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Subject on This Issue:
* Steels & Properties
* Heat Treatment


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REVIEW QUESTIONS ON
BASIC HEAT TREATMENT MATERIALS AND PROCESSES

Heat Treatment Processes

  • What is heat treatment?
  • What heat treatment does?
  • How many types of heat treatment processes?
  • Describe the purposes for conducting quenching, tempering, annealing.
  • What are the differences in processing parameters among the heat treating processes?
  • What is the difference between martempering and austempering?
  • Describe the difference between annealing and normalizing?
  • What is the difference between stress relieving and annealing?

Iron-Cementite Phase Diagram

  • Sketch and label the steel section of the iron-carbon system, using the terms austenite, ferrite and cementite.
  • Explain the terms critical points A1, A3, and Acm
  • What means eutectoid, hypo-eutectoid and hyper-eutectoid?
  • How do the structures of hypo-eutectoid and hyper-eutectoid steels differ at room temperature as a result of them being slowly or fast cooled from the austenitic state?
  • What is the effect of the percentage of carbon in steel on properties?
  • Explain the effects of cooling rate and carbon content on the microstructure and properties of steels.
  • Describe the forms of the microstructure of eutectoid alloy steel.
  • How to relate the phase diagram to heat treatment?
  • How to select soaking temperatures for normalizing, annealing and quenching by reference to the phase diagram?
  • What would be the expected structure of 2363 if it were cooled slowly from the austenitic state?
  • How would the answer to Problem 10 have differed if the steel had been quenched?
  • A carbon steel with 1.1% carbon is to be given a full annealing treatment. What temperature and cooling rate are necessary for such a treatment?
  • Explain, by reference to the iron-carbon thermal equilibrium diagram, the procedures used for case hardening of a low carbon steel.
  • Is the hardness of martensite identical?

TTT Curves

  • How many types of TTT curves?
  • What is the difference between IT and CCT diagram?
  • State what is meant by the critical cooing rate.
  • What is the hardness value if the microstructure contains 50% pearlite and 50% martensite?
  • How to apply TTT diagrams into heat treating operation?

Materials and alloys

  • What means ferrous and non-ferrous alloys? How many types of ferrous alloys?
  • How to classify low, medium and high carbon steels?
  • How to classify tool steels and stainless steels?
  • How many types of tool steels are heat treated in Hitech? Please write down.
  • What means alloying elements? Which elements are the austenite stabilizer?
  • In what way does the alloying element affect the structure of the steels?
  • Explain AISI 1008, AISI 4140, 760, DF2, 2510: Which group? Difference?
  • Grain size 2 and 6, which one is finer?
  • How does the grain size affect the properties of the tool steels?
  • How to control grain size during heat treatment?
  • Why do the materials have different hardnesses?

Heat Treatment of Steels

  • Describe the following heat treatments applied to tool steels:
    • Full annealing
    • Normalizing
    • Stress relieving
    • Hardening
    • Tempering
  • How many types of heat treating processes in Hitech?
  • What means bright annealing?
  • When does the expansion or shrinkage occur during hardening?
  • State the form of heat treatments needed to effect the following changes:
    • 0.4 carbon steel to be made as soft as possible;
    • 0.4 carbon steel to be made as hard as possible;
    • D2 tool steel to be made as hard as possible;
    • D2 tool steel to be made as soft as possible.
  • Alloy steels are typically hardened by oil quenching while plain carbon steels are generally water quenched.  T or F
  • Oil quenching steel DF2 cannot be quenched by gas.  T or F
  • The proper austenitizing temperature for hardening is typically 50º - 90ºC over the upper critical transformation temperature.  T or F
  • Annealing, normalizing and hardening of a given steel are typically done at the same temperature. T or F
  • It is important to know the stock allowance on parts prior to hardening because:
    • It will help determine how much distortion is acceptable.
    • It will determine the type of atmosphere that can be used.
    • It will determine the quality requirements for surface contamination.
    • All of the above.
  • Soak times are a function of:
    • The section thickness of the part
    • The time required for the furnace to reach temperature.
    • The time required to ensure that the center of the most massive part has reached temperature and the necessary transformation has taken place.
    • a and c
    • a and b
  • The longer the soak time, the better properties the parts.  T or F
  • What is the function of preheating during heating up?
  • Why do some alloys need two preheating stages?
  • Give example. How would the hardness of 0.6% carbon steels differ if the following heat treatments were applied?
    • Heat and soak at 800ºC and then quench in cold water.
    • Heat and soak at 800ºC and then quench in oil.
    • Heat and soak at 800ºC and then slowly cool in furnace.
  • How does increasing the temperature at which a tool steel is tempered change the final properties of the steel?
  • How does the hardness of the steel differ for HSP41 as a result of the differing tempering temperatures?
  • Why do some alloys adopt 2 or 3 times tempering?
  • Which types of stainless steel can be hardened?
  • Describe the forms of the microstructure of a tool steel.
  • How does the presence of retained austenite affect the properties of the tool steels?
  • What type of heat treating procedures would you suggest for hardening XW41, D2, SKD11 and 2510?
  • Explain how AISI H13 and ASSAB 760 steels would be hardened. Give details of the temperatures involved.
  • Why are cylindrical objects quenched vertically?
  • Decarburization and scaling are the same thing. T or F
  • What is the most reactive constituent in air?
  • To fully anneal austenitic stainless steels they usually must be heated to 1060-1090ºC and water quenched. Rapid cooling is required to prevent:
    • Excessive oxidation
    • Grain boundary carbide precipitation
    • Excessive distortion
    • Spotty hardness
  • What is hardenability?

Inspection and Testing

  • The hardness of a material is it’s resistance to plastic deformation by penetration.  T or F
  • A Rockwell hardness tester must be calibrated to comply with ASTM standard E-18.  T or F
  • Rockwell hardness test blocks when completely filled with test impressions should be:
    • Reground       
    • Turned over and used on the other side
    • Discarded
    • None of above
  • Rockwell hardness testers are out of calibration when the reading on a test block is:
    • Below, but not above, the certified range
    • Above, but not below, the certified range
    • Above and below the certified range
    • Any of the above
  • When Rockwell testing using a 1/16” ball, a piece of steel with high hardness is tested by mistake, the ball should be:
    • Visually examined for deformation and reused if none is noted.
    • Replaced with a new ball
    • Rotated to a new spot before being reused.
    • None of the above
  • Some factors that determine the suitability of a certain Rockwell scale, include:
    • Type and hardness of the material
    • Thickness of the material being tested
    • Depth of case
    • All of the above  
  • When Rockwell testing, the surface condition of the test area is not important because the minor load will compensate for any irregularities.  T or F
  • The standard Rockwell C diamond and the superficial N diamond are interchangeable if used only a short time.  T or F
  • If Rockwell hardness readings are erratic the cause(s) may be:
    • The back surface of part is uneven       
    • The diamond indentor is chipped.
    • The sample was burned during preparation
    • There is dirt under the indentor or anvil
    • All of the above
  • A correction factor must be used when Rockwell testing cylindrical parts. These numbers are ____ the observed number.
    • Added to
    • Subtracted from
  • Three readings should be taken on a single part inspection so that if one is out of spec it can be ignored.  T or F
  • The Brinell hardness can be used to determine approximate tensile strength of quenched and tempered steel.  T or F
  • A Brinell test is typically used for checking the components with low hardness.  T or F
  • Brinell, Rockwell and microhardness readings are all obtained by measuring the size of the impression.  T or F
  • Grinding an area deep enough to remove surface decarburization is not recommended because it may cause the part to be scraped.  T or F
  • The minor load applied during a hardness test is the same for HRC, HRA and HR15N.  T or F
  • The effective case depth can be measured by etching a sectioned test pin.  T or F
  • A Rockwell C test could be considered a destructive test on finished parts.  T or F
  • The back surface of a part being Rockwell inspected must be smooth, clean and parallel to the surface being tested.  T or F
  • When hardness testing thin parts, some deformation of the back surface is acceptable.  T or F
  • Brinell testing is normally performed using either 3000 or ______kg loads.
    • 6000
    • 1500
    • 500
    • 150
  • Rockwell testing is normally performed using either 100 or ______kg loads.
    • 150
    • 100
    • 50
    • 15
  • Vickers testing is normally performed using either 1000 or ______g loads.
    • 6000
    • 1500
    • 500
    • 100
  • Specify the hardness test methods most appropriate for the following:
    • Quench and tempered steel parts over ½ in. section, _____________________
    • Annealed steel plate under ¼ in. thick,  _______________________________
    • Carburised and hardened parts with 0.020/0.025 in. case, _________________
    • Carburised and hardened parts with 0.03 in. plus case, ___________________
    • Aluminum casting in T6 condition, ___________________________________
    • Hardened tool steel part, ___________________________________________
    • Nitriding part, ___________________________________________________
  • Define “effective case depth” and how is it measured.
  • Unlike standard Rockwell hardness testing, microhardness test impressions are not affected by how close they are to each other because of their small size.  T or F
  • What is the purpose of mounting a specimen prior to preparing it for metallographic examination?
  • Microscopic examination is normally performed at magnification from 100x to 750x.  T or F
  • Hardness can be tested by the microscopic examination.  T or F
 
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