JPH023275B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention has high breaking torque as a material for the metal shell of small spark plugs used in internal combustion engines, especially those with an engine mounting thread diameter of 8 mmφ and pitch of 1.0 mm, and has excellent hot formability and cold formability. This article relates to a small spark plug made of alloy steel with excellent tightening properties. [Prior art and its problems] Conventionally, the metal shell of the spark plug that is screwed onto the cylinder head of an internal combustion engine has been made of S10C~
S20C low carbon steel for mechanical structure is mainly used. On the other hand, in recent years, as automotive engines have become more fuel efficient, lighter, and more powerful, the installation space for spark plugs has become narrower, and for this reason, small spark plugs with an extremely small installation screw diameter of M8mmφ and a pitch of 1.0mm have been adopted. Various methods are being considered. In the metal shell of such a plug, as shown in FIG. 1, the screw neck 1c between the large-diameter body portion 1a of the metal shell 1 and the mounting screw portion 1b is necessarily thin, with a wall thickness of about 0.86 mm. Therefore, when low carbon steel of S10C to S20C is used, there is a problem that fracture A occurs at this screw neck portion when tightening the plug. In addition, it is effective to increase the wall thickness in order to prevent the screw neck from breaking, but further reducing the diameter of the insulator and center electrode arranged inside will improve the structural strength and withstand voltage performance of the insulator. It is difficult to adopt such a method because the wear resistance and heat resistance deteriorate due to the decrease in the thermal conductivity of the center electrode in the axial direction. Therefore, as a result of considering the use of S30C and S35C, which have a high carbon content, in order to improve the fracture strength of the screw neck of the metal shell, it was discovered that a new problem occurred.
That is, as shown in FIG. 1, in the spark plug, the insulator 3 holding the center electrode 2 is inserted into the inner cavity of the metal shell 1, and the step part 3b that continues from the large diameter part 3a of the insulator is attached to the step seat 1d. 4, a sealing material 5 and a packing 6 are disposed between the upper small diameter portion 3c of the insulator and the inner cavity of the metal shell, and the metal shell body 1a and the fastening portion 1e, such as a hexagonal A current is passed through the thin heating portion 1f between the two, or heating is performed by high-frequency induction heating, and the upper end periphery 1g of the metal shell is heated.
The insulator is fixed using the so-called normal heat crimping method. However, when the steels S30C and S35C are used, the heated portion 1f is rapidly cooled to become a martensitic structure, which causes cracks and fractures B, which results in the disadvantage that the product cannot be manufactured. On the other hand, in addition to the above-mentioned hot caulking, cold caulking, which does not apply heat, is also known as a caulking method. It can also be fixed to The above-mentioned S10C and
S20C steel can be cold-forged without any problems, but as mentioned above, it tends to break at the screw neck. When using high carbon steels such as S30C and S35C steels, they do not have sufficient toughness and the screw necks are thin, which causes cracks and cracks during cold forging. Furthermore, in order to solve these problems, we considered applying heat treatment to the screw neck and heated part after forming the metal shell, but this resulted in problems such as higher manufacturing costs and difficulty in heat treatment as each part was narrow. . For this reason, there has been a strong demand for the development of a steel material that has high breaking torque and excellent hot and cold formability without post-heat treatment as a material for the main metal fittings of M8 plugs. [Object of the Invention] The present invention has been made in view of the above circumstances, and is a main metal material with an engine mounting screw diameter of 8 mmφ and a pitch of 1.0 mm. The purpose is to provide a small spark plug with stable performance by using alloy steel with excellent caulking properties. [Means for solving the problem] The present invention has an engine mounting screw diameter of 8 mmφ and a pitch of 1.0 mm.
C0.03~2.0% by weight in the material of the main metal fittings,
Si0.35% or less, Mn0.1~2.0%, P0.025% or less,
Contains S0.025% or less, Al0.005-0.080%, and
Zr0.005~0.25%, Nb0.005~0.10%, V0.03~0.25
%, Ti0.005~0.25%, Cr0.05~0.50%, Ni0.05~
This is a small plug made of alloy steel containing at least one of the following: 0.50%, with the balance consisting of iron and unavoidable impurities. First, the chemical composition of the alloy steel used in the present invention will be explained. C is necessary to give the steel the required strength through solid solution strengthening, and if it is less than 0.03%, the strength of the steel will be insufficient and the zinc phosphate lubricant may not adhere sufficiently, so it should not be cooled. Seizing occurs between the tool and the workpiece during forging, which significantly shortens tool life. However, when adding too much (more than 0.20%), the Vickers hardness (Hv)
This results in a martensitic structure of 450 or more, and cracks occur in the heat-sealed part. Furthermore, when adding too much of more than 0.2%, the toughness of the steel material itself decreases, so when the spark plug main metal fitting is manufactured from such steel material and cold-stamped into the insulator as described above, Cracks will occur in this caulked portion. Preferably, the amount of C is in the range of 0.05-0.20%. Generally, Si dissolves in steel to increase its strength, but in the steel of the present invention, when it exceeds 0.35%, it deteriorates the toughness of the hot caulked part or the toughness of the steel material itself. Since it deteriorates cold forming properties, the upper limit is set at 0.35%. Mn fixes the impurity element S, which is the main cause of cracking during hot rolling and cold forging, as MnS,
It has the effect of making it harmless, and is an effective element for imparting both a predetermined strength and excellent toughness to relatively low-carbon steel, as in the present invention. In order to effectively obtain such effects,
It is necessary to add 0.1% or more, but when added in excess, the workability during molding of the spark plug main metal fitting is deteriorated, and the toughness of the metal main fitting is also deteriorated. Furthermore, since it increases the hardenability of steel and deteriorates both hot and cold formability, the upper limit of the amount added is set at 2.0%. Since P promotes work hardening and deteriorates cold formability as well as the toughness of hot-stamped parts, it is preferable to have it as low as possible, but if it is too low, it will not be effective and will only increase the economic burden of steel manufacturing. be. Purpose of the present invention
Considering the intended use, a content of 0.025% or less is sufficient. S forms sulfide-based inclusions, which become the starting point for cracks during hot forging, and also deteriorates the deformability during cold forging when manufacturing the metal shell, so its content should be kept at 0.025% or less. It is sufficient. However, it can be set even lower depending on the required properties such as the required degree of hot swaging, cold swaging, cold working, machinability, etc., and preferably the upper limit is 0.015%. In addition to its role as a deoxidizing agent during steel melting, Al has the effect of refining crystal grains during heat-stamping, thereby improving the toughness of the heat-stamped part.
Furthermore, it binds with nitrogen (N) and precipitates as AlN, thereby fixing solid solution N and having the function of suppressing strain aging and blue brittleness. However, the content
When it is less than 0.005%, the above effects are not sufficient, while when it exceeds 0.080%, B-based inclusions increase and associated cold forging cracks, hot forging cracks, and cold forging cracks are likely to occur during forming of the metal shell. Therefore, the amount added should be 0.005 to 0.080%. Further, the steel according to the present invention contains at least one member selected from the group consisting of Zr, Nb, V, Ti, Cr, and Ni in addition to the above-mentioned elements. These elements are effective in improving the strength and toughness of steel. Zr, Nb, V, and Ti improve strength through grain refinement and precipitation effects caused by the precipitation of fine carbonitrides during rolling or during the cooling process of the steel after rolling. In addition, grain refinement also improves workability during cold forging, and also improves the toughness of the part during hot forging, and provides excellent cold forging performance when cold forging is performed. Obtainable. In order to effectively obtain these effects, they should be added in the following ranges. That is, Zr0.005~0.25%, Nb0.005~
0.10%, V0.03~0.25%, and Ti0.005~0.25%. If each element is added in excess of the above upper limit, the effect will be saturated and this is not preferable from the economic point of view of steel production. Cr improves hardenability and increases strength. In order to effectively obtain this effect, it is necessary to add 0.05% or more. However, if too much is added, the hardenability will be excessively increased and the hot formability will deteriorate, and the toughness of the steel itself will decrease, resulting in a deterioration of the cold formability, so it should be added within a range of 0.50% or less. Ru. Ni improves the strength and cold workability as well as the toughness of hot-stamped parts, and it is necessary to add 0.05% or more to improve cold heatability. The upper limit of the amount added was set at 0.50 because the effect saturates and the economic efficiency of steel manufacturing is impaired.
%. Next, as a preferred method for manufacturing the alloy steel according to the present invention, hot rolling is performed after heating to 950 to 1150°C. After dissolving the precipitates in the matrix, fine carbon and nitrides are precipitated to refine the crystal grains and precipitation harden them, or to refine the initial grains at 1150°C.
Furthermore, if the temperature is less than 950°C, the deformation resistance increases during hot rolling and productivity decreases, so 950°C is set as the lower limit. In the present invention, after hot rolling, water cooling is performed to set the cooling start temperature at a predetermined cooling rate in the temperature range of 800 to 950°C, and from this temperature range, the average cooling rate is 10
Cool to a temperature range of 500℃ or less at ℃/sec or less. When the cooling start temperature is a high temperature exceeding 950°C, crystal grains become large, toughness and ductility deteriorate, and workability such as cold forging workability, thread rolling property, and cold forging property decreases. On the other hand, the cooling start temperature is 800℃
When it is lower than , the resulting product quality varies greatly and it becomes difficult to maintain constant quality. Cooling is carried out at an average cooling rate of 10°C/sec or less from this temperature range to a temperature range of 500°C or less, which creates a dense ferrite/pearlite structure and achieves the desired strength and toughness, as well as distortion during cold forging. Prevents aging and reduces tool life shortening, but if the cooling rate exceeds 10℃/sec, bainite structure will be present, resulting in higher than desired strength or greater strength variation, and furthermore, toughness and ductility will decrease. However, folding of the threads is likely to occur during thread rolling, and cold forming properties are reduced. Furthermore, the tool life deteriorates. The alloy steel of the present invention is formed into a hexagonal steel bar with a tensile strength of 75 kg/mm ² or more by hot rolling and cold drawing, and then cut into a predetermined shape by cutting. Manufacture the main metal fittings for the mold. [Example] Examples of the present invention will be described below with reference to comparative examples. Steel having the chemical composition shown in Table 1 is melted in a vacuum melting furnace, hot rolled under the rolling conditions shown in Table 1, and then subjected to cold wire drawing with an area reduction of 20 to 30%. The diameter of the mounting screw is adjusted by cutting these steel wires.
We created an M8 metal shell and measured the breaking torque at the screw neck. In Table 1, numbers 1, 2, and 3 are commercially available low carbon steels for mechanical structures. The breaking torque depends on the surface condition (degree of friction) of the jig and the metal shell.
Since this is significantly affected by friction, a comparative evaluation was conducted under a constant state in which both the main metal fittings and jigs were coated with lubricating oil (friction coefficient μ = 0.15). Furthermore, the breaking torque is shown with the value of the comparative product S17C as 100%. As is clear from Table 1, the metal shell cut and formed from the steel material according to this example has sufficient strength, and the thread breaking torque is approximately 50% higher than that of S17C, making it suitable for use in the metal shell of small spark plugs. No problem at all. Next, the thin heated part 1f of the formed metal shell shown in Fig. 1 was energized and heated, and then caulked, and the presence or absence of cracks in this part was examined. No cracks were observed in the metal shell formed from the steel material according to this example. Instead of the above caulking, the insulator was fixed to the metal shell by cold caulking without applying heat. Even in the case of this cold caulking, as shown in Table 1, no cracks were generated in the thin wall portion of the metal shell (corresponding to the heated portion 1f in FIG. 1).

【table】

〔Effect of the invention〕

As described above, a small ignition plug formed using the alloy steel of the present invention into a metal shell with a mounting screw diameter of M8 and a pitch of 1.0 mm has a higher tensile strength than conventional materials even without post-heat treatment. It has the effect of preventing the screw neck of the threaded part from breaking, and also prevents cracking during hot caulking or cold caulking without applying heat.Furthermore, since the same design as conventional ones can be considered, the strength of the insulator and No deterioration in withstand voltage performance,
Further, it has excellent effects such as being able to provide a small spark plug with stable performance without deterioration of heat resistance.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a main part of a small ignition plug showing a broken screw neck part A and a crack B in a heating part, and FIG. 2 is a sectional view of a main part of a small ignition plug showing another embodiment of the present invention. 1... Main metal fitting, 1b... Mounting screw part, 1c...
...Screw neck, 1f...Heating part.

Claims (1)

[Claims] 1 As a material for the main metal fittings with an engine mounting screw diameter of 8 mmφ and a pitch of 1.0 mm, C0.03 to 0.20% by weight,
Si0.35% or less, Mn0.1~2.0%, P0.025% or less,
Contains S0.025% or less, Al0.005-0.080%, and
Zr0.005~0.25%, Nb0.005~0.10%, V0.03~0.25
%, Ti0.005~0.25%, Cr0.05~0.50%, Ni0.05~
A small ignition plug characterized in that it is made of alloy steel containing at least one of the above 0.50%, with the balance consisting of iron and inevitable impurities.