JPH05263128A - Production of wear resistant steel material excellent in breakage resistance - Google Patents

Abstract

PURPOSE:To regulate the hardness in a surface layer part to a specific value or below and to improve breakage resistance by applying hardening and tempering only to a specific part of machine parts made of wear resistant steel and performing heat treatment by a high-frequency heating method. CONSTITUTION:Because a deformed layer consisting of martensitic structure is formed in the sliding part, with bush, of chisel, etc., of civil engineering and construction machinery produced by using a wear resistant steel, such as Cr-Mn-Mo steel, as a stock and breakage due to microcracking is brought about, a high-frequency induction heating coil is attached to the part, liable to break, of the sliding part with bush after the application of hardening and tempering to a chisel and a high-frequency electric current, e.g., of 20kHz is sent and secondary tempering is applied only to the sliding part with bush by means of heating by high-frequency induction current, by which hardness Hs is regulated to <=42. By this secondary tempering, toughness in the sliding part with bush can be improved and breakage resistance can be improved while keeping wear resistance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing wear-resistant steel material having excellent breakability, which is suitable as a chisel for hydraulic excavators, a ripper or the like which is a component of a civil engineering construction machine.

[0002]

2. Description of the Related Art Conventionally, wear resistant steel whose wear resistance is enhanced by C and other elements is applied to a chisel, a ripper point, etc. of a civil engineering construction machine in which abrasion with sand and rocks has been a problem. Has been done.

A typical example of wear-resistant steel is
JIS standard SMn443 steel, SMnC443 steel, S
CM440 steel, SNCM439 steel, etc. are known,
In the above-mentioned civil engineering construction machines, in particular, C: 0.38 to 0.43% (hereinafter,% representing the component ratio shall be% by weight), Si: 0.15 to 0.35%, Mn: 0.60 to 0.85%,
SCM440 steel having a chemical composition containing Cr: 0.90 to 1.20% and Mo: 0.15 to 0.30% has been widely used.

However, in recent years, there has been a demand for further improvement in the performance of these machines, and it has been heard that the above wear-resistant steel cannot satisfy the hardenability and wear resistance. Therefore, some new wear resistant steels have been developed. The present inventors also previously found that C: 0.35 to 0.45%, Si: 0.60 to 1.50%, Mn:
1.80% or less, Cr: 2.50 to 4.50%, Mo: 0.20 to 1.00%, and if necessary V: 0.01 to 0.50%, Nb: 0.01 to 0.10%, W:
0.01 to 0.50%, Ti: 0.01 to 0.10%, B: 0.0005 to 0.
[0030] A wear-resistant steel containing more than 1% or more of 2% and further improved hardenability and wear resistance has been proposed (JP-A-60-
No. 215743), and has responded to the above request.

However, all of these wear-resistant steels, including conventional steels, are used after being subjected to quenching and tempering treatments, but any wear-resistant steels are designed with a component in consideration of wear resistance. Therefore, there is a problem that the toughness is inferior even when the quenching / tempering treatment is performed according to the standard, and it is easily broken during use.

In view of the above, the object of the present invention is to provide a wear-resistant steel material which exhibits not only good wear resistance but also excellent breakage resistance.

[0007]

Therefore, the inventors of the present invention have made earnest studies to achieve the above object, and have been able to obtain the following valuable findings. a) The breakage of the wear-resistant steel member described above tends to be concentrated in “a portion where a working layer is formed by sliding with another member” such as a sliding portion with a bush of a chisel in a civil engineering construction machine, When observing the fracture surface of the broken portion, the starting point of the fracture surface is a microcrack in the processed layer (martensite structure) caused by the sliding,

B) The generation of microcracks in the processed layer is related to the hardness of the base material before the formation of the processed layer. If the base material hardness is high, the microcrack generation rate is high, and if it is soft, the microcracks are generated. To be suppressed,

C) Therefore, if the hardness of the member made of wear-resistant steel is "adjusted only in the portion where the processed layer is formed by sliding with another member", and the surface layer hardness of this portion is made lower than a predetermined value, , While maintaining excellent wear resistance of other parts, it is possible to obtain wear-resistant steel material in which micro-cracking is suppressed in the processed layer generation part and breakage is less likely to occur,

D) The hardness adjustment (softening) of the portion where the processed layer is generated by sliding with other members is made of wear-resistant steel that has been subjected to quenching / tempering treatment to give the required hardness (wear resistance) and other characteristics. Can be easily implemented by partially tempering the surface layer of the member, especially by high-frequency heating.

The present invention has been completed as a result of further research based on the above findings and the like. "A wear-resistant steel member having a sliding portion with another member is subjected to quenching / tempering treatment. After that, by further heat-treating only the sliding portion by high-frequency heating to adjust the surface layer hardness to Hs 42 or less, wear-resistant steel material excellent in breakage resistance can be easily and stably manufactured. It has a great feature in "the point that it did".

[0012]

In other words, according to the present invention, only the "sliding part with another member (such as a bush)" of a member made of wear resistant steel and having a required hardness and the like by quenching and tempering is tempered again by high frequency heating, The main idea is to adjust the hardness of the surface layer of that part (the depth may be about 10 mm from the surface) to Hs 42 or less.
Since the surface layer of the sliding portion is softened, the occurrence rate of microcracks in the processed layer at this portion is significantly reduced, and the breakage resistance is significantly improved. Further, according to the present invention, since the induction hardening is performed only on the sliding portion, the abrasion resistance of other portions is not deteriorated.

Here, the type of wear-resistant steel to be applied is not particularly limited, and the above-mentioned JIS standard SMn is used.
443 steel, SMnC443 steel, SCM440 steel, SNCM
Either 439 steel or wear resistant steel such as proposed in JP-A-60-215743 may be used. Then, the quenching / tempering treatment for imparting the required hardness (wear resistance) or the like to the wear resistant steel material may be carried out under normal conditions. However, after that, induction hardening is performed to soften the surface layer of the sliding portion of the steel material, but the hardness level after softening is particularly limited to Hs 42 or less for the following reason.

A working layer is formed on the surface of the portion where the steel material slides against other members. The rate of occurrence of microcracks in this working layer is related to hardness, and as the hardness increases, the microcracks increase. The occurrence rate of will increase. As described above, the microcracks are the starting points of cracks leading to breakage, but in order to improve the breakage resistance aimed at by the present invention and to obtain the target breakage life (≧ 150 hr), the surface layer portion The hardness of the part (depth up to about 10 mm from the surface) is Hs
It is necessary to keep it below 42. In other words, if the hardness of the steel material in the sliding area exceeds Hs 42, microcracks are likely to occur in the surface layer, and the breakage resistance of the steel material is significantly reduced, making it impossible to secure the required service life. That is, the hardness of the surface layer of the part is regulated to be Hs 42 or less.

In addition, high frequency heating is applied to the secondary tempering for softening the surface layer of the sliding portion of the steel material. However, if high frequency heating is used, partial heating can be carried out quickly and only the necessary surface layer portion can be heated easily. Therefore, it is considered to be a heating means that cannot be replaced in actual work. The heating temperature in the secondary tempering is 400 to 70 depending on the type of wear resistant steel.
The temperature may be about 0 ° C., and the heating and holding time may be several seconds to several minutes. After heating, it may be air-cooled.

Next, the effects of the present invention will be described more specifically by way of examples.

[Example] JI commonly used as wear resistant steel
SCM440 steel of S standard was selected, and this was rolled to manufacture a plurality of actual parts of a chisel for civil engineering and construction machinery having an outer diameter of 125φ as shown in FIG.

Then, these are hardened (880 ° C. × 2 hr
→ oil quenching), tempering (200 ℃ × 2hr → air cooling), after that, except for a part, only the sliding part with the bush (see Fig. 2) is subjected to the secondary tempering by using the high frequency heating coil. went.

Induction tempering at this time (secondary tempering)
The conditions were as follows, and the tempering temperature was variously changed, and chisel products having various surface layer hardnesses at sliding portions were manufactured. Induction tempering (second tempering) conditions Frequency: 20 kHz, heating method: fixed position heating, heating temperature: 400-700 ° C, heating coil inner diameter: 140φ, heating time: 3 seconds, cooling method: air cooling.

Then, each chisel manufactured as described above was incorporated into an actual machine and a field test was conducted to examine the "breakage resistance life" and the "wear resistance". The results are shown in Table 1.
Shown in. The “breakage resistance life” was investigated up to 200 hours. The "wear resistance" was evaluated by measuring the amount of wear of the tip end of the chisel (hatched part in Fig. 2) after 50 hours of use.

[0019]

[Table 1]

As is clear from the results shown in Table 1, the wear resistance of the chisel manufactured according to the method of the present invention (the hardness of the surface portion of the sliding portion of which is adjusted to Hs 42 or less) is shown. While the breakage resistance is significantly improved without decreasing the heat resistance, induction hardening (secondary tempering)
Chisel whose surface layer hardness exceeds Hs 42 (high frequency second
It can be seen that the breakage resistance is not sufficient in the case of (including those manufactured by the conventional method in which the subsequent tempering is not performed).

In this embodiment, the heating temperature in the induction tempering (secondary tempering) conditions was changed to change the hardness of the surface layer, but in addition to this, the frequency, heating method, heating coil inner diameter, It goes without saying that the hardness of the surface layer portion can be arbitrarily controlled by changing the heating time or the cooling method.

[0022]

[Summary of Effects] As described above, according to the present invention, it is possible to easily and stably produce a wear-resistant steel material exhibiting excellent breakage resistance, which is an extremely useful effect in industry. Be brought.

[Brief description of drawings]

FIG. 1 is an explanatory diagram related to the shape of a chisel for civil engineering and construction machinery manufactured in an example and its induction tempered state.

FIG. 2 is a conceptual diagram showing a site where wear resistance is investigated in an example.

Claims (1)

[Claims] 1. A wear-resistant steel member having a sliding portion with another member is subjected to quenching and tempering treatment, and then only the sliding portion is heat-treated by high frequency heating so that the surface layer has a hardness of H.
s 42 or less, a method for producing a wear-resistant steel material having excellent breakage resistance.