HEAT TREATING AND MATERIALS PROCESSING Created by The North Carolina School of Science and Math.The North Carolina School of Science and Math Copyright North Carolina Department of Public Instruction.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) Creative commons image from:

Low-carbon ( ): No heat treating Medium-carbon ( ): Some hardening High-carbon ( ): 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 °CTEMPERING CHART Light blue315Too soft for cutting edges. Blue300Springs, saws for wood, screwdrivers. 290Carving knives, fine saws, saws for bone and ivory. 285Needles, gimlets, axes, adzes, augers. Purple270Flat drills for brass, cold chisels for light work, wood borers. Dark straw or red brown 260Wood chisels, plane irons, stone cutting tools, axes. 250Flat drills, reamers, taps, screwing dies, shears, punches, chasers. Middle straw240Pen-knives, circular cutters for metal, boring cutters. 235Milling cutters, lathe tools, wood engraving tools. Pale straw230Surgical instruments, razors, hammer faces, ivory cutting tools. Pale yellow220Steel 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 (AC 3 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 Creative commons image from:

INJECTION MOLDING Creative commons image from:

PLASTIC THERMOFORMING Creative commons image from:

PULTRUSION Public Domain imager from:

HYDROFORMING Creative commons image from:

DIE CASTING Creative commons image from:

INVESTMENT CASTING Creative commons image from:

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: Hydroforming Die casting Investment casting Injection molding Plastic Thermoforming Pultrusion Blow molding