Properties of Metals

Among the metals used in industrial manufacturing, steel alloys are the most common. According to Polish Standards, the first component in the alloy must represent the significant majority, while the carbon content must not exceed 2.11%. Any higher carbon percentage means the material is classified as cast iron.

Steel also contains other metals, elements, and non-metallic inclusions that influence the final structure and mechanical properties achieved through heat and mechanical processing. You will learn more about this in the following sections.

What Is Metal and What Are Its Properties?

A metal is typically a crystalline material with metallic bonding. Its main characteristics include:

• plasticity

• elasticity

• good electrical and thermal conductivity

• positive temperature coefficient of resistance

• solid state at room temperature (except mercury)

• opacity

• metallic sheen

• no odor

• high mechanical strength

• suitability for machining and forming

Stages of Steel Production and the Resulting Material Properties

Steel production consists of two distinct processes:

1. Smelting pig iron in a blast furnace

2. Steelmaking — refining pig iron into steel

Pig iron produced in the blast furnace is not suitable for machining due to its high content of carbon (~4%), sulfur (0.5%), and phosphorus (0.5%). This makes it brittle and non-malleable. As such, pig iron becomes the raw material for either steel or cast iron production.

During steelmaking, pig iron is refined by removing excess carbon (C), silicon (Si), manganese (Mn), phosphorus (P), and sulfur (S). This reduction takes place through oxidation using oxygen and/or air. The process, known as refining (freshening), allows the metallurgist to achieve the desired steel grade once alloying components are added.

After refining, the molten steel is cast into ingots, prepared for subsequent plastic forming. The solidified steel moves through rollers that stretch and straighten it, after which a gas torch cuts the material into equal segments. These billets (round, square, rectangular, or plate-shaped such as 200×1500 mm) become the base material for producing rods, wires, profiles, rails, or sheets.

The Influence of Alloying Elements on Steel Properties

Production of Steel Sheets, Profiles, and Tubes

A typical steel mill consists of three main departments:

• blast furnace

• steel plant

• rolling mill

Steel from the steel plant undergoes plastic forming — primarily rolling. The rolled product is the essential output of metallurgical processing.

During rolling, the metal obtains its final shape through plastic deformation between rotating rolls, discs, or cylinders. Rolling occurs on an integrated set of equipment known as a rolling line, adapted to the type and temperature of the material and the needed final dimensions.

Rolled products include:

• rods

• wire rod

• profiles

• sheets (thin and thick)

• strips

• tubes

• special products (rails, wheel rims for railway wagons, etc.)

Most products are formed through hot rolling, while cold rolling is used mainly for thin sheets and strips.

The process for aluminum production is very similar to that described for steel.

Mechanical Properties of Metals

Mechanical properties define the performance and usability of steel. These depend on its chemical composition and the type of processing (heat treatment, plastic forming, etc.).

The main mechanical properties include:

• Strength — defined by tensile strength and yield strength

• Ductility — described by elongation and reduction of area

• Toughness — energy absorption capacity determined by impact testing

• Hardness — measured using Brinell, Rockwell, or Vickers methods

Choosing Steel Based on Its Properties

Before manufacturing or construction begins, it is crucial to select the appropriate grade of steel that matches the conditions under which the structure or machine will operate. Today, the industry uses a wide variety of steel grades, each with specific characteristics — identifying the correct one is essential.

Steel Grades — Structural Steel

Used in the construction of common structures, machine parts, and for strengthening other alloys. Categories include:

• General-purpose structural steel — lower-grade alloy used where specific material parameters are not required

• Higher-quality structural steel — precisely controlled carbon and manganese levels, fewer impurities; used for sheets, tubes, and automotive or machine components

• Low-alloy structural steel — carbon content up to 0.22%; valued for strength and corrosion resistance; used in bridges, railcars, and masts

• Carburizing steel — high surface hardness and good core ductility; used for high-strength components

• Nitriding steel — surface saturated with nitrogen; excellent for gears

• Heat-treatable steel — for heavily loaded parts

• Spring steel — high silicon content; used for springs, leaf springs, torsion bars

• Free-cutting (automatic) steel — for screws, washers, nuts

• Bearing steel — extremely controlled composition, produced under strict conditions

Tool Steel

High carbon content and specific heat treatment give tool steel its desirable performance. Used for tools and precision measuring devices, tool steel offers:

• very high hardness

• excellent wear resistance

• resistance to overheating

• dimensional stability under long-term operation

Tool steels include:

• carbon tool steels

• alloy tool steels

• cold-work steels

• hot-work steels

• high-speed steels

Specialty Steels — Types and Applications

Special steels are engineered for highly specific applications. They contain elevated levels of alloying elements, require advanced heat treatment, and are significantly more expensive.

Examples include:

• Stainless steel — corrosion and heat resistant

• Acid-resistant steel — high chromium content; resistant to many acids

• Heat-resistant and creep-resistant steel — withstands oxidation at high temperatures

• Magnetic steel — extremely low carbon content; strong ferromagnetic properties

• Wear-resistant steel — high carbon and manganese content

Summary

We hope this article has provided a solid foundation for understanding metals and their properties. Of course, material science is a deep field worth exploring further.

Remember — when choosing Otinus machines, you gain access to the expertise of our experienced technicians, who will help you select the ideal solutions for the materials you plan to process.

Feel free to contact us or visit our machine showroom in Bydgoszcz at 14b Karola Szajnochy Street.