JPS589142B2 - Stainless steel for spokes - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to stainless steel suitable for spokes used in bicycles, motorcycles, etc. Spokes used in bicycles, motorcycles, etc. are generally JISG350.
Electrogalvanized hard steel wire (medium to high carbon steel) specified in 6 is used, but problems such as increased cost and pollution caused by the electrogalvanizing process are used. On the other hand, the trend of the times is toward higher quality bicycles, motorcycles, etc., and along with this, there is an increasing demand for spoke materials to change from medium carbon steel to stainless steel.

The properties required of the material for spokes are (1) Corrosion resistance: No rust should occur in the salt spray test specified in JIS Z2371 three times.

(2) Strength: Neck strength after processing into spokes: 260 kg or more at No. 14 wire (diameter 1.97 mm), and the number of times the spokes can be bent repeatedly until breakage after processing is 10 times or more.

(3) Good wire drawability.

(4) Good delayed fracture characteristics.

etc.

In order to develop a stainless steel that satisfies these requirements, the inventors of the present invention have conducted various studies and found that the objectives can be achieved by having the following composition and structure.

(1) Carbon: 0.10% or less, silicon 1.0% or less,
1 Manganese 3~5%, copper 1.0% or less, chromium 16~
18%, residual iron and impurities, and (2) martensite and ferrite in the quenched state.
Carbon 0.10% or less, silicon 1.0 or less, manganese 3-5%, copper 1.0% or less, chromium 16-1
This stainless steel for spokes consists of 8% residual iron and impurities.

The reason why the alloy components of the stainless steel for spokes according to the present invention are limited to the above is explained below. (1) Carbon: 0.
10% or less Carbon improves the strength of steel, but it deteriorates corrosion resistance, so it is limited to 0.10% or less.

The best range that satisfies strength and corrosion resistance is 0.04 to 0.1
It is 0%.

(2) Silicon: 1.0% or less Silicon is added as a deoxidizing agent during melting and refining.
A content exceeding 0% reduces the cleanliness of the steel.

(3) Manganese = 3.0% to 5.0% Manganese is added as a deoxidizing agent during melting and refining, and
As an austenite-forming element, it is an important element that causes the austenite + ferrite structure at high temperatures to transform into martensite + ferrite structure after quenching.If it is less than 3%, it has no effect, and if it exceeds 5%, austenite may remain during quenching. and the strength decreases.

(4) Steel: 1.0% or less Copper is an element that improves cold workability, and is contained in a range of 1.0% or less.

(5) Chromium: 16-18% Chromium is an important element for obtaining corrosion resistance of copper and should be contained in an amount of 16% or more, but if it is contained in excess of 18%, the ferrite phase will increase and the expected strength will not be obtained.

(6) Impurities In the stainless steel for spokes of the present invention, phosphorus, sulfur,
Contains nickel, molybdenum, nitrogen, and other impurities, but in consideration of cold workability, corrosion resistance, strength, price, etc., phosphorus and sulfur are each 0.04% or less, and nickel is 0.04% or less. 5% or less, molybdenum 0.2% or less, and nitrogen 0.05% or less.

The stainless steel for spokes of the present invention has an austenite + ferrite structure at high temperature by balancing the above-mentioned components, and a martensite + ferrite structure when quenched, which provides the required corrosion resistance, strength, and workability. For example, if austenite remains during hardening, the strength will decrease.

Therefore, the structure at the time of quenching needs to be a martensite+ferrite structure substantially free of residual austenite.

In addition, the final heat treatment of the stainless steel for spokes of the present invention is 9
It is desirable to carry out the process in a temperature range of 50 to 1025°C.

This is because the stainless steel for spokes of the present invention has a maximum austenite phase at about 1000°C, and the structure at the time of quenching is 60-75% martensite + 40-25% ferrite, resulting in strength (tensile strength) as shown in Figure 1. This is because the maximum value of

Examples After final heat treatment, the test materials shown in Table 1 were made into spokes (diameter 1.
97 mm x length 280 mm) and used for each test.

In Table 1, A and B are stainless steels for spokes of the present invention, and C is comparative steel, both of which are heated at 1000°C x 30min-AC.
The final heat treatment was performed.

Further, D was a hard steel wire (JIS, SWRH57B) conventionally used for spokes, which was subjected to the test after being electrogalvanized.

Table 2 shows the results of various tests on these test materials.

The test method is as follows.

(1) The neck of a No. 14 spoke (diameter 1.97 mm) was fixed with a jig and the load was measured when it broke under tension.

(2) Salt spray test based on JIS, Z2371
Rotate around and observe the state of rust formation.

○: No rust formation △: Slight rust formation (3) With a bending radius of 4 mm, the 90° bent portion of the spoke was bent in a straight line, then 90° in the opposite direction, and repeated in a straight line, and the number of times until breakage was measured.

FIG. 2 is a diagram showing the relationship between working rate and tensile strength of the results of a tensile test after cold working material A (invention material) in Table 1.

Furthermore, FIG. 3 shows the results of a delayed fracture test of the necks of specimens A and D in a 0.1N HCl aqueous solution.

As is clear from the above results, the stainless steel for spokes according to the present invention fully satisfies the various properties required for spokes, and has superior delayed fracture properties compared to the conventional material, hard steel wire. It shows that it has.

[Brief explanation of drawings]

Figure 1 shows the effect of heat treatment temperature on the tensile strength of the steel of the present invention, Figure 2 shows the relationship between tensile strength and cold working rate, and Figure 3 shows the effect of heat treatment on the tensile strength of the steel of the present invention. It is a rupture time-stress curve diagram in a delayed fracture test of the neck.

Claims (1)

[Claims] 1 C: 0.10% or less, Si: 1.0% or less, Mn:
3 to 5%, Cu: 1.0% or less, Cr: 16 to 18%, the remainder substantially consisting of Fe, and having a two-phase structure of martensite and ferrite. .