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