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Metallurgy Chapter 3: Alloy Steels
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Metallurgy Chapter 3: Alloy Steels

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Questions and Answers

What is the maximum percentage of carbon present in steel?

  • 2.0 %
  • 5.0 %
  • 0.5 %
  • 1.5 % (correct)

    • What is the purpose of adding alloying elements to steel?

  • To decrease electrical conductivity
  • To increase strength, toughness and hardenability (correct)
  • To decrease strength and toughness
  • To decrease corrosion resistance

    • What is the percentage of Manganese (Mn) commonly used in alloy steel?

  • 2.0 %
  • 1.0 %
  • 0.5 %
  • 2 % (correct)

    • What are the applications of low alloy steels similar to?

    <p>Plain carbon steels of similar carbon contents</p> Signup and view all the answers

    How are alloys steels classified?

    <p>Into two major types depending on the structural classification</p> Signup and view all the answers

    What is the effect of chromium on the rate of crystal growth?

    <p>It accelerates the rate of crystal growth</p> Signup and view all the answers

    What is the effect of adding 2.5% manganese to a steel containing 0.65% carbon?

    <p>It produces a completely pearlitic structure</p> Signup and view all the answers

    What is the effect of alloying elements on the transformation rates of austenite to martensite?

    <p>They reduce the critical cooling rate</p> Signup and view all the answers

    What is the effect of adding elements such as aluminum, silicon, and chromium to steel?

    <p>They improve the corrosion-resistance of steel</p> Signup and view all the answers

    What is the main reason for alloying steel?

    <p>To effect improvements in the mechanical properties of steel</p> Signup and view all the answers

    What is a key characteristic of high-speed steels?

    <p>Ability to retain hardness at high temperatures</p> Signup and view all the answers

    Which type of stainless steel is typically used in exhaust systems and trim?

    <p>Ferritic</p> Signup and view all the answers

    What is a common application of M2 steel?

    <p>Cutting tools, such as drills and saw blades</p> Signup and view all the answers

    What is a key benefit of austenitic stainless steels?

    <p>Excellent corrosion resistance in a wide range of environments</p> Signup and view all the answers

    What is the purpose of tempering in the heat treatment process for high-speed steels?

    <p>To reduce residual stresses and improve toughness</p> Signup and view all the answers

    What is the primary reason for the high resistance to corrosion of stainless steels?

    <p>Formation of a protective film of chromium oxide</p> Signup and view all the answers

    What is the primary purpose of high-speed tool steels?

    <p>To retain high hardness at high temperatures</p> Signup and view all the answers

    What is the effect of nickel on the critical temperatures of iron?

    <p>Lowering the A4 temperature and raising the A3 temperature</p> Signup and view all the answers

    What is the primary characteristic of maraging steels?

    <p>High strength and ability to be easily machined</p> Signup and view all the answers

    What is the effect of alloying elements such as chromium, tungsten, and vanadium on the microstructure of steel?

    <p>Stabilizing ferrite</p> Signup and view all the answers

    What is the primary alloying element in Stainless Steels?

    <p>Chromium</p> Signup and view all the answers

    What is the typical hardness range of OHNS steels after oil quenching?

    <p>57-62 HRC</p> Signup and view all the answers

    What is the purpose of the tempering process in OHNS steel heat treatment?

    <p>To reduce brittleness</p> Signup and view all the answers

    What is a characteristic of Hadfield's manganese steel?

    <p>It is non-magnetic</p> Signup and view all the answers

    What is the purpose of the solution annealing process in Hadfield's manganese steel heat treatment?

    <p>To avoid carbide precipitation</p> Signup and view all the answers

    Which of the following elements is commonly used in stainless steels and improves toughness, strength, and corrosion resistance?

    <p>Nickel (Ni)</p> Signup and view all the answers

    What is the primary effect of Molybdenum (Mo) on steel?

    <p>Enhances corrosion resistance, especially against pitting corrosion</p> Signup and view all the answers

    Which of the following elements is a ferrite stabilizer and promotes the formation of ferrite and carbides?

    <p>Chromium (Cr)</p> Signup and view all the answers

    What is the primary effect of Vanadium (V) on steel?

    <p>Increases strength, toughness, and wear resistance by refining the grain structure</p> Signup and view all the answers

    Which of the following elements is commonly used in high-speed steels and improves wear resistance by forming stable carbides?

    <p>Tungsten (W)</p> Signup and view all the answers

    What is a characteristic of martensitic stainless steels?

    <p>Magnetic</p> Signup and view all the answers

    What is the typical carbon content in martensitic stainless steels?

    <p>0.1-1.2%</p> Signup and view all the answers

    What is a common application of martensitic stainless steels?

    <p>Cutlery and blades</p> Signup and view all the answers

    What is the cause of weld decay in stainless steels?

    <p>Chromium depletion</p> Signup and view all the answers

    How can weld decay be prevented?

    <p>Using low-carbon grades</p> Signup and view all the answers

    What is the purpose of solution annealing in preventing weld decay?

    <p>To dissolve chromium carbides</p> Signup and view all the answers

    What is the consequence of weld decay?

    <p>Inter-granular corrosion</p> Signup and view all the answers

    How can the susceptibility to inter-granular corrosion be detected?

    <p>Electrochemical tests</p> Signup and view all the answers

    What is the effect of chromium carbide precipitation on corrosion resistance?

    <p>Decreases corrosion resistance</p> Signup and view all the answers

    What is the primary consequence of weld decay?

    <p>Inter-granular corrosion</p> Signup and view all the answers

    Study Notes

    Introduction to Alloy Steels

    • Alloy steels are a type of steel that contains other elements besides iron and carbon.
    • The addition of other elements improves the properties of steel, making it suitable for various applications.

    Classification of Alloy Steels

    • Low alloy steels:
      • Contain up to 3-4% of one or more alloying elements.
      • Similar microstructure to plain carbon steels.
      • Used for increasing strength, toughness, and hardenability.
    • High alloy steels:
      • Possess structures and require heat treatments different from plain carbon steels.
      • Examples: high-speed tool steels, stainless steels, and maraging steels.

    High-Speed Tool Steels

    • Composition: Tungsten, chromium, vanadium, and carbon.
    • Properties:
      • High hardness and wear resistance.
      • Retain hardness at high temperatures.
    • Applications:
      • Cutting tools: drills, taps, end mills, and saw blades.

    Stainless Steels

    • Composition: Chromium (min. 12%) and sometimes nickel.
    • Properties:
      • Corrosion resistance due to chromium oxide film.
      • High-temperature resistance.
    • Applications:
      • Kitchen utensils, medical equipment, and architectural features.

    Maraging Steels

    • Composition: Nickel, cobalt, and small amounts of titanium and other elements.
    • Properties:
      • High strength and toughness.
      • Low carbon content.
    • Applications:
      • Aerospace and defense industries.

    Effects of Alloying Elements

    • Carbide formers: Cr, W, Ti, V, and Mo.
    • Austenite stabilizers: Ni, C, and N.
    • Ferrite stabilizers: Cr, Mo, Si, Ti, and V.
    • Grain refiners: Al, Ti, and Nb.

    Specific Alloying Elements

    • Carbon (C): increases hardness and strength.
    • Chromium (Cr): improves corrosion resistance and hardness.
    • Nickel (Ni): improves toughness and corrosion resistance.
    • Manganese (Mn): improves strength and deoxidizes the steel.
    • Molybdenum (Mo): enhances strength, hardness, and corrosion resistance.
    • Vanadium (V): improves strength, toughness, and wear resistance.

    Heat Treatment

    • Austenitizing: heating to form austenite structure.
    • Quenching: rapid cooling to achieve desired properties.
    • Tempering: heating to reduce brittleness and improve toughness.

    Specific Steel Types

    • OHNS (O1) steel: high-speed tool steel with high hardness, toughness, and wear resistance.
    • Hadfield's manganese steel: high-manganese steel with high toughness and wear resistance.
    • High-speed steel (HSS): used for cutting tools due to high hardness and wear resistance.### Ferritic Stainless Steels
    • Magnetic
    • Good corrosion resistance, particularly in less severe environments
    • Good ductility and formability, but less than austenitic grades
    • Lower cost due to lower nickel content
    • Limited hardenability, only by cold working
    • Applications: automotive parts, kitchen equipment, industrial equipment, and architecture

    Austenitic Stainless Steels

    • Composition: 16-26% Cr, 6-22% Ni, low C (<0.08%), and other elements like Mn, N, and Mo
    • Non-magnetic, but can become slightly magnetic when cold worked
    • Excellent corrosion resistance in a wide range of environments
    • Good weldability without requiring post-weld heat treatment
    • Good toughness and ductility at high and low temperatures
    • Hardenable by cold working
    • Applications: food and beverage equipment, medical devices, chemical and petrochemical industry, construction, and household items

    Martensitic Stainless Steels

    • Composition: 11.5-18% Cr, higher C (0.1-1.2%), and sometimes Ni for toughness
    • Magnetic
    • High strength and hardness, can be significantly hardened by heat treatment
    • Moderate corrosion resistance, lower than austenitic and ferritic grades
    • Good wear resistance due to high hardness
    • Heat treatable to achieve a wide range of hardness and strength levels
    • Applications: cutlery and blades, turbine blades and engine parts, valves and pumps, and springs and fasteners

    Weld Decay

    • Type of intergranular corrosion that occurs in some stainless steels, particularly austenitic grades
    • Occurs in the heat-affected zone (HAZ) adjacent to the weld
    • Caused by chromium carbide precipitation and chromium depletion
    • Prevention methods: using low-carbon grades, stabilized grades, heat treatment, controlled welding techniques, and proper filler materials
    • Detection methods: sensitization tests (e.g., Strauss test) and microstructural analysis
    • Consequences: inter-granular corrosion, reduced mechanical properties, and premature failure

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    Description

    Learn about the composition of steels, their production process, and the importance of alloy steels in modern industries. This chapter covers the history and development of alloy steels.

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