KR101173054B1 - Alloy compound composite for connecting rod and menufacturing method for connecting rod using it - Google Patents

Abstract

The present invention relates to an alloy powder composition for a connecting rod having improved mechanical properties such as yield strength, and a method for manufacturing a connecting rod using the same, in particular, carbon (C) 0.45 to 0.75 wt%, and chromium (Cr) 1.40 to 1.60 wt% , Molybdenum (Mo) 0.15 ~ 0.25% by weight, Manganese (Mn) 0.3 ~ 0.5% by weight, Sulfur (S) 0.05 ~ 0.15% by weight, and alloy powder composed of residual iron (Fe) and other unavoidable impurities Forming a preform by pressing in a press after the injection;
Sintering the preform in a sintering furnace;
Forging the sintered preform by forging in a forging press die;
Cooling the forged preform in a nitrogen atmosphere;
It includes, and lowers the Cr content to 1.5% by weight in the composition of Astaloy CrM (Fe-3.0Cr-0.5Mo) used in the existing sintering gears, it is possible to suppress the oxidation and increase the strength in the general atmosphere sintering furnace It provides a method of manufacturing a connecting rod using the alloy powder composition for a connecting rod.

Description

Alloy powder composition for connecting rod and manufacturing method of connecting rod using same {Alloy compound composite for connecting rod and menufacturing method for connecting rod using it}

The present invention relates to an alloy powder composition for a connecting rod and a method for manufacturing a connecting rod using the same, and to an alloy powder composition for a connecting rod with improved mechanical properties such as yield strength and a method for manufacturing a connecting rod using the same.

In general, the connecting rod for an automobile engine is composed of a small end coupled to the piston pin, a large end coupled to the crankshaft, and a rod portion integrally connecting the small end and the large end, It converts the linear reciprocating motion of the piston into rotational motion.

The semi-circular cap is detachably attached to the said large end part by a bolt.

Since the connecting rod receives loads such as compressive force, tensile force and bending repeatedly, it is necessary to have sufficient strength and rigidity to withstand it.

These connecting rods are also manufactured through hot forging process, but most of them are powder forging materials (Fe-2Cu-0.5C; HPF80) or high strength materials (Fe-3Cu-0.5C; HS150) to reduce the labor and improve the material yield. Sintered products are made using metal powders.

In the conventional method of manufacturing a connecting rod using a metal powder, as shown in FIG. 1, a metal powder of high strength material (HS150; Fe-3Cu-0.5C composition) is put into a mold and compressed to have a density of 6.7 to 6.8 g / cm 3. Shaping the preform of the; Presintering the preform at 930-950 ° C. for 10-20 minutes, and sintering the preform at 1230 ° C.-1250 ° C. for 20 minutes; The heat-sintered sintered product is subjected to compression forging at a density of 7.8 g / cm 3 in a forging press die while being cooled to 900 ° C. to 1000 ° C.

Subsequently, the compression-forged sintered product is cooled with air, the burrs of the corners of the product produced during compression forging are removed, and then oxides on the surface of the product are removed by a shot blast or shot peening method. .

On the other hand, automotive engines in recent years directly inject fuel into a cylinder to satisfy high fuel consumption and environmental regulations (emission gas). Gasoline Direct Injection (GDI) / Turbo Gasoline Direct (TGDI) Injection method is adopted.

Injecting fuel directly into the cylinder in the engine of the GDI / TGDI system generates a higher combustion pressure than the conventional MPI (Multi Point Injection) method, the generated combustion pressure is transmitted to the piston, the connecting rod is tension and The compressive load is continuously and repeatedly received.

However, the conventional powder forging (HPF80) connecting rod has been applied to an MPI engine that requires low combustion pressure, but lacks mechanical properties (tensile strength, yield strength, fatigue strength) and requires high combustion pressure. Difficult to apply to GDI / TGDI engine.

In addition, since the sintering temperature for sufficiently solidifying 3% by weight of Cu in the composition of the metal powder for manufacturing the connecting rod is 1250 ° C, the sintering temperature of the current mass production sintering furnace is 1120 ° C. Not enough to hire

Therefore, after sintering the sintered product, Cu precipitates on the surface of the sintered product during cooling to reduce the fatigue strength of the connecting rod, and when a new high-temperature sintering furnace equipment is introduced, Due to this, there is a problem in that additional costs are required and cost increases.

The present invention has been invented to solve the above problems, by applying a high-strength alloy powder of Fe-1.5Cr-0.2Mo composition in place of the conventional forging material for manufacturing a connecting rod or powder of a high-strength material, thereby improving mechanical properties It is an object of the present invention to provide an alloy steel composition for a connecting rod that can be applied to a GDI / TGDI type engine, and the sintering temperature is also lowered to 1120 ° C. and a method for manufacturing a connecting rod using the same.

In order to achieve the above object, the present invention is a carbon (C) 0.45-0.75% by weight, chromium (Cr) 1.40-1.60% by weight, molybdenum (Mo) 0.15-0.25% by weight, manganese (Mn) 0.3-0.5% by weight Forming a preform by injecting an alloy powder composed of%, sulfur (S) of 0.05 to 0.15 wt% or less, and a residual amount of iron (Fe) and other unavoidable impurities into a mold and then pressing the mold with a press;

Sintering the preform in a sintering furnace;

Forging the sintered preform by forging in a forging press die;

Cooling the forged preform in a nitrogen atmosphere;

It includes, and lowers the Cr content to 1.5% by weight in the composition of Astaloy CrM (Fe-3.0Cr-0.5Mo) used in the existing sintering gears, it is possible to suppress the oxidation and increase the strength in the general atmosphere sintering furnace It provides a method of manufacturing a connecting rod using the alloy powder composition for a connecting rod.

Here, by injecting nitrogen gas into the preform when the preform is transferred from the sintering furnace to the forging press, it is possible to minimize the surface oxide of the sintered body, and to reduce the temperature of the molded body from 1120 ℃ to 1000 ℃ to refine the structure by the forging pressure To contribute (dynamic re-determination).

In addition, by cooling the preform at a rate of 0.8 ~ 1.2 ℃ / s in a nitrogen atmosphere, it is possible to reduce the oxidizing properties and improve the workability.

In addition, an oxide layer having a thickness of 5 to 15 μm may be formed on the notch having the inner diameter of the large end portion of the preform, and the oxide layer may act as a notch when breaking the fracture, thereby facilitating breaking.

Referring to the advantages of the alloy powder composition for a connecting rod according to the present invention and a manufacturing method of a connecting rod using the same.

1. GDI / TGDI method that requires high combustion pressure by improving the mechanical properties such as yield strength by using high strength alloy powder alloyed with Cr and Mo on Fe base as a material, and manufacturing it through molding, sintering, forging and slow cooling process. Applicable to the engine.

2. It is possible to sinter in current mass production sintering furnace by reducing Cr content and use of reducing atmosphere gas, so it is not necessary to introduce equipment and change line of high temperature sintering furnace (1250 ℃), thus reducing cost.

3. It is possible to lighten the connecting rod to improve fuel economy, power and noise.

4. By spraying nitrogen gas during the transfer of the preform from the sintering furnace to the forging press, the surface oxide can be minimized, and the temperature of the molded body can be reduced, thereby contributing to the refinement of the structure by the forging pressure.

5. When transferring the sintered preform to a forging press, an oxide layer having a thickness of 5 to 15 µm is formed on the notch of the inner diameter of the large end of the preform, thereby improving the breaking splitability.

1 is a block diagram showing a manufacturing method of a connecting rod according to the prior art
2 is a schematic view showing the Cr-Mo Pre-alloy powder for the connecting rod according to the present invention
3 is a process diagram showing a manufacturing method of a connecting rod according to an embodiment of the present invention.
4 is a block diagram showing a manufacturing method of a connecting rod according to the present invention.
Figure 5 is a schematic diagram showing a deformation state of the molding notch in the manufacturing process of the present invention
Figure 6 is an enlarged photograph of the molding notch part after forging in Figure 5
Figure 7 is an enlarged photograph showing the microstructure of the development material and the conventional material of the present invention
8 is a graph showing the tensile yield strength according to the material trend and microstructure of the connecting rod

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

2 is a schematic view showing a Cr-Mo Pre-alloy powder for a connecting rod according to the present invention, Figure 3 is a process diagram showing a manufacturing method of a connecting rod according to an embodiment of the present invention, Figure 4 is a connecting according to the present invention It is a block diagram showing the manufacturing method of the rod.

The present invention relates to a manufacturing method of the connecting rod 20 by improving the mechanical properties by manufacturing by sintering a high-strength metal powder composed of Fe, Cr, Mo, C and the like.

The alloy powder used as a material of the connecting rod 20 in the manufacturing process of the present invention is a powder alloyed with Cr and Mo in Fe base, as shown in Figure 2, in particular carbon (C) 0.45 ~ 0.75% by weight, chromium (Cr) 1.40-1.60 wt%, molybdenum (Mo) 0.15-0.25 wt%, manganese (Mn) 0.3-0.5 wt%, sulfur (S) 0.05-0.15 wt% or less, and residual iron (Fe) and other unavoidable It is composed of impurities.

The content and the purpose of the alloy powder is as follows.

1.Carbon (C) 0.45 ~ 0.75 wt%

The carbon is a main element that increases the strength and enables heat treatment, and when the carbon content is less than 0.045% by weight, carbonized precipitates such as ferrite-perlite are formed, which is a factor of lowering strength such as fatigue strength. When the content of carbon exceeds 0.75% by weight, the forging pressure is increased due to the increase in hardness of the sintered material, and the workability is decreased, and it is preferable to add carbon within the range of 0.45 to 0.75% by weight.

2. Chromium (Cr) 1.40 ~ 1.60 wt%

Since the chromium is added to improve the strength, the strength is lowered when the chromium content is insufficient, the ferrite-perlite is produced, when the chromium content is too high, the forging pressure is increased, and the workability is lowered. It is preferable to add chromium in the said 1.40-1.60 weight% range.

3. Molybdenum (Mo) 0.15 ~ 0.25 wt%

Since the molybdenum is added for strength improvement, the strength is reduced when the content of molybdenum is insufficient, the ferrite-perlite is produced, when the content of molybdenum is too high, the forging pressure is increased, and the workability is decreased. It is preferable to add molybdenum in the said 0.15-0.25 weight% range.

4. Manganese (Mn) 0.3 ~ 0.5 wt%

The manganese is added to secure the strength due to the solid solution strengthening effect, and when the content of manganese is too high fatigue strength and elongation is lowered, it is preferable to add manganese within the 0.3 to 0.5% by weight.

Mn and S to be added are molded and sintered by mixing with the raw material powder in the state of MnS compound (powder), and even in the sintering condition, Mn and S do not separate and exist in MnS state, and usually 0.35% by weight of MnS is added.

At this time, when the MnS deviates from 0.3 to 0.5% by weight, problems in fatigue strength deterioration and workability occur.

5. Sulfur (S) 0.15 wt% or less

Sulfur is an element that combines with Mn to form MnS inclusions in steel to improve workability, and is added to improve workability. When sulfur is excessively added, sulfur is excessively formed to limit the sulfur to 0.15% by weight or less. desirable.

In this case, nickel (Ni) is an impurity generated during powder manufacturing, and is limited to 0.10% by weight or less.

The raw material of the alloy powder according to the present invention is Astaloy CrM (3.0Cr-0.5Mo-Fe-based composition), which is a pre-alloy powder developed by Hoeganes Sweden, and this pre-alloy powder is mainly used for transmission SYNC in Europe and North America. -HUB, used for sintered gears (density: 6.8 ~ 7.2), not developed for connecting rod.

In addition, in the present invention, the content of chromium is reduced to 1.5% by weight compared to Astaloy CrM (3.0Cr-0.5Mo-Fe based composition) used in conventional sintered gears, and reducing atmosphere (H ₂ : N ₂ = 1: 9) By sintering at, oxidation can be suppressed and strength can be increased.

In the case of bonding chromium to molten iron powder of the conventional molybdenum, oxidative property is a problem during manufacturing and sintering, but in the present invention, oxidative property is significantly reduced when chromium and molybdenum are melted and homogenized together with pure iron.

In the case of the conventional HS150 (Fe-3.0Cu-0.5C), when the alloying element Cu is sintered, the microstructure and the hardness are uneven as the alloy is diffused into the known powder, but the alloy powder for the connecting rod 20 according to the present invention is uniform. Silver is a powder in which Cr and Mo are alloyed with Fe base, and the microstructure and hardness are uniform.

Next, a method of manufacturing the connecting rod 20 using the metal powder material of the composition and content is as follows.

The manufacturing method of the connecting rod 20 proceeds in the order of molding, sintering, forging, slow cooling, deburring and processing the powder.

1. Molding

The connecting rod is formed by injecting a metal powder of the composition and content into a molding die by pressing the mold at a normal temperature, and the small end 11, the large end 13, the rod 12, and the cap 15 are integrally formed. The preform 10 (preform) of the same shape as (20) is produced.

At this time, it is necessary to form the notch 14 on the inner diameter surface of the preform 10 with a core mold in order to break the large end 13 and the cap 15 later.

The density of the preform 10 is reduced to 6.3 to 6.5 g / cm 3, whereby grain growth (growth of powder and powder) can be suppressed as much as possible.

2. Sintered

For the purpose of chemical bonding between powders, weakly bonded preforms (10) in a sintering atmosphere of 1120 ~ 1140 ℃ sintering gas, that is, gas containing H ₂ : N ₂ = 5 ~ 15: 85 ~ 95 ratio Sinter for 20-25 minutes using.

The sintering refers to a phenomenon that when the powder compact is heated at a temperature equal to or lower than the melting point, bonds between the powder particles are formed to harden into a shaped shape, and the strength of the preform 10 is increased during sintering.

After the sintered preform 10 is transferred from the sintering furnace to the forging press, the gas nozzle is disposed at the small end 11 and the large end 13 of the preform 10 at the time of transfer to the forging press. The N ₂ gas is blown into the hot preform 10 through the gas nozzle so that nitrogen gas flows in the longitudinal direction of the preform 10 while covering the surface of the sintered body, thereby suppressing oxidation of the preform 10. By lowering the temperature of the preform 10 from 1120 ° C. to 1000 ° C., the preform 10 may contribute to tissue refinement by forging pressure.

At this time, the oxidation of the preform 10 is not completely blocked by nitrogen gas injected through the gas nozzle, and when the high temperature preform 10 is transferred from the sintering furnace to the forging press, a small amount of the oxide layer 16 Formed on the surface of the preform 10, this minor amount of surface oxide is rather helpful in terms of fracture splitting.

As described above, the trace amount of the oxide layer 16 formed on the surface of the preform 10 is removed from the surface of the preform 10 by a forging process, which is a subsequent step, except that the large end 13 of the preform 10 is formed. The oxide layer 16 formed in the notch 14 of the inner diameter is left in the large end 13 of the preform 10 in a folded state without being removed by the forging process.

Therefore, after the forging, the notched portion 14 of the inner diameter of the large end 13 of the preform 10 is folded and deformed into a sharp crack by the oxide layer 16 remaining in the notched portion 14. Fracture splitting can be facilitated starting from a crack.

Here, the blow amount of N ₂ gas is appropriately adjusted in the preform 10, and the oxide layer 16 having a thickness of 5 to 15 µm is formed in the notch 14 of the inner diameter of the large end 13 of the preform 10. ), The large end portion 13 of the preform 10 can be easily broken in a later processing step.

At this time, if the amount of the N ₂ gas is blown too much, the formation of the oxide layer 16 is weak. If the amount of the N ₂ gas is blown too little, the oxide layer 16 becomes excessive, and forging and cooling of the base metal adjacent to the oxide layer 16 during forging. Is reacted with the oxide layer 16 to decarburize the surface, and an excessively ductile wavefront is excessively formed when the fracture is broken in the decarburized region generated at the end of the notch 14.

Figure 5 is a schematic view showing a deformation state of the molding notch in the manufacturing process of the present invention, Figure 6 is an enlarged photograph showing a state in which the molding notch portion is folded after forging in FIG.

3. Forging

After the molding and sintering process, the preform 10 is placed on a forging press die, and a constant molding pressure is applied to increase the overall density to 7.75 g / cm 3 or more.

At this time, if a closed die is used as the forging press die, the notch may be easily applied, and burr generation may be reduced compared to an open die.

4. Cooling

After the sintering and forging process, the preform 10 is slowly cooled at a cooling rate of 0.8 to 1.2 ° C./s in an N ₂ atmosphere to prevent oxidation and decarburization.

If the cooling rate of the preform 10 is less than 0.8 ° C./s, a decarburization area is formed on the surface of the preform 10 by 0.15 mm or more, thereby reducing the strength due to the reduction of carbon in the preform 10. If the cooling rate of the preform 10 exceeds 1.2 ° C / s, there is a problem that the surface of the preform 10 is hardened to reduce the workability of the preform 10 in the cooling rate range It is preferable to cool slowly.

5. Burr Removal

After finishing the forging and cooling process of the preform 10, a burr of the corner portion of the preform 10 generated during forging is removed using a tool for removing burr.

6. Short blast

A small diameter shotball is collided on the surface of the preform 10 to remove foreign substances such as rust generated on the surface of the preform 10.

7. Processing

The notch portion 14 formed on the inner end surface of the large end portion 13 of the preform 10 is broken and divided into a large end portion 13 and a cap portion 15.

The breaking division method of the large end part 13 of the preform 10 uses a laser notch method, a broaching notch method, a molding notch method and the like.

At this time, the breaking connecting rod 20 by using the molding notch method has an advantage in breaking conditions, processing conditions, karate and the like compared to other notch methods.

The preform 10 formed using the metal powder of the composition and content is manufactured as a connecting rod 20 through a process such as sintering, forging, slow cooling, and processing.

As the weight of the connecting rod 20 manufactured by the above manufacturing method is reduced, the limit load of the crankshaft and the size of the crankshaft are reduced, and the maximum rotation speed of the crankshaft is increased.

In addition, by reducing the reciprocation and rotational inertia of the crankshaft, reducing the vibration of the engine, and reducing the frictional resistance of the bearing, it is possible to lower the fuel consumption rate and improve the noise and power.

Hereinafter, the present invention will be described in more detail by the following examples, but the present invention is not limited by the following examples.

Examples and Comparative Examples

As shown in Table 1, the preform 10 after the sintering process in the manufacturing method of the connecting rod 20 has different mechanical properties and microstructures according to the cooling rate and the carbon content.

As shown in Table 1, as the carbon content increases, the core hardness, the yield strength, the tensile strength increases, and the elongation decreases.

7 is an enlarged photograph showing the particle size of the development material (Fe-1.5Cr-0.2Mo) and the conventional material (HS150; Fe-3Cu-0.5C) according to the carbon content of the present invention at a level of about 10 to 15 μm or less. .

As shown in Figure 7 (a) to Figure 7 (c), the development material of the present invention has a finer particle size than the conventional material (Fig. 7 (d)).

Table 2 shows the composition and content of the development material and the conventional material used in manufacturing the connecting rod 20 of the present invention, Table 3 shows the mechanical properties of the material before forging.

Using the material of the composition and content shown in Table 2, but in the case of the embodiment was applied to the connecting rod manufacturing method according to the present invention, in the case of the comparative example was applied to the connecting rod manufacturing method according to the prior art to produce a connecting rod 20, After measuring the mechanical properties, the results are shown in Table 3.

Table 4 below is a table comparing the process parameters of the present invention and the conventional comparative example.

In the embodiment, as described above, the metal powder (chromium-molybdenum alloy powder) is compression molded to a density of 6.4 g / cm 3 to make the preform 10, and then the preform 10 is H ₂ ; N ₂ = Sintering is carried out in a sintering furnace at a temperature of 1130 ° C. in a 10:90 ratio gas atmosphere, and a forging is performed at a density of 7.8 g / cm 3 by applying a constant molding pressure to the preform 10 using a closed forging press die. .

At this time, the N ₂ gas is injected into the preform 10 after the sintering process during the transfer from the sintering furnace to the forging press to prevent the surface from being oxidized and decarbonized.

Subsequently, after the sintered and forged preform 10 is cooled slowly at a cooling rate of 1.0 ° C./s in an N ₂ gas atmosphere, deburring, shot blasting and processing are performed to manufacture the connecting rod 20 of the embodiment. It was.

On the other hand, in the comparative example, after forming the preform (10) of HS150 (conventional high strength material) and the like at a molding density of 6.8 g / cm3, the preform (10) is H ₂ ; N ₂ = 15: 85 ratio of gas Presintering is carried out in a sintering furnace at a temperature of 940 DEG C in the atmosphere, main sintering at a temperature of 1240 DEG C, and forging to a density of 7.85 g / cm3 using an open forging press die.

Subsequently, after the sintered and forged preforms 10 were cooled by air, deburring, shot blasting, and processing were performed to prepare connecting rods of a comparative example.

As can be seen from the results of Table 3, it can be seen that the embodiment of the present invention has an excellent durability and fatigue performance by increasing the yield strength, the tensile strength and the fatigue strength, compared to the conventional comparative example, the embodiment also in terms of elongation and hardness All showed excellent results compared to the prior art.

8 is a graph showing the tensile yield strength according to the material trend and microstructure of the connecting rod.

As shown, the tensile yield strength of Example 1 (HPF90S) according to the present invention was increased by about 170 MPa than Comparative Example 2 (HPF80), tensile strength of Example 2 (HPF100) than Comparative Example 2 (HPF80) 220 MPa was increased.

10: preform 11: small end
12: rod portion 13: large end
14: notch 15: cap
16: oxide layer 20: connecting rod

Claims (5)

C 0.45-0.75 wt%, Cr 1.40-1.60 wt%, Mo 0.15-0.25 wt%, Mn 0.3-0.5 wt%, S 0.05-0.15 wt%, and the balance of Fe and other unavoidable impurities Alloy powder composition for connecting rod.
An alloy powder composed of 0.45 to 0.75 wt% C, 1.40 to 1.60 wt% Cr, 0.15 to 0.25 wt% Mo, 0.3 to 0.5 wt% Mn, 0.05 to 0.15 wt% S, and remaining Fe and other unavoidable impurities Molding the preform 10 by pressing in a mold and then pressing the mold with a press;
Sintering the preform 10 in a sintering furnace;
Forging the sintered preform 10 by pressing in a forging press die;
Cooling the forged preform (10) in a nitrogen atmosphere;
Method for producing a connecting rod using the alloying powder composition for a connecting rod, characterized in that comprises a.
3. The method according to claim 2, wherein when the sintered preform 10 is transferred to a forging press, nitrogen is injected into the preform 10 to suppress the formation of the surface oxide layer 16 of the preform 10 and the preform 10. Method for producing a connecting rod using the alloying powder composition for a connecting rod, characterized in that cooling.
The surface oxide layer (16) generated in the preform (10) in the process of transferring the sintered preform (10) to the forging press is removed in the forging step, the large end of the preform (10) (13) The surface oxide layer 16 having a thickness of 5 to 15 µm formed in the notch 14 having an inner diameter is folded into a crack while being forged, and broken into fractures based on the crack, and the surface oxide layer 16 The thickness of the manufacturing method of the connecting rod using the alloy powder composition for a connecting rod, characterized in that controlled by the amount of nitrogen injected into the preform (10).
The method of claim 2, wherein the cooling step is performed at a speed of 0.8 to 1.2 ° C./s.

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