KR20100049264A - Ultra high strength microalloy steel for connecting rod - Google Patents

Abstract

PURPOSE: High-strength microalloyed steel for a connecting rod is provided to minimize deformation by increasing the content of phosphorus and nitrogen, and to reinforce strength by increasing the content of manganese, vanadium, and titanium. CONSTITUTION: High-strength microalloyed steel for a connecting rod is composed of carbon 0.32~0.38 weight%, silicon 0.50~0.90 weight%, manganese 0.90~1.20 weight%, phosphorus 0.005~0.10 weight%, sulfur 0.06~0.10 weight%, aluminum 0.04~0.01 weight%, vanadium 0.2~0.3 weight%, calcium 0.001~0.005 weight%, magnesium 0.0005~0.03 weight%, titanium 0.001~0.1 weight%, nitrogen 0.01~0.03 weight%, residual iron and inevitable impurities.

Description

ULTRA HIGH STRENGTH MICROALLOY STEEL FOR CONNECTING ROD}

The present invention relates to a high-strength non-thick steel for connecting rods that realizes excellent workability and breaking characteristics.

In general, the connecting rod of the vehicle is composed of a small end connected to the piston, a large end connected to the crank pin of the crankshaft, and a rod part integrally connecting the small end and the large end, so that the linear reciprocating motion of the piston is rotated. Converts to.

The method of manufacturing the connecting rod includes a sintering method, a hot forging method and a casting method depending on the molding method, and the method of processing the connecting rod includes a seat surface processing method and a method of breaking apart after integral forging.

The sintering and casting method is easy to break due to the characteristics of the material, so the breaking separation method is mainly used.The hot forging method uses rough steel and conventional medium carbon steel as the seat processing method, and the high carbon non-tough steel with pearlite microstructure has high carbon content. Break separation method is used.

By the way, the sintered material has a high manufacturing cost due to the expensive powder price, cast iron material has a problem of low durability due to low fatigue strength. In particular, the tempered steel is costly due to QT heat treatment for increasing strength and toughness, and the fracture separation method is not possible due to high toughness, so that the seat surface processing method is applied, resulting in an increase in manufacturing cost due to an increase in the number of processing steps. In addition, the high carbon non-alloyed steel has a disadvantage in that it has excellent fracture characteristics but poor cutting property, and endurance fatigue performance is inferior to that of the tempered steel.

An object of the present invention for solving this problem is to provide a high-strength amorphous steel for connecting rods that can improve the workability of the product, minimize deformation during breakage and reinforce the strength.

In order to achieve the above object, the high-strength non-alloyed steel for connecting rods according to the present invention includes carbon (C) 0.32 to 0.38 wt%, silicon (Si) 0.50 to 0.90 wt%, manganese (Mn) 0.90 to 1.20 wt%, phosphorus ( P) 0.005 to 0.10 wt%, sulfur (S) 0.06 to 0.10 wt%, aluminum (Al) 0.04 to 0.01 wt%, vanadium (V) 0.2 to 0.3 wt%, calcium (Ca) 0.001 to 0.005 wt%, magnesium ( Mg) 0.0005 to 0.03% by weight, titanium (Ti) 0.001 to 0.1% by weight, nitrogen 0.01 to 0,03% by weight, and the balance and the balance have a composition containing iron (Fe) and impurities It is characterized by.

The impurity may be 0.3 wt% or less of chromium (Cr), 0.1 wt% or less of molybdenum (Mo), and 0.2 wt% or less of nickel.

According to the present invention, it is possible to reduce the carbon content to improve the processability of the product, to increase the phosphorus and nitrogen content to minimize the deformation during fracture fragmentation, and to increase the strength by increasing the manganese, vanadium, and titanium content There is this.

First of all, in adding reference numerals to the components of each drawing, it should be noted that the same reference numerals are used as much as possible even if displayed on different drawings. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

Embodiments of the present invention will be described in detail with reference to the accompanying drawings.

The present invention adds an appropriate amount of calcium (Ca) and magnesium (Mg) to iron (Fe), carbon (C), silicon (Si), sulfur (S), phosphorus (P) and to minimize deformation during breakage It is characterized by the fact that it provides a high strength amorphous steel for connecting rods having increased strength by increasing nitrogen (N) content and increasing manganese (Mn) and vanadium (V) titanium (Ti) contents.

High-strength non-coarse steel to implement this, carbon (C) 0.32 ~ 0.38% by weight, silicon (Si) 0.50 ~ 0.90% by weight, manganese (Mn) 0.90 ~ 1.20% by weight, phosphorus (P) 0.005 ~ 0.10% by weight, sulfur (S) 0.06 to 0.10 wt%, aluminum (Al) 0.04 to 0.01 wt%, vanadium (V) 0.2 to 0.3 wt%, calcium (Ca) 0.001 to 0.005 wt%, magnesium (Mg) 0.0005 to 0.03 wt%, titanium (Ti) 0.001-0.1 weight%, nitrogen 0.01-0.03 weight%, and remainder and remainder contain iron (Fe) and an impurity.

In the forged steel of such a configuration, each component constituting the high strength non-coated steel has its own characteristics, such as phosphorus and nitrogen to minimize deformation upon fracture breakage, and manganese, vanadium, and titanium to enhance strength. have.

Therefore, in order to produce non-coated steel having excellent workability and fracture characteristics while utilizing the properties of these components, it is required to combine these components in an appropriate ratio. In order to obtain the proper combination ratio, the inventor has undergone numerous trial and error, and as a result, the inventors have found that the configuration of the ratio is most suitable.

Hereinafter, looking at the reason for limiting the composition of the high strength non-coated steel according to the present invention.

(Iii) 0.32 to 0.38 wt% of carbon (C)

Carbon is the element which has the greatest influence on the hardenability of steel, and 0.32 to 0.38% by weight of carbon is a component ratio that secures a desired mechanical strength and enables heat treatment. If the content of carbon is more than 0.38% by weight may adversely affect the workability to reduce the performance of the parts, if the content of carbon is less than 0.32% by weight may not be able to secure the desired mechanical strength.

(Ii) 0.50 to 0.90 wt% of silicon (Si)

Silicon is a stabilizing element for strengthening the ferrite matrix structure and facilitating the conrod fracture, and when silicon content of 0.90% by weight or more is applied, the possibility of component removal occurs, and when silicon content is 0.50% by weight or less, There arises a problem that the strengthening effect of ferrite may be lowered.

(V) Manganese (Mn) 0.90 to 1.20 wt%

Manganese plays an important role as deoxidation or desulfurization agent and prevents MnS inclusion formation and increased toughness. Such manganese may act as a harmful element when its amount is added to 1.20% by weight or more in order to stabilize the tissue, and when manganese is contained in an amount of 0.90% by weight or less, the deoxidation or desulfurization agent may not function properly in the casting process. have.

(Ⅳ) Phosphorus (P) 0.005 ~ 0.10 wt%

Phosphorus is an element that precipitates at grain boundaries to reduce toughness and forms a compound of Fe3p in the steel. When phosphorus content is 0.10 wt% or more, yield strength decreases, and when it is 0.005 wt% or less, the toughness reduction effect may be insignificant.

(Iii) 0.06 to 0.10 wt% of sulfur (S),

Sulfur is an element that combines with manganese (Mn) in steel to form MnS inclusions to improve workability. If the sulfur content is more than 0.10% by weight, the workability is more than necessary, and if the content is less than 0.06% by weight, the function may be insignificant. .

(Iii) Aluminum 0.04 ~ 0.01 wt%

Aluminum is effective as a strong deoxidizer, but if it is added in a large amount, the steel is brittle, so it is better to add it below 0.04%. Nitride AlN is finely precipitated and is effective for refining grains of steel.

(V) Vanadium (V) 0.2 to 0.3 wt%

Vanadium is an element that is added to improve the strength of the material by depositing fine carbonitrides, if the vanadium content is 0.3% by weight or more may increase the brittleness and increase the price, 0.2% by weight or less can not achieve the desired fatigue strength .

(Iii) Calcium (Ca) 0.001 to 0.005 wt%

Calcium is an element that can improve the processability by adding a trace amount, the calcium content is 0.005% by weight or more may form inclusions, and the strength may be reduced, and if the content is 0.001% by weight or less, the function may be insignificant.

(Ⅸ) Magnesium (Mg) 0.0005 ~ 0.03 wt%

Magnesium is an element having the same cutting effect as calcium, and if the magnesium content is 0.03% by weight or more, there is a concern that the cost may be excessively increased. If it is 0.0005% by weight or less, it is difficult to secure the improvement of workability due to the formation of an emulsion.

(Iii) 0.001 ~ 0.1 wt% of titanium

Titanium is an element that generates carbonitride to increase yield strength and fatigue strength due to grain refinement, and when titanium is 0.1 wt% or more, it may lead to dropping, and when it is 0.001 wt% or less, production may be insufficient.

(Iii) 0.01 to 0.03 weight percent of nitrogen,

Nitrogen is an element that has a great influence on the mechanical properties of steel even in the presence of extremely small amounts, which increases tensile strength, yield strength and lowers elongation. If the nitrogen content is more than 0.03% by weight may cause a decrease in strength, if less than 0.01% by weight it may be impossible to produce fine precipitates in combination with vanadium, titanium and the like.

(Ivii) Remainder of iron (Fe)

Iron (Fe) is composed of the remainder (殘部) that is the remainder of the above-described components, if the iron is more than or less than the balance, the ratio of the other components is reduced and the implementation of the function through the other components may be insignificant there is a problem.

(Ⅹⅲ) Chromium (Cr), molybdenum (Mo), nickel (Ni)

Chromium is a ferritic stainless steel stabilizing element, molybdenum is an element that improves hardenability and heat resistance, and nickel is an element that improves hardenability and increases the toughness of the structure. These elements cause workability deterioration and material rise due to hardness increase, and are limited to the impurity concept.

Hereinafter, look at the test example to confirm the superiority of the high-strength non-alloy steel according to the present invention.

Test Example 1

Table 1 below shows a comparison between the high-strength amorphous steel having a composition according to the present invention and a rolled material applied in the prior art, and Table 2 shows the measured mechanical properties of the prepared high-strength non-steel.

[Table 1] Chemical Composition (wt%)

[Table 2] Mechanical Properties

In Table 1, Example is a high-strength non-steel is composed of a chemical component according to the present invention, Comparative Example 1 is a high-carbon amorphous steel according to the prior art that is widely used as a material for breaking split cone rod, Comparative Example 2 is a commercial cone It is a crude alloy steel according to the prior art mainly used as a rod material. For the evaluation of these steels were made of rolled material by electric steelmaking, continuous casting, hot pressure.

In Table 2, the test material is a RB60mm rolled material using the rolled material RB60mm Example 1 and Comparative Example 1 was heated to 1200 ° C and cooled to air or forced air cooling conditions for the production of similar material similar to the non-steel forging conditions, Comparative Example 2 is a crude alloy steel The specimens were fabricated under similar heat treatment conditions.

As a result of evaluation of the test material properties, it was confirmed that the Example can be advantageously applied to the forging method by reducing the toughness compared to Comparative Examples 1 and 2 in the forced air cooling conditions, and the tensile strength and the yield strength are increased to improve the endurance fatigue characteristics. Could know.

Test Example 2

1 is a view showing the drillability evaluation results by comparing the high-strength non-thick steel for connecting rods according to the present invention and the prior art.

As shown in Figure 1, the embodiment was confirmed that the drill holes in all the processing conditions compared to Comparative Examples 1 and 2 have excellent workability. Here, the drill odd number means an odd number that can be processed until one tool wears and breaks. As a result, it was found that the cost reduction due to the reduction of tool life during the machining of the connecting rod large end bolt hole and the reduction of the strain at the breakage due to the reduction of stress due to the small machining load.

Test Example 3

Figure 2 is a view showing the drill workability evaluation results by comparing the high-strength non-ferrous steel for connecting rods according to the present invention and the prior art. In particular, Figure 2 shows the degree of wear of the tool, when turning in the same conditions as in FIG.

As shown in FIG. 2, the wear depth of the tool processed in the embodiment was the smallest, so that it showed the best processing characteristics at the inner diameter of the cone rod / small end.

Test Example 4

Figure 3 is a view of evaluating the permanent strain of the material by comparing the high-strength amorphous steel for connecting rods according to the present invention and the prior art. Here, the roundness of the inner diameter can be estimated by evaluating the permanent strain of the material, the specimen is used to evaluate the permanent strain, the test method is evaluated by the amount of deformation when deformed at a speed of 100mm / sec in a high-speed tensile tester.

As shown in FIG. 3, the fracture splitting connecting rod is manufactured through a process of breaking, recombining, and assembling using a manrail after integral forging of the rod and the cap part. One of the characteristics that affects the fatigue strength. In order to improve such adhesion, the amount of deformation of the inner diameter after breaking should be small. In the test, the permanent strain of the Example and Comparative Example 1, it was found that the Example has a smaller strain than the Comparative Example 1, so that it is easy to break the cone rod.

Test Example 5

4 is a view showing a cooling curve after forging connecting rod forging by comparing the high-strength non-thick steel for connecting rod according to the present invention and the prior art, Table 3 below shows the evaluation results of the properties of the connecting rod forging material manufactured under the conditions of FIG. Table shown.

[Table 3] Property evaluation results

As shown in FIG. 4 or Table 3, the non-coated steel can obtain the required characteristics according to the control cooling conditions, and in the case of the embodiment was controlled cooling by increasing the cooling rate in the A1 transformation point section after trimming compared to Comparative Example 1. In Comparative Example 1, when the cooling rate is the same as that of the example, high-hardness structures other than the required ferrite + pearlite structures are generated, which may adversely affect workability and fracture characteristics. In this test, the Example showed higher tensile strength and yield strength values than Comparative Example 1, it was confirmed that excellent fatigue durability characteristics.

Although the present invention has been described in detail using the preferred embodiments, the scope of the present invention is not limited to the specific embodiments, and should be interpreted by the appended claims. In addition, those skilled in the art should understand that many modifications and variations are possible without departing from the scope of the present invention.

1 is a graph showing the drillability evaluation results by comparing the high-strength non-thick steel for connecting rods according to the present invention and the prior art.

Figure 2 is a graph showing the drillability evaluation results by comparing the high-strength non-thick steel for connecting rods according to the present invention and the prior art.

Figure 3 is a graph evaluating the permanent strain of the material by comparing the high-strength amorphous steel for connecting rods according to the present invention and the prior art.

Figure 4 is a graph showing a cooling curve after forging connecting rod by comparing the high-strength non-thick steel for connecting rod according to the present invention and the prior art.

Claims (2)

By weight%, carbon (C) 0.32-0.38, silicon (Si) 0.50-0.90, manganese (Mn) 0.90-1.20, phosphorus (P) 0.005-0.10, sulfur (S) 0.06-0.10, aluminum (Al) 0.04- 0.01, vanadium (V) 0.2 to 0.3, calcium (Ca) 0.001 to 0.005, magnesium (Mg) 0.0005 to 0.03, titanium (Ti) 0.001 to 0.1, nitrogen 0.01 to 0.03, and the balance of iron (Fe) and High-strength amorphous steel for connecting rods having a composition containing impurities. The method according to claim 1, The impurity is a high-strength non-ferrous steel for the connecting rod composed of 0.3% by weight, Cr (Cr) or less, Molybdenum (Mo) or less, 0.1 or less nickel (Ni).

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