Properties of Metals In order to weld, you must have a basic knowledge of metals.

All of the problems of metal casting are present in fusion welding expansion contraction shrinkage cracks hardening brittleness

Welding effects any metal. Some effects are slight, but they can be harmful if certain rules are not followed.

Metal Numbering Systems Several organizations have numbering systems for the designation of metals.

Society of Automotive Engineers (SAE) American Society for Testing and Materials (ASTM) American Iron and Steel Institute (AISI) American National Standards Institute (ANSI) American Society of Mechanical Engineers (ASME) Aluminum Association (AA)

Unified Numbering System UNS The Society of Automotive Engineers and American Society for Testing and Materials developed the Unified Numbering System as a means for correlating the different numbers for some of the common metals and alloys. In many instances, the UNS numbers contain the same number sequence given by the original organization.

For example, a AISI 1080 steel would be given a G10180 in the Unified Numbering System (UNS) A UNS designation number begins with a letter followed by a 5-digit number.

Nonferrous Metals and Alloys Letter Metal A Aluminum and aluminum alloys C Copper and copper alloys E Rare earth and rare earth-like metals and alloys L Low melting metals and alloys M Miscellaneous nonferrous metals and alloys

P Precious metals and alloys R Reactive and refractor metals and alloys Z Zinc and zinc alloys

Ferrous Metals and Alloys Letter Metal D Specified mechanical property steels F Cast irons G AISI and SAE carbon and alloy steels H AISI H-steels except tool steels

K Miscellaneous steels and ferrous alloys S Heat and corrosion resistant (stainless) steels T Tool steels

AA System for Aluminum The Aluminum Association uses a four-digit numbering system for designating wrought (rolled or extruded shapes) and cast aluminum alloys. Examples would be XXXX for wrought alloys and XXX.X for cast alloys. Letters may follow the numbers series which may indicate annealing, hardening, heat-treated or tempered.

Annealing Softening metal by heat treatment. Relieves metal of internal stress caused by the expansion and contraction during welding.

Hardening The rapid cooling of hot metal.

Heat-treating The process of heating and cooling metals in order to obtain desired properties.

Tempering The heating of a quenched steel in a furnace to a specified temperature below the critical temperature and then allowing it to cool at any desired rate.

Example of structural aluminum The “T-6” means the aluminum has been solution heat-treated and then artificially aged to obtain a desired hardness (temper).

Major Groups of Metals Ferrous Metals metals containing iron and its alloys such as steel Examples cast iron wrought iron steel

Nonferrous Metals metals containing little or no iron Examples copper brass zinc bronze lead aluminum

Metal Melting Points Material Degrees Fahrenheit Aluminum 1218 Brass 1650 Copper 550 Cast iron 2300 Wrought iron 2750 Stainless steel 2550-2750 Mild Steel 2700

Physical Properties of Metals A characteristic of a metal which be observed or measured

Tensile strength the ability of a metal to resist being pulled apart. Ductility the ability of a metal to be stretched. Hardness the quality which allows a metal to resist penetration.

Brittleness means a metal will fracture easily if bent sharply or struck with a sharp blow. Compression strength of a metal measured by how much squeezing force it can stand before it fails. Yield strength the force in psi at which a weld specimen starts to pull apart.

Elongation how much a metal will stretch before it breaks. Malleability the tendency of a metal to be hammered into shape.

Toughness can withstand repeated twisting or bending. Grain size examination of the grain size under a microscope gives a good idea of brittleness, tensile strength, heat treatment and ductility.

Physical properties of steel are effected by: Carbon content carbon combines with iron to form iron carbide, a very hard, brittle substance. this means as the carbon content of the steel increases, the hardness also increases.

Impurities Two harmful impurities are phosphorous and sulphur during welding, sulphur and phosphorous tend to form gas pockets in the molten metal, resulting in gas pockets in the weld. brittleness also increase because of sulphites and phosphates. dirt and slag are other impurities.

Addition of various alloying metals Nickel Chromium manganese Vanadium Other alloys may be added to steel to improve physical properties.

Heat treatment Enable steel to retain the strength of its higher carbon content, yet not have the extreme brittleness usually found with high carbon steels.

Alloy Metals An alloy metal is a mixture of two or more metals. Any ferrous or nonferrous metal may be alloyed to form an alloy metal with new and desirable characteristics. Steel is an alloy of iron and controlled amounts of carbon. Alloy steels are created by adding other metals to plain carbon steel.

How To Identify Iron and Steel The most common tests for shop use are: Spark test File test Fracture test Color test Density test Ring or sound of metal Magnetic test Chip test

Spark test Can be used to separate ferrous from nonferrous metals Lightly touch metal to grinding wheel The type of spark produced will identify the metal Nonferrous metals will not produce sparks.

Wrought Iron large stream volume straw colored stream white colored streaks very few spurts forked spurts

Mild Steel large stream volume white colored stream white colored streaks few spurts forked spurts

Carbon tool steel moderately large stream volume white colored stream white colored streaks very many spurts fine, repeating spurts

Gray cast iron small stream volume red colored stream straw colored streaks many spurts fine, repeating spurts

White cast iron Very small stream volume red colored stream straw colored streaks few spurts fine, repeating spurts

Stainless steel moderate stream volume straw colored stream white colored streaks moderate spurts forked spurts

Copper, Brass and Aluminum no sparks

File test comparison of filings of the “white metals” magnesium float like a feather zinc die cast fall like a rock aluminum in between

A file test can be used to check the relative hardness of a piece of ferrous metal or to see if it is heat treated. Strike an arc with a GTAW torch on the edge of the material and see if a file will cut the area melted by the arc. if the file will not cut the arc area, the metal is heat treated. If the arc area is not noticeably affected (hardened) by the the arc strike, normal weld procedures and filler can be used.

Fracture test breaking a portion of the metal in two. check the grains large grains mean the metal is brittle and weak. small grains mean the metal is usually hard and brittle, or soft and ductile fractures also show the color of the metal, which is a good way to tell one metal from another.

Color test irons and steels gray-white color nonferrous metals yellow or white color aluminum, white metal, aluminum alloys, zinc and the likes silver-gray color

Density test basically the weight of the metal example is lead and aluminum basically the color is somewhat the same, yet lead is more dense than aluminum in other words, lead is somewhat heavier than aluminum

Magnetic test used to identify ferrous from nonferrous metals all steels are affected by magnetism nonferrous metals are not affected by magnetism however, some stainless steels are not magnetic

Chip test cutting action with a chisel indicates the structure and heat treatment cast iron breaks off in small particles mild steel tends to curl and cling to the base piece