Steel: properties, markings, GOST standards, and types of steel

Steel, as one of the most common metals, has received the widest application today. Processing and cutting This material is a task that can be solved using a wide variety of tools and technologies. Properties of steel allow for precise and high-speed processing using the following types of processing:

• mechanical cutting;
• waterjet;
• argon-arc;
• electric arc;
• gas;
• plasma;
• laser.

Depending on steel grades and the required results, use the most appropriate metal processing technology.

Properties of steel

There are 4 main areas of performance that distinguish steel and its alloys.

Among these areas:

• chemical properties of steel;
• technological;
• mechanical properties of steel;
• magnetic properties of steel.

Now let's talk about each one in more detail.

Chemical properties of steel

• Oxidizability. This is a measure of the ability to combine with oxygen. Oxidation increases with increasing metal temperature. Low-carbon steels oxidize to form rust (iron oxides) when exposed to water or moist air;
• Corrosion resistance. Accordingly, this means that the substance does not undergo chemical reactions and does not oxidize. However, it is important to note that this property is not found in all steel alloys and is more characteristic of exceptional grades;
• Heat resistance. Heat resistance characterizes the ability of a material not to oxidize under the influence of high temperatures and not to form scale;
• Heat resistance. Heat resistance determines an alloy's ability to maintain its strength at high temperatures. This allows steel to be used in the creation of components and mechanisms subject to thermal stress.

Technological properties of steel

The technological properties of steel reflect the ability of a metal or alloy to undergo various types of processing. These include:

• Machinability. All steels are quite easy to machine, both by hand (with a hacksaw, chisel, or file) and on machine tools (drilling, turning, or milling).
• Malleability. This property is taken into account during rolling, forging, and stamping. Steel exhibits fairly good malleability when heated.
• Weldability. This process is applicable to all types of steel.
• Flowability. This property is essential for producing semi-finished products—castings that resemble finished parts and require only minor further machining.
• Hardenability. Hardenability depends on the size of the parts and products, as well as the chemical composition of the steel. To increase hardenability, alloying components such as chromium and tungsten are added to the steel.
• Wear resistance. To increase wear resistance, friction parts (gear teeth) are subjected to heat treatment (hardening) and chemical-thermal treatment (carburizing, nitriding). Alloying elements such as manganese and silicon are added to the steel for the same purpose.
• Corrosion resistance. To increase this resistance, nickel, chromium, and titanium are added to steel, producing so-called stainless steels.

Mechanical properties of steel

• Strength. The ability of a metal to withstand significant external loads. This property is characterized by its yield strength and tensile strength.
  • Tensile strength. The maximum mechanical stress above which steel fails.
  • Yield strength. This parameter shows the mechanical stress above which the material continues to elongate under no load conditions.
• Plastic. The ability to change shape under load and maintain it when unloaded. It is quantified by relative elongation and bending angle;
• Impact toughness. The ability of a metal to resist dynamic loads. This characteristic is quantitatively assessed by the work required to fracture the specimen, divided by its cross-sectional area;
• Hardness. The ability to resist the impact of solid objects. Quantitatively characterized by the load per area of the indentation when pressed with a diamond pyramid (Vickers method) or a steel ball (Brinell method).

Magnetic properties of steel

As is known, almost all steels (except some stainless steels) are magnetic.

It is worth saying right away that stainless steel is actually magnetic.

Not all stainless steel is magnetic, but it is still magnetic. There's no definitive statement, as the magnetic properties of alloys are determined by the properties of their structural components. Therefore, one type of stainless steel may successfully attract a magnet, while another is completely indifferent. So, how does it work?

It's all about the structural composition.

Martensite, from the point of view of magnetic properties, is a pure ferromagnet.

Ferrite can have two modifications. At temperatures below the Curie point, it, like martensite, is ferromagnetic. High-temperature delta ferrite is paramagnetic.

Thus, corrosion-resistant steels whose structure consists of martensite are magnetic stainless steels. These alloys react to a magnet like ordinary carbon steel. Ferritic or ferritic-martensitic steels can have different properties depending on the ratio of their phase components, but they are most often ferromagnetic.

As a result, chromium and some chromium-nickel stainless steel alloys are considered magnetic.

Non-magnetic alloys include chromium-nickel and chromium-manganese-nickel steels.

It's quite easy to determine whether the steel you're dealing with is genuine stainless steel. Clean the surface until it shines and then apply and rub in two or three drops of a concentrated copper sulfate solution. If the copper coating shows through (the sulfate becomes a copper coating), it's not stainless steel. If there's no change or impact, you're dealing with genuine stainless steel.

It is important to note that it is impossible to determine at home whether stainless steel is food grade.

Therefore, you should not use untested metals for kitchen utensils.

A little more about the properties of steels

The widespread use of metal is due to a number of advantageous characteristics. Among them are the following: properties of steel:

• Specific heat capacity at 20 °C: 462 J/(kg °C) (110 cal/(kg °C));
• Density: 7700-7900 kg/m³;
• Melting point: 1450-1520 °C;
• Specific gravity: 75500-77500 N/m³ (7700-7900 kgf/m³ in the MKGSS system);
• Specific heat of fusion: 84 kJ/kg (20 kcal/kg, 23 W h/kg);
• The thermal conductivity coefficient varies depending on the type of steel and impurities in its composition and can range from 15.5 W/(m K) to 54.4 W/(m K);
• The coefficient of thermal linear expansion is within the range of 11.9 · 10^-6 1/⁰From 11.0 to 10^-6 1/⁰C and depends on the brand and additional components of the alloy.

The tensile strength is determined for each type of steel separately and has the following indicators, given below:

• Structural 373-412 MPa;
• Silicon-chromium-manganese, used in the production of tools 1.52 GPa;
• Carbon engineering 314-785 MPa;
• Rail 690-785 MPa.

The properties of the material also change depending on the carbon content. The following exist types of steel:

• low carbon (less than 0.25% carbon);
• medium carbon (0.3 – 0.55% carbon);
• high-carbon (0.6 – 2% carbon).

To increase the steel's usability, alloying is performed—the addition of metals to the molten steel alters the alloy's properties (increasing mechanical strength, electrical conductivity, corrosion resistance, and magnetic and thermal conductivity). Molybdenum, aluminum, chromium, nickel, and a number of others are used as alloying metals. The following are distinguished: types of steel alloyed:

• Low-alloy – inclusions of alloying metals no more than 4%;
• Medium alloyed – alloying metals make up no more than 11% inclusions;
• High-alloy – more than 11%.

Steel grades

Steel marking according to GOST is produced by letter designation. Thanks to the orderliness of the designation rules, it is possible to know and read steel markings It's not a difficult task with such designations. There are a number of established designations that are used marking steel By GOST:

• H – nickel;
• M – molybdenum;
• T – titanium;
• X – chrome;
• K – cobalt;
• B – tungsten;
• T – titanium;
• D – copper;
• G – manganese;
• C – silicon;
• F – vanadium;
• R – boron;
• A – nitrogen;
• B – niobium;
• E – selenium;
• C – zirconium;
• U – aluminum;
• Ч – means the presence of rare earth metals.

To designate different types depending on the composition and purpose of the steel, the following series of letter designations are used:

• PS – semi-calm;
• KP – boiling;
• SP – calm.

Accordingly, by seeing the aforementioned designations in the alloy marking, we can determine its composition and understand what kind of material we have in front of us.

A good help would be the steel marking table