JPS6367542B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to materials for engine valve train parts of automobiles and the like, and particularly to materials for rocker arms and the like. Engine valve train components are used to operate the valves of the engine, and usually include a rocker arm that is directly connected to the valve and swings, or a camshaft that causes the rocker arm to swing. In the case of an overhead camshaft (OHC) type valve mechanism, the rocker arm and the camshaft (especially the cam) are in contact with each other, and the camshaft is rotating at high speed, so it is used for both parts. The material must have good abrasion and scuffing resistance. In particular, when looking at the rocker arm, unlike the camshaft where the outer periphery of the cam is in contact evenly, the rocker arm pad, which is one part of the cam, is in constant contact, so there are extremely high demands on the wear resistance of this pad. It will be expensive. However, when two parts are in contact like this, if the wear resistance of one part is increased,
It is preferable for such engine valve train parts to use materials with high wear resistance, as this makes it easier to hit the other part that comes into contact with the one part, the so-called mating part. isn't it. In other words, when it comes to materials for engine valve train parts such as rocker arms, it is necessary to take into account not only their own wear resistance, but also their ability to effectively hit the opponent. Therefore, it is extremely difficult to select materials for engine valve train parts, and a sufficient material has not yet been found, making it an important issue. In view of these points, the inventors of the present invention have conducted various studies, and have found that a steel material with a certain composition is subjected to soft nitriding treatment, and the thickness of the compound layer is specified. The present invention was completed based on the discovery that both of the above-mentioned properties required for a material for use in plastics can be satisfied at the same time. That is, the material for engine valve train parts of the present invention has, in weight percent, C: 0.80 to 1.40%, Mn: 1.50% or less, Si: 1.0% or less, Cr: 5.0 to 9.0%, Mo: 0.2 to
2.5%, at least one type of V or W: 0.67% or less,
Fe and impurities: A steel material consisting of the remaining composition is subjected to soft nitriding treatment to make the surface layer (compound layer) made of the steel material 5μ or more thick, thereby increasing the hardness of the surface layer. Hv600-900, and
It is characterized in that the area ratio of carbide (the particle size of the carbide is preferably 10 μm or less) in the dough is 0.5 to 4.0%. Further, the steel material is preferably subjected to heat treatment before soft nitriding treatment. The heat treatment includes, for example, (a)
Examples include quenching and tempering, (b) quenching (which also serves as tempering through nitrocarburizing treatment), and (c) normalizing. The soft nitriding treatment includes (a) gas soft nitriding and (b) salt bath soft nitriding. The reasons for limiting the ingredients will be described below. C: An element that improves the strength of the dough by forming carbides while obtaining the necessary hardness through quenching, and for this purpose, it must be contained in an amount of 0.80% or more. However, as the content increases, the grain size of the carbide becomes larger, making it easier to attack mating parts, so the upper limit was set at 1.40%. Cr: Combines with C to form carbides, improving the strength and abrasion resistance of fabrics, and also generates nitrides during soft nitriding, forming an extremely hard compound layer and increasing the hardness of the surface layer. It has the effect of increasing the hardening depth, and in order to obtain these effects, it must be contained at 5.0% or more. but,
If the content is too high, the hardness of the compound layer becomes too high, and as shown in Figures 1 and 2, it attacks the mating part (cam) and also wears itself (pad) due to the abrasion powder, so the upper limit is was set at 9.0%. Mo: forms a carbide similar to Cr, and in addition to improving the strength of the fabric, it also increases resistance to tempering and softening, and improves wear resistance by increasing the hardness of the nitrided layer through soft nitriding treatment. It is an element and must be contained at 0.2% or more. However, if the content increases, it will attack the mating part (cam) as shown in Figures 3 and 4, and the wear powder will also wear out itself (pads), so the upper limit cannot be reached.
It was set at 2.5%. V and W: Elements that increase resistance to temper softening and refine carbides, and form a nitrided layer through soft nitriding treatment to increase the hardness of the surface layer. However, if the content exceeds 0.67%, hard carbides are formed and the carbides become coarser, which increases the aggressiveness of the mating parts, so the upper limit was set at 0.67%. Si: It is added as a deoxidizing element along with Mn during scouring, but if it is contained in excess of 1.0%, it will hinder the diffusion of N during soft-nitriding treatment, so the upper limit was set at 1.0%. Mn: In addition to being added as a deoxidizing element like Si, Mn also improves hardenability. However, if the content exceeds 1.5%, processability deteriorates, so the upper limit was set at 1.5%. Next, an example will be described in which the material according to the present invention was actually applied to a rocker arm pad. Based on JIS standard or JIS standard modified cold work tool steel, materials with the compositions shown in Table 1 below, with varying content of each component, were melted and prototype rocker arm pads for vertical engines were produced. Next, this pad was subjected to quenching and tempering treatment, and then nitrocarburizing treatment.

[Table] × marks are outside the range of numerical limitations.The Rocker arm pads treated in this way were then subjected to a motoring test under the following conditions: (Test conditions) Engine speed: 2000r.pm Test time : 200 hours Valve spring load: 150% or more (relative to mass-produced engine assembly load) Lubricating oil: Durable deteriorated oil ~Γ~Γ~Γ~ Camshaft: Alloy cast iron (matching part) And Rotsuka arm parts after the test The wear resistance of the rocker arm pad can be determined by measuring the amount of wear on the pad (Figures 1 and 3), and the amount of cam wear on the camshaft, which is the mating part of the pad, can be evaluated. Regarding aggressiveness towards opposing parts (Figures 2 and 4),
Each was evaluated. In addition, scuffing resistance was evaluated based on the degree of appearance of scratches. Note that Figures 1 and 2 are based on changes in the Cr content, and Figures 3 and 4 are based on changes in the Mo content (the Cr content is within the range of 5 to 8%). It is based on Based on these figures, the evaluation of each characteristic of the rocker arm pad subjected to the above test, namely (a) wear resistance, (b) scuffing resistance, and (c) aggressiveness against mating parts, is as described above. It is also listed in the table below. When considering this table, it is understood that the material according to the present invention is a preferable material that simultaneously satisfies the above three properties (a), (b), and (c). In addition, the content of ingredients shown in the table above for which the reason for limitation is not described, such as phosphorus (P) and sulfur (S), is not limited to the values in the table and is based on JIS standards or JIS standards modified content. It is acceptable as long as it falls within the range of the content of the components in steel for cold work tools. Further, although the table does not list anything containing tungsten (W) as an additive element, as described above, it may be included. Note that such heat treatment and soft nitriding treatment can be performed under normal conditions. However, since changes in the content of each component in the material cause differences in quench hardenability, temper softening resistance, etc., the above conditions should be selected appropriately depending on the change in content. In the embodiment, alloy cast iron was used as the material for the mating part (cam), but similar effects can be achieved with cams made of various other cast irons. As described above, the material of the present invention has excellent wear resistance and scuffing resistance, and is less aggressive to mating parts, so it is suitable as a material for engine valve train parts that require all of these properties at the same time. be.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between Cr content and pad wear amount in the motoring test.
Figure 3 is a graph showing the relationship between Cr content and cam wear, Figure 3 is a graph showing the relationship between Mo content and pad wear, and Figure 4 is a graph showing the relationship between Mo content and cam wear. A graph showing the relationship with the amount of wear. In the figure, the numbers are pad numbers.

Claims (1)

[Claims] 1% by weight, C: 0.80 to 1.40%, Mn: 1.50% or less, Si: 1.0% or less, Cr: 5.0 to 9.0%, Mo: 0.2 to
2.5%, at least one type of V or W: 0.67% or less,
A material for engine valve train parts, characterized in that a steel material having a composition of Fe and the remainder is subjected to soft nitriding treatment so that the thickness of the surface layer made of the steel material is 5μ or more.