Guide To The Types Of Metals

What are the Basic Types of Ferrous and Nonferrous Metals?

Metals divide into two general classifications:

Ferrous Metals Definition

Ferrous Metals primarily contain iron (atomic symbol Fe) and iron alloys. It includes all forms of iron and iron-based alloys, with small percentages of carbon (e.g.; steel) and other elements added to achieve desirable properties such as tool steels, alloy steels, carbon steels, cast iron, and wrought iron.

Nonferrous Metals Definition

Nonferrous metals are composed primarily of some element or elements other than iron. Nonferrous alloys or metals often contain small amounts of iron as an impurity or an alloying element.

What are the Physical Properties of Metal?

Metal physical properties dictate how they perform when used or if they can be welded. Physical properties are related to the atomic structure and density of the material.

Properties include:

• • Color

• • Gravity

• • Density

• • Melting Point

• • Boiling Point

• • Relative Thermal Conductivity

• • The coefficient of Linear Expansion
  • Corrosion Resistance

 Metal Properties

1. 1. 1. Color: How light reflects off metal relates to the color.
      2. Density or Mass: Density or Mass (also called specific gravity) refers to mass with relation to volume.  At a selected temperature, it is the ratio of the mass of the same volume of water to the mass of a given volume of the metal. The temperature is usually 39°F (4°C). For example, the specific gravity of cast iron is the ratio of the weight of one cubic foot of cast iron to one cubic foot of water. Density or Mass is measured in grams per cubic centimeter or millimeter.
      3. Melting point: The melting point of the metal is important when related to welding.
         

         Definition of the Melting Point of Metal

         Fusibility of metal is related to its melting point, the temperature at which the metal changes to a molten state from a solid state.

         Pure substances have a sharp melting point and pass to a liquid state from a solid state at the same temperature (no change). Heat is liberated during freezing and absorbed during melting. The intake or release of thermal energy during a substances state change is called latent heat. At room temperature, the only standard metal in a molten state is Mercury.  Low-temperature heat sources can be used to weld Metals with low melting temperatures. The brazing and soldering processes utilize low-temperature metals to join metals having higher melting temperatures.

      4. Boiling point: Boiling point is also an important factor in welding.

         Definition of the Boiling Point of Metal

         When metal transforms from liquid to vapor, that is the boiling point. A few metals will vaporize when exposed to the heat from an arc.

      5. Conductivity: Electrical and thermal conductivity refers to metal’s ability to transfer or conduct electricity and heat. Thermal conductivity is the capacity to transmit heat throughout the metal mass. Mass when welding is critical since one metal in the welding area could move heat faster than another piece of metal.  Metal thermal conductivity points to the necessity of determining the size and amount of preheating that is required.  When discussing thermal conductivity it more times than not relates to copper. The highest thermal conductivity of the common metals is found in copper (silver is the only metal that has more thermal conductivity).  Another common metal, aluminum, has fifty percent of the thermal conductivity of copper. Steel has one-tenth the conductivity of copper.

         How is thermal conductivity measured?

         The measure of thermal conductivity in meters is Calories per square centimeter per second per degree, or in the U.S. it is Calories per square inch.

         What is electrical conductivity?

         The capacity of a metal to conduct an electric current is electrical conductivity.  It is represented as a percentage related to silver or copper.  Conductivity decreases when the metal temperature increases, a factor that is related to understanding electrical circuits and resistance welding.

         What is electrical resistivity?

         The opposite of electrical conductivity is resistivity, which is measured in micro-ohms per cubic centimeter at a standard temperature, usually 20°C.

      6. The coefficient of linear thermal expansion:  With few exceptions, solids expand when they are heated and contract when they are cooled

         Definition of the Coefficient of Linear Thermal Expansion

         The coefficient of linear thermal expansion is a measure of the linear increase per unit length based on the change in temperature of the metal.  The expansion is the increase in the dimension of a metal caused by heat. The expansion of metal in a longitudinal direction is known as the linear expansion. The coefficient of linear expansion is expressed as the linear expansion per unit length for one degree of temperature increase.

          

         

         Relationship Governing the Linear Expansion of a Long Thin Metal Rod

         Definition of volumetric expansion

         Volumetric expansion refers to when metals increase in size; they grow not only in length but thickness and breadth. In different metals, the coefficient of linear and volumetric expansion changes. The largest coefficient of expansion is seen in Aluminum, for the same temperature change, it expands almost 2x as much as steel.  The implications for welding have to do with welding together different materials, fixturing, warpage control and warpage.

      7. Corrosion resistance:

         Definition of Corrosion Resistance

         Corrosion resistance is the resistance to wearing away or eating away by moisture, other agents or air.

1. 1. Tensile strength:
      

      What is the definition of Tensile Strength or Ultimate Strength?

      Tensile strength is defined as the maximum load in tension a material will withstand before fracturing, or the ability of a material to resist being pulled apart by opposing forces. Also known as ultimate strength, it is the maximum strength developed in metal in a tension test.

      

      Tensile Strength of Metal is the Number of Pounds of Force Required to Pull Apart a Bar of Material 1.0 inch wide and 1.0 inch thick

      How is Tensile Metal Strength determined?

      The behavior of metal under an actual stretch loading is referred to as a tension test. This test provides the elastic limit, reduction in area, yield strength, yield point and elongation of metal. Value is assigned to metal strength (tensile strength) expressed in kiloPascals (kPa) or pounds per square inch (psi). Expressed another way; tensile strength is pounds of force needed to take a material bar and pull it apart 24.5mm wide (1 inch) and 25.4mm thick (1.0 inch)

   2. Shear strength:

      What is the definition of shear strength?

      The ability of a metal to resist being fractured by opposing forces not acting in a straight line or to resist being fractured by opposing forces acting on a straight line but not in the same plane is shear strength.

       

      

      Shear Strength is the Ability of a Metal to Resist Being Fractured by Opposing Forces not Acting in a Straight Line or the Ability of a Material to Resist Being Fractured by Opposing Forces Acting of a Straight Line, but Not in the Same Plane

   3. Fatigue strength:

      What is the definition of metal fatigue strength?

      During a large number of reversals, the maximum load a material can withstand without failure is fatigue strength.

      A weight supporting rotating shaft has compressive forces at the bottom of the shaft and tensile forces at the top of the shaft.  As the shaft rotates, there is a repeated cyclic change in compressive and tensile strength. The design of structures such as aircraft wings which are subject to rapidly fluctuating loads requires fatigue strength values. Fatigue strength is influenced by surface condition, microstructure, cold work, and a corrosive environment.

      When there are frequent repetitions of a stress, some metals will fail or rupture, even when sufficient stress may not result in permanent deformation if continuously applied for a relatively brief time. Stress repetition can happen when in places such as a rock drill shank. Stress alternation can produce failure more rapidly than a recurrence of stress. Stress variations mean the alternate compression and tension on any material. Fatigue definition is the failure of alloys and metals that are subjected to alternating or repeated stresses too small to produce a permanent deformation when statically applied.

   4. Compressive strength:

      What is the definition of compressive strength?

      The maximum load in compression a material will withstand a predetermined amount of deformation, or the ability of a material to withstand pressures acting in a given plane is compressive strength.

      The compressive strength of both cast iron and concrete are greater than their tensile strength. For most materials, the reverse is true.

Elasticity

What is the definition of metal elasticity?

Metal’s ability to return to its original size, shape, and dimensions after being pulled out of shape, stretched or deformed is elasticity. The point at which permanent damage starts is the elastic limit. The point when definite damage occurs with little or no increase in load is the yield point. The number of pounds per square inch (kiloPascals) it takes to produce deformation or damage to the yield point is called yield strength.

What is the Modulus of Elasticity?

The ratio of the internal stress to the strain produced is the modulus of elasticity.  It expresses the stiffness of the material. For steel and most metals, this is a constant property and is affected very little by heat treatment, hot or cold working, or the actual ultimate strength of the metal.

What is Hooke’s Law?

According to Hooke’s Law: “The degree to which an elastic body bends or stretches out of shape is in direct proportion to the force (stress) acting upon it.” But, this law only applies within a certain range.

Ductility

What the definition of ductility of metal?

The property which allows the metal to be stretched without a break or to be changed while also not breaking is referred to as the ductility of metal. It is the ability of a material, such as copper, to be permanently stretched or drawn without fracturing. A tensile test can determine the ductility of a metal by measuring the elongation percentage. The lack of ductility is when you do not see the permanent damage before the metal breaks or cracks (such as with cast iron).

Specifically,   the ability to be drawn from a larger to a smaller diameter of the wire is ductility. This operation involves both elongation and reduction of area.

Plasticity

What is the definition of the plasticity of metal?

Plasticity is the ability of metal, such as lead, silver or gold,  to be deformed extensively without rupture. Plasticity is similar to ductility.

Plasticity together with strength, is considered to be the two most important properties that metal can possess.

Malleability

Malleability is the ability of a material to deform permanently under compression without fracture or rupture. It is this property which allows the rolling and hammering metals into thin sheets.

Most types of metals have increased malleability and ductility at higher temperatures. For example, iron and nickel are very malleable when heated bright red.

Different metals do not possess the same two properties of malleability and ductility to the same degree. Tin, silver, lead and Gold exhibit high malleability. Exceptional malleability is seen in gold and can be rolled into sheets thin enough to transmit light. Tin and lead are relatively malleable but do not have the tensile strength needed to become fine wire.

Area Reduction

This is a measure of ductility. It is taken from a tensile test after failure by recording the original cross-sectional area of a specimen to a cross-sectional area.

Brittleness

The property opposite of ductility or plasticity is brittleness.  It can rupture with not much deformation. Hard metals are often brittle.  The terms should not be synonymous or confused. A brittle metal is one that cannot be visibly deformed permanently or one that lacks plasticity.

Sudden failure is referred to as “brittleness.” It occurs when metal breaks with no warning or permanently visible deformation. When metal reaches its elastic limit, it has little resistance to rupturing.

Toughness

Toughness is a combination of medium ductility and high strength. It is the ability of a material or metal to resist fracture, plus the capacity to resist failure after the damage has begun. A hardened metal, such as a cold chisel, is one that can withstand considerable stress, suddenly or slowly or applied, and which will deform before failure. Toughness is the ability of material to resist the start of permanent distortion plus capacity to resist shock or absorb energy.

The ability of a material to absorb energy, including the energy of both plastic deformation and elasticity under a gradually applied load, is referred to as toughness. Generally speaking, toughness applies to both plasticity and strength. Thus, a low strength easily deformed substance is tough. The material of high strength, but with little plasticities, such as hardened tool steel is also not tough. The real tough metal is one that will distribute rapidly within itself both the resulting strain and stress caused by a quickly applied load.

Machinability and weldability

The property of machinability and weldability is the ease or difficulty with which types of metals lend themselves to being machined or welded.

Resistance

Abrasion Resistance Definition

Resistance to wearing by friction is abrasion resistance.

Corrosive Resistance and Fatigue Definition

The resistance to atmospheric wearing or eating away, moisture, or other agents, such as an acid is corrosive resistance.

A type of fatigue failure is corrosion fatigue where the endurance limit has been lowered by corrosion with the formation of pits which act as centers for the development of fatigue cracks. Moreover, when fatigue stresses break any metal protective film, corrosion produces cavities which spread through the cracks in the film acting as stressors.

If a fatigued metal piece is exposed to corrosive agents, such as oil that hasn’t been freed from acid or a damp atmosphere, the stress necessary to cause failure is lowered. The unit stress of strong heat treated alloy steel exposed to corrosion fatigue will be no more than relatively weak structural steel. It is important to protect material surfaces subject to fatigue against corrosion by plating and galvanizing.

Impact Resistance

The resistance of the metal to impacts is evaluated regarding impact strength. A metal may possess satisfactory ductility under static loads but may fail under dynamic loads or impact. The impact strength of metal is determined by measuring the energy absorbed in the fracture.

Hardness

What is the definition of metal hardness?

The ability of a metal to resist penetration and wear by another metal or material is referred to as hardness. It takes a combination of toughness and hardness to stand up to a heavy pounding. Metal hardness limits the ease with which it can be machined since hardness increases as toughness decreases.

A heat treatment can harden Steel. The reason to heat treat steel is to make the steel better suited, structurally and physically, for some each particular application.

The table below illustrates the hardness of various metals.

Types of Metals: Hardness Tests

• Brinell hardness test:  A hardened steel ball is slowly pushed by a known force against the tested metal surface. The dent diameter in the surface is measured. Using standard tables, the Brinell hardness number (bhn) is identified.
• Rockwell hardness test: This test measures any variance between the depth to which a test point is pushed into a metal by a light load and the depth to which it is driven in by a heavy load. First, the light load is applied. Then, while keeping the piece stationary, the heavy load is applied. A dial indicates the hardness number. Letter designations, such as B and C from a Rockwell scale indicate the amount of heavy load and the type of penetrator used.
• Scleroscope hardness test:  Hardness is measured by using a diamond-tipped hammer that falls by its own weight from a fixed height and rebounds from the surface.  A scale measures the rebound off of a smooth surface.

Mechanical Properties of Metals
(Ranked in Order of Having Property)

Toughness	Brittleness	Ductility	Maleability	Corrosion
Copper Nickel Iron Magnesium Zinc Aluminum Lead Tin Cobalt Bismuth	White Cast Iron Gray Cast Iron Hardened Steel Bismuth Manganese Bronzes Aluminum Brass Structured Steels Zinc Monel Tin Copper Iron	Gold Silver Platinum Iron Nickel Copper Aluminum Tungsten Zinc Tin Lead	Gold Silver Aluminum Copper Tin Lead Zinc Iron	Gold Platinum Silver Mercury Copper Lead Tin Nickel Iron Zinc Magnesium Aluminum

How To Identify Metals

When you are selecting types of metals to use in fabrication, to perform a mechanical repair, or even to determine if the metal is weldable, you must be able to identify its basic type. 
Some field metal identification methods can be used to identify a piece of metal. Some common methods are:

• surface appearance
• spark test
• chip test
• magnet test
• hardness test

Powder Metallurgy

Powder Metallurgy (PM) is the use of metal powder such as iron powder to create unique materials that cannot be created through melting or other processes. It is frequently used in automotive and other industries such as tungsten carbide which is used to cut other metals.

 Free Brochures on the Types of Metals

Types of Metal: Characteristics, Pros, and Cons of Each Type, Common Uses

Mechanical Properties-of-Metals: Table ranking metals based on mechanical properties

References

Structure of Metals
University of Illinois

Metals and Alloys
Chemical Reactions, Mechanisms, Organic Spectroscopy