JPH08300174A - Composite sintered part and its manufacturing method - Google Patents

Abstract

(57) [Summary] [Object] To provide a method for obtaining a joint strength comparable to that of a base material without a welding defect in a sintered part welded by laser welding. [Structure] When manufacturing ferrous sintered parts or a joined part of a sintered part and a steel material, they are welded and joined by a laser welding method. Good composite parts of sintered parts can be obtained by sound welding of as-sintered material, or mechanical processing before welding in dry type, and selection of conditions such as heating in the case of wet type. Further, it has a good machinability after welding and supplies a planetary carrier and the like.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to laser welding when a planetary carrier for automobile transmission parts is to be obtained by compounding iron-based sintered parts. It relates to the conditions and pretreatment for obtaining a sound welded joint between.

[0002]

2. Description of the Related Art As a conventional technique for eliminating welding defects such as blowholes in laser welding of sintered parts containing pores, (1) Japanese Patent Laid-Open No. 59-118801 discloses steam treatment, resin impregnation, copper Sealing treatment of sintered material such as infiltration, (2) JP-A-6
Japanese Laid-Open Patent Application No. 4-66086 discloses a re-sintering treatment for removing oil / dehydration and dirt after machining a sintered part, (3) JP-A-6-287.
No. 782, Japanese Patent Laid-Open No. 6-287783, and Japanese Patent Laid-Open No. 6-293903 disclose oil by pretreatment of heating in a reducing gas or an inert gas at 400 to 600 ° C. in an atmosphere or steam gas atmosphere. Removal of water, dirt, etc., (4) JP-A-6-297172, heat treatment at 400 to 600 ° C. after welding, (5) JP-A-4-284989, Fe-Mn-Ni-Cr based solution It has been shown to use additives. In addition, the planetary carrier as a transmission part for automobiles is not laser welding of sintered parts and steel parts, but it is practical to make sintered parts by sintering brazing.
It is disclosed in Japanese Patent Publication No. 6-25643 and Japanese Patent Publication No. 6-37644.

[0003]

Originally, fusion welding such as laser welding of a sintered material having pores is more difficult than that of a molten material having no pores. In addition, there are substantive but essential problems such as stains due to the existence of the pores and oil and water soaking. As-sintered material, that is, dimensional correction,
It has been mentioned that laser welding with relatively few defects is possible with the as-sintered material without performing mechanical heat treatment or re-sintering (Japanese Patent Laid-Open No. 64-66086).
Japanese Patent Laid-Open No. 6-293903) does not disclose anything about the amount of oxygen contained at that time, impurities such as surface contamination, or the value of groove clearance. Although it is possible to prevent defects by using filler metal (Japanese Patent Laid-Open No. 4-284989), even with that, sufficient properties cannot be obtained only by using filler metal, and heat treatment before welding is required. Yes (Japanese Patent Laid-Open No. 6-29
3903), that is, the strength is remarkably inferior when there is no heat treatment before welding.

Therefore, the present invention is a subject of the welding technology of as-sintered material which has not been established yet, that is, the limit of dirt, the limit of groove gap (hereinafter referred to as clearance) of the joint, or the sintered part before welding. When the machining of steel is inevitable, the process such as deoiling conditions is fundamentally studied, and for example, the process of completely removing oil and the influence of the weight of the sintered part are clarified, which is not possible with the conventional technology. The object of the present invention is to provide a sound welded joint by simplifying the treatment work by easily defining the standard technique of the treatment work which was sufficient and easily eliminating welding defects.

[0005]

Means for Solving the Problems According to the present invention, an iron-based material of an as-sintered material containing 0.3% or less as impurities of dirt such as oil and water and 0.2% or less of oxygen contained as a material. It is a sintered part, with a groove clearance of 0.2 mm or less, and a sound laser welded steel part.

Further, according to the present invention, when machining before welding is required, dry machining is performed,
Also, when wet machining or sizing must be performed before the welding process, the wet-machined iron-based sintered parts should be placed in an atmosphere of reducing gas, inert gas such as nitrogen, or vacuum. , 610 ℃ to eutectoid transformation temperature (Fe
(Iron) -Fe ₃ C (Cementite) system does not reach the temperature corresponding to 723 ℃) After heating to deoil, dehydrate, and remove dirt,
The iron-based sintered component and the steel component are to be laser-welded. Further, according to the present invention, according to the above heat treatment conditions,
In iron-based sintered parts such as Fe-Ni-Mo alloys, it gives good machinability after welding.By compounding such sintered parts and steel materials by laser welding, A good and inexpensive planetary carrier is supplied, and in this case, the sintered parts are joined together by "sintering brazing" in which a powder compact is combined and brazing is performed at the same time as sintering. A steel material part suitable for a steel material from the viewpoints of strength, wear resistance, shaping, etc. and the above-mentioned sintered part are joined by laser welding according to the method of the present application.

[0007]

[Function] As a factor that controls the physical and mechanical properties of iron-based sintered materials, alloying elements are important, except for those related to the manufacturing method such as the density of the compact and the sintered body and the sintering temperature. is there. Chemical composition (% by weight) of the iron-based sintered material of the present invention.
Hereinafter, simply expressed as%. ) Will be explained.

(C) In the case of iron-based sintered materials as well as ordinary steel materials, it is the most important element that influences the various characteristics. C mixed as graphite powder forms a solid solution in iron during sintering. Then, during cooling, various tissues are formed according to the cooling rate. In the ordinary cooling process after sintering, a structure in which ferrite, pearlite, and both are mixed is formed. If it is hardened or contains a large amount of alloying elements that enhance hardenability, it becomes a martensite or bainite structure. Generally, as the amount of C increases, it becomes harder and the elongation becomes smaller. In the case of sintered materials, the tensile strength becomes maximum around 0.8% C. Therefore, the C content of iron-based sintered materials used as structural materials and machine parts is 1% or less, usually 0.2 to 0.8%.
It is in the C range.

(Cu) When Cu is added, since the sintering temperature exceeds the melting point of Cu, the dissolved liquid phase Cu promotes the sintering of Fe and increases the strength of the sintered material. As for the effect on dimensional change, Cu addition works on the expansion side, so by using it together with C addition on the contraction side, the role of reducing the dimensional change before and after sintering and improving the dimensional accuracy of sintered products There is. Cu does not combine with C to form its own carbide. More than 10% Cu powder may be added to oil-impregnated bearings,
The amount of Cu added in the case of iron-based sintered materials used as structural materials and machine parts is in the range of 0.5 to 3.0%. Also C 0.4
Cu1.5-2.0% is often used for ~ 0.8%.

(Ni) An element effective in improving toughness, particularly toughness at low temperatures. That is, by adding Ni, it is possible to increase tensile strength while having elongation. Ni is also Mo and Cr, which will be described later.
Improves hardenability with Mn. That is, in the isothermal transformation diagram, the transformation to ferrite or pearlite shifts to the long-term side by the addition of Ni. Ni also does not combine with C to form its own carbide. Therefore, even if the cooling rate is slow, it is likely to be baked (it tends to have a martensitic structure), and therefore the mechanical properties of the heat-treated material as well as the as-sintered material are improved. In the case of iron-based sintered materials used as structural materials and machine parts, the Ni content is 1-5%.

Similar to (Mo) Ni, it is effective in improving toughness. In the case of the addition of Mo, in the isothermal transformation diagram, the transformation to ferrite or pearlite shifts to the longer side, but the transformation to bainite shifts only slightly. Mo has a strong ability to form carbides in steel. Therefore, even if the as-sintered material has high hardness and high strength by adding Mo, mechanical properties comparable to those of heat-treated materials can be obtained. The amount of Mo in the case of iron-based sintered material is 0.5 to 1.5%.

(Cr) The role of Cr in steel is almost the same as that of Mo. As a role in the iron-based sintered material added to it, it has a strong affinity with oxygen like Mn described later,
Therefore, the sintering atmosphere is important, and usually vacuum sintering was essential. However, by being reduced (not oxidized) from the graphite added in the raw material stage of the iron-based sintered material, Cr as well as Mo can contribute to the strengthening of the sintered material. In the case of iron-based sintered material, the Cr content is 0.9 to 1.2%.

(Mn) Mn, like Cr, is easily oxidized, so it is not used alone as Mn powder, but is used as a prealloy alloy steel powder containing Mn. Mn lowers the martensitic transformation start temperature and improves hardenability. It also combines with S in steel to form MnS, which improves toughness. In the case of iron-based sintered material, the amount of added Mn is 0.1 to 0.8%. In the case of powder metallurgy, MnS powder of about 0.5% may be blended to improve machinability. In this case, the strength is reduced by about 10%.

Next, the present invention will be described in more detail. In order to perform laser welding of an iron-based sintered material (usually containing 91% by weight or more of Fe) as-sintered in a sound manner, we examined what kind of material effect it has. . As an element in the sintered material, we have confirmed that the smaller the amount of C, the fewer welding defects, but in reality, various sintered parts with varying amounts of C must be laser-welded. Is 0.8%
As the composition, 2.0% Cu mixed powder, which is widely used, was used as the raw material powder. It was also confirmed that the higher the density, the fewer welding defects, and this was also investigated at 6.9 g / cm ³ , which is often used. The size of the sample is 45 ×
20 × 4t. Although the sintering temperature was 1120 ° C and the sintering was performed in nitrogen gas,
The oxygen content in the sintered material was changed by changing the dew point in nitrogen. From Table 1 showing the relationship between the oxygen content and the welding defects (welding conditions are shown after Table 1), the oxygen content is 0.2%.
It has been found that a welded joint having no welding defects and good strength can be obtained as follows. This means that the oxygen content is adjusted by pretreatment so that it does not exceed 0.2%. In the case of laser welding of an iron-based sintered material that does not use an Fe-Mn-Ni-Cr-based filler wire, blowholes and other welding defects occurred under any conditions. Therefore, all Fe-Mn-Ni-Cr based filler wires were used in the following tests.

[0015]

[Table 1]

Welding conditions-Sintered material: Fe-2 wt% Cu-0.8 wt% C, mating material: SS41-Fe-Mn-Ni-Cr based filler wire (φ1.2) -Groove clearance ≤0.02 mm -Stored in a desiccator after sintering-Laser welding conditions-Output 4.2kW-Welding speed 1.5m / min-Wire speed 3.0m / min-Beam focus-5.0mm-He gas atmosphere

Next, as a result of investigating the quality of the welded joint by changing the clearance between the objects to be welded, as shown in Table 2, when the clearance exceeds 0.2 mm, variation in strength increases and a test of low strength is made. Examination of one piece revealed some defects. Therefore, the clearance at the welded part, which is the penetration part, must be 0.2 mm or less. Further, when left or stored under various conditions, or when intentionally soiled specimens are welded, the results are shown in Table 3. One technical point is how to store the sintered parts after sintering until laser welding, and it is important to control the storage atmosphere for a long time, at least the oxygen content is 0.2% or less, oil etc. If the ratio of the amount of dirt including the organic component and water to the whole sintered material is 0.3% or less, a welded joint having no welding defects and good strength can be obtained.

[0018]

[Table 2]

[0019]

[Table 3]

In order to ensure the required dimensional accuracy after welding, there is a case where machining before welding is necessary because machining is impossible after welding. When the influence of various pre-welding treatments after machining on the quality of the welded joint was examined, the results shown in Table 4 were obtained. Unlike the case of a normal steel material having no pores, the dry type is preferable even if it is machined in the case of a sintered material which is easily oxidized and easily soiled and which is difficult to completely clean (Table 4). In the case of wet type, in order to remove oil, dehydrate, and remove dirt without depending on the weight of parts, it is necessary to heat at a temperature of 610 ° C or higher, and the eutectoid transformation temperature (eg Fe 723 for (iron) -Fe ₃ C (cementite) system
When the temperature exceeds (° C) (850 ° C) or re-sinters, welding defects such as blow holes and cracks disappear, but the dimensional accuracy deteriorates (Table 4). Good results have also been obtained with vacuum deoiling treatment at 350 ° C, but the treatment time is long. Therefore, the heating range must be 610 ° C. or higher and a temperature that does not reach the eutectoid transformation temperature.

[0021]

[Table 4]

A basic study was conducted in connection with this pretreatment by heating. Figure 1 shows the results of a descaling process with temperature increase in Ar using a thermobalance. Further, FIG. 2 shows the molecular weight detected by mass spectrometry. From FIGS. 1 and 2, it can be confirmed that although the oil is deoiled up to 350 ° C., it must be over 600 ° C. to completely deoil or change the organic content to the inorganic content. Table 4 shows the effects of various pretreatments and the weight of sintered parts on the oil removal rate. If the weight of the sintered part is small, it is considerably deoiled by vacuum deoiling at 200 ° C. or washing with trichlene, but if it is heavy, the effect of heat treatment in the temperature range of the present application is remarkable.

If a part is divided, it may become a part (called a "piece") having a shape and characteristics suitable for sintering. One of such parts is a planetary carrier for parts used in automobile 4WD and automatic transmissions. The bosses and bridges are suitable for forming sintered parts because they can be made thicker than sheet metal to increase rigidity, and the gear parts are preferably made of steel because they require wear resistance and fatigue strength. In this way, if each part is manufactured with an inexpensive material / manufacturing method and then compounded by laser welding, the total cost is low and the quality is improved.

[0024]

【Example】

(Example 1) The prepared sample for the torsional fatigue test is a planetary carrier having the shape shown in FIG. 3, 1 is a laser welding portion, 2 is a sintered material, 3 is an SS41 material, and 4 is a jig for applying torque. The hole 5 is a hole for fixing. The inside is a sintered material and the outside is a steel material. Fix the hole on the sintered material side,
Insert the jig into the hollow of the steel material on the outside and apply torque to test. The steel material is a 4 mm thick SS41 stamped product that is machined to the specified dimensions. Sintered material is Fe-2% Cu-0.8
The as-sintered% C material was wet machined to size. After that, deoiling treatment was performed in a reducing atmosphere through a belt furnace at 650 ° C. It takes 1 hour at 650 ° C and 5 hours from the time of putting in the furnace to the time of leaving. The clearance between the groove of steel and sintered material is 0.
02 mm or less. Using Fe-Mn-Ni-Cr filler wire, the conditions are almost the same as in Table 1 (output 3.8kW, beam focus −4
mm, others are the same). The torsional fatigue test is performed with a servo-type material testing machine at 5 to 10 Hz by one-sided swing. The test results are shown in Table 5. All of them fractured at the parts other than the welded part, and showed the same strength as the welded material of SS41 materials.

[0025]

[Table 5]

Example 2 A planetary carrier made of the material having the shape shown in FIG. The member 6 (boss portion) and the member 7 (bridge portion) were respectively combined after powder compaction and sintered and brazed (also simultaneously brazed at the same time) using a brazing material at a predetermined position. That is, the members 6 and 7 are united after sintering. The member 8 (gear portion) is a heat-treated steel material in which a helical gear is toothed on the inner diameter side. The welded portion of the member 8 is machined to ensure accuracy. The bottom of the member 7 is the member 8
It is machined so that the inner diameter of the welded part and the press-fitting margin are -10 μm to +10 μm. Machining of this member 7 (actually, the sintered material that is united with the member 6) is a dry process that does not use cutting fluid, without welding pretreatment (a), and welding after wet processing that uses cutting fluid. 61 as pretreatment
When heat-treated in nitrogen at 0 ° C (up to 6 hours until leaving the furnace in a mesh belt furnace, holding at 610 ° C for up to 1 hour)
Both of (b) were carried out.

[0027]

[Table 6]

After fitting the sintered brazed product in which the members 6 and 7 were united and the member 8 were machined under the above-mentioned conditions, the Fe-Mn-Ni-Cr type filler wire (φ1.2) was attached. Laser welding was performed under the following conditions. -Laser welding conditions-Output 4.2kW-Welding speed 1.5m / min-Wire speed 3.0m / min-Beam focus-5.0mm-He gas atmosphere After welding, all the beads were good by visual inspection. (Even in the cross-sectional structure after the test, almost no welding defects such as blowholes were observed.) The dimensional accuracy of the composite was also within the predetermined range.

With respect to the planetary carrier thus obtained, a torsion torque test and a torsion fatigue test by an entity were conducted by the apparatus shown in FIG. The results are shown in Table 7. All of the breakage points were the base material portion of the sintered material other than the welded portion (also other than the sintered brazing portion). From this, it was confirmed that a good planetary carrier can be manufactured by laser welding of the sintered material and the steel material. Also, the members of sintered material 6,7
It was revealed that further improvement in strength can be expected by improving the material and shape of the base metal.

[0030]

[Table 7]

(Example 3) For a planetary carrier similar to that of Example 2, a material test which also serves as an examination of machinability is conducted. Therefore, a planetary carrier made of a sintered material having a material shown in Table 8 was prepared. A real torsional torque strength test and a machinability test were carried out. The members 6 and 7 in FIG. 4 are made of the same sintered material, and are integrated by sintering brazing, and the member 8 is a steel material SCR420H.
The welding part was machined dry and laser welding was performed without pretreatment before laser welding. The welding conditions are the same as in Example 2.

[0032]

[Table 8]

The obtained planetary carrier after laser welding was subjected to a twisting torque test of the substance using the tester shown in FIG. In the machinability test, the life of the drill was measured under the following conditions.

The results are shown in Table 9. All of the fractures in the torsion torque strength test occurred in the base metal portion other than the welded portion. For both pre-alloyed low alloy steel powder and partially diffused low alloy steel powder, the addition of MnS reduces the torsional torque strength but improves the drill life. Comparing the pre-alloy type low alloy steel powder and the partial diffusion type low alloy steel powder, in the case of the densities shown in Table 8, the pre-alloy type has better torsional torque strength and drill life.

[0035]

[Table 9]

[0036]

As described above, in the field where a ferrous sintered material and a steel material are compounded to manufacture one component, it is possible to utilize the characteristics of each part by laser welding. That is, in order to obtain a sound weld without generating welding defects, the amount of oxygen in the sintered material to be welded, the amount of impurities such as dirt, and the amount of groove clearance are set to a predetermined value or less, and sintering is performed. When it is necessary to machine the welded portion of the material, it is effective to carry out dry processing or, if wet processing cannot be avoided, deoiling / dehydrating by heating within a predetermined temperature range. Further, it is preferable to utilize the composite of the sintered material and the steel material by this method for manufacturing the planetary carrier. At that time, it is more effective if the parts of the sintered material having a complicated shape are united by sintering brazing and further laser-welded to the steel material.

[Brief description of drawings]

[Fig. 1] In a sintered material containing oil for wet processing,
It is the result of expressing the mass change based on deoiling with a thermobalance.

FIG. 2 is a result of mass spectrometry of molecules generated when the thermobalance shown in FIG. 1 is heated.

FIG. 3 is a schematic shape of a sample for a torsional fatigue test of a planetary carrier.

FIG. 4 is a schematic diagram of a planetary carrier entity.

FIG. 5 is a device for a torsion torque test of a planetary carrier substance.

[Explanation of symbols]

 9: Actuator 10: Shaft fixing jig 11: Spline shaft 12: Test body 13: Test piece mounting flange 14: Load cell

Claims (11)

[Claims] 1. When an iron-based sintered part as-sintered and a steel part are joined by a laser welding method to produce a composite sintered part, the oxygen content of the iron-based sintered part is 0.2% by weight. The following is the compound baking characterized in that the amount of impurities such as surface stains on the welded part is 0.3% by weight or less, and the groove clearance at the joint with the steel material part of the mating material is 0.2 mm or less. Manufacturing method of connection parts. 2. The method for producing a composite sintered component according to claim 1, wherein machining of the joint portion of the iron-based sintered component is performed without using a cutting fluid. 3. Machining of the joint portion of the iron-based sintered component is performed using a cutting fluid, and thereafter, in a reducing gas, an inert gas, or a vacuum within a range from 610.degree. The method for producing a composite sintered component according to claim 1, wherein heating is performed to deoil, dehydrate, and remove dirt. 4. The composite sintered body according to claim 1, wherein the composition of the iron-based sintered component contains Fe as a main component and contains Cu: 0.5 to 3.0% by weight and C: 0.2 to 0.8% by weight. Manufacturing method of parts. 5. The composition of the iron-based sintered component is mainly composed of Fe, Cu: 0.5 to 3.0% Ni: 1.0 to 5.0% Mo: 0.5 to 1.5% Cr: 0.9 to 1.2% Mn: 0.1 to 0.8 % C: 0.2-0.8% (above weight%) is contained, The claim 1 thru | or 3 characterized by the above-mentioned.
A method for manufacturing the composite sintered part described. 6. The composition of the iron-based sintered component is Cu: 1.5 to
2.0% by weight, C: 0.4 to 0.8% by weight, The method for producing a composite sintered component according to claim 4 or 5, wherein 7. The method for producing a composite sintered component according to claim 1, wherein a filler material is used in the laser welding. 8. A composite sintered component manufactured by the manufacturing method according to claim 1. 9. The composite sintered part according to claim 8, wherein the composite sintered part is a planetary carrier. 10. The composite sintered component according to claim 9, wherein the planetary carrier is formed by simultaneously sintering and brazing two sintered components and laser-welding a steel component to them. 11. The composite sintered component according to claim 8, wherein the steel component is a high alloy heat treated steel.