JPS6362859A - Machine structural member for high surface pressure - Google Patents

Abstract

PURPOSE:To produce a machine structural member for high surface pressure having excellent pitting resistance and long life by subjecting a steel stock contg. specific ratios of C, Si, Mn,Cr, and Mo to a carbo-nitriding treatment and specifying the sum of the concns. of C and N down to the specific thickness from the surface. CONSTITUTION:The steel stock contg., by weight %, 0.10-0.30% C, <=1.50% Si, <=0.60% Mn, 0.52-2.50% Cr, and 0.30-1.0% Mo and consisting of the balance Fe and impurities is prepd. The steel stock is subjected to the carbo- nitriding treatment so that the sum of the concn. of C and N down to 0.1mm depth from the surface attains 0.70-1.30wt%. The content of Si+Cr is more preferably adjusted to 1.50-3.0wt%. The steel products which are useful as the machine structural members such as gears, shafts and sliding members which are subjected to high surface pressure are thereby obtd.

Description

[Detailed Description of the Invention] [Purpose of the Invention (Industrial Application Field) The present invention is directed to high surfaces that are used for transfer or sliding under high surface pressure, such as gears, shafts, and sliding members. It relates to pressure mechanical structural members (including parts and materials).

(Prior Art) Taking a gear, which is a typical example of a mechanical structural member, as an example, its lifespan factors are broadly classified into fatigue and impact fracture from the tooth base, and tooth surface damage.

Among the various gears, the Hertzian stress is 200 kgf.
For high surface pressure gears or high speed rotating gears where the pressure exceeds ./mm2, fatigue strength of the tooth surfaces, that is, pitting resistance, is particularly required.

Pitting occurs when slippage occurs on the surface of gears, that is, when there is a difference in circumferential speed between the tooth surfaces of meshing gears, maximum shear stress is generated on the surface, and pitting occurs due to the fatigue phenomenon during rolling. This term refers to defects that appear as defects in In general, the higher the 5-face pressure, the greater the shear stress, and therefore the shorter the pitting life.

By the way, surface hardening treatment has been conventionally applied to mechanical structural members for high surface pressure, and gas carburizing treatment is the main one among various surface hardening treatments.

However, as mentioned above, when the usage conditions are severe, such as when Hertzian stress is large, the normal gas carburizing treatment is often insufficient, and therefore new surface hardening treatments are being developed. There is.

One of these new surface hardening treatments is carbonitriding and carbonitriding, which aim to make effective use of retained austenite by infiltrating the steel surface with a combination of C and N to make a large amount of retained austenite appear. be.

In such surface hardening treatment, several tens of percent of retained austenite remains on the surface, and the surface pressure strength is increased by utilizing work hardening and martensitization during transfer.

(Problems to be Solved by the Invention) However, in the above-mentioned surface hardening treatment that intentionally causes retained austenite to appear, the retained austenite may not necessarily act effectively depending on the usage conditions, and the appropriate amount of retained austenite and There is a problem in that the actual situation is that the steel suitable for carbonitriding has not yet been fully investigated.

Furthermore, the present inventors noticed the following new phenomenon in the process of developing mechanical structural members for high surface pressure. In other words, with conventional materials, especially when applied to parts used under high-speed rotation, when the surface temperature rises to about 150 to 200 degrees Celsius during use, the surface softens, resulting in increased surface pressure strength and #pitting resistance. ) has been found to be problematic in that the phenomenon of a decrease in

(Object of the Invention) The present invention has been made by focusing on the above-mentioned conventional problems, and is suitable for carbonitriding and carbonitriding, and is suitable for carbonitriding and carbonitriding, and is suitable for reducing the amount of residue remaining on the surface after carbonitriding or carbonitriding. Using steel that can obtain austenite content,
It is an object of the present invention to provide a mechanical structural member for high contact pressure, which has an excellent property of high softening resistance at low temperatures, particularly at 200° C. or lower, has excellent pitting resistance, and has a long life.

[Structure of the Invention] The mechanical structural member for high surface pressure (including parts and materials) according to the present invention has, in weight%, C: 0.10 to 0.30%, Si
: 1.50% or less, Mn: 0.60% or less, Cr: 0.
50 to 2.50%, Mo: 0.30 to 1.0%,
Furthermore, if necessary, AfL: 0.1% or less, N: 0.
03% or less, Tf: 0.5% or less, V: 0.5% or less.

The material is steel containing one or more of Nb: 0.5% or less, Ta: 0.5% or less, and the balance is Fe and impurities, and C from the surface to a depth of 0.1 mm. The # symbol indicates that the carbonitriding treatment or carbonitriding treatment is performed in which the sum of the N concentration is 0.70 to 1.30% by weight, and more preferably, the amount of Si + Cr is 1.50% by weight.
~3.0% by weight.

The mechanical structural member for high surface pressure according to the present invention has the above-mentioned specific composition and is subjected to carbonitriding treatment or carbonitriding treatment.
＝'Reason (%L しょうぎんか）L I'll explain in two parts.

C: 0. 1O ~ 0.30% C is an effective element for ensuring the core strength required for mechanical structural members such as gears, shaft necks, and sliding members, and in order to obtain this effect, 0.10% % or more.

However, if it is too large, the strength of the core increases but the toughness of the 6th part deteriorates, so it is set at 0.30% or less.

Si: 1.50% or less St acts as a deoxidizing agent during melting and also remains as an impurity in the steel, but it can be actively added especially when it is necessary to increase the softening resistance. However, if the content is too large, the forgeability and machinability will deteriorate, so even if it is actively added, the content needs to be 1.50% or less.

Mn: 0.60% or less Mn acts as a deoxidizing agent and desulfurizing agent during melting, and also remains as an impurity in steel, but it is actively used as an element to improve hardenability, especially when it is necessary to improve hardenability. Can be added. However, depending on the balance with the amounts of Cr and Mo, the amount added to ensure hardenability is 0.
Since up to 60% is sufficient, the upper limit was set at 0.60%.

Cr: 0.50-2.50% Cr contributes to improving hardenability, especially at 200℃
It is an element that contributes to increasing the softening resistance at low temperatures and improving the pitting resistance, and in order to obtain this effect, the content is set to 0.50% or more. However, 2.
Even if it is added in an amount exceeding 50%, the effect of improving pitting resistance is saturated and the machinability is deteriorated, so it is set at 2.50% or less.

Mo: 0.30 N1.0% Mo is an element that contributes to improving pitting resistance, and in order to obtain such an effect, it was contained in an amount of 0.30% or more.

However, even if added in excess of 1.0%, the effect of improving pitting resistance is saturated, and since it is an expensive element,
% or less.

Al: 0.1% or less, N: 0.03% or less.

Ti: 0.5% or less, V: 0.5% or less, Nb: 0.5
% or less, Ta: 0.5% or less An, N, Ti, V, Nb, and Ta all form fine carbonitrides during carbonitriding and carbonitriding. Since it is an effective element for contributing to grain refinement during processing and increasing the toughness of mechanical structural members, it is also a good idea to add one or more of these as necessary. During nitriding treatment and carbonitriding treatment, austenite crystal grains may become coarser, so in such cases, by adding one or more of these in advance, the crystal grains can be made finer. However, if the amount added is too large, the above effect will be saturated and the mechanical properties may deteriorate, so even if AM is added, the amount of AM should be 0.1 % or less, for N 0.03% or less,
I"i, V.

Nb and Ta must each be 0.5% or less.Si+
Cr: 1.50-3.0% As mentioned above, Sf and Cr are effective elements for increasing softening resistance at low temperatures, especially below 200°C, and improving pitting resistance, but Si, In order to obtain this effect of Cr even more effectively, it is necessary to combine SL and Cr.
It is more desirable to maintain a balance with S.
It is desirable that the amount of i+Cr is in the range of 1.50 to 3.0%.

The mechanical structural member for high surface pressure according to the present invention is made of steel having the above-mentioned composition, and is made of steel with a depth of 0.1 mm from the surface.
The sum of C and N concentrations up to 0.70 to 1.30% by weight
The carbonitriding treatment or carbonitriding treatment has been performed. The reason for this is that in order to form an appropriate amount of retained austenite through carbonitriding or carbonitriding and to effectively utilize this retained austenite to increase blood pressure strength, C+N must be at least 0.70%. Depends on something. The amount of retained austenite in this case is about 20%. However, if the amount of C+N is increased more than necessary, the amount of retained austenite will also be too large, and C+
When Ni exceeds 1.30%, the amount of retained austenite exceeds approximately 60%, which softens significantly and causes parts (components and materials) to wear out before work hardening during transfer. It is necessary to perform carbonitriding or carbonitriding so that the amount is 1.30% or less.

(Example) Steel with the chemical composition shown in Table 1 (class 4 A-J is steel of the present invention example, steel type is steel equivalent to JISSCM418 of comparative example)
After melting, it is made into ingots and hot rolled to a diameter of 30 mm.
Next, after normalizing each of the above-mentioned materials.

A roller peeling test piece 1 shown in FIG. 1 was prepared. This roller pitching test piece 1 has a central large diameter portion 1
The diameter D1 of a is 28 mm, the length Ll is 28 mm,
The diameter D2 + 03 of the small diameter portions 1b and lc on both sides is 21m
m,! SaL2. L3 has a dimension of 51 mm. Then, each roller pitting test piece 1 was subjected to carbo-nitriding treatment to be described later, and then a roller pitting test was conducted.

Here, the principle of the roller pitting test is shown in Figure 2, namely, roller pitting test piece 1 (small roller; material is steel type A to K in Table 1) and counterpart material 2 (large roller; material is equivalent to JISSCM418) and 300k
The pitting resistance was evaluated by rotating at high speed (rotation speed: 101000 rpm) under a surface pressure of g f / m = n 2 (pressure direction P), and determining the life (rotation speed) until pitching occurs.In addition, in this case The difference in circumferential speed between the roller pitching test piece 1 (small roller) and the mating material 2 (large roller), that is, the slip rate, was -40%.

Then, after conducting tests for each of the five-wood roller pitting test pieces 1 under each condition, Weibull plotting was performed to determine the 50% probability of failure life (Bso life) and evaluate the pitting resistance. The results are shown in Table 2.

Furthermore, the carburizing and nitriding treatment for each roller pitting test piece 1 is carried out while holding each test piece 1 at 880 to 920°C for 80 minutes, and during the process of cooling and holding at 800 to 870°C, NH3 is flowed. Nitrification was carried out by this method. After that, after being put into an oil bath at 40-60℃ and quenched, 1
Tempering was performed at 80° C. for 2 hours. The properties after such surface hardening treatment were as shown in Table 2.

Note that the amount of C+N was determined by collecting chips from the surface of each roller pitting test piece 1 to a depth of 0.1 mm and chemically analyzing them. Moreover, both the hardness and the amount of retained austenite are the results of measurement at a depth of 0.05 mm.

Furthermore, the Charpy impact test piece used to measure the Charpy impact value was equipped with a 2mm deep IOR notch.
After surface hardening treatment was performed only on the notch surface, a Charpy impact test was conducted. The results are shown in Table 2.

Table 1 and! As shown in the s2 table, it is clear that in the case of No. 1 to 1O, which satisfy the steel composition and the amount of C+N on the surface of the present invention, the B5o life is long and the pitting resistance is excellent. In particular, it is clear that pitting resistance is even better in the case of No. 7, 8 and No. 9.10, in which the Si + Cr content is in the range of 1.50 to 3.0%, and V ,Ti,
Nb.

In the case of No. 4, 5, 6 and No. 9.10, which are made of steel containing one or more types of N, the impact value is higher due to the refinement of the crystal grains. That is clear.

On the other hand, although the steel composition is satisfactory, the amount of C+N on the surface after carburizing and nitriding is too small.

In the case of 11.14, since the amount of retained austenite is too small, the effect of converting the retained austenite to martensite cannot be sufficiently obtained, and it is clear that the pitting resistance is not good. On the other hand, in the case of No. 12゜13 where the amount of C+N on the surface is too large, the amount of retained austenite is too large, so the surface hardness is quite low, and the pitting resistance is also good in this case. It is clear that there is no.

Furthermore, it is clear that pitting resistance is also poor in the case of No. 15.16, which is made of steel that does not satisfy the chemical composition specified in the present invention.

[Effects of the Invention] As explained above, the mechanical structural member for high surface pressure according to the present invention has c: 0.10 to 0.30%, S: 0.10% to 0.30%, S
i: 1.50% or less, Mn: 0.60% or less, Cr: 0
．． 50 to 2.50%, Mo: 0.30 to 1.0%, rough A, 0.1% or less, N: 0.03% or less, T
i: 0.5% or less, V: 0.5% or less.

The material is steel containing one or more of Nb: 0.5% or less, Ta: 0.5% or less, and the balance is Fe and impurities, and C from the surface to a depth of 0.1 mm. and carbonitriding treatment or carbonitriding treatment in which the sum of the N concentration is 0.70 to 1.30% by weight, it is suitable for carbonitriding treatment and carbonitriding treatment, and is suitable for carbonitriding treatment Or, since steel materials are used that form an appropriate amount of retained austenite on the surface after carbonitriding, the residual austenite formed after the carbonitriding or carbonitriding can be fully utilized to reduce surface pressure. The strength has been significantly improved, and due to the increased surface pressure strength, the pitting resistance has been significantly improved. In particular, it has high softening resistance at low temperatures below 200°C, so when used under high speed rotation, the surface temperature will drop to 15°C.
It is extremely excellent in that pitting resistance does not deteriorate even when the temperature rises to about 0 to 200°C. Therefore, the mechanical structural member for high surface pressure according to the present invention significantly increases the pitting resistance of mechanical structural members subjected to high surface pressure, such as gears, shaft necks, sliding members, etc., and significantly extends the life of the mechanical structural member. It is possible to bring about a very good effect.

A pA demand n-even amount 1
The figure is an explanatory diagram of the roller pitching test piece used in the examples of the present invention, and FIG. 2 is a diagram explaining the principle of the roller pitting test conducted using the roller pitching test piece of diagram M1.

Claims (4)

[Claims] (1) In weight%, C: 0.10-0.30%, Si: 1
．． 50% or less, Mn: 0.60% or less, Cr: 0.50
~2.50%, Mo: 0.30~1.0%, and the remainder is Fe and impurities, and the sum of C and N concentrations from the surface to a depth of 0.1 mm is 0. .70
A mechanical structural member for high surface pressure, characterized by being subjected to carbo-nitriding treatment or carbonitriding treatment of ~1.30% by weight. (2) A mechanical structural member for high surface pressure according to claim (1), characterized in that the amount of Si+Cr is 1.50 to 3.0%. (3) In weight%, C: 0.10-0.30%, Si: 1
．． 50% or less, Mn: 0.60% or less, Cr: 0.50
~2.50%, Mo: 0.30~1.0%, further Al: 0.1% or less, N: 0.03% or less, Ti: 0
．． 5% or less, V: 0.5% or less, Nb: 0.5% or less,
The material is steel containing one or more of Ta: 0.5% or less, with the balance consisting of Fe and impurities, and the sum of C and N concentrations from the surface to a depth of 0.1 mm is 0.5%.
A mechanical structural member for high surface pressure, characterized by being subjected to a carbonitriding treatment or a carbonitriding treatment of 70 to 1.30% by weight. (4) A mechanical structural member for high surface pressure according to claim (3), characterized in that the amount of Si+Cr is 1.50 to 3.0%.