Construction method of maraging steel with gradient nanostructure

Abstract

The invention belongs to the technical field of material composite reinforcement, and particularly relates to a construction method of maraging steel with a gradient nanostructure. A gradient nanostructure layer with a certain depth is formed on the surface of the maraging steel by utilizing a surface nanocrystallization technology, and the surface of the maraging steel is remarkably strengthened. The core of the method lies in that rigidity compensation is provided in the treatment process to intensify the surface plastic deformation degree, and temperature field acceleration interface segregation and interface structure adjustment are provided. And finally, a gradient nanostructure layer with the obvious strengthening characteristic is obtained on the surface of the maraging steel, and the anti-fatigue performance of the maraging steel is greatly improved.

Description

Technical Field

[0001] The invention belongs to the technical field of material composite strengthening, and in particular relates to a method for constructing gradient nanostructured martensitic aging steel. Background Art

[0002] Maraging steel is the main material for low-temperature and high-load transmission shaft components of gas turbines, and has the advantages of high strength and good formability. After solution + aging treatment, the average size of the laths in maraging steel is generally in the submicron scale, and a high-density disc-shaped nano-scale precipitation phase is dispersed inside. Precipitation phase strengthening increases the hardness of maraging steel from 3.3GPa to 5.6GPa, with a significant strengthening effect. However, the poor structural stability of the precipitate phase under load conditions can easily lead to local softening, causing stress concentration and then causing damage. Therefore, as a transmission shaft component, the rotational bending fatigue limit of maraging steel is only 1 / 3 of the yield strength, which affects its application range and service safety.

[0003] The strength of metal materials can be effectively improved by refining the grains to the nanometer scale. Therefore, using nano-grains to replace the nano-precipitated phase with poor mechanical stability as a strengthening unit is expected to improve the mechanical properties of maraging steel. However, maraging steel has poor plastic deformation ability and it is difficult for deformation to be transferred to the matrix, so the surface deformation layer is very shallow. By using the stiffness compensation method to increase the depth of influence of surface deformation, it is expected to achieve the preparation of a thicker deformation layer. In addition, according to the grain size-strength relationship, to replace the strengthening effect (5.6GPa) provided by the precipitated phase, the grain size needs to be refined to less than 30nm. This is difficult to achieve with the current traditional plastic deformation technology (rolling / equal channel extrusion, etc.). Surface nano-crystal technology has a high shear deformation rate and can achieve a large deformation amount. The final nano-crystal size can often break through the traditional plastic deformation method and is currently an effective way to refine grains. Although the introduction of grain refinement through surface nano-crystal technology is expected to replace precipitation strengthening, it cannot achieve significant strengthening of maraging steel (hardness value higher than 7GPa). The strength of nanostructured metal materials is significantly affected by temperature. When the nanocrystalline grain size remains unchanged and no precipitate phase is produced, temperature changes can further increase the strength of nanometal materials by about 30%. The main mechanism depends on the element distribution fluctuations and interface structure adjustments caused by temperature changes.

[0004] In summary, it is very difficult to further strengthen maraging steel through existing plastic deformation technology. It is necessary to integrate surface nano-crystallization technology to provide stiffness compensation and introduce temperature parameters to obtain gradient nanostructured maraging steel with a deep deformation layer, good grain refinement and obvious surface strengthening, and improve its service performance (fatigue resistance) by constructing gradient nanostructure technology. Summary of the invention

[0005] The purpose of the present invention is to provide a method for constructing a gradient nanostructured maraging steel. The technical problem to be solved is to achieve the construction and strengthening of a gradient nanostructured maraging steel in a deeper range by providing stiffness compensation and introducing a temperature field.

[0006] The technical solution of the present invention is:

[0007] A method for constructing a gradient nanostructured maraging steel, wherein the surface of the maraging steel is nano-processed to form a gradient nanostructured layer with a depth of more than 200 μm and the surface grains are significantly refined to the nanometer level, and the distribution, size and morphology of the precipitated phase are simultaneously changed, and the surface strengthening effect of the maraging steel is achieved through fine grain strengthening and interface segregation.

[0008] The method for constructing the gradient nanostructured martensitic aging steel realizes a gradient nanostructured layer with a depth of 200 μm through surface nano-processing, and improves the microhardness and fatigue limit by more than 20% after surface strengthening.

[0009] The method for constructing the gradient nanostructured maraging steel comprises the following steps: for a maraging steel workpiece with mechanical surface treatment, the workpiece is subjected to stiffness compensation by means of an additional external stiffness compensation device; and a temperature field is applied in situ on the workpiece surface, with the temperature adjustment range being 200°C to 400°C.

[0010] According to the method for constructing the gradient nanostructured maraging steel, the depth of the gradient nanostructured layer of the maraging steel reaches 200 μm, and the surface grain size of the maraging steel is greatly reduced from 350 nm to below 30 nm.

[0011] The method for constructing the gradient nanostructured maraging steel is suitable for strengthening the maraging steel.

[0012] The design concept of the present invention is:

[0013] The present invention is used to perform multiple passes of surface plastic deformation treatment on the material surface, and provide stiffness compensation and temperature field (200°C to 400°C) in situ at different passes. Among them, the stiffness compensation increases the severity of surface deformation and forms a gradient nanostructure layer with a thicker depth. The temperature field accelerates the interface diffusion of maraging steel and adjusts the grain boundary structure, further enhancing the mechanical properties of the material.

[0014] Furthermore, the surface of the maraging steel is subjected to plastic deformation treatment, including surface mechanical deformation treatments such as surface mechanical crushing technology and surface mechanical rolling technology, and the gradient nanostructure of the maraging steel is constructed in combination with an in-situ stiffness compensation device and a temperature field.

[0015] Furthermore, the key to stiffness compensation is to ensure that the geometric shape of the material will not change (bend) due to the surface plastic deformation treatment, including the following details: the stiffness compensation device is embedded in the CNC machine tool to ensure the stability of the sample during processing, and the bending deformation of the material caused by the surface plastic deformation (surface mechanical rolling technology, surface mechanical rolling technology, etc.) is offset during the nano-processing process, so that the maraging steel undergoes more severe surface deformation. The key technology of the applied in-situ temperature field treatment is the temperature field control, including the following details: the temperature field application can be applied to the entire process of plastic deformation nano-processing, and / or, in the last 1 to 3 steps of plastic deformation nano-processing. First, plastic deformation nano-processing is used to refine the grains. When the grains are refined to the nanometer level and the interface volume fraction increases, which is conducive to the rapid diffusion of elements, the in-situ temperature field treatment applied by the subsequent plastic deformation treatment causes interface segregation and interface structure adjustment, and achieves significant surface strengthening. The temperature selection range is 200℃~400℃.

[0016] The advantages and beneficial effects of the present invention are:

[0017] 1. The construction method of the present invention mainly uses surface nano-crystallization technology to form a gradient nanostructure layer with a certain depth on the surface of maraging steel, and significantly strengthens its surface. The core of this method is: providing stiffness compensation during the treatment process to intensify the degree of surface plastic deformation, and providing a temperature field to accelerate interface segregation and interface structure adjustment. Finally, a gradient nanostructure layer with obvious strengthening characteristics is obtained on the surface of maraging steel, and the fatigue resistance of maraging steel is greatly improved.

[0018] 2. The construction method of the present invention integrates surface nano-crystallization technology to provide stiffness compensation and introduces temperature parameters to obtain a gradient nanostructured maraging steel with a deep deformation layer, good grain refinement effect and obvious surface strengthening. By constructing a gradient nanostructure technology, its service performance (fatigue resistance) is improved, so that a gradient nanostructure can be constructed on the surface of the maraging steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the processing of gradient nanostructured C250 steel in the embodiment.

[0020] Figure 2 4 is a design drawing of the stiffness compensation device in the embodiment.

[0021] Figure 1-Figure 2 Among them, 1. SMGT processing tool, 2. sample, 3. chuck, 4. top shaft, 5. stiffness compensation device (51 sliding sleeve, 52 arc groove, 53 top screw, 54 base, 55 stiffness compensation frame, 56 stiffness compensation rod).

[0022] Figure 3This is the organizational structure diagram of gradient nanostructured C250 steel.

[0023] Figure 4 This is a diagram of the characteristic dimensions of the nano-micron gradient structure of gradient nanostructured C250 steel.

[0024] Figure 5 This is the microhardness distribution diagram of the strengthening layer of gradient nanostructured C250 steel.

[0025] Figure 6 Comparison of fatigue properties between gradient nanostructured C250 steel sample and original sample. DETAILED DESCRIPTION

[0026] In the specific implementation process, the present invention provides a composite strengthened maraging steel and method, including constructing a metal material with grain size and / or nano-precipitation phase and / or interface segregation strengthening, and a preparation method thereof. Specifically, the surface of the metal material is subjected to plastic deformation nano-processing and stiffness compensation and temperature field are provided in situ, the grains are refined to nano-crystals, and the composite strengthening of the metal material is achieved.

[0027] Furthermore, plastic deformation treatment of the surface of maraging steel includes surface mechanical rolling technology, surface mechanical rolling technology, etc. combined with in-situ temperature field to realize the construction of gradient nanostructured maraging steel. The above technical implementation method has been embodied in the applicant's existing patents, and the present invention will not be described in detail. The technical core of the present invention is to realize the design and assembly of fasteners for stiffness compensation in the gradient nano-construction method and the selection of processing temperature field; the stiffness compensation device is nested in the CNC machine tool to control the stability of the sample shape during the surface nano-process; the temperature field can be applied to the entire process of plastic deformation nano-processing, and / or, the last 1 to 3 steps of plastic deformation nano-processing. The temperature selection range is 200℃~400℃. Under this temperature field, the atoms in the nanostructure have a faster short-range diffusion rate, thereby further improving the strength and hardness of the metal material.

[0028] Below, the present invention is further described in detail by examples and comparative examples.

[0029] Example 1

[0030] Taking C250 maraging steel as an example, gradient nanostructure construction is carried out to achieve composite strengthening effect. The specific steps are:

[0031] 1) Grinding the surface of C250 steel;

[0032] 2) Assemble the stiffness compensation device and adjust it to fit the sample tightly. Then, the C250 steel obtained in step 1) is subjected to surface mechanical deformation treatment under the premise of maintaining a certain temperature in the second half of the processing process, so that the surface structure of the C250 steel is significantly refined and presents a gradient distribution feature.

[0033] Specifically, the surface nano-crystallization technology used is surface mechanical rolling treatment technology (SMGT). Figure 1-Figure 2 As shown, the surface treatment is carried out on a special CNC surface nano-processing equipment, which includes an SMGT processing tool 1, a chuck 3, a top spindle 4, a stiffness compensation device 5, and a material surface specific temperature maintenance mechanism (such as a hot blowing device), specifically as follows: the sample 2 is arranged between the chuck 3 and the top spindle 4 in the horizontal direction, one end of the sample 2 is fixedly mounted on the chuck 3 and rotates with the chuck 3 at a rotation speed V1, and the other end of the sample 2 is supported by the tip of the top spindle 4, the SMGT processing tool 1 is located above the sample 2 and moves horizontally at a speed V2, and the stiffness compensation rod 56 of the stiffness compensation device 5 is located below the sample 2. Between the to-be-processed area and the processed area of ​​the sample, a temperature field is applied by a temperature maintenance mechanism, and stiffness compensation is applied in the bending deformation direction of the material by a stiffness compensation device. In this embodiment, the rotation speed V1 of the sample is 300 to 600 rpm, and the horizontal moving speed V2 of the SMGT processing tool is 4.5 to 12 mm / min.

[0034] Among them, the stiffness compensation device 5 includes a sliding sleeve 51, an arc groove 52, a top screw 53, a base 54, a stiffness compensation frame 55, and a stiffness compensation rod 56. The sliding sleeve 51 and the stiffness compensation frame 55 are respectively provided on both sides of the top of the base 54. The sliding sleeve 51 is installed on the top shaft 4 and is in sliding cooperation with the top shaft 4. The stiffness compensation rod 56 corresponding to the bending deformation side of the sample 2 is symmetrically installed on the stiffness compensation frame 55. An arc groove 52 is provided on one side of the sliding sleeve 51 on the top shaft 4. The top screw 53 is inserted into the arc groove 52 and connected with the sliding sleeve 51. The sliding sleeve 51 is adjusted to slide on the top shaft 4 by the top screw 53, thereby ensuring that the stiffness compensation rod 56 corresponds to the area to be processed and the processed area of ​​the sample, and the bending deformation is tightened by the stiffness compensation rod 56.

[0035] The SMGT machining tool rolls the surface of C250 steel at high speed, causing high-speed plastic shear deformation on the surface of the C250 steel to be processed, forming a gradient nanostructure layer with a thick depth on the surface of the C250 steel and significantly refining the surface grains to the nanometer level. The stiffness compensation device stabilizes the sample geometry during the severe deformation process to provide a more severe surface deformation capability and expand the depth of the affected layer of the surface treatment. During the first pass of processing, the tool head of the SMGT machining tool is pressed into the surface of the bearing steel. At the same time, the tool head of the SMGT machining tool is fed along the axial direction of the bearing steel or in a direction perpendicular to the rotating surface of the bearing steel; during the last pass of processing, the SMGT machining tool and the bearing steel surface are rolled and rubbed, resulting in heating, but the temperature is unstable, and a hot air blowing device is required to heat the machining surface of the bearing steel to maintain the surface temperature at 400°C. During the last pass of surface nano-treatment of the treated C250 steel, hot air is blown on the bearing surface using hot air blowing equipment to ensure that the bearing surface temperature is stable at 400°C. The last pass of treatment in a high temperature environment can promote the aggregation of Ni and Mo atoms at the interface, greatly improving the hardness of the C250 steel surface.

[0036] like Figure 3 As shown in FIG. 1 , the organization structure diagram of the gradient nanostructured C250 steel can be seen from the figure that the present invention can introduce a significant deformation layer of 200 μm on the surface of the C250 steel.

[0037] like Figure 4 As shown in the figure, the characteristic size diagram of the nano-micron gradient structure of the gradient nanostructured C250 steel. It can be seen from the figure that after treatment, the grain size gradually increases from 20nm to 350nm from the surface to the inside, showing an obvious gradient distribution characteristic.

[0038] like Figure 5 As shown, the microhardness distribution diagram of the strengthening layer of the gradient nanostructured C250 steel. It can be seen from the figure that the surface of the C250 steel sample after blowing hot air is hardened to 8.5GPa, and the hardening effect is obvious.

[0039] like Figure 6 As shown, there is a comparison diagram of fatigue performance between the gradient nanostructured C250 steel sample and the original sample. It can be seen from the figure that after the C250 steel is processed by the invention, its fatigue limit is increased from 650MPa to 850MPa, which significantly improves its rotational bending fatigue performance.

[0040] Comparative Example 1

[0041] The material and surface nano-processing method are the same as those in the example, except that no heating treatment is used; after the surface nano-processing, the maximum surface temperature of the material only reaches 6.5 GPa, and the surface aging precipitation strengthening phase is completely dissolved back, so the strengthening effect is not significant.

[0042] Comparative Example 2

[0043] The material and surface nano-processing method are the same as those in the example, except that the last step is heated at 100°C; after the surface nano-processing, the maximum surface stress of the material is only 6.5 GPa, and the surface aging precipitation strengthening phase is completely dissolved, so the strengthening effect is not significant.

[0044] Comparative Example 3

[0045] The material and surface nano-processing method are the same as those in the example, except that the last pass is heated to 600° C.; the surface nano-processing performance is poor and the surface is chipped.

[0046] It can be seen from the results of the examples that the surface strengthening method provided by the present invention is simple to implement. During the nano-treatment of the surface of C250 steel, local severe plastic deformation occurs on its surface, and the surface grain size is greatly reduced (350nm to 20nm); on the surface of C250 steel, Ni and Mo atoms are concentrated at the interface of the nanosheet structure, greatly improving the surface hardness (6.5GPa to 8.5GPa). And due to the introduction of the stiffness compensation device, the thickness of the gradient strengthening layer of C250 steel reaches 200μm, and the surface residual compressive stress is greater than 1500MPa. Therefore, this method can effectively construct a gradient nanostructure on the surface of maraging steel.

Claims

1. A method for constructing a gradient nanostructured maraging steel, characterized in that: The surface nano-treatment of maraging steel forms a gradient nanostructure layer with a depth of more than 200μm and significantly refines the surface grains to the nanometer level, while simultaneously changing the distribution, size and morphology of the precipitated phase, achieving the surface strengthening effect of maraging steel through grain refinement and interface segregation.

2. The method for constructing gradient nanostructured maraging steel according to claim 1, characterized in that: Through surface nano-processing, a gradient nano-structure layer with a depth of 200μm is achieved, and the microhardness and fatigue limit after surface strengthening are increased by more than 20%.

3. The method for constructing gradient nanostructured maraging steel according to claim 1, characterized in that: For maraging steel workpieces with mechanical surface treatment, the workpiece stiffness is compensated by an additional external stiffness compensation device during treatment; at the same time, a temperature field is applied in situ on the workpiece surface, and the temperature adjustment range is 200°C to 400°C.

4. The method for constructing gradient nanostructured maraging steel according to claim 1 or 3, characterized in that: The depth of the gradient nanostructured layer of maraging steel reaches 200μm, and the surface grain size of maraging steel is greatly reduced from 350nm to below 30nm.

5. The method for constructing gradient nanostructured maraging steel according to claim 1 or 3, characterized in that: This method is suitable for strengthening maraging steel.

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