Applying Heat Treating Processes Interest Approach I am going to heat this piece of metal with my gas torch. Once the metal is hot, what can I now do with this piece of metal and why? Is there a connection here for treating metals with heat? Student Learning Objectives Identify the tools and equipment used for hot metal work. Explain the processes of measuring and holding metal. Describe the methods of heating, cutting, squaring, drawing out, upsetting, bending, twisting, and punching holes in hot metal. Student Learning Objectives Describe the heat treating processes: hardening, tempering, and annealing. Identify the safety practices to follow when working with hot metal. Terms Annealing steel Cementite Ferrite Hardening steel Martensite Pearlite Tempering steel What are the tools and equipment used for hot metal work? There are several pieces of equipment used for hot metal work. Hot Metal Tools Equipment used in the heating of stock may be a gas welding/cutting torch, a carbon arc torch, a forge, a furnace or a stove. Hot Metal Tools A forge is the most economical way to heat large areas of metal. Hot Metal Tools When the metal to be heated cannot be removed from a machine, or when the area to be heated is small, a gas welding/cutting torch or a carbon arc torch can be used. Torch When heating with the gas welding/cutting torch or carbon arc torch, care must be exercised because of the intense heat. If too much heat is used, the metal may oxidize and checking of the metal may occur. Hot Metal Tools Anvils and bases are a necessity in hot metal work and are also used in other repair jobs, such as bending, straightening, cutting, and riveting cold metal. Anvils and Bases The anvil should be of good quality; otherwise, the steel face will crack and chip. Anvils and Bases Various types of anvil bases are used; chunks of wood, masonry, or metal frames with the top of the anvil at a convenient working height. If concrete or metal frames are used, a two inch block of wood should separate the anvil from the base to serve as a cushion. Hot Metal Tools The cutting edge of the anvil hardy is similar to a cold chisel. It has a square shank that fits into the hardy hole of an anvil and is used to cut both hot and cold metal. Hot Metal Tools The anvil fullers are used for making grooves and rounding inside corners and angles, and fits into the hardy hole of the anvil. The anvil swages are used to shape round or oval objects. Hot Metal Tools Blacksmith’s hammers, used only with one hand, range in weight from 1 to 14 lbs., with a 1.5 to 2 lb. used for most jobs. Hot Metal Tools Blacksmith’s sledges require the use of both hands and are used for heavy bending and shaping. Weights range from 5 to 20 lbs., however an 8 lb. sledge is big enough for most jobs. Hot Metal Tools Hot cutters have handles, can be purchased with cutting edges of different widths, and are used to cut metal that has been heated. A hot cutter is generally used when a helper is available to do the striking. Hot Metal Tools Handled punches are made with round and square points and are used for punching holes in hot metal. Hot Metal Tools Flatters are used to remove hammer marks and to make the surface of the metal smooth and flat. A magnet is necessary to determine when the metal is hot enough to lose its magnetic properties. Hot Metal Tools Set hammers are used for making square, sharp corners and shoulders. –They are placed on the metal and struck with a hammer or sledge. Small metal squares are used to measure stock and to check rightangle bends. Hot Metal Tools Tongs come in many shapes and sizes for hot metal work, the most common are straight-lip for flat metal and bolt for round stock. A strong heavy-duty machinist’s vise with six inch jaws is necessary for the heavy bending and shaping of hot metal. How is metal measured and held? In order to measure and work metal satisfactorily, the stock must be securely and properly held. Measuring stock Measuring In stock is very important. construction work it is best to secure a plan or a blueprint, if possible, which will indicate exact dimensions. Measuring stock Measure the required length and mark with chalk. If the piece is to be heated, the mark must be made with a center punch or a file because a chalk mark will burn off. Measuring stock If a bent piece of metal is to be duplicated, take a lightweight piece of wire and follow the bends with the wire. Then remove the wire, straighten it, and measure its total length. The wire should be placed near the center of the piece being measured. Measuring stock The amount of material required for making a ring is 3.5 times the diameter of the ring plus ½ the diameter of the stock. In measuring a piece to be welded, add the length needed for upsetting to the total length needed. After the stock to be worked has been marked it must be properly held. Select tongs which fit the work. –The jaws should be parallel when clamped on the stock. –If necessary, heat the jaws to a cherry red and bend them to fit and hold the stock firmly. After the stock to be worked has been marked it must be properly held. Keep the tongs cool by dipping them frequently in water. Be careful not to bend the jaws or handles of the tongs. After the stock to be worked has been marked it must be properly held. There are several different kinds of tongs, but only a few are frequently used in agricultural mechanics. –The type of tongs to use depends upon the kind of work that is to be done. Tongs Flat-jawed tongs with a lengthwise groove in the middle of each jaw help hold materials securely. Link tongs with a crosswise groove in the jaws help in holding links, rings, and similar materials. Tongs Bolt tongs have a curved opening in the jaws. –This permits the holding of round or square materials. How is metal heated, cut, squared, drawn out, upset, bent, twisted, and hole punched? Proper procedures must be followed to properly heat, cut, square, draw out, upset, bend, shape, twist, and hole punch metal. Heating Metal When heating metal, heat should be applied to all parts of the metal being fabricated. Heating in one spot may cause damage to the metal due to uneven expansion. Heating Metal Do not use excessive air or oxygen in heating. –This will cause the metal to scale, and increase the time required for heating. Working any metal heated to less than a cherry red may cause it to crack. Heating Metal Wrought iron and low carbon steel can be heated to a white heat for shaping. –If the heated part sparkles, cut off that part because its value has been destroyed. Heating Metal Tool steel or high carbon steel should be heated only to a cherry red to prevent cracking the metal, damaging the grain structure, and destroying the carbon content. Heating Metal Malleable cast iron cannot be heated above 1,375°F, because it will revert to some of the characteristics of white cast iron when cooled. Hot metal may be cut with a hot chisel, a hardy and a cutter, an oxyacetylene cutting torch, or an electric arc. Hot Metal Cutting Hot chisels and cutters are used for cutting generally large and heavy metals. Hot Metal Cutting When cutting a light piece of material, often it is not necessary to use the cutter. –Merely place the stock over the hardy and deliver hammer blows directly to the stock. When squaring hot metal follow these set procedures: 1. Mark the piece to be squared with a file, using a steel square. 2. Heat the piece to a cherry red color. –Only a small portion should be heated; other-wise, the piece may enlarge when it is struck on its end. When squaring hot metal follow these set procedures: 3. Place the piece over an anvil, and hammer it. –Be sure that the face of the hammer falls parallel with the face of the anvil. 4. Continue to hammer, turning the piece until it is square. When squaring hot metal follow these set procedures: 5. Reheat to a cherry red color if the piece becomes cool before it is squared. Drawn Out Procedure When a piece of iron or steel is pounded so that it is longer and smaller in diameter, it is said to be drawn out. Drawn Out Procedure This procedure is as follows: 1. Heat the portion of the stock to be enlarged to a white heat. 2. Place the stock on the anvil in a perpendicular position, forming right angles to the face of the anvil to prevent the stock from bending. Drawn Out Procedure 3. Strike the cold end of the stock with hard blows. –If the stock bends, place it over the anvil and straighten it. When metal is upset, it is placed on end and hammered until it is enlarged and shortened to the correct size. Metal Upset Procedure 1. The metal must be heated uniformly over the entire section to prevent it from increasing in size at one point. 2. Strike the metal with a sharp, welldirected blow so the entire heated section will be upset uniformly. One of the important phases of metal work is the bending of materials. Bending Procedures 1. Small pieces often may be bent cold, but some pieces should be heated before they are bent. Bending Procedures 2. Square and angle bends can be made by placing the heated metal over the edge of the anvil and hammering the end down along the side. –Clamp one end of the metal in a heavy vise and bend it against the jaws. Hot metal may be twisted by clamping one end in a vice and turning the other end with a wrench. Twisting Procedure 1. To make a long twist without bending the metal, slip a piece of pipe over the metal between the vise and the wrench. Twisting Procedure 2. The length of the twist will be determined by the distance between the vise jaws and the wrench. Holes are punched in hot metal with the handled punch. Hole Punch Procedure 1. The end of the punch must be kept flat and the sides shaped so the corners or edges will be sharp. –In most cases a helper is needed to strike the punch with a larger hammer or sledge. Hole Punch Procedure 2. To punch a square hole lay out and center punch the location of the hole. 3. Heat the metal to nearly white. 4. Quickly place the metal flat on the face of the anvil. –Center the end of the punch over the mark. Hole Punch Procedure 5. Strike the head of the punch with a sledge, driving the point about twothirds of the way through the piece. –The punch should be cooled frequently in water to prevent drawing its temper and upsetting its end. Hole Punch Procedure 6. Turn the piece over, and then set the punch directly over the hole that was started from the other side. Hole Punch Procedure 7. Drive the punch in from this side until almost through. –Then, slide the metal over the round hole of the anvil to allow the metal to be punched completely to the same size from the top side. How is metal hardened, tempered, and annealed? Heat treating steel includes hardening, tempering, and annealing. Hardening Steel Hardening steel is making it hard by heating it to a light cherry red and then cooling it quickly in warm water. Steel Hardening The hardness of steel is determined by two factors: the amount and type of carbon present in the steel and the heat-treating process used in hardening the steel. Steel Hardening The presence of carbon affects the physical properties most; however, carbon content and heat treatment go together. –Carbon content will change the physical properties only slightly without heat treatment. Heat treatment would have little effect if not for the carbon content of the steel. Steel Hardening Carbon is important to the treating process. During heat treatment, carbon atoms can bond or link up with iron atoms to form new compounds with different physical properties. Basic elemental iron is called ferrite. When ferrite has carbon dissolved in it, a new form, cementite or iron carbide will form. Cementite is usually found in a mixture with ferrite. The resulting mixture is called pearlite, because it is pearly white crystals. Pearlite Steel that has not been heat treated is pearlite. Steel can be hardened by heat treatment because pearlite, when heated to 1,320–1340°F, then quickly cooled by warm water becomes martensite. Pearlite The steel takes an intermediate form, austenite, during heating above 700°F. Martensite Austenite forms martensite upon quick cooling. Martensite is a new substance with a crystal structure that gives steel its hardness. The more martensite present, the harder and more brittle the steel. Tempering steel Tempering steel is reheating hardened steel to obtain the desired hardness and toughness. Tempering steel The second heating is to a lower temperature which must be very carefully controlled. –This is to allow some of the hard martensite to revert to its original pearlite form. –Then the steel is cooled slowly or quenched in warm water. Tempering steel The process of changing martensite back to pearlite is dependent on heat increase, usually within one of three of the following ranges: Tempering steel The first range is obtained by reheating the steel to a temperature between 200 and 400°F. Steel that is heat treated to this temperature retains most of its original hardness but does gain some strength and toughness. Tempering steel The second range is obtained by reheating the steel to a temperature between 400 and 700°F. In this range steel is moderately hard and moderately tough. Tempering steel The third range is between 700 and 1,000°F. Steel reheated to this temperature range retains only a little of its original hardness; however, it becomes very strong and tough. Annealing steel Annealing steel is softening the metal and removing the brittleness. The annealing process allows hardened or tempered steel to be made soft so it can be filed, cut, or shaped. Annealing steel To anneal a piece of steel, heat it until all the steel is in the austenite form, light cherry red or above 1,320°F, depending on the carbon content. Annealing steel Then allow it to cool slowly in an insulating material such as vermiculite. This allows the austenite to be-come soft pearlite instead of martensite. What are the safety practices to be followed when working with hot metal? Observe the following general safety practices for working hot metal. Safety Practices Obtain the instructor’s permission before using any tool or machine. Safety Practices Wear industrial quality eye protection to protect eyes from sparks and metal chips. Safety Practices To protect against burns, wear clothing such as coveralls, high-top shoes, leather aprons, and leather gloves. Remove all paper from pockets, and wear cuff-less pants. Safety Practices Protect hair and scalp by restraining long hair and wearing a cap. Safety Practices In the event of an emergency, all students involved in or observing the emergency should call for help immediately. You should know the location of fire extinguishers and fire blankets and how to use them. You should also know the approved procedure for exiting the laboratory. Safety Practices Report all injuries or accidents to the instructor immediately, no matter how slight. Safety Practices Keep the work area and tools clean. Dirty, greasy, and oily tools and floors can cause accidents. Clean and put away all unneeded tools and materials. Clean up oil spills and scrap metal from the floor and equipment. Safety Practices Always use the right size tool and only for its intended purpose. Use tongs or pliers for carrying hot metal. Safety Practices Loud talking, as well as, pushing, running, and scuffling while working with hot metal can cause serious accidents. Keep your mind on your work. Safety Practices Work in a well-ventilated area. Fumes and intense heat are a part of hot metalwork and require that work be done outdoors or in a forced-ventilated area. Safety Practices When lifting heavy objects, obtain help. Lift with the legs and not the back. Straining to lift heavy objects can cause serious injury. Safety Practices To avoid the possibility of accidental burns, keep hot metal in a safe place until it cools. Use tongs or pliers for handling hot metal. Safety Practices Before leaving the laboratory or work station, make certain the heat source is shut off and cool. Safety Practices Do not perform hot metalwork on wood floors or near flammable materials. Never work on containers that have been used for storage of combustible material. Safety Practices Keep cables and hoses from coming in contact with hot metal and sharp objects. Never hoses. point a flame at cables or Safety Practices Use warm water instead of quenching oil for quenching. Quenching other oils. oil is easily confused with Review Identify the tools and equipment used for hot metal work. Explain the processes of measuring and holding metal. Describe the methods of heating, cutting, squaring, drawing out, upsetting, bending, twisting, and punching holes in hot metal. Review Describe the heat treating processes: hardening, tempering, and annealing. Identify the safety practices to follow when working with hot metal.