Chemistry Yield Tensile Total Steel Carbon Manganese Phosphorus Sulfur Strength Strength Elong. Designations (%) (%) (%) (%) (ksi) (ksi) (ksi) Commercial Steel Type A ¹ - 20¹ Type B ¹ - 20¹ Type C ¹ - 15¹ Structural Steel Grade Grade Grade Grade 50CL Grade 50CL Grade 50CL Grade 60³ Grade 80CL

11 Quality Assurance Attributes and Compliance Coil Metallurgical Testing Attributes: Strip Thickness, Strip Hardness, Strip Formability, Coating Mass, Coating Adhesion Mechanical Properties, Strip Fluting Characteristics Coating Composition Strip Passivation Integrity Testing Compliance: Comply with metallic coating and paint weight requirements Meet steel mechanical properties as specified Not too low/not too high Meet customer s surface quality requirements Uniform appearance throughout the coil No coating sags/ripples No metallic coated streaks/scratches No dross marks Inspect regularly/continually Check flatness Monitor coating adhesion lock seam, drop impact, flat bend Perform lab tests to ensure proper film weight is applied 11

12 Quality Assurance-How is Product Tested? Non-Destructive Means: The use of on-line monitoring devices o X-ray o Temperature o Coating thickness o Flatness Destructive Means: The use of a sample cut from the finished coil o Mechanical properties o Coating thickness o Hardness o Strip thickness 12

13 Quality Assurance-How is Product Tested? Strip Thickness: Total strip thickness o Thickness of cold band + coating thickness Strip thickness checked by o In-line x-ray gauge o Micrometer Strip Flatness: Typically looking for edge wave or center buckle Measurement: o 3 foot section of strip is measured for flatness o Wave height and length is measured o I-Unit value is determined from ASTM I-Unit chart 13

14 Quality Assurance-How is Product Tested? Mechanical Property Testing: Mechanical properties can be determined by a tensile test A sample of metal is pulled until it breaks. Sample results in these material properties: o Yield Strength (YS) o Ultimate Tensile Strength (UTS) o % Elongation Stress/Strain Curve (below): 14

15 Quality Products Make Happy Customers All of this testing ensures a quality product which meets or exceeds our customers expectations. If we do not ensure a high quality product to each of our customers. Somebody else will. Questions? Thank you for your time! 15