JPH0578781A - High strength and high toughness wear resistant steel - Google Patents

Abstract

PURPOSE:To improve wear resistance at high temp., strength and toughness by specifying the amts. of C, Si, Mn, P, S, Cr, Mo, V, B, etc. CONSTITUTION:This steel has a compsn. consisting of, by weight, 0.35-0.55% C, <=0.5% Si, <=0.5% Mn, <=0.015% P, <=0.01% S, 1-2.5% Cr, 1-2% Mo, 0.05-0.3% V, 0.0003-0.005% B, 0.005-0.1% Al, 0.005-0.2% Nb and the balance Fe or further contg. 0.01-0.15% Zr and/or 0.01-0.1% Ti, has >=250 Rockwell hardness (HRC), such high strength as >=180kgf/mm<2> tensile strength and high toughness by tempering to 500 deg.C, and is used for the edge of the excavating blade of civil engineering and construction machinery, etc.

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-resistant steel having high strength and toughness and good wear resistance at high temperatures, which is used for excavating cutting edges of civil engineering construction machines and the like.

[0002]

2. Description of the Related Art A bulldozer ripper point is a typical example of a cutting edge of a civil construction machine. This is to attach a bulldozer to a special excavation mechanism and push it into the rock to break it. FIG. 1 shows this ripper point with a shank. In the figure, the ripper point 1 is attached to a shank 2, and this shank 2 is attached to an excavation mechanism (not shown) of the bulldozer.

Conventionally, the necessary properties of the steel material used for such an excavating cutting edge are tensile strength of 150 kgf / mm ² or more and hardness HRC 50.
As described above, it is necessary that the Charpy impact value is 5 kgf-m / cm ² or more and that the bending characteristics are good, and satisfying this, Ni-Cr-Mo low alloy steel (JIS SNCM240 has been widely used.
Etc.). However, the environment in which such a drilling edge is used has become more severe year by year, and the characteristics required for the steel material used for the drilling edge have become stricter accordingly.

For example, when hard rock is excavated using the ripper point, the surface temperature of the ripper point is the highest.
Since the temperature reaches 450 ° C or higher, the conventional JIS SNCM240 has a large decrease in hardness and becomes severely worn. However, if the hardness level is increased to improve wear resistance at high temperatures, bending stress during use will cause cutting damage and the like.

The steel for drilling proposed in Japanese Examined Patent Publication No. 60-25498 and the like has good toughness and wear resistance at high temperatures, and is excellent in hot workability during its production. When these steels are used under severe operating conditions as in recent years, the strength and toughness are not sufficient, and cutting damage and severe wear occur. Further, these steels are high alloy steels, and it is not economical because it is necessary to raise the quenching temperature. Moreover,
Recently, there are strong demands from consumers for further extension of service life and cost reduction, and there is a demand for the development of superior steel grades that satisfy all of these demands.

[0006]

Therefore, a general object of the present invention is 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 since the working temperature of the ripper point reaches 450 ℃ or more, the tempering temperature is 500 ℃ or more, the tensile strength is 180
kgf / mm ² or more, hardness HRC 50 or more, Charpy impact value 5 kg
It is to provide a steel having a bending strength of fm / cm ² or more, a bending strength of 30 mm or more, high strength, high toughness, and good wear resistance at high temperatures.

[0007]

Means for Solving the Problems The inventors of the present invention have found that it is effective to satisfy the following conditions as a result of intensive experiments and research for obtaining a steel having such required properties. Completed this invention. Reduction of grain boundary segregation by lowering P and S and cleaning, and strengthening of grain boundaries by lowering Mn are effective for improving toughness. By increasing the amount of Mo and adding Nb, the grain refinement of steel is significantly promoted, and along with that, segregation of grain boundaries is reduced and toughness is improved.

The combined addition of Nb, Cr and Mo remarkably enhances the temper softening resistance of the steel, whereby a high tempering temperature can be adopted, toughness is improved, and softening due to temperature rise during use is prevented. To be done. Here, the present invention, by weight%, C: 0.35 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 to 2.00%, V: 0.05 to
0.30%, B: 0.0003 to 0.0050%, Al: 0.005 to 0.10
%, Nb: 0.005 to 0.20%, and optionally 1 or 2 of Zr: 0.01 to 0.15% and Ti: 0.01 to 0.10%, with the balance being substantially Fe and unavoidable impurities. It is a high strength and high toughness wear resistant steel having the following steel composition.

[0009]

In the present invention, the reasons for limiting the components of steel will be described below. In this specification,% means% by weight unless otherwise specified. C: 0.35 to 0.55% C is a component necessary not only for ensuring hardenability and strength but also for refining the crystal structure, but 0.35%
If 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 quench cracking during quenching increases, and the toughness deteriorates in association with other alloy components. Therefore, it was set to 0.35 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, if it exceeds 0.50%, it segregates and deteriorates the toughness, so the content was made 0.50% or less. Mn: 0.50% or less Mn is an element effective not only for deoxidizing action but also for improving hardenability. However, if contained in a large amount, grain boundary embrittlement phenomenon occurs and deterioration of toughness occurs. Further, since it is combined with S and becomes a starting point of cracking, its content must be reduced as much as possible in order to improve toughness. Therefore, the Mn content is 0.50%
Below.

P: 0.015% or less P does not completely eliminate the grain boundary segregation by any heat treatment, and lowers the grain boundary strength and deteriorates the toughness. Therefore, the P content is 0.015% or less. Limited to. S: 0.010% or less S is a starting point for cracking when MnS is formed by combining with Mn, and even segregates at grain boundaries to promote embrittlement, so it is necessary to limit the content as low as possible. .. In this invention, it is limited to 0.010% or less.

Cr: 1.00 to 2.50% Cr has the effects of improving the hardenability of steel and imparting temper softening resistance to steel. In particular, Mo and Nb have the effect of imparting remarkable softening resistance to steel by the combined addition, but if the content is less than 1.00% the desired effect is not obtained, while Cr is an expensive alloy element, so it is economical. The upper limit was set to 2.50% in consideration of sex.

Mo: 1.00 to 2.00% Mo has the effect of improving the hardenability of steel and imparting temper softening resistance to the steel. Particularly, by adding Cr and Nb in combination, the temper softening resistance is significantly increased, It is also effective in improving toughness by enabling the use of high tempering temperature. But 1.00
If it is less than%, the above effect is not exhibited and the desired effect cannot be obtained. On the other hand, even if added over 2.00%, the effect is saturated and only cost rises, so its content is 1.
It was set to 00 to 2.00%.

V: 0.05 to 0.30% V has an effect of imparting temper softening resistance and is effective for preventing crystal grain coarsening and improving wear resistance, but if it is less than 0.05%, the effect is not exhibited. The desired effect cannot be obtained. On the other hand, if it exceeds 0.30%, the hot workability, machinability and toughness are deteriorated, so the content was made 0.05 to 0.30%.

B: 0.0003 to 0.0050% B has an effect of improving the hardenability and is an element effective for ensuring high strength. However, if it is less than 0.0003%, the effect cannot be obtained, and on the other hand, it exceeds 0.0050%. In addition, the addition amount of B was set to 0.0003 to 0.0050% in order to deteriorate the toughness of steel.

Al: 0.005 to 0.10% Al is an effective component for stabilizing the deoxidation of steel, homogenizing the crystal structure and grain refining, but 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 will be saturated, and flaws will occur due to the increase of inclusions,
Since the toughness also deteriorates, the Al content in this invention is 0.005.
It was set to 0.10%.

Nb: 0.005 to 0.20% Nb is effective for improving the strength and toughness of steel and for grain refining. Particularly, by adding Cr and Mo together, the steel is remarkably grain refined and the temper softening resistance is remarkably increased. It is an element that is extremely effective in improving toughness because it is increased, but 0.005 is required to secure its effect.
% Or more is required. On the other hand, if it exceeds 0.20%, the effect is saturated and the cost is high, so 0.005-0.20%
And

Zr: 0.01 to 0.15% and / or Ti: 0.01
˜0.10% Zr, Ti may be added if desired to improve toughness. Zr
Has the effect of further improving the toughness by making the carbides in the steel spherical and finely dispersed. Particularly in the case of high strength steel, it is preferable to add it in order to obtain high toughness, but if it is less than 0.01%, its effect is small, and if it exceeds 0.15%, toughness is rather deteriorated, so it was made 0.01 to 0.15%.

Ti also has the effect of further improving the hardenability of steel. Especially when the steel product size is large, it is preferable to contain it for the purpose of ensuring high strength, but if it is less than 0.01, its effect cannot be obtained, while if it exceeds 0.10%, it deteriorates the toughness of the steel and 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 made into a steel piece by continuous casting or an ingot making method, and then hot or cold working is appropriately performed to obtain a predetermined shape. Then, quench and temper. As a result, a steel having properties such as an HRC hardness of 50 or more, an impact value of 5 kgf-m / cm ² or more, and a deflection amount of 30 mm or more can be obtained, which is a material particularly suitable for use as an excavating cutting edge of a civil construction machine.

[0021]

EXAMPLES Steels A to Q having the components shown in Table 1 were melted by a usual 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 making these steel into billet by continuous casting method or ingot making method,
After heating at 1200 to 1250 ° C., it was rolled into a round bar having a diameter of 30 mm by a usual method, and then quenched and tempered under the heat treatment conditions shown in Table 2. Since tempering raises the temperature up to around 400 ° C during use, a higher temperature is required, so it was kept constant at 500 ° C.

After that, various test pieces were processed and their characteristics were investigated. The results are shown in Table 2. The impact value is the Charpy test value, and the deflection amount is across the width of the test piece (dimensions: 22 × 20 × 170 mm) 4 placed on the two fulcrums 3 as shown in FIG. A bending test in which a load is applied from the direction of the arrow by the pressing piece 5 is carried out, and the amount of deflection when broken is shown.
If the amount of deflection does not break at 30 mm or more, the sample was not broken. From the results in Table 2, it is clear that all the steels according to the present invention satisfy the target performance in each required characteristic and exhibit excellent strength and toughness.

Further, some of these steels were experimentally manufactured at a ripper point, which is a typical example of a cutting edge, and the amount of wear after actually using for one hour was examined. The results are shown in Table 2. Since the use conditions were the same, the wear resistance can be evaluated by comparing the wear amounts. It has been found that all the steels according to the present invention have good wear resistance. The steel P corresponds to the steel disclosed in Japanese Patent Publication No. 60-25498. The amount of wear 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 the coexistence of Cr, Mo and Nb on the temper softening resistance of each of the steels of this example, and shows the HRC hardness when the tempering temperature is kept constant at 500 ° C. The softening resistance is evaluated. In the figure, the area surrounded by the broken line is the area of the present invention, and each 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, HRC of 50 or more when tempered at 500 ° C and 180 kgf / mm in tensile strength.
It is possible to obtain high-strength, high-toughness steel with high strength of ² or more, high toughness, and good cold bending properties, so it is inexpensive for excavating cutting edges and tools used in civil engineering construction machines. It has a great effect that it can be provided as alloy steel.

[Brief description of drawings]

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

FIG. 2 is an explanatory diagram of the 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 Support point 4 Test piece 5 Push piece

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshiyuki Wakunami 1 Kunomi-cho, Kokurakita-ku, Kitakyushu City Sumitomo Metal Industries, Ltd. Kokura Works (72) Inventor Tomihiro Tagawa 3-1-1 Ueno, Hirakata-shi, Osaka Komatsu Ltd. (72) Inventor Kazuhide Okawa 3-1-1 Ueno, Hirakata City, Osaka Prefecture Komatsu Ltd.

Claims (2)

[Claims] 1. By weight%, C: 0.35 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
~ 2.50%, Mo: 1.00 ~ 2.00%, V: 0.05 ~ 0.30%, B: 0.00
A high-strength, high-toughness wear-resistant steel having a steel composition containing 03 to 0.0050%, Al: 0.005 to 0.10% Nb: 0.005 to 0.20%, and the balance being substantially Fe and inevitable impurities. 2. The high-strength, high-toughness wear-resistant steel according to claim 1, further containing Zr: 0.01 to 0.15% and / or Ti: 0.01 to 0.10%.