Broadly speaking, heat treatment is the method of heating, holding and cooling the solid metal to change its internal organization, so as to obtain the required mechanical properties and the use of performance of the process. Almost all cold, warm and hot forgings are to become qualified parts through heat treatment, heat treatment technology level on the performance, accuracy, stability and service life of the parts to ensure and improve the decisive role; at the same time, forging raw materials, heating, forging process and cooling also affect the quality of heat treatment of forgings, the two are closely related and inseparable.
Heat treatment of metals is a process of obtaining desired properties through internal tissue transformation, i.e. phase change or tissue adjustment, which is the basis of heat treatment and the basis on which metals can change their properties through heat treatment. Heating, holding and cooling are the organizational means to induce phase change in steel to obtain the desired properties, so the main technologies are heating, holding and cooling.
According to the different heating temperature range and cooling rate, the overall heat treatment process of steel parts is divided into annealing, normalizing, quenching and tempering, commonly known as the "four fires". Since tempering is mainly used to adjust the quenching organization and the corresponding performance (hardness, etc.), the two are often used together, known as "quenching and tempering", in which quenching plus high temperature tempering is also known as quenching and tempering heat treatment.
Forging organizational state after forging, for iron and steel materials, due to forging, forming, through the heating, deformation and cooling process, forgings due to material composition and the size of forgings and presents a different organizational state, summarized in the following two points:
This type of forging is mainly used to roll the billet die forging profiles, the sub-condensitic steel (medium carbon steel, medium carbon low-alloy structural steel), the final forging after air cooling to room temperature, generally get coarse massive ferrite and laminated pearlite organization; on the over-condensitic steel, especially high-carbon high-alloy steel, final forging after slow cooling, generally get more coarse annealed state organization. Also due to the shape of the forging cross-sectional differences and uncontrollable cooling, its organization is often uneven, at the same time, due to temperature stress (also known as thermal stress) and the role of organizational stress, forgings will produce residual internal stress, so it is necessary to adopt heat treatment technology to improve and eliminate.
The free forgings produced in 10MN forging hydraulic press (shaft parts greater than 5t, disk parts greater than 2t) - generally known as large forgings, such forgings are generally forged directly using ingots to form. Due to the forging, the number of heating (6 fire or more), uneven deformation, cross-sectional differences, high degree of material alloying, large forgings organization is the most prominent feature of the high residual hydrogen content, organization of serious degree of non-uniformity exists (mixed crystal phenomenon), which is an important factor affecting the performance of large forgings, and therefore is also the heat treatment technology design of large forgings need to focus on solving the problem.
The above information is provided by forging supplier.
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