JPS62202027A - Stainless steel tapping screw - Google Patents

Abstract

PURPOSE:To obtain a titled screw having high surface hardness and corrosion resistance by forming an alloy layer of Ni and P on the surface of the screw formed of an austenitic stainless steel stock and subjecting the screw to a hardening treatment by heating. CONSTITUTION:The austenitic stainless steel stock 5 is formed to the tapping screw 1 constituted of a head part 2, a stem part 3 which has a circular columnar shape and a pointed top end and a screw thread part 4 provided on the outside periphery thereof. The alloy layer 6 of Ni and P is thereafter formed by electrolessplating on the stock 5 of the screw 1 and the screw 1 is subjected to the heating treatment to improve the adhesiveness between the stock 5 and the allow layer 6 and to precipitation-harden the surface. Such screw has the surface hardness higher than the surface hardness of the conventional steel screw, has the better corrosion resistance than the conventional steel screw and is adequate for fastening of automobile parts, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a stainless steel tab/screw suitable for fastening parts where surface hardness and corrosion resistance are required, such as fastening automobile parts.

(Prior art) Recently, especially in the automobile industry, parts made of high-strength steel plates and austenitic stainless steel materials have been frequently used for the purpose of weight reduction, and self-tapping screws and other fastening parts have surfaces that are compatible with these. Hardness and corrosion resistance are required.

Typical self-tapping screws are made of steel by heading or rolling, then carburized and quenched to improve surface hardness, and then coated with zinc and chrome on the surface.

It has been subjected to corrosion-resistant treatment by plating with nickel or the like, and its surface hardness is set at HV450 or higher according to the JIS standard.

However, when these steel tapping screws are used for the above-mentioned fastening, they tend to have the disadvantage that they can only guarantee corrosion resistance for a certain period of time, and that they easily corrode if the surface plating layer is damaged or peeled off.

There are also self-tapping screws made of austenitic stainless steel, but since the stainless steel material cannot be hardened, they rely solely on the hardenability produced by plastic working such as rolling.

Therefore, the surface hardness of the screw has a minimum value of HV320 (
JIS Standard), the maximum value is HV 4008 degrees even when using a material with very high work hardening properties (for example, 5US304), and it was not possible to obtain a surface hardness of HV 450 or higher for the steel tapping screw. Moreover, if a material with high work hardening properties is used, the productivity of screws will deteriorate, and since a material with a high nickel content (for example, 5US305) is generally used, the maximum value of surface hardness decreases to about HV380.

Additionally, there are self-tapping screws made of martensitic stainless steel that have been hardened, and those that have been further plated with nickel, etc., but all of these are insufficient in terms of corrosion resistance. .

(Problems to be Solved by the Invention) Therefore, the present invention improves the drawbacks of the prior art and provides a stainless steel tapping screw with high surface hardness and excellent corrosion resistance. It is designed to be used for concluding agreements and other purposes.

(Means for Solving the Problems) The gist of the present invention is that a thread is machined into an austenitic stainless steel material, the surface of the thread is electrolessly plated with nickel and phosphorus to form an alloy layer, and the thread is heated. This is a stainless steel tapping screw that has been hardened by.

(Example) Examples of the present invention will be described below based on the drawings. Third
The drawing shows an overall front view of a self-tapping screw 1. The self-tapping screw 1 is composed of a head 2, a cylindrical shaft portion 3 with a pointed tip, and a threaded portion 4 provided on the outer periphery of the shaft portion 3. There is.

The self-tapping screw 1 is formed by using austenite I-series stainless steel, such as 5US340, as the material 5, and the screw shaft is formed by rolling with a die, and the head is formed by hollow-groove processing, as in the case of conventional screw forming.

The tapping screw 1 is attached to the material 5 after molding as shown in FIG.
An alloy layer 6 of nickel and phosphorus is formed thereon, and the screw is subjected to heat treatment (baking) to improve the adhesion between the material 5 and the alloy layer 6 and to harden the surface by precipitation.

The alloy layer 6 is formed by electroless plating by immersing it in a reducing agent mixed with nickel (L) and phosphorus (nickel) after screw forming.
Phosphorus should be 10% or less compared to 0%, and the plating thickness should be approximately IOμ.
It is m. Further, the baking is performed at 200°C to 500°C.
It is carried out for 1 to 4 hours at a temperature of .degree.

As a result, it is possible to obtain a tapping screw whose surface hardness is at least the value of the above-mentioned conventional steel tapping screw (HV450 or higher), and whose corrosion resistance is far superior to that of the steel tambour screw.

Incidentally, FIG. 4 shows a characteristic curve obtained by actually measuring the relationship between baking temperature and surface hardness, and the measurement was carried out by applying a measuring load of 500 gr to the head 2 of the above-mentioned tapping screw 1.

As shown in this characteristic curve, when the material 5 without the alloy layer 6 is used alone, the surface hardness is HV380, but when the alloy layer 6 is provided, the surface hardness becomes at least HV450 or more, and by baking it, the material 5 and the alloy The adhesiveness with layer 6 is improved, and the above-mentioned hardness or even harder state can be maintained for a long period of time.

(Effects of the Invention) As is clear from the above examples, the tamping screw according to the present invention has a surface hardness greater than or equal to the conventional steel tapping screw, and has improved corrosion resistance compared to the steel tapping screw. Therefore, it is suitable for fastening parts using high-tensile steel plates or austenitic stainless steel materials, and contributes to reducing the weight of automobiles, improving durability, and so on.

[Brief explanation of drawings]

Fig. 1 is an overall front view of a self-tapping screw according to an embodiment of the present invention, Fig. 2 is a sectional view of the main part of Fig. 1, Fig. 3 1d Fig. 2 A
FIG. 4, an enlarged view of a portion, is an actually measured characteristic curve showing the relationship between baking temperature and surface hardness. [Explanation of symbols] l... Tapping screw 2... Head 3... Shaft part
4...Threaded part 5...Material
6... Alloy layer patent applicant 1 Co., Ltd. - Della Figure 1 Figure 2 Figure 3! Figure 4 'c

Claims (2)

[Claims] (1) A screw is machined into an austenitic stainless steel material, the surface of the screw is electrolessly plated with nickel and phosphorus to form an alloy layer, and the screw is hardened by heating. Stainless steel self-tapping screws. (2) The stainless steel tapping screw according to claim (1), wherein the surface hardness of the tapping screw is HV450 or higher.