Materials & Processes in Manufacturing. Introduction. Introduction ME 151. Chapter 6 Ferrous Metals and Alloys

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1 2003 Bill Young Materials & Processes in Manufacturing ME 151 Chapter 6 Ferrous Metals and Alloys 1 Introduction Figure 6-1 Page Bill Young 2 Introduction Metals are example of a material (The materials final properties are affected by the processing history) Initial production and solidification dictate purity levels, contaminants, and structural features that can be transmitted to the final product Initial processing influences future operations and final product Production of Ferrous Metals Pig Iron - Ore, Limestone, Coke (carbon), Air Composition - Carbon % Sulfur % Manganese % Phosphorus % Silicon % Pig Iron is: Cast to shape as cast iron (small percentage) [Most cast iron is remelted scrap & steel] Processed into steel (largest percentage) 2003 Bill Young 3

2 Production of Pig Iron and Steel 2003 Bill Young Source: ASM Metals Handbook 4 Steel Manufacturing The manufacture of steel is an that decreases amount of carbon, silicon, manganese, phosphorus and sulfur in a mixture of molten pig iron and steel scrap Air or oxygen passes over or through the molten metal to drive a variety of refining reactions and burn out impurities Basic Steel Manufacturing Processes Open-Hearth Furnace Oxygen Furnace Electric Arc Furnaces Refining (Secondary Refining) Molten metal transferred to ladles Fine tune chemistry and temperature Improve steels cleanliness Solidification Direct cast to shape Solidified into a form suitable for further processing Produce Ingots Continuous Casting 2003 Bill Young 5 Contaminants rise to top Shrinkage occurs in region of last material to be liquid Solidification occurs inward from mold walls and up from bottom Ingot Solidification problems 1 Ingot Processing 1) Solidification shrinkage Oxides & Surface Contaminants Piping controlled by Hot Top or Exothermic Topping 2) Trapped gases Porosity Problems Figures 6-2 & 6-3 Page Bill Young 6

3 Deoxidized Steels Controlling Trapped Gases Produces high quality steel by removing prior to solidification Elements added to molten metal which react with oxygen to produce solid metal oxides dispersed throughout structure Steels known as: Killed (High Carbon Steels) Semikilled (Lower Carbon Steels) Rimmed (<0.2% Carbon Steels) Degassified Steels Produces high quality steel by removing all dissolved gases prior to solidification Used with alloy steels since many of the alloying elements can react with these gases Types of processes: Vacuum Degassing Consumable-Electrode Remelting Electroslag Remelting 2003 Bill Young 7 Continuous Casting Process which overcomes many related problems (Piping, Entrapped Slag, Structure Variations, etc.) Advantages of continuous casting: Produces a final shape close to desired product Eliminates all molding problems Requires less energy Reduces scrap Improved surface quality More uniform chemical composition Fewer inclusions Figure 6-5 Page Bill Young 8 Types of Steels Plain-Carbon Steels Composition: Iron, Carbon, Manganese, Sulfur Phosphorous, Silicon Strength is a function of materials content Increasing carbon ductility & hardenability Classified into 3 subgroups: Low Carbon Steels (<0.30% carbon) Table 6-1 Page 111 Good formability & weldability, poor hardenability Medium Carbon Steels (0.30% % carbon) Best balance of properties (toughness, ductility, strength & hardness) High Carbon Steels (> 0.80% carbon) Poor toughness & formability, high hardness & wear resistance 2003 Bill Young 9

4 Alloy Steels Types of Steels Steels with more than normal percentage of elements or if a definite or minimum amount of alloying element is specified Common alloying elements: Chromium, Nickel, Molybdenum, Vanadium, Tungsten, Cobolt, Boron, Copper, plus elements normally present (Manganese, Sulfur Phosphorous, Silicon) Alloys are added in small percentages (< 5%) to improve strength and hardenability Alloys are added in percentages up to 20% for corrosion resistance and high temperature stability 2003 Bill Young 10 Effect of Alloying Table 6-3 Page Bill Young 11 AISI - SAE Classification System Standardized identification system for plain-carbon & low-alloy steels Classifies alloys based on Type of Process Supplemental Element Grade X X X X E 4340 Carbon Content (0.00 %) Alloy Subgroup Major Alloy Example Type of Process (Electric Arc Furnace) 0.40 % Carbon Content Alloy Subgroup (Cr & Ni) Major Alloy (Mo) Other classification systems based on specific applications ASTM - American Society for Testing and Materials US Government - MIL and Federal specifications 2003 Bill Young 12

5 Standard Steel Designations Table 6-4 Page Bill Young 13 Selecting Steels A steels properties are affected by 3 things: content elements treatments Steel selection for an application involves: Defining required properties Determining best microstructure to provide those properties Selecting steel with best carbon content and hardenability characteristics to meet requirements Understanding the manufacturing process required 2003 Bill Young 14 Types of Alloy Steels High-strength low-alloy (HSLA) Rely on chemical composition to obtain properties % weight savings over plain-carbon steels Alloying improves strength properties Quenched and Tempered Structural Steels Properties developed by thermal treatment Designed for their high strength Microalloyed Steels Small percentages of alloys added to provide grain refinement and / or precipitation hardening Maximum strength with minimum carbon while preserving weldability, machinability, and formability Free-Machining Steels Alloys enhance machinability and aid in the formation of small chips Alloys act as lubricants to improve cutting tool life Silicon Steels Alloys enhance electrical and / or magnetic properties 2003 Bill Young 15

6 Types of Alloy Steels Precoated Steel Sheet Pre-finished at mill to eliminate finishing operations Finishes include dipped and plated metals, vinyls, paints Maraging Steels Applications requiring high strength & good toughness High Temperature Steels Good strength characteristics, corrosion resistance and creep resistance at high operating temperatures Stainless or Corrosion Resistant Steels Excellent corrosion resistance and/or outstanding appearance 3 types of stainless steels: Austenitic - nonmagnetic, high corrosion resistance Martensitic - magnetic, increased strength Ferritic - good weldability, cheapest Tool Steels Provide wear resistance and toughness combined with high strength 2003 Bill Young 16 Stainless Steels Figure 6-11 Page Bill Young 17 Tool Steels Table 6-7 Page Bill Young 18

7 Chapter 6 - Ferrous Metals & Alloys Basic concept of how iron and steel are produced Plain-carbon steels and primary subgroups Alloy steels and effects of alloying General understanding of AISI classification system Types of alloy steels Review Questions: 2003 Bill Young 19