Annealing Processes All the structural changes obtained by hardening and tempering may be eliminated by annealing. to relieve stresses to increase softness, ductility, and toughness to produce a specific microstructure Process consists of heating to the desired temperature holding cooling to room temperature annealing time must be long enough to allow for any necessary transformation reactions

Normalizing - used to refine the grains cooling in air, less expensive, some sections of a part may cool too fast Full anneal: Utilized in low and medium carbon steels that will be machined or plastically deformed cooling in furnace to room temperature final product is coarse perlite (soft and ductile) Spheroidizing for medium and high carbon steels Fe3C will turn into the spheroids

Some parts should be hard on the surface but soft and ductile inside shafts, gears, guideways of machine tools carious surface hardening processes heating on the surface only and quenching it flame hardening (by torch) induction hardening carburizing

Precipitation Hardening Hardening of non-allotropic alloys The properties of nonferrous substances that do not readily form allotropes cannot be changed by controlled cooling. Such substances are known as non-allotropic alloys, and include aluminum, copper, and magnesium alloys as well as stainless steels containing Ni. The method of hardening is called precipitation hardening and age hardening. Precipitation involves the formation of a new crystalline structure through the application of controlled quenching and tempering. Precipitation disperses hard particles throughout the existing more ductile material.

These particles disrupt long dislocation planes of the material, restricting the movement of dislocations and increasing the strength and stiffness of the alloy. The final step is to hold the material at a specific temperature for a given amount of time. When aluminum is quenched in water to room temperature, the solubility of copper is drastically decreases and a compound of copper aluminide forms that slowly disperses along grain boundaries and slip planes to harden the alloy.

Summary primarily interest to increase YS it means increase the load-carrying capacity of elements the methods to increase YS are based on the various mechanisms of interfering with dislocation movements. Methods: Obtaining fine grain material combination of hot working and recrystallization annealing after cold work Cold work (strain hardening) the total amount of strain is limited by a total loss of ductility Solid solution treatment for alloys in which a solute-rich solid-solution phase exists at room temperature

Precipitation hardening for alloys in which substantial solid solubility exists at an elevated temperature followed by quenching it yields a supersaturated solution that releases fine, coherent precipitate Allotropic hardening only for steels heating up to austenite and quenching leads to a martensitic structure (very hard and brittle) tempering is followed in order to get some ductility

Engineering Metals This section describes the most common metallic alloys, their properties, and their usage. The alloys considered are steels, cast irons, alloys of aluminum, copper, titanium, and Ni- and Co-based superalloys. The production volumes in tons per year in the United States of the individual classes of metals are given below: Steels and cast irons: 100 million Aluminum alloys: 36 million Copper alloys: 1 million Ni-based alloys: <100,000 The significance of the individual classes of metals is not entirely expresses by these tonnages. For example, the Ni-based alloys are extremely important for gas turbines and jet engines; without them modern aircraft would not exist, and there would not be such a great need for aluminum alloys.

Steels: Carbon Steels no alloying elements other than C impurities: Si, S, and P adverse effect on ductility and toughness Mn improves hardenability low carbon steels (nonhardenable) with less than 0.2% C thin sheet steel for car bodies, appliances, and for sidings of houses, heavy steel plates for ships and tanks, for the structures and frames of heavy machinery hardenable steels medium carbon steels, with more than 0.3% C high carbon steels hot rolled carbon steels cold rolled carbon steels

Low alloy steels almost always used in a heat treated (quenched and tempered) state

High alloy steels contain over 5% of alloying elements austenite could be present at room temperature, Ni widens the field, Cr narrows Two classes stainless steels tool steel

Tools steels: Each grade of tool steel is designed for a specific purpose, and as such, there are few generalizations that can be made about tool steel. Each tool steel exhibits its own blend of the three main performance criteria: toughness, wear resistance, and hot hardness. Some of the few generalizations possible are listed here: An increase in carbon content increases wear resistance and reduces toughness. An increase in wear resistance reduces toughness. Hot hardness is independent of toughness. Hot hardness is independent of carbon content.

Aluminum alloys pure Al is light, about three times lighter than iron excellent electric conductor excellent ductility good resistance to corrosion Tm = 660 degree C could be strengthened by cold work used from electric wire to extruded structural shapes for housing construction it is usually used as an alloy alloying elements: Si, Cu, Mn, and Mg above 3% of Si improves fluidity above 12% Si improves hardness and wear resistance Cu improves the age hardenability, it is a primary element in achieving high mechanical strength in aluminum alloys at elevated temperatures.

Magnesium its density is 2/3 that of Al Tm = 650 degree C is alloyed with Al, Zn, Mn, Ce, and Ag main use in the aerospace industry UTS below 350 MPa it is difficult to cold form extrusion, forging, and deep drawing possible on higher temperature