JPS5931850A - Soft-nitrided low-alloy steel - Google Patents

Abstract

PURPOSE:To obtain the titled steel having a large extent of bending deflection and causing hardly cracking during strain relieving by soft-nitriding a low alloy steel contg. specified amounts of C, Al and Cr while restricting the relation between the N content of a surface compound layer and the treatment temp. to regulate the surface hardness to a specified value or below. CONSTITUTION:A low alloy steel contg., by weight, <=0.5% C, Al and Cr satisfying Al(%)+0.1XCr(%)<=0.2% is soft-nitrided under conditions represented by the equation [where N is the N content (%) of a surface compound layer, and T is the treatment temp. ( deg.C)] to regulate the surface hardness Hv to <=700. The steel has a large extent of bending deflection after the soft nitriding and causes hardly cracking during strain relieving. It has superior relievability.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a low-alloy nitrocarburized steel with excellent straightening properties.

Traditionally, in office equipment and automobiles, a large number of parts have been used that are made of mild steel or case-hardened steel and have been carburized to improve wear resistance and fatigue strength. There are disadvantages such as 1) high defect rate due to distortion generated during carburizing and quenching, and (2) depending on the part, correction is required for all parts to remove distortion, which tends to increase costs. .

On the other hand, in contrast to such carburizing and quenching, which causes large heat treatment distortions, there are heat treatments with small heat treatment distortions, such as surface hardening treatment and soft nitriding treatment, which are surface hardening treatments below the A□ transformation point. This evaporation treatment and nitrocarburizing treatment are methods in which the material to be treated is placed in NH3 gas and heated to increase the hardness of the tuber surface by infiltrating the throat with nitrogen, but the surface hardness is approximately 1-IV) 750 Because of this, the bending deflection meter for parts after nitriding or soft-nitriding is small, and the 9i'? +, 'l[E] It had the disadvantage that cracks may occur when it is applied.

This invention was made in order to eliminate the above-mentioned (7) conventional drawbacks, and it has a large bending deflection (J) after soft nitriding treatment, is difficult to crack when straightening distortion, and has excellent straightening properties. /ζ Our primary focus is to provide low-alloy soft softening steel.

The low alloy soft nitrided steel according to the present invention is C, At.

Cr content is also 1, c < 0.5 weight, i%, At(,i
ft%) 10, IX Or (heavy'n'r%)
<0.2'fFc kalp%, (-(7) (lh, table during soft nitriding treatment depending on necessity) n1 In order to control the hardness, Ti, V, Nb, Ta, Z
One or more types of r, Si, Mn to strengthen the strength of the base.

At least one or more of CIl, Mo, W, Co, S, I'b,
For low alloy steel containing 1fIIi or two or more of Te and Se, (740-16,3N)/T>
It is characterized by a surface hardness of Hv (700) by performing soft nitriding treatment under the conditions of 1.0 (N: nitrogen of the surface compound layer M, (wt%), T: treatment temperature (°C)). In addition, the low-alloy soft nitrided steel referred to in Specification 4 includes not only the use as a material for parts but also the parts and products themselves.In this case, the low-alloy soft nitrided steel with the above components is formed into a predetermined part or product shape (e.g., roll, shaft, crankshaft, bottle, leaf spring, etc.) by forging, cutting, punching, etc., and then injected with liquid, gas, or a combination of both. The surface hardness is set to Hv (700) by chemical treatment, and then straightening is performed to achieve high dimensional accuracy.

Next, the reason for limiting the composition of the low alloy soft nitrided steel of the present invention will be explained.

C: C is an element necessary to increase the toughness of the steel, but if it is too much, it will actually reduce the toughness and also deteriorate the workability, so it should be kept at 0.5 wt-A% or less, especially For applications involving press working or cold forging, it is desirable that the thickness be 0.25 M or less.

At, Cr: At and Cr form nitrides through soft nitriding treatment to increase surface hardness, but if the content is too large, the surface hardness due to the nitrides becomes too high, and the surface hardness nv≦700.
is no longer obtained, and there is a risk that cracks will occur in the compound layer during straightening after soft-nitriding treatment. Therefore, At
and Crt is At(M, M'%) + 0. IX
In relation to Cr (mtbo%), the debt shall be 0.2 or less.

Ti, V, Nb, Ta, Zr: Ti
, V, Nb, Ta, and Zr are elements that are effective in shortening the soft-nitriding treatment time required to obtain the desired surface hardness, but even if they are added in a large amount of J/l, the above effects cannot be achieved. It is preferable to add one or more of these to the extent that no increase in toughness is obtained, but rather a decrease in toughness.

Si, Mn, Cu'tMo, W,
CO; Si, Mn, Cu, Mo, W,
Co is an element that contributes to improving the strength of steel before treatment and also to improving the core strength after soft-nitriding treatment, but even if it is added in large amounts, no increase in effect can be expected; It will be uneconomical, so when adding it, sl≦1.5
Heavy weight, M, n≦1.5 weight! I: CH, Cu≦1.5 weight tt%, MO≦1.5 heavy electric current, WS2.5 weight (%,
It is preferable to add one or two of these in the range of co≦1.5 weight.

S, Pb, Te, Se: S, Pb
, Te, and Se are effective elements for improving the machinability of steel, but when added to In-rich alloys, they impair hot workability and deteriorate strength and toughness. S (0,155 weight, Pb + Te≦0.
1 of these in the range of 4% by weight, se≦0.3 weight 10 knees
It is good to add a species or two or more species.

Table 114r hardening treatment for Sakai alloy steel with such composition was limited to soft nitriding treatment because carburizing and carbonitriding treatments generate large distortions and it is difficult to improve dimensional accuracy by straightening. This is because the nitriding process has disadvantages such as a decrease in productivity, and in the nitriding process, a brittle phase is formed in the outermost layer, so it is necessary to remove the brittle phase after the nitriding process). This is because it has drawbacks such as the risk of cracks occurring at the 9B hour after treatment.

On the other hand, if the surface hardness is 1v (700 or 1) and the surface hardness is 1v (700), although there is a slight decrease in strength due to the decrease in surface hardness, the straightening properties can be significantly improved and the dimensional accuracy can be improved. One part or product can be obtained from high-alloy, low-alloy soft-nitrided steel.

Surface hardness I(v (
700, the soft nitriding treatment is performed using liquid, gas, or a combination of these, and the surface hardness is
IV (700), but at this time, in the relationship between the treatment temperature T (1::) and the nitrogen thread of the surface compound layer, 740-16.3 N 1 ≧1.0. This can be achieved by setting the nitrocarburizing treatment conditions as follows.This can be achieved by setting the nitrocarburizing treatment conditions as follows:
This is because if the surface Lm hardness after nitrocarburizing treatment is too high, the amount of bending deflection will be small and there is a risk of cracking during straightening.

Example 1 Steel having the chemical composition shown in Table 1 was melted, then formed into an ingot, rolled and cut to a thickness of 5 mm, width of 10 mm,
A rectangular bar-shaped test piece with a length of 150 mm was prepared, and the test piece was subjected to nitrocarburizing treatment under various conditions.

Next, the surface of each test piece after the nitrocarburizing treatment was subjected to puff polishing, and then the surface hardness was measured using a Vickers hardness meter (Kakuzume 5002). Span 1 for the customer test piece
A bending test was conducted under the conditions of 00 rm+ and a pusher tip radius of 10 degrees, and the bending flexure seam at the time of occurrence of a coarse crack was measured. These results are also shown in Table 1.

As is clear from the results shown in the first disaster, At+0・1×
Boiled 3, JFy, 6 with a Cr content of more than 0.2% by weight
.

All of the melons 9 have surface hardness that is too high, so the bending angle +X is small and the straightening properties are poor.

Example 2) A rectangular rod-shaped test piece made from steel with the chemical composition shown in Table 41 as yfa 2 K was treated so that the value given by (740-16,3N)/T became the value shown in Table 2. The temperature and NH3 mixing ratio were determined, and the soft nitriding treatment was performed for a treatment time of 3 hours. Next, in the same manner as in Example 1, the surface hardness and bending deflection of the test piece after soft nitriding were measured in m.
11, the results are also shown in Table 2.

As shown in Table 2, as the value of (740-16,3N)/T increases, the surface hardness decreases, the amount of bending deflection when large cracks occur during the bending test increases, and the straightening property gradually decreases. It was confirmed that there was an improvement. However, as the surface hardness decreases, the wear resistance and fatigue strength of the surface tend to deteriorate, so it is necessary to take these into consideration. It has become clear that it is more desirable to perform the soft nitriding treatment by setting heat treatment conditions such that the value of 16,3N)/T is 1 or more.

As explained above, according to the present invention, the dimensional accuracy is high due to the excellent straightening properties after surface hardening treatment, and the yield rate can be improved because cracks are less likely to occur during straightening. Low-alloy soft nitride steel material with good wear resistance and fatigue strength.

It has a very good effect of being able to obtain parts or products.

Claims (1)

[Claims] ('') Cv htF Cr-containing mechanism C 0.5t
i%, At(heavy:!l:%)+0. IXCr (weight 5J
)<0-2% by weight, the low-alloy soft-nitrided steel is subjected to soft-nitriding treatment under the following conditions''!, and the surface hardness is 1-h 700 or less.However, N :Nitrogen in the surface compound layer!E (heavy screen) T:Treatment temperature (℃)
．． 85 double layer, Nb + Ta < 0.2 layer, Zr
Low alloy soft nitriding steel according to claim (1) containing one or more types of (0.2 weight head).
2) The low alloy soft nitrided steel described in section 2). (4) Low alloy steel has S < 0.15 wt%, Pb +
Te<0.4 side! t5%, Se <0.3 MUk
Claim No. 1 containing one or more types of %(
The low-alloy nitrocarburized steel described in item 1), item (2), or item (3).