JPS6140033B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method of forming a carbide layer on the surface of a treated material using a molten salt method. As methods of this type, there are a method using borate in a salt bath as disclosed in Japanese Patent Publication No. 47-19844, and a method using a neutral salt as disclosed in Japanese Patent Publication No. 53-35637, but both of these methods coat carbides containing only Group A elements. However, there are various problems from an industrial perspective. The present inventor has also invented a method for forming a double carbide layer of a group A element and a group a element by adding appropriate amounts of the group a element and the group a element, and has filed a separate application. Since then, we have continued to study a better method for forming double carbides, and in the above method, we have added a total of 2 to 10wt of Group A element salts and one or more Group A element salts.
It has been found that the following industrially advantageous properties can be obtained by adding %. (1) Uniform carbide coating is possible regardless of the location in the processing furnace. (2) Longer pot life. In particular, in the conventional method, the carbide layer formed on the surface of the workpiece immersed in the upper part of the furnace is thinner than the lower part, or in some cases, no carbide layer is formed at all. However, group a element salts and group a
When one or more group element acid salts are added,
It became possible to form a carbide layer with a uniform thickness right up to the surface of the salt bath, which is in contact with the atmosphere. It is unclear why the addition of Group A element salts and Group A element salts provides a uniform coating of the carbide layer and extends the life of the pot, but experimental evidence shows that the total amount is 2 to 10 wt%. The effect appears when added within this range. If it is less than 2 wt%, the effect of addition is small, and if it is added in excess of 10 wt%, the life of the bath will be shortened, which is not good. Group A element salts and Group A element acid salts are kept as is if anhydrous, and those with crystal water are heated to 200°C.
It is best to dry it nearby for a long time before use. It is preferable that the addition be carried out at room temperature, thoroughly mixed with the salt bath agent and metal powder, and then heated and melted. Even if Group A element salts and Group A element salts are added in the scope of the claims of the present application, other properties such as carbide formation rate, bath viscosity, evaporation, and ease of removing deposited salts will not be affected. It doesn't change. Therefore, in the above-mentioned method invented by the present inventor, a total of 2 groups of group a element salts and group a element salts of one or more types are added.
It is only necessary to add ~10wt%, and the treatment steps and treatment conditions may be the same as in the above method. In particular, as shown in the invention by the present inventor (Japanese Patent Application No. 55-81842), a salt bath agent contains one or more chlorides of Group A and Group A elements of the periodic table and 5 to 30 mo% of the chloride. The method using mixed salts of borates is industrially superior.
At this time, Group A elements or substances containing them must be added in an amount of 1 to 4 wt% as Group A elements, and Group A elements or substances containing them must be added in an amount of 5 to 40 wt% as Group A elements. There is. If the amount of Group A elements is less than 1wt%, double carbides are not formed; conversely, if it exceeds 4wt%, some of the borate will be reduced, and if the amount of Group A elements is less than 5wt%, double carbides will not be formed. No carbide layer is formed, on the contrary
This is because if the content exceeds 40 wt%, the viscosity of the bath becomes significantly large. As the Group A element or the substance containing the Group A element, it is desirable to use its alloy powder. Furthermore, titanium and vanadium are used as group a elements and group a elements, and titanate and vanadate are used as group a element salts and group a element salts, respectively, which are the characteristics of the coated carbide. It is desirable from the viewpoint of economic efficiency. Alternatively, electrolysis may be carried out in a molten bath using the material to be treated as a cathode. Examples are shown below. Example 1 Four types of salt bath compositions shown in the table were prepared, and an inner diameter of 46
It was heated and melted in the air in a φ SUS304 pot. Symbols A to C are the methods of the present invention, and symbol D is the conventional method. Na ₂ B ₄ O ₇ is an anhydrous primary reagent, BaC ₂
An industrial grade was used. Fe-V and Fe-Ti were used as fine powders with a purity of 7% and 70%, respectively, and a mesh size of 100 or less. NaVO ₃ was industrial NaVCO ₃ 4H ₂ O, and crystal water was decomposed and evaporated by heating at high temperature for a long time. All of these were mixed at room temperature. The surface of the material to be treated was ground with a SKD11 plate, then degreased and held in the bottom of the pot. Processing temperature is 1000℃
After holding it for 4 hours, it was cooled with oil in the atmosphere. After washing and removing salts adhering to the surface of the treated material, the material, chemical composition, thickness, etc. of the coating layer were investigated by X-ray diffraction, X-ray microanalyzer analysis, and optical microscopy. The results are also shown in the table, and the coating layers were all made of (VTi)C double carbide with Ti dissolved in VC carbide, and the thickness of the layer was about 9μ, which was constant regardless of the composition.

[Table] Next, after heating the same salt bath as described in the table to 1000 →
As shown in the figure, the treated material SKD11 is made of SUS304 so that the upper 20 mm is exposed from the surface of the molten salt bath.
The depth of immersion in the pot is approximately 150 mm. Immediately before immersion, the molten salt bath was thoroughly stirred, and after the material to be treated was immersed, it was allowed to stand still until the treatment was completed. The treatment time was 4 hours, after which it was cooled in oil and the attached salts were washed and removed. When the thickness of the coating layer was measured at each position on the treated material using an optical microscope, it was found that in the salt bath compositions of the present invention with symbols A to C, (VTi)C carbide of about 9 μm was uniformly formed up to the very edge of the bath surface. However, in the conventional method of symbol D, no carbide coating was observed up to a depth of approximately 30 mm from the bath surface. Furthermore, steel is likely to be eroded at locations where the salt bath and the atmosphere come into contact. Therefore, when we measured the amount of dimensional reduction due to erosion of the treated material corresponding to that position, no dimensional reduction was observed in the compositions of symbols A to C of the present invention, but it was slight in the composition of symbol D of the conventional method. (approximately 0.25 mm) due to erosion. As described above, the bath composition of the present invention has an extremely small corrosive effect on steel, and is therefore advantageous for extending the life of heat-resistant steel pots. Example 2 30wt% Fe-V and 8wt% Fe-Ti were added to a salt bath agent made by mixing NaC and _BaC2 in a molar ratio of 61:39.
%, and further 5 wt% NaVO ₃ and 3 wt% Na ₂ TiO ₃ were mixed at room temperature. When treated in the same manner as in Example 1, a (VTi)C double carbide of approximately 8 μm was formed. Furthermore, the carbide layer was formed up to about 15 mm from the salt bath surface, which was found to be more effective than the salt bath composition in which NaVO ₃ and Na ₂ TiO ₃ were not added. Furthermore, no erosion phenomenon was observed on the salt bath surface. Example 3 BaC2 and _BaC2 with a molar composition ratio of 86:14 were added to a salt bath agent.
Using Na ₂ B ₄ O ₇ , Fe―Nb15wt%, Fe―
3wt% of Ti and 5wt% of NaNbO ₃ were added and mixed. When treated in the same manner as in Example 1, a (NbTi)C double carbide layer of about 10 μm was formed. Furthermore, the carbide layer was formed uniformly up to the very edge of the salt bath surface, confirming the effect of NaNbO ₃ addition. There was almost no reduction in size due to erosion, and the effect of adding NaNbO ₃ was recognized. Example 4 Bacl ₂ , Cacl ₂ at a molar composition ratio of 2:4:1,
Based on BaB ₄ O ₇ mixed salt, 10wt% of Nb + Ta alloy powder, 2wt% of Fe-Zr powder and
5wt% of NaTaO ₃ was added and mixed. When treated in the same manner as in Example 1, about 10 μm of carbide was coated. When the composition of this carbide was investigated by EPMA, Nb, Ta, and a small amount of Zr were detected.
It was presumed to be Ta, Zr)C double carbide. The bath conditions were good, with little erosion, and the effects of NaTaO ₃ were recognized. Example 5 Bacl ₂ , CaC ₂ , with a molar composition ratio of 2:4:1
Using Na ₂ B ₄ O ₇ mixed salt, add 10wt of Fe-V powder to it.
%, Fe-Ti powder 3wt% and CaVO ₃ 5wt% were added and mixed. When treated in the same manner as in Example 1, a (VTi)C double carbide layer of approximately 10 μm was formed. The condition of the bath and the degree of erosion were good. Example 6 Nacl, Licl, K ₂ B ₄ O ₇ with a molar composition ratio of 3:4:1
Using a mixed bath, add 10wt% Fe―Nb powder and Fe―
3 wt% Ti powder and 5 wt% KNbO ₃ were added and mixed. When treated in the same manner as in Example 1,
A (NbTi)C double carbide layer of approximately 10μ was formed. The bath conditions and erosion conditions were good, and the effects of KNbO ₃ were recognized.

[Brief explanation of the drawing]

The figure is a schematic diagram showing the method of immersing a sample in an experiment conducted to examine whether double carbide was uniformly coated even in the upper part of a salt bath. : Processed material, : Molten salt bath, : Pot.

Claims (1)

[Scope of Claims] 1. The salt bath agent is a chloride of one or more chlorides of Group A and Group A elements of the Periodic Table, and further comprises an acid salt of a Group Va element and an acid salt of a Group A element of the Periodic Table. Add one or more types of 2 to 10 wt% in total,
The added amount of Group A elements or substances containing them is 2 to 10 wt% as Group A elements, and the added amount of Group A elements or substances containing them is 5 to 40 wt% as Group A elements. Heat and melt,
A surface treatment method characterized by forming a double carbide layer of a group A element and a group A element on the surface of a workpiece immersed in a bath. 2. The salt bath agent contains 5 to 30 mo of one or more chlorides of Group A and Group A elements of the periodic table.
2. The surface treatment method according to claim 1, wherein the mixed salt is a mixed salt consisting of % borate, and the amount of the Group A element or the substance containing it is 2 to 4 wt% as the Group A element. 3. Claims 1, 2, or 3, wherein the group a element is titanium, the group Va element is vanadium, the group a element salt is titanate, and the group a element salt is vanadate. The surface treatment method according to item 3.