JPH06256896A - Wear-resistant steel excellent in surface property and its production - Google Patents

Abstract

PURPOSE:To obtain steel inexpensively improved in wear resistance without increasing hardness and small in surface defects pausing cracks by limiting the content of Ti in steel having a specified compsn. by a specified parameter and applying continuous casting. CONSTITUTION:Molten steel contg., by weight, 0.10 to 0.45% C, 0.1 to 1.0% Sr, 0.1 to 2.0% Mn, <=0.04 P, <=0.04% S, 0.10 to 1.0% Ti, <=0.01% N and 0.01 to 0.1% Al, and the balance Fe and in which Ti* shown by the formulae I to IV is regulated to 0.05 to <0.4 is subjected to continuous casting; where Ti, C, N and S denote their amounts to be added (wt.%). Then, in this stage, coarse precipitates of >=0.5mum essentially consisting of TiC are precipitated in the cast slab. Successively, the cast slab is heated to the temp. range of <=1300 deg.C to prevent the precipitates from reentering into solid solution and reprecipitating, and hot working and hardening treatment are executed, by which the objective wear resistant steel contg. the same precipitates by >=400 pieces per mm<2> can be obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is an industrial machine / part / carrying machine (power shovel, bulldozer, hopper, bucket, etc.) used in the fields of construction, civil engineering, mining, etc.
The present invention relates to a wear-resistant steel used for a member which is subjected to abrasive wear, sliding wear, impact wear, etc. due to rock, sand, ore and the like, and a method for producing the same, and particularly relates to wear-resistant steel having excellent surface properties and a method for producing the same.

[0002]

2. Description of the Related Art Construction,
Industrial machinery, parts, and transportation equipment (power shovels, bulldozers, hoppers, bucket conveyors, rock crushers, etc.) used in the fields of civil engineering, mining, etc. are subject to abrasive or impact wear due to rock, sand, ore, etc. Steel having excellent wear resistance is used for the members in order to prolong the life of those machines, devices, parts and the like. It has been conventionally known that the wear resistance of steel is improved by increasing the hardness of steel, and it is manufactured by performing heat treatment such as quenching on alloy steel containing a large amount of alloy elements such as Cr and Mo. High hardness steels have been used.

As the prior art relating to wear-resistant steel for ensuring high hardness, Japanese Patent Laid-Open Nos. 62-142726 and 63-63 are known.
169359 and Japanese Patent Application Laid-Open No. 1-142023. The steel disclosed therein has a hardness (HB, etc.) at room temperature of about 300.
As described above, the weldability, toughness, bending workability, and the like are improved, and the wear resistance is improved by achieving high hardness.

However, the wear resistance required of the wear resistant steel in recent years has become more severe, and the conventional method of merely increasing the hardness does not improve the essential wear resistance. The current situation is not.

Further, in order to increase the hardness, it is general to utilize hardening by solid solution, hardening by transformation, hardening by precipitation, etc. When the hardness is remarkably increased by utilizing the transformation and precipitation hardening, the weldability and the workability are deteriorated as a result, and the cost is remarkably increased due to high alloying. Therefore,
It is easily expected that it will be practically difficult to remarkably increase the hardness in order to improve the wear resistance of the practical steel.

Further, wear-resistant steel, under actual use conditions, causes rocks, ores, etc. to come into contact with and collide with the surface thereof, so that the presence of defects on the surface causes cracks and the like. Since such a surface defect becomes a starting point of crack generation, the surface quality is an important characteristic.

The present invention has been made in view of the above circumstances, and it is possible to improve wear resistance at low cost without increasing hardness, and to have excellent surface properties with few surface defects that cause cracks. Abrasion resistant steel and its manufacturing method.

[0008]

In order to solve these problems, the inventors of the present invention firstly conducted extensive studies to improve wear resistance without increasing hardness, and as a result, only wear resistance was found. From the viewpoint of improving the
Coarse TiC during solidification using steel with a specific composition containing
It has been found that it is effective to generate a precipitate mainly composed of. Further, in order to improve wear resistance based on such a principle, steel is inexpensive because it is not necessary to use a large amount of expensive alloy components. However, in the subsequent research,
It has been found that the following problems occur when depositing such a coarse TiC-based precipitate.

(1) In ingot casting, the solidification rate is remarkably slow, so the precipitates that are produced become remarkably large and simply fall off during actual use, making it impossible to improve wear resistance. is there. The upper limit size must be 50 μm or less at most. (2) Further, in ingot casting, a large amount of Ti exists in the final solidified portion, and it is difficult to obtain a uniform distribution of precipitates throughout the steel material.

(3) Since Ti is an element with a strong oxidizing property, during casting and during heating and hot rolling of steel material, the steel near the surface is markedly oxidized more than that of ordinary steel in the case where a large amount of Ti is added. Is promoted and the surface properties are significantly deteriorated.

The inventors of the present invention have conducted further research to eliminate such problems, and as a result, the above (1)
The problem shown in (2) can be solved by applying continuous casting, and the problem of the deterioration of the surface property due to the addition of a large amount of Ti in (3) limits the value of the parameter shown by Ti * described later. It was found that this can be improved. The present invention has been made based on such findings of the inventors of the present application,

First, C: 0.10 to 0.4, in% by weight.
5%, Si: 0.1 to 1.0%, Mn: 0.1 to 2.0
%, P: 0.04% or less, S: 0.04% or less, Ti:
0.10 to 1.0%, N: 0.01% or less, Al: 0.
1 mm ^{2 of} a precipitate mainly containing TiC having a size of 0.5 μm or more, containing 0.1 to 0.1% and the balance Fe and unavoidable impurities. 400 or more per unit, and Ti * represented by the following formula is 0.05% or more 0.4
%, And the wear-resistant steel having excellent surface properties is characterized by being formed by continuous casting. <Expression> log [Ti] [C] = (-10580 / T) +4.3
8 [Ti] = 4 × [C] + {Ti (a) -4 × C} where Ti (a) = Ti − {(48/14) N + (48
/ 32) S} Ti, C, N, and S represent addition amounts (% by weight). Ti * = Ti (a)-[Ti]

Secondly, molten steel having the above composition and having Ti * of 0.05% or more and less than 0.4% is continuously cast, and coarse TiC is mainly contained in the slab at that stage. The precipitates to be deposited are subsequently deposited, and subsequently, coarse precipitates mainly composed of TiC present in the cast slab are substantially re-dissolved and heated to a temperature range of 1300 ° C. or lower so as not to be re-precipitated, and hot working and The present invention provides a method for producing wear-resistant steel having excellent surface properties, which is characterized by performing quenching treatment.

Further, in the above composition, in an additional weight%, Cu:
0.1 to 2.0%, Ni: 0.1 to 10.0%, Cr:
0.1 to 3.0%, Mo: 0.1 to 3.0%, B: 0.
One or two or more of 0003 to 0.01% may be contained, and Nb: 0.005 to 1.0%, V: 0.0
You may contain 1 type or 2 types in 1-1.0%.
Further, both of these additive groups may be contained. Hereinafter, the present invention will be described in detail.

The present invention having the above-mentioned structure is based on a completely different idea from the conventional wear-resistant steel as described above. That is, in the conventional wear resistant steel utilizing high hardness, the purpose of adding Ti is mainly utilizing precipitation hardening by fine precipitates of TiC. The size of TiC for utilizing precipitation hardening needs to be 0.1 μm or less. In order to deposit such minute deposits, it is necessary to once solid-dissolve Ti and then deposit it in the manufacturing process. Specifically, Ti is solid-soluted during heating or heat treatment in the hot rolling step and is precipitated during rolling or heat treatment such as tempering.

Further, in conventional steel, T other than precipitation hardening is used.
The purpose of adding i is to fix N, which easily binds to B, as TiN in order to secure a solid solution B effective for hardenability. Depending on the N content, for example, the N content is 0.01 weight%
In the case of, the addition amount is at most about 0.04% by weight or less. When Ti is used as TiN, it may be used also for the purpose of preventing coarsening of crystal grains during high temperature heating, and the Ti addition amount in this case is at most about 0.04 wt% or less. However, it is generally believed that TiN deteriorates ductility,
As a result, a method of reducing the amount of N in steel as much as possible in the steelmaking stage and minimizing the amount of Ti added to reduce the amount of TiN is adopted, and the added amount is at most about 0.02% by weight. . The following is a summary of the concept of the addition of Ti and the amount of addition in the prior art as described above. (1) The precipitation hardness of fine TiC precipitates is utilized to increase the matrix hardness of steel. Utilizing this hardness increasing effect, wear resistance is improved.

(2) In the case of utilizing TiN for the purpose of utilizing the hardenability improving effect of B or refining the crystal grains, the maximum amount is about 0.04% by weight, and practically It is about 0.02% by weight or less.

In contrast to the prior art described above, the present invention uses a steel containing a large amount of Ti, which is capable of positively forming a large amount of coarse precipitates mainly composed of TiC during solidification during continuous casting. Therefore, the wear resistance is remarkably improved. In the steel of the present invention, a precipitate mainly composed of TiC of 0.5 μm or more (for example, TiC precipitate or TiC
And a composite precipitate of TiN and TiS). Such a coarse precipitate mainly composed of TiC, which has not been studied so far, has a high hardness and can significantly improve the wear resistance.

In order to exert precipitation hardening conventionally, it is necessary that the precipitate size is 0.1 μm or less as described above. However, the precipitate size of 0.5 μm or more specified in the present invention is It does not contribute to precipitation hardening at all. In the present invention, one of the important characteristics is that not only the wear resistance is excellent, but also the presence of coarse precipitates rather lowers the matrix hardness at the same time. That is, the amount of solid solution C is reduced by the precipitation of a large amount of TiC-based precipitates.
The hardness of the steel matrix is rather reduced by the precipitation of precipitates. The effect of this decrease in hardness is that the bending workability can be improved. Therefore,
The steel of the present invention has the features of being extremely excellent in wear resistance and also having good workability. From a practical point of view, the upper limit of hardness is 600 at most in Brinell (HB) hardness, but even if the Brinell hardness is 600 or more, there is naturally an effect of improving wear resistance due to coarse precipitates, and bending workability is completely eliminated. When it is not necessary, it is possible to improve wear resistance by the same idea as in the present invention.

In order to make full use of the effect of such coarse precipitates, 0.5 that was precipitated during solidification during continuous casting was used.
It is important that the precipitates mainly composed of coarse TiC having a size of μm or more and the composite precipitates are hardly dissolved in the subsequent steps as much as possible. That is, practically, it is necessary to stably exist the precipitates mainly composed of TiC and the composite precipitates even at a heating temperature or a heat treatment temperature during hot working of about 1300 ° C. or less. In this coarse precipitate,
In the steel to which Nb, V, etc. are added in combination, precipitates such as Nb (C, N) or V (C, N) are also present,
There are also complex precipitates containing Ti, Nb, V, etc. at the same time. Ti-based precipitates are most effective for wear resistance, but Nb-based and V-based precipitates are also effective.

As described above, the present invention has been made from the viewpoint of improving wear resistance without increasing hardness, and can be applied to a member having low hardness and requiring workability. , It is an original product that is completely different from conventional wear resistant steel. That is, when compared at the same hardness level, the wear resistance of the conventional steel is significantly lower than the wear resistance of the steel according to the present invention, and conversely when the wear resistance is emphasized, the conventional steel Therefore, it is necessary to remarkably increase the hardness, and it is practically impossible to apply it to a member requiring workability.

On the other hand, as described above, the problems of excessive coarsening of precipitates and uneven distribution of precipitates, which are expected when forming Ti-based coarse precipitates to improve wear resistance, Is solved by applying continuous casting. Since continuous casting has a faster solidification rate than ingots, coarse precipitates can be uniformly dispersed and, in addition, not significantly coarse precipitates and 0.5 to 20 μm
It will be about. That is, by adopting continuous casting, it is possible to include a large amount of coarse precipitates that do not easily fall off in actual use, and to evenly disperse the precipitates. Therefore, the wear resistance of the continuously cast material is stable, uniform, and good as compared with the ingot material.

Further, since a large amount of Ti is contained, the vicinity of the surface is remarkably promoted to be oxidized more than ordinary steel, and the surface property is significantly deteriorated. Such deterioration of the surface property is caused by the above-mentioned Ti *. It was revealed that limiting the amount of parameters shown could improve. In other words, Ti *
By setting the value within a predetermined range, it becomes possible to secure good wear resistance and excellent surface properties at the same time. By increasing Ti * beyond this range, it is possible to improve only the wear resistance, but in that case, the surface properties deteriorate and it becomes impossible to put it to practical use. Next, the reasons for limiting the composition of the present invention will be described. The following%
All the indications show weight%. C: 0.10 to 0.50%

C is an essential element for forming a precipitate composed mainly of TiC. However, 0.10%
If it is less than 0.4%, a precipitate mainly composed of TiC cannot be effectively precipitated. On the contrary, if it exceeds 0.45%, the hardness is increased and the weldability and workability are deteriorated. Therefore, the C content is specified in the range of 0.10 to 0.45%. Si: 0.1-1.0%

Si is an element effective as a deoxidizing element,
In order to obtain the effect, it is necessary to add at least 0.1% or more. Further, Si is an element effective also for solid solution strengthening, but if it is contained in an amount exceeding 1.0%, there are problems such as reduction of ductility and increase of inclusions. Therefore, the Si content is specified in the range of 0.1 to 1.0%. Mn: 0.1-2.0%

Mn is an effective element from the viewpoint of ensuring hardenability, and in order to obtain this effect, addition of 0.1% or more is necessary. However, when the content exceeds 2.0%, the weldability deteriorates. Therefore, the Mn content is 0.1-2.
Specify in the range of 0%. P: 0.04% or less

P is an impurity element, which reduces the ductility and toughness of the steel, so it is desirable to reduce it as much as possible, but if it is extremely reduced, the cost increases significantly. Therefore, the P content is specified to be 0.04% or less from the viewpoint of not having such an adverse effect and not significantly increasing the cost. S: 0.04% or less

When S is added in a large amount, the hot ductility decreases,
It is desirable to reduce the ductility as much as possible in order to reduce the ductility, but if it is extremely reduced, the cost increases. Therefore, the S content is specified to be 0.04% or less from the viewpoint of not having such an adverse effect and increasing the cost. Ti: 0.10 to 1.0 wt%

In the present invention, Ti is the most important element together with C, and is an element essential for stably forming a large amount of coarse precipitates mainly composed of TiC. From the viewpoint of generating such a coarse precipitate, it is necessary to contain at least 0.10%. If it exceeds 1.0%, the wear resistance is good, but the cost rises and the weldability and workability deteriorate. Therefore, the Ti content is specified to be 0.1 to 1.0%. N: 0.0015 to 0.01%

N, like S, forms a precipitate and has the effect of facilitating uniform dispersion of TiC. Further, the hardness of TiN itself is high, and there is an effect of improving wear resistance. However, if less than 0.0015%, the effect cannot be obtained, and addition of a large amount of N exceeding 0.01% deteriorates the surface properties and also the weldability. Therefore, the content of N is 0.0015 to 0.01
Specified in the range of%.

In the present invention, in addition to these, Cu: 0.1 to
2.0%, Ni: 0.1 to 10.0%, Cr: 0.1
3.0%, Mo: 0.1 to 3.0%, B: 0.0003
It is also possible to contain one or more of 0.01% to 0.01%. Cu: 0.1-2.0%

Cu is an element that enhances hardenability and is an element that is effective for controlling hardness according to the purpose.
If it is less than 1%, this effect cannot be exhibited and 2.0
%, The hot workability decreases and
The cost also rises. Therefore, when Cu is contained, the amount is specified within the range of 0.1 to 2.0%. Ni: 0.1 to 10.0%

Ni is an element that enhances the hardenability and the low temperature toughness, but if it is less than 0.1%, this effect cannot be exerted, and if it exceeds 10.0%, the cost is remarkably increased. To rise. Therefore, when Ni is contained, its amount is specified in the range of 0.1 to 10.0%. Cr: 0.1-3.0%

Although Cr is an element that enhances hardenability,
If it is less than 1%, this effect cannot be exhibited and 3.0
If it is added in excess of%, the weldability deteriorates and the cost rises. Therefore, when Cr is contained, its amount is specified in the range of 0.1 to 3.0%. Mo: 0.1-3.0%

Mo is an element that enhances hardenability, but
If it is less than 1%, this effect cannot be exhibited and 3.0
If it is added in excess of%, the weldability deteriorates and the cost rises. Therefore, when Mo is contained, its amount is specified in the range of 0.1 to 3.0%. B: 0.0003 to 0.01%

B is an element that enhances hardenability by adding a trace amount, but if it is less than 0.0003%, this effect cannot be exhibited, and if it exceeds 0.01%, weldability deteriorates and Rather, the hardenability deteriorates. Therefore, when B is contained, its amount is 0.0003 to 0.01 wt.
Specify in the range of%.

In the present invention, in addition to the above basic composition or the composition to which the above selective element is added, Nb:
One or two of 0.005 to 1.0% and V: 0.01 to 1.0% can be contained. Nb: 0.005-1.0%

Nb is an element effective for precipitation strengthening, has the effect of controlling the hardness of steel according to the purpose, and is also effective for the formation of large coarse deposits, like Ti. However, if it is less than 0.005%, these effects cannot be exhibited, and if it exceeds 1.0%, the weldability deteriorates. Therefore, when Nb is contained, its amount should be 0.0
It is specified in the range of 05 to 1.0%. V: 0.01 to 1.0%

V is an element effective for precipitation strengthening, has the effect of controlling the hardness of steel according to the purpose, and is also effective for the formation of coarse coarse deposits, like Ti. However, if it is less than 0.01%, these effects cannot be exhibited, and if it exceeds 1.0%, the weldability deteriorates.
Therefore, when V is contained, the amount is 0.01 to
Specify in the range of 1.0%.

In the steel according to the present invention, in addition to such compositional limitation, the size and number of precipitates are also limited. That is, a coarse precipitate mainly composed of TiC and having a size of 0.5 μm or more is removed by 1 mm ² It is necessary to include 400 or more per unit. Wear resistance, which is the most important property in the present invention, is
A large amount of coarse precipitates or composite precipitates mainly composed of TiC is produced. Small precipitates of less than 0.5 μm have a small effect of improving wear resistance, and small precipitates have a hardness or hardness due to precipitation hardening. With increasing strength. Therefore, the softening effect of the matrix due to precipitation, which is the object of the present invention, cannot be achieved. Therefore, the size of the coarse precipitate needs to be 0.5 μm or more. Furthermore, even if a precipitate of 0.5 μm or more is present, 1 mm ² If the number of hits is less than 400, there is almost no effect of improving wear resistance. Therefore, the size of TiC-based precipitates is 0.5 μm or more, and the number is 1 mm ² The number is set to 400 or more. Also,
It is also necessary that Ti * represented by the following formula is 0.05% or more and less than 0.4%. log [Ti] [C] = (-10580 / T) +4.3
8 [Ti] = 4 × [C] + {Ti (a) -4 × C} where Ti (a) = Ti − {(48/14) N + (48
/ 32) S} Ti, C, N, and S represent addition amounts (% by weight). Ti * = Ti (a)-[Ti]

The amount represented by Ti * is a parameter indicating conditions for securing a predetermined amount of precipitates mainly composed of TiC and stably securing excellent surface properties. When Ti * is in the range of 0.05% to less than 0.4%,
It is possible to secure good wear resistance and excellent surface properties. If Ti * is less than 0.05%, the wear resistance deteriorates, and if it is 0.4% or more, the wear resistance is good, but the surface properties deteriorate significantly.

The present invention is premised on the use of a continuously cast slab. In the production of high-Ti steel such as the present invention, in the slab of a general ingot, the solidification rate is remarkably slow, so the segregation at the ingot shaft center portion and the head becomes remarkable, and further, the segregation portion and the final solidification portion. Precipitates mainly composed of TiC are concentrated on the surface, and uniform characteristics cannot be obtained over the entire final product. On the other hand, in a slab produced by continuous casting with a high solidification rate, compared with an ingot, TiC precipitates are more uniform.
It is possible to disperse the composite precipitate, and continuous casting is essential in the present invention. The continuous casting method is also advantageous in terms of cost. Next, a method for producing wear resistant steel according to the present invention will be described.

In the present invention, T having the above composition,
Molten steel having i * satisfying the above range is continuously cast, and coarse precipitates mainly composed of TiC are deposited in the cast at that stage, and subsequently coarse precipitates mainly composed of TiC existing in the cast. So as not to substantially re-dissolve and re-precipitate 13
Hot working and quenching are performed by heating in a temperature range of 00 ° C. or less.

When molten steel having the above composition and Ti * in the above range is used to perform continuous casting under ordinary continuous casting conditions, the desired size and number of TiC are mainly contained in the slab at that stage. A deposit can be deposited.

What is important in the hot working and quenching treatment in the next step is that in the hot working and quenching steps, coarse precipitates mainly composed of TiC produced by continuous casting are substantially solid-dissolved and re-formed. It is not to deposit. However, the parameter Ti * should be 0.05-
If less than 0.4%, reprecipitation does not substantially occur and there is no problem. From the viewpoint of not substantially solid-dissolving and re-precipitating coarse precipitates mainly composed of TiC, it is better to lower the heating temperature, but if the heating temperature is extremely low, hot ductility decreases and rolling is difficult. As a result, productivity decreases.
From the above points, the upper limit of the heating temperature is defined as 1300 ° C. From the viewpoint of obtaining a desired precipitate, heating at 1200 ° C. or lower is desirable, and if possible, heating at 1100 ° C. or lower is preferable. On the other hand, when the heating temperature exceeds 1300 ° C., the oxidation during heating progresses remarkably, and in particular, since a large amount of Ti is contained in the present invention, the generation of oxide scale increases, and as a result, the surface The property will deteriorate. From this point of view, the heating temperature is 1300 ° C.
Limited to:

After heating, the steel finished into a predetermined shape by hot working is subjected to quenching treatment in the final product stage.
The purpose of quenching treatment is to utilize transformation hardening,
The purpose is to stabilize the wear resistance. When conventional steel is subjected to such a quenching treatment, transformation hardening becomes remarkable, and workability and weldability are deteriorated.
Since the matrix hardness is reduced due to the presence of a large amount of coarse precipitates, the increase in hardness can be suppressed to be low as a result.

[0047]

EXAMPLES Examples of the present invention will be described below.

Slabs or ingots were obtained by continuous casting or ingot casting, and these were heated to a predetermined temperature, followed by hot working and quenching to obtain steels having the compositions shown in Table 1. Table 1
Among them, Steels 1 to 22 are Examples included in the scope of the present invention, and Steels AK are Comparative Examples outside the scope of the present invention.

[0049]

[Table 1]

Table 2 shows the manufacturing conditions of the sample steel. Table 2
Medium "CC" indicates continuous casting, and ING indicates ingot casting. The steels of the examples are all manufactured by continuous casting, whereas the steels of the comparative examples partially employ ingot casting. Then, the heating temperature is set to 1000 to 1250.
Hot working is performed by setting various temperatures in the range of ℃, and the quenching temperature is 850 to 970 ℃. Table 2 also shows the number of precipitates. The number of precipitates referred to here is Ti whose size is 0.5 μm or more.
1 mm of C-based precipitate (or composite precipitate)
² Indicates the number inside.

Regarding the test steel thus manufactured,
The Brinell hardness HB was measured and the abrasion resistance and surface properties were tested. The abrasion resistance was measured by an abrasion test according to ASTM G-65, and the abrasion resistance of SS400 (mild steel) was set to 1.0 and indicated by the abrasion resistance ratio. That is, the larger the abrasion resistance ratio, the better the abrasion resistance. In this test, 100% SiO ₂ sand was used as abrasion sand. The surface property was determined as a surface defect, for a defect having a depth of 0.2 mm or more, by the area ratio and the following criteria. ◯: Total area of the above defects is 25 cm ² / 1m ² Less than x: The total area of the above defects is 25 cm ^2. / 1m ² The above results are also shown in Table 2.

[0052]

[Table 2]

As is clear from Table 2, in Steels 1 to 22 satisfying the range of the present invention, the wear resistance ratio is high and the surface properties are good, although the surface hardness is relatively low. It was confirmed.

On the other hand, in Comparative Examples Steels A to D, the Ti addition amount was low outside the range of the present invention, and particularly in Steels A, B and D, the number of precipitates was 0, which is the most important aspect of the present invention. It was confirmed that the effect of various precipitates was not exhibited. Therefore, the surface properties are good, but the wear resistance is extremely low, and the characteristics as wear resistant steel have not been obtained. For steel C, T
Since the amount of i added was low and the number of precipitates was small, the wear resistance was significantly lower than that of Steel 4, which is an example.

Steels E and K are comparisons of Steels 5 and 9, respectively. The steels E and K satisfy the components of the present invention and also satisfy Ti *, but the manufacturing method is an ingot, and a significantly coarse precipitate is formed. In addition, the wear resistance is also deteriorated as compared with the steels of the examples. Regarding the amount of precipitates, when comparing steels E and K which are comparative examples with steels 5 and 9 which are examples, since the size of the precipitates is large in steels E and K, the number of precipitates is rather steel 5,
It is less than nine. The comparative steels are inferior in wear resistance to the steels of the present invention because remarkably coarse precipitates fall off under wear conditions.

Steels F to J are produced by continuous casting,
It was confirmed that the value of Ti * was out of the range of the present invention and the wear resistance was good, but the surface quality was remarkably deteriorated, and it was difficult to apply it in actual use.

[0057]

As described above, according to the present invention, the wear resistance can be improved at a low cost without increasing the hardness, and the wear resistance is excellent in the surface properties with few surface defects which are the starting points of cracking. A steel and a method for manufacturing the same are provided. Therefore,
Conventionally, it is possible to obtain a remarkable effect that the life of machines, parts, and the like, which have been often shortened due to remarkable wear during use and the occurrence of cracks, can be extended.

Front Page Continuation (72) Inventor Kenji Hirabe 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Steel Pipe Co., Ltd. (72) Innovator Yasunobu National 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Within the corporation

Claims (6)

[Claims] 1. By weight%, C: 0.10 to 0.45.
%, Si: 0.1 to 1.0%, Mn: 0.1 to 2.0
%, P: 0.04% or less, S: 0.04% or less, T
i: 0.10 to 1.0%, N: 0.01% or less, A
L: 0.01-0.1%, balance Fe and unavoidable impurities, and T having a size of 0.5 μm or more.
1 mm ^{2 of} precipitates mainly composed of iC A wear-resistant steel having excellent surface properties, characterized by containing 400 or more per unit of Ti * and having a Ti * represented by the following formula of 0.05% or more and less than 0.4%, and being formed by continuous casting. <Expression> log [Ti] [C] = (-10580 / T) +4.3
8 [Ti] = 4 × [C] + {Ti (a) -4 × C} where Ti (a) = Ti − {(48/14) N + (48
/ 32) S} Ti, C, N, and S represent addition amounts (% by weight). Ti * = Ti (a)-[Ti] 2. Further, Cu: 0.1-2.
0%, Ni: 0.1 to 10.0%, Cr: 0.1 to 3.
0%, Mo: 0.1 to 3.0%, B: 0.0003 to
The wear-resistant steel having excellent surface properties according to claim 1, which contains one or more of 0.01%. 3. Further, Nb: 0.005 by weight%.
1.0%, V: 0.01-1.0% 1 type or 2 types are included, The wear-resistant steel excellent in surface quality of Claim 1 or 2 characterized by the above-mentioned. 4. C: 0.10 to 0.45 in% by weight.
%, Si: 0.1 to 1.0%, Mn: 0.1 to 2.0
%, P: 0.04% or less, S: 0.04% or less, T
i: 0.10 to 1.0%, N: 0.01% or less, A
1: 0.01 to 0.1%, and the remainder is Fe and unavoidable impurities, and Ti * represented by the following formula has a Ti * of 0.05% or more and less than 0.4% and is continuously cast. At that stage, coarse precipitates mainly composed of TiC are deposited in the slab, and subsequently, coarse precipitates mainly composed of TiC present in the slab are not substantially re-dissolved and re-precipitated. A method for producing wear-resistant steel having excellent surface properties, which comprises heating to a temperature range of 1300 ° C. or lower and performing hot working and quenching treatment. <Expression> log [Ti] [C] = (-10580 / T) +4.3
8 [Ti] = 4 × [C] + {Ti (a) -4 × C} where Ti (a) = Ti − {(48/14) N + (48
/ 32) S} Ti, C, N, and S represent addition amounts (% by weight). Ti * = Ti (a)-[Ti] 5. Further, Cu: 0.1 to 2.
0%, Ni: 0.1 to 10.0%, Cr: 0.1 to 3.
0%, Mo: 0.1 to 3.0%, B: 0.0003 to
The method for producing wear-resistant steel with excellent surface properties according to claim 4, characterized in that it contains one or more of 0.01%. 6. Further, Nb: 0.005 by weight%.
1.0%, V: 0.01-1.0% 1 type or 2 types are included, The manufacturing method of the wear-resistant steel excellent in the surface quality of Claim 4 or 5 characterized by the above-mentioned.