JP4198268B2 - Iron alloy parts - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an iron alloy component that has been surface-hardened (carburized or carbonitrided).
[0002]
[Prior art]
Conventionally, as this type of iron alloy part, there are a connecting rod, a crankshaft, a reduction gear, and the like, which are one part of an engine or the like.
[0003]
A load such as torsion torque acts on a component that transmits a driving force, such as a connecting rod or a crankshaft, so that the fatigue resistance can be improved by making the surface harder. Further, if the surface is hardened, the wear resistance can be improved, which is effective with a gear or the like.
[0004]
As a technique for hardening the surface, there is a method called carburizing treatment. This is a method in which low carbon steel is heated in a carburizing agent, carbon (C) is infiltrated from the steel surface, and the C concentration near the surface is increased. When the carburized product is rapidly cooled from the high temperature austenite state, the steel surface is martensitic and hardens, but the inside is low carbon, so it does not harden and retains its tenacity. As the carburizing agent, any of solid, liquid, and gas can be used.
[0005]
[Problems to be solved by the invention]
However, the present inventors have intensively studied whether or not the surface strength and the like can be further improved as compared with such a conventional carburizing method, and as a result, have come up with the present invention.
[0006]
Accordingly, an object of the present invention is to provide an iron alloy part having improved surface strength.
[0007]
[Means for Solving the Problems]
In order to achieve this object, the invention according to claim 1 is characterized in that C is 0.1 to 0.5% by weight, Si is 0.1 to 0.5% by weight, and Cr is 0.3 to 0.3 as chemical components. In an iron alloy part containing 1.5% by weight of iron as a base material, a grain having a structure in the range of at least 100 μm from the surface containing martensite or further retained austenite by surface hardening (carburization or carbonitriding). And Fe or Cr or both carbides or further Fe or Cr nitride is precipitated between the crystal grains, and the martensite or further retained austenite has a crystal grain size equal to the austenite grain size of the steel. Particle size measurement method using a microscope for the particle size measurement target surface specified in the test method (JIS G0551), and average particle size based on this microscope measurement No. calculation method and when measuring calculating a particle size calculation method in the same manner, as a 7 to 10, and, a hardness in the range of at least 100μm from the surface and at least Hv700 or more, effective curing the hardness is Hv550 An iron alloy part having a depth of 1 to 2 mm is used .
[0009]
Invention according to claim 2, together with the addition to the structure described, the average particle diameter before Symbol carbide or and the nitride from the surface and 10μm from 0.5μm in the range of at least 100μm to claim 1, wherein the range The area ratio of the carbide or nitride in the structure is set to 1 to 20%.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
[0011]
Embodiment 1 of the Invention
1 to 17 and FIGS. 34 to 38 show a first embodiment of the present invention.
[0012]
First, the structure will be described. In the iron alloy part 1 of the first embodiment, C is 0.1 to 0.5% by weight, Si is 0.1 to 0.5% by weight, and Cr is 0.3% as chemical components. To 4.0% by weight of iron as a base material and surface hardening treatment (carburizing or carbonitriding). FIG. 1 and FIGS. 34 to 38 show standards for chemical components of the base material that can be adopted as the iron alloy part of the present invention. This standard is made by hot working such as hot rolling and hot forging. In general, it is defined for structural steel materials that are further subjected to processing such as forging and cutting and heat treatment, and that are guaranteed for one-end hardenability, mainly used for mechanical structures. In Embodiment 1 of the present invention, SCM 420 is used as a substrate in FIGS. 1 and 34 to 38.
[0013]
And this iron alloy component 1 is constituted by a surface hardening treatment (carburization or carbonitriding) including a structure in the range of at least 100 μm from the surface including martensite 2, and the grain size of the martensite 2 has a grain size, When measuring and calculating by the same method as the particle size measurement method and particle size calculation method based on this microscope measurement, and the particle size measurement method for the particle size measurement target surface specified in the steel austenite grain size test method (JIS G 0551) 7 to 10. FIG. 2 shows that when steel is heated to a temperature above the transformation point or to a solution heat treatment temperature for annealing, normalizing, quenching, carburizing and other purposes according to the austenite grain size test method for steel (JIS G 0551). the austenite grain determined by the temperature and holding time the size, the grain size number obtained by measuring by the method of defining a predetermined particle size, the correlation of the average cross-sectional area of the number and the crystal grain cross-sectional area 1mm per ² grains 2 is also applied to the grain size number in the martensite 2 structure (measured and calculated by the same method as defined in the above-mentioned steel austenite grain size test method (JIS G 0551)). Thus, the number of crystal grains per 1 mm ² cross-sectional area or the average cross-sectional area of crystal grains can be roughly determined.
[0014]
Further, at least one carbide 3 of Fe or Cr is precipitated on the surface by surface hardening treatment, and the average particle size of the carbide 3 in this structure is 0.5 to 10 μm, and the area ratio of the carbide 3 in the structure Is in the range of 1 to 20 percent, at least 100 μm in hardness in the range of HV700 or more, and the surface roughness Ra2 or less.
[0015]
The surface hardening treatment of the iron alloy component 1 is performed as follows.
[0016]
First, the material of SCM420H is used as the base material of the iron alloy component 1 as described above.
[0017]
Then, the substrate is carburized for the first time. That is, when carburizing with gas, when the horizontal left-right direction is the longitudinal direction of the carburizing furnace, the side surfaces in the front-rear direction, the ceiling surface, and the bottom surface are closed walls, and at least the front and rear side surfaces and the ceiling surface are electrically heated or gas The heating means by a burner is arrange | positioned, and it becomes what respectively arrange | positioned the opening-and-closing door at both ends of the left-right direction. One of the open / close doors serves as a carry-in entrance for the iron alloy member 1 placed on a metal pallet subjected to a carbon-proof treatment, and the other serves as a carry-out exit. In the carburizing furnace, in order to further create a carbon atmosphere, a gas inlet for introducing a carburizing gas composed of a hydrocarbon gas such as CO gas or methane, and CO2 gas or water vapor that does not penetrate the surface of the iron alloy member 1 (heating heat) Exhaust gas outlets (including gases that can result from combustion) are provided. Carburization is performed by introducing the carburizing gas into the furnace and heating the carburizing gas to a predetermined temperature by a heating means on the wall surface, or stopping the heating and stopping the heating (furnace cooling). Heating is performed by detecting the heating color of the surface of the iron alloy component 1 and measuring the temperature, or by measuring the temperature with a temperature sensor inserted in the furnace and controlling the heating amount. The carbon atmosphere concentration is calculated by detecting a 02 gas concentration and using a predetermined calculation program. In order to make the carbon atmosphere concentration constant, the feed amount of the carburizing gas is feedback-controlled while detecting the 02 gas concentration. In this embodiment, as shown in FIG. 4, the carbon atmosphere concentration is CP (carbon potential) = 1.60, and after carburizing by heating at 950 ° C. for 3 hours, the temperature of the Al wire ( Or iron alloy heated together with the pallet in an oil tank or a water tank containing a predetermined volume or more of oil or water. Quenching (MQ) for immersing the member 1 is performed. That is, CP is the value of the steel concentration shown in FIG. 3 so that the carbon concentration (C%) is in the range from the S point (0.8% C) to the E point (2.1% C). While it is set to 1.60, it is set to a temperature range above the Al wire, here 950 ° C. In this way, the surface of the excessively carburized steel exhibits a hypereutectoid structure in which free cementite appears in the grain boundaries.
[0018]
As for the metal structure formed by this first carburization, the average grain size of the martensite 2 crystal grains is about 20 μm as shown in FIG. 5, and further expanding this, as shown in FIG. Between the crystal grains of the large martensite 2, a net-like carbide 3 is precipitated. Further, as shown in FIG. 7, the average grain size of the martensite 2 crystal grains is about 25 μm at the center.
[0019]
Next, the second carburization is performed on the first carburized one. In this case, the carbon atmosphere concentration is heated at 900 ° C. for 2 hours at CP = 1.20, and then heated at 850 ° C. for 20 minutes. That is, CP is the value of the steel concentration shown in FIG. 4 so that the carbon concentration (C%) is in the range from the S point (0.8% C) to the E point (2.1% C). While it is set to 1.20, it is set to a temperature range below the Acm line and above the Al line, here 900 ° C.
[0020]
By this treatment, carbon in the excessive carburized layer is diffused into the inside and C% of the surface is kept at 0.8% or more. If it is less than 0.8%, the carbide 3 does not precipitate on the surface.
[0021]
Then, quenching (MQ) of either oil quenching or water quenching is performed, and tempering is performed by heating at 160 ° C. for 1 hour 30 minutes.
[0022]
As for the metal structure formed by the second carburizing, the average grain size of the martensite 2 crystal grains is about 5 μm as shown in FIG. 8, and when this is enlarged, as shown in FIG. As the grain size of the martensite 2 becomes smaller than the first, the carbide 3 changes from a network to a fine grain.
[0023]
In the central portion, as shown in FIG. 10, the average grain size of the martensite 2 crystal grains is approximately 14 μm.
[0024]
In addition, when cooling after the first carburizing is performed by quenching instead of furnace cooling, the austenite crystal grains are not all martensite 2 in the surface, and residual austenite may be mixed. 2 and the residual austenite crystal grains have an average diameter of about 20 μm, and the remaining austenite crystal grains remain after quenching after the second carburizing regardless of the cooling method after the first carburizing. There is also. Even in this case, the average diameter of the martensite 2 and retained austenite grains is approximately 5 μm, and the grain sizes of the martensite 2 and retained austenite grains are specified in the austenite grain size test method for steel (JIS G 0551). The particle size measured and calculated by the same method as the method can be 7 to 10. That is, in a state where heat treatment is completed after a plurality of carburizing steps and post treatments, a structure in the range of at least 100 μm from the surface can be configured to include martensite even if residual austenite crystal grains are mixed. .
[0025]
By performing carburization a plurality of times in this way, the surface of the iron alloy component 1 is composed of martensite 2 as described above, and carbide 3 (Fe ₃ C or Cr ₃ C) is precipitated. And while carburizing from the surface of the iron alloy component 1 to a deep place, the carbide | carbonized_material 3 will disperse | distribute particle | grains, and intensity | strength will improve.
[0026]
Furthermore, as shown in FIG. 11, in the surface layer of 0.1 mm from the surface, when analyzing the image of three circular field ranges (field 1, field 2, field 3) having a diameter of 44.06 μm, The dispersion state of the carbide 3 particles is as shown in FIG. That is, the average values of the visual fields 1 to 3 are as follows. The total area (μm ² ) of the particles is 90.93 μm ² , the area ratio (%) is 5.97%, the number of particles is 69.67, and the maximum particle size (μm ) Is 3.56 μm, the minimum particle size (μm) is 0.35 μm, and the average particle size (μm) is 1.1 μm. This fine carbide 3 inhibits the growth of the martensite 2 crystal grains, the grain size of the martensite 2 near the surface can be made fine (average particle size of 1 to 10 μm), the surface stress is increased, and the bending strength is improved. be able to. The normal average particle size is about 10 to 20 μm.
[0027]
That is, FIG. 13 shows the relationship between depth and hardness (Hv) in the case where the base material of SCM420 is carburized as described above. According to this, the effective hardening depth which becomes Hv550 is 1.45 mm (E1.45), the surface hardness is Hv890, and the center hardness is Hv441.
[0028]
The effective curing depth may be changed in the range of 1 to 2 mm by lowering or increasing the surface hardness from Hv890 while maintaining the hardness in the range of 100 μm from the surface at Hv700 or higher.
[0029]
FIG. 14 shows the relationship between the martensite crystal grain size and 10 ⁷ times fatigue strength. It can be seen that when the crystal grain size is 10 μm or less, the fatigue strength rapidly increases. If it tries, since an average particle diameter can be made into about 1-10 micrometers by carburizing several times as mentioned above, fatigue strength can also be enlarged.
[0030]
Further, FIG. 15 shows data in the case where the smoothed material carburized as described above was subjected to the Ono-type rotary bending test at room temperature, and FIG. 16 shows the stress amplitude (MPa) and the number of repetitions of fracture ( N). According to this, in the measurement units 1, 2, 3, 4, 5, 8, 9, and 11, the number of repetitions of destruction (N) is 1.00E + 07 (10 ⁷ ). In the measurement units 8, 9, and 11, the stress amplitude (MPa) exceeds 1000.
[0031]
On the other hand, FIG. 17 shows data when a smoothing material carburized once as in the prior art is subjected to an Ono-type rotary bending test at room temperature, and FIG. 18 shows the stress amplitude (MPa) and fracture. The relationship with the number of repetitions (N) is shown. According to this, the number of repetitions of destruction (N) is 1.00E + 07 (10 ⁷ ) in the measurement units 1, 2, and 3. In these measurement units 1, 2, and 3, the stress amplitude (MPa) is smaller than 800.
[0032]
Therefore, it can be seen that the strength against repeated stress is improved by performing the carburization a plurality of times as in the first embodiment of the present invention.
[0033]
Furthermore, when the surface roughness is set to Ra2 or less, it is possible to prevent a decrease in strength due to stress concentration, and it is possible to further improve the strength by combining shot peening with the above-mentioned multiple carburization.
[0034]
[Embodiment 2 of the Invention]
FIG. 19 shows a second embodiment of the present invention.
[0035]
The second embodiment is different from the first embodiment in the carburizing method. That is, the first carburization is performed on the base material of the iron alloy component 1 similar to that of the first embodiment. This is because the carbon atmosphere concentration is CP (carbon potential) = 1.40, carburized by heating at 950 ° C. for 3 hours, and then cooled to a temperature below the temperature of the Al wire (727 ° C.). (FC) or quench (MQ).
[0036]
Next, the second carburization is performed on the first carburized one. This is done by heating at 850 ° C. for 20 minutes after heating at 900 ° C. for 2 hours in a CP atmosphere of CP = 1.20.
[0037]
Thereafter, quenching (MQ) with oil or water is performed.
[0038]
Even if it does in this way, the effect substantially the same as Embodiment 1 is acquired.
[0039]
Embodiment 3 of the Invention
FIG. 20 shows a third embodiment of the present invention.
[0040]
In the third embodiment, carburization is performed three times. That is, the first carburization is performed on the base material of the iron alloy component 1 similar to that of the first embodiment. This is because the carbon atmosphere concentration is CP (carbon potential) = 1.60, carburized by heating at 950 ° C. for 3 hours, and then cooled to a temperature below the temperature of the Al wire (727 ° C.). (FC) or quench (MQ).
[0041]
Next, the second carburization is performed on the first carburized one. In this case, carburization is performed by heating at 900 ° C. for 2 hours in a carbon atmosphere concentration of CP = 1.20, and then the furnace is cooled to a temperature lower than the temperature of the Al wire (727 ° C.).
[0042]
Further, the third carburization is performed on the finished carburization of the second time. In this case, carburization is performed by heating at 820 ° C. for 1 hour while the carbon atmosphere concentration is CP = 1.20.
[0043]
Thereafter, quenching (MQ) with oil or water is performed.
[0044]
Even if it does in this way, the effect substantially the same as Embodiment 1 is acquired.
[0045]
[Embodiment 4 of the Invention]
In FIG. 20, the first carburizing is performed on the base material of the iron alloy component 1 similar to that of the first embodiment. This is because the carbon atmosphere concentration is CP (carbon potential) = 1.05, and after carburizing by heating at 850 ° C. for 2 hours, the furnace is cooled to a temperature below the temperature of the Al wire (727 ° C.). (FC) or quench (MQ).
[0046]
Next, the second carburization is performed on the first carburized one. In this case, carburization is performed by heating at 800 ° C. for 30 minutes in a CP atmosphere of CP = 1.00.
[0047]
Thereafter, quenching (MQ) with oil or water is performed.
[0048]
[Embodiment 5 of the Invention]
FIG. 22 shows a fifth embodiment of the present invention.
[0049]
In the fifth embodiment, the first carburization is performed on the base material of the iron alloy component 1 similar to the first embodiment. This is because the carbon atmosphere concentration is CP (carbon potential) = 1.20, carburized by heating at 900 ° C. for 1 hour, and then cooled to a temperature below the temperature of the Al wire (727 ° C.). (FC) or quench (MQ).
[0050]
Next, the second carburization is performed on the first carburized one. In this case, carburization is performed by heating at 800 ° C. for 30 minutes in a CP atmosphere of CP = 1.00.
[0051]
Thereafter, quenching (MQ) with oil or water is performed.
[0052]
Here, it can be seen that the martensite crystal grain size in the iron alloy part 1 manufactured by the method described in the first to fifth embodiments has a distribution as shown in FIG. 22 and is smaller than 10 μm. As a result, since the average particle size becomes about 5 μm by carburizing a plurality of times as described above, the fatigue strength rapidly increases as is apparent from FIG. Incidentally, in the case of one-time carburization, as shown in FIG. 23, since the crystal grain size is about 14 μm, it can be seen that the fatigue strength is greatly reduced as compared with the above.
[0053]
[Sixth Embodiment of the Invention]
24 to 33 show a sixth embodiment of the present invention.
[0054]
In the sixth embodiment, the entire iron alloy part is not carburized a plurality of times, but has a part carburized once and a part carburized twice.
[0055]
That is, FIGS. 24 and 25 show the integrated connecting rod 11.
[0056]
The connecting rod 11 has a small end portion 11a connected to a piston side (not shown) and a large end portion 11b connected to a crankshaft side (not shown), and these are connected via a connecting rod portion 11c. ing.
[0057]
And since the small end part 11a and the large end part 11b are connected with a piston and a crankshaft, since the hardness of the surface is required, the connecting rod part 11c is in contrast to being carburized twice. Since the hardness of the surface is not so required, it is carburized once.
[0058]
More specifically, the regions having a hardness of HV700 or higher are the large end portion 11b and the small end portion 11a, which are at least 0.5 mm or more from the surface, and are less than 0.5 mm at the connecting rod portion 11c.
[0059]
The structure of the surface layer is composed of martensite 2, and the average particle size of the carbide 3 in the structure is 0.5 μm to 10 μm in the surface layer of the large end portion 11b and the small end portion 11a, and the connecting rod portion The surface layer of 11c is less than 0.5 μm.
[0060]
The area ratio of the carbide 3 in the structure is 1% or more in the surface layer of the large end portion 11b and the small end portion 11a, and is less than 1% in the surface layer of the connecting rod portion 11c.
[0061]
The martensite grain size of the large end portion 11b and the small end portion 11a is set to a grain size number (JIS G 0551) 7 to 10, and the surface roughness is Ra 2 μm in the surface layer of the large end portion 11b and the small end portion 11a. Thus, the surface layer of the connecting rod portion 11c is less than Ra2 μm.
[0062]
Next, the manufacturing process of the connecting rod 11 will be described. As shown in FIG. 25, first, the material before forging is forged (1), deburred (2), and then the small end 11a is small. End face processing (3) is performed for the end hole 11d, the large end hole 11e of the large end portion 11b, and the small end portion 11a and the large end portion 11b.
[0063]
Thereafter, the connecting rod portion 11c is masked (4) by copper plating or the like, and after the first carburization (5), the masking removal process (6) is performed, and the second carburization (7) is performed.
[0064]
Next, strain removal (8) is performed, and the small end hole 11d and the large end hole 11e are polished (9) to complete the manufacture of the connecting rod 11.
[0065]
On the other hand, as another manufacturing process, for example, the first carburization (10) is performed after the end surface processing (3) of the small end hole 11d, the large end hole 11e, the small end portion 11a, and the large end portion 11b. Then, masking (11) is performed. Thereafter, after performing the second carburization (12), the strain removal (13) is performed, and the small end hole 11d and the large end hole 11e can be polished (14).
[0066]
26 and 27 show the split connecting rod 11.
[0067]
The connecting rod 11 has a small end portion 11a connected to a piston side (not shown) and a large end portion 11b connected to a crankshaft side (not shown), and these are connected via a connecting rod portion 11c. ing. The large end portion 11b is divided, and a large end hole 11e is formed by attaching a cap 11f with a bolt 11g.
[0068]
And since the small end part 11a and the large end part 11b are connected with a piston and a crankshaft, since the hardness of the surface is required, the connecting rod part 11c is in contrast to being carburized twice. Since the hardness of the surface is not so required, it is carburized once.
[0069]
Next, the manufacturing process of the connecting rod 11 will be described. As shown in FIG. 27, first, the material before forging is forged (1) and deburred (2), then the small end hole 11d, End hole 11e processing and small end portion 11a and large end portion 11b end surface processing (3) are performed.
[0070]
Thereafter, the connecting rod portion 11c is masked (4) by copper plating or the like, and after the first carburization (5), the masking removal process (6) is performed, and the second carburization (7) is performed.
[0071]
Next, the strain removal (8) is performed, the large end portion 11b is divided (9), and the large end portion 11b is coupled (10) with the bolt 11g. Then, the small end hole 11d and the large end hole 11e are polished (11) to complete the manufacture of the connecting rod 11.
[0072]
On the other hand, as another manufacturing process, for example, the first carburization (12) is performed after the end face processing (3) of each of the small end hole 11d, the large end hole 11e, the small end portion 11a, and the large end portion 11b. Then, masking (13) is performed. Then, after performing the second carburization (14), the distortion removal (15) is performed, the large end portion 11b is divided (16), and the large end portion 11b is coupled (17) with the bolt 11g. Then, the small end hole 11d and the large end hole 11e are polished (18) to complete the manufacture of the connecting rod 11.
[0073]
28 and 29 show the crankshaft 13.
[0074]
As shown in FIG. 28 (a), the crankshaft 13 includes a crankpin portion 13a to which a connecting rod is connected, a journal portion 13b to be connected to a crankcase, a crank web portion 13c for generating an inertial force during rotation, and the like. In addition, as shown in FIG. 28B, an oil hole 13d, an end screw portion 13e, and the like are formed.
[0075]
And since the crankpin part 13a and the journal part 13b are connected with a connecting rod and a crankcase, and the surface hardness is required, the crank web part 13c Since the surface hardness is not so required, it is carburized once.
[0076]
Next, the manufacturing process of the crankshaft 13 will be described. As shown in FIG. 29, first, the material before forging is forged (1) and deburred (2), and then the crankpin portion 13a, The journal part 13b, the oil hole 13d, and the end screw part 13e are processed (3).
[0077]
Thereafter, the first carburization (4) is performed, and the crank web portion 13c is masked (5). In this masking method, first, the entire crankshaft 13 is plated with copper, and then the outer peripheral plating of the journal portion 13b and the crankpin portion 13a is removed.
[0078]
Next, after performing the second carburization (6), the distortion removal (7) is performed, and the outer periphery polishing (8) of the journal portion 13b, the crankpin portion 13a and the like is performed, and the manufacture of the crankshaft 13 is completed.
[0079]
30 and 31 show the reduction gear 15.
[0080]
As shown in FIG. 29, the reduction gear 15 is formed with an insertion hole 15b into which a shaft is inserted into the middle intermediate disk portion 15a. A bush 15c is press-fitted into the insertion hole 15b after the reduction gear 15 is completed. It is like that. A boss portion 15e having a plurality of boss holes 15d is formed around the intermediate disk portion 15a, and a large number of tooth portions 15f are formed at the peripheral portion.
[0081]
The tooth surface of the tooth portion 15f is carburized twice because the surface hardness is required, whereas the intermediate disk portion 15a and the boss portion 15e other than that have a surface hardness that much. Since it is not required, it has been carburized once.
[0082]
Next, the manufacturing process of the reduction gear 15 will be described. As shown in FIG. 31, first, the material before forging is forged (1) and deburred (2), and then the outer shape, the boss hole 15d. Then, processing (3) of the end surface of the boss 15e, the tooth surface, etc. is performed.
[0083]
Thereafter, the intermediate disk portion 15a and the boss portion 15e are masked (4) by copper plating, and then the first carburization (5) is performed to perform the masking removal process (6). Then, second carburization (7) is performed, tooth surface polishing (8) is performed, and the production of the reduction gear 15 is completed.
[0084]
On the other hand, as another manufacturing process, for example, after processing (3) the outer shape, the boss hole 15d, the end surface of the boss portion 15e, the tooth surface, etc., after performing the first carburization (9), the intermediate disk portion 15a and the boss portion Mask 15e (10). Next, the second carburization (11) is performed, the tooth surface 15f is ground (12), and the production of the reduction gear 15 is completed.
[0085]
32 and 33 show the piston pin 17.
[0086]
This piston pin 17 connects a piston and a connecting rod, and as shown in FIG. 31, a through hole 17b is formed inside a rod-like piston pin main body 17a.
[0087]
And since the outer peripheral surface of this piston pin main body 17a requires surface hardness, it is carburized twice, whereas the inner peripheral surface of the through-hole 17b does not require so much surface hardness. Carburized once.
[0088]
Next, the manufacturing process of the piston pin 17 will be described. As shown in FIG. 32, first, the rod is cut at both end faces (1), and the through hole 17b, outer shape, and end face processing (2) are performed. Then, the inner peripheral portion of the through hole 17b is masked (3), the first carburization (4) is performed, and the masking removal (5) is performed. Next, after performing the second carburization (6), outer shape centerless polishing (7) is performed, and the manufacture of the piston pin 17 is completed.
[0089]
On the other hand, as another manufacturing process, for example, after the through hole 17b, outer shape, and end face processing (2), the first carburization (8) is performed, and then the inner peripheral portion of the through hole 17b is masked (9). Next, the second carburization (10) is performed, the outer shape centerless polishing (11) is performed, and the manufacture of the piston pin 17 is completed.
[0090]
Thus, in the sixth embodiment, carburizing can be performed more rationally by carburizing only a portion requiring surface strength a plurality of times and carburizing the other portions once.
[0091]
In addition, masking or masking removal is performed in a plurality of forging steps of the connecting rod 11 shown in FIGS. 25 and 27, the crankshaft 13 shown in FIG. 29, the reduction gear 15 shown in FIG. 31, and the piston pin 17 shown in FIG. However, the carburizing tank is only the surface of the iron alloy parts, the inside is sufficiently tough, and the toughness of the surface tank is not particularly required (in the case of internal combustion engine parts where the output of the internal combustion engine is small, etc.) In addition, masking may not be performed during a plurality of carburizing steps of the iron alloy parts such as the connecting rod 11, the crankshaft 13, the reduction gear 15 and the piston pin 17, and a surface hardened structure may be formed on the entire iron alloy parts by a plurality of carburizing processes. .
[0092]
Still further, in each of the multiple carburizing heat treatments shown in FIGS. 4 and 19 to 22, the iron alloy part is further heated to a temperature of approximately 160 ° C. and maintained at a temperature of approximately 160 ° C. for about 1 hour 30 minutes, and then air cooling You may make it implement tempering. Thereby, distortion can be removed while maintaining the surface hardened structure.
[0093]
Furthermore, in the case of carbonitriding, a carbon / nitrogen atmosphere is created by introducing a carbonitriding gas in which ammonia gas is added to a hydrocarbon gas such as CO gas or methane into a heating furnace. In this case, while controlling the nitrogen atmosphere concentration to be a predetermined value, other heating temperature, heating holding time, carbon atmosphere concentration, number of heating and cooling, cooling method, and the like are shown in FIG. 4 or FIGS. It may be the same as. Thus, carbonitriding may be performed a plurality of times, or one of the plurality of heat treatments may be carburized and the other may be carbonitrided. It is the same as in the case of multiple carburization that masking is not required during the multiple carbonitriding process of iron alloy parts or during the combined multiple carburizing and carbonitriding process. Multiple carburization, multiple carbonitriding, carburizing and carbonitriding combined multiple treatments not only increase the surface hardness of iron alloy parts, but also the surface structure is composed only of dense martensite crystal grains, or dense residual austenite is mixed It is made of dense martensite crystal grains and can improve wear resistance and fatigue strength. By adding a carbonitriding step, a structure in the range of at least 100 μm from the surface is added to crystal grains containing martensite or further retained austenite, and Fe or Cr or both carbides are added to this crystal grain boundary. Alternatively, it can be configured by depositing both nitrides. Then, by heating and cooling in each of the above embodiments, the average particle diameter of the nitride in addition to the carbide is set to 0.5 μm to 10 μm in the range of at least 100 μm from the surface, and the carbide in the structure in the range Alternatively, the area ratio of the nitride may be 1 to 20%. This can further improve wear resistance and fatigue strength.
[0094]
Furthermore, the data of FIGS. 13 to 17 are for the case where SCM420H is used as a base material, but a plurality of carburized steels with all the structural steel materials described in FIGS. 1 and 34 to 38 as base materials. By performing a plurality of combinations of multiple carbonitriding, carburizing and carbonitriding, it is possible to improve the wear resistance and fatigue strength of the iron alloy component.
[0095]
【The invention's effect】
As described above, according to the invention described in each claim, the surface strength of the iron alloy component can be improved as compared with the conventional one, and the wear resistance and fatigue strength can be improved.
[Brief description of the drawings]
FIG. 1 is a table showing symbols and chemical components of steel material types according to Embodiment 1 of the present invention.
FIG. 2 is a table showing martensite grain size numbers according to the first embodiment.
FIG. 3 is a state diagram of steel according to the first embodiment.
FIG. 4 is an explanatory diagram of a carburizing method according to the first embodiment.
FIG. 5 is an enlarged view showing the metal structure of the surface of the iron alloy part when carburized once according to the first embodiment.
6 is a further enlarged view of the surface of the metal structure shown in FIG. 5 according to the first embodiment.
FIG. 7 is an enlarged view showing a metal structure of a central portion of an iron alloy part when carburized once according to the first embodiment.
FIG. 8 is an enlarged view showing a metallographic structure of the surface of the iron alloy part when carburized twice according to the first embodiment.
9 is a further enlarged view of the surface of the metal structure shown in FIG. 8 according to the first embodiment.
FIG. 10 is an enlarged view showing the metal structure of the central portion of the iron alloy part when carburized twice according to the first embodiment.
11 is a view showing the surface of the iron alloy component according to Embodiment 1. FIG.
FIG. 12 is a table showing a dispersion state of carbide particles in the twice-carburized metal structure according to the first embodiment.
FIG. 13 is an altitude curve diagram according to the first embodiment.
14 is a graph showing the relationship between the martensite crystal grain size and the 10 ⁷ times fatigue strength according to Embodiment 1. FIG.
15 is a table showing the life and the like in each part of the iron alloy component according to Embodiment 1. FIG.
FIG. 16 is a graph showing the relationship between the number of fracture repetitions and the stress amplitude according to the first embodiment.
FIG. 17 is a table showing the life of each part of a conventional iron alloy part.
FIG. 18 is a graph showing the relationship between the number of repeated fractures and the stress amplitude in each part of a conventional iron alloy part.
FIG. 19 is an explanatory diagram of a carburizing method according to Embodiment 2 of the present invention.
FIG. 20 is an explanatory diagram of a carburizing method according to Embodiment 3 of the present invention.
FIG. 21 is an explanatory diagram of a carburizing method according to Embodiment 4 of the present invention.
FIG. 22 is an explanatory diagram of a carburizing method according to Embodiment 5 of the present invention.
FIG. 23 is a graph showing the martensite crystal grain size in the first to fifth embodiments.
FIGS. 24A and 24B are views showing an integrated connecting rod according to Embodiment 6 of the present invention, in which FIG. 24A is a front view of the connecting rod, FIG. 24B is a cross-sectional view taken along line AA in FIG. ) Is a cross-sectional view taken along line BB in FIG.
25 is a diagram of a manufacturing process of the connecting rod shown in FIG. 24 according to Embodiment 6. FIG.
26A and 26B are diagrams showing a split type connecting rod according to the sixth embodiment, where FIG. 26A is a front view showing a cross section of a part of the connecting rod, and FIG. 26B is a cross section showing a split portion at the large end of the connecting rod. It is.
27 is a diagram showing a manufacturing process of the connecting rod shown in FIG. 26 according to the sixth embodiment. FIG.
FIG. 28 shows a crankshaft according to the sixth embodiment, where (a) is a front view of the crankshaft and (b) is a partially enlarged sectional view of the crankshaft.
29 is a diagram of a manufacturing process of the crankshaft shown in FIG. 28 according to the sixth embodiment. FIG.
30 is a view showing a reduction gear according to Embodiment 6, wherein (a) is a front view of the reduction gear, and (b) is a cross-sectional view taken along line CC of (a). FIG.
FIG. 31 is a diagram of a manufacturing process of the reduction gear shown in FIG. 30 according to the sixth embodiment.
32 is a sectional view showing a piston pin according to the sixth embodiment. FIG.
33 is a diagram of a manufacturing process of the piston pin shown in FIG. 32 according to the sixth embodiment. FIG.
FIG. 34 is a table showing steel type symbols and chemical components according to another embodiment of the present invention.
FIG. 35 is a table showing symbols and chemical components of steel material types according to other embodiments of the present invention.
FIG. 36 is a table showing steel material type symbols and chemical components according to another embodiment of the present invention.
FIG. 37 is a table showing symbols and chemical components of steel material types according to other embodiments of the present invention.
FIG. 38 is a table showing symbols and chemical components of steel types according to other embodiments of the present invention.
[Explanation of symbols]
1 Iron alloy parts 2 Martensite 3 Carbide

Claims (2)

Iron alloy parts based on iron containing 0.1 to 0.5 wt% C, 0.1 to 0.5 wt% Si, 0.3 to 1.5 wt% Cr as chemical components In the above, by surface hardening treatment (carburization or carbonitriding), a structure in the range of at least 100 μm from the surface, martensite or crystal grains containing residual austenite, and Fe or Cr or both carbides between these crystal grains or further It is composed of a precipitate of Fe or Cr nitride, and the crystal grain size of the martensite or further retained austenite is the particle size by the microscope of the surface of the particle size measurement target specified in the austenite grain size test method (JIS G0551) of steel. The measurement method and the average particle size number calculation method and particle size calculation method based on this microscopic measurement are used for measurement and calculation. If, as a 7 to 10, and, as at least Hv700 or more hardness in the range of at least 100μm from the surface,
An iron alloy part characterized in that the effective hardening depth at which the hardness is Hv550 is 1 to 2 mm . While before Symbol carbide or and surface average particle size of the nitride and 10μm from 0.5μm in the range of at least 100 [mu] m, the area ratio of the carbide or and the nitride in the tissue of the range of 1 to 20% iron alloy part of claim 1 Symbol mounting, characterized in that the the.

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