JPS5938301B2 - Nitriding steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a steel for nitriding treatment which prevents the occurrence of swelling and peeling of the surface layer through nitriding treatment.

The surface hardening treatment hardens the surface of the mechanical member and thus improves the properties of the treated layer. Among these, nitriding treatment performed at 500 to 600° C. diffuses nitrogen into the surface layer of the material, but depending on the steel type, the surface layer where nitrogen has diffused can be significantly hardened. Therefore, when imparting wear resistance to the friction contact parts of mechanical parts of equipment, nitriding treatment has conventionally been carried out as one method. However, although the normal nitriding treatment yields satisfactory results in terms of post-treatment properties, i.e., the hardness and depth of the nitrided layer, dots on the surface of the nitrided layer (diameter 0.2~2.0m
m) Or the peeling phenomenon in which the bulge part peels off is often observed, and when parts in which these phenomena occur are applied to mechanical parts of equipment, the function will be significantly degraded Especially in martensitic stainless steel (JIS, SUS403), The frequency of these occurrences is remarkable. An object of the present invention is to provide a steel for nitriding that eliminates the swelling and peeling phenomena that occur on the surface of the nitrided layer during nitriding, thereby producing a good nitrided product.

The characteristics of the present invention are by weight: Co, 15% or less, Si0.5
0% or less, Mn1, 00% or less, Po, 040% or less,
50.030% or less, Cr11.50-13.00%,
Martensitic stainless steel consisting of 1.5% to 2.0% Ni and the balance Fe, with a crystal grain size of 4 to 10 according to the JIS standard grain size number to prevent swelling and peeling of the nitrided layer. It is. That is, the feature of the present invention is that the grain size number of martensitic stainless steel is 4 to 10.
and the amount of δ ferrite is 3% or less,
Furthermore, martensitic stainless steel has a weight of 1.5
~2.0% Ni is contained, and the grain size number is 4.
-10, it is possible to further prevent swelling and peeling of the nitride layer.

When the grain size number is 4 or less, swelling and peeling phenomena occur,
Further, if the grain size is less than 10, even if the crystal grain size is made finer than this, the effect is poor. In addition, in order to investigate the effects of additive elements in steel, we varied Ni and grain size based on the composition of 13Cr stainless steel (SUS403), and conducted experiments to determine the relationship between the occurrence of swelling and peeling phenomena.
JIS standard) Nil. in the range of waterfalls 4 to 10. 5-2
．． By adding 0%, we were able to develop a product that does not cause the above phenomenon.
The reason for setting the amount of Ni to 464-10 is thought to be largely due to the synergistic effect with Ni on the above-mentioned phenomenon. The reason for setting the amount of Ni to 1.5-2.0% is due to the relationship with the crystal grain size. If the crystal grain size is less than 1.501% in the range of 4 to 10, swelling and peeling phenomena will occur. This is because there is no greater effect than that.〇Example Using commercially available 13Cr stainless steel SUS4O3, the treatment conditions shown in Table 1, namely treatment temperature, change in ammonia gas decomposition degree, and change in the nitrided layer surface generated by nitriding treatment, were used. Figure 0 shows the relationship between swelling and peeling phenomena, and commercially available 13Cr
Using stainless steel SUS4O3, this figure shows the relationship between swelling, the crystal grain size of the material, and the amount of δ ferrite.
In the figure, 0 indicates no swelling, 1 indicates patchy, and 2 indicates the occurrence of swelling.
is minute, 3 is small, and 4 is large.0 From these results, it can be seen that the above-mentioned phenomena do not occur in the absence of δ ferrite at a crystal grain size of 4 or more.0(a) Table 2 shows the chemical composition (% by weight) of the samples used.

Table 3 shows the relationships between crystal grain size, Nl content, and the occurrence of swelling and peeling phenomena using SUS4O3 as a base and varying the amount of Ni added. The nitriding treatment in this case was performed according to Table 1.

According to this, it can be seen that when the crystal grain size is as coarse as 1 to 3 regardless of the presence or absence of Ni addition, swelling or peeling phenomenon occurs. However, when the crystal grain size becomes finer than Taki 4, the degree of swelling or peeling changes depending on the amount of Ni added. That is, the Ni-free waterfall 3 shows the degree of occurrence of a small group with respect to the five-stage evaluation standard classified as the degree of occurrence of swelling and peeling phenomena. Even if Ni is added at 0.35% (Sample Taki 5), there is almost no effect, and the same swelling and peeling phenomena occur as when no Ni is added.When Ni is added at 1%, these phenomena are minimal. However, it can be seen that it does not disappear completely.0 but 1.5
% or more (6, 7, 8, and 2), when the grain size is 4 or more, the occurrence of swelling and peeling phenomena completely disappears, and a good nitrided layer surface is exhibited. The effect of the amount of Ni on preventing the occurrence of is 1.
5! ) or more, it can be seen that it is sufficient if the sample contains 0 or more.
In Nl2. It can be seen that swelling and peeling do not occur at all with the addition of O%.0 Also, the reason why MO was added in Taki 2 is to nitride SUS4O3 and to prevent swelling and peeling phenomena on the surface of the nitrided layer. This is to prevent the high-temperature creep strength from decreasing when MO is added.If the content is 0.15% or more, the effect is great for preventing the creep strength from decreasing when MO is added. (approximately 0.2 to 2.0 φ) When a material that has swelled and peeled off is applied to a friction contact portion, it causes abnormal wear. However, the present invention prevents the swelling and peeling of the nitride layer and solves the problem of abnormal wear, resulting in an excellent effect on extending the life of equipment subject to wear.

[Brief explanation of drawings]

The figure is a diagram showing the relationship between the grain size number and the occurrence of swelling.

Claims (1)

[Claims] 1 By weight, C0.15% or less, Si0.50% or less,
Mn 1.00% or less, P 0.040% or less, S0.03
0% or less, Cr11.50-13.00%, Ni1.5
A steel for nitriding, characterized in that the size of crystal grains of the steel is 4 to 10 according to the JIS standard grain size number.