KR20140016619A - Method of heat treating steel component and methof of manufacturing track link using the same - Google Patents

Abstract

Disclosed are a method for heat treating a steel component which is capable of improving wear resistance of the steel component, and a method for manufacturing a track link using the same. According to the present invention, a method of heat treating a steel component comprises: a step for increasing surface hardness by quenching and primary tempering a steel component; and a step for lowering a residual austenite content to less than or equal to 1% in an area ratio by secondary tempering a steel component where the surface hardness is improved. [Reference numerals] (AA) START; (BB) END; (S110) Steel component forming; (S130) Secondary tempering

Description

Heat treatment method of steel parts and track link manufacturing method using same {METHOD OF HEAT TREATING STEEL COMPONENT AND METHOF OF MANUFACTURING TRACK LINK USING THE SAME}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel component manufacturing technology such as a track link, and more particularly, to a heat treatment method for a steel component capable of improving wear resistance of a steel component and a track link manufacturing method using the same.

In the case of steel parts such as track links, which are endless tracks, excellent wear resistance is required.

For example, in a caterpillar, the track link holds another shoe, the pin and pin, and connects the shoe continuously. The track link makes contact with the rail to drive the machine. Therefore, abrasion occurs due to the contact between the rail surface and the track link.

In general, the rail contact portion of the track link is subjected to high frequency heat treatment to improve surface hardness. However, in the case of a normal track link, austenite remains at least 1% in an area ratio even after high frequency heat treatment, and such a retained austenite is a factor that lowers the wear resistance of the track link.

In connection with the present invention, Korean Patent Laid-Open Publication No. 10-2010-0001290 (published Jan. 6, 2010) discloses a method of manufacturing a track link.

It is an object of the present invention to provide a heat treatment method for a steel part that can improve wear resistance.

It is another object of the present invention to provide a tracklink manufacturing method excellent in wear resistance and surface hardness.

Heat treatment method of a steel component according to an embodiment of the present invention for achieving the above object comprises the steps of increasing the surface hardness by quenching and primary tempering the steel component; And lowering the residual austenite fraction in an area ratio of 1% or less by secondary tempering the steel component having the high surface hardness.

At this time, the secondary tempering may be performed at 150 ~ 210 ℃, it is more preferably carried out at 150 ~ 190 ℃.

Track link manufacturing method according to an embodiment of the present invention for achieving the other object by weight, carbon (C): 0.2 ~ 0.5%, silicon (Si): 0.1 ~ 0.5%, manganese (Mn): 1.0 ~ 1.6%, phosphorus (P): 0.03% or less, sulfur (S): 0.03% or less, nickel (Ni): 0.02 ~ 0.1%, chromium (Cr): 0.1 ~ 0.3%, molybdenum (Mo): 0.01 ~ 0.05% , Copper (Cu): 0.05-0.2%, titanium (Ti): 0.01-0.05%, aluminum (Al): 0.01-0.05%, boron (B): 0.001-0.004%, nitrogen (N): 0.01% or less and Forming a molded body by molding a steel material consisting of remaining iron (Fe) and other unavoidable impurities into a predetermined track link shape; Quenching and primary tempering the molded body; And secondary tempering the molded body at 150 to 210 ° C.

At this time, the secondary tempering is more preferably carried out at 150 ~ 190 ℃.

In the heat treatment method of the steel component according to the present invention, the austenite remaining in the steel component can be lowered to 1% or less in area ratio through a double tempering process, thereby improving wear resistance of the steel component.

In addition, the heat treatment method of the steel component according to the present invention can also prevent the surface hardness decrease by performing the secondary tempering at 190 ℃ or less.

1 schematically shows a heat treatment method of a steel component according to an embodiment of the present invention.
2 shows the residual austenite area ratio of the specimens according to Examples 1 to 3 and Comparative Example 1.
3 to 5 show the surface hardness change of Examples 1 to 3 after the secondary tempering.

Advantages and features of the present invention and methods for achieving them will be apparent with reference to the embodiments described below in detail with the accompanying drawings. It should be understood, however, that the invention is not limited to the disclosed embodiments, but is capable of many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, To fully disclose the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims.

Hereinafter, a heat treatment method for a steel component and a track link manufacturing method using the same according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

1 schematically shows a heat treatment method of a steel component according to an embodiment of the present invention.

Referring to Figure 1, the heat treatment method of the steel component according to the present invention includes a quenching / primary tempering step (S120) and the secondary tempering step (S130). Steel part forming step (S110) in Figure 1 is to produce a predetermined steel part shape by a method such as forging a steel material, the heat treatment method of the steel part according to the present invention targets the manufactured steel parts.

First, in the quenching / primary tempering step (S120), the surface hardness is increased by quenching and primary tempering the steel parts.

Quenching may be performed by a heat treatment method using high frequency induction heating to improve the surface hardness, and more specifically, steel parts are subjected to high frequency induction heating to Ac3 or more, approximately 900 to 940 ° C., and then water cooled. Can be.

Primary tempering serves to mitigate the brittleness of steel when the surface hardness is excessively high due to quenching. Primary tempering may be performed for about 3 to 7 hours at a temperature of about 200 ~ 300 ℃.

The above quenching and primary tempering are described by way of example, and various well-known heat treatment methods performed for improving surface hardness in track link manufacturing, etc., in addition to the above conditions may correspond thereto.

In the second tempering step (S130), the steel part having the high surface hardness is secondary tempered. As a result of the secondary tempering, the fraction of austenite remaining in the steel parts was lowered to less than 1% by area ratio.

Residual austenite is a factor that inhibits wear resistance. Conventionally, after primary tempering, such austenite remains 1% or more in area ratio, and thus it is difficult to secure sufficient wear resistance. However, in the present invention, as a result of additional secondary tempering, the wear resistance can be greatly improved by lowering the residual austenite fraction to 1% or less as an area ratio.

The secondary tempering is preferably performed for about 3 to 7 hours at 150 ~ 210 ℃. If the temperature of secondary tempering is less than 150 degreeC, a tempering effect is hard to be obtained. On the contrary, when the secondary tempering temperature exceeds 210 ° C., there is a big problem of lowering the surface hardness.

On the other hand, when the secondary tempering was carried out at 150 ~ 190 ℃, along with the improvement of wear resistance according to the austenite fraction decrease, the surface hardness also did not decrease. Therefore, the most preferable secondary tempering temperature is 150-190 degreeC.

The heat treatment method as described above may be applied to a track link manufacturing method that is a part of a caterpillar.

The tracklink manufacturing method according to the present invention includes a forming body forming step, a quenching / primary tempering step and a second tempering step similarly to that shown in FIG.

In the step of forming the molded body, by weight%, carbon (C): 0.2-0.5%, silicon (Si): 0.1-0.5%, manganese (Mn): 1.0-1.6%, phosphorus (P): 0.03% or less, sulfur (S) ): 0.03% or less, nickel (Ni): 0.02 ~ 0.1%, chromium (Cr): 0.1 ~ 0.3%, molybdenum (Mo): 0.01 ~ 0.05%, copper (Cu): 0.05 ~ 0.2%, titanium (Ti) : 0.01 ~ 0.05%, Aluminum (Al): 0.01 ~ 0.05%, Boron (B): 0.001 ~ 0.004%, Nitrogen (N): 0.01% or less and steel material consisting of remaining iron (Fe) and other unavoidable impurities The molded article is formed by molding by a method such as hot forging into a track link shape.

Hereinafter, the role and content of each component will be described.

Carbon (C) is added to secure the strength of the steel. The carbon is preferably added in 0.2 to 0.5% by weight of the total weight of the steel. When the amount of carbon added is less than 0.2% by weight, it may be difficult to secure strength. On the contrary, when the content of carbon (C) exceeds 0.5% by weight, the strength of the steel is increased, but there is a problem that the impact value and the weldability are lowered.

Silicon (Si) acts as a deoxidizer and contributes to strength enhancement through solid solution strengthening. The silicon is preferably added in 0.1 to 0.5% by weight of the total weight of the steel. If the content of silicon is less than 0.1% by weight, the silicon addition effect may not be properly exhibited. On the contrary, when the content of silicon exceeds 0.5% by weight, there is a problem in that an oxide is formed on the surface of the steel to reduce weldability of the steel.

Manganese (Mn) is an element that increases the strength and toughness of steel and increases the hardenability of steel, and the addition of manganese has less deterioration in ductility when increasing strength than the addition of carbon (C). Manganese also contributes to the hardenability of the steel. The manganese is preferably added at 1.0 to 1.6% by weight of the total weight of the steel. When the amount of manganese added is less than 1.0% by weight, it is difficult to secure sufficient strength. On the contrary, when the amount of manganese exceeds 1.6% by weight, the amount of MnS-based nonmetallic inclusions increases, which may cause defects such as cracking during welding.

Phosphorus (P) contributes to the improvement in strength in part, but the lower the content is better as a representative element to reduce the secondary workability. Thus, in the present invention, the content of phosphorus is limited to 0.03% by weight or less of the total weight of the steel.

Sulfur (S), like phosphorus (P), is an impurity element present in steel. The sulfur (S) is an inclusion forming element, and forms a sulfide (Sulfide) in the form of MnS. Such sulfides impair the impact properties of steel for track shoes. Thus, in the present invention, the sulfur content is limited to 0.03% by weight or less of the total weight of the steel.

Nickel (Ni) fine grains and solidify in the austenite and ferrite to strengthen the matrix. The nickel is preferably added in 0.02 ~ 0.1% by weight of the total weight of the steel. When the amount of nickel added is less than 0.02% by weight, the effect of addition is insufficient. On the contrary, when the addition amount of nickel exceeds 0.1 weight%, there exists a possibility of causing red brittleness.

Chromium (Cr) is an effective element for improving hardenability by improving hardenability. The chromium is preferably added at 0.1 to 0.3% by weight of the total weight of the steel. If the amount of chromium added is less than 0.1% by weight, the addition effect cannot be properly exhibited. On the contrary, when the amount of chromium added exceeds 0.3% by weight, there is a problem of deteriorating the weldability or the weld heat affected zone (HAZ) toughness.

Molybdenum (Mo) contributes to improvement of strength and toughness, and also contributes to ensuring stable strength at room temperature or high temperature. The molybdenum is preferably added in 0.01 to 0.05% by weight of the total weight of the steel. When the addition amount of molybdenum is less than 0.01% by weight, the addition effect is insufficient. On the contrary, when the addition amount of molybdenum exceeds 0.05% by weight, there is a problem of lowering the weldability and increasing the yield ratio by precipitation of carbide.

Copper (Cu) is an effective element for increasing strength and improving toughness. In addition, copper contributes to the solid solution strengthening effect through constant content control together with silicon (Si) and manganese (Mn). The copper is preferably added at 0.05 to 0.2% by weight of the total weight of the steel. When the addition amount of copper is less than 0.05 weight%, the addition effect is inadequate. On the contrary, when the addition amount of copper exceeds 0.2 weight%, there exists a possibility that the surface characteristics of steel may fall.

Titanium (Ti) forms TiN upon reheating, inhibits austenite grain growth, and serves to refine the structure of the steel. The titanium is preferably added in 0.01 to 0.05% by weight of the total weight of the steel. When the addition amount of titanium is less than 0.01% by weight, the addition effect is insufficient. On the contrary, when the addition amount of titanium exceeds 0.05 weight%, TiN precipitate will coarsen and the grain growth inhibitory effect will fall.

Aluminum (Al) acts as a deoxidizer to remove oxygen in the steel. The aluminum is preferably added in 0.01 to 0.05% by weight of the total weight of the steel. When the addition amount of aluminum is less than 0.01% by weight, the addition effect is insufficient. On the contrary, when the addition amount of aluminum exceeds 0.05% by weight, there is a problem of lowering the impact characteristics of the steel.

Boron (B) is a strong hardenable element and contributes to the improvement of strength of steel. The boron is preferably added in 0.001 ~ 0.004% by weight of the total weight of the steel. When the addition amount of boron is less than 0.001% by weight, the addition effect is insufficient. On the contrary, when the addition amount of boron exceeds 0.004% by weight, there is a problem of causing material variation due to grain boundary segregation and lowering the impact characteristic.

Nitrogen (N) combines with aluminum to form nitrides, thereby contributing to the improvement of mechanical properties due to the miniaturization of austenite grains. However, excessive content of nitrogen inhibits hot forging. It is preferable that the said nitrogen is contained in 0.01 weight% or less of the total weight of steel materials. If the content of nitrogen exceeds 0.01% by weight may inhibit the hot forging.

Next, in the quenching / primary tempering step, the track-link shaped body is quenched and primary-tempered. For quenching and tempering, conventional QT (Quenching and Tempering) applied after hot forging in track link manufacturing may be applied, and a high frequency induction heating method may be proposed as a heating method. High frequency induction heating is not to be carried out over the entire portion of the molding tape, it may be carried out only on the roller contact portion of the track link.

Next, the secondary tempering step is secondary tempering at 150-210 ° C. for about 3-7 hours. As described above, as the secondary tempering is performed, the fraction of the retained austenite can be lowered to 1% or less in area ratio, thereby improving wear resistance.

At this time, the secondary tempering is more preferably carried out at 150 ~ 190 ℃ without surface hardness decrease.

Example

Hereinafter, the configuration and operation of the present invention through the preferred embodiment of the present invention will be described in more detail. It is to be understood, however, that the same is by way of illustration and example only and is not to be construed in a limiting sense.

Details that are not described herein will be omitted since those skilled in the art can sufficiently infer technically.

For specimens 1 to 4 having the composition shown in Table 1, after heating to 920 ℃ by a high frequency induction heating method, water cooled, and the first tempering was performed at 200 ℃ for 5 hours.

[Table 1]

At this time, secondary tempering was performed for 5 hours at 170 ° C. for specimen 1 (Example 1). Secondary tempering was performed for 5 hours at 190 ° C. for specimen 2 (Example 2). Specimen 3 was subjected to secondary tempering for 5 hours at 210 ° C. (Example 3). In addition, secondary tempering was not performed on specimen 4 (Comparative Example 1).

2 shows the residual austenite area ratio of the specimens according to Examples 1 to 3 and Comparative Example 1.

Referring to FIG. 2, in the case of the specimens according to Examples 1 to 3, which performed the secondary tempering, the residual austenite area ratio was 1% or less, but in the case of the specimen according to Comparative Example 1 that did not perform the secondary tempering. The residual austenite fraction exceeded 1%.

Therefore, in the case of the specimens according to Examples 1 to 3, which performed the secondary tempering, it can be seen that the wear resistance is more excellent.

3 to 5 show the surface hardness change of Examples 1 to 3 after the secondary tempering.

3 and 4, in the case of the specimens according to Examples 1 and 2, which were subjected to secondary tempering at temperatures of 170 ° C. and 190 ° C., when compared to the specimens according to Comparative Example 1, about 5 mm from the surface. It can be seen that there is little change in hardness up to the distance. On the other hand, referring to Figure 5, in the case of the specimen according to Example 3, which is subjected to the secondary tempering at a temperature of 210 ℃, it can be seen that the surface hardness is slightly reduced.

Therefore, in consideration of improvement of wear resistance and prevention of surface hardness reduction, secondary tempering is more preferably performed at 190 ° C or lower.

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments. Such changes and modifications are intended to fall within the scope of the present invention unless they depart from the scope of the present invention. Accordingly, the scope of the present invention should be determined by the following claims.

S110: Steel Part Forming Steps
S120: quenching and first tempering step
S130: 2nd tempering step

Claims (5)

Quenching and primary tempering the steel part to increase the surface hardness; And
And tempering the steel component having a higher surface hardness to lower the residual austenite content to 1% or less in an area ratio.
The method of claim 1,
The second tempering is
Heat treatment method of a steel component, characterized in that carried out at 150 ~ 210 ℃.
3. The method of claim 2,
The second tempering is
Heat treatment method of a steel component, characterized in that carried out at 150 ~ 190 ℃.
By weight%, carbon (C): 0.2-0.5%, silicon (Si): 0.1-0.5%, manganese (Mn): 1.0-1.6%, phosphorus (P): 0.03% or less, sulfur (S): 0.03% Nickel (Ni): 0.02 to 0.1%, Chromium (Cr): 0.1 to 0.3%, Molybdenum (Mo): 0.01 to 0.05%, Copper (Cu): 0.05 to 0.2%, Titanium (Ti): 0.01 to 0.05 %, Aluminum (Al): 0.01 ~ 0.05%, Boron (B): 0.001 ~ 0.004%, Nitrogen (N): 0.01% or less and steel consisting of remaining iron (Fe) and other unavoidable impurities in a predetermined track link shape Molding to form a molded body;
Quenching and primary tempering the molded body; And
Comprising the second step of tempering the molded body at 150 ~ 210 ℃; Tracklink manufacturing method comprising a.
5. The method of claim 4,
The second tempering is
Track link manufacturing method characterized in that carried out at 150 ~ 190 ℃.

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