JPH02243777A - Production of engine valve - Google Patents

Abstract

PURPOSE:To produce an engine valve having excellent wear resistance by forming an alloyed layer consisting of Cr, C and Fe and having a specified composition on the valve face of a heat-resistant steel valve main body with high-density heating energy and then applying specified heat treatment. CONSTITUTION:The alloying material powder contg. Cr and C is arranged on the valve face 2 of the valve main body 1 made of a martensitic heat- resistant steel. High-density heating energy such as laser light is then impressed on the powder to rapidly melt the alloying material along with the lower valve main body base material layer. The materials are alloyed, and an alloyed layer 3 contg., by weight, 20-50% Cr, 1-3% C and the balance essentially Fe is formed. The alloyed layer 3 is then heated at 400-700 deg.C for 5min to 5hr, and then quenched by water, etc. Consequently, the structure of the alloyed layer 3, in which a eutectic carbide is crystallized in the matrix consisting essentially of hard martensite, is formed. By this method, an engine valve having the valve face 2 consisting of the alloyed layer 3 having excellent wear resistance is obtained at a low cost.

Description

[Detailed Description of the Invention] Industrial Application Field This invention relates to an engine valve used for the intake valve of an engine of an automobile, etc., and in particular has excellent wear resistance on the contact surface with the valve seat (valve face surface). The present invention relates to a method of manufacturing an engine valve with an alloyed layer formed thereon.

As is well known in the prior art, the surface of an engine valve that contacts the valve seat, that is, the valve face surface, is required to have excellent wear resistance. Therefore, it has conventionally been possible to deposit and weld CO-based or Ni-based heat-resistant and wear-resistant materials, such as stellite, onto the valve face surface of the valve body made of martensitic aged steel. It is being done.

On the other hand, quenching and nitriding treatments have been conventionally known as methods for improving the wear resistance of engine valves through heat treatment.

As mentioned above, if CO-based or Ni-based heat-resistant and wear-resistant materials are deposited, the wear resistance will certainly improve, but CO-based or Ni-based materials
All of the i-based materials are extremely expensive, which poses a serious problem that increases the cost of engine valves.

Direct quenching provides high hardness as a surface hardening process, but since high compressive residual stress is generated on the surface of the quenched layer, once wear occurs, the stress is released and wear becomes more likely. It is known that In addition, the heat resistance strength of the hardened layer decreases in the folding temperature state, and therefore, there is a problem in applying it to engine valves by hardening alone.

Furthermore, nitriding has the advantage of generating less distortion due to the low processing temperature, but the thickness of the treated layer is extremely thin, about 5 to 10 strands, so if even a part of the treated layer disappears due to foreign matter getting caught, etc. There is a problem that wear progresses rapidly.

Therefore, the present inventors have focused on alloying treatment as a measure to improve the wear resistance of the valve face surface of engine valves, and are proceeding with research for its practical application.

This alloying process involves placing the material to be alloyed on the valve face of the valve body made of various types of aging-resistant steel such as martensitic aging-resistant steel, and applying high-density heating using laser, TIG arc, plasma, etc. A method of applying energy to simultaneously melt the alloying material and the surface layer of the valve body below, and forming a layer (alloyed layer) having a predetermined alloy composition by rapid resolidification through self-cooling. can be,
According to this alloying process, by appropriately selecting the materials to be alloyed, an alloyed layer with excellent wear resistance and heat resistance strength can be formed on the valve face surface at a relatively low cost with a considerable thickness. can be formed.

As one of the techniques for forming an alloyed layer with excellent wear resistance on the valve face surface by alloying treatment, the present inventors have already disclosed Japanese Patent Application No. 142498/1983 (Japanese Patent Application Laid-Open No. 62-298).
No. 6984) provides a technique for forming an alloyed layer containing 1 to 15 wt% of MO on a valve face using MO or a MO-containing material as an alloying material.

Problems to be Solved by the Invention As mentioned above, in the proposed technology of alloying MO or MO-containing material on the valve face surface, MO itself is expensive, so although the amount used is relatively small, The high cost of M (cannot be reduced).

On the other hand, a material that has the potential to form an alloyed layer with excellent wear resistance at low cost is a material mainly composed of Or and C. Cr20~50wt%, 01~
It is conceivable to form a high Cr and high C Fe=cr-C alloy layer of about 3 wt%. However, even in such an l''e-Or -C alloyed layer, its hardness is l
It was found that the wear resistance was still insufficient for engine valves used under severe conditions. Of course, if the C content of the alloyed layer is further increased, the hardness will increase, but in that case, cracks will occur, and therefore there is a limit to increasing the C content.

This invention was made against the background of the above circumstances, so F.
In manufacturing an engine valve in which an e-Cr-C alloy layer is formed on the valve face, the present invention aims to provide a method for obtaining an engine valve in which the wear resistance of the valve face alloy layer is sufficiently improved. This is the purpose.

Means for Solving the Problems The method for manufacturing engine valves of this invention basically consists of:
After forming a high Cr and high C FeCr-C alloyed layer on the valve face surface, the retained austenite in the alloyed layer is converted to martensite by applying appropriate heat treatment, thereby converting the remaining austenite from only martensite to martensite. The objective is to obtain an engine valve having an alloyed layer in which eutectic carbides are crystallized in a matrix.

Specifically, the method for manufacturing an engine valve of the present invention includes:
The valve face of the valve body made of hardened steel is alloyed with a material containing Or and C using high-density heating energy to form alloys containing 20 to 50 wt% of Or, 1 to 3 wt% of C,
An alloyed layer is formed in which the remainder is substantially made of Fe, then heated to a temperature in the range of 400 to 700°C for 5 minutes to 5 hours, and then rapidly cooled to change the structure of the alloyed layer so that the matrix is substantially It is characterized by having a structure consisting of martensite and having eutectic carbide crystallized in the matrix.

Function: In the manufacturing method of the present invention, first, a valve body made of ripening-resistant steel such as martensitic ripening-resistant steel is prepared in accordance with a conventional method, and C is applied to the valve face surface of the valve body.
Materials containing r and C (alloyed materials), e.g. high C
A FeCr-C alloy with r1 high C is alloyed using high-density heating energy such as a laser, TIG arc, plasma, or electron beam. Specifically, an alloy material such as Fe-0r-C alloy is placed on the valve face surface of the valve body, and high-density heating energy is applied from above to melt the alloyed material and the valve body base material below. Rapidly melts the surface layer of As a result, the alloying material and the underlying base material hardening steel are melted and integrated, that is, alloyed. Subsequently, by moving the application position or stopping the application of high-density heating energy,
Heat rapidly moves toward the base material, and the molten alloyed layer is rapidly cooled and rapidly solidified.

Here, the component composition and arrangement amount (alloying amount) of the alloyed material are such that the component composition of the alloyed layer is Cr20 to 501
%, Q1 to 3 wt%, and the balance is determined to be substantially Fe. Of course, the composition of the alloyed layer is also affected by the composition of the base material and the melting depth of the base material surface during alloying treatment, so it is necessary to set the composition of the alloyed material and the amount of alloying accordingly. .

As mentioned above, in the alloying process using high-density energy, the cooling solidification after melting becomes rapid cooling, so the alloyed layer made of Fe-20~50%Cr1~3%C alloy obtained by the alloying process This is an Ill weave in which eutectic carbides (mainly Cr--Fe carbides) are crystallized in a matrix consisting of a mixed phase structure of martensite and retained austenite. Here, retained austenite is soft, so if the matrix had no retained austenite, that is, a matrix consisting almost only of martensite, the hardness would be higher and the wear resistance would be significantly better, but in reality It is unavoidable that about 30% residual austenite exists in the alloyed layer as it has been alloyed.

Therefore, in the method of this invention, 400 to 7
Heat treatment is performed by heating to a temperature within the range of 00°C for 5 minutes to 5 hours and then rapidly cooling with water or oil cooling. By performing such heat treatment, almost all of the retained austenite in the matrix of the alloyed layer changes to martensite, and as a result, the alloyed layer has Qr- This results in a structure in which eutectic carbides mainly composed of Fe-based carbides crystallize. The matrix of such an alloyed layer is composed of martensite with almost no residual austenite, so it is extremely hard, and since hard eutectic carbides are crystallized in the matrix, it has excellent wear resistance. Remarkably superior.

Note that retained austenite is unstable, so if a large amount of retained austenite is present, it will gradually become more stable over time, often causing deformation of the component.
As described above, by making the alloyed layer have a structure in which almost no retained austenite exists, the occurrence of such deformation over time can be prevented.

According to experiments conducted by the present inventors, it has been found that if the temperature in the heat treatment after alloying treatment is lower than 400°C, the effect of converting retained austenite into martensite and increasing hardness cannot be obtained. ing. On the other hand, if the heat treatment temperature is 700° C. or higher, the eutectic carbide will form a solid solution in the matrix, resulting in a decrease in wear resistance. Therefore, the heating temperature in the heat treatment needs to be within the range of 400 to 700°C. Also, the heating time of this heat treatment is 5
If the heating time is less than 5 minutes, a significant amount of retained austenite will remain, whereas if the heating time is longer than 5 hours, a reduction in the hardness of the martensite already formed in the matrix will occur. Therefore, the heating time of the heat treatment was within the range of 5 minutes to 5 hours. Note that this heat treatment is performed in a vacuum or N
It is desirable to carry out the process in a non-oxidizing atmosphere such as 2 atmosphere or Ar atmosphere.

The composition of the alloyed layer after the alloying treatment may be Cr -20 to 50 wt%, C1 to 3 wt%, and the balance substantially Fe, as described above, but the reason for setting it this way is as follows. That's right. In other words, Or increases hardenability, contributes to the formation of martensitic phase, and also contributes to the formation of Cr-Fe-based eutectic carbides, contributing to improved hardness and abrasion resistance, but if it is less than 20 wt%, the effect In particular, the effect of improving wear resistance due to the formation of eutectic carbides cannot be sufficiently obtained, and on the other hand, if the content exceeds 50 wt%, cracks may occur during alloying treatment. C also improves hardenability, contributes to the formation of martensitic phase, and also contributes to the formation of 0r-Fe co-carbide, contributing to improvement of hardness and wear resistance, but if it is less than 1 wt%, it has no effect. In particular, the effect of improving wear resistance due to the formation of eutectic carbides was not sufficiently obtained;
If it exceeds t%, it becomes brittle and cracks are likely to occur.

Examples [Example 1] An engine valve as shown in FIG. 1 was manufactured as follows.

That is, Cr8.0wt%, 3i1.5wt%, CO
, 5wt%, and others M n O, 6wt% or less, Q u O, 3wt% or less, N i O, 6wt%
A valve body 1 is made according to a conventional method using 5UHI i material, which is a martensitic aged steel with a composition regulated as follows and the remainder is essentially Fe, and the valve face surface 2 of the valve body 1 is Fe as alloying material
-52wt%Cr-2, 51%C alloy powder is placed,
Alloying treatment was performed using a laser at an alloying rate of 50% to form an alloyed layer 3. Here, the alloying rate is calculated by assuming that the molten cross-sectional area of the master part in the vertical cross-section of the molten part during alloying treatment is A1, and the total molten cross-sectional area in the vertical cross-section of the molten part is A+8, and the alloying ratio (%) − It is expressed as AX 100/(A×B). As a result of analysis, the composition of the obtained alloyed layer was Fe -30wt%Q r -1,5wt%C
-0.75wt%C. Thereafter, the alloyed layer was subjected to heat treatment of heating at 520° C. for 30 minutes and cooling with oil.

FIG. 2 shows the structure of the alloyed layer after heat treatment. In Figure 2, the white part is the martensite phase, and the black part is 0r-
It is a eutectic carbide made of Fe-based carbide. Furthermore, X-ray diffraction revealed that approximately 30% retained austenite existed in the dendrite portion of the alloyed layer before heat treatment, but most of the retained austonite changed to martensite after heat treatment. was approved by fI.

Furthermore, when we investigated the hardness of the alloyed layer, it was lv 380-420 before heat treatment, but after heat treatment it was lv
v 530-600 (average Hv 570), indicating that the hardness increased by approximately Hv 100.

[Example 2] A wear test test piece base material made of the same 5UH11 material as in Example 1 was subjected to the same alloying treatment as in Example 1, and then the formed alloyed layer was subjected to the same alloying treatment as in Example 1. Heat treatment was applied.

The alloyed layer of the test piece after heat treatment obtained in Example 2, the alloyed layer of the test piece that was only alloyed without heat treatment as a comparative material, and the alloyed layer of Stellite No. 6 as a conventional material. Figure 3 shows the results of a large-mirror type abrasion test conducted on the built-up layer of the test piece at room temperature.
Figure 4 shows the results of an ultra-high pressure wear test at 0°C. In addition, this large-mirror type wear test used a Fe-based sintered valve seat alloy as the mating material (rotor), and the load was 6.3 kg.
Sliding distance 100m, sliding speed 0.3'R/SeC
The wear resistance was evaluated based on the wear scar area after the test.

As is clear from FIGS. 3 and 4, Embodiment 2 of the present invention
It was found that the alloyed layer subjected to the heat treatment had excellent wear resistance with a wear area equal to or higher than that of the 30-b overlay layer compared to the comparative material subjected to only the alloying treatment.

[Example 3] After forming an alloyed layer under the same conditions as Example 1,
After heating for 30 minutes at various heating temperatures within the range of 800°C, the mixture was cooled in oil. The results of examining the hardness of the alloyed layer after heat treatment are shown in FIG. 5 in correspondence with the heating temperature.

As is clear from FIG. 5, when the heating temperature was less than 400°C, no sufficient improvement in hardness was observed, and by heating at a temperature of 400°C or higher, the hardness could be sufficiently improved. Note that when heated at 800°C, the eutectic carbide dissolved into a solid solution and became a completely martensitic structure.
Although the hardness itself was high, it was confirmed that sufficient wear resistance was not obtained.

Effects of the Invention According to the method of this invention, high Cr, high C Fe-0r-
〇When manufacturing engine valves in which an alloyed layer made of an alloy is formed on the valve face, the alloyed layer is made to have almost no retained austenite, so that the structure of the alloyed layer is changed so that the matrix is substantially Since the structure is composed only of hard martensite with hard eutectic carbides mainly composed of CrFe-based carbides crystallized in the matrix, the hardness of the alloyed layer constituting the valve face is Hv. It is possible to obtain an engine valve with extremely high wear resistance of about 500 or more, and extremely excellent wear resistance. In addition, the engine valve obtained by the method of the present invention has almost no unstable residual austenite in the alloyed layer constituting the valve face.
It is possible to prevent deformation over time caused by retained austenite.

[Brief explanation of drawings]

FIG. 1 is a partial cross-sectional front view showing the essential parts of an example of an engine valve obtained by the method of the present invention, and FIG. 2 is a front view in section of Example 1.
Figure 3 is a graph showing the results of a large mirror wear test at room temperature on the alloyed layer, and Figure 4 is the same as that of the alloyed layer. FIG. 5 is a graph showing the relationship between the heating temperature of the heat treatment after the alloying treatment and the hardness of the alloyed layer after the heat treatment. 1... Valve body, 2... Valve face surface,
3...Alloyed layer. Figure 3 Figure 4 Whirlpool degree += 400'C Mountain 5th figure force 0~-■t4 (0c)

Claims (1)

[Claims] Materials containing Cr and C are alloyed on the valve face surface of the valve body made of hardened steel using high-density heating energy to produce 20 to 50 wt% Cr, 1 to 3 wt% C,
An alloyed layer is formed in which the remainder is substantially made of Fe, then heated to a temperature in the range of 400 to 700°C for 5 minutes to 5 hours, and then rapidly cooled to change the structure of the alloyed layer so that the matrix is substantially A method for producing an engine valve, characterized in that the structure is made of martensite and has a structure in which eutectic carbides are crystallized in the matrix.