SU1678861A1 - Method for thermo-mechanical treatment of steel - Google Patents

Abstract

The invention relates to metallurgy and can be used in the development of advanced technology for hardening steel, mainly low-alloyed thickness of 15-100 mm. The goal is to increase the mechanical properties by grinding the structure. The method includes preliminary deformation before cooling the workpiece and multistage deformation carried out in two passes with a pause between them less than 5 s. Each stage is repeated 3-4 times, cooling between stages 30 50 ° C . The first stage is carried out at a temperature Agz (d) - (30-40 ° C), the first passage of the last stage is at a temperature Aci (g) (30-40) ° C, and the second pass at a temperature of not less than An (d). 1 tab.

Description

The invention relates to metallurgy, in particular, to the technology of thermomechanical treatment of steels, mainly low alloyed thickness of 15-100 mm.

The aim of the invention is to increase the mechanical properties by grinding the structure,

The method of thermomechanical processing includes heating the workpiece, rough rolling, pressing to thermoplastic processing temperature, and thermoplastic processing in several cycles, including a multi-stage deformation with compression between stages. Each stage of deformation during thermoplastic processing is carried out in two passes, with the first stage being carried out at a temperature Agz (d) - 30–40 ° C, and between the stages (only 3-4 stages), the blank is dried at 30–50 ° C. . A pause between two passes in each stage is set to not more than 5 seconds, with the first pass in the last stage being

at a temperature of Aci (g) - (30-40 ° C), the temperature of the end of the last stage is chosen not lower than An (d)

The designation of critical points with the sign (d), for example Aci (g), corresponds to the dynamic positions of these points that have changed their positions under the action of deformation.

The combination of all these actions is the main method of achieving the goal. In this case, conditions are created in the metal for the passage of multiple phase c &} recrystallizations, in particular in the inner layers x due to their heating due to the heat of plastic deformation and cooling in the pauses between the two paired passages, and in the outer layers due to the cooling effect. t tool during deformation and heat by heat transfer from the inside in the pauses between the aisles.

Such fluctuations in temperature, reaching 35-40 ° C in the interior, as in .fi "c.

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The result of the summation of heat from two passes in each stage, and 100–200 ° C in the outer layers, during rolling in a predetermined temperature range, makes it possible to develop from stage to stage multiple phase transformations, which leads to phase hardening. The passage of phase transformations under the conditions of external plastic deformation creates favorable conditions for the refinement of the structure.

At the first stage, during processing by the proposed method, hot deformation of austenite leads to a sharp increase in structural defects, in particular, dislocations. This increases the thermodynamic potential and shifts the point Agz to the position Agz (e). Immediately in the regions of the metal with a temperature below Arg (e), the y, a-transformation will begin. The presence of a dislocation in the y-phase increases the likelihood of nucleation of the a-phase. After the first stage, there is a pause during which the temperature of the workpiece decreases. In this case, due to the deformation bands in the y-phase, and, consequently, due to the increased value of the nucleation sites, fine A-fzz is formed. During the pause, unresolved austenite is only partially relieved of lattice defects due to the processes of polygonization.

Before the second stage, the structure is austenite with a certain number of small, but thermodynamically stable a-phase centers. The deformation of ferrite in the second stage increases the thermodynamic potential and, accordingly, reduces Aci to Aci (g). Increasing the temperature due to the heat of plastic deformation allows most of the deformed its phase (with the substructure) to be turned back into a fine-grained phase. However, new portions of the γ phase will form in other parts of the forming structure. Repetition of the described cycles allows to involve in the process of phase transformations all new and new volumes of the metal. This leads to phase dispersion, an increase in the interphase, intergranular, and subgrain boundaries, which facilitates the yi accelerates the subsequent phase transformations.

Thus, in addition to grinding the structure at the micro level, grinding also occurs at the submicroscopic level, namely, fragmentation and polygonization of ferritic grains. This becomes possible due to the fact that during processing the temperature of the workpiece before each new stage of deformation decreases, which leads to the formation of new portions of ferrite, which is then immediately subjected to plastic deformation. So by the end

processing the entire volume of the low-temperature phase is shredded. This is evidenced by experiments involving electron microscopy.

Boosting between stages at 300–50 ° C is necessary from the point of view of nucleation during the cooling period of the optimum amount of the low-temperature phase and depends on the intercritical range of the steel;

5 temperature holding last.

The pause between the two paired passages in the stage should be minimal (not more than 5 s) and determined by the design and speed features of the rolling,

0 as well as the size of the processed product. During this time (5 s), it does not have time to imbibe the warm-up from the previous pass, and thus the heat release in two passes, folding, gives the necessary (up to

5 35-40 ° C) temperature rise in the inner layers of the workpiece.

The final stage of deformation should be carried out at a temperature not lower than An (e) with the condition that the temperature rise does not exceed Aci (g), and the first pass in this stage at Aci (g) temperature - (30-40 ° C). In this case, all the generated grain a-phase will have a substructure. If a

5, the first pass at the final stage is carried out at Aci (g) - 40 ° C, then it is possible to rivet a part of the ferrite, which will not undergo transformations and thereby adversely affect the coplastic properties in case of deformation at Aci (g) - 30 ° C, as a result of the reverse (y-a) transformation, part of the ferrite will not have a subgrain structure and the maximum possible strengthening effect will not reach 5.

Example. Processing ingots weighing 20 tons of steel 10HSND (Agz (d) for steels 10HSND 840 ° C, h An (g) 730 ° C, Aci (g) 740 ° CO carried out on the proposed and well-known

0 ways. The ingots are heated by rolling, then rough rolling is carried out on a plate-type rolling mill 3600, after which it is forced to a temperature Agz (d) - 30–40 ° C and in the finishing mill stand

5 3500 multistep rolling, consisting of 3-4 stages, for a thickness of 35 mm. Each stage includes two passes with intervals between passes not exceeding 5 seconds. After each stage, the peal is cooled at 30-50 ° C. With

Thereby, the first pass in the last stage is carried out at Aci (g) -30-40 ° C, and the end-stage temperature of the last stage is set no lower than An (e).

Processing modes, structure characteristics and properties are listed in the table.

The advantages of the proposed thermomechanical treatment method in comparison with the known method are that it crushes the subgrain structure more than three times, increases the temporary tensile strength by 7-8%, the yield strength by 15-17% and the impact strength at 40 ° С 45-50%.

Claims (1)

Invention Formula Method of thermomechanical processing of steel, mainly low-alloyed0 five 15-100 mm thick. including heating the workpiece, cooling to a predetermined temperature and plastic multistage deformation with intensification between stages, characterized in that, in order to improve the mechanical properties by grinding the structure, before cooling the preform is deformed, each deformation stage is carried out in two passes with a pause between them less than 5 s, the number of stages is set within 3-4, the cooling between stages leads to 30-50 ° C, the first stage being carried out at Agz (d) - (30-40 ° C), the first pass of the last herd and - if Aci (g) - (30-40 ° C) and its second pass - at a temperature not less An (g). The number 8 is the number of passes.