JP2991943B2 - Tough steel with excellent machinability - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tough steel having excellent machinability. More specifically, the present invention relates to a tough steel having excellent cutting characteristics, which is suitable as a steel material for various pistons used in civil engineering and construction machines, such as a piston incorporated in a hydraulic breaker of a hydraulic shovel.

[0002]

2. Description of the Related Art Various types of pistons used in civil engineering and construction machinery, including the pistons shown in FIG. 1 incorporated in a hydraulic breaker of a hydraulic excavator, violently collide with a chisel or the like, and therefore have a high strength (hardness). And toughness are both required. That is, the piston 1 collides with an extremely hard part such as a chisel to cause a so-called “burr”, which prevents a smooth movement due to the “burr” 2. "Kaeri" 2
Hardness is required to prevent However, if the steel is too hard, the toughness will be low, and there will be a problem that a crack 3 may occur without being able to withstand a severe impact at the time of a collision, so that toughness is required at the same time.

[0003] Conventionally, in order to provide the pistons with both strength (hardness) and toughness, SNC631 steel (JIS G 4102 (1979)) and SNCM42, which are excellent in both, are used.
Ni-added steels whose components have been improved based on steel No. 0 (JIS G 4103 (1979)) and the like have been used.

[0004] However, the addition of a large amount of Ni increases machinability, in particular,
When using the above-mentioned conventional steel, the cutting chips become too long and wrap around because the cutting chips characteristics are extremely deteriorated, so the cutting chips wrapped during cutting machining must be removed, and an NC lathe must be used. In addition, automation becomes difficult, resulting in a decrease in workability and an increase in cost.

[0005] Therefore, from the industry, as a material for various pistons for civil engineering and construction machinery, it does not contain a large amount of Ni in order to obtain good chipping properties, and has a strength equal to or higher than that of Ni-added steel. Development of inexpensive steel having (hardness) and toughness has been expected.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide machinability suitable for various types of steel for pistons used in civil engineering and construction machines, such as a piston incorporated in a hydraulic breaker of a hydraulic shovel, and in particular, chip characteristics. Another object of the present invention is to provide an excellent tough steel at low cost.

[0007]

Means for Solving the Problems The present inventor has repeatedly studied to achieve the above-mentioned objects, and as a result, obtained the following findings (a) to (d).

(A) The hardness at the center of the piston is 4 in HRC.
If it is 0.0 or more, even if it collides with extremely hard parts such as chisel, it is extremely difficult for the piston to "set", so the problem of "burring" is resolved and smooth piston movement is achieved What you can do.

(B) As a result of a preliminary test incorporated in the actual machine, in order to ensure that the piston sufficiently withstands the impact during use and does not crack, it is necessary to set R from the center of the piston at the portion a, which is a thin portion in FIG. / 2 position (where R is the radius at a part of the piston, hereinafter the R / 2 part from the center of the piston at a part is simply called the R / 2 part of the piston. Also, the R / 2 part from the center is (Hereinafter simply referred to as R / 2 part). The toughness of the JIS No. 3 test piece at room temperature should be 38.0 J / cm ² or more.

(C) Even if a large amount of Ni is not added, by adding an appropriate amount of Cr, Mo and V in combination, the strength (hardness) and toughness are remarkably improved, and the toughness is equal to or higher than that of Ni-added steel. And the chipping characteristics are extremely good as compared with Ni-added steel.

(D) Regarding strength and toughness, the following fn
1, and when the value is 2.0% or more, the predetermined hardness and toughness shown in (a) and (b) above can be obtained.

Fn1 = (2/3)% Cr + (4/5)% Mo + 2% V However,% Cr means weight% of the Cr content, and the same applies to% Mo and% V.

The present invention based on the above findings provides the following (1) to
The gist is a steel for nitriding having the chemical composition shown in (4) and having excellent toughness.

(1) By weight%, C: 0.25 to 0.45
%, Si: 0.05-1.00%, Mn: 0.35-
2.00%, Cr: 1.00 to 4.00%, Mo: 0.
50-1.50%, V: 0.05-0.50%, Ni:
0.50% or less, B: 0.0100% or less, N: 0.0
0.30 to 0.02% , the balance being Fe and inevitable impurities, and the value of fn1 being 2.0 to 5.0.
A tough steel with excellent machinability of 0%.

(2) In addition to the components described in the above (1), 0.005 to 0.050% by weight of Nb, 0.
0.01 to 0.10% Ti and 0.010 to 0.100
% Of Al, and the fn1
Is a tough steel excellent in machinability with a value of 2.0 to 5.0%.

(3) In addition to the components described in the above (1), 0.005 to 0.100% of S, 0.0% by weight is further added.
1 to 0.30% Pb, 0.005 to 0.100% T
e, 0.01-0.30% Bi and 0.0005-
A tough steel excellent in machinability containing at least one of 0.0100% of Ca and having a value of fn1 of 2.0 to 5.0%.

(4) In addition to the components described in (1) above, 0.005 to 0.050% by weight of Nb, 0.
0.01 to 0.10% Ti and 0.010 to 0.100
% Of Al, and 0.005 to 0.1
00% S, 0.01-0.30% Pb, 0.005
0.10% Te, 0.01-0.30% Bi and 0.0005-0.0100% Ca, and the value of fn1 is 2.0-0.1%. 5.0
% Tough steel with excellent machinability.

[0018]

The reason for limiting the chemical composition of steel in the present invention as described above will be described below. “%” Means “% by weight”.

C: C is an element effective for securing desired strength (hardness), but is also an element that lowers toughness. Smooth movement of the piston is achieved by securing the hardness at the center of the piston and suppressing "burrs" due to "sags", and it absorbs severe impacts by securing the R / 2 part toughness of the piston. A balance between hardness and toughness is necessary to improve the cracking property. To obtain the minimum hardness (hardness at the center of the piston is 40.0 or more in terms of HRC), C is 0.25%. It is necessary to contain the above. On the other hand, when the content exceeds 0.45%, the toughness is remarkably reduced, and the predetermined toughness (the impact value at room temperature with a JIS No. 3 test piece as the R / 2 part toughness of the piston is 38.
0 J / cm ² or more). Therefore, C
Was 0.25 to 0.45%.

Si: Si is an element necessary for deoxidizing steel and also for imparting a predetermined strength (hardness). However, if the content is less than 0.05%, the desired effect cannot be obtained, and if it exceeds 1.00%, the toughness is remarkably deteriorated and the predetermined toughness cannot be secured. To 1.00%.

Mn: Mn is required for deoxidation,
It has the effect of increasing hardenability and improving hardness and toughness.
However, if the content is less than 0.35%, the desired effect cannot be obtained, and if it exceeds 2.00%, the toughness is rather deteriorated and the desired toughness cannot be obtained.
5 to 2.00%.

Cr: Cr has the effect of enhancing hardenability and improving hardness and toughness. Its action is particularly Mo
The effect is greatly exhibited by the composite addition with V and V, and toughness equal to or higher than that of the Ni-added steel is obtained. However, if the content is less than 1.00%, the desired effect cannot be obtained, and 4.00%
, The effect is saturated and the economy is impaired, so the content was made 1.00 to 4.00%.

Mo: Mo is an element that is extremely effective in improving hardenability and improving hardness and toughness. In particular, Cr and V
The effect is remarkable by the composite addition with Ni, and toughness equal to or higher than that of the Ni-added steel is obtained. However, its content is 0.50
%, The desired effect cannot be obtained. On the other hand, if the content exceeds 1.50%, the effect is saturated and only the cost increases. %
And

V: In addition to the effect of increasing the temper softening resistance and improving the hardness, V significantly enhances the hardness and toughness by adding Cr and Mo in combination, and has a toughness equal to or higher than that of Ni-added steel. Has the effect of imparting to steel. However, if the content is less than 0.05%, the desired effect cannot be obtained,
On the other hand, if it exceeds 0.50%, the V carbonitrides are agglomerated and coarse,
On the contrary, the toughness is reduced and the crack resistance is deteriorated, so the content is set to 0.05 to 0.50%.

Ni: Ni may not be added. When added, it has the effect of improving strength and toughness.

To ensure this effect, Ni should be 0.1
The content is preferably 0% or more. However, when the content exceeds 0.50%, the machinability, especially, the chip characteristics are extremely deteriorated, and the intended object of the present invention cannot be achieved. Therefore, the content of Ni needs to be 0.50% or less.

B: B may not be added. If added, there is an effect that the hardenability is improved. In order to surely obtain this effect, the content of B is desirably 0.0005% or more.

However, if the content exceeds 0.0100%, the hot workability decreases. Therefore, the upper limit of the B content is set to 0.0100%.

[0029] N: N has the effect that if brought into containing chromatic form a nitride improving and toughness fine crystal grains. In order to surely obtain the effect on the improvement in toughness, it is desirable that the content of N is 0.0030% or more. However, the content is 0.0
If it exceeds 2%, nitrides aggregate and crystal grains are coarsened to deteriorate toughness. Therefore, the upper limit of the N content is set to 0.02%.

Fn1: Strength (hardness) and toughness are remarkably improved by adding an appropriate amount of Cr, Mo and V in combination, and toughness equal to or higher than that of Ni-added steel is obtained. As described above, when% X is the content of the element X, the strength and toughness can be arranged by the value of fn1 = (2/3)% Cr + (4/5)% Mo + 2% V. If the value of fn1 is less than 2.0%, good strength and toughness cannot be obtained. That is,
The hardness of the center of the piston is 40.0 or more in terms of HRC, and the R / 2 part toughness of the piston has both the desired hardness and toughness with an impact value of 38.0 J / cm ² or more at room temperature with a JIS No. 3 test piece. Can not. On the other hand, if this value exceeds 5.0%, the effect of toughness and saturation will be saturated, and economic efficiency will be impaired. Therefore, the value of fn1 is 2.0 to 5.0%.
And

The tough steel having excellent machinability according to the present invention further comprises at least one of Nb, Ti, and Al and / or S, Pb, Te, Bi, and Ca in addition to the above components. May be included. The effects and desirable contents of these alloy elements are as follows.

Nb, Ti and Al: Nb, Ti and Al have the effect of refining crystal grains and improving toughness.

Therefore, Nb, Ti and Al may be added as needed. However, in the case of Nb, 0.0
If the content is less than 0.05%, the desired effect cannot be obtained, and
If the content exceeds 50%, the toughness is reduced, and the crack resistance is deteriorated. On the other hand, in the case of Ti, if the content is less than 0.01%, the desired effect cannot be obtained. If the content is more than 0.10%, the crystal grains become coarser, the toughness is reduced, and the crack resistance is lowered. It causes deterioration. Further, also in the case of Al, if the content is less than 0.010%, the desired effect cannot be obtained, and if the content exceeds 0.100%, the crystal grains become coarser and the toughness is reduced, so that the crack resistance is lowered. It causes deterioration.
Therefore, when one or more of these alloying elements are added, Nb: 0.005 to 0.050%, Ti: 0.01%
The content is preferably 0.10% to 0.10% and Al: 0.010% to 0.100%.

S, Pb, Te, Bi and Ca: S, P
b, Te, Bi and Ca have the effect of improving machinability, especially tool life. Therefore, S, Pb, Te, B
i and Ca may be added as needed. Where S
In the case of, a desired effect cannot be obtained if the content is less than 0.005%, and if the content exceeds 0.100%, the toughness is significantly reduced. In the case of Pb, if the content is less than 0.01%, the desired effect cannot be obtained, and if it exceeds 0.30%, the toughness decreases. In the case of Te, if the content is less than 0.005%, the desired effect cannot be obtained,
If the content exceeds 0.100%, hot workability deteriorates. On the other hand, in the case of Bi, if the content is less than 0.01%, the desired effect cannot be obtained, and if the content exceeds 0.30%, the toughness deteriorates. Furthermore, also in the case of Ca, 0.0005
%, The desired effect cannot be obtained, and 0.010% or less.
If the content exceeds 0%, the toughness decreases. Therefore,
When one or more of these alloying elements are added, S: 0.
005 to 0.100%, Pb: 0.01 to 0.30%,
Te: 0.005 to 0.100%, Bi: 0.01 to
0.30% and Ca: 0.0005 to 0.0100%
Is good.

[0035] The steel having the above chemical composition is melted by a usual method, then rolled or forged, for example, hot, and then, if necessary, is tempered, and then tempered by a normal method. , Into a desired piston shape. Thereafter, in general, a nitriding treatment is performed by a usual method for imparting wear resistance. In the refining process, quenching is 90
After heating to a temperature of about 0 to 950 ° C., it may be cooled with water or oil. Tempering is performed at a temperature not higher than the Ac ₁ transformation point. Temperature range in which the R / 2 part toughness of the piston is obtained,
For example, it may be performed at a temperature of about 500 to 550 ° C. For cooling after tempering, an appropriate method such as accelerated cooling or cooling may be selected. Further, the nitriding treatment may be performed at a temperature of about 520 to 540 ° C.

[0036]

【Example】

(Example 1) Steels having the chemical compositions shown in Tables 1 and 2 were melted by a conventional method using a 3-ton test furnace. Steels 1 to 15 in Table 1 are steels of the present invention, and Steels 16 to 33 in Table 2
Is a comparative steel in which one of the components is out of the content range specified in the present invention. Note that among the comparative steels in Table 2, steel 32 and steel 33 correspond to conventional steels.

Next, the steel of the present invention and the comparative steel were rolled to 150 mmφ by a usual method, and then a heat-treated material having a diameter of 130 mmφ and a length of 1000 mm was processed from these test steels for toughness investigation. Heat treatment was performed at 930 ° C. for 2 hours to perform water quenching, and then tempering was performed at 530 ° C. for 5 hours to perform air-conditioning treatment. Thereafter, nitriding treatment was performed at 530 ° C. for 60 hours, followed by air cooling treatment.

The obtained 130 mm after nitriding treatment
A hardness test piece was cut out from the center of the φ steel material, and a JIS No. 3 Charpy impact test piece was cut out from the R / 2 position.
The center hardness and R / 2 part toughness at room temperature were investigated. The results are shown in Tables 3 and 4.

On the other hand, a rolled material having a diameter of 150 mm
They were cut into lengths and used for machinability studies on a lathe. That is,
Using Igetaroy ST40E (trade name) carbide tool,
Using wet lubrication, cutting was performed with a lathe under the conditions of a cutting speed of 100 m / min, a feed of 0.2 mm / rev, and a cutting depth of 1.5 mm, and the machinability (the state of wrapping of cutting chips) was investigated. The results of the machinability survey are also shown in Tables 3 and 4. In addition, the evaluation was given as ○ for those in which it was determined that automation of lathe cutting was possible because the winding of the cutting powder was less than 2 turns and it was cut off naturally during cutting and came off the workpiece.
When the winding of the cutting powder exceeded 2 turns and did not come off from the workpiece naturally during the cutting, the evaluation was x.

Each of the steels 1 to 15 of the present invention has a good center hardness at room temperature (40.0 or more in terms of HRC) and R /
It is evident that it has two-part toughness (38.0 J / cm ² or more) and good chipping properties (see Table 3).

On the other hand, steels 16 to 16 which are comparative steels in which one of the components is out of the range of the content specified in the present invention.
No. 33 does not satisfy the above-mentioned values in one or both of the central part hardness and the R / 2 part toughness at room temperature or has poor chipping properties (see Table 4).

(Example 2) A piston for a hydraulic breaker of a hydraulic shovel (size: steel 2 (inventive steel), steel 16 and 17 (comparative steel)) shown in Tables 1 and 2 above was used in a conventional manner. Is the diameter of section a in FIG. 1: 120 mmφ, b
(Part diameter: 140 mmφ, length: 500 mm) were manufactured for each five steel types, and they were assembled into actual machines and subjected to a 100-hour field test. Note that the tempering treatment and the nitriding treatment were the same as those in the first embodiment.

As a result of a field test using an actual machine, all pistons using the steel 2 of the present invention had no problem in sag resistance and cracking resistance, and were in a healthy state even after 100 hours of actual use. . On the other hand, the pistons using the comparative steels 16 and 17 have problems in either or both of the sag resistance and the cracking resistance. And the product life was short.

[0044]

[Table 1]

[0045]

[Table 2]

[0046]

[Table 3]

[0047]

[Table 4]

[0048]

According to the present invention, it is possible to obtain inexpensively tough steel excellent in cutting powder characteristics suitable for various piston steel materials used in civil engineering construction machines such as a piston incorporated in a hydraulic breaker of a hydraulic shovel. Is possible, and the industrial effect is extremely large.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a state of “burrs” and cracks due to “sags” generated in a piston incorporated in a hydraulic breaker of a hydraulic shovel.

[Explanation of symbols]

1: Piston, 2: "Return" by "fall", 3:
Crack

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Masaki Sakamoto 1 Koumi-cho, Kokurakita-ku, Kitakyushu-shi, Fukuoka Prefecture Sumitomo Metal Industries Co., Ltd. Kokura Works (56) References JP-A-3-202441 (JP, A) JP-A-6-184694 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C22C 38/00-38/60

Claims (4)

(57) [Claims] (1) C: 0.25 to 0.45% by weight, S
i: 0.05 to 1.00%, Mn: 0.35 to 2.00
%, Cr: 1.00 to 4.00%, Mo: 0.50 to
1.50%, V: 0.05 to 0.50%, Ni: 0.5
0% or less, B: 0.0100% or less, N: 0.0030
０．０0.02% or less, the balance being Fe and unavoidable impurities, and the value of fn1 below is 2.0 to 5.0.
% Tough steel with excellent machinability. fn1 = (2/3) [% Cr] + (4/5) [% Mo] +2 [% V] where [% X] is the weight% of the element X. 2. The composition according to claim 1, further comprising 0.005 to 0.050% by weight of Nb, 0.01 to 0.05% by weight.
0.10% Ti and 0.010-0.100% A
1. A tough steel excellent in machinability, containing at least one of the above-mentioned l and having the following fn1 value of 2.0 to 5.0%. fn1 = (2/3)% Cr + (4/5)% Mo + 2% V where% X is the weight% of element X. 3. The composition according to claim 1, further comprising 0.005 to 0.100% of S, 0.01 to 0.1% by weight.
30% Pb, 0.005 to 0.100% Te, 0.
01-0.30% Bi and 0.0005-0.01
Contains at least one of Ca of at least 100% and the following f
A tough steel excellent in machinability, in which the value of n1 is 2.0 to 5.0%. fn1 = (2/3)% Cr + (4/5)% Mo + 2% V where% X is the weight% of element X. 4. The composition according to claim 1, further comprising 0.005 to 0.050% by weight of Nb, 0.01 to 0.05% by weight.
0.10% Ti and 0.010-0.100% A
l or more, and 0.005 to 0.100%
S, 0.01 to 0.30% Pb, 0.005 to 0.
It contains one or more of 100% Te, 0.01 to 0.30% Bi and 0.0005 to 0.0100% Ca, and has the following fn1 value of 2.0 to 5.0. % Tough steel with excellent machinability. fn1 = (2/3)% Cr + (4/5)% Mo + 2% V where% X is the weight% of element X.