JP3360687B2 - High-strength, high-toughness wear-resistant steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength, high-toughness wear-resisting steel having high strength, toughness, and good wear resistance at high temperatures used for a cutting edge of an earth-moving construction machine.

[0002]

2. Description of the Related Art A bulldozer ripper point is an example of a typical excavation edge of a civil engineering construction machine. In this method, a bulldozer is attached to a special excavation mechanism and pushed into the rock to break the rock. FIG. 1 shows this ripper point with a shank. In the figure, a ripper point 1 is attached to a shank 2 which is mounted on a bulldozer excavating mechanism (not shown).

[0003] Conventionally, the required properties of a steel material used for such a cutting edge include a tensile strength of 150 kgf / mm ² or more and a hardness of HRC 50 or more.
As described above, it is required that the Charpy impact value is 5 kgf-m / cm ² or more and the bending properties are good.
Etc.). However, the use environment in which such a cutting edge is used is becoming more severe year by year, and accordingly, the characteristics required for steel materials used in the cutting edge are becoming severer.

For example, when hard rock is excavated using a ripper point, the surface temperature of the ripper point is highest.
Since the temperature reaches 450 ° C or higher, the conventional JIS SNCM240 has a large decrease in hardness and wear is severe. However, when the hardness level is increased to improve wear resistance at a high temperature, a cut-off or the like occurs due to bending stress during use.

The excavating steel proposed in Japanese Patent Publication No. 60-25498 has good toughness and wear resistance at high temperatures, and is excellent in hot workability during its production. Even in these steels, when the use conditions are severe as in recent years, the strength and toughness are not sufficient, and cut-off, severe wear and the like are generated. In addition, these steels are high alloy steels and are not economical because the quenching temperature needs to be high. Moreover,
Recently, there has been a strong demand from consumers for further extension of the service life, cost reduction, and the like, and the development of a superior steel type that satisfies all of these demands has been demanded.

[0006]

Accordingly, it is a general object of the present invention to provide a steel having high strength, high toughness and good wear resistance at high temperatures. A specific object of the present invention is that the use temperature of the ripper point reaches 450 ° C. or more, so that the tempering temperature is 500 ° C. or more and the tensile strength is 180 ° C.
kgf / mm ² or more, hardness HRC 50 or more, Charpy impact value 5 kg
The purpose of the present invention is to provide a steel having a high strength, a high toughness and a high wear resistance at high temperatures, having a fm / cm ² or more and a bending property of a deflection of 30 mm or more.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive experiments and studies to obtain steel having such required characteristics, and have found that it is effective to satisfy the following conditions. The present invention has been completed. Reduction and purification of grain boundary segregation by lowering P and S, and strengthening of grain boundaries by lowering Mn to be effective for improving toughness. The increased amount of Mo and the addition of Nb significantly promote the refining of steel, thereby reducing grain boundary segregation and improving toughness.

[0008] The combined addition of Nb, Cr and Mo significantly increases the tempering softening resistance of steel, whereby a high tempering temperature can be adopted, toughness is improved, and softening due to an increase in temperature during use is prevented. Be done. Here, in the present invention, C: 0.40 to 0.55%, Si: 0.50% or less, Mn: 0.50% or less, P: 0.015% or less, S: 0.010% or less, Cr: 1.00 to 2.50%, Mo: : 1.00 ~ 2.00%, V: 0.10 ~ 0.30%, B: 0.0003 ~ 0.0050%, Al: 0.005 ~ 0.10%, Nb: 0.005 ~ 0.20%, Zr: 0.01 ~ 0.15%, Ti: 0.
Contains 0.1 to 0.10% of one or two kinds, with the balance being substantially
Tempering with steel composition consisting of Fe and unavoidable impurities
Tensile strength at a temperature 500 ℃ 180kg / mm ² or more, HRC50 or more, shea
It is a high-strength, high-toughness wear-resistant steel with a Kalpy impact value of 5 kgf-m / cm ² or more .

[0009]

In the present invention, the reasons for limiting the components of steel are described below. In this specification,% is% by weight unless otherwise specified. C: 0.40 ~0.55% C not only for ensuring the hardenability and strength, it is a necessary component also for grain refining of crystal structure, 0.40%
If it is less than 0.5%, the hardenability deteriorates and the desired strength cannot be ensured. On the other hand, if it exceeds 0.55%, the susceptibility to quenching cracking during quenching increases and the toughness deteriorates in relation to other alloy components. Therefore, it was set to 0.40 to 0.55%. Preferably, it is 0.40 to 0.50%.

Si: 0.50% or less Si is an element effective for deoxidizing steel and ensuring strength. However, when the content exceeds 0.50%, segregation is caused to deteriorate toughness. Therefore, the content is set to 0.50% or less. Mn: 0.50% or less Mn is an element effective in improving hardenability in addition to deoxidizing action. However, when it is contained in a large amount, grain boundary embrittlement occurs to cause deterioration of toughness. Furthermore, since it becomes a starting point of a crack when combined with S, its content must be reduced as much as possible in order to improve toughness. Therefore, the Mn content is 0.50%
It was as follows.

P: 0.015% or less P can not completely eliminate its grain boundary segregation by any heat treatment and lowers the grain boundary strength and deteriorates toughness. Therefore, the P content is 0.015% or less. Restricted to. S: 0.010% or less S is the starting point of cracking when MnS formed by combining with Mn, and further segregates alone at the grain boundaries to promote embrittlement. Therefore, it is necessary to limit the content of S as low as possible. . In the present invention, it is limited to 0.010% or less.

Cr: 1.00-2.50% Cr has the effect of improving the hardenability of steel and imparting tempering softening resistance to steel. In particular, the addition of Mo and Nb has the effect of imparting remarkable softening resistance to steel. However, if the content is less than 1.00%, the desired effect cannot be obtained. On the other hand, Cr is an expensive alloy element, and Considering the properties, the upper limit is set to 2.50%.

Mo: 1.00% to 2.00% Mo has the effect of improving the hardenability of steel and imparting temper softening resistance to steel. Particularly, the combined addition of Cr and Nb significantly increases the temper softening resistance. It is possible to employ a high tempering temperature, and it is also effective in improving toughness. But 1.00
%, The effect is not exhibited, and the desired effect cannot be obtained. On the other hand, even if it is added in excess of 2.00%, the effect saturates and only raises the cost.
00-2.00%.

V: 0.10 to 0.30% V has the effect of imparting tempering softening resistance and is effective in preventing the coarsening of crystal grains and improving the wear resistance. However, when V is less than 0.10 %, the effect is not exhibited. The desired effect cannot be obtained. On the other hand, if the content exceeds 0.30%, the hot workability, machinability and toughness are reduced, so the content is set to 0.10 to 0.30%.

B: 0.0003% to 0.0050% B has an effect of improving the hardenability and is an element effective in securing high strength. However, if less than 0.0003%, the effect cannot be obtained, and on the other hand, more than 0.0050% Therefore, the amount of B added is set to 0.0003 to 0.0050% in order to cause deterioration of the toughness of the steel.

Al: 0.005 to 0.10% Al is an effective component for stabilizing the deoxidation of steel, homogenizing the crystal structure and reducing the grain size. However, if it is less than 0.005%, the desired effect cannot be obtained. On the other hand, even if it exceeds 0.10%, the effect is saturated, and a flaw occurs due to an increase in inclusions,
Since the toughness also deteriorates, in the present invention, the Al content is 0.005.
-0.10%.

Nb: 0.005 to 0.20% Nb is effective for improving the strength and toughness of the steel and for reducing the grain size. In particular, the combined addition of Cr and Mo significantly reduces the grain size of the steel and significantly reduces the temper softening resistance. It is an element that is extremely effective in improving toughness, but in order to secure the effect, 0.005
% Is required. On the other hand, if it exceeds 0.20%, the effect will be saturated and the cost will be high, so 0.005 to 0.20%
And

Zr: 0.01-0.15% and / or Ti: 0.01
-0.10% Zr and Ti may be added as required for improving toughness. Zr
Has an effect of further improving the toughness by making the carbides in the steel into spherical fine particles and dispersing them. In particular, in the case of high-strength steel, it is preferable to add it to obtain high toughness. However, if it is less than 0.01%, its effect is small, and if it exceeds 0.15%, toughness is rather deteriorated.

[0019] Ti also has the effect of further improving the hardenability of steel. In particular, when the steel product size is large, it is preferable to include it for the purpose of securing high strength. However, if the content is less than 0.01, the effect is not obtained, and if it exceeds 0.10%, the toughness of the steel is deteriorated, so that the content is 0.01 to 0.10%. did.

In the production of the steel according to the present invention, the steel adjusted to the above composition is melted and formed into a steel slab by continuous casting or ingot forming method, and then subjected to appropriate hot or cold working to obtain a predetermined shape. And then quenched and tempered. As a result, steel having an HRC hardness of 50 or more, an impact value of 5 kgf-m / cm ² or more, and a deflection of 30 mm or more can be obtained, and is a material particularly suitable for use as a cutting edge of civil engineering and construction machinery.

[0021]

EXAMPLES Steels A to Q having the components shown in Table 1 were melted by a conventional method. Among these steels, steels A to I have compositions within the scope of the present invention, and steels J to Q are comparative steels outside the composition range specified by the present invention. After turning these steels into slabs by continuous casting or ingot casting,
After heating to 1200 to 1250 ° C., it was rolled into a round bar having a diameter of 30 mm by an ordinary method, and then quenched and tempered under the heat treatment conditions shown in Table 2. The tempering temperature was raised to around 400 ° C. during use, so a higher temperature was required.

Thereafter, various test pieces were processed and their characteristics were examined. Table 2 shows the results. The impact value is a Charpy test value, and the deflection amount is as shown in FIG. 2 across the width direction of a test piece (dimensions: 22 × 20 × 170 mm) 4 placed on two fulcrums 3. A bending test in which a load is applied from the direction of the arrow by the pressing piece 5 is performed, and the amount of deflection when the test piece is broken is shown.
When the amount of deflection was 30 mm or more and did not break, it was determined that no break occurred. From the results shown in Table 2, it is clear that the steel according to the present invention satisfies the target performance in each of the required characteristics and exhibits excellent strength and toughness.

Some of these steels were trial-produced at ripper points, which are representative of the cutting edge, and the wear after one hour of actual use was examined. Table 2 shows the results. Since the use conditions were all the same, the wear resistance can be evaluated by comparing the respective wear amounts. It has been found that all of the steels according to the present invention have good wear resistance. Incidentally, steel P corresponds to the steel disclosed in Japanese Patent Publication No. 60-25498. The wear amount was almost double that of the steel according to the present invention.

[0024]

[Table 1]

[0025]

[Table 2]

FIG. 3 shows the synergistic effect of each steel of this example on the tempering softening resistance due to the coexistence of Cr, Mo and Nb, and shows the HRC hardness at a constant tempering temperature of 500 ° C. This is to evaluate softening resistance. In the figure, the area surrounded by the broken line is the area of the present invention, and each of them shows an impact value of 5 kgf-m / cm ² or more and an HRC hardness of 50 or more.

[0027]

As described above, according to the present invention, the HRC is equal to or more than 50 at a tempering temperature of 500 ° C. and the tensile strength is 180 kgf / mm.
High-strength, high-toughness steel with high strength of ² or more, and high toughness and good cold bending properties can be obtained. This has a great effect that it can be provided as an alloy steel.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view showing a ripper point attached to a bulldozer.

FIG. 2 is an explanatory diagram of a procedure of a bending test.

FIG. 3 is a graph showing the coexistence effect of Cr, Mo, and Nb.

[Explanation of symbols]

 1 ripper point 2 shank 3 fulcrum 4 test piece 5 push piece

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Tetsuya Hirouchi 1 Konomi-cho, Kitakyushu City, Kokura-Kita-ku Sumitomo Metal Industries Co., Ltd. Kokura Works (72) Inventor Yoshiyuki Wakunami 1-Konomicho, Kita-Kyushu City, Sumitomo Gold (72) Inventor Tomihiro Tagawa 3-1-1 Ueno, Hirakata-shi, Osaka Co., Ltd. Komatsu Ltd. (72) Inventor Kazuhide Okawa 3-1-1 Ueno, Hirakata-shi, Osaka (56) References JP-A-1-149921 (JP, A) JP-A-60-138055 (JP, A) JP-A-2-179842 (JP, A) JP-A-1-301838 (JP) JP-A-61-12850 (JP, A) JP-A-61-12852 (JP, A)

Claims (2)

(57) [Claims] C .: 0.40 to 0.55%, Si: 0.50% or less, Mn: 0.50% or less, P: 0.015% or less, S: 0.010% or less, Cr: 1.00 to 2.50%, Mo: 1.00% by weight. 2.00%, V: 0.10 to 0.30%, B: 0.0003 to 0.0050%, Al: 0.005 to 0.10% Nb: 0.005 to 0.20%, with the balance having a steel composition consisting essentially of Fe and unavoidable impurities strength 180kg / mm ² or more tension at a temperature of 500 ℃ tempering
High, high-strength, tough, wear-resistant steel with an HRC of 50 or more and a Charpy impact value of 5 kgf-m / cm ² or more . 2. The high-strength, high-toughness wear-resistant steel according to claim 1, further comprising 0.01 to 0.15% of Zr and / or 0.01 to 0.10% of Ti.