JP2006326595A - Bore pin for casting cylinder block - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a bore pin for casting a cylinder block, which bore pin has the longevity longer than that of a bore pin made of a conventional material by reducing its wear caused in its drawing-out by keeping the fitting accuracy between the bore pin and a liner high through reducing the thermal expansion coefficient of the bore pin. <P>SOLUTION: The bore pin for casting the cylinder block is made of a ferrous alloy having a mean thermal expansion coefficient of 8×10<SP>-6</SP>/°C to 11×10<SP>-6</SP>/°C within the range from the room temperature to 100°C, and the ferrous alloy is a high speed steel alloy and is composed of an Fe alloy containing 1.0 to 4.0 mass% of C, 0.1 to 2.0 mass% of Si, 0.1 to 2.0 mass% of Mn, 0 to 4.5 mass% of Ni, 10.0 to 20.0 mass% of Cr, 0 to 9.0 mass% of Mo, 0 to 10.0 mass% of W, and 1.0 to 10.0 mass% of V. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a bore pin used when casting a cylinder block of an automobile engine or the like.

  A cylinder block of an automobile engine is formed by casting a light alloy material such as an aluminum alloy by a die casting method or the like in order to reduce the weight. In the cylinder block, cylinder bores, which are parts where the piston slides, are formed according to the number of cylinders. However, when the cylinder bore is formed of a single light alloy material such as an aluminum alloy, sufficient wear resistance against sliding of the piston cannot be obtained. For this reason, a cylindrical liner (also referred to as a sleeve) made of a wear-resistant material is placed in the cylinder bore portion in the mold during cylinder block molding, and the cylinder bore is formed by casting the liner with a light alloy. Has been made.

  As a liner having excellent wear resistance provided on the inner surface of a cylinder bore, cast iron or a composite material in which reinforcing materials such as silicon carbide particles and reinforcing fibers are dispersed in an aluminum alloy is used.

  When molding a cylinder block with this type of liner, a bore pin (also referred to as a nesting) protrudes into the cavity of the mold, and the liner is fitted into the bore pin and held in the aluminum. Fill with molten metal such as alloy. Examples of prior art relating to such a cylinder block casting bore pin include the following.

  In Patent Document 1, a bore pin for mounting a sleeve is disposed at a position where a cylinder bore in a cylinder block casting mold is to be formed, and the bore pin is moved from the proximal end side to the distal end side along the axial direction thereof. In the cooling structure of the bore pin in which the cooling chamber is formed and the cooling pipe is inserted and disposed on the base end side of the bore pin with the opening end facing the cooling chamber, the position of the opening end of the cooling pipe is A cooling structure of a cylinder block casting bore pin at the position of the mold head cylinder joint joint forming surface or the inner position of the mold near this position when the mold is disposed is described.

  In Patent Document 2, a cylindrical cylinder liner that forms a bore portion is inserted into a casting mold having a bore mold pin that becomes a nest for forming a cylinder bore, and the bore mold pin is inserted. A cylinder block casting method including a step of pouring a molten aluminum alloy into a casting mold, and solidifying by casting. A bore mold pin is formed in a cylinder liner after casting. A cylinder block casting method is described in which the inner surface of the cylinder liner is deformed by the residual stress after casting so that the outer surface is a perfect circle.

  In Patent Document 3, a step of pouring molten aluminum or molten aluminum alloy into a mold having an insert and a flow path of the melt formed by the insert and the inner surface of the mold are rapidly narrowed. The step of flowing through the narrowed narrow passage portion, the step of filling and holding the molten metal in the cavity between the mold and the insert after flowing through the narrow passage portion, and the molten metal filled and held in the cavity are solidified. A step of providing a recess in the end face of the nest adjacent to the niche part and delaying solidification of the melt in the niche part by flowing the melt into the recess. Has been.

JP-A-6-71405 JP 2002-153967 A JP 2002-178133 A

  When molding a cylinder block with a liner as described above, a bore pin is projected into the mold cavity, and the liner is fitted into the bore pin, and the cavity is filled with a molten metal such as an aluminum alloy. To do. Then, after the molten metal in the mold is solidified, the cylinder block in which the liner is cast is taken out from the mold, and the liner is pulled out from the bore pin.

  Therefore, the bore pin is required to have sufficient heat resistance since it is pulled out from the liner made of the wear-resistant material together with sufficient heat resistance. As a conventional bore pin, a hot tool steel equivalent to JIS SKD61, or one that has been subjected to heat treatment such as quenching and tempering and then subjected to soft nitriding treatment to impart heat resistance and wear resistance, etc. is used. Yes.

  On the other hand, since the cylinder bore of the cylinder block is required to have a high precision in the formation position, the bore pin and the liner are closely fitted to each other. Further, the bore pin is heated and expands under the influence of the heat of the molten metal or the mold that is repeatedly used.

  In such a state, when the bore pin and the liner are attached and detached, both are easily gnawed. For this reason, in the conventional bore pin, there is a problem that the wear on the surface of the bore pin becomes remarkable, the accuracy of the formation position of the cylinder bore cannot be maintained well, and the service life is shortened due to damage.

  In view of this problem, the object of the present invention is to reduce the thermal expansion coefficient of the bore pin so that the fitting between the bore pin and the liner is maintained with good accuracy, and the wear during pulling is reduced, thereby reducing the wear of the conventional material. The object is to provide a cylinder block casting bore pin having a longer service life compared to the above.

The bore pin for casting a cylinder block according to the present invention is a bore pin that is used by being fitted into a liner when casting a cylinder block, and has an average coefficient of thermal expansion of 8 × 10 ⁻⁶ / ° C. to 11 × 10 from room temperature to 100 ° C. It is made of an iron-base alloy having a temperature of ⁻⁶ / ° C.

  In the present invention, the iron-base alloy is a high-speed alloy.

  In the present invention, the iron-based alloy is in mass%, C: 1.0 to 4.0%, Si: 0.1 to 2.0%, Mn: 0.1 to 2.0%, Ni: 0 to Fe-based alloy containing 4.5%, Cr: 10.0 to 20.0%, Mo: 0 to 9.0%, W: 0 to 10.0%, V: 1.0 to 10.0% It is characterized by comprising.

  In the present invention, the iron-base alloy further contains at least one of Co: 10.0% or less and Nb: 10.0% or less in terms of mass%.

  In the present invention, the iron-based alloy has a smaller average thermal expansion coefficient from room temperature to 100 ° C. than the liner.

  In the bore block for cylinder block casting of the present invention, the thermal expansion coefficient is made smaller than that of the liner, so that it does not expand, wear during drawing can be reduced, and the alloy is made of a high-speed alloy having excellent wear resistance. Compared to the above, the wear resistance can be remarkably improved.

Generally, the thermal expansion coefficient of cast iron used for a liner is 11 × 10 ⁻⁶ / ° C. to 12 × 10 ⁻⁶ / ° C., whereas the iron-based alloy of the present invention has a thermal expansion coefficient of 8 × 10 ⁻⁶ / ° C. 11 × 10 ⁻⁶ / ° C. and smaller than cast iron.

The iron-based alloy of the present invention is a high alloy material containing a large amount of V and Cr as compared with SKD61 steel, and sufficient wear resistance is obtained because carbides are finely dispersed. Among iron-based alloys, one or more of MC carbide, M ₂ C carbide, M ₆ C carbide, M ₇ C ₃ carbide, M ₄ C ₃ carbide and M ₂₃ C ₆ carbide are compared. Therefore, the wear resistance can be remarkably improved.

Furthermore, in order to ensure hardness, the sum of the area ratios of particularly hard MC-based carbides and M ₂ C-based carbides is preferably 10% or more. Further, if the amount of eutectic carbides in the form of needles or networks is excessive, necessary mechanical properties, particularly toughness, cannot be ensured. However, by properly crystallizing MC carbides, M ₂ C carbides, M ₇ It is possible to cut the C ₃ carbide network to ensure toughness.

  The chemical composition (mass%) of the iron-based alloy related to the bore block for casting a cylinder block of the present invention is preferably in the following range.

C: 1.0-4.0%
C is necessary for the formation of carbide for improving the wear resistance and the improvement of the hardness of the base during quenching and tempering by solid solution in the base. C produces MC, M ₂ C, M ₆ C, M ₇ C ₃ , M ₄ C ₃ , and M ₂₃ C ₆ -based carbides that contribute to improved wear resistance. When C is less than 1.0%, there is little crystallization of carbide effective for improving the wear resistance, and there is not enough C dissolved in the matrix, and sufficient matrix hardness cannot be obtained even by quenching. On the other hand, if it exceeds 4.0%, the carbides become coarse and the amount of crystallization becomes excessive, and the toughness tends to deteriorate.

Si: 0.1 to 2.0%
The Si content is preferably 0.1 to 2.0%. Since Si acts as a deoxidizer and is contained in M ₆ C-based carbide as a solid solution by substituting elements such as W and Mo, it is intended to save expensive elements such as W and Mo. It is effective for. If Si is less than 0.1%, the deoxidation effect is insufficient and casting defects are likely to occur. Moreover, when it exceeds 2.0%, embrittlement tends to occur.

Mn: 0.1 to 2.0%
The Mn content is preferably 0.1 to 2.0%. Mn has a deoxidizing action like Si. Moreover, there exists an effect | action which fixes S which is an impurity as MnS. When Mn is less than 0.1%, deacidification is poor. On the other hand, if it exceeds 2.0%, retained austenite tends to be generated, and sufficient hardness cannot be maintained stably.

Ni: 0 to 4.5%
Ni does not necessarily need to be added, but when added, it has the effect of improving hardenability and increasing hardness. If the Ni content exceeds 4.5%, the retained austenite becomes excessive and high hardness cannot be obtained. A more preferable Ni content is 0 to 2.0%.

Cr: 10.0% to 20.0%
Cr is the most characteristic element of the present invention, and combines with C to crystallize and generate carbides. Further, it dissolves in the matrix and increases the hardness of the matrix, thereby improving the wear resistance.
Further, when Cr exceeds 10.0%, a large amount of chromium carbide (Cr ₇ C ₃ , C ₂₃ C ₆ ) having a low thermal expansion coefficient is generated, and thus the thermal expansion coefficient of the iron-based alloy is 11 × 10 ⁻⁶ / It becomes smaller than ℃. If the carbide content exceeds 20.0%, the toughness decreases, which is not preferable.

Mo: 0 to 9.0%
Mo does not necessarily need to be added, but when added, it combines with C like Cr and produces hard M ₂ C and M ₆ C carbides. Moreover, when tempering at high temperature, it is an element which contributes strongly to the secondary hardening. When the Mo content exceeds 9.0%, in the balance of C, V, and Mo, a large amount of M ₂ C and M ₆ C carbides are crystallized, and the toughness decreases. A more preferable Mo content is 1.0 to 8.0%.

W: 0 to 10.0%
W does not necessarily need to be added, but when added, it enhances the hardenability of the matrix and combines with C to produce hard M ₂ C and M ₆ C carbides. Further, W produces hard carbides like Cr and Mo, and can be substituted for these elements and added. If the W content exceeds 10.0%, the M ₆ C carbide is coarsened and the brittleness deteriorates, which is not preferable.

V: 1.0-10.0%
V forms a hard MC-based carbide, M ₄ C ₃ -based carbide, which contributes most to the improvement of wear resistance. When V is less than 1.0%, the generation of carbide is small and the wear resistance is insufficient. When V exceeds 10.0%, austenite, MC, or M ₄ C ₃ carbides are crystallized as primary crystals due to the balance with the C content. If austenite crystallizes in the primary crystal, the hardness becomes insufficient. Further, if MC and M ₄ C ₃ type carbides are crystallized as primary crystals, it is not preferable since they cause segregation during aggregation and cause brittle deterioration. A more preferable content of V is 2.0 to 8.0%.

  The balance is Fe and impurity elements. Furthermore, in addition to the above, any one or more of Co and Nb can be contained.

Co: 10.0% or less Co is dissolved in the base irrespective of the formation of carbides, and has the effect of increasing toughness and improving high-temperature hardness and wear resistance. If Co exceeds 10.0%, the effect is saturated and expensive, so this was made the upper limit.

Nb: 10.0% or less Nb, like V, forms a hard MC-based carbide, M ₄ C ₃ -based carbide, which contributes most to the improvement of wear resistance. When Nb exceeds 10.0%, toughness is reduced, and austenite, MC, or M ₄ C ₃ carbide is crystallized as the primary crystal due to the balance with the C content. If austenite crystallizes in the primary crystal, the hardness becomes insufficient. Further, if MC and M ₄ C ₃ are crystallized as primary crystals, they are aggregated and segregated during solidification to cause brittle deterioration.

  Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic sectional view showing a bore pin according to an embodiment of the present invention.

As the bore pin 1 of the present invention, the chemical components are C: 2.2%, Si: 0.8%, Mn: 0.4%, Cr: 15.1%, Mo: 5.7%, V: An ingot of 6.5% Fe: the remaining high-speed alloy material was melted at 1450 ° C. and cast into a mold to prepare a base material 2 of a bore pin. Thereafter, the base material 2 was processed into a predetermined shape to manufacture the bore pin 1. The average thermal expansion coefficient of the bore pin 1 thus produced from room temperature to 100 ° C. was 9.2 × 10 ⁻⁶ / ° C.

  Further, a hollow cooling chamber 5 may be provided inside the bore pin 1. A cooling liquid such as water is poured into the cooling chamber 5 to cool the bore pin 1 to suppress thermal expansion of the bore pin 1 and make it easier to pull out the fitted liner 3. Reference numeral 4 denotes a mold, and a base portion of the bore pin 1 is fixed by a bolt or the like.

As a comparative example, the same bore pin was made using SKD61 steel which is a conventional material. The average thermal expansion coefficient of the bore pin from room temperature to 100 ° C. was 11.7 × 10 ⁻⁶ / ° C.

  When these bore pins of the present invention and conventional bore pins are actually used for die casting of a cylinder block of an automobile engine, the wear resistance of the surface of the bore pin made of the iron-based alloy of the present invention can be remarkably improved. It was confirmed that the formation position accuracy of the film could be maintained well over a long period of time, and the service life was about twice that of the conventional material.

  The surface of the bore pin of the present invention may be subjected to a surface treatment such as nitriding treatment, chromium nitriding treatment, superhard spraying, ceramic spraying, various platings and the like.

  According to the cylinder block casting bore pin of the present invention, the wear resistance of the bore pin surface can be remarkably improved in the casting of the cylinder block, the formation accuracy of the cylinder bore can be maintained well, and the service life is longer than that of the conventional material. Therefore, high quality cylinder blocks can be manufactured stably.

It is a schematic sectional drawing which shows the bore pin of the Example of this invention. It is a schematic sectional drawing which shows the bore pin of the other Example of this invention.

Explanation of symbols

  1 Bore pin, 2 Base material, 3 Liner, 4 Mold, 5 Cooling chamber

Claims (5)

A bore pin that is used by being fitted into a liner when casting a cylinder block, from an iron-based alloy having an average coefficient of thermal expansion from room temperature to 100 ° C. of 8 × 10 ⁻⁶ / ° C. to 11 × 10 ⁻⁶ / ° C. A bore pin for casting a cylinder block. The bore block for cylinder block casting according to claim 1, wherein the iron-based alloy is a high-speed alloy. The iron-based alloy is in mass%, C: 1.0 to 4.0%, Si: 0.1 to 2.0%, Mn: 0.1 to 2.0%, Ni: 0 to 4.5% Cr: 10.0 to 20.0%, Mo: 0 to 9.0%, W: 0 to 10.0%, and V: 1.0 to 10.0%. The bore pin for cylinder block casting according to claim 1 or 2, characterized by the above-mentioned. 4. The cylinder block casting according to claim 1, wherein the iron-based alloy further contains at least one of Co: 10.0% or less and Nb: 10.0% or less in terms of mass%. Bore pin for. The bore block for cylinder block casting according to claim 1, wherein the iron-based alloy has a smaller average thermal expansion coefficient from room temperature to 100 ° C. than the liner.