The earliest known production of steel dates back to 1800 BC and is found in iron tools, discovered at archaeological sites in Anatolia. This means that this material has been in use for at least 4000 years! For centuries, this product has helped construct and build civilization. It serves as a basic construction material, as well as in the automotive and environmental industries. How can it be processed? What is its composition and mechanical properties? We write about this below!
Composition of Steel
General purpose structural steel is an alloy of iron and carbon, containing up to 2% carbon (material with a higher carbon content is called cast iron). Steel is by far the most popular material used for the construction of global infrastructure and industry, used to produce everything from sewing needles to tankers. Additionally, the tools needed for the construction and production of such items are also made of steel. Analyzing its structure in more detail, it should be pointed out that it is an iron-carbon alloy containing less than 2% carbon and 1% manganese with small amounts of:
- silicon,
- phosphorus,
- sulfur,
- oxygen.
Since it is an alloy, not a pure element, it does not belong to the domain of metals. Although steel itself contains iron belonging to this group, carbon and other elements also included in this alloy composition exclude the possibility of classifying steel as a metal. Currently, steel is the most important construction material in the world, existing in every aspect of our lives. Its wide application can be seen for example in:
- cars,
- construction products,
- refrigerators,
- washing machines,
- freight ships,
- surgical knives,
and of course in many, many other areas of industry.
Properties of steel
Steel has many properties, including particular hardness, plasticity, tensile strength, yield point, elongation, fatigue strength, corrosion resistance, and others.
Among the parameters defining the properties of steel, we should mention:
- Hardness - is the ability of a material to withstand friction and wear. It's worth noting that while in colloquial language it means the same as durability and plasticity, in the context of metal properties it is something completely different than durability and plasticity.
- Durability - refers to the ability to absorb energy without cracking or tearing. It is also defined as the resistance of a material to cracking under stress. It is usually measured in joules per square centimeter. It is important to distinguish this from hardness, as a material that deforms significantly without cracking can be considered very strong, but not rigid.
- Expandability and plasticity - It is expressed as a percentage of the test length and is located between the tensile strength and the yield point (i.e., the percentage of material that bends before breaking). This characteristic of steel, which allows it to be processed, is an extremely valuable aspect for CNC operators. The yield point is the moment up to which the steel does not get damaged during stretching.
The above mechanical properties of steel make it an extremely practical material.
Basic physical properties of steel
Steel has a density of 7,850 kg/m3, which means it is 7.85 times denser than water. It has a melting temperature of 1510°C, higher than most metals. For comparison, bronze has a melting temperature of 1040°C, copper 1083°C, cast iron 1300°C, and nickel 1453°C. On the other hand, tungsten has a melting temperature of 3410 degrees Celsius, which is not surprising, as this element is used in light bulbs. The linear expansion coefficient of steel (expressed in µm per meter per degree Celsius) is 11.1 at a temperature of 20°C, which makes it stronger than copper (16.7), tin (21.4), or lead (29.1).
Alloy Metals, and Steel
Iron, as the main component of steel, is one of the most widespread elements in the Earth's crust. In most alloy steels, the main component is iron with 0.002-2.1% wt. of carbon. Within this range, carbon-iron bonds create a strong molecular structure. The resulting microstructure of the network helps to achieve some properties of steel that we depend on, such as tensile strength and hardness. Although all steel consists of iron and carbon, different types of it contain specific percentages of these elements. It may also contain other elements, such as:
- nickel,
- molybdenum,
- manganese,
- titanium,
- boron,
- cobalt
- vanadium.
Adding various elements to the "recipe" of a steel alloy affects its material properties. The methods of production and processing of steel further increased these possibilities. A noteworthy group of steel alloys contains chromium. All these alloys are commonly referred to as stainless steel.
What is the melting temperature of steel?
The melting range of this alloy is within the range of 2500-2800°F or 1370-1540°C. Why such a range? Because there are different types of alloys. The word "alloy" is currently almost always misused. In practice, this word really means a mixture of metals, any kind of metal. Almost all metals used today are mixtures, and therefore alloys. Other metals are added to most steels to tune their properties, such as strength, corrosion resistance, or ease of production. Steel is simply iron that has been processed to control the carbon content. Iron melts at a temperature of about 1510 degrees Celsius (2750 degrees Fahrenheit). Steel usually melts at a temperature of about 1370 degrees Celsius (2500 degrees Fahrenheit).
What is the melting point of stainless steel?
The melting temperature of stainless steel ranges from 2550 to 2790°F or from 1400 to 1530°C. The melting temperature of a specific type of stainless steel depends on its exact chemical composition. Each element contributes its own melting temperature to the equation. The main elements that make up stainless steel are iron, chromium, and nickel. Pure iron has a constant melting temperature of 1535°C, chromium 1890°C, and nickel 1453°C. Compare these numbers with the range of temperatures 1400-1530°C for stainless steel.
Each type of stainless steel has a slightly different combination of elements. Hence, the exact melting temperature varies depending on the type.
How does the melting temperature differ in different types?
There are five series and over 150 types of stainless steel. However, in practice, only 15 of these categories are used daily in various constructions. The two most popular types are
- 304
- 316.
They belong to austenitic stainless steels, characterized by a cubic crystalline structure concentrated on the surface, and the fact that they remain solid at all temperatures from cryogenic to melting. The melting temperature of 316 stainless steel ranges from 1375 ° C, and up to 1510 ° C for 430 grade steel. The most popular grade, 304, has a melting temperature of 1400-1450 ° C.
Different types of steel
The four main types of steel are as follows:
- Carbon
- Alloy
- Stainless
- Tool
Carbon steel
It appears matte and is very susceptible to corrosion. Generally speaking, this steel is divided into three subtypes:
- low-carbon steel,
- medium-carbon steel,
- high-carbon steel.
The first subtype contains about 0.30% of carbon, in the second the amount of this element is 0.60%, and in the case of high-carbon steel it is 1.5%. The name itself comes from the fact that it contains very small amounts of other alloying elements.
Alloy steel
Another type is alloy steel, which is created by combining carbon steel with various alloying elements, giving it unique properties. There are many types of alloy steels. Due to the wide range of alloy steels, elements can be used to create steel with almost any imaginable property. As a result, some of them are relatively expensive. They are usually more resistant to corrosion and are often the preferred choice for some car parts, pipes, boat hulls, and mechanical components.
Tool Steel
Tool steels are known for their durability, heat resistance, and scratch resistance. The name comes from the fact that they are commonly used in the manufacture of metal tools, such as hammers. They typically consist of molybdenum, vanadium, tungsten, and cobalt. It is worth noting that tool steels are
- heat resistant,
- durable
- strong.
There are 5 types of tool steel:
- Carbon steels.
- Steels for cold work.
- Steels for hot work.
- Sintered alloy steels.
- High-speed steels.
Stainless steel
Stainless steel is probably the most popular type of this material on the market. This type is shiny and generally contains about 10% to 20% chromium, which is its main alloying element. The above combination makes the steel resistant to corrosion and can be easily formed into various shapes. Due to its ease of handling, flexibility, and quality, stainless steel is used in surgical equipment, household applications, cutlery, and even as external cladding in commercial or industrial buildings.
Applications of Steel
Steel is environmentally friendly and sustainable. It is characterized by high durability. Compared to other materials, it requires very little energy to produce lightweight steel structures. Steel is the most processed material in the world and can be easily recycled. Its unique magnetic properties make it a material that can be easily detected, for example, at the bottom of water tanks. Structures made of steel are used in general engineering and manufacturing industry. It also has a wide application in the automotive industry. Various types of steel are used in the body, doors, engine, suspension, and interior of the car. On average, 50% of common car parts are made of it. Essentially, all types of energy sectors require steel for infrastructure construction and resource extraction.
Its stainless counterpart is used in offshore platforms and pipelines, but also in renewable energy sources, such as:
- solar energy,
- hydropower
- wind energy,
where certain elements are made of this material. In addition, stainless steel provides a hygienic environment, hence its use is particularly revealed in surgical implants. Most household appliances, such as refrigerators, televisions, ovens, sinks, etc. are also made of steel. Thanks to the ease of welding and aesthetic finish, steel has become a characteristic element of modern architecture. These parameters characterizing the usefulness of steel make it the most popular construction material.