Hard- Surfacing, Building Fusion Welding Carbon Welding Non-Ferrous Metals Heating & Heat Treating Braze Welding Welding Cast Iron Welding Ferrous Metals Brazing & Soldering Equipment Set-Up Operation Equipment For OXY-Acet Structure of Steel Mechanical Properties of Metals Oxygen & Acetylene OXY-Acet Flame Physical Properties of Metals How Steels Are Classified Expansion & Contraction Prep For Welding OXY-Acet Welding & Cutting Safety Practices Manual Cutting Oxygen Cutting By Machine Appendices Testing & Inspecting
2 This chapter will cover what are termed the physical properties of metal. Chapter 8 will be devoted to the mechanical properties of metals, with emphasis on steel. The physical properties of a material are properties not related to the ability of the material to withstand external mechanical forces, such as pushing, pulling, twisting, bending, etc. These properties include density, melting point, specific heat, heat of fusion, thermal conductivity, thermal expansion, electrical conductivity, and corrosion resistance. Density. The measure of unit mass; in everyday terms, the weight of a unit volume. Density is variously expressed as grams per cubic centimeter (g/cm3), kilograms per cubic meter (kg/m3), pounds per cubic inch (lb./in.3), pounds per cubic foot (lb./ft.3). For comparative purposes, density is often expressed as specific gravity, the ratio of the density of the material to the density of water. The specific gravity of aluminum is 2.70 – in other words, it is nearly three times as heavy as water. Iron has a specific gravity of 7.86; for gold, the value is 19.3. Melting Point. Every pure metal has a specific melting point. If you apply heat to a solid specimen, its temperature will rise until it reaches that melting point. It will then start to melt, and it will remain at the melting point temperature, even though the heating is continued, until the specimen is completely melted. Then, and only then, will the temperature of the liquid metal start to rise once more. The amount of heat required to melt a unit mass of metal includes the heat required to raise that mass to its melting point, and the additional quantity of heat required to accomplish complete melting once the melting point has been reached. Melting Point of Alloys. Most alloys do not melt completely at a specific temperature. Melting starts when the material has reached a certain temperature, but is not completed until a somewhat higher temperature has been reached. This is a fact of great significance in the welding of steel; we’ll get into this more deeply in Chapter 10, and when we get to talk about the practice of welding. Specific Heat. The amount of heat required to raise a unit mass of solid metal one degree in temperature is termed specific heat. The lighter the metal, the greater the specific heat. In other words, it takes more heat to raise the temperature of one kilogram of aluminum one degree than it takes to raise the temperature of one kilogram of iron one degree.