JPS5952685B2 - How to impart galling resistance to stainless steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for imparting caulking resistance to stainless steel using a simple process without impairing corrosion resistance.

Stainless steel generally has poor galling resistance, so it cannot be used as mechanical components in locations where stainless steel members slide in contact with each other under high surface pressure.

For this reason, if you absolutely want to use stainless steel from the standpoint of corrosion resistance, either use a material with excellent galling resistance for the mating material, or weld or weld a material with excellent galling resistance to the stainless steel surface of the contact part. This is supplemented by overlaying using metal spraying, etc. However, using only a material with good galling resistance as the mating material does not provide a basic solution, and even if overlaying is performed, the corrosion resistance of the overlay metal becomes a problem, and the overlay work and overlay There is a problem in that the manufacturing cost is extremely high because finishing work (mechanical cutting, polishing work, etc.) is required for the contact surface of the metal. However, in recent years, the number of mechanical components that require corrosion resistance and galling resistance (for example, valve seats and seat rings of gate valves frequently used in chemical plants) has increased significantly, and it has become difficult to apply the overlay described above. It is clear that if galling resistance could be imparted to stainless steel itself, it would make a huge contribution to various fields.

As a result of various studies on stainless steel in order to obtain both the properties of corrosion resistance and galling resistance, the present invention was developed using an extremely simple process of shot blasting the surface of stainless steel containing 10 to 30% by weight of chromium. It has been found that this material can be suitably applied to members that require corrosion resistance and galling resistance as described above.

The method of the present invention can be applied effectively to any of martensitic, ferritic, or austenitic stainless steels, but if the Cr content is less than 10□%, there is a problem in terms of corrosion resistance. A stainless steel with a Cr content of 10 to 30% by weight is required for the purpose of the present invention, since steel with a Cr content of 10 to 30% by weight is expensive and cannot be used as an economical member.

For JIS standard stainless steel containing 10% or more of chromium, there is no significant difference in the surface pressure at which galling occurs, but when shot blasting is applied to this,
As is clear from the examples below, the galling resistance is surprisingly improved. The higher the degree of shot blasting and the greater the surface roughness, the higher the critical surface pressure for galling. Regarding the degree of surface roughness,
The maximum surface roughness (Rmax) is preferably 2μ or more, preferably 3μ or more. Even if a surface with such surface roughness is formed by focusing only on this surface roughness, for example, by paper polishing, the critical surface pressure for galling can be improved to some extent, but it will not be improved as much as in the present invention. By shot blasting according to the present invention, the surface roughness can be reduced by 2
If the value is more than μ, preferably more than 3 μ, the surface should be made as rough as possible by paper polishing (for example, Rmax'-
．． A galling critical surface pressure higher than the maximum galling critical surface pressure that can be achieved (as 20μ) can be obtained. On the other hand, no matter how much the hardness is increased by cold rolling treatment or quenching and tempering treatment, the critical surface pressure for galling does not increase, and the galling resistance is not affected. Therefore, the method of the present invention is clearly different from shot blasting, which merely performs surface hardening treatment, in its purpose and effect. When carrying out the method of the present invention, the dimensional changes caused by shot blasting and the required surface roughness are taken into consideration in advance (this can be determined easily by performing it several times), and the processing conditions are set to achieve the desired amount of corrosion resistance and surface roughness. Gender can be assigned at will.

Needless to say, this shot blasting process is extremely easy to work with and has a low manufacturing cost compared to the conventional overlay method, which consists of overlay work and surface finishing work. Durability of overlay metal. Corrosion is not a problem, the inherent corrosion resistance of stainless steel is maintained, and a mechanical member of a desired shape with excellent corrosion resistance and galling resistance can be easily obtained. In addition, since the surface imparted with galling resistance according to the method of the present invention is usually used for mechanical elements in places where contact and sliding occur, the surface roughness is defined as the maximum surface roughness (Rma phantom greater than 20μ). This deteriorates the sealing performance, etc. Therefore, the surface roughness of the surface to be treated when implementing the present invention is the maximum surface roughness (Rmax).
It is preferable that the thickness is in the range of 2 to 20μ. The method of the present invention will be specifically explained below using Examples.

[Conditions for shot blasting treatment]

Shot pressure of 0.5 to 5 kg/ for each sample material.
Cm'' was varied in the range of sample numbers 1 to 4 shown in Table 1 to prepare test pieces.

At that time, shot blasting agent is glass beads (250
~500μ), the distance from the spray nozzle to the sample surface was maintained at 75 mm, and the spray was for 3 seconds over 10 m2. [Observation of surface condition after shot blasting]
The maximum surface roughness of each treated material after the above treatment was measured. As shown in Table 1, this is 1.5μ to 13.0μ
It was within the range of [Creation of comparative material] In order to make the surface roughness of the comparative material without shot blasting the same as that of the shot blasted specimen, first, we calculated the surface roughness of the shot blasted material.
As shown in Table 1, the corresponding paper polishing number was determined, and the surface of the comparison material was polished using this paper abrasive paper to prepare comparative materials having the same surface roughness as each treated material.

[Conditions for galling resistance test]

The shot-blasted material or comparison material prepared under the above conditions was used as the test material, and the same or different type of steel was used as the counterpart material, and the critical surface pressure for galling was investigated in a dry state without lubrication at a sliding speed of 1 to 10 mm/Sec. .

[Results of galling resistance test] (1) Regarding martensitic stainless steel.

For SUS4O3 steel having a martensitic structure of 1 to 1, a shot blasted product and a paper polished product (comparison material) were prepared as test materials as described above, and the same <4 as the counterpart material.
Figure 1 summarizes the results of examining galling resistance using 03 steel. In Fig. 1, the solid line A is for the SUS4O3 Shot Plus 1 product with hardness around HB32O after Shot Plus 1, and the broken line B is for the SUS4O3 paper polished product (comparative material) of HB32O that has been quenched and tempered. The galling generation limit surface pressure for each is shown.

However, the mating material is SUS4O3 without Shot Plus 1, which is a quenched and tempered material (HB26O). From the results shown in Figure 1, the SUS4O3 shot-blasted product according to the method of the present invention has a significantly higher galling generation limit surface pressure than the comparative product that is not subjected to this process, even if the surface hardness and surface roughness of the two are the same. This tendency increases as the surface roughness increases, and it is clear that the galling resistance has been greatly improved.

Incidentally, photographs of one example of the test results are shown in FIGS. 4 and 5.

FIG. 4 is a photograph of the surface appearance of a comparative paper-ground product (grinded product No. 500) of quenched and tempered SUS4O3 material (HB32O) after being tested at a surface pressure of 100 kg/cm2. Figure 5 shows a shot-blasted product made of SUS4O3 (test number 2 - see Table 1) with a surface pressure of 300kg/Cm2.
This is a photograph of the surface appearance after testing. Figures 4 and 5
As is clear from the figure, the galling resistance is greatly improved when the present invention is used. (2) Regarding ferritic stainless steel.

We created test materials of shot-blasted SUS43O with ferrite structure and paper-ground product (comparison material), and used SUS4O3 (with martensitic structure) as the counterpart material.
Figure 2 summarizes the results of examining galling resistance using HB3lO). In FIG. 2, the solid line A represents the shot-plast product, and the broken line B represents the paper-abrasive product (comparative material).

It is clear from the results shown in FIG. 2 that similarly to FIG. 1, when the present invention is followed, the critical surface pressure for galling becomes very high, and the galling resistance is significantly improved.

(3) Regarding austenitic stainless steel.

SUS3Q4 test materials with an austenitic structure were shot blasted and paper polished (comparison material), and the other material was SUS4O with a martensitic structure.
Fig. 3 summarizes the results of examining galling resistance using HB31O. In Fig. 3, the solid line A shows the shot blasted product, the broken line B shows the paper polished product (comparative material), and the dashed line C shows the surface hardened (H.32O) by cold working to the same hardness as the shot blasted product. This is a comparison material that was later sanded with paper.

From the results shown in FIG. 3, it is clear that when the present invention is followed, the critical surface pressure for galling is extremely high, and the galling resistance is significantly improved.

Moreover, the galling resistance was not improved by the surface hardening treatment by cold rolling as in the present invention, indicating that simply increasing the surface hardness does not effectively improve the galling resistance. In addition to the above examples, we investigated the galling resistance of stainless steels in other combinations, and confirmed that the galling resistance was greatly improved by shot blasting as shown in the above examples. No significant differences were observed.

[Brief explanation of drawings]

Figures 1 to 3 are relationship diagrams between shot pressure or surface roughness and galling generation limit pressure. Figure 1 is for martensitic stainless steel, Figure 2 is for ferritic stainless steel, and Figure 3 is for austenitic stainless steel. This is a diagram plotting the results of an investigation on stainless steel, where the solid line A is the shot-blasted material of the present invention, the broken line B is the comparative material that was paper-polished to have the same surface roughness as the shot-blasted product, and one point. The chain line C indicates a comparative material which was work-hardened by cold rolling and then subjected to paper polishing. Figures 4 and 5 are metal cross-sectional views of stainless steel ('SUS3O4 steel), respectively. Figure 4 shows the resistance when the method of the present invention is not applied, and Figure 5 shows the resistance when the method of the present invention is applied. The state after the stiffness test is shown.

Claims (1)

[Claims] 1. A method of imparting galling resistance to stainless steel containing 10 to 30% by weight of chromium, characterized by subjecting the surface of the stainless steel to a maximum roughness of 2 to 20μ by subjecting the surface to shot blasting. .