JPH0534431B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for surface treatment of steel materials for plastic working, which are used as materials for bolts, wire rods, etc. This type of steel is mainly treated with a phosphoric acid film prior to plastic working to prevent rust and impart wettability. Conventionally, phosphoric acid coating treatment involves contacting the steel surface with mineral acids such as sulfuric acid, hydrochloric acid, or nitric acid to remove rust that occurs when the steel is left for a long time and scale that occurs when heat treated. In order to remove the smut generated when the steel surface comes into contact with mineral acid in the above-mentioned descaling treatment, the steel surface is brought into contact with a mixed solution of potassium permanganate and sodium hydroxide, etc. After pretreatment, phosphoric acid film treatment was performed. However, the phosphoric acid coating produced by the above conventional method does not have sufficient adhesion to the steel surface.
It has the disadvantage that it is easily peeled off during subsequent plastic working. The purpose of the present invention is to solve the above-mentioned conventional problems, and after descaling or descaling and desmutting the surface of steel materials for plastic working,
(w/v)% sulfuric acid at 60 to 90° C. for 1 to 3 minutes to activate the surface, and then form a phosphoric acid film. The present invention will be explained in detail below. Steel materials suitable for plastic working used in the present invention are SMC418, 420, 435, 440, SCR481,
420, 435, 440, etc., and these steel materials have Mn of 0.1
~2.0% by weight, contains about 0.1 to 0.6% by weight of C, and contains Cr
It contains Mo at 1.5% by weight or less, and Mo at 0.5% by weight or less. Those containing a high concentration of Mn tend to form scales, and those containing a high concentration of C tend to form smuts. The above examples are not intended to limit the invention. For steel materials that have scale formed on their surfaces, descaling is performed. For descaling, the surface of the steel material is brought into contact with, for example, sulfuric acid, hydrochloric acid, a sulfuric acid-hydrochloric acid mixture, or a sulfuric acid-nitric acid mixture. The processing conditions at this time are, for example, 10 to 20
(w/v)% sulfuric acid is used at room temperature.
If 10 to 15 (w/v)% hydrochloric acid is used, the contact is carried out for about 5 to 15 minutes at about 50 to 80°C.
The contact between the surface of the steel material and the treatment liquid is usually carried out by immersing the steel material during the treatment. When the above-mentioned descaling treatment is carried out, a reaction occurs between the steel components and the acid in the above-mentioned treatment liquid, and the resulting product, smut, is formed, especially in steel materials containing a high concentration of C, as mentioned above. It is desirable to carry out a desmutting treatment following the scaling treatment. To perform desmutting treatment, usually 60 to 150 g of potassium permanganate and 80 to 150 g of sodium hydroxide are used.
A treatment solution containing 150 g/ml is brought into contact with the surface of the steel material. The processing conditions are usually heated to about 80 to 90℃.
Contact is performed for ~15 minutes. Instead of the chemical desmutting described above, physical desmutting may be performed in which water is sprayed onto the surface of the steel material and the smut layer is peeled off by water pressure. The above-mentioned descaling and desmutting are not necessarily necessary depending on the condition of the surface of the steel material, and only one of them may be performed. After the above pretreatment, the activation treatment of the present invention is performed. The processing agent used in the activation treatment of the present invention is sulfuric acid. Sulfuric acid has good corrosivity to steel surfaces. The concentration of sulfuric acid used is 10-25 (w/
v)%, preferably 15 to 20 (w/v)%, the treatment time is 60 to 90°C, preferably 75 to 85°C, and the treatment time is 1 to 3 minutes, preferably around 2 minutes. If the treatment time exceeds 3 minutes, smuts will be formed on the surface of the steel material again, so care must be taken. In the above activation treatment, the surface of the steel material is roughened due to corrosion, the number of positions that become nuclei for coating increases, and in the phosphoric acid coating treatment, the P ratio of the phosphoric acid coating produced (P ratio = P/
(P+H), where P is Zn ₂ Fe (PO ₄ ) ₂・4H ₂ O, H
is Zn ₃ (PO ₄ ) _{2.4H 2} O) and homogenization. In the above-mentioned surface roughening, the adhesion of the film improves due to the increase in the surface area of the steel material and the anchor effect, and as the number of core positions increases, the crystal structure of the film becomes finer and a uniform film is obtained, which improves the adhesion. Also, the increase and uniformity of the P ratio is thought to be due to the activation treatment increasing the transfer rate of Fe ⁺⁺ in the steel to the phosphoric acid coating; High adhesion to steel surfaces. As described above, since the phosphoric acid coating formed in the present invention exhibits good adhesion to the steel surface, the coating will peel off even afterward, for example, due to shearing force applied when plastic working the wire rod with a header. Therefore, rust prevention is maintained, and problems such as galling and seizure do not occur due to the wettability of the coating. [Example] 10 bar-shaped steel materials (13 mmφ) made of SCM418
(w/v)% hydrochloric acid aqueous solution for 35 minutes at room temperature to descale, and then immersed in a mixed aqueous solution of 100 g of potassium permanganate and 100 g of sodium hydroxide for 20 minutes at 85°C. After desmutting, 70% was added to a 20 (w/v)% sulfuric acid aqueous solution.
Activation treatment is performed by immersing at ℃ for 2 minutes. Then add 8g/1 to 50℃ of sodium hydroxide aqueous solution.
After neutralization by immersion for a minute, a phosphoric acid coating treatment is performed using a conventional method. The properties of the phosphoric acid coating thus obtained are shown in Table 1.

[Table] According to Table 1, it can be seen that the coating weight of the Example is larger than that of Comparative Examples 1 and 2, and a dense coating is formed, and the P ratio of the Example is higher than that of the Comparative Examples. It can be seen that it is larger than 1 and 2 and is uniform. The bar material subjected to the above treatment is subjected to header processing using a header machine to form a bolt 1 as shown in FIG. In the figure, the length of part 1A is 16
mm, length of part 1B 20mm, diameter 13mm, surface loss rate 0
%, the taper angle of portion 1C is 12°, the length of portion 1D is 130 mm, the diameter is 12 mm, and the surface loss rate is 15%. The results of the header test above are shown in Table 2.

[Table] According to Table 2, the coating retention rate of the example was higher than that of Comparative Examples 1 and 2, indicating that the adhesion of the coating was better, and therefore, there was no galling and the appearance was very good. There is.

[Brief explanation of drawings]

FIG. 1 is a side view of a bolt formed in an example. In the diagram, 1...volt.

Claims (1)

[Claims] 1 After descaling or descaling and desmutting the surface of the steel material for plastic working, 10 to 25
(w/v)% sulfuric acid at 60 to 90°C for 1 to 3 minutes to activate the surface, and then form a phosphoric acid film.