JPH0362788B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention generally relates to an improvement in the method of forming a heat-resistant and corrosion-resistant coated steel material formed on the surface of a plate, pipe, bar, etc. for the purpose of exhibiting heat resistance and corrosion resistance at the same time. It is. [Prior art] Conventionally, this type of heat-resistant and corrosion-resistant steel material has been produced by applying Zn-Ni or Zn to the surface of the steel material by electroplating, for example.
In practical use, a plating film made of -Ti alloy or the like was applied, or a plating film made of Al or Al-Zn alloy etc. was applied by a melting method. However, in the case of the former, although the corrosion resistance is satisfactory to a certain extent, the heat resistance is still insufficient, and there is a problem in that the adjustment and maintenance of the bath composition during the electroplating treatment causes extremely troublesome management. However, in the latter case, corrosion resistance is still insufficient, and on the other hand, not only does the work during hot-dip plating become extremely complicated, but also the uniformity of the film thickness is generally poor, and the occurrence of pinballs cannot be avoided. This process produces a brittle intermetallic compound layer in the middle, which causes problems such as cracking and peeling of the plating film during post-processing, which both satisfy heat resistance and corrosion resistance at the same time. The current situation is such that improvements are desired. [Problems to be solved by the invention] The present invention solves the above-mentioned conventional problems on the surface of steel materials.
Particularly Fe- due to the diffusion of Ni and Cr into some steel substrates.
By forming a coating layer of Ni-Cr alloy, the surface condition approximates as much as possible the microstructural structure of austenitic stainless steel, and by using a simple coating formation method, we can effectively solve the problem and simultaneously achieve heat resistance and corrosion resistance. The purpose of this study is to propose a method for forming a coated steel material with satisfactory heat and corrosion resistance. [Means for Solving the Problems] The present invention applies 2 to 6μ of Ni and 4 to 15μ of Ni by electroplating on the surface of a steel material that has been pretreated by degreasing, derusting, etc.
A multilayer plating film is formed with Cr, and then immersed in a molten salt bath consisting of a mixture of borax and boric acid and heat treated at a temperature of 750°C to 950°C for 1 to 4 hours. The gist is a coating formation method in which a coating layer of Fe-Ni-Cr alloy is formed on the surface by removing molten salt adhering to the surface, as Ni and Cr partially diffuse into the steel base. The present invention will be explained below with reference to the drawings. FIG. 1 is an enlarged cross-sectional view of a steel plate material as a heat-resistant and corrosion-resistant coated steel material constructed by the coating forming method of the present invention, in which (1) is a steel sheet material that has been subjected to pretreatment such as degreasing and derusting. On the surface 1', a 6-layer film consisting of a 2-6μ Ni plating film and a 4-15μ Cr plating film is formed by electroplating.
A multilayer plating film with a thickness of 21μ to 21μ is formed. The reason for limiting the Ni plating film and Cr plating film to the above film thickness is that if the Ni plating film is less than 2μ, the amount of diffusion to the steel material surface will be insufficient and the desired corrosion resistance will not be obtained; This is because there is no difference in the effect on diffusion even if the film is formed with a thickness exceeding 4 μm.Also, in the case of a Cr plating film, if it is less than 4μ, the amount of diffusion to the steel material surface is sufficient as in the case of a Ni plating film. Because it is not
The desired corrosion resistance cannot be obtained, and on the other hand, if the thickness exceeds 15μ, the structure will not be similar to that of austenitic stainless steel, which has corrosion resistance, and it will take more than an hour to nail, which is not efficient. After that, it is immersed in a molten salt bath consisting of borax or a mixture of borax and boric acid at a temperature of 750°C to 950°C.
Heat treatment is performed for 1 to 4 hours,
Furthermore, by removing the molten salt adhering to the surface, the boron catalyst wrapped in the heating device (in the molten salt bath) causes some of the Ni and Cr to diffuse into the steel base on the surface 1'. -It is a steel material on which a coating layer 2 of Ni-Cr alloy is formed. It goes without saying that either the Ni plating film or the Cr plating film may be used as the upper layer or the lower layer. In addition, the reason why borax and boric acid were used as the molten salt bath is that both borax and boric acid have a fracking effect.
The oxides on the surface of the plating film and the oxides generated by the accompanying oxygen during immersion in the molten salt bath are removed (fluxing) from the surface of the plating film to promote diffusion and form a uniform Fe-Ni-Cr diffusion coating layer. This is because it can be formed. On the other hand, regarding the range of each of these plating films, Ni diffuses into the grain boundaries and is difficult to diffuse into the ferrite grains.
Compared to Cr, the Ni and Cr components in the coating layer 2 should be kept in a thinner range as described above, and exhibit the most effective heat resistance and corrosion resistance.
Since it is desired that the ratio be 8% Ni and 18% Cr, the range of Cr is determined in relation to these ratios and the alloying speed. Furthermore, regarding the temperature and time of heat treatment, 750
If it is less than ℃, the speed to form an alloy is slow, and the viscosity of the molten salt increases, so that a large amount of molten salt adheres to the steel material after the treatment, making it difficult to remove it and making it extremely uneconomical. while
If the temperature exceeds 950°C, the crystal grains of the steel material will grow and deteriorate the mechanical properties of the steel material, and if the temperature is less than 1 hour, alloying will not be performed sufficiently.
On the other hand, if it exceeds 4 hours, it becomes saturated and does not contribute much to the further progress of the alloy. [Function] The gist of the present invention is a method for forming the above-mentioned coating layer 2, so that the coating layer has a structure similar to that of austenitic stainless steel that has corrosion resistance even in high temperature conditions, and is oxidized. It can be constructed with a passivated surface state that does not passivate, thus exhibiting excellent heat resistance and corrosion resistance at the same time, and is further constructed by partially diffusing into the steel material. Therefore, it is possible to obtain properties with excellent subsequent processability. [Example] Example 1 - Steel material: A steel plate made of SPCC material and having a thickness of 1.0 mm, a width of 50 mm, and a length of 100 mm is pretreated to degrease and remove rust using a conventional method. ●Ni electroplating treatment... Using a plating bath consisting of 300 g of nickel sulfate, 45 g of nickel chloride, and 40 g of boric acid, the steel plate is used as a cathode and the nickel plate is used as an anode at a temperature of 60°C and a cathode current density of 4 A/. Electricity was applied for 7 minutes at dm ² to obtain a Ni-plated film with a thickness of 5 μm. ●Cr electroplating treatment...Chromic anhydride 250g/, sulfuric acid
A Cr plating film with a film thickness of 14 μm was formed by using a plating bath with a composition of 2.5 g/m2, using the steel plate as a cathode and the lead plate as an anode, and applying current at a temperature of 60°C and a cathode current density of 30 A/dm ² for 47 minutes. I got it. ●Heat treatment: The steel plate subjected to the multi-layer plating treatment is immersed in a molten salt bath containing 40% by weight of borax and 60% by weight of boric acid at a temperature of 900°C for 3 hours, and after being taken out, the steel plate is further coated. As a result of removing the molten salt adhering to the surface with hot water, Ni and Cr were removed on the surface.
Approximately 43μ on average due to diffusion into some steel substrates
A coating layer of Fe-Ni-Cr alloy was obtained. FIG. 2 is a metallographic micrograph of the cross section of the coating material obtained in Example 1, magnified 200 times, and FIG. 4 is an X-ray photograph magnified 1000 times that of FIG. It can be seen from Figures 2 and 4 that some Ni and Cr have diffused to the surface of the steel material. In addition, as a result of analyzing each component at point X in FIG. 4, it was found to be 61.72% Fe, 30.94% Ni, and 7.33% Cr. Example 2 ●Steel material: Same as Example 1 ●Cr electroplating treatment: Same as Example 1, except that electricity was applied for 37 minutes to obtain a Cr plating film with a thickness of 12μ. ●Intermediate pretreatment: Immerse in 10% hydrochloric acid aqueous solution for 5 seconds, then rinse with water. ●Strike Ni electroplating treatment...Nickel sulfate 240
Using a plating bath with the following compositions: boric acid 30g/, hydrochloric acid 80ml/, the temperature was 50°C and the cathode current density was set using a steel plate as a cathode and a nickel plate as an anode.
A current of 6 A/dm ² was applied for 1 minute, and immediately thereafter, the next Ni plating process was performed. ●Ni electroplating treatment: Same as Example 1, except that electricity was applied for 5 minutes to obtain a Cr plating film with a thickness of 4μ. ●Heat treatment: The steel plate subjected to the multilayer plating treatment was immersed in a molten salt bath containing 30% by weight of borax and 70% by weight of boric acid at a temperature of 850°C for 2.5 hours,
After taking it out, the molten salt adhering to the steel plate was further removed with hot water, and as a result, an average of about 26 μ of Fe−Ni− was found on the surface due to the diffusion of some Ni and Cr into the steel base.
A coating layer of Cr alloy was obtained. Figure 3 is a photograph similar to Figure 2 of the cross section of the coating material obtained in Example 2, and this figure also shows
The diffusion state of Ni and Cr can be seen. The results of comparative characteristics of the products of the present invention (Examples 1 and 2) and conventional products through heat resistance and corrosion resistance tests are shown in Tables 1 and 2 below. ●Heat resistance test results (Continuous heating in the atmosphere at a temperature of 700℃, and after each time period, cooling in the atmosphere and cooling down to atmospheric temperature. The increase in the weight of the entire sample due to the degree of oxidation. It was measured.)

[Table] However, as for the conventional product, the sample is a steel plate of the same size as the product of the present invention, and is made by hot-dipping Al alone. Corrosion resistance test results (measured according to the salt spray test method according to JISZ-2371) .)

[Table] However, the conventional product is a sample made of a steel plate of the same size as the product of the present invention, and is made by hot-dip plating of Al alone as described above. In the table, r indicates a red rust spot of less than 1 mm, R indicates a red rust spot of 1 mm or more, and W indicates a white corrosion product. Also, the numbers attached to these generated items represent the number of generated items. [Effects of the Invention] As described above, the heat-resistant/corrosion-resistant coated steel material and the coating forming method according to the present invention provide Fe, which is partially formed on the surface 1' of the steel material 1 as Ni and Cr diffuse into the steel base. -By the coating layer 2 of Ni-Cr alloy,
It has a structure similar to that of austenitic stainless steel, which has corrosion resistance, and has a passivated surface structure that does not oxidize, which satisfies both heat resistance and corrosion resistance at the same time. Due to the partially diffused structure of Ni and Cr, bending and punching can be performed in other processing without peeling or cracking, and it can be heated at temperatures of 750 to 950℃.
This low-temperature heat treatment has almost no effect on the steel material due to heat, and furthermore, it is possible to form a diffusion layer extremely efficiently.

[Brief explanation of drawings]

FIG. 1 is an enlarged cross-sectional view of a steel plate material as a heat-resistant and corrosion-resistant coated steel material according to an embodiment of the present invention, and FIGS. Microscopic cross-section photo of metal structure,
FIG. 4 is a photograph of the metal structure of the cross section of the sample according to Example 1 taken with an X-ray microanalyzer at a magnification of 1000 times. 1...Steel material, 1'...Surface, 2...Coating layer.

Claims (1)

[Claims] 1 Steel material 1 that has been pretreated such as degreasing and derusting
2 to 6μ of Ni and 4 to 15μ of Ni are deposited on the surface 1′ of the plate by electroplating.
A multilayer electroplated film is formed with Cr, and then immersed in a molten salt bath made of borax or a mixture of borax and boric acid, and heat treated at a temperature of 750°C to 950°C for 1 to 4 hours. Furthermore, by removing the molten salt adhering to the surface, Ni and Cr are added to the surface.
A method for forming a heat-resistant and corrosion-resistant coated steel material, characterized in that a coating layer 2 of Fe-Ni-Cr alloy is formed by partially diffusing Fe-Ni-Cr alloy into a steel base material. 2. The forming method according to claim 1, wherein the multilayer plating layer is formed with Ni as an upper layer and Cr as a lower layer. 3. The forming method according to claim 1, wherein the multilayer plating layer is formed with Cr as an upper layer and Ni as a lower layer.