Preparation method of ferrite / martensitic steel surface coating

Abstract

The invention provides a preparation method of a ferritic / martensitic steel surface coating. The preparation method comprises the following steps: carrying out grinding, polishing and cleaning pretreatment on the ferritic / martensitic steel surface; carrying out bias reverse sputtering cleaning on the surface of the ferrite / martensitic steel in magnetron sputtering equipment; pre-sputtering the surfaces of the Cr target and the Al target in an Ar atmosphere; depositing a Cr coating on the surface of the ferrite / martensitic steel through Cr target sputtering; depositing a CrAl coating on the surface of the ferrite / martensitic steel through double-target co-sputtering of a Cr target and an Al target; a Cr / CrAl multi-layer coating with the total layer number of 4-32 and the total thickness of 5-20 microns is formed on the surface of ferrite / martensitic steel by alternately depositing a Cr coating and a CrAl coating; and the surface coating of the ferrite / martensitic steel is subjected to destressing and correction deformation treatment. According to the preparation method of the ferrite / martensitic steel surface coating, the ferrite / martensitic steel surface coating has good high-temperature liquid lead and bismuth corrosion resistance.

Description

Technical Field

[0001] The invention relates to the technical field of structural materials for nuclear reactors, and in particular to a method for preparing a ferrite / martensitic steel surface coating. Background Art

[0002] Nuclear energy has always attracted international attention as a clean, efficient and sustainable energy source. Lead-cooled fast reactor, one of the fourth-generation reactors, has higher safety, economy and nuclear proliferation suppression than the third-generation reactor. Lead / bismuth eutectic alloy (LBE) is considered to be a promising candidate coolant material in lead-cooled fast reactors due to its excellent thermophysical properties and low chemical activity. However, the corrosion of lead / bismuth eutectic alloy (LBE) to steel structural materials is one of the important factors limiting its practical engineering application in lead-cooled fast reactors.

[0003] The corrosion of lead / bismuth eutectic alloy (LBE) on steel structure is mainly oxidation corrosion, penetration and dissolution corrosion of lead-bismuth alloy and erosion corrosion of materials by high-speed liquid lead-bismuth alloy. In order to solve the corrosion problem of lead / bismuth eutectic alloy (LBE), new lead-bismuth corrosion-resistant alloys can be developed or the surface of ferrite / martensite (F / M) steel structure materials can be treated.

[0004] The main way to treat the surface of ferrite / martensite (F / M) steel is to prepare a protective coating on the surface of the structural steel to prevent the ferrite / martensite (F / M) steel from dissolving or corroding in a lead-bismuth environment. The Cr coating is prepared on the surface of the material, which can form a dense and stable Cr2O3 oxide layer on the surface, hinder the diffusion of oxygen and inhibit the penetration of LBE, thereby protecting the structural material, improving the safety of reactor operation and the life of the cladding material. However, there are two problems with the Cr coating in the lead-bismuth environment: first, the growth of Cr2O3 is accompanied by a large growth stress (the growth stress of Cr2O3 / Cr is 2.07, Pilling-Bedworth), which makes the Cr2O3 oxide layer prone to cracks, warping or peeling, resulting in a shortened service life or even failure of the coating; second, the operating temperature of the lead-bismuth reactor is as high as 500-600℃, which can easily lead to excessive growth of the Cr coating grains, destroying the surface oxide film, and the long straight grain boundaries produced will also provide rapid diffusion channels for lead, bismuth and oxygen elements.

[0005] In view of the above problems, the alloying design concept is introduced to improve the performance of Cr coating by adding Al elements. A dense Al2O3 film is formed on the surface of CrAl coating, which is thinner than the protective oxide film formed on the surface of pure Cr coating and can effectively alleviate the problem of coating growth stress. However, during the oxidation process, the Al element in the CrAl coating will migrate rapidly to the coating surface, resulting in a large number of Al vacancies in the coating. The vacancies will induce other elements to diffuse into the coating or substrate. At the same time, the aggregation of vacancies will form holes and may derive cracks, causing the coating to peel off and cause coating failure.

[0006] Therefore, in order to address the problems of oxide layer cracks, warping or peeling in single Cr and CrAl coatings, as well as the intense migration of elements and excessive grain growth at high temperatures, it is currently urgent to develop a new method for preparing ferrite / martensitic steel surface coating so that when ferrite / martensitic steel is used in the liquid lead-bismuth coolant environment of a lead-cooled fast reactor, the coating on the ferrite / martensitic surface can improve the ferrite / martensitic matrix material's resistance to high-temperature liquid lead-bismuth corrosion. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a method for preparing a ferrite / martensitic steel surface coating with good resistance to high-temperature liquid lead-bismuth corrosion.

[0008] In order to solve the above technical problems, the present invention provides a method for preparing a ferrite / martensitic steel surface coating, which is suitable for preparing a liquid lead-bismuth corrosion-resistant coating on the surface of ferrite / martensitic steel in a lead / bismuth eutectic alloy coolant of a lead-cooled fast reactor, and comprises the following steps:

[0009] Grinding, polishing and cleaning pretreatment of ferrite / martensitic steel surface;

[0010] Bias reverse sputtering cleaning of ferrite / martensitic steel surfaces in magnetron sputtering equipment;

[0011] The surfaces of the Cr target and the Al target were pre-sputtered in an Ar atmosphere;

[0012] A Cr coating with a thickness of 600 to 4000 nm is deposited on the surface of ferrite / martensitic steel by sputtering a Cr target;

[0013] A CrAl coating with a thickness of 600 to 4000 nm is deposited on the surface of ferrite / martensitic steel by co-sputtering of a Cr target and an Al target;

[0014] By alternately depositing a Cr coating and a CrAl coating, a Cr / CrAl multilayer coating having a total number of 4 to 32 layers and a total thickness of 5 to 20 μm is formed on the surface of the ferrite / martensitic steel;

[0015] Stress relief and deformation correction treatment of ferrite / martensitic steel surface coating.

[0016] Furthermore, the pretreatment step of the ferrite / martensitic steel surface comprises:

[0017] Processing and cutting ferrite / martensitic steel to predetermined size according to design dimensions;

[0018] Use 240#, 600#, 1000#, 1500#, and 3000# water-abrasive sandpaper to grind the surface of ferrite / martensitic steel in turn;

[0019] Polishing of ferrite / martensitic steel with polishing paste on a metallographic polishing machine;

[0020] The ferrite / martensitic steel was ultrasonically cleaned with acetone and anhydrous ethanol for 10 to 20 minutes respectively and then dried.

[0021] Furthermore, the step of bias reverse sputtering cleaning of the ferrite / martensitic steel surface comprises:

[0022] Fixing the ferrite / martensitic steel on a sample stage in a vacuum furnace chamber of a magnetron sputtering device;

[0023] The sample stage is rotated so that the side of the sample stage fixing the ferrite / martensitic steel faces away from the target material;

[0024] Evacuate the vacuum furnace to a vacuum degree not higher than 2×10 -4 After the vacuum degree reaches 2-4 Pa, Ar gas is introduced into the vacuum furnace;

[0025] The ferrite / martensitic steel surface is cleaned by bias reverse sputtering for 15 to 20 minutes at a bias voltage of -500 to -700 V and a target-substrate distance of 8 to 12 cm.

[0026] Furthermore, the step of pre-sputtering the surfaces of the Cr target and the Al target under Ar atmosphere comprises:

[0027] After the bias reverse sputtering cleaning of ferrite / martensitic steel is completed, the argon gas is turned off;

[0028] After the vacuum degree of the vacuum furnace reaches the background vacuum degree, adjust the argon flow rate to 50-80 sccm to make the vacuum furnace pressure reach 0.5-1.0 Pa;

[0029] Under the conditions of pre-sputtering gas pressure of 0.5-1.0 Pa and pre-sputtering power of 150-300 W, turn on the power of Cr target and Al target, and pre-sputter clean the surface of Cr target and Al target for 5-15 minutes.

[0030] Furthermore, the purity of the Cr target is 99.99%, and the purity of the Al target is 99.999%.

[0031] Furthermore, the step of depositing a Cr coating on the surface of the ferrite / martensitic steel comprises:

[0032] After the pre-sputtering of the target material is completed, turn off the power supply of the Al target and keep the Cr target in the glowing state;

[0033] Using Ar as working atmosphere, setting argon gas flow rate 50-80sccm, sputtering pressure 0.4-1.0Pa, target-substrate distance 8-12cm, bias working voltage -50--150V, deposition temperature 150-400℃, Cr target sputtering power 600-800W;

[0034] The sample stage is rotated so that the ferrite / martensitic steel faces the target;

[0035] Cr target sputtering deposits a Cr coating with a thickness of 600 to 4000 nm on the surface of ferrite / martensitic steel.

[0036] Furthermore, the step of depositing a CrAl coating on the surface of the ferrite / martensitic steel comprises:

[0037] In the working atmosphere of Cr target sputtering, turn on the power supply of Al target;

[0038] Set the argon gas flow rate to 50-80sccm, the sputtering gas pressure to 0.4-1.0Pa, the target-substrate distance to 8-12cm, the bias working voltage to -50--150V, the deposition temperature to 150-400℃, the Cr target sputtering power to 600-800W, and the Al target sputtering power to 200-1000W;

[0039] The Cr target and the Al target are co-sputtered to deposit a CrAl coating with a thickness of 600 to 4000 nm on the Cr coating on the surface of the ferrite / martensitic steel.

[0040] Further, the step of alternately depositing the Cr coating and the CrAl coating comprises:

[0041] After the deposition of the CrAl coating on the surface of the ferrite / martensitic steel is completed, the power supply of the Al target is turned off, and the Cr target is sputtered repeatedly to deposit the Cr coating on the CrAl coating on the surface of the ferrite / martensitic steel;

[0042] Turn on the power supply of the Al target, repeat the co-sputtering of the Cr target and the Al target on the ferrite / martensitic steel surface to deposit the Cr coating and then the CrAl coating;

[0043] This process is repeated until the total number of coating layers on the ferrite / martensitic steel surface is 4 to 32 layers, and the total thickness is 5 to 20 μm.

[0044] Furthermore, the stress relief and deformation correction treatment of the ferrite / martensitic steel surface coating is to cool the ferrite / martensitic steel with the surface coating to below 100°C in the vacuum furnace after closing the working atmosphere, and then close the vacuum system and let it stand in the vacuum furnace for 5h to 10h before taking it out.

[0045] Furthermore, the Al content in the CrAl coating is 3wt% to 20wt%.

[0046] The present invention provides a method for preparing a ferrite / martensitic steel surface coating, which is suitable for preparing a liquid lead-bismuth corrosion-resistant coating on the surface of ferrite / martensitic steel in a lead / bismuth eutectic alloy coolant of a lead-cooled fast reactor. The method repeatedly deposits a plurality of Cr / CrAl coatings consisting of a Cr coating and a CrAl coating on the surface of the ferrite / martensitic steel through a Cr target sputtering deposition and a Cr target Al target dual-target magnetron co-sputtering deposition process, and can combine the excellent properties of the Cr coating and the CrAl coating together. At the same time, the interlayer interface introduced between each adjacent coating through a multilayer structure and the number of interlayer interfaces of the coating can effectively inhibit the diffusion migration of elements and grain growth, so that the material has higher chemical and structural stability, and can effectively slow down the diffusion of lead and bismuth elements into the matrix to form an oxide film with a protective effect, thereby greatly improving the lead-bismuth corrosion resistance of the ferrite / martensitic steel in the lead / bismuth eutectic alloy coolant of the lead-cooled fast reactor.

[0047] In addition, the present invention provides a method for preparing a ferrite / martensitic steel surface coating, which forms several layers of Cr / CrAl coatings composed of Cr coating and CrAl coating in sequence by repeatedly depositing on the surface of ferrite / martensitic steel, and performing stress relief and deformation correction treatment on the surface coating of ferrite / martensitic steel, thereby avoiding the rapid migration of Al elements in the CrAl coating to the coating surface during oxidation, and avoiding the appearance of a large number of Al vacancies in the coating to induce other elements to diffuse into the coating or substrate. At the same time, it also avoids the problems of vacancy aggregation to form holes that may derive cracks, causing coating peeling, causing coating failure, etc., thereby alleviating the stress concentration problem caused by Al element aggregation, improving the safety of the ferrite / martensitic steel surface coating, achieving the effective improvement of the coating's resistance to lead-bismuth corrosion in the lead / bismuth eutectic alloy coolant, improving the stability of the coating, solving the problem of obvious corrosion of the ferrite / martensitic steel surface in the lead-bismuth environment, and thus improving the service life of the lead-bismuth reactor fuel cladding structural material. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 A flow chart of a method for preparing a ferrite / martensitic steel surface coating provided by an embodiment of the present invention;

[0049] Figure 2The morphology and element analysis of the ferrite / martensitic steel surface coating prepared by the preparation method provided in Example 1 of the present invention, wherein (a) is the coating surface morphology and EDS element analysis, and (b) is the coating cross-sectional morphology;

[0050] Figure 3 The morphology and element analysis of the ferrite / martensitic steel surface coating prepared by the preparation method provided in Example 2 of the present invention, wherein (a) is the coating surface morphology and EDS element analysis, and (b) is the coating cross-sectional morphology;

[0051] Figure 4 The morphology and element analysis of the ferrite / martensitic steel surface coating prepared by the preparation method provided in Example 3 of the present invention, wherein (a) is the coating surface morphology and EDS element analysis, and (b) is the coating cross-sectional morphology;

[0052] Figure 5 The morphology and element analysis of the ferrite / martensitic steel surface coating prepared by the preparation method provided in Example 4 of the present invention, wherein (a) is the surface morphology and EDS element analysis of the coating, and (b) is the cross-sectional morphology of the coating;

[0053] Figure 6 A scratch morphology image of the ferrite / martensitic steel surface coating prepared by the preparation method provided in Example 1 of the present invention under a dynamic load of 0-100N on a scratch tester;

[0054] Figure 7 A scratch morphology image of the ferrite / martensitic steel surface coating prepared by the preparation method provided in Example 2 of the present invention under a dynamic load of 0-100N on a scratch tester;

[0055] Figure 8 A scratch morphology image of the ferrite / martensitic steel surface coating prepared by the preparation method provided in Example 3 of the present invention under a dynamic load of 0-100N on a scratch tester;

[0056] Fig. 9 A scratch morphology image of the ferrite / martensitic steel surface coating prepared by the preparation method provided in Example 4 of the present invention under a dynamic load of 0-100N on a scratch tester;

[0057] Fig.10 Surface morphology of the ferrite / martensitic steel surface coating prepared by the preparation method provided in Examples 1-4 of the present invention after being corroded in liquid lead-bismuth at 550°C for 500 hours. DETAILED DESCRIPTION

[0058] See also Figure 1 , a method for preparing a ferrite / martensitic steel surface coating provided by an embodiment of the present invention comprises the following steps:

[0059] Step 1) Pre-treating the surface of ferrite / martensitic steel by grinding, polishing and cleaning.

[0060] The pretreatment of the ferrite / martensitic steel surface specifically includes the following steps:

[0061] First, the ferrite / martensitic steel is processed and cut to a predetermined size according to the design dimensions.

[0062] Then, the surface of the ferrite / martensitic steel was polished with 240#, 600#, 1000#, 1500#, and 3000# water-abrasive sandpaper in turn.

[0063] The ground ferrite / martensitic steel surface is then polished using a metallographic polishing machine with polishing paste.

[0064] Finally, the surface of the ferrite / martensitic steel was ultrasonically cleaned with acetone and anhydrous ethanol for 10 to 20 minutes respectively, and then dried for later use.

[0065] Through the above pretreatment, not only impurities such as grease and adsorbents on the surface of the ferrite / martensitic steel substrate can be removed, but also the surface of the ferrite / martensitic steel substrate can have better adhesion to facilitate the subsequent deposition of the Cr / CrAl multilayer coating.

[0066] Step 2) The ferrite / martensitic steel surface is cleaned by bias reverse sputtering in a magnetron sputtering device.

[0067] The biased reverse sputtering cleaning of the ferrite / martensitic steel surface specifically includes the following steps:

[0068] First, the ferrite / martensitic steel is fixed on the sample stage in the vacuum furnace chamber of the magnetron sputtering equipment.

[0069] The sample stage is then rotated so that the side of the sample stage holding the ferrite / martensitic steel faces away from the target.

[0070] Then evacuate the vacuum furnace to a vacuum degree not higher than 2×10 -4 After 300 Pa, Ar gas is introduced to make the vacuum degree of the vacuum furnace reach 2-4Pa.

[0071] It is best to perform bias reverse sputtering cleaning on the ferrite / martensitic steel for 15 to 20 minutes under the conditions of a bias voltage of -500 to -700 V and a target-substrate distance of 8 to 12 cm, so as to complete the bias reverse sputtering cleaning of the ferrite / martensitic steel surface.

[0072] By using bias reverse sputtering cleaning on the surface of ferrite / martensitic steel, the oxide layer, machining burrs, oil stains and dirt on the surface of ferrite / martensitic steel can be further removed.

[0073] Step 3) Pre-sputtering the Cr target and Al target surfaces in an Ar atmosphere.

[0074] The pre-sputtering of the Cr target and the Al target surface under Ar atmosphere specifically includes the following steps:

[0075] After the bias back sputtering of the ferrite / martensitic steel surface was completed, the argon gas was turned off.

[0076] Then, after the vacuum degree of the vacuum furnace reaches the background vacuum degree, the argon flow rate is adjusted to 50-80 sccm so that the vacuum furnace pressure reaches 0.5-1.0 Pa.

[0077] Then, under the conditions of a pre-sputtering gas pressure of 0.5-1.0 Pa and a pre-sputtering power of 150-300 W, turn on the power supplies of the Cr target and the Al target, and pre-sputter clean the surfaces of the Cr target and the Al target for 5-15 minutes.

[0078] By pre-sputtering the surfaces of the Cr target and the Al target, oxides and / or adsorbed impurities on the surfaces of the Cr target and the Al target can be removed respectively, thereby achieving the purpose of cleaning the surfaces of the Cr target and the Al target.

[0079] In order to improve the subsequent deposition of high-quality Cr coating and CrAl coating on the surface of ferrite / martensitic steel, the purity of the Cr target is 99.99%, and the purity of the Al target is 99.999%.

[0080] Step 4) depositing a Cr coating with a thickness of 600 to 4000 nm on the surface of the ferrite / martensitic steel by sputtering a Cr target.

[0081] The deposition of Cr coating on the surface of ferrite / martensitic steel specifically includes the following steps:

[0082] After the pre-sputtering of the Cr target and the Al target is completed, turn off the power supply of the Al target first and keep the Cr target in the ignited state.

[0083] Then, Ar is used as the working atmosphere, the argon flow rate is set to 50-80 sccm, the sputtering pressure is set to 0.4-1.0 Pa, the target-substrate distance is set to 8-12 cm, the bias working voltage is set to -50--150 V, the deposition temperature is set to 150-400°C, and the Cr target sputtering power is set to 600-800 W.

[0084] The sample stage is then rotated so that the ferrite / martensitic steel on the sample stage faces the target.

[0085] Finally, Cr target sputtering is performed to deposit a Cr coating with a thickness of 600 to 4000 nm on the surface of the ferrite / martensitic steel.

[0086] The deposition time of the Cr coating is set according to the required thickness of the Cr coating.

[0087] Step 5) depositing a CrAl coating with a thickness of 600 to 4000 nm on the surface of the ferrite / martensitic steel by co-sputtering of a Cr target and an Al target.

[0088] The deposition of CrAl coating on the surface of ferrite / martensitic steel specifically includes the following steps:

[0089] While maintaining the working atmosphere of Cr target sputtering, turn on the power supply of Al target.

[0090] Then set the argon gas flow rate to 50-80sccm, the sputtering gas pressure to 0.4-1.0Pa, the target-substrate distance to 8-12cm, the bias working voltage to -50--150V, the deposition temperature to 150-400°C, the Cr target sputtering power to 600-800W, and the Al target sputtering power to 200-1000W.

[0091] Finally, a Cr target and an Al target are co-sputtered to deposit a CrAl coating with a thickness of 600 to 4000 nm on the Cr coating on the surface of the ferrite / martensitic steel.

[0092] The deposition time of the CrAl coating is set according to the required thickness of the CrAl coating, and the power supply of the Al target is immediately turned off after the deposition of the CrAl coating is completed, so as to carry out the next deposition of the Cr coating.

[0093] Step 6) By alternately depositing a Cr coating and a CrAl coating, a Cr / CrAl multilayer coating with a total number of 4 to 32 layers and a total thickness of 5 to 20 μm is formed on the surface of the ferrite / martensitic steel.

[0094] The alternate deposition of the Cr coating and the CrAl coating specifically includes the following steps:

[0095] After the CrAl coating deposition on the ferrite / martensitic steel surface is completed, the Al target power supply is turned off, and then the Cr target sputtering in step 4) is repeated to deposit another Cr coating with a thickness of 600 to 4000 nm on the CrAl coating on the ferrite / martensitic steel surface.

[0096] Then, the power supply of the Al target is turned on, and the Cr target and the Al target are co-sputtered in step 5) to deposit another CrAl coating with a thickness of 600 to 4000 nm on the Cr coating on the surface of the ferrite / martensitic steel.

[0097] This process is repeated until the total number of coating layers on the surface of the ferrite / martensitic steel is 4 to 32 layers, with a total thickness of 5 to 20 μm.

[0098] Wherein, the Al content in the CrAl coating is 3wt% to 20wt%.

[0099] By repeatedly depositing on the surface of ferrite / martensitic steel to form several layers of Cr / CrAl coatings composed of Cr coating and CrAl coating in sequence, the excellent properties of Cr coating and CrAl coating can be combined together. At the same time, an interlayer interface is introduced between adjacent coatings through a multi-layer structure, and the number of interlayer interfaces of the coating is adjusted. The diffusion migration of elements and grain growth can be effectively inhibited, so that the material has higher chemical and structural stability, and the diffusion of lead and bismuth elements into the matrix can be effectively slowed down to form an oxide film with a protective effect, thereby greatly improving the lead-bismuth corrosion resistance of ferrite / martensitic steel in the lead / bismuth eutectic alloy coolant of a lead-cooled fast reactor.

[0100] In addition, forming several layers of Cr / CrAl coatings composed of Cr coating and CrAl coating in sequence on the surface of ferrite / martensitic steel can also avoid the rapid migration of Al elements in the CrAl coating to the coating surface during oxidation, and avoid the appearance of a large number of Al vacancies in the coating to induce other elements to diffuse into the coating or substrate. At the same time, it also avoids the problems of vacancies gathering to form holes and possibly deriving cracks, causing coating peeling, causing coating failure, etc., thereby alleviating the stress concentration problem caused by Al element aggregation, improving the safety of the ferrite / martensitic steel surface coating, and achieving the goal of effectively improving the lead-bismuth corrosion resistance of the coating in the lead / bismuth eutectic alloy coolant, improving the stability of the coating, solving the problem of obvious corrosion of the ferrite / martensitic steel surface in the lead-bismuth environment, and thus improving the service life of the lead-bismuth reactor fuel cladding structural material.

[0101] Step 7) performing stress relief and deformation correction treatment on the surface coating of ferrite / martensitic steel.

[0102] After the ferrite / martensitic steel surface coating is completed, the working atmosphere is closed to allow the ferrite / martensitic steel to cool to below 100° C. along with the vacuum furnace, and then the vacuum system is closed and the ferrite / martensitic steel is allowed to stand in the vacuum furnace for 5 to 10 hours before being taken out, thereby preparing the ferrite / martensitic steel surface coating of the present invention.

[0103] Since magnetron sputtering has a certain stress, allowing the ferrite / martensitic steel surface coating to cool naturally with the vacuum furnace in the heat preservation is conducive to eliminating the stress inside the coating, preventing the coating from peeling off, and making the coating more tightly bonded to the substrate. Therefore, the present invention can avoid stress peeling and surface oxidation of the coating caused by external pressure and temperature mutation by relieving stress and correcting deformation of the ferrite / martensitic steel surface coating. In addition, the higher the temperature when the coating is deposited on the ferrite / martensitic steel surface, the longer the standing time should be.

[0104] The following is a specific description of the method for preparing a ferrite / martensitic steel surface coating provided by the present invention through examples.

[0105] Example 1

[0106] In this embodiment, the multilayer coating on the surface of ferrite / martensitic steel (hereinafter referred to as F / M steel) is prepared according to the following steps:

[0107] (1) Pretreatment

[0108] The F / M steel substrate was processed into a square piece with a side length of 10*10*1mm, and polished from coarse to fine with 240#, 600#, 1000#, 1500#, and 3000# water-abrasive sandpaper in sequence. Finally, it was polished on a metallographic polishing machine with polishing paste. After polishing, it was ultrasonically cleaned with acetone and anhydrous ethanol for 15 minutes respectively. After cleaning, it was dried for use.

[0109] (2) Biased reverse sputtering cleaning

[0110] The F / M steel substrate treated in step (1) was fixed on the sample stage in the vacuum furnace chamber of the magnetron sputtering equipment by edge pressing. The sample stage was rotated so that the side with the F / M steel was facing away from the target. A low vacuum was first drawn using a mechanical pump, and then a high vacuum was drawn using a molecular pump until the background vacuum reached 2×10 -4 Pa, argon was introduced as the working gas, and the F / M steel substrate was cleaned by bias reverse sputtering under the conditions of -600 V bias, 3 Pa reverse sputtering gas pressure, and 10 cm target-substrate distance. The cleaning time was 20 min.

[0111] (3) Target pre-sputtering

[0112] After the backsputtering cleaning of the F / M steel substrate surface is completed, the argon flow rate is adjusted to 80sccm to make the pre-sputtering gas pressure reach 1.0Pa. The Cr target and Al target are quickly ignited using a DC magnetron power supply. Then, the Cr target and Al target are pre-sputtered under the conditions of a pre-sputtering gas pressure of 1.0Pa and a pre-sputtering power of 300W. The pre-sputtering time is 10min.

[0113] (4) Deposition of Cr coating

[0114] Maintaining the argon atmosphere in step (3), turn off the Al target power supply, and sputter the Cr target material under the conditions of sputtering gas pressure of 0.6 Pa, sputtering power of 800 W, bias working voltage of -50 V, and deposition temperature of 300°C, and the sputtering time is 50 min.

[0115] (5) Deposition of CrAl coating

[0116] Maintaining the argon atmosphere in step (4), under the conditions of sputtering pressure of 0.6 Pa, Cr target sputtering power of 800 W, Al target sputtering power of 200 W, bias working voltage of -50 V, and deposition temperature of 300 ° C, turn on the Al target power supply to make the Cr target and Al target co-sputter to deposit the CrAl coating, and the sputtering time is 48 min.

[0117] (6) Alternating deposition of Cr / CrAl coating

[0118] Repeat steps (4) and (5) to alternately deposit Cr layers and CrAl layers to obtain F / M steel with a Cr / CrAl multilayer coating having a total number of 4 layers deposited on the surface.

[0119] (7) Stress relief and deformation correction

[0120] After the Cr / CrAl multilayer coating was deposited on the surface of the F / M steel substrate, the gas was stopped and the vacuum was evacuated to 4×10 - 4 Pa, then stand still for 4 hours under the deposition temperature conditions, then cool with the furnace to below 100°C, then turn off the vacuum system and stand still for 8 hours, so as to complete the stress relief and deformation correction treatment of the multi-layer coating on the surface of the F / M steel substrate and obtain a coating for the lead-bismuth corrosion resistance of the F / M steel surface.

[0121] In the ferrite / martensitic steel surface coating prepared in the embodiment of the present invention, the Al content in the single-layer CrAl layer is about 3wt%, the thickness of the single-layer coating is about 3.75μm, the total thickness of the multi-layer coating is about 15μm, and the total number of layers of the multi-layer coating is 4.

[0122] The morphology and element analysis of the ferrite / martensitic steel surface coating prepared in the embodiment of the present invention were performed using a scanning electron microscope and an energy dispersive spectrometer. The surface morphology and EDS element analysis of the obtained coating are as follows: Figure 2 (a) shows the cross-sectional morphology of the obtained coating. Figure 2 (b) as shown.

[0123] The bonding strength of the ferrite / martensitic steel surface coating prepared in the embodiment of the present invention was estimated using an automatic scratch tester. The coating was subjected to a scratch test under a linear dynamic load increase. The scratch morphology was observed using a scanning electron microscope. The scratch morphology of the coating under a load of 0-100N was obtained as shown in FIG. Figure 6 shown.

[0124] The surface morphology of the ferrite / martensitic steel surface coating prepared in the embodiment of the present invention after being corroded in a 550°C liquid lead-bismuth environment for 500 hours is shown in FIG. Fig.10 (a) shown.

[0125] Example 2

[0126] In this embodiment, the multilayer coating for the surface of F / M steel is prepared according to the following steps:

[0127] (1) Pretreatment

[0128] The F / M steel substrate was processed into a square piece with a side length of 10*10*1mm, and polished from coarse to fine with 240#, 600#, 1000#, 1500#, and 3000# water-abrasive sandpaper in sequence. Finally, it was polished on a metallographic polishing machine with polishing paste. After polishing, it was ultrasonically cleaned with acetone and anhydrous ethanol for 10 minutes respectively, and dried for use after cleaning.

[0129] (2) Biased reverse sputtering cleaning

[0130] The F / M steel substrate treated in step (1) was fixed on the sample stage in the vacuum furnace chamber of the magnetron sputtering equipment by edge pressing. The sample stage was rotated so that the side with F / M steel was facing away from the target. A low vacuum was first drawn using a mechanical pump, and then a high vacuum was drawn using a molecular pump until the background vacuum reached 2×10 -4 Pa, argon was introduced as the working gas, and the F / M steel substrate was cleaned by bias reverse sputtering under the conditions of reverse sputtering voltage of -700 V bias and reverse sputtering gas pressure of 2 Pa, and the cleaning time was 15 min.

[0131] (3) Target pre-sputtering

[0132] After the backsputtering cleaning of the F / M steel substrate surface is completed, the argon flow rate is adjusted to 80sccm to make the pre-sputtering gas pressure reach 1.0Pa. The Cr target and Al target are quickly ignited using a DC magnetron power supply. Then, the Cr target and Al target are pre-sputtered under the conditions of a pre-sputtering gas pressure of 1.0Pa and a pre-sputtering power of 200W. The pre-sputtering time is 15min.

[0133] (4) Deposition of Cr coating

[0134] Maintaining the argon atmosphere in step (3), turn off the Al target power supply, and sputter the Cr target under the conditions of sputtering gas pressure of 0.8 Pa, sputtering power of 800 W, bias working voltage of -100 V, and deposition temperature of 300°C, and the sputtering time is 8.4 min.

[0135] (5) Deposition of CrAl coating

[0136] Maintaining the argon atmosphere in step (4), under the conditions of sputtering pressure of 0.8 Pa, Cr target sputtering power of 800 W, Al target sputtering power of 600 W, bias working voltage of -100 V, and deposition temperature of 300°C, turn on the Al target power supply to allow the Cr target and Al target to be co-sputtered to deposit the CrAl coating, and the sputtering time is 8 min.

[0137] (6) Alternating deposition of Cr / CrAl coating

[0138] Repeat steps (4) and (5) to alternately deposit Cr layers and CrAl layers to obtain F / M steel with a Cr / CrAl multilayer coating having a total number of 32 layers deposited on the surface.

[0139] (7) Stress relief and deformation correction

[0140] After the Cr / CrAl multilayer coating was deposited on the surface of the F / M steel substrate, the gas was stopped and the vacuum was evacuated to 4×10 - 4 Pa, then let it stand for 6 hours under the deposition temperature conditions, then cool to below 100°C with the furnace, turn off the vacuum system, and let it stand for 6 hours, so as to complete the stress relief and deformation correction treatment of the multi-layer coating on the surface of the F / M steel substrate and obtain a coating for the lead-bismuth corrosion resistance of the F / M steel surface.

[0141] In the ferrite / martensitic steel surface coating prepared in the embodiment of the present invention, the Al content in the single-layer CrAl layer is about 9.2wt%, the thickness of the single-layer coating is about 0.6μm, the total thickness of the multi-layer coating is about 19.2μm, and the total number of layers of the multi-layer coating is 32.

[0142] The morphology and element analysis of the ferrite / martensitic steel surface coating prepared in the embodiment of the present invention were performed using a scanning electron microscope and an energy dispersive spectrometer. The surface morphology and EDS element analysis of the obtained coating are as follows: Figure 3 (a) shows the cross-sectional morphology of the obtained coating. Figure 3 (b) as shown.

[0143] The bonding strength of the ferrite / martensitic steel surface coating prepared in the embodiment of the present invention was estimated using an automatic scratch tester. The coating was subjected to a scratch test under a linear dynamic load increase. The scratch morphology was observed using a scanning electron microscope. The scratch morphology of the coating under a load of 0-100N was obtained as shown in FIG. Figure 7 shown.

[0144] The surface morphology of the ferrite / martensitic steel surface coating prepared in the embodiment of the present invention after being corroded in a 550°C liquid lead-bismuth environment for 500 hours is shown in FIG. Fig.10 (b) as shown.

[0145] Example 3

[0146] In this embodiment, the multilayer coating for the surface of F / M steel is prepared according to the following steps:

[0147] (1) Pretreatment

[0148] The F / M steel substrate was processed into a square piece with a side length of 10*10*1mm, and polished from coarse to fine with 240#, 600#, 1000#, 1500#, and 3000# water-abrasive sandpaper in sequence. Finally, it was polished on a metallographic polishing machine with polishing paste. After polishing, it was ultrasonically cleaned with acetone and anhydrous ethanol for 20 minutes respectively. After cleaning, it was dried for use.

[0149] (2) Biased reverse sputtering cleaning

[0150] The F / M steel substrate treated in step (1) was fixed on the sample stage in the vacuum furnace chamber of the magnetron sputtering equipment by edge pressing. The sample stage was rotated so that the side with F / M steel was facing away from the target. A low vacuum was first drawn using a mechanical pump, and then a high vacuum was drawn using a molecular pump until the background vacuum reached 2×10 -4 Pa, argon was introduced as the working gas, and the F / M steel substrate was cleaned by bias reverse sputtering under the conditions of reverse sputtering voltage of -700 V bias and reverse sputtering gas pressure of 2 Pa, and the cleaning time was 20 min.

[0151] (3) Target pre-sputtering

[0152] After the backsputtering cleaning of the F / M steel substrate surface is completed, the argon flow rate is adjusted to 80sccm to make the pre-sputtering gas pressure reach 1.0Pa. The Cr target and Al target are quickly ignited using a DC magnetron power supply. Then, the Cr target and Al target are pre-sputtered under the conditions of a pre-sputtering gas pressure of 1.0Pa and a pre-sputtering power of 200W. The pre-sputtering time is 10min.

[0153] (4) Deposition of Cr coating

[0154] Keep the argon atmosphere in step (3), turn off the Al target power supply, and sputter the Cr target under the conditions of sputtering gas pressure of 0.6 Pa, sputtering power of 800 W, bias working voltage of -50 V, deposition temperature of 300 ° C, and the sputtering time is 10 min.

[0155] (5) Deposition of CrAl coating

[0156] Maintaining the argon atmosphere in step (4), under the conditions of sputtering pressure of 0.6 Pa, Cr target sputtering power of 800 W, Al target sputtering power of 800 W, bias working voltage of -50 V, and deposition temperature of 300°C, turn on the Al target power supply to allow the Cr target and Al target to be co-sputtered to deposit the CrAl coating, and the sputtering time is 7.5 min.

[0157] (6) Alternating deposition of Cr / CrAl coating

[0158] Repeat steps (4) and (5) to alternately deposit Cr layers and CrAl layers to obtain F / M steel with a total of 8 layers of Cr / CrAl multilayer coating deposited on the surface.

[0159] (7) Stress relief and deformation correction

[0160] After the Cr / CrAl multilayer coating was deposited on the surface of the F / M steel substrate, the gas was stopped and the vacuum was evacuated to 4×10 - 4 Pa, then stand at the deposition temperature for 4 hours, then cool with the furnace to below 100°C, close the vacuum system, and stand for 8 hours to complete the stress relief and deformation correction treatment of the multilayer coating on the surface of the F / M steel substrate, and obtain a coating for the F / M steel surface resistant to lead-bismuth corrosion.

[0161] In the ferrite / martensitic steel surface coating prepared in the embodiment of the present invention, the Al content in the single-layer CrAl layer is about 14wt%, the thickness of the single-layer coating is about 0.75μm, the total thickness of the multi-layer coating is about 6μm, and the number of multi-layer coating layers is 8.

[0162] The morphology and element analysis of the ferrite / martensitic steel surface coating prepared in the embodiment of the present invention were performed using a scanning electron microscope and an energy dispersive spectrometer. The surface morphology and EDS element analysis of the obtained coating are as follows: Figure 4 (a) shows the cross-sectional morphology of the obtained coating. Figure 4 (b) as shown.

[0163] The bonding strength of the ferrite / martensitic steel surface coating prepared in the embodiment of the present invention was estimated using an automatic scratch tester. The coating was subjected to a scratch test under a linear dynamic load increase. The scratch morphology was observed using a scanning electron microscope. The scratch morphology of the coating under a load of 0-100N was obtained as shown in FIG. Figure 8 shown.

[0164] The surface morphology of the ferrite / martensitic steel surface coating prepared in the embodiment of the present invention after being corroded in a 550°C liquid lead-bismuth environment for 500 hours is shown in FIG. Fig.10 (c) as shown.

[0165] Example 4

[0166] In this embodiment, the multilayer coating for the surface of F / M steel is prepared according to the following steps:

[0167] (1) Pretreatment

[0168] The F / M steel substrate was processed into a square piece with a side length of 10*10*1mm, and polished from coarse to fine with 240#, 600#, 1000#, 1500#, and 3000# water-abrasive sandpaper in sequence. Finally, it was polished on a metallographic polishing machine with polishing paste. After polishing, it was ultrasonically cleaned with acetone and anhydrous ethanol for 15 minutes respectively. After cleaning, it was dried for use.

[0169] (2) Biased reverse sputtering cleaning

[0170] The F / M steel substrate treated in step (1) was fixed on the sample stage in the vacuum furnace chamber of the magnetron sputtering equipment by edge pressing. The sample stage was rotated so that the side with F / M steel was facing away from the target. A low vacuum was first drawn using a mechanical pump, and then a high vacuum was drawn using a molecular pump until the background vacuum reached 2×10 -4 Pa, argon was introduced as the working gas, and the F / M steel substrate was cleaned by bias reverse sputtering under the conditions of -600 V bias and 3 Pa reverse sputtering pressure, and the cleaning time was 15 min.

[0171] (3) Target pre-sputtering

[0172] After the backsputtering cleaning of the F / M steel substrate surface is completed, the argon flow rate is adjusted to 80sccm to make the pre-sputtering gas pressure reach 1.0Pa. The Cr target and Al target are quickly ignited using a DC magnetron power supply. Then, the Cr target and Al target are pre-sputtered under the conditions of a pre-sputtering gas pressure of 1.0Pa and a pre-sputtering power of 250W. The pre-sputtering time is 15min.

[0173] (4) Deposition of Cr coating

[0174] Keeping the argon atmosphere in step (3), turn off the power supply of the Al target, and sputter the Cr target under the conditions of sputtering pressure of 0.8 Pa, sputtering power of 600 W, bias working voltage of -150 V, deposition temperature of 300 ° C., and the sputtering time is 18 min.

[0175] (5) Deposition of CrAl coating

[0176] Maintaining the argon atmosphere in step (4), under the conditions of sputtering pressure of 1.0 Pa, Cr target sputtering power of 600 W, Al target sputtering power of 1000 W, bias working voltage of -150 V, and deposition temperature of 300 ° C, turn on the Al target power supply to make the Cr target and Al target co-sputter to deposit the CrAl coating, and the sputtering time is 15 min.

[0177] (6) Alternating deposition of Cr / CrAl coating

[0178] Repeat steps (4) and (5) to alternately deposit Cr layers and CrAl layers to obtain F / M steel with a total of 16 layers of Cr / CrAl multilayer coating deposited on the surface.

[0179] (7) Stress relief and deformation correction

[0180] After the Cr / CrAl multilayer coating was deposited on the surface of the F / M steel substrate, the gas was stopped and the vacuum was evacuated to 4×10 - 4 Pa, then let it stand for 4 hours under the deposition temperature conditions, then cool it to below 100°C with the furnace, turn off the vacuum system, and let it stand for 10 hours, so as to complete the stress relief and deformation correction treatment of the multi-layer coating on the surface of the F / M steel substrate and obtain a coating for the lead-bismuth corrosion resistance of the F / M steel surface.

[0181] In the ferrite / martensitic steel surface coating prepared in the embodiment of the present invention, the Al content in the single-layer CrAl layer is about 20wt%, the thickness of the single-layer coating is about 1.25μm, the total thickness of the multi-layer coating is about 20μm, and the total number of layers of the multi-layer coating is 16.

[0182] The morphology and element analysis of the ferrite / martensitic steel surface coating prepared in the embodiment of the present invention were performed using a scanning electron microscope and an energy dispersive spectrometer. The surface morphology and EDS element analysis of the obtained coating are as follows: Figure 5 (a) shows the cross-sectional morphology of the obtained coating. Figure 5 (b) as shown.

[0183] The bonding strength of the ferrite / martensitic steel surface coating prepared in the embodiment of the present invention was estimated using an automatic scratch tester. The coating was subjected to a scratch test under a linear dynamic load increase. The scratch morphology was observed using a scanning electron microscope. The scratch morphology of the coating under a load of 0-100N was obtained as shown in FIG. Fig. 9 shown.

[0184] The surface morphology of the ferrite / martensitic steel surface coating prepared in the embodiment of the present invention after being corroded in a 550°C liquid lead-bismuth environment for 500 hours is shown in FIG. Fig.10 (d) as shown.

[0185] from Figure 2-Figure 5 It can be seen that the surfaces of the ferrite / martensitic steel surface coatings prepared in Examples 1-4 of the present invention are dense and continuous, no obvious defects are observed in a large range, their cross-sectional interfaces are clear, and the coatings are dense. No obvious defects are observed on the surfaces of each coating, indicating that the quality of the ferrite / martensitic steel surface coatings prepared in Examples 1-4 of the present invention is good.

[0186] from Figure 6-Figure 9It can be seen that in the scratch test of the ferrite / martensitic steel surface coating prepared in Examples 1-4 of the present invention, no acoustic emission signal was observed at a loading force of 0 to 100 N, indicating that the coating is tightly bonded to the substrate, and the bonding force between the coating and the substrate surface exceeds 100 N, indicating that the coating has excellent bonding performance with the substrate, which is crucial for the coating to meet practical engineering applications.

[0187] from Fig. 9 It can be seen that after the lead-bismuth corrosion, no obvious cracks were observed on the surface of the ferrite / martensitic steel surface coating prepared in Examples 1-4 of the present invention, and the surface was still well preserved, showing good resistance to lead-bismuth corrosion.

[0188] The invention provides a method for preparing a ferrite / martensitic steel surface coating. Through Cr target sputtering deposition and Cr target Al target dual-target magnetron co-sputtering deposition processes, 4 to 32 layers of Cr / CrAl coatings with a thickness of 5 μm to 20 μm, which are sequentially composed of a Cr coating and a CrAl coating, are repeatedly deposited on the surface of the ferrite / martensitic steel. The Cr coating and the CrAl coating have excellent properties that are combined together, and an interlayer interface is introduced between adjacent coatings through a multilayer structure. The diffusion and migration of Pb and Bi elements to a substrate can be effectively slowed down, and the stress concentration problem caused by the aggregation of Al elements can be slowed down, so as to form an oxide film with good protective effect, thereby making the ferrite / martensitic steel have good corrosion resistance in a high-temperature liquid lead-bismuth eutectic coolant, and improving the safety of the ferrite / martensitic steel surface coating.

[0189] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A method for preparing a ferrite / martensitic steel surface coating, which is suitable for preparing a high-temperature liquid lead-bismuth corrosion-resistant coating on the surface of ferrite / martensitic steel in a lead / bismuth eutectic alloy coolant of a lead-cooled fast reactor, characterized in that: The steps include: Grinding, polishing and cleaning pretreatment of ferrite / martensitic steel surface; Bias reverse sputtering cleaning of ferrite / martensitic steel surfaces in magnetron sputtering equipment; The surfaces of Cr target and Al target were pre-sputtered in Ar atmosphere; A Cr coating with a thickness of 600 to 4000 nm is deposited on the surface of ferrite / martensitic steel by sputtering a Cr target; A CrAl coating with a thickness of 600 to 4000 nm is deposited on the surface of ferrite / martensitic steel by co-sputtering of a Cr target and an Al target; By alternately depositing a Cr coating and a CrAl coating, a Cr / CrAl multilayer coating having a total number of 4 to 32 layers and a total thickness of 5 to 20 μm is formed on the surface of the ferrite / martensitic steel; Stress relief and deformation correction treatment of ferrite / martensitic steel surface coating.

2. The method for preparing a ferrite / martensitic steel surface coating according to claim 1, characterized in that: The pretreatment step of the ferrite / martensitic steel surface comprises: Process and cut the ferrite / martensitic steel to a predetermined size according to the designed dimensions; Use 240#, 600#, 1000#, 1500#, and 3000# water-abrasive sandpaper to grind the surface of ferrite / martensitic steel in turn; The ferrite / martensitic steel surface is polished with polishing paste on a metallographic polishing machine; The surface of ferrite / martensitic steel was ultrasonically cleaned with acetone and anhydrous ethanol for 10 to 20 minutes respectively and then dried.

3. The method for preparing a ferrite / martensitic steel surface coating according to claim 1, characterized in that: The step of bias reverse sputtering cleaning of the ferrite / martensitic steel surface comprises: Fixing the ferrite / martensitic steel on a sample stage in a vacuum furnace chamber of a magnetron sputtering device; The sample stage is rotated so that the side of the sample stage fixing the ferrite / martensitic steel faces away from the target material; Evacuate the vacuum furnace to a vacuum degree not higher than 2×10 -4 After the vacuum degree reaches 2-4 Pa, Ar gas is introduced into the vacuum furnace; The ferrite / martensitic steel surface is cleaned by bias reverse sputtering for 15 to 20 minutes at a bias voltage of -500 to -700 V and a target-substrate distance of 8 to 12 cm.

4. The method for preparing a ferrite / martensitic steel surface coating according to claim 1, characterized in that: The step of pre-sputtering the surfaces of the Cr target and the Al target under Ar atmosphere comprises: After the bias reverse sputtering cleaning of ferrite / martensitic steel is completed, the argon gas is turned off; After the vacuum degree of the vacuum furnace reaches the background vacuum degree, adjust the argon flow rate to 50-80 sccm to make the vacuum furnace pressure reach 0.5-1.0 Pa; Under the conditions of pre-sputtering gas pressure of 0.5-1.0 Pa and pre-sputtering power of 150-300 W, turn on the power of Cr target and Al target, and pre-sputter clean the surface of Cr target and Al target for 5-15 minutes.

5. The method for preparing a ferrite / martensitic steel surface coating according to claim 4, characterized in that: The purity of the Cr target is 99.99%, and the purity of the Al target is 99.999%.

6. The method for preparing a ferrite / martensitic steel surface coating according to claim 1, characterized in that: The step of depositing a Cr coating on the surface of the ferrite / martensitic steel comprises: After the pre-sputtering of the target material is completed, turn off the power supply of the Al target and keep the Cr target in the glowing state; Using Ar as working atmosphere, setting argon gas flow rate 50-80sccm, sputtering pressure 0.4-1.0Pa, target-substrate distance 8-12cm, bias working voltage -50--150V, deposition temperature 150-400℃, Cr target sputtering power 600-800W; The sample stage is rotated so that the ferrite / martensitic steel faces the target; Cr target sputtering deposits a Cr coating with a thickness of 600 to 4000 nm on the surface of ferrite / martensitic steel.

7. The method for preparing a ferrite / martensitic steel surface coating according to claim 1, characterized in that: The step of depositing a CrAl coating on the surface of ferrite / martensitic steel comprises: In the working atmosphere of Cr target sputtering, turn on the power supply of Al target; Set the argon gas flow rate to 50-80sccm, the sputtering gas pressure to 0.4-1.0Pa, the target-substrate distance to 8-12cm, the bias working voltage to -50--150V, the deposition temperature to 150-400℃, the Cr target sputtering power to 600-800W, and the Al target sputtering power to 200-1000W; The Cr target and the Al target are co-sputtered to deposit a CrAl coating with a thickness of 600 to 4000 nm on the Cr coating on the surface of the ferrite / martensitic steel.

8. The method for preparing a ferrite / martensitic steel surface coating according to claim 1, characterized in that: The step of alternately depositing the Cr coating and the CrAl coating comprises: After the deposition of the CrAl coating on the surface of the ferrite / martensitic steel is completed, the power supply of the Al target is turned off, and the Cr target is sputtered repeatedly to deposit the Cr coating on the CrAl coating on the surface of the ferrite / martensitic steel; Turn on the power supply of the Al target, repeat the co-sputtering of the Cr target and the Al target on the ferrite / martensitic steel surface to deposit the Cr coating and then the CrAl coating; This process is repeated until the total number of coating layers on the ferrite / martensitic steel surface is 4 to 32 layers, and the total thickness is 5 to 20 μm.

9. The method for preparing a ferrite / martensitic steel surface coating according to claim 1, characterized in that: The stress relief and deformation correction treatment of the ferrite / martensitic steel surface coating is to cool the ferrite / martensitic steel with the surface coating to below 100° C. in a vacuum furnace after closing the working atmosphere, and then close the vacuum system and let it stand in the vacuum furnace for 5 hours to 10 hours before taking it out.

10. The method for preparing a ferrite / martensitic steel surface coating according to any one of claims 1 to 9, characterized in that: The Al content in the CrAl coating is 3wt% to 20wt%.

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