KR20090049642A - High strength microalloyed steel composition for connecting rod and manufacturing of fracture splittable connecting rods using the same - Google Patents

Abstract

The present invention relates to a high-strength non-coated steel composition and a connecting rod manufacturing method using the same, and more particularly, to replace the existing coarse steel and non-coated steel for manufacturing the connecting rod, it is possible to realize a weight reduction according to cost reduction and fatigue strength improvement It relates to a high strength non-coated steel composition and a connecting rod manufacturing method using the same.

To this end, the present invention is based on iron (Fe), carbon (C) 0.30 to 0.40% by weight, silicon (Si) 0.50 to 0.80% by weight, manganese (Mn) 0.90 to 1.20% by weight, phosphorus (P) ) 0.045 wt% or less, sulfur (S) 0.06 to 0.10 wt%, chromium (Cr) 0.30 wt% or less, molybdenum (Mo) 0.10 wt% or less, nickel (Ni) 0.20 wt% or less, aluminum (Al) 0.040 wt% Hereinafter, the material composed of 0.10 to 0.30% by weight of vanadium (V) and 0.05 to 0.3% by weight of nitrogen (N) is melted to form a molten metal, followed by continuous casting through deoxidation, desulfurization, and vacuum degassing. Manufacturing the cast material through a process; Reheating the cast material to 1100 ° C. or more to produce a rolled material through a rolling process; Reheating the rolled material to 1200 ° C. or higher, then performing forging molding at 1100 ° C. or higher, and then performing trimming processing; Cooling to 80 to 200 ° C./min from 1100 ° C. to 600 ° C. after the trimming, and performing controlled cooling to form a ferrite + pearlite two-phase structure; Processing the control-cooled forged material into the connecting rod, but notifying the inner diameter of the large end of the connecting rod to perform a forced fracture to manufacture the final connecting rod; It provides a method for producing a fractured split connecting rod using a high strength non-coated steel composition, characterized in that made.

Non-Steel Steel, Break Split, Connecting Rod, Rolled Material, Forgings, Casting Materials

Description

High Strength Microalloyed Steel composition for Connecting Rod and Manufacturing of Fracture Splittable connecting rods using the same}

The present invention relates to a high-strength non-coated steel composition and a connecting rod manufacturing method using the same, and more particularly, to replace the existing coarse steel and non-coated steel for manufacturing the connecting rod, it is possible to realize a weight reduction according to cost reduction and fatigue strength improvement It relates to a high strength non-coated steel composition and a connecting rod manufacturing method using the same.

As a material for manufacturing a vehicle connecting rod, tempered steels and non-quenched steels are used, and domestic and overseas automobile companies use tempered steels and tempered steels having the components shown in Tables 1 and 2 below.

High carbon-based non-coated steel is to reduce the toughness according to the high carbon, and to enhance the strength of the uniform pearlite structure by the appropriate controlled cooling during forging, and the grain boundary is to reduce the fraction of the reticulated ferrite to facilitate the breakage.

However, since the carbon content is high, there is a concern about the deterioration of workability due to high hardness, and there is a limit to the addition of components such as V and Mn for high strength.

Therefore, weight reduction cannot be achieved in the application of a high-power engine that requires a high strength of 45 kgf / mm 2 or more.

In addition, the existing tempered steel (SCM440) has a cost increase of more than 25% per unit compared to forging-split non-thick steel, making it difficult to apply the mass production.

In view of the above, the present invention is to provide a medium-carbon forged split non-coated steel connecting rod capable of realizing high strength compared to existing high carbon-based non-coated steel and achieving cost reduction compared to co-alloyed steel. An object of the present invention is to provide a high-strength non-coarse steel composition capable of improving partitioning properties, securing workability, and a method of manufacturing a split split connecting rod using the same.

One embodiment of the present invention for achieving the above object is: iron (Fe) as a main component, carbon (C) 0.30 to 0.40% by weight, silicon (Si) 0.50 to 0.80% by weight, manganese (Mn) 0.90 to 1.20 wt%, phosphorus (P) 0.045 wt% or less, sulfur (S) 0.06 to 0.10 wt%, chromium (Cr) 0.30 wt% or less, molybdenum (Mo) 0.10 wt% or less, nickel (Ni) 0.20 wt% Hereinafter, 0.040% by weight or less of aluminum (Al), 0.10 to 0.30% by weight of vanadium (V), and 0.05 to 0.3% by weight of nitrogen (N) are provided.

Another embodiment of the present invention for achieving the above object is: iron (Fe) as a main component, carbon (C) 0.30 to 0.40% by weight, silicon (Si) 0.50 to 0.80% by weight, manganese (Mn) 0.90 to 1.20 wt%, phosphorus (P) 0.045 wt% or less, sulfur (S) 0.06 to 0.10 wt%, chromium (Cr) 0.30 wt% or less, molybdenum (Mo) 0.10 wt% or less, nickel (Ni) 0.20 wt% Hereinafter, a material composed of 0.040% by weight or less of aluminum (Al), 0.10 to 0.30% by weight of vanadium (V), and 0.05 to 0.3% by weight of nitrogen (N) is melted into a molten metal, followed by deoxidation, desulfurization, and vacuum degassing. Manufacturing a cast material through a continuous casting process through a clean process through; Reheating the cast material to 1100 ° C. or more to produce a rolled material through a rolling process; Reheating the rolled material to 1200 ° C. or higher, then performing forging molding at 1100 ° C. or higher, and then performing trimming processing; Cooling to 80 to 200 ° C./min from 1100 ° C. to 600 ° C. after the trimming, and performing controlled cooling to form a ferrite + pearlite two-phase structure; Processing the control-cooled forged material into the connecting rod, but notifying the inner diameter of the large end of the connecting rod to perform a forced fracture to manufacture the final connecting rod; It provides a method for producing a fractured split connecting rod using a high strength non-coated steel composition, characterized in that made.

Through the above problem solving means, the present invention can provide the following effects.

By replacing the existing tempered steel, cost savings over QT heat treatment and production cycle time can be achieved, saving more than 25%.

By replacing the existing non-coated steel, it is possible to realize cost reduction by reducing the weight by more than 10% and eliminating the shot peening process by increasing the fatigue strength by 30%.

Hereinafter, the present invention will be described in more detail.

The non-alloyed steel according to the present invention has a compositional component ratio described in comparison with the existing materials in Table 1 below, and the following component design was performed to improve yield strength and fatigue strength, improve breakage property, and processability compared to existing high carbon systems. .

① Strength Improvement (Fatigue Strength, Yield Strength): It is superior in strength to existing non-thick steel, and in order to cope with high-power engines, it is required to have a high strength of 45kgf / mm2 or more, which can replace SCM440 grade alloy steel. In order to refine the grain size, the content of V, Si, Mn was increased.

② Improvement of fracture splitting: In order to secure a structure having good fracture splitting characteristics, grain breakdown must occur at the time of fracture splitting, not ductile fracture. In order to increase the V and Si content, ferrite was strengthened, and pearlite and grain boundaries were dropped to promote grain boundary fracture.

③ Processability: Machinability is important for cost reduction and productivity in the machining process. Conventional non-steel has a high C content and has limited workability. Therefore, to reduce the C content and increase the S content in the non-coated steel of the present invention was to secure the processing characteristics or more equivalent to the existing material.

Here, the main components of the present invention and the reason for limitation of the content are described as follows.

1) Carbon (C) 0.30 ~ 0.40 wt%

Carbon is the element that most affects hardenability. It is the main element that increases the strength and enables heat treatment. However, carbon has an adverse effect on the workability when it is added more than 0.40% by weight. Therefore, carbon should be added in the range of 0.30 to 0.40% by weight. .

2) Silicon (Si) 0.50 ~ 0.80 wt%

Silicon was added to increase the ferrite strengthening effect and the fatigue strength, and to reduce the toughness that facilitates the fracture splitting of the connecting rod, and was limited to 0.50 to 0.80 wt% in the present invention.

3) Manganese (Mn) 0.90 ~ 1.20 wt%

Manganese (Mn) was added to secure strength due to the solid solution strengthening effect, and the content was limited to 0.90 to 1.20% by weight because segregation could be generated.

4) Phosphorus (P) 0.045 wt% or less

Phosphorus is an impurity concept. In other words, it is good to be absent, but due to problems in steelmaking technology, the upper limit is generally restricted.

5) Sulfur (S) 0.06 ~ 0.10 wt%

Sulfur (S) is an element that combines with Mn in the steel to form MnS inclusions to improve the processability, and was added to improve the processability. When excessively added, the sulfur (S) is limited to 0.06 to 0.10 wt%.

6) chromium (Cr) 0.30% by weight or less

Chromium was added to improve strength, and in the present invention, the upper limit is limited to 0.30% by weight or less.

7) Molybdenum (Mo) 0.10 wt% or less

Molybdenum was added to improve the strength, in the present invention will be limited to 0.01% by weight.

8) Nickel (Ni) 0.20 wt% or less

Nickel is a representative element that is added to improve the high temperature properties, and when added, it is an element that greatly affects not only strength but also elongation and ductility at high temperatures, but is limited to 0.02 weight or less because the price is very expensive.

9) Aluminum (Al) 0.040 wt% or less

High aluminum content causes austenite coarsening, so it is limited to 0.040% by weight or less in the present invention.

10) Vanadium (V) 0.10 ~ 0.30 wt%

Vanadium was added because it precipitates fine carbonitrides to improve the strength of the material, in the present invention will be limited to 0.1 to 0.30% by weight.

11) Nitrogen (N) 0.05 ~ 0.3 wt%

Nitrogen combines with aluminum to form nitrides in the crude steel. If the content is less than 0.05% by weight, sufficient nitrides are not formed. If the content exceeds 0.3% by weight, the amount of solid solution nitrogen increases and the toughness is impaired. It is preferable to limit it to -0.3 weight%.

Here, a method of manufacturing a connecting rod using the non-coarse steel of the present invention having the composition as described above is as follows.

① Rolling material manufacturing process

Iron (Fe) as a main component, and the material formed in the melt to make a molten, and then produced by casting through a continuous casting process through a clean process through deoxidation, desulfurization, vacuum degassing.

The cast material is reheated at 1100 ° C. or higher to produce a rolled material through a rolling process.

② Forging process: After the rolled material is heated to above 1200 ℃, perform forging molding at above 1100 ℃ and then trimming.

After trimming, controlled cooling is carried out, and cooling is performed at a cooling rate of 80 ~ 200 ℃ / min from 1100 ℃ to around 600 ℃ to form ferrite + pearlite two-phase structure. And precipitation strengthening can be achieved.

After the forging process, the appearance of the connecting rod is shown in FIG.

③ Machining process: Forging material is matched with the required weight and size through turning, milling and drilling process, and forcibly broken by giving notch to the inner diameter of the large end of the connecting rod for coupling with the crank pin.

The broken connecting rod was fastened to a bolt by a constant pressure, and manufactured a finished product by a process such as final turning and milling, and the final manufactured connecting rod is shown in FIG. 2.

Hereinafter, the embodiment of the present invention will be described in more detail with a comparative example, but the present invention is not limited to the following examples.

Example

0.35 wt% carbon (C), 0.70 wt% silicon (Si), 1.00 wt% manganese (Mn), 0.045 wt% phosphorus (P), 0.08 wt% sulfur (S), 0.30 wt% chromium (Cr), molybdenum ( Mo) 0.10% by weight, nickel (Ni) 0.20% by weight, aluminum (Al) 0.040% by weight, vanadium (V) 0.20% by weight, nitrogen (N) 0.1% by weight of the composition as described above, Forging process (forging temperature: 1100 ~ 1300 ℃, cooling conditions: air cooling, forced air cooling), was manufactured by connecting rod through the processing process.

Comparative example

0.70% by weight of carbon (C), 0.30% by weight of silicon (Si), 0.50% by weight of manganese (Mn), 0.045% by weight of phosphorus (P), 0.05% by weight of sulfur (S), 0.20% by weight of chromium (Cr), molybdenum ( Mo) 0.10% by weight, 0.50% by weight of nickel (Ni), 0.010% by weight of aluminum (Al), 0.30% by weight of vanadium (V) as described above through the rolling material manufacturing process, forging process, processing process Made by rod.

Experimental Example 1

After the rolling material manufacturing process, the physical properties of the specimens of the Examples and Comparative Examples, that is, the specimens of the test specimen plate of a certain size were measured using a conventional equipment, and the results are shown in Table 4 below. .

Table 4 above shows the mechanical properties according to the test material conditions of the present invention and the existing material in the rolled state.

The test materials were evaluated by different heating temperature and cooling conditions to find the optimum forging condition. The present invention has tensile strength, yield strength and yield ratio (YS / TS) which affect the fatigue strength at 1200 ℃ quenching condition. High elongation and low impact value affecting breaking splitability were the best conditions.

In addition, the present invention was found that the tensile strength of about 6%, yield strength 31.5%, yield ratio 14% or more higher than 1200 ℃ quenching conditions, the best condition of the existing material.

Experimental Example 2

After the rolling material manufacturing process, the microstructure of the specimens of the Examples and Comparative Examples, that is, the specimens of the test specimen plate of a certain size was observed through an electron microscope, and the results are as shown in FIG. .

In Figure 3, the present invention is a microstructure in the cooling and quenching conditions at 1200 ℃ and the quenching conditions of the existing material, it can be seen that the difference in the microstructure according to the cooling rate difference.

In the quenching condition, the grain size was refined compared to the cooling condition, and the ferrite fraction was reduced by more than 50%, which corresponds to the mechanical property results of Table 4 above.

Experimental Example 3

After the rolling material manufacturing process, the tensile compressive fatigue test for the specimens of the Examples and Comparative Examples, that is, the specimens of the specimen plate of a certain size was measured by a conventional equipment, the results are shown in the graph of FIG. As shown.

As shown in FIG. 4, as a result of the tensile compressive fatigue test of the rolled specimen, the present invention according to the embodiment was found to exhibit a 29% fatigue strength improvement compared to the comparative material according to the comparative example.

Experimental Example 4

After the rolled material manufacturing process and the forging process, the mechanical properties of the forging materials of the Examples and Comparative Examples were measured using a conventional equipment, the results are as shown in Table 5 below.

Table 5 above is a mechanical property result evaluated differently as shown in Figure 5 attached to the cooling conditions in the forging process based on the evaluation results of the test materials conditions for the raw materials of Table 4.

In the quenching condition of the present invention according to the embodiment, the tensile strength was 8%, the yield strength was 11% higher than the air cooling condition, and compared with the quenching condition of the existing material, the tensile strength was 14% and the yield strength was improved by 50%. The results were in good agreement with the evaluation results.

Experimental Example 5

After the rolled material manufacturing process and the forging process, the structure of the forging material of the Examples and Comparative Examples was observed, the results are as shown in the accompanying photo of FIG.

6 is a result showing the microstructure, hardness and the ferrite fraction after forging, the present invention, but the ferrite content is higher than the existing material, but by strengthening the intraoral ferrite structure by the precipitation of V (C, N) according to the high V content, It was found that both the quenching and air-cooling conditions were higher in hardness than the conventional materials, and the quenching structure of the present invention had a higher cooling rate than the air-cooling structure, resulting in increased hardness due to grain refinement and lowering of ferrite fractions. The same mechanical properties were shown.

Experimental Example 6

After fracture of the present invention quenched product according to the embodiment and the existing quenched product according to the comparative example, the fracture surface of the finished workpiece of the connecting rod was observed, the results are as shown in the photo of FIG.

In the present invention, the micro cleavage wave surface according to the microcrystalline grains is observed at both the start and end portions of the break, but the existing material has a large cleavage wave surface, and the fine end wave fracture appears when the break end portion is fast along the grain boundary. It is becoming.

This is due to the formation of a fine cleavage surface at the time of breakage due to the grain refinement due to V (C, N) precipitation, the enhancement of intragranular ferrite structure and the embrittlement of grain boundary due to the increase of V and Si components.

Experimental Example 7

The roundness of the connecting rod according to the embodiment and the comparative example was measured, and the results are shown in Table 6 and FIG. 8.

Table 6 above shows the roundness results between the boring end (a) of the machining process and the bolt assembly process (d) after breaking.

The smaller the deviation value in each process, the better the roundness.

As shown in Table 6, the present invention material quenching product was found to exhibit a roundness equal to or higher than that of the development material air-cooling product and the existing material quenching product.

In addition, as shown in FIG. 8, the developed material quenched product had a smaller roundness after fracture than the existing material quenched product, and it is judged that the developed product quenched product may have good mass productivity.

Fracture splitability is easy because plastic deformation is less likely to occur when the break load, load difference, and parallax are small.Because the break time is small, fracture occurs at both ends of the bolt hole at almost the same time. It is known to be low.

As a result of this test, even if the fracture splitability was evaluated by the splitting condition of the existing material, if the splitting condition suitable for the present invention is selected by showing the result equal to or greater than that of the existing material of the present invention, the large end near the roundness without the plastic deformation is formed. Of course, it is determined that the possibility of failure such as a rod-cap seat mismatch is reduced.

1 is a photograph showing the forging state of the connecting rod,

2 is a photograph showing the finished product of the connecting rod,

Figure 3 is a microstructure photograph of the rolling material specimens of the existing material according to the present invention and the comparative example according to the embodiment,

Figure 4 is a graph showing the tensile compressive fatigue test results of the rolling material specimens of the present invention and the existing material according to the comparative example according to the embodiment,

5 is a schematic diagram illustrating a manufacturing process of a forging material according to an embodiment;

Figure 6 is a photograph showing the forging material structure of the present invention according to the embodiment and the existing material according to the comparative example,

7 is a photograph comparing the wavefront of the fracture split connecting rod according to the present invention and the fracture surface of the fracture split connecting rod according to the comparative example;

Figure 8 is a graph comparing the roundness of the broken split connecting rod according to the present invention and the broken split connecting rod according to the comparative example.

Claims (2)

Iron (Fe) as a main component, 0.30 to 0.40% by weight of carbon (C), 0.50 to 0.80% by weight of silicon (Si), 0.90 to 1.20% by weight of manganese (Mn), 0.045% by weight or less of phosphorus (P), Sulfur (S) 0.06 to 0.10 wt%, Chromium (Cr) 0.30 wt% or less, Molybdenum (Mo) 0.10 wt% or less, Nickel (Ni) 0.20 wt% or less, Aluminum (Al) 0.040 wt% or less, Vanadium (V) 0.10 to 0.30% by weight, 0.05 to 0.3% by weight of nitrogen (N) is characterized in that the high-strength amorphous steel composition. Iron (Fe) as a main component, 0.30 to 0.40% by weight of carbon (C), 0.50 to 0.80% by weight of silicon (Si), 0.90 to 1.20% by weight of manganese (Mn), 0.045% by weight or less of phosphorus (P), Sulfur (S) 0.06 to 0.10 wt%, Chromium (Cr) 0.30 wt% or less, Molybdenum (Mo) 0.10 wt% or less, Nickel (Ni) 0.20 wt% or less, Aluminum (Al) 0.040 wt% or less, Vanadium (V) Melt the material composed of 0.10 ~ 0.30% by weight and 0.05 ~ 0.3% by weight of nitrogen (N) to make molten metal, and then clean it through deoxidation, desulfurization and vacuum degassing to cast material through continuous casting process. Manufacturing step; Reheating the cast material to 1100 ° C. or more to produce a rolled material through a rolling process; Reheating the rolled material to 1200 ° C. or higher, then performing forging molding at 1100 ° C. or higher, and then performing trimming processing; Cooling to 80 to 200 ° C./min from 1100 ° C. to 600 ° C. after the trimming, and performing controlled cooling to form a ferrite + pearlite two-phase structure; Processing the control-cooled forged material into the connecting rod, but notifying the inner diameter of the large end of the connecting rod to perform a forced fracture to manufacture the final connecting rod; Breaking connecting rod manufacturing method using a high-strength non-coarse steel composition, characterized in that made.

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