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.

TYPES OF HEAT TREATMENT

• Hardening• Tempering• Normalizing/Annealing

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)

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• 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

PHASE DIAGRAM

• 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

INADVERTENT HEAT TREATING

• Welding• Braking systems• Engines• Furnaces

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?

MORE MANUFACTURING PROCESSES

PROCESSES

• Molding• Blow• Injection

• Casting• Die• Investment

• Pultrusion• Hydroforming• Composites

BLOW MOLDING

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INJECTION MOLDING

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PLASTIC THERMOFORMING

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PULTRUSION

Public Domain imager from: http://upload.wikimedia.org/wikipedia/commons/thumb/6/61/Pultrusion_process_01.png/800px-Pultrusion_process_01.png

HYDROFORMING

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DIE CASTING

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INVESTMENT CASTING

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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