JPS6333516A - Production of timepiece parts - Google Patents

Abstract

PURPOSE:To produce inexpensive timepiece parts having good finish appearance and stable quality by heating a middle carbon steel contg. a specific ratio of carbon to a specific temp., then hardening and tempering the steel and turning the steel to a desired shape. CONSTITUTION:The raw wire of the free-cutting middle carbon steel contg., by weight, 0.3-0.6% carbon is subjected to annealing and drawing repeatedly 3 times to form a wire rod 5. The wire rod 5 is taken up by a torque motor 2 from such wire rod coil 6 and is held at the Ac3 transformation point or above in a soaking zone 4 of a high temp. furnace 1 in which an N2 atmosphere is maintained, then the wire rod is quickly cooled in a cooling tank 3 and is thus hardened. The wire rod 5 is thereafter tempered at 500-700 deg.C in a tempering furnace 7 in which the N2 atmosphere is maintained. The wire rod 5 taken up on the torque motor 2 is straightened to a bar and is then subjected to centerless working. The structure in which spheroidal cementite is uniformly dispersed by aggregation into the fine equiaxed ferrite grains and the grain boundaries is thereby obtd. and the bar having an excellent free-cutting property and strength is obtd.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for manufacturing timepiece parts.

C. Summary of the Invention] In order to manufacture watch parts such as Kana, which are extremely small and have a complicated shape, and which require high dimensional accuracy, a watch component containing 0.3 to 0.6% carbon by weight ( After heating and holding medium carbon steel (hereinafter referred to as %C) above the Acff transformation point, it is quenched and tempered, and then processed using an automatic lathe.

[Conventional technology]

Conventionally, carbon steel for watch parts, which is processed using automatic lathes, is drawn and annealed several times to obtain dimensions close to the desired dimensions, and then the wire is linearly processed and centerless processed to obtain the desired dimensions. It is used as a bar material.

Therefore, in the carbon steel for watch parts processed by the above-mentioned conventional method, the cementite in the carbon steel becomes spheroidized to a grain size of about 2 to 3 μm during annealing during the wire drawing process (hereinafter referred to as spherical cementite), and the cementite in the carbon steel is spheroidized to a ferrite ground. This FJi-like cementite becomes individually and independently dispersed. In addition, in order to adjust the particle size of spherical cementite, spheroidizing annealing is performed during the wire drawing process.

[Problem that the invention seeks to solve]

However, if the metal structure obtained by the conventional processing method is maintained, medium carbon steel will have less spheroidal cementite cracking than ferrite. Furthermore, during the annealing during the wire drawing process, the carbon atoms in the pearlite phase of the raw cotton do not sufficiently diffuse into the ferrite, and the spherical cementite is not uniformly dispersed but aggregates in areas with a high carbon content. This results in less dispersion of spherical cementite. The proportion of only ferrite base becomes very large, and this ferrite is stretched in the wire drawing direction, so that it exists in a state like a ferrite band.

Ferrite is extremely soft and sticky, and processing stress from wire drawing remains. Carbon steel with a large amount of ferrite can reduce cutting force and increase cutting speed, but cracks occur most effectively at the interface with a hard phase with a relatively large grain size. A structure without such a phase has poor chip control, and
Even if strong wire drawing is applied, strength and wear resistance cannot be sufficiently increased, and the hide pressure during turning places a load on the material, causing eccentric rotation, resulting in large variations in dimensional accuracy. The surface finish is extremely poor. Furthermore, the presence of ferrite band-like materials causes variations in hardness and machinability.

Therefore, in order to solve these conventional drawbacks, the present invention aims to manufacture inexpensive precision-machined parts that have strength that cannot be obtained only by drawing medium carbon steel during turning, and that enable continuous turning for long periods of time. The purpose is to provide a method.

[Means for solving problems]

In order to solve the above-mentioned problems, the present invention provides a 0.3-0.
A medium carbon steel containing 6% C was heated and maintained at a temperature equal to or higher than the AC:l transformation point, then quenched and tempered, and then turned.

[Effect]

Medium carbon! 4 (hypo-eutectoid steel) is rapidly cooled to a temperature above the A0 transformation point to form altenside, and then tempered at 500 to 700°C, spheroidal cementite aggregates within the fine equiaxed ferrite grains and at the grain boundaries, creating a uniform structure. Become a dispersed organization.

In such a two-phase mixed steel of ferrite and agglomerated cementite, the agglomerated cementite phase is difficult to deform during cutting, so strain concentrates on the soft ferrite phase in the cutting process, and microcracks occur due to work hardening. Since it is easily broken down into small pieces, the ability to dispose of cutting chips is significantly improved. At this time, the agglomerated cementite mixed therein acts as an obstacle and reduces the size of the new castle, reducing the cutting resistance applied to the cutting tool.

The present invention is achieved by converting medium carbon steel into a two-phase mixed phase of ferrite and agglomerated cementite having the above characteristics.

〔Example〕

The present invention will be explained in detail with reference to Examples below.

FIG. 1 is a diagram showing a manufacturing process according to a conventional method and a manufacturing process according to the method of the present invention, and FIG. 2 is a diagram showing a schematic diagram of a continuous wire heat treatment apparatus used in the present invention.

Example-1 Table 1 Table 1 shows the chemical components of the test materials used in the present invention. The raw material of this composite free-cutting medium carbon steel with a diameter of 5.5N was annealed and wire-drawn three times, and a wire rod with a diameter of 1.5N was made into a second wire.
Insert into the wire continuous quenching equipment shown in the figure. The quenching process is performed by applying tension with the torque motor 2 shown in Figure 2 and winding it up at a speed that passes through the soaking zone 4 of the high-temperature furnace 1 in a N2 atmosphere maintained at 880°C in 5 minutes. After cooling rapidly through an oil tank in a separate room separated by an N2 gas curtain, the N2 gas was kept at 650°C.
Tempering was performed by passing through a tempering furnace 7 with two atmospheres. The wire rod wound by the torque motor 2 was set in a straightening machine as a coil, and after straightening it into a bar material, centerless processing was performed to obtain the dimensions. Since the present invention performs quenching treatment after wire drawing, it is possible to eliminate spheroidizing annealing, which requires complicated heat treatment conditions during the wire drawing process.

Table 2 shows a comparison of the material strength of the workpiece obtained in this manner, particularly the properties required for turning, with conventional materials.

Table 2 Thin wire rods for precision parts with complex shapes have traditionally been required to have a tensile strength of 100 kg/mm and a hardness of about 1 lv300 for turning processing. The present invention has greater strength than conventional products, and it has also become possible to process parts with complex shapes that were not possible with conventional products.

The turning machinability test was conducted by machining the kana parts, which require the highest dimensional accuracy and appearance finish among watch parts, using an automatic lathe, and comparing the chips and finished appearance with conventional materials. .

The chips of the present invention were finely divided into lengths of about 1 to 211, and were significantly finer than the length of the conventional material, which was about 101. Additionally, the finished appearance was smoother with fewer irregularities than conventional materials.

Example 2 Here, carbon steel with a carbon content in the range of 0.3 to 0.6% C was used in the present invention because if the carbon content is 0.3% or less, it is difficult to achieve both material strength and machinability. , 0.6%C or more, the quenching hardness becomes extremely hard, making it difficult to perform continuous heat treatment of quenching and tempering.

Using 0.3%C and 0.6%C carbon steel wire, 0°3
%C carbon steel was quenched at 900°C and tempered at 500°C, and 0.6%C carbon steel was quenched at 840°C and tempered at 700°C, resulting in a hardness of Hv280.I.
The Iv300 was obtained, and the chip shape and finished appearance were also good as in Example-1.

Example-3 Using 0.5% C carbon steel fine wire that does not contain free-cutting components,
When treated in the same manner as in Example-1, the hardness was H.
v292, which was almost the same as a material containing a free-cutting component. The chip shape and finished appearance were also good as in Example-1.

〔Effect of the invention〕

As explained above, the present invention has been developed by using thin medium carbon steel wires, which are conventionally used in wire-drawn wires, with insufficient strength and machinability as they are drawn. , AB3
After quenching from the temperature range above the transformation point, 500 to 700
By tempering in the temperature range of °C, it is possible to obtain strength that cannot be achieved by wire drawing of medium carbon steel, and by taking advantage of its excellent free machinability, it is possible to improve the length, which has been a bottleneck in precision machined parts. The present invention has the effect of providing a method for manufacturing precision parts with stable quality and low cost, which enables continuous processing over time and has a good finished appearance.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a process diagram showing manufacturing steps according to a conventional method and the method of the present invention, and FIG. 2 is a schematic diagram of a continuous wire rod quenching and tempering apparatus used in the present invention. 1... High temperature furnace 2... Torque motor 3... Cooling tank 4... Soaking zone 5... Carbon steel thin wire 6... Carbon steel thin wire coil 7... Tempering furnace or higher

Claims (3)

[Claims] (1) Carbon steel containing 0.3 to 0.6% carbon by weight is brought to a temperature above the Ac_3 transformation point, then quenched and tempered, and then turned into the desired shape. Characteristic manufacturing method for watch parts. (2) The method for manufacturing a timepiece component according to claim 1, wherein the tempering temperature is 500 to 700°C. (3) The method for manufacturing a timepiece component according to claim 1, wherein the carbon steel is a free-cutting carbon steel containing a free-cutting component or a component added for the purpose of free-cutting.