JPH0353389B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for surface hardening a cast iron member such as a camshaft or a rocker arm using a plasma arc, in which a part of the surface layer is a remelted layer having excellent wear resistance.

In an internal combustion engine, the rotation of the crankshaft and the opening and closing of the valves are controlled via the camshaft and rocker arm in order to open and close the valves at appropriate times to introduce the mixture into the combustion chamber and release fuel gas. It is linked. Here, in the case of the OHC type, a part of the camshaft and the rocker arm are in direct sliding contact, and in the case of the OHV type, a part of the tappet and a part of the camshaft and rocker arm are in sliding contact. Therefore, a portion of the surface layer of the camshaft and rocker arm is required to have higher wear resistance than other portions.

Therefore, in the past, when manufacturing cast iron parts such as camshafts that require parts with excellent wear resistance, high hardness metals such as Cr and Mo are added to the molten metal during casting. At the same time, a chilled metal is set in a part of the mold, and a chilled layer with excellent wear resistance is formed at the same time as casting in the area that the chilled metal touches.

By the way, in order to increase the hardness of the chilled layer and further improve its wear resistance, it is sufficient to increase the amount of high-hardness metal added to the molten metal. The hardness of parts, such as journal shafts, increases as a result of adding high-hardness metals,
Cutting after casting becomes difficult, and in some cases, a chill structure is formed in areas where the cold metal is not applied, making subsequent cutting extremely difficult.

Therefore, considering the subsequent cutting process, the proportion of high hardness metal added is 1.0wt% when added alone.
However, even when multiple types of high-hardness metals are added, the upper limit of the amount added is 1.4 wt%, and it has been practically difficult to add more than this. Therefore, in the case of conventional cast iron members, the wear resistance formed in a part thereof cannot be said to be sufficient.

The present invention was made in view of the above-mentioned conventional problems, and its purpose is to provide extremely easy cutting processing, and a part of the surface layer that has extremely high hardness, wear resistance, and pitting resistance. An object of the present invention is to provide a method for surface hardening using plasma arc, which allows a partially hardened cast iron member to be formed with a remelted layer having excellent properties.

In order to solve the above problems, the present invention disposes a plasma torch and a metal powder introduction pipe opposite to a part of the surface layer of the cast iron member, and uses a plasma arc ejected from the torch to partially form the surface layer of the cast iron member. At the same time a molten pool is formed in the part, Cr,
A high-hardness metal powder of a single substance, an alloy, or a compound such as Mo, Ni, W, V, or Nb is introduced into the plasma arc, and the high-hardness metal powder is forcibly fed into the molten pool. A surface hardening method for a cast iron member using a plasma arc to form a remelted layer in which the high-hardness metal powder is solid-dissolved or dispersed in a pond, the method comprising: The high hardness metal powder is added from the introduction tube to the molten pool at a rate of at least 1.0 to 15.0wt%, and 0.5% of the high hardness metal powder is added to the molten pool.
Carrying into the plasma arc at a conveying speed of m/sec or more and at the same time forcibly supplying the high hardness metal powder into the molten pool by the plasma arc, relative movement between the torch and the cast iron member. The method is characterized in that a stirring action is produced in the molten pool, so that the high-hardness metal powder is mixed substantially uniformly over a very deep layer down to the bottom of the molten pool.

For example, the Cr, Mo, Ni, W, V or Nb
A single substance or a compound of high hardness metals, such as, is supplied to the molten pool in combination of two or more types, and the addition ratio is 0.7 to 15.0 wt% individually, and 1.4 to 1.4 wt% as a whole.
It may be 16.0wt%.

Furthermore, the above Cr, Mo, Ni, W, V or Nb
Compounds of high hardness metals such as sulfur are added to form sulfides, and the addition ratio of sulfur may be 0.2 to 1.5 wt% with respect to the remelted layer.

Embodiments of the present invention will be described below based on the accompanying drawings.

FIG. 1 is a sectional view showing the internal structure of a plasma torch 1 used for manufacturing a cast member according to the present invention. A passage 4 for a shielding gas such as an inert gas is formed between the nozzle 2 and the nozzle 3. Further, a passage 5 for a working gas such as argon gas is formed in the center of the nozzle 3, and a cooling passage 6 is formed around this passage 5. A tungsten electrode 7 is provided in the working gas passage 5, and the lower end of the passage 5 is used as a plasma gas spraying passage 8. Further, cylindrical guides 9, 9 are installed diagonally through the shield cap 2, and a metal powder introduction tube 10 is attached to the cylindrical guides 9, 9 so that the extension of the axis thereof is an extension of the axis of the plasma gas spray passage 8. It is inserted and fixed so that it intersects with the Note that the number of cylindrical guides 9 is not limited to two, but a plurality of cylindrical guides 9 may be arranged around the shield cap 2 at equal intervals.

A method for manufacturing a cast iron member according to the present invention using the plasma torch 1 having the above configuration will be described below.

First, cast iron parts are cast using normal methods, that is, without the addition of high-hardness metals that would interfere with cutting.
In addition, a part of the surface layer of the cast iron member 11 that has been cut, that is, a part where wear resistance and pitting resistance are required, is cut by cutting the cast iron member without using a chilled metal. The plasma torches 1 are set facing each other as shown in FIG.

Next, using the cast iron member 11 as the other electrode, the tungsten electrode 7 and the cast iron member 11 are connected to a DC power source, and a shielding gas is supplied from the shielding gas passage 4, and a working gas such as argon gas is supplied from the working gas passage 5. Flow.

Then, an electric discharge occurs between the electrodes, the working gas turns into plasma, and this plasma gas is condensed in the plasma gas blowing passage 8 to generate a high-temperature and high-speed plasma arc 1.
Ejects as 2 (plasma jet). The ejected plasma arc 12 is blown onto the surface layer of the cast iron member 11 which has a positive potential with respect to the tungsten electrode 7, and forms a molten pool 13 in this portion.

Meanwhile, while performing the above operations, the metal powder introduction tube 1
A high-hardness metal 14 is supplied in powder form into the plasma arc 12 through the plasma arc 12 . Here, the high hardness metals 14 to be supplied include Cr, Mo, Ni, W, V,
Various materials such as Nb alone, alloys of these metals or other metals, or compounds with carbon, etc. are possible, and as a means of feeding into the plasma arc 12, the above-mentioned high hardness metals alone can be used. or a combination of two or more. When it is supplied alone, the weight ratio to the molten pool 13 is 1.0.
The amount is preferably 15.0 wt%, and when two or more metals are supplied in combination, one metal is preferably 0.7 to 15 wt%, and the total amount is 1.4 to 16.0 wt%.
The reason for specifying the weight ratio in this way is that if it is less than the above ratio, there will be little difference in wear resistance from conventional chilled cast iron parts, and sufficient hardening will not be obtained, and if it is above the above ratio, This is because the hardness becomes extremely high, making it brittle, and on the contrary, the pitting strength decreases, making it more likely that cracks will occur during polishing and air cooling after melting.

The high hardness metal 14 supplied into the plasma arc 12 at such a ratio is confined in the plasma arc 12, and the confined high hardness metal 14
is accelerated and heated by the plasma arc 12, hits the molten pool 13 at high speed and high temperature, and sinks into the molten pool 13. On the other hand, the molten pool 13 has a dent caused by the pressure of the plasma arc 12, and this dent flows upward, downward, and in the moving direction as the torch moves, so the molten pool 13 has a stirring action. arise. As a result, the high-hardness metal that has penetrated into the molten pool 13 is uniformly mixed in the molten pool 12 due to the above stirring action. If the supplied high-hardness metal 14 has a low melting point or is easily melted, it is mixed with the base material components in the molten pool 13 to precipitate a compound through an alloy or precipitation reaction; It is dispersed in the molten pool 13 in its initial composition state.

When the molten pool 13 is cooled, the cast iron is formed with a remelted layer formed on a part of the surface layer, which has excellent wear resistance and pitting resistance due to the high hardness metal being uniformly dispersed or dissolved in solid solution. A member is obtained.

Next, specific operating conditions for forming a remelted layer having wear resistance and pitting resistance as described above will be described below.

First, the gas flow rate in the metal powder introduction tube 10 is preferably 0.5 m/sec or more to reliably contain the metal powder in the plasma arc 12, and the working gas flow rate is preferably 0.3 to 3.0/min or more. ,
It is desirable to prevent the molten metal from scattering from the molten pool 13 by significantly reducing the amount compared to normal plasma spraying. In addition, the particle size of the high hardness metal 14 is set to 1 to 1 in order to reduce the amount of working gas supplied as described above.
The thickness is preferably 200μ, preferably 1 to 100μ.
Furthermore, the arc current needs to be set appropriately depending on the material, size, shape, and depth of the melting base metal, amount of additive powder, melting area, torch movement speed, etc., but it is approximately 30 to 200 A, 20 It is best to do this at ~30V.

Incidentally, the above is an example of the implementation of the present invention, and sulfur may be added alone or as a sulfur compound together with the above-mentioned high hardness metal 14. In this case, the high hardness metal is uniformly dispersed or dissolved in the remelted layer in the form of sulfide, thereby increasing the lubricity and further improving the wear resistance. However, if the addition ratio of sulfur is 1.5wt% or more, the remelting layer becomes brittle and the pitting strength decreases.
If the sulfur content is 0.2wt% or less, the lubricity will not be so high, so the proportion of sulfur added should be 0.2 to 1.5wt.
% is preferable.

FIG. 2 is a graph showing the results of EPMA analysis (X-ray microanalyzer) of a remelted layer formed by adding sulfur within the above range using Cr and Mo alone as high hardness metals, As can be seen from this graph, sulfur (S), Cr, and Mo are present almost uniformly in the remelted layer, and the above elements are not contained in the areas other than the remelted layer. I understand.

Next, an experimental example comparing the cast iron member according to the present invention with a conventional cast iron member will be described below.

Experimental Example 1 A cast camshaft made of FC30 for automobiles was roughly cut, and while the surface of the cam lift part was remelted using a plasma arc, Cr metal powder was added, and remelted and hardened under the following conditions.

Conditions: ●Plasma arc current 85A ●〃Gas amount 20.3/min ●Additional amount of Cr powder 1.4g/min ●Torch speed 1m/min The depth of the resulting remelted layer (chill hardened layer) in the cam lift section is 1.6mm. The same part contains about 13% Cr almost uniformly, and its hardness is HRC63.
It was hot. This was finished by cam grinding and used as test material A. On the other hand, a camshaft in which 0.9% of Cr was included in the casting material composition and chilled by applying a cold metal only to the cam lift portion was cam-ground and used as test material B for actual machine testing. The test conditions were an engine speed of 1000 rpm, an oil temperature of 65°C, and an endurance time of 200 hours. As a result, the maximum wear depth of the cam part was
The abrasion resistance of specimen B was 25μ, and that of test piece B was 105μ, indicating that specimen A had much better abrasion resistance.

Experimental Example 2 An FCD55 cast camshaft for a motorcycle was roughly cut, and Mo ₂ C metal powder with a particle size of 10 to 50 μm was added to the surface of the cam lift portion under the following conditions while being remelted using a plasma arc.

Conditions: ● Plasma arc current 80A ● 〃 Gas amount 20.5/min ● Mo ₂ C powder addition amount 0.3 g/min ● Torch speed 1.2 m/min The obtained chill depth was 1.8 mm, and the Mo concentration was 1.5
%, and the hardness was HRC57. This was finished by cam grinding to obtain a test piece C. On the other hand, FCD55
A cast chill camshaft was finished by cam grinding to obtain test piece D. When this was tested in the same actual machine test as in Experimental Example 1, the amount of wear was 80μ for test piece C.
Test piece D had a diameter of 120 μm and had better wear resistance than D.

Experimental example 3 A cast camshaft made of FC30 for automobiles was rough cut, and then the surface of the cam lift part was remelted with Cr ₃ C ₂ powder under the following conditions using a plasma arc.
Each weight ratio of metal powder of Mo powder (2~60μ)
They were mixed at 50% and remelted and hardened.

Conditions: ● Plasma arc current 80A ● 〃 Gas amount 0.5/min ● Torch speed 1m/min ● Addition amount of Cr ₃ C ₂ (50%) + Mo (50%) 0.3 g/min Chill hardening depth of the obtained cam part The length is 1.7mm,
Moreover, it contained about 0.9% Mo and about 0.8% Cr.
Incidentally, the hardness was HRC58, and this was finished by cam grinding and used as test piece E. On the other hand, FC30 material
An alloy chill camshaft containing 0.3% Mo and 0.6% Cr was made by casting and finished by cam grinding to obtain test material F. As a result of testing these on actual machines,
The abrasion depth was 63μ for test piece E and 110μ for test piece F, indicating that test piece E had extremely excellent wear resistance.

Experimental example 4 A cast camshaft made of FC30 for automobiles was roughly cut, and then the surface of the cam lift part was remelted with Cr ₃ C ₂ powder under the following conditions.
Mo powder (2~60μ) metal powder, 65% of the former,
The latter was remelted and hardened at a rate of 35%.

Conditions: ● Plasma arc current 80A ● 〃 Gas amount 0.5/min ● Torch speed 0.5m/min ● Addition amount of Cr ₃ C ₂ (65%) + Mo (35%) 1.6 g/min Chill hardening of the obtained cam part The same part, which was 1.5 mm deep, contained approximately 5.6% Mo and 9.4% Cr.
The hardness was HRC64. This was finished by cam grinding and used as a test piece G. On the other hand, Mo0.3 for FC30 material
Test material F was made by casting an alloy chill camshaft containing 0.6% and 0.6% of Cr and finishing with cam grinding. As a result of subjecting these to an actual machine test, the wear depth was 38μ for test piece G and 110μ for test piece H. As a result, it was found that test piece G had extremely excellent wear resistance.

Experimental Example 5 A cast camshaft made of FC30 for an automobile was rough cut, and then the surface of the cam lift part was remelted with Cr ₃ C ₂ powder under the following conditions using a plasma arc.
MoS ₂ powder (2 to 10μ) and metal powder were mixed in a weight ratio of 50% each and remelted and hardened.

Conditions: ● Plasma arc current 80A ● 〃 Gas amount 0.5/min ● Torch speed 0.9m/min ● Addition amount of Cr ₃ C ₂ (50%) + MoS ₂ (50%) 0.8 g/min Chill of the obtained cam part The hardened portion had a hardening depth of 1.6 mm, contained about 3.4% Mo, about 4.8% Cr, and about 0.82% S, and had a hardness of HRC63. This was finished by cam grinding and used as a test piece I. In contrast to this
An alloy chill camshaft made of Fc30 material containing 0.3% Mo and 0.6% Cr was made by casting and finished by cam grinding to obtain test material F. As a result of testing these by subjecting them to actual machine tests, the wear depth of test piece I was 26μ.
As a result, it was found that Test Piece I had extremely excellent abrasion resistance.

As explained above, according to the present invention, a remelted layer in which high-hardness metals such as Cr and Mo are uniformly dispersed or dotted is formed on a part of the surface layer of cast iron members such as camshafts and rocker arms that have been cast. In this case, when a molten pool is formed on a part of the surface layer of a cast iron member by a plasma arc, and at the same time, high-hardness metal powder is introduced into the plasma arc and the high-hardness metal powder is forcibly fed into the molten pool, Cr,
Addition ratio of high hardness metals such as Mo, Ni, W, V or Nb to the molten material at least individually.
0.5m/0.5m of high hardness metal powder at 1.0~15.0wt%
The high-hardness metal powder is transported into the plasma arc at a transport speed of sec or more, and at the same time, the plasma arc forces the high-hardness metal powder into the molten pool, and at the same time, the relative movement between the plasma torch and the cast iron member creates a stirring effect on the molten pool. This allows the high-hardness metal powder to be mixed almost uniformly over an extremely deep layer down to the bottom of the molten pool, so it is possible to grind out the bulges and bead-like marks after solidification due to the surface tension of the molten pool for practical use. Even when obtaining a smooth sliding surface for grinding, it is difficult to obtain a highly hard alloy layer with sufficient depth on the sliding surface that requires wear resistance and pitting resistance even after grinding. The hardness of the other parts can be kept low to make cutting easier, and therefore it has the contradictory properties of having excellent wear resistance and pitting resistance as well as excellent machinability. It can be a cast iron member that has both functions. Therefore, it is extremely effective when applied to camshafts or rocker arms.

Furthermore, if sulfur is added in addition to the above-mentioned high-hardness metals, many effects such as further improvement in wear resistance can be achieved.

[Brief explanation of drawings]

Fig. 1 is a partial cross-sectional view of a plasma torch used for manufacturing a cast iron member according to the present invention, and Figs. 2 A to C are EPMA analysis graphs showing the distribution state of major elements in the remelting treatment layer of the cast iron member. . In addition, in the drawing, 1 is a plasma torch, 2 is a shield cap, 3 is a nozzle, 4 is a shield gas passage,
5 is a working gas passage, 7 is a tungsten electrode, 11
1 is a cast iron member, 12 is a plasma arc, 13 is a molten pool, and 14 is a high hardness metal.

Claims (1)

[Scope of Claims] 1. A plasma torch and a metal powder introduction pipe are arranged opposite to a part of the surface layer of the cast iron member, and a plasma arc ejected from the torch forms a molten pool in the part of the surface layer of the cast iron member. At the same time, a high-hardness metal powder of a single substance, alloy, or compound of Cr, Mo, Ni, W, V, or Nb, etc., is carried into the plasma arc from the introduction pipe to form the high-hardness metal powder into the molten pool. Cr, The high hardness metal powder, such as Mo, Ni, W, V, or Nb, is added at least individually to the molten pool at a rate of 1.0 to 15.0wt%, and the high hardness metal powder is added to the molten pool by 0.5m/
The high-hardness metal powder is transported into the plasma arc at a transport speed of sec or more, and at the same time the high-hardness metal powder is forcibly supplied into the molten pool by the plasma arc, and at the same time, the A method for surface hardening a cast iron member using a plasma arc, characterized in that the high-hardness metal powder is substantially uniformly mixed in an extremely deep layer down to the bottom of the molten pool by creating a stirring action in the molten pool. 2. The single or compound high hardness metals such as Cr, Mo, Ni, W, V, or Nb are supplied to the molten pool in combination of two or more, and the addition ratio is determined individually.
0.7~15.0wt%, overall 1.4~16.0wt
%. A method of surface hardening a cast iron member using a plasma arc according to claim 1. 3 The compound of high hardness metal such as Cr, Mo, Ni, W, V or Nb becomes a sulfide by adding sulfur, and the addition ratio of sulfur is 0.2 to 1.5 wt% to the remelting layer. A method of surface hardening a cast iron member by plasma arc according to claim 1 or 2, characterized in that: