The 40Х round after heat treatment allows achieving an optimal combination of strength, elasticity, and plasticity of the material. Forgings from this alloy, hardened in oil at a temperature of +860°C and then tempered in the range of +500 – +800°C, demonstrate excellent operational characteristics.
Hardening of steel rod 40Х
It is advisable to order a 40Х round after hardening to increase its hardness and wear resistance. The process involves heating the metal to a temperature of 840-880°C followed by rapid cooling in water or oil.
As a result of this process, martensite is formed in the steel structure – a very hard and strong metastable microstructure. The hardened 40Х round has significantly better mechanical properties of steel, but makes it more brittle, so tempering is essential after hardening.
The hardening process of products made from steel rod 40Х includes the following stages:
The workpiece is placed in an electric furnace, where the holding time depends on the diameter of the rod (from a few minutes to over 20 minutes for large cross-sections), to ensure the necessary characteristics of austenitization, i.e., heating the steel to a temperature above the critical point, at which its structure transforms into austenite.
The heated product is quickly immersed in an oil bath for rapid cooling to fix the necessary internal structural changes.
A properly performed hardening procedure involves uniform heating of the rolled metal, the heating color changes from cherry to bright yellow depending on the temperature, which is only a visual guide for controlling the process.
It is recommended to buy hardened steel round 40Х for parts where strength and long service life of the finished product under constant load are priority indicators.
Tempering and normalization of rod steel 40Х
It is worth buying a 40Х round that has been tempered after hardening to reduce brittleness and increase the plasticity of the steel. As a result of such manipulations, internal stresses in the metal are relieved, improving impact toughness and other mechanical properties of the steel.
There are three main types of tempering:
low-temperature tempering (150-250°C) – used to reduce internal stresses and increase toughness; this tempering minimally reduces the hardness of the steel;
medium-temperature tempering (350-500°C) – used to improve the balance between hardness and plasticity, helps stabilize the martensite structure and reduce its brittleness;
high-temperature tempering (500–650°C) – leads to a noticeable reduction in hardness while simultaneously increasing the impact toughness and plasticity of the metal; this method is often used for producing parts that are frequently subjected to impact loads.
Normalization is another important heat treatment process that affects not only the price of the 40Х round but also aims to improve the structures and mechanical properties of the steel. In the normalization process, the metal is heated to a high temperature, held, and then cooled in air. This process ensures a uniform distribution of carbon and alloying elements in the steel structure, improving its strength and forming a more uniform structure.
Tempering and normalization of steel are critically important heat treatment processes, as these methods of influencing steel ensure high quality of final products, as well as improve their reliability and durability in operation.
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