JPH0533805A - Very hard and corrosion resistant drilling tapping screw - Google Patents

Abstract

PURPOSE:To provide a drilling screw having screw and drill blade tip and capable of self drilling and tapping at a low cost by applying electroless plating excellent in strength and corrosion resistance without softening the matrix of the screw cold headed or hardened. CONSTITUTION:An electroless plating layer is constituted on the surface of the base metal of a drilling tapping screw. The plating layer includes P of 8 to 10mass% and Ni of 90 to 92mass%, and has thickness of 10 to 60m and hardness of 600 or more in Vickers hardness and high corrosion resistance. In addition, only the blade tip of the head part is plated. To the surface of the blade tip, high intensive P eutectoid electroless Ni plating is applied, and the hardness of the part of 0.2mm or less under the surface is hardened to 400 or more in Vickers hardness and is resistant against the return deformation in drilling. A threaded shaft part is made to 240 or more in Vickers hardness so as to be resistant against torque force. By this constitution, a drilling screw capable of self drilling and tapping can be obtained at a low cost.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a screw used for applications requiring rust resistance such as construction / construction materials and vehicles.

[0002]

2. Description of the Related Art In recent years, stainless steel products have come to be widely used for construction, building materials, vehicles, etc. from the viewpoint of sensitivity and rust resistance. This type of stainless steel product is mainly used by being attached to the surface of a structure by spot welding or screwing. When screwing, the two holes of a stainless steel product that has been drilled (medium hole) so that a screw can be inserted with a structure that has been conventionally drilled are aligned.
The screw was stopped through both holes.

However, in recent years, in order to improve work efficiency and reduce costs, a method of directly screwing from the surface of stainless steel using a special screw called a drilling screw without drilling a prepared hole or a hollow hole has been implemented. Has become. That is, a method has been adopted in which the tip of a screw is drilled into a cutting edge, and a stainless steel plate and a lower structure are drilled and tapped at the screw portion.

Therefore, the Vickers hardness of the cutting edge portion of the screw is required to be 600 or more, and that of the screw portion is required to be 400 or more.
Further, since the head of the screw nail is exposed on the surface of the stainless steel plate, rust resistance equivalent to that of SUS304 and high hardness so as not to be damaged during screwing are required. Further, it is required for the thread material that the cutting edge processing, the thread cutting processing and the heading processing are easy.

However, at present, no material having the above-mentioned required properties has been developed, and SUS305 and SUSXM7 are not available.
A self-drilling tapping screw in which a drill-shaped tool steel is joined to the tip of a screw made by strengthening cold-working stainless steel is used. However, since this construction method is expensive, development by an integrated product has been attempted. As a representative example of a monolithic product, a product in which SUS305, SUSXM7 or the like is hardened by nitriding after cold working is being studied. However, the disadvantage of softening the matrix strengthened by cold working due to heat history during nitriding The treated surface has rust resistance of SUS3
Since it has a defect that is inferior to that of No. 04, it cannot be used at present. Furthermore, although attempts have been made to use martensitic and precipitation hardened stainless steels, the rust resistance and workability are poor and the purpose cannot be achieved.

[0006]

DISCLOSURE OF THE INVENTION The present invention is an electroless plating treatment which is excellent in high hardness and rust resistance without softening the matrix of a cold-worked or quench-hardened screw having a screw and a drill cutting edge. The above problem is solved by applying the method described above, and an inexpensive drilling screw capable of self-drilling and tapping is supplied.

[0007]

In order to solve the above-mentioned problems, a surface treatment method which has both rust resistance and high hardness without deteriorating the hardness of the cutting edge and the threaded portion after threading was examined. As a result, it has been found that both properties are satisfied when an electroless Ni plating film having a codeposition of P is formed on the surface to a thickness of 10 to 60 μm and by heat treatment at 500 ° C. or less after the film formation.

That is, in the present invention, the base material of the drilling tapping screw has a Vickers hardness of the shaft portion of 240 or more, and a Vickers hardness of the surface layer portion extending from the surface to 200 μm: 40.
0 or more, and an electroless plating (hereinafter referred to as plating) layer is provided on the surface of the base material of the drilling tapping screw, and the plating layer has a composition: P: 8 to 10 mass%, Ni: 90 to 9
It is a drilling tapping screw with high hardness and rust resistance, which contains 2 mass% and has a thickness of 10 to 60 μm and a Vickers hardness of 600 or more. Further, the plating layer portion of the surface layer is the tip of the tip. This is to provide a drilling tapping screw with high hardness and high rust resistance which is only a part.

The reason why the scope of the present invention is limited to the above is described below. The surface of the cutting edge is subjected to high hardness P eutectoid electroless Ni plating, but in order to withstand torsional deformation during drilling, at least 0.2 mm below the surface must have a Vickers hardness of 400 or more, The lower limit of the hardness of the cutting edge was limited to 400 or more.

The screw part and the head part may or may not be plated with P-eutectoid electroless Ni plating, but in both cases, at least under the surface, in order to withstand torsional deformation during tapping. The Vickers hardness of 2 mm or less is required to be 400 or more, and the lower limit of the hardness of the screw portion and the head is limited to 400 or more. The screw shaft portion must have a Vickers hardness of 240 or more in order to withstand the torque force during drilling and tapping, and the lower limit is limited to 240 or more.

The hardness of the electroless Ni plating film increases as the content of P in the eutectoid increases, but in order to increase the content of P, the amount of sodium hypochlorite as a reducing agent is increased and the acidity of the bath is increased. It is necessary to increase the degree, and the deposition rate of the film decreases, which is not economical. Therefore, the upper limit of the P content is limited to 10% or less. If the content of P is less than 8%, the rust resistance and hardness decrease, so the lower limit was limited to 8% or more.

When the electroless Ni plating film is thin, the lower limit is limited to 10 μm or more because the blade edge and the underlying portion of the screw portion are crushed during drilling and tapping. The thicker the film, the better the drilling and tapping properties and the rust resistance, but the margin for improvement gradually decreases, and if it is 60 μm or more, the improvement effect on the increase in thickness is small. On the other hand, if the film becomes too thick, the plating film is likely to crack, and the manufacturing cost is high and it is not economical, so the upper limit is 60 μm.
Limited to:

The electroless Ni plating on which P is co-deposited is usually amorphous, but is crystallized by further heat treatment at a high temperature. Along with this, the hardness increases. That is,
It is desirable to add a high temperature heat treatment after the film formation, because the hardness of the film portion can be increased by applying the heat treatment. Hardness increases by heat treatment at a temperature of 500 ° C. or lower, but if it exceeds 500 ° C., the increase in hardness is small and the hardness of the cold work-strengthened matrix portion decreases, so the upper limit is 500. Desirably below ℃. The hardness increases with the heat treatment time, but if the hardness exceeds 60 minutes, the increase in hardness saturates. Therefore, from the viewpoint of productivity, the upper limit is preferably 60 minutes or less.

The drilling tapping screw is formed by quench hardening and cold work hardening of γ type stainless steel. The former is after forming carbon steel or martensitic stainless steel,
By heating after quenching in the austenite temperature range and quenching, martensite is formed and the entire screw has a Vickers hardness of 400 or more. After quenching, if the material is subject to quench cracking, a low temperature tempering process at 500 ° C or less is performed.

On the other hand, the latter has a Vickers hardness of the shaft portion of 24
After the wire drawing is performed so as to be 0 or more, the cutting edge, the screw portion and the head are further formed by cold working so that the Vickers hardness within 0.2 mm below the surface is 400 or more.

A large number of bath compositions have been proposed for electroless Ni plating. When sodium hypophosphite is used as a reducing agent, the plating thickness is uniform regardless of the surface irregularities, and P is included. In that case, it is already known that the Vickers hardness becomes 1000 or more when heated at 400 ° C. (Handbook of Anticorrosion Technology, edited by Japan Society for Corrosion Protection, P545, 1986).
The present invention is one in which these techniques are applied to a drilling tapping screw, and a pH obtained by adding glycol or succinic acid to nickel chloride or nickel sulfate + sodium hypophosphite + sodium acetate or sodium citrate or sodium oxyacetate.
4-5, 70 ° C-90 ° C In a Brenner type bath, soak the above-formed nail for 30 minutes to 2 hours and apply 1 to the nail surface.
It was manufactured by co-depositing Ni and P of 0 to 60 μm. Also,
The present invention can also be achieved by treating with a Kanigen treatment liquid.

[0017]

EXAMPLES Table 1 shows the chemical components of the drilling tapping screw materials of the present invention example and the comparative example and the hardness of each screw portion before P eutectoid electroless Ni plating. Table 2 shows P eutectoid electroless Ni plating conditions and screw characteristics.

[0018]

[Table 1]

[0019]

[Table 2]

[0020]

[Table 3]

[0021]

[Table 4]

No. 1 to 14 are examples of the present invention. No. 15
-25 are comparative examples. The hardness was measured according to JISZ2244. The hardness of the present invention example is 400 Vickers hardness at the position of 0.2 mm below the surface of the cutting edge, thread and head of the screw material.
Have the above. Further, the P eutectoid electroless Ni plating film portion has a Vickers hardness of 600 or more.

The drilling tapping property was determined by a screwing test of a stainless steel plate having a thickness of 2 mm and an SS400 laminated plate having a thickness of 4 mm from the stainless steel side, and judging whether or not the screwing can be performed without damage. The inventive example could be screwed in without damage.

The rust resistance evaluation test is carried out by the P-eutectoid electroless Ni of Table 2
After plating, it was evaluated according to JISZ2371. The rust resistance rank of the examples of the present invention is JIS rating 9.5 or more.

Inventive Example No. 1-No. 14 and Comparative Example No. 1
5 to No. No. 18 is a screw made of carbon steel and martensitic stainless steel, and the effect of quenching hardness was investigated. Comparative Example No. 15 and No. Comparative Example No. 17 has a low quenching hardness. 16 and No. No. 18 has a low hardness after tempering and is inferior in drilling tapping property. Inventive Example No. 5 to No. 6 and Comparative Example No. 19-No. 20 is SUS
The effect of the surface hardness of the material was investigated with a screw made of XM7. In each of the comparative examples, the surface hardness of the material is low. No. 19 has a cutting edge portion and Comparative Example No. 20
Is inferior because it cannot be used because the blade edge and head are crushed.

Inventive Example No. 7-No. 8 and Comparative Example No. 21
~ No. No. 22 is a screw made of a precipitation hardening stainless steel as a material to investigate the influence of the P amount of the P eutectoid electroless Ni plating. Comparative Example No. In No. 21, the P content of the plating film is less than the range of the present invention, and therefore the rust resistance and the self-drilling and tapping properties are poor. Comparative Example No. In No. 22, the P content of the plating film exceeds the range of the present invention, and the rust resistance and the self-drilling and tapping properties are the same as those of the present invention, but the amount of plating bath chemical used is increased and the plating time is long. It is inferior in economic efficiency.

Inventive Example No. 9-No. 12 and Comparative Example No. Two
3 to No. No. 24 is a screw made of SUS305, which is an investigation of the influence of the P-eutectoid electroless Ni plating film thickness and the influence of plating only on the cutting edge. Comparative Example No. No. 23 has a plating film thickness less than that of the present invention and is inferior in rust resistance and drilling tapping property. Comparative Example No. No. 24 has a plating film thickness exceeding the range of the present invention, and has the same rust resistance and drilling tapping property as those of the present invention, but it is economically inferior because of an increase in the amount of plating bath chemical used and a long plating time. There is.

Further, in the present invention No. 1 in which only the cutting edge is plated. 1
1 and No. No. 12 is the whole plated 9 and No. 10
It has the same drilling tapping property and rust resistance as the above, and if the screw head has sufficient rust resistance, good results can be obtained by plating only the cutting edge.

[0029]

According to the present invention, it is possible to supply a drilling tapping screw having excellent rust resistance, and an industrially effective effect is brought about.

Claims (2)

[Claims] 1. The base material has a Vickers hardness of the shaft portion: 240.
As described above, the Vickers hardness of the surface layer extending from the surface to 200 μm is 400 or more, and the electroless plating layer is provided on the surface of the base material, and the electroless plating layer has a composition: P: 8 to 10
mass%, Ni: 90-92 mass% is included, thickness: 10
-60 μm, Vickers hardness: 600 or more, a high hardness and high rust resistant drilling tapping screw. 2. The drilling tapping screw with high hardness and high rust resistance according to claim 1, wherein the electroless plating layer portion of the surface layer is only a cutting edge portion at the tip.