Metallic Materials

Two-thirds of all elements found in nature are metals. They exhibit unique mechanical properties, have shiny surfaces, a high thermal conductivity, and are electrically conductive. Due to their diversity, it is not easy to provide an exact definition of the term “metallic material.” Metals have the ability to combine with one another and with other substances to form alloys. Because of their technical importance, users classify metallic materials into ferrous metals and nonferrous metals. The field that deals with the production and processing of metals and metal alloys is metallurgy. The scientific discipline is called metallography.

In materials science, metallic materials are classified based on the base metal, the material properties, or the intended use:

• Iron-based materials, such as steel or cast iron, consist primarily of iron plus a defined amount of carbon.
• Non-ferrous metals: e.g., aluminum, copper, titanium, magnesium, and their alloys
• Hard metals
• Soft metals

The distinction between hard metals and soft metals is not uniformly defined in the literature. In most cases, authors classify all metals that are softer than iron and steel as soft metals.

The category of iron materials deals with the two-component system of iron and carbon, specifically with iron-carbon alloys. Generally, materials engineers classify iron-based materials into steels (carbon content less than 2.06%) and cast iron materials (carbon content greater than 2.06%). Additional alloying elements determine the composition of the individual iron and steel grades as well as their specific properties. Accordingly, the following classification options arise:

• by carbon content
• by exact chemical composition
• by grade, based on practical application requirements

Steels and cast irons are iron-carbon compounds that differ in terms of carbon content and, consequently, their plastic deformability. Steels contain up to 2% carbon and are what are known as wrought alloys. This means that they are plastically deformable. For this reason, steel materials are very well suited for the production of semi-finished products and technical castings.

Engineering cast iron and cast iron alloys contain up to 3.5% carbon. Since the higher carbon content results in a comparatively strong alloy, the primary manufacturing method for iron casting materials is casting.

Consequently, the carbon content in an iron alloy has a decisive influence on the material properties. Even small changes in carbon concentration can have significant effects. An important tool for illustrating the different behaviors of steel and cast iron as a function of carbon content is the iron-carbon diagram.

It is not only the carbon content but also the addition of various alloying elements that influence the properties of iron-based materials, particularly steel. Chemical elements that can be added to the iron-carbon mixture include heavy metals such as lead and cadmium, light metals such as aluminum and copper, and nonmetals such as silicon. Depending on the alloy content, the following types of steel are distinguished:

• unalloyed steels with less than 1% alloy content
• Alloyed steels with an alloy content ranging from 1% to 5%
• High-alloy steels with an alloy content of more than 5%

Depending on the required performance characteristics (e.g., formability, weldability, hardness), steels are classified by grade into basic steels, high-quality steels, and stainless steels. While, for example, standard steels do not require any special measures during production, the chemical composition, degree of purity, and manufacturing of stainless steels are subject to tight tolerances.

When classifying steels by application, materials experts distinguish between structural steels, engineering steels, and tool steels. Cast iron is classified into gray cast iron, malleable cast iron, ductile cast iron, and hard cast iron, depending on the manufacturing method and properties.

Materials scientists refer to all metals found in nature, as well as alloys that are not iron or iron alloys, as non-ferrous metals. Non-ferrous metals are further classified into heavy metals and light metals based on their density. It is also common to classify them into non-ferrous metals (e.g., copper, aluminum, cobalt, nickel, zinc) and precious metals (silver, gold, platinum).

Since the material class “non-ferrous metals” encompasses a wide variety of materials, it is not possible to make a general statement regarding their overall properties. Depending on the metal, certain characteristics—whether desirable or less so in practical applications—are more or less pronounced. Some nonferrous metals are particularly lightweight, others have a distinctive appearance, while still others possess high electrical conductivity or are magnetic. The following properties apply to nearly all nonferrous metals:

• Corrosion resistance
• Wear resistance
• Castability
• Good alloyability
• High conductivity
• Good machinability

Non-ferrous metals of technical interest are often more expensive than ferrous metals. However, due to their special characteristics, they are essential for certain technical applications or are preferred for other reasons.

Non-ferrous metals are used in the following industries:

• Electrical engineering, electronics
• Machinery and plant engineering
• Automotive manufacturing
• Aerospace and shipbuilding
• Mold, fixture, and tool manufacturing
• Food Industry
• Packaging Industry
• Optics and lighting technology
• Arts and Crafts and Jewelry

The term “non-ferrous metals” encompasses all pure metals and metallic alloys in which the majority of the composition consists of elements other than iron. Depending on their density, non-ferrous metals used in engineering are classified as light metals or heavy metals. Light metals include, for example, magnesium, titanium, and aluminum. The latter is most commonly used in industry and technology, primarily in the form of alloys. The most important heavy metals for technical applications include zinc, tin, copper, and their alloys, such as bronze, red brass, and brass.

Cemented carbides are a type of composite material. They consist of 90 to 94% tungsten carbide and up to 10% cobalt. The defining characteristics of cemented carbides are their high wear resistance and hardness, particularly their excellent hot hardness. As a result, they are ideally suited for the manufacture of tools and parts that are subjected to above-average frictional forces.

Classic applications for cemented carbides include saw blades, drill bits, milling cutters, and turning tools for machining a wide variety of workpieces. Knives for industrial use, as well as tools in mills and mines, are also frequently made from special cemented carbides.

Depending on the manufacturing process, experts distinguish between

• between cast cemented carbides and
• sintered cemented carbides

Depending on their intended use, cemented carbides are divided into the P, M, and K groups. The grades are identified by a code that describes the material’s toughness and wear resistance.

The term “soft metal” is not clearly defined in materials science. In principle, this product group includes all metals that are softer than iron and iron alloys, such as aluminum, gold, silver, platinum, tin, zinc, and copper.