40X Structural Alloy Steel

Table of contents:

40X Structural Alloy Steel
40X Structural Alloy Steel
Anonim
steel 40x
steel 40x

Of all the materials used in mechanical engineering, machine tool building, instrument making and other industrial fields, steel is the most widely used. The choice of its grades is huge, depending on its composition, any steel has certain qualities and belongs to different groups according to its indicators. Steel 40X belongs to the class of structural alloy steels.

Chemical components included in the composition

If we consider the percentage composition of the presented alloy, the number 40 means that it contains a percentage of carbon up to a value of 0.44%, the letter X - determines the presence of an alloying additive - chromium up to 1.1%. A more detailed composition of the chemical components is presented in the table below. An equivalent replacement for this grade can be alloys such as 40XH, 45X, 40XH, 40XC.

Chemical composition of steel grade 40X

Carbon, % Chrome, % Silicon, % Manganese, % Nickel, % Phosphorus, % Sulfur, % Copper, %
0, 36-0, 44 0, 8-1, 1 0, 17-0, 37 0, 5-0, 8 to 0, 3 to 0, 035 to 0, 3 to 0, 035

Alloyed steels are obtained by remelting or by production on fresh charge. If a charge is used, the preliminary calculation of the chromium content in it should take into account losses during smelting, but this value should not exceed the parameter 0.4%, otherwise high-alloyed waste will be obtained in the process. Metal refining with alloying elements is carried out with strong deoxidizers, after which slag treated with carbon and silicon is introduced. After exposure to reducing slag, the structural steel deoxidizes well, which ensures good hardening.

Heat treatment

steel 40x characteristics
steel 40x characteristics

For 40X steel, the heat treatment sequence is as follows. First, quenching is carried out in an oil medium, and then tempering in oil or in air. For each part, its own heat treatment mode is selected, it depends on the loads in which this part is used, since different modes give different hardness of the product. The heat treatment mode is calculated depending on the critical points, reaching which the material undergoes physical and chemical changes and changes its properties and characteristics. Steel 40X has the following critical points: Ac1=743, Ar1=693 Ac3=782, Ar3=730. Hardening is carried out at a temperature of 860 ºС, the medium is oil, the hourly interval is 4 hours. Then a low tempering is performed at a temperature of 200 ºС in air, or a temperature parameter of 500 ºС can be applied and processed in an oil medium. After such a heat treatment mode, the following strength of steel HB - 217 and HRC - 45 is achieved.

Quality indicators

A strong and hard material that can withstand heavy loads and not be destroyed - this is how you can evaluate steel 40X. Characteristics she possesses:

  • good corrosion properties;
  • resistant to temperature fluctuations;
  • high strength performance;
  • aesthetic qualities.

But in addition to positive indicators, 40X steel also has negative properties. These include:

  • prone to flocculation;
  • temper brittleness;
  • poor weldability.

Flockenosensitivity

internal defects
internal defects

This is a defect that occurs during accelerated cooling of the alloy after casting, in the form of internal cracks. It can occur during hot deformation of alloy steel. It can also appear on the surface in the form of clear areas of an oval or zigzag shape. The formation of this defect can occur due to an excess of hydrogen evolution during heat treatment. This disadvantage can be overcome with the help of high-temperature heat treatment and an optimal cooling regime. You can also use the alloy vacuumization method, which will help reduce the percentage of hydrogen.

Temper brittleness

Occurs during the slow cooling of alloyed structural steels after tempering, it is caused by a sharp decrease in viscosity. For comparison, the viscosity value can drop by 5-10 times compared to the same indicator when the steel is rapidly cooled. Slow cooling affects only the impact strength, it does not lower the other characteristics of the steel. Cooling too quickly can cause internal stresses that can cause the product to warp.

steel 40
steel 40

Welding difficulties

Steel 40X belongs to the fourth group in terms of weldability. Welding seams can lead to cracking. The manifestation of these defects can be reduced by preheating. Edge preparation is also required. You can perform welding work of this brand by arc welding: manual or electroslag, you can also use contact welding. After contact-point, additional heat treatment is required. For manual welding, special electrodes for alloyed steels E85 UONI-13/85 are used. The type and position of the welded seam can be any.

Scope of application

steel products 40x
steel products 40x

This steel grade has a number of properties due to which it covers a fairly wide range of applications. It is used to make billets of sectional and shaped rolled metal products of various profiles, as well as to produce sheets, pipes, forgings obtained by forging. Apply such rolled metal for cutting tools. Steel 40, which has not been heat treated, is very advantageous to use for non-working tail parts - tap bodies, nozzles, reamers.

Improved alloy, obtained under the influence of heat treatment, which we reviewed earlier, is used for critical structures. These include: gear rims, shafts, axles, bushings, bolts, plungers. This brand has found its application in structures that are operated at low temperatures in the open air, it is used in the northern latitudes for the arrangement of railway and road bridges.

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