A method for improving plastic deformation of a dual-phase TRIP steel

Abstract

The application belongs to the technical field of steel plastic deformation, and discloses a plastic deformation improvement method for dual-phase TRIP steel, wherein pulse current treatment is performed on the TRIP steel with austenite and ferrite during deformation, the pulse current parameters are as follows: frequency 1-200 Hz, pulse width 20 mu s-1 ms, duty cycle 0.02%-5%, and peak current density 1-100 A / mm 2 The application reduces the austenite dislocation density by applying pulse current during deformation, improves stress concentration at the grain boundary by promoting cross-slip of ferrite, and further slows down the rate of austenite to martensite transformation during deformation.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of plastic deformation of steel, and relates to a plastic deformation treatment of dual-phase TRIP steel, in particular to a method for improving forming performance by applying a pulse current during the deformation process of dual-phase TRIP steel. BACKGROUND

[0002] The TRIP effect refers to the martensitic transformation of metastable austenite during the deformation process, which plays a role in improving the strength and plasticity. The TRIP effect is an important means for TRIP steel to improve the plastic deformation capacity, including medium-manganese steel, Q&P steel and other third-generation advanced automobile high-strength steel. Compared with the second-generation advanced high-strength steel, it has excellent mechanical properties, and its suitable alloy content is more reasonable in cost than the second-generation advanced high-strength steel. The mechanical properties of TRIP steel can be improved by adjusting the austenite stability through composition design and improved heat treatment process. At the same time, the TRIP effect is also affected by the deformation temperature. Within 0-200℃, the plasticity decreases with the increase of temperature, and the plastic deformation capacity of TRIP steel containing Al is more obviously affected by the temperature.

[0003] Current-assisted plastic forming is to apply current to the metal during the plastic forming process of the material, based on the Joule heating effect, skin effect, magnetostriction effect, etc., to improve the plasticity of the material and ensure that the material can be formed efficiently and with high quality. For dual-phase TRIP steel, there are three mechanisms of dislocation slip, phase-induced plasticity and twinning-induced plasticity during plastic deformation. How to consider multiple mechanisms and improve the plastic forming capacity of dual-phase TRIP steel is one of the key technical problems in the research of current-assisted plastic forming. SUMMARY

[0004] The present application aims to provide a dual-phase TRIP steel plastic deformation improvement method, which applies a pulse current during the deformation process of dual-phase TRIP steel, reduces the austenite dislocation density through the direct action of electrons and atoms and the action of electron wind force, promotes the cross-slip of ferrite to improve the stress concentration at the grain boundary, and thus slows down the rate of austenite to martensite transformation during the deformation process, thereby affecting the plastic deformation mechanism to improve the plasticity of dual-phase TRIP steel.

[0005] The dual-phase TRIP steel plastic deformation improvement method provided by the present application applies a pulse current during the deformation process of TRIP steel with austenite and ferrite, and the pulse current parameters are as follows: frequency 1-200Hz, pulse width 20μs-1ms, duty cycle 0.02%-5%, and peak current density 1-100A / mm 2The present application reduces the austenite dislocation density by applying pulse current during deformation, and improves the stress concentration at the grain boundary by promoting the cross slip of ferrite, thereby slowing down the rate of austenite to martensite transformation during deformation.

[0006] The above-mentioned method for improving the plastic deformation of dual-phase TRIP steel, the TRIP steel is a steel with a metastable austenite structure and a ferrite structure, specifically, the dual-phase TRIP steel is medium manganese steel, Q&P steel or dual-phase stainless steel, etc. The steel is prone to deformation-induced martensitic transformation during deformation. In this process, the electric effect slows down the rate of deformation-induced martensitic transformation, thereby significantly enhancing the plastic deformation ability under the same temperature tensile conditions.

[0007] The above-mentioned method for improving the plastic deformation of dual-phase TRIP steel, the pulse current parameters are preferably frequency 20-200Hz, pulse width 100μs-1ms, duty cycle 1%-4%, peak current density 10-30A / mm 2 .

[0008] The above-mentioned method for improving the plastic deformation of dual-phase TRIP steel, during the pulse treatment of the TRIP steel, the surface temperature of the TRIP steel is 0-200℃; in the preferred implementation, the surface temperature of the TRIP steel is 25-100℃.

[0009] The above-mentioned method for improving the plastic deformation of dual-phase TRIP steel, the pulse current treatment is performed during the deformation of the cold-rolled plate or the hot-rolled plate. The deformation methods include stamping forming, extrusion forming, stretching, drawing, rolling and various automobile panel forming methods.

[0010] Therefore, compared with the prior art, the method for improving the plastic deformation of dual-phase TRIP steel provided by the present application has the following beneficial effects:

[0011] (1) The present application synchronously applies pulse current during the deformation of dual-phase TRIP steel, reduces the austenite dislocation density and promotes the cross slip of ferrite by current adjustment, thereby slowing down the rate of austenite to martensite transformation during deformation, adjusting the deformation-induced martensitic transformation ability during deformation, and improving the plastic deformation ability

[0012] (2) The present application can achieve better deformation ability at a lower treatment temperature, which is manifested as an increase in elongation on the stress-strain curve; thereby avoiding the rapid increase of stress, which affects the plastic deformation ability. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 Tensile curve of cold-rolled and annealed dual-phase TRIP steel in Example 1 under pulse current and same temperature heat comparison tensile conditions;

[0014] Figure 2 Tensile curve of cold-rolled and annealed dual-phase TRIP steel in Example 2 under pulsed current and hot comparison tensile conditions at the same temperature;

[0015] Figure 3 Tensile curve of cold-rolled and annealed dual-phase TRIP steel in Example 3 under pulsed current and hot comparison tensile conditions at the same temperature;

[0016] Figure 4 Tensile curve of cold-rolled and annealed dual-phase TRIP steel in Example 4 under pulsed current and hot comparison tensile conditions at the same temperature;

[0017] Figure 5 Microstructure of cold-rolled and annealed dual-phase TRIP steel corresponding to Example 4; wherein (a) is a STEM image, and (b) is a Mn element distribution map corresponding to (a). DETAILED DESCRIPTION

[0018] The principles and features of the present application are described below, and the examples are only used to explain the present application, and are not used to limit the scope of the present application.

[0019] In the following examples, the equipment used for pulsed current treatment is a pulsed power supply.

[0020] Example 1

[0021] In this example, a cold-rolled plate with a composition of Fe-0.23C-9.85Mn-2.15Al (wt.%) is subjected to uniaxial tensile deformation with pulsed current treatment; the specific operation steps are as follows:

[0022] (1) The raw materials are melted in a 10 kg vacuum induction melting furnace according to the composition ratio of Fe-0.23C-9.85Mn-2.15Al (wt.%), and cast into an ingot; then forged into a 10 mm wide and 20 mm thick forging blank; the forging blank is hot rolled to a 4 mm thick hot rolled plate between 1150°C and 800°C, and then soft annealed at 700°C for 1 hour; the hot rolled plate after soft annealing is pickled and cold rolled from 4 mm to 2 mm.

[0023] (2) The above cold-rolled plate is subjected to critical annealing at 675°C for 30 minutes to obtain a high strength and plastic product dual-phase TRIP steel with excellent performance; the annealed cold-rolled plate is made into a uniaxial tensile specimen with a length of 20 mm, a width of 5 mm and a thickness of 2 mm, and the surface of the specimen is polished to a bright finish with sandpaper.

[0024] (3) The clamping head of the tensile machine is insulated so that the current passes through the parallel section of the tensile specimen during the entire tensile process; the two ends of the tensile specimen are fixed on the clamping head, and then the output end of the pulsed power supply is fixed on the tensile specimen, and the speed of the tensile machine is set to 5×10 -4 s -1, the pulse parameters are: frequency 100 Hz, pulse width 100 μs, duty cycle 1%, peak current density 15.4 A / mm 2 The temperature of the tensile sample under this parameter is 60℃ measured by a thermocouple. At the same time, a thermal contrast tensile test is carried out at the same temperature (60℃).

[0025] The samples under the pulse current tensile and thermal tensile are analyzed, as shown in Figure 1 , the elongation under the pulse current condition is 49%, and the elongation under the same thermal contrast tensile condition is 30%, indicating that the pulse current synchronous treatment improves the plastic deformation ability. It can be seen from the figure that by adjusting the pulse current parameters, the surface temperature of the sample is maintained at 60℃, which can maintain a high elongation while avoiding excessive engineering stress, which will help to improve the plastic deformation ability of TRIP steel.

[0026] Example 2

[0027] In this example, a cold-rolled plate with a composition of Fe-0.21C-8.9Mn-1.46Al (wt.%) is subjected to unidirectional tensile deformation with pulse current treatment; the specific operation steps are as follows:

[0028] (1) The raw materials are melted in a 50kg vacuum induction melting furnace according to the composition ratio of Fe-0.21C-8.9Mn-1.46Al (wt.%), and cast into ingots; then forged into 10mm wide and 30mm thick forgings; then hot rolled to 4mm thick hot rolled plate at 1150℃-800℃, and then soft annealed at 660℃ for 5 hours; then pickled and cold rolled from 4mm to 1.5mm.

[0029] (2) The above cold-rolled plate is subjected to critical annealing treatment at 660℃ for 30 minutes to obtain a high strength and plastic product dual-phase TRIP steel with excellent performance; the annealed cold-rolled plate is made into a uniaxial tensile sample with a length of 20mm, a width of 5mm and a thickness of 1.5mm, and the surface of the sample is polished to a bright finish with sandpaper.

[0030] (3) The clamping head of the tensile machine is insulated so that the current passes through the parallel section of the tensile sample during the entire tensile process; the two ends of the tensile sample are fixed on the clamping head, then the output end of the pulse power supply is fixed on the tensile sample, and the speed of the tensile machine is set to 5×10 -4 s -1 , the pulse parameters are: frequency 20 Hz, pulse width 1ms, duty cycle 2%, peak current density 24.2 A / mm 2 , the temperature of the tensile sample under this parameter is 60℃ measured by a thermocouple; at the same time, a thermal contrast tensile test is carried out at the same temperature (60℃).

[0031] The samples under the pulse current tensile and thermal tensile are analyzed, as shown inFigure 2 As shown, the elongation under pulsed current conditions is 45%, while the elongation under the same thermal contrast tensile conditions is 32%, indicating that synchronous pulsed current treatment improves its plastic deformation capacity. The figure also shows that by adjusting the pulsed current parameters, this embodiment maintains the sample surface temperature at 60°C, which helps maintain a high elongation while avoiding excessive engineering stress, thus contributing to improved plastic deformation capacity of TRIP steel.

[0032] Example 3

[0033] This embodiment applies pulsed current treatment during uniaxial tensile deformation of a hot-rolled plate with a composition of Fe-0.21C-8.9Mn-1.46Al (wt.%); the specific operation steps are as follows:

[0034] (1) The raw materials were melted in a 50kg vacuum induction melting furnace according to the composition ratio of Fe-0.21C-8.9Mn-1.46Al (wt.%) and cast into ingots; then forged into 10mm wide and 30mm thick forging blanks; the forging blanks were hot rolled into 4mm thick hot-rolled plates between 1150℃ and 800℃.

[0035] (2) The hot-rolled plate was critically annealed at 680°C for 30 minutes to obtain high-strength, high-ductility dual-phase TRIP steel with excellent performance; the annealed hot-rolled plate was made into a uniaxial tensile specimen with a parallel section length of 20mm, a width of 5mm, and a thickness of 1.5mm, and the surface of the specimen was polished with sandpaper until it was bright.

[0036] (3) The clamps of the tensile testing machine are insulated so that the current passes through the parallel section of the tensile specimen throughout the tensile process; the two ends of the tensile specimen are fixed to the clamps, and then the output of the pulse power supply is fixed to the tensile specimen. The speed of the tensile testing machine is set to 5×10. -4 s -1 The pulse parameters are: frequency 200Hz, pulse width 200μs, duty cycle 4%, and peak current density 23.4A / mm². 2 The temperature of the tensile specimen under these parameters was measured to be 100℃ using a thermocouple; at the same time, a thermal comparison tensile test was conducted at the same temperature (100℃).

[0037] Analysis was performed on specimens subjected to pulsed current tensile and thermal tensile tests, such as... Figure 3 As shown, the elongation under pulsed current conditions is 42%, while the elongation under the same thermal contrast tensile conditions is 36%, indicating that synchronous pulsed current treatment improves its plastic deformation capacity. The figure also shows that, by adjusting the pulsed current parameters, this embodiment maintains the sample surface temperature at 60°C, which helps maintain a high elongation while avoiding excessive engineering stress, thus contributing to improved plastic deformation capacity of TRIP steel.

[0038] Example 4

[0039] In this embodiment, a unidirectional tensile deformation pulse current treatment is applied to a cold-rolled steel plate with a composition of Fe-0.21C-8.9Mn-1.46Al (wt.%). The specific operation steps are as follows:

[0040] (1) The raw material is melted in a 50 kg vacuum induction melting furnace according to the composition of Fe-0.21C-8.9Mn-1.46Al (wt.%), and cast into an ingot; then forged into a 10 mm wide and 30 mm thick forging blank; the forging blank is hot rolled to a 4 mm thick hot-rolled plate between 1150°C and 800°C, and then soft annealed at 660°C for 5 hours; the soft annealed hot-rolled plate is pickled and then cold-rolled from 4 mm to 1.5 mm.

[0041] (2) The above cold-rolled plate is subjected to critical annealing treatment at 680°C for 30 minutes to obtain a high strength and plastic product dual-phase TRIP steel with excellent performance; the annealed cold-rolled plate is made into a uniaxial tensile specimen with a length of 20 mm, a width of 5 mm and a thickness of 1.5 mm, and the surface of the specimen is polished to a bright finish with sandpaper.

[0042] (3) The clamping head of the tensile machine is insulated so that the current passes through the parallel section of the tensile specimen during the entire tensile process; the ends of the tensile specimen are fixed on the clamping head, and then the output end of the pulse power supply is fixed on the tensile specimen; the speed of the tensile machine is set to 5×10 -4 s -1 , and the pulse parameters are: frequency 200 Hz, pulse width 200 μs, duty cycle 4%, peak current density 17.1 A / mm 2 ; air cooling is carried out during the tensile process, and the temperature of the tensile specimen under this parameter is 25°C measured by a thermocouple; at the same time, a hot comparison tensile test is carried out at the same temperature (25°C).

[0043] Figure 5 The microstructure of the cold-rolled and annealed dual-phase TRIP steel prepared in this embodiment is shown in the figure, which shows that the dual-phase TRIP steel contains ferrite with low Mn content and metastable austenite with high Mn content, and the unstable metastable austenite will transform into martensite during deformation. The samples treated by pulse current + air cooling tensile and hot tensile are analyzed, as shown in Figure 4 , the elongation under the condition of pulse current + air cooling tensile is 57%, and the elongation under the condition of room temperature (25°C) hot comparison tensile is 42%, indicating that the pulse current synchronous treatment improves the plastic deformation ability of the dual-phase TRIP steel. Temperature affects the TRIP effect of the sample, and the lower the temperature, the stronger the TRIP effect. It is found through research that the TRIP effect can affect both strength and plasticity. In this embodiment, both strength and plasticity exhibit good performance.

[0044] The above is only part of the specific embodiments of some single crystal superalloy samples in the present application. In the present application, the 10 min-3 h time range is based on the size range of laboratory single crystal superalloy samples, and is applied to actual production. The pulse current treatment time of the single crystal superalloy varies with the size of the material itself.

[0045] The scope of protection of the present application is not limited to the above-mentioned embodiments. Any person skilled in the art can make equivalent replacements of similar materials, equipment or adjustments of related technical parameters within the technical scope disclosed in the present application and according to the technical solutions and inventive concepts of the present application, which should be covered within the scope of protection of the present application.

Claims

1. A method of plastic deformation boosting of a dual phase TRIP steel, characterized in that, For the dual-phase TRIP steel with metastable austenite structure and ferrite structure, the dual-phase TRIP steel is medium manganese steel, pulse current treatment is carried out in the deformation process of cold-rolled plate or hot-rolled plate, the surface temperature of the TRIP steel is controlled to be 25-100℃; the pulse current parameters are frequency 20-200Hz, pulse width 100μs-1ms, duty cycle 1%-4%, and peak current density 10-30A / mm 2 .

2. The plastic deformation boosting method of the dual-phase TRIP steel according to claim 1, characterized in that, The deformation method includes punch forming, extrusion forming, stretching, drawing, and rolling various automobile plate forming methods.

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