An anti-fatigue ultra-fine grain dual-phase steel based on segregation of interfacial alloying elements and a manufacturing process thereof

Abstract

The application discloses an anti-fatigue ultra-fine grain dual-phase steel based on phase interface alloy element segregation and a manufacturing process thereof. The chemical composition (wt%) of the ultra-fine grain ferrite / martensite dual-phase steel is as follows: C: 0.2-0.45, Mn: 1.5-2.26, Si: 1.0-2.0, Cr: 1.0-2.0, Mo: 0.35-0.39, V: 0.1-0.11, Al: 0.01-1.5, N: <=0.002, S: <=0.004, P: <=0.02, and the rest is Fe. The anti-fatigue ultra-fine grain dual-phase steel has the phase interface alloy element segregation characteristic. The ferrite and the martensite are alternately distributed in the form of lamellar to form a layered dual-phase structure. The thickness of the martensite and the ferrite lamellar is 0.1-1.0 mu m. The alloy element and the carbon element segregated at the interface form nanometer carbide with a coherent structure with the matrix. The application can stabilize the phase interface, resist the interface damage in the fatigue loading process, inhibit the strain localization in the fatigue loading process of the ultra-fine grain steel and reduce the fatigue crack propagation rate.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ultra-fine grain steel, and particularly relates to an anti-fatigue ultra-fine grain dual-phase steel based on phase interface alloy element segregation and a manufacturing process thereof. BACKGROUND

[0002] Ultra-fine grain steel is considered as an effective means to improve the mechanical properties of materials because its strength can be doubled compared with coarse-grained materials when the grain is refined to the level of ultra-fine grain or nanocrystalline. However, in actual engineering applications, fatigue failure accounts for about 90% of mechanical equipment failure reasons, and fatigue performance is an important indicator that cannot be ignored in the process of material design and development. Through the summary of the research results of the fatigue performance of different ultra-fine steels, it is found that under the stress-controlled high-cycle fatigue cyclic loading, the fatigue crack initiation resistance of ultra-fine grain and nanocrystalline metals is enhanced, and the fatigue life limit is improved, while under the strain-controlled low-cycle fatigue cyclic loading, the low-cycle fatigue performance of ultra-fine grain and nanocrystalline metals deteriorates obviously, showing the contradiction that high-cycle fatigue performance and low-cycle fatigue performance cannot be compatible.

[0003] For example, M Okayasu et al. ("Fatigue properties of ultra-fine grained dual-phase ferrite / martensite low carbon steel." International Journal of Fatigue 30.8 (2008): 1358-1365.) prepared an ultra-fine grained ferrite / martensite low carbon steel by equal channel angular pressing (ECAP), and the fatigue strength of the steel was improved compared with its corresponding coarse-grained material, but its low-cycle fatigue performance deteriorated sharply during low-cycle fatigue loading due to strain localization;

[0004] Liu, Y.X. et al. ("Fatigue behaviors of 2205 duplex stainless steel with gradient nanostructured surface layer." International Journal of Fatigue 147 (2021): 106170.) prepared a 2205 dual-phase stainless steel with a gradient nanostructured surface layer by ultrasonic technology, which improved the high-cycle fatigue performance of the steel, but the hard and brittle martensite phase reduced the plasticity of the material, and its low-cycle fatigue life was lower than that of its corresponding coarse-grained material.

[0005] Therefore, how to solve the two pairs of contradictions between the strength and plasticity of ultra-fine grain steel and the high and low cycle fatigue performance is a challenging and important work. SUMMARY

[0006] In order to overcome the defects of the prior art, the present application provides an anti-fatigue ultra-fine grain dual-phase steel based on phase interface alloy element segregation and a manufacturing process thereof, which can stabilize the phase interface, resist interface damage in the fatigue loading process, inhibit strain localization in the fatigue loading process of the ultra-fine grain steel, and reduce the fatigue crack propagation rate.

[0007] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is:

[0008] An anti-fatigue ultra-fine grain dual-phase steel based on phase interface alloy element segregation, in which ferrite and martensite are alternately distributed in the form of lamellar to form a lamellar dual-phase structure, the average thickness of the martensite and ferrite lamellar is 0.1-1.0 μm, and the alloy elements C, Cr, Mn and Mo added in the material are enriched at the interface between the martensite and ferrite, forming segregation (local high concentration of alloy elements at the interface), and combining with carbon elements to form nanometer carbide with a coherent structure with the matrix.

[0009] The coherent nanometer carbide can stabilize the interface and resist interface damage in the fatigue loading process, and the lamellar dual-phase structure can inhibit strain localization in the fatigue loading process of the ultra-fine grain steel and reduce the fatigue crack propagation rate, thereby significantly improving the low-cycle and high-cycle fatigue performance of the ultra-fine grain steel.

[0010] This lamellar heterogeneous structure based on phase interface alloy element segregation endows the material with excellent mechanical properties, the yield strength of the alloy can reach 1200-1400 MPa, and the elongation rate is 20%-25%; under the condition of tensile-compressive symmetric loading (R=-1), the fatigue limit is greater than 600 MPa, and the life under strain-controlled fatigue loading with a strain amplitude of 0.8% is higher than 1000 cycles.

[0011] The chemical composition (wt%) of the ultra-fine grain ferrite / martensite dual-phase steel is as follows: C: 0.2-0.45, Mn: 1.5-2.26, Si: 1.0-2.0, Cr: 1.0-2.0, Mo: 0.35-0.39, V: 0.1-0.11, Al: 0.01-1.5, N: ≤0.002, S: ≤0.004, P: ≤0.02, and the rest is Fe.

[0012] A manufacturing process of an anti-fatigue ultra-fine grain dual-phase steel based on phase interface alloy element segregation, comprising the following steps:

[0013] Step 1: pre-heat treatment

[0014] Uniform annealing is performed according to the components of the ultra-fine grain ferrite / martensite dual-phase steel to obtain an austenite structure without carbide, then the square billet is forged or rolled, and finally quenched to obtain a martensite structure;

[0015] Step 2: Rolling

[0016] The martensite structure is heated to the ferrite and austenite (a+g) two-phase region and is kept for a certain time, so that the alloying elements C, Cr, Mn and Mo are segregated at the ferrite and austenite interface; then hot rolling is performed, so that the ferrite and austenite are distributed in lamellar form along the rolling direction, (and the lamellar thickness of the ferrite and austenite can be controlled to achieve microstructure refinement by adjusting the rolling reduction), and then quenching is performed, to obtain an ultra-fine grained ferrite / martensite dual-phase steel with lamellar structure characteristics;

[0017] Step 3: Tempering treatment

[0018] The ultra-fine grained ferrite / martensite dual-phase steel with lamellar structure characteristics is subjected to tempering treatment, so that the alloying elements and carbon elements segregated at the interface form nanocarbides with a coherent structure with the matrix, to obtain an anti-fatigue ultra-fine grained dual-phase steel.

[0019] For the pre-heat treatment in step 1, the following process is included:

[0020] Step 1) Homogenization annealing

[0021] The alloy of the composition is heated to 1200±20℃ and kept for a certain time, and the holding time is determined according to the workpiece thickness, i.e. 1-1.5 min / mm, and then forged into a square billet and air-cooled to room temperature;

[0022] Step 2) Quenching

[0023] The square billet after forging in step 1) is heated to a temperature 30-50℃ above Ac3 for quenching to obtain a martensite structure.

[0024] For the rolling in step 2, the following process is included:

[0025] Step 1) Pre-rolling heat treatment

[0026] The martensite structure is rapidly heated to a temperature in the ferrite+austenite two-phase region (Ac1-Ac3) at a speed greater than 2℃ / s (the volume fraction of austenite is controlled at 40-70%) and kept for 1-30 min, to obtain a ferrite / austenite structure with a lamellar feature and make the alloying elements segregate at the interface;

[0027] Step 2) Warm rolling

[0028] The heat-insulated alloy is hot-rolled, the rolling reduction is controlled between 50% and 85%, the lamellar orientation is parallel to the rolling direction and the lamellar thickness is refined, and the rolled material is quenched to room temperature immediately, in the quenching cooling process, the lamellar austenite is transformed into martensite, and the ultra-fine grain ferrite / martensite dual-phase steel with the lamellar structure characteristics and the alloying elements segregated at the interface of ferrite and martensite is obtained.

[0029] For the tempering treatment of step 3, the process is as follows:

[0030] The ultra-fine grain ferrite / martensite dual-phase steel with the lamellar structure characteristics prepared in the above process is tempered at 250-300℃ for 1-2h, so that the alloying elements and carbon elements segregated at the interface form the nanometer carbide with the coherent structure with the matrix.

[0031] The beneficial effects of the present application are as follows:

[0032] 1. In the anti-fatigue ultra-fine grain dual-phase steel based on the segregation of alloying elements at the phase interface prepared by the present application, the alloying elements and carbon elements segregated at the interface can form the nanometer carbide with the coherent structure with the matrix, the special structure can stabilize the phase interface and resist the interface damage in the fatigue loading process, and the lamellar dual-phase structure can inhibit the strain localization and reduce the fatigue crack propagation rate in the fatigue loading process of the ultra-fine grain steel. The unique structure breaks through the technical bottleneck that the high and low cycle fatigue performance of the ultra-fine grain steel is difficult to be improved simultaneously.

[0033] 2. The yield strength of the alloy prepared by the present application can reach 1200-1400MPa, the elongation is 20%-25%, the fatigue limit is greater than 600MPa under the tensile-compressive symmetric loading condition (R=-1), and the life is higher than 1000 cycles under the strain control fatigue loading with the strain amplitude of 0.8%.

[0034] 3. The process route of the anti-fatigue ultra-fine grain dual-phase steel based on the segregation of alloying elements at the phase interface is simple, the production equipment requirement is low, and the large-scale production can be applied. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 The TEM energy spectrum of the anti-fatigue ultra-fine grain dual-phase steel based on the segregation of alloying elements at the phase interface before and after the fatigue loading of the present application is as follows: (a) before the fatigue loading; (b) after the fatigue failure. DETAILED DESCRIPTION

[0036] The present application will be further described in detail below with reference to the drawings.

[0037] The application discloses a manufacturing process of fatigue-resistant ultra-fine grain dual-phase steel based on phase interface alloy element segregation, and the implementation steps of the application are as follows: firstly, alloys with selected components are heated to 1200±20 DEG C, and the holding time is determined according to the thickness of the workpiece at 1-1.5 min / mm, then the alloys are forged or rolled into square billets and air-cooled to room temperature to obtain carbide-free austenite organization, and the square billets obtained after forging or rolling are re-heated to a temperature of 30-50 DEG C above the Ac3 temperature for quenching to obtain martensite organization; then the martensite square billets are rapidly heated to a temperature in the range of Ac1-Ac3 (in the ferrite + austenite two-phase region, and the volume fraction of the austenite phase is controlled to be 40-70%) at a speed of greater than 2 DEG C / s and are kept for 1-30 min, so that ferrite / austenite organization with lath characteristics is obtained and alloy elements are segregated at the interface; then the square billets are hot-rolled, and the cumulative rolling reduction is controlled to be between 50% and 85%, so that the lamellar orientation is parallel to the rolling direction and the lamellar thickness is refined, and then the rolled material is quenched to room temperature immediately, and the lamellar austenite is transformed into martensite during the quenching cooling process; finally, the ultra-fine grain ferrite / martensite dual-phase steel with the lamellar structure characteristics obtained is tempered at 250-300 DEG C for 1-2 h, so that the alloy elements and carbon elements segregated at the interface form nanometer carbides with a coherent structure with the matrix, and the ultra-fine grain ferrite / martensite dual-phase steel with the alloy elements segregated at the phase interface and the lamellar structure characteristics is obtained.

[0038] As shown in Figure 1 The lath heterostructure based on phase interface alloy element segregation endows the material with excellent mechanical properties, the yield strength of the alloy can reach 1200-1400 MPa, and the elongation rate is 20%-25%; under the condition of tensile-compressive symmetrical loading (R=-1), the fatigue limit is greater than 600 MPa, and the service life is higher than 1000 cycles under the strain control fatigue loading with a strain amplitude of 0.8%.

[0039] Example 1

[0040] The chemical components are selected as follows in terms of mass percentage (wt%): C: 0.3, Mn: 1.5, Si: 2.0, Cr: 1.9, Mo: 0.35, V: 0.1, Al: 0.01, N: ≤0.002, S: ≤0.004, P: ≤0.02, and the rest is Fe. The Ac3 and Ac1 temperatures of the alloy are measured by the differential thermal analysis method and are 830 DEG C and 740 DEG C respectively.

[0041] The alloy of the component is heated to 1200℃ and the holding time is determined according to the workpiece thickness as 1.5 min / mm, then it is forged into a square billet and air-cooled to room temperature, then the square billet obtained by forging is reheated to 40℃ above the Ac3 temperature for quenching to obtain a martensite structure; then the martensite square billet is rapidly heated to 770℃ at a speed of 2.2℃ / s and held for 20 min, then it is hot-rolled with a cumulative rolling reduction of 85%, and then the rolled material is immediately quenched to room temperature; finally, it is tempered at 300℃ for 1h to obtain an ultra-fine grain ferrite / martensite dual-phase steel with alloying elements segregated at the phase interface and having a lamellar structure feature with a lamellar thickness of 0.1μm.

[0042] The mechanical properties thereof are: the yield strength can reach 1400MPa, the elongation is 24%, the fatigue limit is 650MPa under the condition of tensile-compressive symmetric loading (R=-1), and the life is 2000 cycles under the condition of strain-controlled fatigue loading with a strain amplitude of 0.8%.

[0043] Example 2

[0044] The chemical composition is selected as follows in terms of mass percentage (wt%): C: 0.2, Mn: 2.26, Si: 1.0, Cr: 1.01, Mo: 0.39, V: 0.11, Al: 0.7, N: ≤0.002, S: ≤0.004, P: ≤0.02, and the rest is Fe.

[0045] The Ac3 and Ac1 temperatures thereof are measured by differential thermal analysis method as 850℃ and 745℃ respectively. The alloy of the component is heated to 1220℃ and the holding time is determined according to the workpiece thickness as 1.3 min / mm, then it is forged into a square billet and air-cooled to room temperature, then the square billet obtained by forging is reheated to 30℃ above the Ac3 temperature for quenching to obtain a martensite structure; then the martensite square billet is rapidly heated to 785℃ at a speed of 2.5℃ / s and held for 5 min, then it is hot-rolled with a cumulative rolling reduction of 80%, and then the rolled material is immediately quenched to room temperature; finally, it is tempered at 270℃ for 1h20min to obtain an ultra-fine grain ferrite / martensite dual-phase steel with alloying elements segregated at the phase interface and having a lamellar structure feature with a lamellar thickness of 0.42μm.

[0046] The mechanical properties thereof are: the yield strength can reach 1370MPa, the elongation is 23.4%, the fatigue limit is 643MPa under the condition of tensile-compressive symmetric loading (R=-1), and the life is 1800 cycles under the condition of strain-controlled fatigue loading with a strain amplitude of 0.8%.

[0047] Example 3

[0048] The chemical composition is selected as follows in terms of mass percentage (wt%): C: 0.45, Mn: 1.8, Si: 1.5, Cr: 1.5, Mo: 0.36, V: 0.11, Al: 1.2, N: ≤0.002, S: ≤0.004, P: ≤0.02, and the rest is Fe.

[0049] The Ac3 and Ac1 temperatures of the alloy are measured by differential thermal analysis method to be 825 ℃ and 730 ℃ respectively. The alloy of the composition is heated to 1180 ℃, and the holding time is determined according to the workpiece thickness as 1.0 min / mm, and then the alloy is forged into a square billet and air-cooled to room temperature, and then the square billet obtained by forging is reheated to 50 ℃ above the Ac3 temperature for quenching to obtain a martensite structure; the martensite square billet is rapidly heated to 765 ℃ at a speed of 2.6 ℃ / s and held for 15 min, and then hot-rolled with a cumulative rolling reduction of 70%, and then the rolled material is immediately quenched to room temperature; finally, the material is tempered at 250 ℃ for 2 h to obtain an ultra-fine grain ferrite / martensite dual-phase steel with an alloy element segregation at the phase interface and a lamellar structure characteristic, and the lamellar thickness is 0.5 μm.

[0050] The mechanical properties are as follows: the yield strength can reach 1355 MPa, and the elongation is 23%; under the condition of tensile-compressive symmetric loading (R=-1), the fatigue limit is 635 MPa, and the life is 1680 cycles under strain-controlled fatigue loading with a strain amplitude of 0.8%.

[0051] Example 4

[0052] The chemical composition is selected as follows in terms of mass percentage (wt%): C: 0.35, Mn: 2.0, Si: 1.8, Cr: 1.3, Mo: 0.37, V: 0.1, Al: 1.5, N: ≤0.002, S: ≤0.004, P: ≤0.02, and the rest is Fe.

[0053] The Ac3 and Ac1 temperatures of the alloy are measured by differential thermal analysis method to be 815.6 ℃ and 726.5 ℃ respectively. The alloy of the composition is heated to 1190 ℃, and the holding time is determined according to the workpiece thickness as 1.4 min / mm, and then the alloy is forged into a square billet and air-cooled to room temperature, and then the square billet obtained by forging is reheated to 25 ℃ above the Ac3 temperature for quenching to obtain a martensite structure; the martensite square billet is rapidly heated to 758 ℃ at a speed of 2.3 ℃ / s and held for 30 min, and then hot-rolled with a cumulative rolling reduction of 50%, and then the rolled material is immediately quenched to room temperature; finally, the material is tempered at 280 ℃ for 1 h 20 min to obtain an ultra-fine grain ferrite / martensite dual-phase steel with an alloy element segregation at the phase interface and a lamellar structure characteristic, and the lamellar thickness is 1 μm.

[0054] The mechanical properties are as follows: the yield strength can reach 1203 MPa, the elongation is 20.3%, the fatigue limit is 603 MPa under the condition of tensile-compressive symmetric loading (R=-1), and the service life is 1025 cycles under the condition of strain control fatigue loading with a strain amplitude of 0.8%.

[0055] The application proposes a preparation method of anti-fatigue ultra-fine grain dual-phase steel based on phase interface alloy element segregation from deformation and phase change coupling control theory. First, according to the phase equilibrium principle, the temperature interval of ferrite and austenite two-phase region is kept warm. Because of the nucleation and growth of austenite and the different solubility of alloy elements in the two phases, the alloy elements will diffuse into the austenite and stabilize the austenite. At the same time, the segregation of such alloy elements can reduce the transformation temperature of austenite, so that the austenite preferentially nucleates at the lath martensite and grows along the lath, thereby obtaining a ferrite / austenite structure with lath characteristics and alloy elements segregated at the interface. Secondly, the ferrite and martensite lamella are made to be parallel to the rolling direction and the lamella is refined by warm rolling, and then the lamellar austenite is transformed into martensite by quenching and inherits the segregation of alloy elements. Finally, the alloy elements and carbon elements segregated at the interface form nanometer carbides with coherent structure with the matrix by tempering, thereby obtaining anti-fatigue ultra-fine grain dual-phase steel based on phase interface alloy element segregation.

[0056] The above is a further detailed description of the application in combination with specific preferred embodiments, and the specific implementation of the application cannot be limited to these descriptions. For ordinary skilled persons in the technical field to which the application belongs, some simple deductions or substitutions can be made without departing from the concept of the application, and all of them should be regarded as falling within the protection scope of the application.

Claims

1. A fatigue resistant ultra-fine grained dual phase steel based on the segregation of interfacial alloying elements, characterized in that, The ferrite and martensite are alternately distributed in the form of lamellar to form a lamellar dual-phase structure, the average thickness of the martensite and ferrite lamellar is 0.1-1.0 μm, the alloy elements C, Cr, Mn and Mo added in the material are enriched at the interface between the martensite and ferrite to form segregation, and combined with carbon elements to form nanometer carbide with a coherent structure with the matrix; The chemical composition (wt%) of the ultra-fine grain dual-phase steel is: C: 0.2-0.45, Mn: 1.5-2.26, Si: 1.0-2.0, Cr: 1.0-2.0, Mo: 0.35-0.39, V: 0.1-0.11, Al: 0.01-1.5, N: ≤0.002, S: ≤0.004, P: ≤0.02, and the rest is Fe.

2. The manufacturing process of the anti-fatigue ultra-fine grain dual-phase steel based on the segregation of alloy elements at the phase interface according to claim 1, comprising the following steps: Step 1: pre-heat treatment homogenizing annealing according to the components of the ultra-fine grain ferrite / martensite dual-phase steel to obtain an austenite structure without carbide, then forging or rolling into a square billet, and finally quenching to obtain a martensite structure; Step 2: rolling heating the martensite structure to the ferrite and austenite (α+γ) two-phase region and keeping it, so that the alloy elements C, Cr, Mn and Mo are segregated at the interface between the ferrite and austenite; then hot rolling to make the ferrite and austenite distributed in the form of lamellar along the rolling direction, and then quenching to obtain the ultra-fine grain ferrite / martensite dual-phase steel with a lamellar structure characteristic; Step 3: tempering treatment tempering the ultra-fine grain ferrite / martensite dual-phase steel with a lamellar structure characteristic to make the alloy elements and carbon elements segregated at the interface form nanometer carbide with a coherent structure with the matrix, thereby obtaining the anti-fatigue ultra-fine grain dual-phase steel.

3. The manufacturing process of the anti-fatigue ultra-fine grain dual-phase steel based on the segregation of alloy elements at the phase interface according to claim 2, for the pre-heat treatment in step 1, comprising the following process: Step 1) homogenizing annealing heating the alloy elements to 1200±20℃ and keeping it, the holding time is determined according to 1-1.5 min / mm, then forging into a square billet and air cooling to room temperature; Step 2) quenching heating the square billet after forging in step 1) to a temperature 30-50℃ above Ac3 for quenching to obtain a martensite structure.

4. The manufacturing process of the anti-fatigue ultra-fine grain dual-phase steel based on the segregation of alloy elements at the phase interface according to claim 2, for the rolling in step 2, comprising the following process: Step 1) pre-rolling heat treatment rapidly heating the martensite structure to a temperature in the range of Ac1-Ac3 at a speed greater than 2℃ / s and keeping it for 1-30 min to obtain ferrite / austenite structure with a lamellar characteristic and make the alloy elements segregated at the interface; Step 2) warm rolling The heat-insulated alloy is hot-rolled, the rolling reduction is controlled between 50% and 85%, the lamellar orientation is parallel to the rolling direction and the lamellar thickness is refined, and the rolled material is immediately quenched to room temperature. During the quenching cooling process, the lamellar austenite is transformed into martensite, and the ultra-fine grain ferrite / martensite dual-phase steel with the alloying element segregation at the interface of ferrite and martensite and the layered structure characteristics is obtained.

5. The manufacturing process of the anti-fatigue ultra-fine grain dual-phase steel based on the phase interface alloying element segregation according to claim 4, wherein the Ac1-Ac3 temperature interval is in the ferrite + austenite two-phase region, and the volume fraction of the austenite phase is controlled to be 40-70%.

6. The manufacturing process of the anti-fatigue ultra-fine grain dual-phase steel based on the phase interface alloying element segregation according to claim 2, wherein the tempering treatment of step 3 is as follows: The ultra-fine grain ferrite / martensite dual-phase steel with the layered structure characteristics prepared in the above process is tempered at 250-300°C for 1-2h.

Images