JPH0535234B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention relates to a method for producing a Zn-Ni alloy coated steel sheet with excellent press formability. <Conventional technology> Zn-Ni alloy plated steel sheets have 5 to 10 times higher corrosion resistance than Zn-plated steel sheets with the same amount of coating, which has caused problems in recent years in the use of road deicing agents in winter for automobiles. The amount of steel used as a countermeasure against early corrosion in car bodies is increasing, and it is being used in a wide variety of areas, from front fenders to bonnets and trunk lid outer parts. The plated steel plates used ranged from the single-sided plated steel plates that were used on the outside of the car body to have a rust-preventing effect (prevention of hole rust) in areas where the coating was not sufficiently covered, such as the inner surface of the car body in the early days of using the plated steel plate. A shift is being made to double-sided plated steel sheets, which aim to improve corrosion resistance (prevent external rust) after the paint film peels off after being splashed with pebbles, etc. When converting this Zn--Ni alloy plated steel plate into double-sided plating, the double-sided plated plate requires different characteristics from that of the single-sided plated plate. One of them is press formability. Considering the purpose of use of single-sided plated steel plates as mentioned above, the plated side should be on the inside of the punch during press working,
In other words, since the cold-rolled surface often becomes an overhanging surface during press working, there was little influence on the press formability of the plated surface. However, with double-sided plated steel sheets, the plated surface becomes an overhanging surface during press working, and friction on the plated surface itself has begun to become a problem. Of course, using a press oil with a high viscosity during press processing makes it easier to press, but in reality, in order to make it easier for the user to degrease and paint, a low viscosity rust preventive oil is applied to the plated steel plate. Each user performs press processing with this anti-rust oil in place. Plated plates require good workability with this anti-rust oil. As a method for improving the press formability of Zn-Ni alloy plating, as disclosed in JP-A-60-141894, two layers of Zn-Ni alloy plating are used.
There is a method of increasing the Ni content in the upper layer. This method uses powdering of the Zn-Ni layer that is the upper plating layer to improve press formability, so when a large number of samples are continuously molded, the peeled powder may adhere to the press mold. It is not practical because it accumulates and causes star eyes. <Problems to be Solved by the Invention> The present invention aims to solve the problem of deterioration in press formability due to the frictional resistance of the plated surface of Zn-Ni alloy plated steel sheets, and in particular, The purpose is to improve press formability without powdering the layer. <Means for Solving the Problems> In other words, the present invention has a method in which the surface of the steel plate has a Ni content.
10 to 17 wt% Zn-Ni alloy plating is applied, and then the plated surface is treated with H ₂ PO ₄ ^- ions and HPO ₄ ^2-
At least one of the ions and K ⁺ ion, Na ⁺ ion, Mg ²⁺ ion, Ca ²⁺ ion, NH ⁴⁺ ion,
Zn-, which has excellent press formability, is soaked in a solution of a salt containing one or more Al ³⁺ ions, preferably with a pH in the range of 4 to 10.
This is a method for manufacturing Ni alloy plated steel sheet. <Function> First, the progress that led to the present invention will be explained. Figure 3 shows a cold-rolled sheet and one-sided Zn-Ni alloy plated steel sheet.
The degree of difficulty in press workability of double-sided Zn-Ni alloy plated steel sheets was expressed as the limit drawing ratio (LDR) in a cylindrical deep drawing test. The critical drawing ratio is determined by measuring the blank diameter by 60 mm using a cylindrical deep drawing tester as shown in Figure 4.
It was measured by changing the diameter between ~80φ and taking the ratio of the punch diameter to the blank diameter when the plate breaks. In this test, the steel sheet plated with Zn-Ni alloy on one side was tested so that the cold-rolled surface was on the overhanging side. The oil used was Daphne Oil Coat Z5 (trade name), a rust preventive oil manufactured by Idemitsu Kosan Co., Ltd., and the steel plate material was kept constant (equivalent to SPCC) in order to see only the effect of the plating layer. The Ni content of the plating layer was 12.5%. As is clear from this figure, compared to cold-rolled sheets, double-sided plated sheets have a smaller LDR and are several steps inferior in formability. Galvanized steel sheets are a substitute for cold-rolled sheets, so they are pressed using press dies designed for cold-rolled sheets, but press dies designed specifically for use with ultra-deep drawn steel sheets can cause the plates to break. It was cracked. Next, since the low LDR of plated plates was thought to be affected by the friction on the plated plate's surface, we determined the frictional resistance of the plated plate's surface using a sliding resistance test. The shape of the testing machine used is shown in Figure 5. This testing machine pinches a sample and pulls it at a constant speed, and evaluates the surface friction force based on the amount of load required at that time. The test was conducted without oil. The test results are shown in Figure 6. As is clear from this figure, the surface friction of the cold-rolled plate and the plated plate is different, and this seems to have an effect on formability. Next, we conducted further intensive research to clarify the factors that govern the friction coefficient of the plated surface of Zn-Ni alloy coated steel sheets, and as a result, we found the following. Changing the outermost surface of the plating layer changes press formability. There is no noticeable deterioration in the quality of the cold-rolled sheet due to plating. After focusing on this and further considering it, we found that
The Zn−Ni plating surface is coated with at least one of H ₂ PO ₄ ^- and HPO ₄ ^2- ions, K ⁺ ions, Na ⁺ ions,
Mg ²⁺ ion, Ca ²⁺ ion, NH ⁴⁺ ion, Al ³⁺
It has been discovered that press formability is significantly improved by soaking in a solution of a salt containing one or more types of ions. Figure 1 shows 4 Zn-Ni alloy plated plates in the following solution.
It shows the change in LDR when immersed for seconds. The Ni content of the tamping plate used was 12.5%, and the steel type used was
SPCC was used. Treatment liquid NaH ₂ PO ₄ K ₂ HPO ₄ 200g/150g/Liquid temperature 60°C PH 5.8 It can be seen that LDR increases by treatment with this liquid. Glow discharge analysis (GDS)
As a result, it is known that a P peak exists on the surface of the plated plate after dipping, and the P peak on the plated surface
It is thought that this improves lubricity and press formability. The present invention has been constructed based on the above findings, and the specific construction will be explained in more detail below. The solution used to soak the plated surface contains at least one of H ₂ PO ₄ ^- ions and HPO ₄ ^2- ions and K ⁺
ion, Na ⁺ ion, Mg ²⁺ ion, Ca ²⁺ ion,
It is a solution of salt consisting of one or more of NH ⁴⁺ ions and Al ³⁺ ions. Although there are no limitations on the concentration or temperature of this solution, in the case of immersion treatment, it may take some time for the effect to be obtained, so it is preferable to increase the temperature and concentration in order to obtain a quick effect. For short-time processing of less than 10 seconds, which is suitable for industrial production, the immersion temperature is 40°C or higher, and the concentration of the immersion liquid is 100 g / H ₂ PO ₄ ^- and HPO ₄ ^{2 -} in total.
The above is preferable. In addition, the plated plate used also has a Ni content of 10~
17 wt%, preferably in the range of 11 to 15%. Ten
If it is less than 17%, this treatment method is ineffective, and if it exceeds 17%, the Zn-Ni plated layer is likely to cause powdering. Therefore, in the present invention, the Ni content of the target Zn-Ni alloy plated steel sheet is set to 10 to 17wt. %.
In addition, Co, Fe, Cr, Cu, Co, Fe, Cr, Cu,
Adding Mn, Al, etc. in a few percent or less does not impair the purpose of the present invention. The pH of the solution is preferably about 4 to 10. If it is less than 4, the dissolution of Zn in the plating layer will be severe, and the amount of plating will be greatly reduced, making it impractical. If it is more than 10, there will be no improvement in press formability, so the pH of the solution should be set to 4 to 10. limited to. The cations contained in the liquid used are K ⁺ ,
It should be electrochemically less noble than Zn and Ni of Na ⁺ , Mg ²⁺ , Ca ²⁺ , NH ₄ ⁺ , Al ³⁺ . This is because when a plating plate is soaked in a liquid containing metal ions,
This is because metals that are electrochemically more noble than Zn and Ni may cause a substitution reaction with Zn and Ni, depositing on the plated surface and deteriorating the appearance. The amount of P attached to the plating surface is 0.1 in terms of P.
~5 mg/ ^m2 is preferred. If it is less than 0.1 mg/m ² , it will not be effective, and if it is more than 5 mg/m ² , the chemical conversion properties will deteriorate, which is not preferable. <Example> Table 1 also shows the test steel sheets, their plating conditions, dipping conditions, and press formability expressed in LDR.
The lubricating oil is Daphne Oil Coat Z5 manufactured by Idemitsu Kosan Co., Ltd., which is used as a rust preventive oil.
(trade name) was used in all cases. Regarding Example 1 and Comparative Examples 1 and 2,
The LDR values are shown in FIG. 2 to further clarify the effects of the present invention.

【table】

[Table] <Effects of the Invention> According to the present invention, the press formability of the Zn-Ni alloy plated steel sheet is improved to the same level as that of a cold-rolled sheet, and press cracks during pressing are eliminated. Since press formability is similar regardless of the Ni content in the range of 10 to 17%, press forming is possible due to changes in the plating layer composition caused by changes in the plating bath composition or line speed, etc. There is no change in gender. It is possible to produce Zn-Ni alloy coated steel sheets with stable formability, and has great industrial value.

[Brief explanation of drawings]

Figure 1 shows the effect of the present invention after immersion treatment.
Graph of LDR, Figure 2 is an example showing the change in LDR after immersion treatment, Figure 3 is a comparison diagram of LDR of Zn-Ni alloy plated sheet and cold rolled sheet, Figure 4 is cylindrical deep drawing test machine 5 is a schematic diagram of a sliding resistance tester, and FIG. 6 is a diagram showing the difference in sliding resistance between a Zn-Ni alloy plated plate and a cold-rolled plate.

Claims (1)

[Claims] 1. Zn− with a Ni content of 10 to 17 wt% on the surface of the steel plate.
After applying Ni alloy plating, the plated surface is
At least one of H ₂ PO ₄ ^- ion and HPO ₄ ^2- ion and K ⁺ ion, Na ⁺ ion, Mg ²⁺ ion,
A method for producing a Zn-Ni alloy plated steel sheet with excellent press formability, which comprises soaking it in a solution of a salt consisting of one or more of Ca ²⁺ ions, NH ⁴⁺ ions, and Al ³⁺ ions. 2 Salt consisting of at least one of H ₂ PO ₄ ^- ion and HPO ₄ ^2- ion and one or more of K ⁺ ion, Na ⁺ ion, Mg ²⁺ ion, Ca ²⁺ ion, NH ⁴⁺ ion, Al ³⁺ ion 2. The method for producing a Zn-Ni alloy coated steel sheet with excellent press formability according to claim 1, wherein the pH of the solution is in the range of 4 to 10.