JPS5916923A - Method for hardening surface of metal member by remelting - Google Patents

Abstract

PURPOSE:To uniformly and rapidly harden the surface of a metal member over a wide range, by pulse oscillating energy to be inputted to said metal member from the source of high density energy. CONSTITUTION:The remelt case-hardening treatment with a TIG arc is applied, for instance, to the sliding surface 2 of a locker arm 1 to be incorporated in the diesel engine of an automobile which comes in sliding contact with a cam. Hereon, a DC pulse current having a peak value of 120-350A and a time of 0.05-0.4sec for the continuation of said peak value is pref. applied with voltage of 12-30V for about 0.5-3sec. Thus, the broad domain of the sliding surface 2 is rapidly and uniformly hardened.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for remelting and surface hardening a metal member using a so-called high energy density source such as a Ding JG arc or a laser.
More specifically, the present invention relates to a remelting surface hardening treatment method suitable for application to metal members having a relatively small heat capacity.

A remelting surface hardening treatment method using a high energy density source such as a TIG arc is widely used in various technical fields as a treatment method for locally hardening the surface of a metal member. For example, hardening the surface of a metal member over a certain range using a TIG arc has conventionally been done by weaving a welding torch, or by overlapping single beads to melt the surface of the metal member and rapidly cool it. This is done by

However, when using these methods, the part of the metal member that has already been remelted and hardened is reheated by the TIG arc passing nearby, so the hardness of that part decreases.
Furthermore, there is a problem in that because the structure of the overlapping portion of the electrodes becomes non-uniform, the wear resistance in that portion is not necessarily sufficiently improved. In addition, when using the weaving method as described above, the timing to achieve sufficient melting at the bead end becomes a problem in processing technology, and defects such as cracks and blowholes are likely to occur at the bead end. There is a problem.

In view of the defects in surface hardening heat treatment by such weaving method, etc., as a re-melting surface hardening treatment method for metal parts with particularly small heat capacity, a method similar to arc spot welding is used for metal parts to be surface hardened. A method has been devised in which the welding torch is kept stationary and the surface to be hardened is melted into a ribbon shape. However, in this method, the part of the metal part directly under the welding torch is melted extremely deeply and the surrounding part is not sufficiently melted, so the surface area around the part directly under the welding torch is also melted and hardened. If this is to be done, the current must be increased or the surface of the metal member must be treated at several points. In this case, if the current is increased,
The heat input to the metal member becomes excessive, the crystals of the generated chill layer become coarse, and the hardness and wear resistance of the surface of the metal member are not sufficiently improved. Furthermore, when the surface of a metal member is processed at several points, not only the processing efficiency deteriorates, but also problems similar to those of the above-mentioned weaving method occur.

In view of the various defects in the conventional remelting surface hardening treatment method as described above, the inventors of the present application have conducted several experimental studies, and have found that the penetration of metal members by a high energy density source such as a TIG arc It has been found that it is preferable to pulse the heat.

The present invention is based on the results of experiments conducted by the inventors of the present application,
It is an object of the present invention to provide a method that can uniformly and quickly harden the surface of a metal member to be surface hardened over a relatively wide range.

According to the present invention, this object is a remelting a surface hardening treatment method for a metal member using a high energy density source, characterized in that heat input to the metal member by the high energy density source is pulsed. This is achieved by remelting and surface hardening treatment of metal parts.

According to the remelting surface hardening treatment method according to the present invention, a molten pool is formed on the surface of the metal member by the high current side pulse of the high energy density source, and this serves as a screen and the heat applied to the metal member is absorbed by the metal member. Because the heat is transmitted to the surrounding parts along the surface of the part directly received rather than in the depth direction, welding can be performed over a relatively wide area without having to move the weld 1-1 along the surface of the metal member. It is possible to melt to a relatively uniform depth over a relatively wide area, thereby making it possible to uniformly and quickly harden the surface of a metal member to be surface hardened over a relatively wide area. can.

In addition, compared to the conventional remelting surface hardening treatment method described in (II) above, even when melting reaches the edge of the surface of the metal member to be surface hardened, shoulders that occur at the edge The sagging is very small, its suppression and control is easy, and post-processing such as shape modification after surface hardening can be easily performed.

In addition, the high energy density source in the remelting surface hardening treatment method according to the present invention may be a TIG arc, a laser, etc. In particular, when a TIG arc is used as the high energy density source, the material of the material to be treated may be Voltage 12-3OV, peak current 120-35'
OA, peak current time 0.01 to 0.2 seconds, base current 10 to 50△, base current time 0.05 to 0.4 seconds, DC noll ≦ pulse current is applied for about 0.5 to 3 seconds. is preferred.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to embodiments with reference to the accompanying drawings.

Example As shown in Fig. 1, the sliding surface 2 (11 x 12 mm) of the rocker arm 1 which is incorporated into an automobile diesel engine and the sliding surface 2 (11 x 12 mm) between the cam and the nom shaft was regenerated by TIG arc under the treatment conditions shown in the table below. Melt surface hardening treatment (△
and B) were carried out and incorporated into a 400'0OC 4-cycle diesel engine, and a wear test was conducted to examine the amount of wear.

For comparison purposes, the conventional weaving method
- Treatment (C) and arc spot treatment (1)
) A similar wear test was also conducted on the rocker arm.

The rocker arm as the material to be treated is made of spheroidal graphite cast iron (
JIS standard F CD 7'O), weight is 8'
O(]. Also, each process is T
The test was carried out with the IG l-chi stationary above the center 3 of the sliding surface 2.

The test results showed that in the conventional weaving method (C), it took a long time (6 seconds) to treat the entire sliding surface of the rocker arm, and the amount of wear at the overlapping part of the weaving bead was small. It was found that the hardness and abrasion resistance of the sliding surface after treatment were non-uniform because it was larger than other parts. Also, conventional arc spot treatment ([])
In this case, the weld penetration in the area directly under the TIG arc is extremely deep to E1, and it takes a relatively long time (4 seconds) to melt the surrounding area, and as a result, the TIG arc cannot be directly applied. It was observed that the structure of the chill layer in the affected area was coarsened and the amount of wear was significantly greater than in other areas.

On the other hand, the sliding surfaces of the rocker arms treated according to the present invention (Δ and B) have better hardness and wear resistance than the rocker arms treated with the above-mentioned treatments C and D, and the depth of the remelted layer is also lower. It was found that it was uniform. FIG. 2 is a photograph showing a cross section of a rocker arm subjected to treatment A in a direction perpendicular to its longitudinal direction at a magnification of 6.2 times. As can be seen from FIG. 2, according to the above-mentioned process A, substantially the entire area of the sliding movement is uniformly remelted and uniformly hardened in a short period of time.

Example 2 As in Example 1, the top surface of the valve stem of an exhaust valve to be incorporated into an automobile deep-pil engine was remelted and hardened. The processing conditions adopted were: voltage 18V, peak current 1p = 12'OA, base current Ib.
= 2'OA, peak current time Tp = 'Q, 1 second, base current time Tb = '0°1 second, processing time 1 second, and the exhaust valve as the material to be treated is heat-resistant steel LIIS standard S tJ
It had a weight of 1'05 Ill and was made of t-13>.

When the structure of the cross section was observed after the treatment, it was found that a very fine martensitic structure II'X was formed over substantially the entire top surface of the valve stem.

In addition, when the same processing as in the above two embodiments (e) was carried out by using a laser torch and pulsating its output beam, the surface to be processed was much smaller than when using a steady beam with a constant output. It was observed that the hardness was uniformly improved.

From the above explanation, it will be understood that according to the remelting surface hardening treatment method for metal members according to the present invention, a relatively wide square area of the treated material can be hardened quickly and uniformly.

Although the present invention has been described in detail with respect to specific embodiments above, the present invention is not limited to these embodiments, and various embodiments are possible within the scope of the present invention. This will be clear to those skilled in the art.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing a rocker arm as a material to be treated in Example 1, and FIG. 2 is a perspective view showing a rocker arm as a material to be treated in Example 1, and FIG. It is a photograph showing a cross section perpendicular to the longitudinal direction of the sliding surface of the rocker arm at 6.248. 1...Rocker arm, 2...Sliding surface, 3...Center of sliding surface

Claims (1)

[Claims] A method for remelting and surface hardening a metal member using a high energy density source, the method comprising pulse oscillation of heat input to the metal member by the high energy density source.