RU2643119C2 - Method of deformation-thermal processing of high-manganese steel - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: preliminary deformation-thermal processing is carried out, including diffusion annealing of the ingots with the plasticity effect induced by twin formation in the furnace at a temperature of 1150°C for 4 hours, forging at a temperature of 1150°C to the total absolute degree of deformation ε= 1 followed by diffusion annealing in the furnace at a temperature of 1150°C for 4 hours. Further, the forging is hot rolled in a temperature range from 500 to 1150°C in 5 passes with a total absolute degree of deformation ε not less than 1.5, followed by diffusion annealing for 1 hour at a temperature of 1150°C. After that, high-manganese steel with the TWIP effect is subjected to bilateral forging under conditions of warm deformation at a temperature of 400°C to the absolute degree of deformation ε= 3. The invention may be applicable for manufacturing damper elements of seismic resistant structures.

EFFECT: obtaining high damping properties.

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Description

The invention relates to the field of metallurgy, in particular to the processing of metals by pressure, and in particular to a technology for producing blanks from austenitic steel with TWIP (Twinning Induced Plactisity) effect and can be used in the manufacture of damper elements of earthquake-resistant structures.

The most dangerous for technical objects are vibration effects. Alternating stresses caused by vibration influences lead to the accumulation of damage in the material, which causes the appearance of fatigue cracks and leads to failure. Ways to increase fatigue strength can be divided into technological and structural.

Structural methods are associated with imparting to parts so-called streamlined (smoothed) shapes that contribute to lower stress concentrations and therefore are favorable for fatigue strength.

Technological methods are aimed at the formation of the microstructure of materials with increased resistance to fatigue failure. Today, one of the most common ways to increase fatigue strength is deformation-heat treatment (DTO). DTO leads to an increase in hardness, yield strength and temporary tensile strength. In addition, methods of surface hardening of parts are used: bead-blasting and centrifugal-ball processing, roller processing, chasing. It has been established that hardening of the surface layer of parts by plastic deformation leads to a significant increase in the durability of machine parts not only under normal fatigue, but also in aggressive environments; in addition, surface hardening helps to increase the wear resistance of rubbing surfaces.

The most common and effective types of heat treatment aimed at increasing fatigue strength are surface hardening with low tempering and chemical-thermal treatment. Surface hardening consists in heating (with a gas flame, high-frequency currents, irradiation) a thin surface layer to the temperature of formation of austenite in it and subsequent rapid cooling. As a result of structural changes in the surface layer, large residual stresses arise due to the formation of structures with a large specific volume in the surface layer. In addition to increasing fatigue strength, the wear resistance of working surfaces is significantly increased by increasing their hardness [A.P. Zhilyaev, I. Shakhova, A. Belyakov, R. Kaibyshev, T.G. Langdon, Wear resistance and electroconductivity in copper processed by severe plastic deformation, Wear. 305 (2013) 89–99. doi: 10.1016 / j.wear.2013.06.001; D.-Z. Li, Y.-H. Wei, L.-F. Hou, W.-M. Lin, Microstructural Evolution of Surface Layer of TWIP Steel Deformed by Mechanical Attrition Treatment, J. Iron Steel Res. Int. 19 (2012) 38–46].

Steel with the TWIP effect during plastic deformation demonstrate the formation of nanoscale strain twins (the thickness of twin plates is 20-50 nm). The formation of a large number of twin boundaries creates obstacles to the movement of dislocations. In addition, the formation of the boundaries of deformation twins leads to an increase in the dislocation density to high values, up to 2..4 × 10 ¹⁵ m ^-2 . In addition, the formation of a large number of high-angle boundaries of deformation twins leads to a refinement of the structure to nanoscale values (less than 100 nm) [O. Bouaziz, S. Allain, CP Scott, P. Cugy, D. Barbier, High manganese austenitic twinning induced plasticity steels: A review of the microstructure properties relationships, Curr. Opin. Solid State Mater. Sci. 15 (2011) 141–168; O. Bouaziz, Strain-hardening of twinning-induced plasticity steels, Scr. Mater. 66 (2012) 982-985].

A known method of producing ferritic steel having resistance to fatigue failure (US2011 / 0305595 A1, published 12/15/2011). As the basis for the invention, STPG370 steel was used. According to the invention, the steel contains 0.47% C, 0.18% Si, 0.63% Mn, 0.014% P, 0.003% S, 0.11% Cu, 0.1% Ni, 0.08% Cr. The method of deformation-heat treatment consists in forging at 1170 ° C for an hour, followed by cooling in air and then rolling at 560 ° C for 95%, after cooling in water. Additionally, annealing at 600 or 700 ° C for 1 hour with cooling in air can be applied. This achieves a fine-grained structure with a grain size of 1 micron.

The disadvantage of this method is the fatigue endurance limit of more than 10 million cycles, equal to 150 MPa, which is significantly lower than the values presented by modern requirements.

A known method of producing rolled steel having high wear resistance and resistance to fatigue failure (EP1026276 A4, published 05.08.1999). The method of deformation-heat treatment of steel having a composition, weight. %: C: 0.02-0.2; Mn, Si, Cr, Al, Ti <0.1; Ni: 0.8-3.0; Cu: 0.8-2.0; Mo: 0.4-0.7; N: 0.001-0.01; P <0.1; S <0.006, as well as iron and unavoidable impurities, consists in hot rolling after heating in the temperature range 1100 - 1300 ° C, preferably for 4.5 hours, and then hot rolling at a temperature not exceeding 950 ° C to provide an overall reduction in thickness not less than 40%. As a result of such deformation-heat treatment, steel has an endurance limit of 481 MPa.

The disadvantage of this method is the fatigue endurance limit equal to 481 MPa, which is significantly lower than the values presented by modern requirements.

Closest to the proposed invention, the method adopted for the prototype is described in the publication A.S. Hamada et al. Fatigue Behavior of Four High-Mn Twinning Induced Plasticity Effect Steels, Metallurgical and Materials Transactions A (2010) vol. 41 5, pp. 1102–1108. The method of deformation-heat treatment of steels containing manganese in an amount of from 18 to 22 weight. % from 0.3 to 0.6 wt.% carbon, as well as 0-3 wt.% aluminum, 0-3 wt.% silicon and niobium, consisted in the fact that all steels were obtained by casting, hot rolling, homogenization annealing, followed by cold rolling and another annealing at a temperature of 1000 ° C for 5 minutes. After that, the steels had an equiaxed fully austenitic structure with an average grain size of about 35 microns. The publication demonstrated the fatigue properties of four high manganese austenitic steels. In this study, it was shown that all steels, regardless of chemical composition, demonstrate a fatigue endurance limit of more than 10 million cycles at stresses of 400 MPa. Moreover, the mechanical properties of all steels are: conditional yield strength in the region of 270-350 MPa, temporary tensile strength from 810 to 930 MPa, elongation at break of about 95% for all four steels.

The disadvantage of this method is that obtaining steel billets in this way provides high ductility values, but does not provide high values of tensile strength and fatigue resistance tests. The fatigue endurance limit of more than 10 million cycles, equal to 400 MPa, is significantly lower than the values imposed by modern requirements.

The objective of the invention is to develop a method of deformation-heat treatment of high manganese steel with the effect of plasticity induced by twinning to obtain high damping properties containing manganese, carbon and aluminum in the chemical composition.

The problem is solved by the proposed method of deformation-heat treatment of high manganese austenitic steel with the effect of plasticity induced by twinning with a manganese content of at least 15 weight. %, aluminum, not less than 1.5 weight. %, carbon content of not less than 0.3% in such quantities that the energy of steel packaging defects lies in the range from 20 to 40 mJ / m ² , which includes: casting, hot rolling, homogenization annealing, and also hot forging as a preliminary deformation-heat treatment as well as double-sided warm multiple forging as the main deformation-heat treatment and quenching in water. At such energies of packing defects, the effect of plasticity induced by twinning is realized, as a result of which deformation twins are formed upon deformation [O. Bouaziz, S. Allain, CP Scott, P. Cugy, D. Barbier, High manganese austenitic twinning induced plasticity steels: A review of the microstructure properties relationships, Curr. Opin. Solid State Mater. Sci. 15 (2011) 141–168]. In this case, the preliminary deformation-thermal treatment consists in homogenizing annealing in the temperature range 950–1150 ° С for 2–8 h, repeated forging in the temperature range 950–1150 ° С. The total true degree of deformation after forging should be at least ε = 1.2. After reaching the required degree of deformation, the material is subjected to homogenization annealing in the temperature range 950–1150 ° С for 2–8 h, followed by repeated hot rolling in the temperature range from 500 to 1150 ° С, the total true degree of deformation is not less than ε = 2. At the final stages of preliminary deformation-heat treatment of high-manganese steel with the effect of plasticity induced by twinning, are annealed in the temperature range from 950 - 1150 ° C for 1 - 2 hours to obtain equiaxed single-phase ACS shadow structure. Next, the workpiece is subjected to double-sided forging under conditions of warm deformation at a temperature of 400-600 ° C with a true degree of deformation per pass of at least ε = 0.5 to a total true degree of deformation of at least ε = 3, followed by quenching in water.

The technical result is that:

- bilateral forging under conditions of warm deformation with a total deformation of ε = 3 at a temperature of 400-600 ° C leads to intense strain hardening due to twinning and dislocation slip;

- increased forging temperature (400-600 ° C) leads to dynamic return processes, as a result of which high-manganese steel with the effect of ductility induced by twinning has a ductility margin after double-sided warm forging;

- intensive strain hardening due to twinning and dislocation glide leads to a significant increase in the damping properties of high manganese steel with the effect of plasticity induced by twinning.

Examples of implementation

Example 1. An ingot of high manganese austenitic steel with a twin-induced ductility effect of the nominal chemical composition Fe-0.6% C-18% Mn-1.5% Al was subjected to preliminary heat-treatment. Initially, the starting material in the cast state in the form of an ingot with dimensions of 140x140x140 mm ³ was subjected to homogenization annealing in a furnace at a temperature of 1150 ° C for 4 hours. Then this ingot was forged at a temperature of 1150 ° C in three steps: 140 mm → 100 mm, 100 mm → 70 mm, 70 mm → 50 mm, the total true degree of deformation was ε = 1. After that, high manganese steel was repeatedly subjected to homogenization annealing in a furnace at a temperature of 1150 ° C for 4 hours. Next, the forging was subjected to hot rolling in the temperature range from 500 to 1150 ° C 5 passes with the following change in height: 1) 50 mm → 34 mm, 2) 34 mm → 25 mm, 3) 25 mm → 17 mm, 4) 17 mm → 13 mm, 5) 13 mm → 10 mm, while the total the true degree of deformation was ε = 1.6. When passing through the rolls, the high manganese steel was not subjected to reheating. After rolling, the steel was annealed for 1 hour at a temperature of 1150 ° C. After that, high-manganese steel with the effect of plasticity induced by twinning was subjected to double-sided forging under conditions of warm deformation at a temperature of 400 ° C to the true degree of deformation ε = 3. As a result, the steel has an increased fatigue endurance limit of 600 MPa based on 10 million cycles.

This example is characterized by the following graphic materials:

Figure 1 is a diagram of the deformation-heat treatment of high manganese steel with the effect of ductility induced by twinning. Here ε is the true degree of deformation.

Figure 2 - Curve of the dependence of the number of cycles before the destruction of high manganese steel subjected to thermomechanical processing in the form of two-sided forging at a temperature of 400 ° C to the true degree of deformation ε = 3, on the applied stress.

Example 2. An ingot of high manganese austenitic steel with a twin-induced ductility effect of the nominal chemical composition Fe-0.6% C-18% Mn-1.5% Al was subjected to preliminary deformation-heat treatment. Initially, the starting material in the cast state in the form of an ingot with dimensions of 140x140x140 mm ³ was subjected to homogenization annealing in a furnace at a temperature of 1150 ° C for 4 hours. Then this ingot was forged at a temperature of 1150 ° C in three steps: 140 mm → 100 mm, 100 mm → 70 mm, 70 mm → 50 mm, the total true degree of deformation was ε = 1. After that, high manganese steel was repeatedly subjected to homogenization annealing in a furnace at a temperature of 1150 ° C for 4 hours. Next, the forging was subjected to hot rolling in the temperature range from 500 to 1150 ° C in 5 passes with the following change in height: 1) 50 mm → 34 mm, 2) 34 mm → 25 mm, 3) 25 mm → 17 mm, 4) 17 mm → 13 mm, 5) 13 mm → 10 mm, while the total the true degree of deformation was ε = 1.6. When passing through the rolls, the high manganese steel was not subjected to reheating. After rolling, the steel was annealed for 1 hour at a temperature of 1150 ° C. After that, high-manganese steel with the TWIP effect was subjected to double-sided forging under conditions of warm deformation at a temperature of 600 ° C to a true degree of deformation ε = 3. As a result, the steel has an increased fatigue strength of 600 MPa based on 10 million cycles.

Thus, the task of developing a new method of deformation-heat treatment of high manganese steel to obtain high damping properties has been completed. The proposed processing method leads to the production of high manganese steel, characterized by increased fatigue resistance, which can be used in the manufacture of damper elements of earthquake-resistant structures.

Claims (4)

1. The method of deformation-heat treatment of billets of high manganese steel, including obtaining an ingot of steel containing manganese, aluminum, carbon with the effect of plasticity induced by twinning, homogenization annealing and hot rolling, characterized in that the ingot is sized 140 × 140 × 140 mm ³ , the ingot is homogenized annealed in an oven at a temperature of 950–1150 ° C for 2–8 h, then at this temperature, multiple hot forging is carried out with a total true degree of deformation of at least ε = 1.2 in three steps Yen: 140 mm → 100 mm, 100 mm → 70 mm, 70 mm → 50 mm, the resulting forgings are subjected to repeated homogenization annealing in an oven at a temperature of 950-1150 ° C for 2-8 hours and subsequent hot rolling in the temperature range from 500 to 1150 ° C in 5 passes with a total true degree of deformation of at least ε = 2, while after hot rolling, homogenization annealing is carried out for 1-2 hours at a temperature of 950-1150 ° C, and then bilateral forging under conditions of warm deformation at a temperature 400-600 ° C to a true degree of deformation of at least ε = 3. 2. The method according to p. 1, characterized in that the two-way forging is carried out in the temperature range from 400 to 600 ° C, followed by cooling in water. 3. The method according to p. 1, characterized in that the bilateral forging is carried out in the temperature range from 400 to 600 ° C, followed by cooling in oil. 4. The method according to p. 1, characterized in that the bilateral forging is carried out in the temperature range from 400 to 600 ° C, followed by cooling in air.

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