JP7180987B2 - Track shoes with links welded after heat treatment and manufacturing method thereof - Google Patents

Description

TECHNICAL FIELD The present invention relates to a track shoe in which links are welded after heat treatment, and a manufacturing method thereof.

Track shoes used for track belts are manufactured by the following procedure. That is, first, a steel slab of low-carbon alloy steel or medium-carbon alloy steel is manufactured, hot-rolled, shaped according to the shape of the track shoe, and then cut. Next, the track shoe is heated to a temperature equal to or higher than the Ac3 transformation point, then quenched and quenched, and then tempered to secure the mechanical properties of the track shoe as a whole.

A link that connects adjacent track shoes in the track belt is formed independently of the track shoes, and is assembled to the track shoes after the above-described quenching and tempering (hereinafter referred to as "heat treatment"). In addition to bolting, welding is used as a method of assembling the track shoe and the link.

Japanese Patent Application Laid-Open No. 2016-2901

However, in the above-described conventional track shoe, when a link is welded to a heat-treated track, there is a problem that cold cracking occurs at the welded portion. Although such cold cracking can be alleviated by preheating or post-heating the welded portion, there is a problem that the productivity is deteriorated and the mechanical properties obtained by the heat treatment are deteriorated.

In order to prevent such cold cracking, it is conceivable to review the welding conditions so as to increase the amount of heat input. Since the length, leg length, penetration amount, etc. are specified, it is difficult to review the welding conditions.

Therefore, there arises a technical problem to be solved in order to suppress the cold cracking of the shoe, and an object of the present invention is to solve this problem.

By reducing the content of C contained in the steel material, the carbon equivalent (JIS) (hereinafter, the carbon equivalent in accordance with JIS is simply referred to as "carbon equivalent") and the weld crack sensitivity index are lowered, and the cold cracking of the track shoe is reduced. and that Si, Mn, Cr, and Mo can suppress the deterioration of the hardenability of track shoes due to a decrease in the C content. Based on these findings, the present inventors conducted intensive research and found that by containing appropriate amounts of Si, Mn, Cr, and Mo, it is possible to suppress low-temperature cracking to a practical level even though it is a medium-carbon alloy steel. Found it.

In order to achieve the above object, a track shoe according to the present invention is a track shoe for welding a link after heat treatment, and has C: 0.23 to 0.27% and Si: 0.25 to 0 in mass %. .35%, Mn: 1.30 to 1.40%, Cr: 0.30 to 0.40%, Mo: 0.02 to 0.03% , Ni: 0.25% or less , and the balance Fe and impurities containing at least P, S, Sn, and Cu .

According to this configuration, it is possible to suppress cold cracking at the welded portion of the track shoe and the link while ensuring the hardenability of the track shoe.

Further, a method for manufacturing a track shoe according to the present invention is a method for manufacturing a track shoe in which links are welded after heat treatment. .35%, Mn: 1.30 to 1.40%, Cr: 0.30 to 0.40%, Mo: 0.02 to 0.03% , Ni: 0.25% or less , and the balance Fe and a step of preparing a steel material having a chemical composition composed of impurities containing at least P, S, Sn, and Cu ; a step of forming the steel material according to a shape of a shoe shoe; a step of heat-treating the shoe shoe; and welding the link to the track shoe.

According to this configuration, it is possible to suppress cold cracking at the welded portion of the track shoe and the link while ensuring the hardenability of the track shoe.

ADVANTAGE OF THE INVENTION This invention can suppress the cold crack in the weld location of a track shoe and a link, ensuring the hardenability of a track shoe.

1 is a perspective view schematically showing a shoe shoe according to an embodiment of the present invention; FIG. 2 is an exploded view of the track belt including the track shoe shown in FIG. 1; FIG. 4 is a graph showing the relationship between cooling rate and hardness in Examples and Comparative Examples. It is a graph which shows the relationship between hardening edge distance and hardness in an Example and a comparative example.

An embodiment of the present invention will be described based on the drawings. In addition, hereinafter, when referring to the number, numerical value, amount, range, etc. of the constituent elements, unless otherwise specified or clearly limited to a specific number in principle, it is limited to the specific number It does not matter if the number is greater than or less than a certain number.

In addition, when referring to the shape or positional relationship of components, etc., unless otherwise specified or in principle clearly considered otherwise, etc. include.

In addition, the drawings may exaggerate characteristic parts by enlarging them in order to make the characteristics easier to understand.

FIG. 1 is a perspective view schematically showing a shoe shoe 1 according to this embodiment. FIG. 2 is an exploded view of the track belt including the track shoe 1. FIG. The track shoe 1 is formed by hot-rolling a steel material, which will be described later, into a desired shape, and is heat-treated.

The shoe plate 1 includes a grouser portion 1a and a plate portion 1b. The grouser portion 1a is a portion protruding from the surface of the plate portion 1b. A plurality of grouser portions 1 a may be provided on one shoe shoe 1 . Moreover, the height of each grouser part 1a may be the same or different. Reference numeral 1c denotes a mud removal hole formed in the plate portion 1b.

A pair of links 2 are joined to approximately the center of the back surface of the plate portion 1b. The link 2 is joined to the plate portion 1b by welding the base of the outer surface (the welded portion shown in FIG. 1) and the base of the inner surface.

A bush 3 and a pin 4 are attached to the pair of links 2 . Both ends of the bush 3 are fitted into the bush holes 2a. Both ends of the pin 4 are fitted into the pin holes 2b.

The track shoe 1 is made of low-carbon alloy steel, and specifically has the following chemical composition. In the following description, "%" for alloying elements means "% by mass".

Table 1 shows the chemical composition of the base steel material for the shoe shoe 1 .

C is added to improve hardenability and ensure strength. If the content is less than 0.23, the effect is not sufficient, and if the content exceeds 0.27%, the risk of cold cracking increases.

Si is added for deoxidation during steelmaking. If the content is less than 0.25%, the effect is not sufficient, and if the content exceeds 0.35%, the rolling resistance increases and hot rolling becomes difficult.

Mn is added to increase the strength of steel materials. If the content is less than 1.30%, the effect is not sufficient, and if the content exceeds 1.40%, crystal grains in the steel material become large and the mechanical strength decreases.

Cr is added to improve the high-temperature strength of steel. If the content is less than 0.30%, the effect is not sufficient, and if the content exceeds 0.40%, the raw material cost of the steel material increases compared to the above-mentioned effect.

Mo is added to improve the high-temperature strength of steel. If the content is less than 0.02%, the effect is not sufficient, and if the content exceeds 0.03%, the weldability and toughness deteriorate, and the mechanical strength decreases.

P is selectively added to improve the workability of steel materials. P greatly degrades the toughness after quenching, and if the content exceeds 0.03%, it segregates at the interfaces of crystal grains and boundary cracks are likely to occur.

S is selectively added in order to improve the workability of steel materials. S greatly deteriorates the toughness after quenching, and if the content exceeds 0.03%, inclusions such as MnS increase and the mechanical strength decreases. More preferably, the S content is 0.015% or less.

Cu is an impurity that is inevitably contained in scrap metal, and when the content exceeds 0.3%, it segregates at the interfaces of crystal grains and boundary cracks are likely to occur.

Sn is selectively added in order to improve the workability of steel materials. When the content exceeds 0.08%, segregation occurs at the interfaces of crystal grains, and boundary cracks are likely to occur. Also, even when the sum of the respective contents of Cu and Sn exceeds 0.35%, segregation occurs at the interfaces of crystal grains, and boundary cracking is likely to occur.

Ni is selectively added to improve the hardenability of steel materials. If the content exceeds 0.25%, the raw material cost of the steel increases compared to the above effects.

The steel material according to the present embodiment is so-called non-boron steel, and B, which is known to improve hardenability, is not added.

Next, a method for manufacturing the shoe plate 1 will be described.

First, a base steel material having the chemical composition described above is prepared. Next, the steel material is hot-rolled and then cut to form a shoe shoe 1 having a desired shape. Note that the method of forming the steel material into a shoe-track shape is not limited to rolling, and may be, for example, forging.

Next, the shoe plate 1 is heat-treated. For quenching, for example, the shoe 1 is heated at 800 to 930° C. for 30 minutes to a temperature equal to or higher than the Ac3 transformation point, and then rapidly cooled to harden the shoe 1 and harden it. After that, it is heated again in the heating furnace at 420° C. for 60 minutes and then water-cooled to temper the shoe shoe 1 and secure its mechanical properties.

Next, the link 2 is welded to the shoe plate 1 . The welding conditions are, for example, using a welding wire of Φ 1.4 mm, the outside of the pair of links 2 is set to a current of 280 A, the voltage of 28 V, and the feed rate of 380 mm / min, the inside of the pair of links 2 is set to a current of 200 A, Set the voltage to 22 V and the feed rate to 470 mm/min. For example, for a track shoe with a width of 60 mm and a thickness of 5.5 mm, the welding amount is set to a welding length of 50 mm and a penetration amount of 1.2 mm. The heat treatment conditions and welding conditions described above are merely representative values, and are not limited to these.

Table 2 shows chemical compositions of base steel materials according to examples of the present invention and base steel materials according to comparative examples of the present invention. In addition, the Example which concerns on this invention does not limit this invention. According to Table 2, it can be seen that the content of C is reduced from 0.337% in the comparative example to 0.250% in this example.

Also, the carbon equivalent Ceq in Table 2 is a numerical value obtained by converting the chemical components contained in the steel material into carbon, and generally, the higher the numerical value, the more difficult welding becomes. Comparing the carbon equivalent Ceq between the example and the comparative example, it can be seen that the present example is reduced from 0.613 of the comparative example to 0.565. Formula 1 shows the formula for calculating the carbon equivalent Ceq.

Formula 1

The weld crack susceptibility index Pcm is a numerical value that indicates the effect of chemical components on cold cracking. Generally, the higher the numerical value, the more likely cold cracking occurs. Comparing the weld crack susceptibility index Pcm in Table 2 between the example and the comparative example, it can be seen that the value of the present example is reduced from 0.433 of the comparative example to 0.357. Equation 2 shows the equation for calculating the weld crack susceptibility index Pcm.

formula 2

As described above, in the present embodiment, by reducing the C content, the carbon equivalent Ceq and the weld crack sensitivity index Pcm are lowered to suppress cold cracking at the welded portion between the track shoe 1 and the link 2. can be done.

Graphs comparing the hardenability of the examples and the comparative examples by simulation are shown in FIGS. In FIG. 3, the horizontal axis indicates the cooling rate (° C./SEC), and the vertical axis indicates the hardness (HRC). In FIG. 4, the horizontal axis indicates the quenching end distance (mm), and the vertical axis indicates the hardness (HRC).

3 and 4, it can be seen that the hardenability of this example is equal to or higher than that of the comparative example. That is, generally speaking, since the hardenability of the track shoe 1 is lowered by reducing the content of C, it is necessary to enhance the cooling capacity, etc. However, in this embodiment, appropriate amounts of Si, Mn, Cr, and Mo are added. By doing so, the hardenability of the track shoe 1 is ensured, and the hardening treatment can be performed with conventional equipment.

In addition, the present invention can be modified in various ways without departing from the spirit of the present invention, and it is natural that the present invention extends to such modifications.

REFERENCE SIGNS LIST 1 : Track shoe 1a : Grouser part 1b : Plate part 2 : Link 3 : Bushing 4 : Pin

Claims (2)

A track shoe for welding links after heat treatment,
% by mass, C: 0.23-0.27%, Si: 0.25-0.35%, Mn: 1.30-1.40%, Cr: 0.30-0.40%, Mo: 0.02 to 0.03% , Ni: 0.25% or less , and the balance being Fe and impurities containing at least P, S, Sn, and Cu . A method for manufacturing a track shoe in which links are welded after heat treatment,
% by mass, C: 0.23-0.27%, Si: 0.25-0.35%, Mn: 1.30-1.40%, Cr: 0.30-0.40%, Mo: A step of preparing a steel material having a chemical composition containing 0.02 to 0.03% Ni and 0.25% or less Ni , the balance being Fe and impurities including at least P, S, Sn, and Cu ;
A step of shaping the steel material according to the shape of a shoe shoe;
a step of heat-treating the footwear;
a step of welding a link to the track shoe;
A method of manufacturing a shoe plate, comprising:

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