JP2024055225A - Construction Machinery Parts - Google Patents

Abstract

[Problem] To provide a construction machine part that combines high levels of wear resistance and toughness. [Solution] To provide a construction machine part made of cast steel containing Fe, containing, by mass%, C: 0.1-0.35%, Si: 0.2-0.4%, Mn: 0.8-1.4%, Cr: 0.7-1.8%, Mo: 0.2-0.5%, and V: 0.0-0.1%, and having a structure mainly composed of martensite. The construction machine part may contain Ni, Nb, Ti, and Zr in a total amount of 0.5% or less. [Selected Figure] Figure 6

Description

The present invention relates to cast steel parts used in construction machinery, such as shoes and other undercarriage materials and teeth materials.

Cast steel, which combines wear resistance and toughness, is often used for wear-resistant parts in construction machinery. In particular, high Mn steel is often used as wear-resistant cast steel for parts that require wear resistance, such as undercarriage materials such as shoes and teeth materials. High Mn steel has an austenitic matrix that is highly tough, and when it undergoes plastic deformation, it hardens and the surface becomes hard.

Methods for improving the toughness of high Mn cast steel include, for example, increasing the C content or adding carbide-forming elements such as Ti, V, Nb, Zr, and B to refine the crystal grains and disperse spherical carbides within the crystal grains (Patent Document 1, etc.).

Japanese Patent Application Laid-Open No. 1-142058

In recent years, construction machinery has become larger and has a longer life span in response to demands for improved processing capacity, and wear-resistant cast steel parts, such as shoes and other undercarriage materials and teeth materials, are exposed to increasingly harsh environments. For this reason, wear-resistant cast steel parts for such construction machinery are required to have high levels of wear resistance and toughness while enduring more severe operating conditions. However, while the method disclosed in Patent Document 1 has a certain degree of improvement in the toughness of cast steel, it is unable to sufficiently improve wear resistance while maintaining toughness.

The object of the present invention is to provide construction machinery parts that combine high levels of wear resistance and toughness.

To achieve the above object, the present invention provides a construction machine part made of cast steel containing Fe, containing, by mass%, C: 0.1-0.35%, Si: 0.2-0.4%, Mn: 0.8-1.4%, Cr: 0.7-1.8%, Mo: 0.2-0.5%, and V: 0.0-0.1%, and having a structure mainly composed of martensite.

The present invention makes it possible to provide construction machinery parts that combine high levels of wear resistance and toughness.

FIG. 1 is a perspective view showing the appearance of a hydraulic excavator as an example of a construction machine to which a construction machine part according to an embodiment of the present invention is applied; FIG. 1 is a perspective view of an idler, which is an example of a part for a construction machine according to an embodiment of the present FIG. 1 is a perspective view of a drive tumbler, which is an example of a part for a construction machine according to an embodiment of the present invention; FIG. 1 is a perspective view of a shoe, which is an example of a part for a construction machine according to an embodiment of the present invention; FIG. 1 is a perspective view of a tooth member which is an example of a part for a construction machine according to an embodiment of the present invention; Table showing the composition of the inventive material from which the test specimens were made Table showing the composition of the comparative materials from which the test specimens were made Table showing the evaluation results of the test pieces Schematic diagram of the test equipment for the sand abrasion test A diagram showing an example of the metal structure of the inventive material. FIG. 1 is a schematic diagram of a crusher that is an example of an application target of a construction machine part according to an embodiment of the present invention. FIG. 1 is a schematic diagram of a fork grapple, which is an example of an application target of a construction machine part according to an embodiment of the present invention. FIG. 1 is a schematic diagram of a breaker, which is an example of an application target of a construction machine part according to an embodiment of the present invention.

The following describes an embodiment of the present invention using the drawings.

-Construction machinery-
Fig. 1A is a perspective view showing the appearance of a hydraulic excavator as an example of a construction machine to which the wear-resistant cast steel part for a construction machine according to one embodiment of the present invention is applied. In the following embodiment, the front of the operator's cab 18 (the left side in Fig. 1A) is the front of the revolving body 12 of the hydraulic excavator 1. Figs. 1B to 1E are views showing several examples of construction machine parts according to one embodiment of the present invention extracted from the hydraulic excavator shown in Fig. 1A. Specifically, Fig. 1B is a perspective view of an idler 13, Fig. 1C is a perspective view of a drive tumbler 14, Fig. 1D is a perspective view of a shoe 17, and Fig. 1E is a perspective view of a tooth member 27.

The hydraulic excavator 1 shown in FIG. 1A includes a vehicle body 10 and a front work unit 20. The vehicle body 10 includes a running body 11 and a rotating body 12.

In this embodiment, the running body 11 is equipped with left and right crawlers (running devices) 16 having endless track belts 15 that are looped around idler wheels 13 (FIG. 1B) and drive tumblers 14 (FIG. 1C) that are drive wheels. The drive tumblers 14 are driven by left and right running motors (not shown), and the endless track belts 15 that are looped around the idler 13 and drive tumbler 14 rotate and circulate, causing the hydraulic excavator 1 to run. For example, a hydraulic motor is used as the running motor. The endless track belt 15 is formed into a ring shape by connecting multiple shoes 17 (FIG. 1D).

The rotating body 12 is mounted on the upper part of the running body 11 via a rotation device (not shown) so that it can rotate left and right. The rotation device that connects the rotating body 12 to the running body 11 includes a rotation motor (not shown), and by driving the rotation motor, the rotating body 12 rotates left or right relative to the running body 11. For example, a hydraulic motor is used as the rotation motor. A cab 18 in which an operator sits is provided at the front of the rotating body 12 (the front left side in this embodiment). The rotating body 12 is also equipped with a prime mover, a hydraulic system, etc.

The front work machine 20 is a multi-joint arm-type working device for performing work such as excavating soil and sand, and is attached to the front of the rotating body 12 (to the right of the cab 18 in this embodiment). This front work machine 20 is composed of a boom 21, an arm 22, and a bucket 23.

The boom 21 is connected to the base frame of the revolving body 12, called a revolving frame, by a pin, and is driven by a boom cylinder 24 to rotate up and down relative to the revolving body 12. Both ends of the boom cylinder 24 are rotatably connected to the boom 21 and the revolving body 12 by pins. The arm 22 is connected to the tip of the boom 21 by a pin, and is driven by an arm cylinder 25 to rotate back and forth relative to the boom 21. Both ends of the arm cylinder 25 are rotatably connected to the arm 22 and the boom 21 by pins. The bucket 23 is connected to the tip of the arm 22 by a pin, and is driven by a bucket cylinder 26 to rotate up and down relative to the arm 22. Both ends of the bucket cylinder 26 are connected to the boom 21 and the bucket 23 by pins. The tip of the bucket 23 is provided with a plurality of teeth members 27 (Fig. 1E) that correspond to the teeth of the bucket 23.

-Construction machinery parts-
The tooth material 27, shoe 17, idler 13, and drive tumbler 14 of the hydraulic excavator 1 in Fig. 1A are representative examples of construction machine parts formed of a new wear-resistant cast steel for construction machines (hereinafter referred to as the inventive material) developed by the present inventors. The tooth material 27 and shoe 17 are parts that come into intense contact with soil and sand under high loads during excavation and traveling, and are highly susceptible to wear due to the soil. The idler 13 and drive tumbler 14 also come into intense contact with the shoe 17 (crawler track 15) and with soil that gets caught between the shoe 17 and the drive tumbler, and are similarly susceptible to wear. The inventive material is suitably applied to such parts.

The inventive material was developed through extensive research by the present inventors into improving both the wear resistance and toughness of cast steel, not just high Mn cast steel, but a wide range of cast steels in particular. During the research stage, they focused on the wear resistance and impact resistance to soil and sand as particularly important parameters.

The invented material also has better wear resistance than conventional cast steel by utilizing martensitic transformation to improve the hardness of the wear surface. Specifically, high toughness is achieved by adjusting the composition so that the C and Si contents are much lower than in conventional cast steel, and high wear resistance is achieved by creating a low-carbon structure mainly composed of martensite. The low-carbon structure mainly composed of martensite is formed by carrying out a specified heat treatment.

-Component composition-
The inventive material is made of cast steel containing Fe as the main component, and the more detailed composition, in mass %, is C: 0.1-0.35%, Si: 0.2-0.4%, Mn: 0.8-1.4%, Cr: 0.7-1.8%, Mo: 0.2-0.5%, and V: 0.0-0.1%, with the balance being Fe and unavoidable impurities. The inventive material is made by subjecting cast steel with this low carbon composition to martensitic transformation by heat treatment, which will be described later, to change the structure to martensite.

The material of the present invention is also permitted to contain elements that contribute to further improving wear resistance or toughness as the balance of the above composition, if necessary. Specifically, at least one of Ni, Nb, Ti, and Zr can be selected, and the selected at least one element can be contained in a total amount of 0.0 to 0.5%.

The following describes the preferred composition of each component that makes up the inventive material.

[C]
The C (carbon) content is preferably 0.1 to 0.35% by mass. C is added to ensure hardenability for obtaining a martensite structure (including a retained austenite phase) when heat treating cast steel. C is also an element that improves wear resistance. The C content must be 0.1% or more to ensure the desired wear resistance. On the other hand, if the C content exceeds 0.35%, the steel becomes prone to cracking, and is therefore limited to 0.35% or less in order to obtain the desired high toughness.

[Si]
The content of Si (silicon) is preferably 0.2 to 0.4% by mass. In order to ensure the fluidity of the molten metal during casting and to deoxidize the metal during melting and refining, it is necessary to add 0.2% or more, preferably 0.3% or more of Si. On the other hand, if Si is added in excess of 0.3%, the precipitation of carbides at grain boundaries is promoted, resulting in a decrease in toughness, so the Si content is limited to 0.3% or less.

[Mn]
The Mn (manganese) content is preferably 0.8 to 1.4% by mass. Mn is an austenite stabilizing element, and together with C, it suppresses the excessive generation of martensite, which reduces toughness during water cooling after austenitization. In order to ensure the desired wear resistance of the inventive material, the Mn content must be 0.8% or more. However, if the Mn content exceeds 1.4%, the wear resistance begins to decrease. In order to ensure the desired wear resistance, the Mn content is limited to 1.4% or less.

[Cr]
The Cr (chromium) content is preferably 0.7 to 1.8% by mass. Cr improves the work hardening characteristics of cast steel and increases wear resistance. In order to obtain the desired wear resistance of the inventive material, the Cr content must be 0.7% or more. On the other hand, if the Cr content exceeds 1.8%, it promotes the precipitation of grain boundary carbides, leading to a decrease in toughness. The Cr content is limited to 1.8% or less.

[Mo]
The content of Mo (molybdenum) is preferably 0.2 to 0.5% by mass. Mo is effective in suppressing the formation of grain boundary carbides and acicular carbides during heat treatment, particularly water quenching, and must be added in an amount of 0.2% or more. However, Mo is an expensive element, and adding more than 0.5% reduces the degree of effect improvement compared to the amount added. Therefore, the Mo content is limited to 0.5% or less.

[V]
The content of V (vanadium) is preferably 0.0 to 0.1% by mass. Like Mo, V is effective in suppressing grain boundary carbides and acicular carbides that are generated during heat treatment, particularly during water quenching. However, V is an expensive element, and adding more than necessary reduces the cost-effectiveness. Therefore, taking into account the amounts of other elements added and costs, 0.0 to 0.1% is added as necessary.

[Ni/Ti/Nb/Zr]
The content of Ni (nickel), Ti (titanium), Nb (niobium), and Zr (zirconium) is preferably 0.5% or less in total by mass%. Ni is an austenite stabilizing element, and like Mn, it forms martensite and contributes to improving wear resistance. However, if Ni is added at 0.5% or more, the amount of retained austenite increases and wear resistance decreases. Ti, Nb, and Zr have the effect of forming and precipitating carbides to increase wear resistance, and also of refining crystal grains to improve work hardening characteristics and toughness. However, they also have the effect of reducing ductility, for example. In addition, the addition of these elements increases costs. Therefore, the content of Ni, Ti, Nb, and Zr is limited to 0.5% or less in total.

-Heat treatment-
A preferred example of the heat treatment carried out in the manufacturing process of the inventive material will now be described.

When manufacturing the inventive material, first cast steel with the above-mentioned chemical composition is cast, and the cast steel is cooled to room temperature. At this time, there is no need to cast at a low temperature, which is prone to casting defects.

The cast steel is then reheated from room temperature, preferably using a vacuum furnace, and held at a temperature range of 900-1200°C for 1-50 hours, then cooled in the furnace, and homogenized. The low carbon martensite structure of the inventive material is formed by utilizing solidification segregation during casting. Cast steel, that is, steel ingots as cast, are prone to cracking, so the homogenization process described above is necessary to prevent cracking.

If the homogenization temperature is below 900°C, the homogenization is not sufficient, and conversely, if it exceeds 1200°C, the structure will become enlarged and homogenized too much, and the low-carbon martensite composite structure required for the inventive material will not be obtained. The processing time for the soaking process is at least one hour to fully adjust the structure. However, if it exceeds 50 hours, the homogenization will progress too far, and the low-carbon martensite composite structure required for the inventive material will not be obtained. For these reasons, the temperature and time conditions are set so that the low-carbon martensite structure of the inventive material is formed by utilizing solidification segregation during casting, and the homogenization process is performed by holding the temperature in the range of 900 to 1200°C for 1 to 50 hours, for example 4.5 hours, and then cooling in the furnace.

The homogenized cast steel is then reheated from room temperature, preferably using a vacuum furnace, and again held at a temperature range of 900-1200°C for 1-50 hours, for example 4.5 hours, and then water quenched to cause martensitic transformation. Quenching by water cooling or the like performed after this soaking is important for obtaining a structure of the inventive material that is mainly composed of low carbon martensite. In order to obtain a structure mainly composed of low carbon martensite, and also to prevent or suppress the precipitation of carbides at the grain boundaries, it is desirable to have as fast a cooling rate as possible during the quenching of the cast steel. For this reason, in this example, the homogenized cast steel is water quenched.

Finally, the water-quenched cast steel is reheated and held at a temperature range below 500°C (e.g., 250°C) for 1 to 50 hours (e.g., 4.5 hours) for normalization, and then left to cool to form the inventive material. Normalization is performed on martensitic cast steel that has become sufficiently hardened by quenching in order to reduce the hardness and improve toughness. Depending on the properties required for the inventive material, the temperature can be changed in the range of 200 to 500°C. For example, if hardness is important, normalization is performed at about 200°C. For example, if toughness is important, normalization is performed by increasing the processing temperature to about 500°C.

Figure 6 shows an example of the metal structure of the inventive material obtained by the above process, that is, a low-carbon martensite structure. As shown in the figure, in the inventive material, a martensite structure 100 is formed from low-carbon cast iron with the above-mentioned composition.

After normalizing, the cast steel, i.e., the inventive material, is machined by cutting, grinding, etc., and if necessary, surface treatment is performed, and it is finished into construction machinery parts that are used under harsh conditions, such as teeth material 27, shoes 17, idlers 13, and drive tumblers 14.

- Characteristic evaluation method -
FIG. 2 is a table showing the composition of the inventive material from which the test specimens were made, FIG. 3 is a table showing the composition of the comparative material from which the test specimens were made, and FIG. 4 is a table showing the evaluation results of the test specimens.

To evaluate the properties of the inventive materials, 50 kg of cast steel with the composition adjusted to the above range was first melted in a high-frequency induction melting furnace, and the melted cast steel was heat-treated to form inventive materials A1 to A7 (Figure 2). Inventive materials A1 to A7 have different amounts of each component added within the above range.

For comparison with the inventive materials A1 to A7, 50 kg of cast steel with a composition outside the range defined for the inventive materials was melted in the same high-frequency induction melting furnace, and the resulting cast steel was heat-treated to form comparative materials B1 to B5 (Figure 3). Comparative materials B1 to B5 also have different amounts of each component added. Furthermore, 50 kg of cast steel with a composition that falls within the range defined for the inventive materials was melted in the same high-frequency induction melting furnace, and comparative material B6 (Figure 4) was formed as cast steel without subsequent heat treatment.

Then, the center and intermediate portions of the surface of the inventive materials A1 to A7 and the comparative materials B1 to B6 were cut out and machined to produce test pieces (such as test piece 30 in Figure 5). Five each of the inventive materials A1 to A7 and the comparative materials B1 to B6 were prepared (number of samples N = 5).

The heat treatment applied to the inventive materials A1 to A7 and the comparative materials B1 to B5 was the same. Specifically, the cast steel was first cooled to room temperature, heated to 940°C in a vacuum furnace and held there for 4.5 hours for homogenization, then heated again to 920°C and held there for 4.5 hours, and then water-cooled. The water-cooled cast steel was then heated to 230°C and held there for 4.5 hours, and then cooled to room temperature.

Then, the test pieces of the inventive materials A1 to A7 and the comparative materials B1 to B6 were evaluated for hardness, tensile tests, Charpy tests, and sand abrasion tests. For each evaluation item of the inventive materials A1 to A7 and the comparative materials B1 to B6, the average value of the respective number of samples N was taken. The evaluation methods and standards for each item of hardness, impact resistance, and sand abrasion resistance are as follows:

[hardness]
Regarding hardness, a Vickers hardness tester was used to measure the surface hardness (Hv) of each test piece at seven points under a load of 1.0 kgf, and the average of the five values excluding the highest and lowest values for each test piece was calculated. The general standard of wear-resistant cast steel parts for conventional construction machinery was assumed to be 450 Hv, and the hardness of each test piece was evaluated using this assumption as the standard value. In other words, test pieces with a hardness of 450 Hv or more were evaluated as meeting the standard for hardness (OK), and test pieces with a hardness of less than 450 Hv were evaluated as not meeting the standard for hardness (NG).

[Impact resistance]
The impact resistance was evaluated by a Charpy impact test using a JIS No. 3 test piece with a 2 mm notch, with a hammer load of 294.2 N (30 kgf) and a test temperature of room temperature. The Charpy impact value (J) was calculated by dividing the absorbed energy by the cross-sectional area of the test piece [J/cm ² ]. The general standard of a wear-resistant cast steel part for conventional construction machinery was assumed to be a Charpy impact value of 25 J/cm ² , and the impact resistance of each test piece was evaluated using this assumption as the reference value. That is, test pieces with a Charpy impact value of 25 J/cm ² or more were evaluated as meeting the standard for impact resistance (OK), and test pieces with a Charpy impact value of less than 25 J/cm ² were evaluated as not meeting the standard for impact resistance (NG).

[Abrasion resistance by soil and sand]
The abrasion resistance to soil was evaluated by a rubber wheel test conforming to ASTM G65, simulating the environment in which the tooth material 27 is used. Specifically, plates measuring 10×20×65 mm were cut out from each of the inventive materials A1 to A7 and the comparative materials B1 to B6, and these plates were used as test pieces for the abrasion test. The abrasion resistance of these test pieces was evaluated using a test device shown in Fig. 5. The test device in Fig. 5 is structured such that a test piece 30 fixed to a lever 32 is pressed against the outer circumferential surface of a rotating rubber wheel 31 by the load of a weight 33, and sand from inside a hopper 34 is supplied between the test piece 30 and the rubber wheel 31 through a nozzle 35.

In the test, the rubber wheel 31 was rotated at 200 rpm for 10 minutes using the test device shown in FIG. 5, and sand was poured into the contact surface between the rubber wheel 31 and the test piece 30 at a constant flow rate (0.35 kg/min) while pressing the test piece 30 against the outer circumferential surface of the rotating rubber wheel 31. The weight of the weight 33 was then changed and the same test was repeated to estimate the specific wear rate of the test piece 30. The general standard of abrasion-resistant cast steel parts for conventional construction machinery was assumed to be a specific wear rate of about 6.0, and the abrasion resistance of each test piece was evaluated using this assumption as the standard value. In other words, test pieces with a specific wear rate of 6.0 or less were evaluated as meeting the standard for abrasion resistance to sand (OK), and test pieces with a specific wear rate of more than 6.0 were evaluated as not meeting the standard for abrasion resistance to sand (NG).

-Material evaluation results-
From the above tests, the evaluation results of the characteristic values shown in Figure 4 were obtained for the inventive materials A1 to A7 and the comparative materials B1 to B6. As shown in Figure 4, the test pieces of the inventive materials A1 to A7 all had a Charpy impact value of 25 J/ ^cm2 or more and a specific wear rate of 6.0 or less, which satisfied the evaluation criteria described above. In addition, all of the inventive materials A1 to A7 had a hardness of 450 Hv or more.

In this way, the test pieces of the inventive materials A1 to A7 all had a Charpy impact value of 25 J/ ^cm2 or more, and it was confirmed that they have a toughness higher than that of conventional wear-resistant cast steel parts for construction machinery. In addition, the test pieces of the inventive materials A1 to A7 all had a specific wear rate of 6.0 or less, and it was confirmed that they have a wear resistance higher than that of conventional construction machinery parts such as undercarriage materials such as the shoe 17 and tooth material 27. In addition, an improvement in hardness was also confirmed.

In contrast, for comparative materials B1 to B5, whose composition falls outside the range of the inventive materials, the same heat treatment was carried out as for inventive materials A1 to A7, but the impact resistance and abrasion resistance did not meet the above criteria. Furthermore, for comparative material B6, whose composition is within the range defined as an inventive material but which was not heat treated, the impact resistance also does not meet the above criteria. For comparative material B6, the failure to undergo martensitic transformation is thought to be the reason it does not meet the criteria. Thus, for none of comparative materials B1 to B6, the above criteria were simultaneously met for both impact resistance and abrasion resistance.

-effect-
As described above, the construction machine parts in this embodiment are made of cast steel containing Fe, contain additives such as those described above, and have a structure mainly composed of martensite. As specific examples, the invention materials A1 to A7, which are adjusted to the above-mentioned composition and have a low-carbon martensite structure, have been demonstrated to have superior properties compared to conventional wear-resistant cast steels for construction machines, that is, properties that provide a high level of balance between wear resistance and toughness.

Another major benefit is that the amount of expensive elements such as V, Ni, and Cr added can be reduced, resulting in low material costs. Furthermore, it is possible to obtain wear resistance and toughness that is greater than that of conventional high Mn cast steel without casting at low temperatures, which makes casting defects more likely to occur, and it is also possible to suppress cracking of construction machinery parts during or after manufacturing.

By using the inventive material for undercarriage materials such as the shoes 17, idlers 13, and drive tumblers 14, which are subject to heavy wear from soil and sand, as well as for the tooth material 27 of the bucket 23, the lifespan of these consumable parts such as the shoes 17 and tooth material 27 can be extended, which can also lead to improved operating efficiency of the construction machinery.

--Modifications--
In the above embodiment, the tooth material 27, the shoe 17, the idler 13, and the drive tumbler 14 are exemplified as application targets of the inventive material, but the application targets of the inventive material are not necessarily limited to these parts. The inventive material can be applied to other parts that require wear resistance and high toughness, and similar effects can be obtained.

In addition, in the above embodiment, the hydraulic excavator 1 has been described as an example of a construction machine, but the construction machine parts of the present invention can also be appropriately applied to other construction machines, such as wheel loaders and carrier crawlers.

In addition, hydraulic excavators, wheel loaders, and the like may have different attachments depending on the work being performed. For example, FIG. 7 shows a crusher 40 for breaking into smaller pieces and used at demolition sites, FIG. 8 shows a fork grapple 50 for scrap processing and transportation of waste materials, and FIG. 9 shows a breaker 60 for excavating and crushing rock and concrete. The crusher 40, fork grapple 50, and breaker 60 are all attachments that are attached to the tip of the arm of a front work machine in place of a bucket.

Like the tooth material 27 of the bucket 23, the crushing teeth 41 of the crusher 40 in FIG. 7 also come into strong contact with the concrete and rocks being broken into smaller pieces, and wear out. Similarly, the forks 51 of the fork grapple 50 in FIG. 8 come into strong contact with the concrete rubble and demolished materials being grasped. The chisel 61 of the breaker 60 in FIG. 9 also comes into strong contact with the rocks and concrete being crushed, and wears out. In addition to the bucket 23 shown in FIG. 1A, there are many attachments that wear out due to strong contact with concrete, etc., depending on the size of the hydraulic excavator. The inventive material can be suitably applied to the parts of these attachments that come into contact with concrete, etc., such as the crushing teeth 41, forks 51, and chisels 61 in the examples of FIGS. 7 to 9, and can achieve the same effects as the above embodiment.

1... Hydraulic excavator (construction machinery), 13... Idler (construction machinery part), 14... Drive tumbler (construction machinery part), 16... Crawler, 17... Shoe (construction machinery part), 23... Bucket, 28... Tooth material (construction machinery part), 41... Crushing teeth (construction machinery part), 51... Fork (construction machinery part), 61... Chisel (construction machinery part), 100... Martensite structure

Claims (4)

A construction machine part made of cast steel containing Fe,
A construction machine part comprising, by mass%, C: 0.1-0.35%, Si: 0.2-0.4%, Mn: 0.8-1.4%, Cr: 0.7-1.8%, Mo: 0.2-0.5%, and V: 0.0-0.1%, and having a structure mainly composed of martensite. The construction machine part according to claim 1,
A part for construction machinery, comprising Ni, Nb, Ti and Zr in a total content of 0.5% or less. The construction machine part according to claim 1,
A part for construction machinery, characterized in that it has a surface hardness of 450 Hv or more and a Charpy impact value of 25 J/ ^cm2 or more. The construction machine part according to claim 1,
The part for a construction machine is a tooth material for a bucket, a shoe for a crawler, an idler or a drive tumbler.

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