JPS619555A - Rapid soft-nitriding steel - Google Patents

Abstract

PURPOSE:To manufacture a rapid soft-nitriding steel which can be soft-nitrided in a short time by adding specified amounts of C, Si, Mn, Cr, V and Al to the steel. CONSTITUTION:The composition of the rapid soft-nitriding steel is composed of, by weight, 0.5-0.7% C, <0.5% Si, <1.5% Mn, 0.5-2% Cr, <0.2% V, 0.05-0.3% Al and the balance Fe with inevitable impurities. When the steel is soft-nitrided at such a relatively low temp. as 570-600 deg.C in a short time, it is hardened to a depth equal to the depth of hardening obtd. by carburization and equal to or larger than the depth of hardening obtd. by nitriding.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a steel for rapid nitrocarburizing that can be nitrocarburized in a short period of time.

Conventional technology Automobiles, construction machinery, etc. have many parts that slide at high surface pressures and high speeds, and damage due to pitting and wear is a problem.In particular, gears and other gears are hardened by carburizing and quenching or nitriding. There is.

Problems to be Solved by the Invention In the carburizing and quenching method, large quenching distortions occur, resulting in a high defect rate, and there are also many damages due to deterioration of gear accuracy.

On the other hand, in drilling, it is necessary to obtain a predetermined hardness and hardening depth [5
It requires more than 0 hours, and there is a problem with productivity.

Means and operations for solving the problems The present invention was conceived in view of the above, and includes 570
The present invention relates to a steel for rapid nitrocarburizing which is capable of obtaining hardness and hardness equal to or greater than carburizing or nitriding through nitrocarburizing treatment performed at ~600° C. for a short time, and which is inexpensive.

That is, the steel for rapid nitrocarburizing according to the present invention has, in weight% (the same applies hereinafter), C: α50 to 0.70%, other = 0.5% or less,
Mn+ 1.5% or less, Cr+ 0.5-20%, V
+0.2b or less, /it: α05-0.30-1 This is a steel for rapid soft nitriding, with the balance being Fe.

Next, the reason why each element is limited as described above will be explained.

As the content of CIC increases, the surface hardness and base hardness increase, but even if the normalized structure exceeds 0.7, toughness and rigidity will be lost. To ensure pressure resistance, it should be 0.4'4 or more. Also, set C to 0
．． When the content is 5 to 0.6%, the surface hardening function due to At is emphasized, and even if the amount of addition is 0.2% or less, the effect is sufficient and does not impair the cleanliness of the steel.Si, Mn: At the time of scouring It is included for the purpose of deoxidizing and adjusting the strength level of the substrate, but if Si exceeds 0.5 mm or M 1.5 mm, it is not preferable because it impairs rigidity.

Cr: The amount of Cr that ensures a surface hardness of HRC60 in carburizing and quenching is α5% or more, and since the hardening depth becomes shallow rapidly above 20 millimeters, the amount of Cγ added was limited to 0.5 to zO−.

Although J4t=At is an extremely effective element for improving surface hardness, it is well known that it lowers the cleanliness of steel, for example, reduces fatigue life and worsens TFC stiffness. Therefore, in the steel of the present invention, the surface hardening function of the steel is increased by increasing the C content, and the upper limit of the amount of 2a added is suppressed to 0.3- or less.

V:r is an element with the same surface hardening function as At, but since it is a very expensive element, it is used to make the austenite crystal grains finer during normalization and to adjust the strength level of the base material. Additions were limited to 2- or less.

Example Figure 1 shows the hardness of the nitrocarburized surface at a position 50μ below the surface.
" and 7a were investigated, and the basic composition was Cr:
0.99-1.06%5,5i:0.20-0.49
'4, Mn: 0.7 l-1,06%, r: 00
μ is 0.10% for 8-0.11%, 0.05%
, 0.02% of three foods, and the surface hardness [Hv] of these with respect to changes in C content was investigated.

Figure 2 shows a comparison of roller pitting life. The asterisks in the figure indicate SNCM 420H carburized, 3
The square mark indicates carburized 5Cr420H, and the circle mark indicates nitrocarburized steel according to the present invention.The surface pressure during the test was 250 K sea.

As is clear from FIGS. 1 and 2 above, the surface hardness of At is increased by setting C higher. Furthermore, it can be seen that the steel of the present invention has a roller pitting life equal to or longer than that of the conventional steel. Furthermore, if the hardening depth is increased to approximately α5W1 or more, it is estimated that the surface pressure resistance is greater than that of carburized and quenched products.

Figure 3 shows the effect of C on the soft-nitrided surface hardness at a position 50μ below the surface.
This study investigated the influence of r, and the basic composition is C: O, + 8
~0.20%, Si: 0.38~0.49%, Mn:
0.7 l ~O-83%, AlFo, 05%, i:o
,l.

The surface hardness (Hv) increases as the Cr content increases with respect to
becomes higher.

Figure 4 shows oil at 570℃ x 4A? fi (0, Q+ heat treatment [hardness distribution and SCM 435 of two examples of the invention steel
This is a comparison of the hardness distribution of SCM 435.
It can be seen that the steel of the present invention is superior in both surface hardness and hardening depth.

Effects of the Invention According to the present invention, it is possible to obtain an inexpensive steel for quick nitriding that achieves a hardening depth equivalent to that of carburizing and equal to or greater than that of nitriding through soft nitriding treatment performed in a short time at a relatively low temperature of 570 to 600°C. Can be done.

[Brief explanation of drawings]

Figure 1 is a diagram showing the influence of C and flooding on soft-nitrided surface hardness, Figure 2 is a diagram showing the roller pitting life, and Figure 3 is a diagram showing the influence of C″r on soft-nitrided surface hardness. FIG. 4 is a diagram showing the hardness distribution after nitrocarburizing.

Claims (1)

[Claims] C: 0.50-0.70%, Si: 0.5% or less, Mn
: 1.5% or less, Cr: 0.5-2.0%, V: 0.2
% or less, Al: 0.05 to 0.30%, and the balance is Fe.