heat treating and materials processing created by the north carolina school of science and math.the...
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HEAT TREATING AND MATERIALS PROCESSING
Created by The North Carolina School of Science and Math. Copyright 2012. North Carolina Department of Public Instruction.
HEAT TREATING
• Heat treatment: a method used to alter the physical, and sometimes chemical, properties of a material
• It involves the use of heating or cooling to achieve a desired result such as hardening or softening of a material.
HEAT TREATMENT PROCESSES
• Heating the metal to a predetermined temperature.
• Holding the metal at this elevated temperature for a certain period of time.
• Cooling the metal at a certain rate of time.
HARDNESS OF STEEL
• Hardness is a measure of a material’s resistance to localized plastic deformation
• Most common method of measuring hardness is the Rockwell test
• Higher Rockwell Number, the Harder the Steel
• Hardness of steel can be affected by temperature and carbon content• At lower temperatures the steel is not as hard
(1045– medium carbon steel)
Creative commons image from: http://upload.wikimedia.org/wikipedia/commons/6/66/Dur%C3%B3metro_Rockwell.jpg
• Low-carbon (0.05-0.30): No heat treating
• Medium-carbon (0.30-0.60): Some hardening
• High-carbon (0.60-1.5): can be made extremely
hard
CARBON CONTENT AND HARDNESS
• Check carbon content of steel • Heat furnace to the upper critical
temperature (1400 to 1700 °F)• Check heat treating and carbon graph to determine this
value.
• Allow steel time to completely heat throughout.
• Cool or quench heated steel as rapidly as possible in water, brine, or oil. • Steel should now be very hard, brittle and ready to
temper.
STEPS FOR HARDENING
TEMPERING
Tempering: a heat treatment process to allow a material to achieve a desired hardness
Steps For Tempering• Harden the material• Heat steel up to a temperature based on the
desired hardness.• Cool at a moderate rate, perhaps in air. Not
quenched.
TEMPERING CHART
°C TEMPERING CHART
Light blue 315 Too soft for cutting edges.
Blue 300 Springs, saws for wood, screwdrivers.
290 Carving knives, fine saws, saws for bone and ivory.
285 Needles, gimlets, axes, adzes, augers.
Purple 270 Flat drills for brass, cold chisels for light work, wood borers.
Dark straw or red brown
260 Wood chisels, plane irons, stone cutting tools, axes.
250 Flat drills, reamers, taps, screwing dies, shears, punches, chasers.
Middle straw 240 Pen-knives, circular cutters for metal, boring cutters.
235 Milling cutters, lathe tools, wood engraving tools.
Pale straw 230 Surgical instruments, razors, hammer faces, ivory cutting tools.
Pale yellow 220 Steel engraving tools, scrapers, light turning tools.
Annealing is a heat treatment process to soften steel and remove internal stress
Steps For Annealing• Heat steel up to the upper critical
temperature (AC3 on Chart)
• Hold steel at this temperature and heat thoroughly throughout (soaking).
• Cool steel very slowly by removing it from the furnace and packing it in sand until it reaches room temperature.
ANNEALING
Case-hardening is a surface only hardening process. It combines hardness with strength and toughness.
Steps to Case-harden• Usually done with lower carbon steels.• Pack steel in powered carbon • Carburize by heating in a furnace at the
required temperature for 8 To 12 hours.• Now harden steel with the normal
hardening method.
CASE HARDENING
HEAT TREATING REVIEW
• Why is heat treatment done?• What happens to the steel during hardening.
• What is tempering, what does it change, and why is it done?
• What is annealing, what does it change, and why is it done?
• What is case-hardening why is it done?
PROCESSES
• Molding• Blow• Injection
• Casting• Die• Investment
• Pultrusion• Hydroforming• Composites
BLOW MOLDING
Creative commons image from: https://upload.wikimedia.org/wikipedia/commons/thumb/2/22/Blow_molding.png/800px-Blow_molding.png
INJECTION MOLDING
Creative commons image from: http://upload.wikimedia.org/wikipedia/commons/thumb/d/dd/Injection_moulding.png/800px-Injection_moulding.png
PLASTIC THERMOFORMING
Creative commons image from: http://upload.wikimedia.org/wikipedia/commons/7/7d/Plastic_moulding_machine.jpg
PULTRUSION
Public Domain imager from: http://upload.wikimedia.org/wikipedia/commons/thumb/6/61/Pultrusion_process_01.png/800px-Pultrusion_process_01.png
HYDROFORMING
Creative commons image from: http://upload.wikimedia.org/wikipedia/commons/c/c6/Idroformatura_animata.gif
DIE CASTING
Creative commons image from: http://upload.wikimedia.org/wikipedia/commons/thumb/6/6f/Cold-chamber_die_casting_machine_schematic.svg/685px-Cold-chamber_die_casting_machine_schematic.svg.png
INVESTMENT CASTING
Creative commons image from: http://upload.wikimedia.org/wikipedia/en/e/e8/Nuclear_valve_01.jpg
MANUFACTURING PRODUCTS ACTIVITY
In this activity, you and a partner will work together to answer the following questions regarding each manufacturing process we have discussed.1. What type of material(s) is(are) used with each
process?2. Name 1-2 products that are created using this
process (other than those mentioned in lecture).Review of processes:HydroformingDie castingInvestment casting
Injection moldingPlastic ThermoformingPultrusionBlow molding