JPH0534418B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention has excellent rust resistance and high hardness after quenching and tempering, as well as good workability, and is particularly applicable to linear motion bearings and miniature bearings.
The present invention relates to a new steel suitable for use in screws, cylinders, molds, ejector pins for plastic injection molding machines, cylinders for plunger pumps that require corrosion resistance, and cutlery that requires corrosion resistance. [Conventional technology] A linear motion axis is composed of a rail and a bearing.In contrast to the conventional sliding linear guide, this system uses rolling guidance using balls built into the bearing, resulting in highly accurate straightness with less wear loss. It is a linear guide component that provides positioning. Its applications span a wide range of fields, including machine tools such as NC lathes and machining centers, as well as robots, OA equipment, and computers. Material steel types include S55C, AISI4150, SCM415,
SCM420, SUJ2, SUS420J2, etc. are used. Recently, there are many applications that require no lubrication and are maintenance-free, and materials with high precision and excellent rust resistance are required.
S55C plated with Cr or martensitic stainless steel SUS440C are used. On the other hand, among miniature bearings, SUS440C or martensitic stainless steel with properties similar to this has traditionally been used for applications such as medical equipment and precision instruments that require rust resistance and high hardness. Similarly, SUS420J2 and SUS440C are used for plastic injection molding machine screws, cylinders, molds, ejector pins, etc.
Other examples include plunger pump cylinders that require corrosion resistance, and cutlery that requires corrosion resistance. [Problems to be solved by the invention] However, as the quality of products has improved in recent years,
The various mechanical parts and tools mentioned above have come to be exposed to increasingly harsh operating environments. For example, due to maintenance-free steel, the characteristics required for steel for linear motion shafts or miniature bearings include higher hardness, good rust resistance, and extremely low content of giant primary carbides that impede workability. It became like that. As a guideline, the hardness should be about 57 or higher, the rust resistance should be on par with SUS440C, and there should be very few large carbides larger than 5 μm. In other words, the SUS420J2 class lacks hardness (approximately HRC55),
On the other hand, although SUS440C fully satisfies the requirements in terms of hardness (approximately HRC60) and rust resistance, it contains many gigantic carbides with a diameter of more than 10 μm, making it difficult to pull out, cut, or cut.
This is a problem in terms of workability such as grinding. In particular, miniature bearings used in precision equipment often produce large vibrations and noise during high-speed rotation because the existence of giant carbides limits the surface roughness during grinding. These required characteristics also apply to screws, cylinders, molds, ejector pins of plastic injection molding machines, cylinders of plunger pumps that require corrosion resistance, and cutlery that requires corrosion resistance. For example, due to the improved performance of plastic resin, the screws in injection molding machines have become
When using SUS420J2, its low hardness causes significant wear during use and short life. Therefore, in order to improve wear resistance, it is possible to use SUS440C, which has high quenching hardness and a large number of hard carbides, but this steel type has poor workability and is expensive, as well as toughness due to giant carbides. Due to the decrease in the temperature, cracks are more likely to occur during use. For the various uses mentioned above, 0.7%C-
Although 13% Cr-based martensitic stainless steel has already been developed, even this steel has some problems with rust resistance, so it cannot be said that it fully satisfies the requirements. [Means for Solving the Problems] In order to solve these problems, the present inventor investigated the composition balance of C and Cr, which are the main elements of conventional high martensitic stainless steel, and found that the rust resistance It was found that Mo has a particularly large influence on the coarsening of carbides and carbides. At this time, in consideration of coarsening of carbides and rust resistance, C should be kept as low as possible within the range of 0.4 to 0.6% to ensure quenched hardness.
Although Cr improves rust resistance, it coarsens carbides, impairs workability, and lowers the hardness of the matrix. Therefore, considering the effect of adding Mo to improve rust resistance, %) lower than 11%. In order to obtain the desired hardness, rust resistance, carbide particle size, etc. within these C-Cr component ranges, it is recommended that Mo be added within the range of formulas (1) to (3) below. I found it. That is, (a) The compositional conditions to obtain a hardness of approximately HRC57 or higher are Cr% + 0.3Mo% - 16.3C% ≦5.0 ... (1) (b) The compositional conditions to obtain rust resistance are Cr% + 1 .2Mo%−11.5C%≧4.5 …(2) (c) The composition condition for suppressing as much as possible giant carbides with a major axis of 5 μm or more, which are included for the purpose of improving grindability, workability, and toughness, is Cr% + 2.7Mo. %+21.5C%≦26.0…(3). Note that these formulas were derived by regression analysis of experimental data. That is, the present invention contains C: 0.4% or more and less than 0.6% Si: Less than 1.0% Mn: 1.0% or less Cr: 6.0% or more and less than 11.0% Mo: 0.5% or more and less than 4.0%, and the main components This is a rust-resistant and wear-resistant steel in which C, Cr, and Mo satisfy the above formulas (1) to (3), and the balance is Fe and unavoidable impurities. [Effect] First, the experimental process that led to the discovery of equations (1) to (3) will be described. C: 0.35-1.0%, Cr: 10-16% Mo: 0.05-2.0
A large number of test steels with % as the main component and each component varied within this range were tapped in a 100Kg vacuum induction melting furnace, cast into an ingot with an average diameter of 190mm, and this was poured into an ingot with an average diameter of 25mm.
It was forged and stretched to make a sample material. Each specimen was heated to 1050℃ for 15
After holding for a minute, quench in oil and temper at 180℃.
After holding for a time, it was air cooled and used for each test. Rust resistance is determined under an environment of temperature 70℃ and relative humidity 95%.
After 96 hours of exposure, the presence or absence of rust was evaluated using a 10x magnifying glass. On the other hand, pitting potential in 0.5% NaCl was used as a method to quantify rust resistance;
As will be discussed later, there was a significant correlation with this exposure test. The number of carbides with a major axis of 5 μm or more was measured using an image analysis device. In addition, the measurement area is 1.125×
The field size was 10 ⁶ μm ² (50 fields of view). The above experiments were conducted on all sample materials, and the heat treatment hardness, pitting potential, exposure test results, and major axis
As a result of organizing the amount of carbides of 5 μm or more by C, Cr, and Mo, the following findings were obtained. As shown in Figure 1, heat treatment hardness is determined by the formula (Cr% +
0.3Mo%-16.3C%), hardness HRC57
In order to obtain the desired degree, the value of this formula must be at least 5.0 or less, taking into account variations. As shown in Figure 2, the pitting corrosion potential Vc is determined by the formula (Cr%+
1.2Mo%−11.5C%), and this value is 4.5
In the above cases, no resistance to development was observed in the exposure test. As shown in FIG. 3, the amount of carbides with a major diameter of 5 μm or more can be summarized by the formula (Cr + 2.7 Mo% + 21.5 C%), and when this value exceeds 26 to 27, it increases rapidly. Taking into account variations, the standard for satisfying the application of the present invention was set at 26.0 or less. Next, the reasons for limiting the chemical components of the present invention will be described. C is an essential element to obtain sufficient matrix hardness through quenching and tempering, and HRC56
To obtain a hardness of ~57 or higher, at least
0.4% is required. On the other hand, if more than 0.6% is added, huge carbides are generated, impairing grindability and toughness, and the effective amount of Cr in the matrix is reduced, resulting in a decrease in rust resistance, so the upper limit was set to less than 0.6%. Si is mainly added as a deoxidizing agent to improve hardenability, but if it is added in an amount of 1.0% or more, toughness deteriorates, so the upper limit was set to less than 1.0%. Like Si, Mn is added as a deoxidizer to improve hardenability, but adding more than 1.0% reduces toughness and temper softening resistance, so the upper limit should be set.
It was set at 1.0%. Cr is an element that combines with C to form a hard carbide and improves wear resistance, and also dissolves in the matrix to improve rust resistance. For this purpose, 6.0% or more is required. However, if it exceeds 11.0%, giant carbides tend to form and the hardness decreases, making it impossible to obtain a hardness of about HRC 56 to 57, so the upper limit was set to less than 11.0%. Like Cr, Mo is an effective element for improving wear resistance and rust resistance, and 0.5% or more is required to obtain this effect. However, adding more than 4.0% promotes coarsening of carbides, so the upper limit was set at 4.0%. [Example] Next, an example of the present invention will be described. Based on the previously obtained knowledge, 10 steel types A to J having the components shown in Table 1 were newly produced in the same process as the above-mentioned experimental process. Table 1 shows the components and values of equations (1) to (3) of the steel of the present invention, comparative steel, and conventional steel. Table 2 also shows the 1050℃ quenching and 180℃ quenching of each sample material.
Hardness after tempering, amount of giant carbides with major diameter of 5μm or more,
Furthermore, the presence or absence of rusting is shown in an exposure test at a temperature of 70°C, relative humidity of 95%, and a holding time of 96 hours. As is clear from this, the steel of the present invention is superior to the conventional steel in all aspects of hardness, rust resistance, and macrocarbide content. [Effects] By using the steel of the present invention for parts such as linear motion axes and miniature bearings that conventionally used SUS440C class, grindability has been improved.

【table】

[Table] Things.
We were able to reduce part processing costs due to the above, and improve product precision and vibro-acoustic characteristics due to improved surface roughness, while maintaining other functional characteristics at the same level or higher. Similarly, SUS420J2 and
The steel of the present invention will be used for the screws, cylinders, molds, and ejector pins of plastic injection molding machines that used SUS440C, as well as the cylinders of plunger pumps that require corrosion resistance, as well as cutlery that requires corrosion resistance. This resulted in a reduction in processing costs and an improvement in service life.

[Brief explanation of the drawing]

Figure 1 shows the relationship between hardness and the amounts of C, Cr, and Mo. Figure 2 shows pitting potential and exposure test results and C,
A diagram showing the relationship between Cr and Mo, and Figure 3 shows the major axis
It is a figure showing the relationship between the amount of carbides of 5 μm or more and the amounts of C, Cr, and Mo.

Claims (1)

[Claims] 1 Contains C: 0.4% or more and less than 0.6% Si: Less than 1.0% Mn: 1.0% or less Cr: 6.0% or more and less than 11.0% Mo: 0.5% or more and less than 4.0%, and C The relationship between Cr and Mo is Cr%+0.3Mo%-16.3C%≦5.0...(1) Cr%+1.2Mo%-11.5C%≧4.5...(2) Cr%+2.7Mo%-21.5C %≦26.0……(3) A rust-resistant and wear-resistant steel that satisfies (3) and consists of the remainder Fe and unavoidable impurities.