JPH0577042A - Method for reforming surface of cast iron parts - Google Patents

Abstract

PURPOSE:To simply carry out desired surface reforming without any precipitation of graphite by deposit-welding a heat resistant material after a position for reforming object is changed to white pig iron. CONSTITUTION:In the position 11 for the reforming object, e.g., in a valve interval part, etc., at the lower face part of a cast iron-made cylinder head, a recessed part 12 is formed and this is changed to the white pig iron. To the recessed part 12 under condition of covering with the white pig iron layer 13, by using an MIG welder 14, the deposit-welding is executed so as to fill up the recessed part 12 with a welding wire 15 containing the heat resistant metal of Co, Ni, Mo, etc., as a consumable electrode. Then, accompanied with this welding, a crack 16 is justly developed by input heat in the white pig iron layer 13 having no elongation the welding metal is incorporated into the crack, a and the deposit metal and the cast iron are firmly joined with an anchor effect.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for modifying the surface of cast iron parts by utilizing high density energy.

[0002]

2. Description of the Related Art Recently, there is a demand for a technique for partially strengthening (surface modifying) cast iron parts. As a background thereof, for example, in the field of automobile parts, there is a problem that a high load of an engine causes a mechanical load to increase at the same time as a thermal load due to a temperature rise in the cast iron cylinder head.

That is, as shown in FIG. 4, due to such an increase in load, the lower surface 2 of the cylinder head 1, especially between the intake port 3 and the exhaust port 4 which are relatively thinner parts than other parts (intervalve part). ), And a portion 6 between these and the fuel injection nozzle hole (or the pre-combustion chamber hole) 5 causes thermal cracks. Further, as shown in FIG. 6, also in the piston 7, the periphery of the combustion chamber 8 having a large load (indicated by the diagonal lines in the figure) is a portion to be strengthened.

The local strengthening method conventionally adopted as a countermeasure against this has the following techniques. Alloying: A heat resistant component (Cr, Mo, Cu, Ni, etc.) is added in an appropriate amount to improve heat resistant strength. Cast-in: Cast-in a steel material or heat-resistant metal material in the area where heat cracks occur. Nitriding treatment: After processing, nitriding treatment is performed in gas or liquid to form a nitriding layer on the surface.

However, these conventional techniques have the following problems. Alloying ... In addition to high cost, castability deteriorates due to addition of alloys, and casting defects such as "shrinkage cavities" occur, resulting in deterioration of productivity and yield. Further, due to the deterioration of the castability, the number of micro-shrinkages which have a great influence on the heat resistance increases, and the alloying rather deteriorates the heat resistance. Cast-in ... In order to ensure cast-in performance, oxidation prevention, thorough control of cast-in temperature, and non-destructive inspection after cast-in are required, resulting in a significant increase in man-hours.
Nitriding process: At the same time as cost is high, the whole is exposed to high temperature of 560 to 580 ° C, so deformation or crevice inside cast iron parts becomes a problem. Further, in order to perform nitriding more completely, it is necessary to remove graphite in the cast iron material.

As another technique, a method of spraying heat-resistant ceramics or heat-resistant material onto the corresponding portion (lower surface of the cylinder head) has been proposed, but it is put into practical use because of the problem of early peeling of the sprayed layer. Has not reached.

[0007]

In order to avoid the problems of the above-mentioned prior arts, as a new technology, as a new technology, a heat-resistant metal (Co , Ni, Mo, etc.) have been considered (for example, “Cylinder head crack prevention method”, Japanese Patent Laid-Open No. 1-231076). However, when this method is applied to cast iron parts, there is a problem that brittle cementite (Fe ₃ C) is deposited at the boundary between the refractory metal and the base material in the manufacturing process. This cementite is not only fragile but also causes a significant decrease in machinability.

Further, in this conventional method, graphite (C) in the cast iron of the base material is gasified during welding, and the generated gas is trapped in the weld metal as pinholes by the rapid cooling after welding, and the strengthening of the welded portion is reduced. Will be a factor. As one method of solving this problem, there is a method of chemically treating the graphite on the welded portion surface of cast iron, removing the graphite, and then overlay welding the refractory metal (“corrin treatment”). However, this measure is not suitable for the treatment of a large number of pieces, because the labor required for increasing the man-hours, the management of the treated liquid and the treatment of the waste liquid become problems. Furthermore, the processing cost is also high.

In view of the above-mentioned circumstances, the present invention was devised to improve the strengthening method by weld overlay, and to provide a surface reforming method that is free from precipitation of graphite and the like and is simple.

[0010]

According to the present invention, a heat resistant material is welded to the surface after the portion to be modified is white pig iron.

[0011]

By the above method, the heat-resistant substance can be deposited without depositing graphite or the like.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the surface modification method for cast iron parts according to the present invention will be described below with reference to the accompanying drawings.

First, as shown in FIG. 1, a recess 12 is formed in a portion 11 to be reformed, for example, an intervalve portion of the lower surface of a cylinder head made of cast iron, and this is made into white pig iron (chilled). .. The recess 12 may be formed during casting or may be formed by cutting after casting. Further, in the white pig iron formation, the white pig iron layer 13 can be easily formed by setting a chill metal during casting.

Next, as shown in FIG. 2, a refractory metal is welded to the recess 12 covered with the white pig iron layer 13 using a MIG welding machine 14. That is, a welding wire 15 containing Co, Ni, Mo or the like is used as a consumable electrode, and a metal is deposited to fill the recess 12. At this time, the TIG welding torch (not shown) preheats the recess 12 in advance,
Immediately afterwards MIG welding will give even better results.

With this welding, a crack 16 is naturally generated in the white pig iron layer 13 which does not extend due to the heat input, but the weld metal enters the crack 16 and forms a weld metal 17 as shown in FIG. The base material (cast iron) is more firmly joined by the anchor effect.

When the white pig iron layer 13 is thin, the white pig iron is in a tempered state due to heat input when welding the refractory metal. When the white pig iron layer 13 is thick, part of the deep white pig iron remains. This is a level that does not pose a problem in space, but it can be tempered by high frequency.

In the process of white pig iron, T for the purpose of residual heat is used.
IG welding may be performed by increasing the heat input energy, and the phenomenon that the surface of cast iron is melted and rapidly turned to white pig iron by quenching may be used.

As the MIG welding wire, a welding wire having capsule particles filled in a sheath material may be used. Capsule particles are made by attaching particles having a smaller particle size, for example, Cu particles that are well compatible with the base material, to the surface of the particles of the heat-resistant substance, and applying an impact force by a rolling device or the like to form the core of the heat-resistant substance. The particles are particles and Cu is a coated particle. By using such capsule particles,
It is possible to widen the selection range of welding conditions.

[0019]

In summary, according to the present invention, the following excellent effects are exhibited.

Since the refractory material is welded and deposited after the portion to be modified is white pig iron, there is no precipitation of graphite or the like, and the desired modification can be performed easily.

[Brief description of drawings]

FIG. 1 is a side cross-sectional view of a modification target portion for explaining an embodiment of a surface modification method for a cast iron component according to the present invention.

FIG. 2 is a side sectional view for explaining the next step of FIG.

FIG. 3 is a side sectional view for explaining the next step in FIG.

FIG. 4 is a bottom view showing a modification target portion for explaining the problem of the conventional technique.

FIG. 5 is a perspective view showing a modification target portion for explaining another problem of the conventional technique.

[Explanation of symbols]

 11 Site to be modified 13 White pig iron layer 17 Weld metal

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yuji Matsunami 8 Tsutana, Fujisawa City, Kanagawa Prefecture Isuzu Central Research Institute Co., Ltd.

Claims (1)

[Claims] 1. A method for surface modification of a cast iron component, which comprises depositing a refractory substance by welding after depositing a portion to be reformed with white pig iron.