JP2017088911A - Quenching method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of suppressing strain of a wall part 26a of a steel component 24A when hardening the steel component 24A having a pair of wall parts 26a and 26a.SOLUTION: In a hardening method of the present invention, a lowering upper 24a provided with a thick part 32, and a pair of tabular pin boss wall parts 26a and 26a erecting vertically from the thick part 32 is arranged on a tray 6. Here, the lowering upper 24a has a vertical attitude where a parting plane 28 stands up vertically from a flat surface 6a of the tray 6. Then, so as to surround a lower part of the lowering upper 24a on the tray 6, a thermal conductive tool 23 having four plate parts 19, 20, 21 and 22 is arranged. At this time, the plate part 19 covers an opening surface 33a of a groove 33, and the plate parts 20 and 21 stick fast to outer side surfaces 36 and 36 of the pin boss wall parts 26a and 26a. With the lowering upper 24A surrounded by the tool 23, nitrogen gas is supplied toward the tray 6.SELECTED DRAWING: Figure 7

Description

  The present invention relates to a method for quenching steel parts.

  The quenching of steel parts is a heat treatment technique for obtaining a martensite structure by rapidly cooling a steel part after it is brought to a high temperature state. At the time of quenching, the steel part expands with the martensitic transformation, so that the steel part is deformed according to the expansion. The degree of deformation (strain) of a steel part is determined by the degree of expansion, the difference in expansion amount due to the part of the steel part, the difference in expansion timing depending on the part, and the like.

  Patent Document 1 discloses an austempering method for rapidly cooling a steel part using a pair of forming heat treatment molds having a heater inside. In this processing method, after the steel part heated to the austenite region is cooled to a temperature higher than the martensitic transformation start temperature, the temperature of the steel part is raised to some extent by the heater and then kept constant. Then, the steel part is cooled to a temperature lower than the martensitic transformation start temperature.

JP-A-9-296214

  However, since the cooling of steel parts is once stopped in the austempering method of Patent Document 1, when the austempering method of Patent Document 1 is applied to the quenching method of steel parts to obtain a martensite structure, the cooling rate of the steel parts Becomes slower.

  Moreover, in patent document 1, since the exclusive heat processing type | mold corresponding to the shape of steel parts is used, the structure of a cooling device becomes complicated and the cost concerning an apparatus increases.

  In the present invention, a steel part having a U-shaped cross section having a pair of walls is arranged on a tray capable of flowing refrigerant, and the steel part is cooled and quenched by supplying the refrigerant toward the tray. The steel part is disposed on the tray so that the U-shaped surface of the steel part becomes the bottom surface on the tray, and has at least three surfaces surrounding the steel part, and has a thermal conductivity. Using the provided jig, the one surface of the jig covers the opening surface of the U-shaped steel part, and the two surfaces of the jig are in close contact with the outer surfaces of the pair of wall portions of the steel part. The coolant is supplied toward the tray in a state where the steel part is surrounded by the jig.

  Therefore, a passage is formed by covering the opening surface between the pair of wall portions with one surface of the jig, and the inner surface of the wall portion is reliably cooled by the refrigerant flowing in the passage.

  Moreover, the outer surface of the wall is cooled by the refrigerant flowing outside the wall via a jig.

  According to the present invention, since the difference between the cooling rate of the inner side surface of the wall portion and the cooling rate of the outer side surface is reduced, the distortion generated in the wall portion during quenching is reduced.

It is sectional drawing of the gas quenching furnace of one Example. It is explanatory drawing of the components of one Example. It is explanatory drawing which shows the package figure of the components of one Example. It is explanatory drawing which shows the package figure of the components of a comparative example. It is a graph which shows the result of the variation | change_quantity of the distance between two wall parts in the gas quenching method of a comparative example, and the gas quenching method of one Example. It is explanatory drawing of the lower link of one Example. It is explanatory drawing which shows the gas quenching method of a 2nd Example.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 shows a gas quenching furnace 1 used in the gas quenching method of the present invention. This gas quenching furnace 1 is a box-type device in which six faces are constituted by a front wall (not shown), a rear wall 2, a pair of side walls 3a, 3b, an upper wall 4, and a lower wall 5. . The gas quenching furnace 1 has, on one side wall 3a, an inlet 7 for carrying a steel part 12 (or 24A) to be gas quenching target, which will be described later, together with the tray 6 into the gas quenching furnace 1, The other side wall 3b opposite to one side wall 3a has an outlet 8 for carrying the steel part 12 and the tray 6 after gas quenching out of the gas quenching furnace 1. During gas quenching, a tray 6 on which one or more steel parts 12 (only one is shown in FIG. 1) is arranged is provided above the lower wall 5 and between the inlet 7 and the outlet 8. Yes.

  The gas quenching furnace 1 is provided with a gas introduction section (not shown) for introducing a cooling gas (refrigerant), for example, nitrogen gas into the gas quenching furnace 1. At the time of gas quenching, the gas quenching furnace 1 is filled with nitrogen gas supplied by the gas introduction unit.

  Inside the gas quenching furnace 1 is formed a gas passage 9 in which nitrogen gas flows from the upper part to the lower part in the gas flow direction G indicated by the arrow in FIG.

  A cooling fan 11 driven by a motor 10 is provided above the gas passage 9. When the motor 10 is driven, the cooling fan 11 causes the nitrogen gas to flow in the gas flow direction G so as to cross the tray 6 vertically in the gas passage 9, thereby rapidly cooling, ie quenching, the steel part 12 on the tray 6. The tray 6 is configured in a lattice shape so that nitrogen gas can flow therethrough.

  FIG. 2 shows a part 12 as an example of a steel part to which the present invention is applied. The component 12 includes a plate-like connecting portion 13 and a pair of wall portions 14 and 14 that rise vertically from the connecting portion 13 so that the cross section of the component 12 is substantially U-shaped. A groove 15 opened upward in FIG. 2 is formed between the pair of wall portions 14. In the component 12 having such a configuration, the outer side surface 14a of the wall portion 14 is more susceptible to cooling than the inner side surface 14b during gas quenching. Therefore, the wall part 14 is easily distorted due to the difference between the cooling rates of the two, and in many cases, the wall part 14 is distorted so as to open toward the outer side surface 14a.

  The material of the component 12 is, for example, SCr420H. As for the dimensions of the component 12, for example, the thickness T of the wall portion 14 is 3.8 mm, the distance D between the pair of wall portions 14, 14 is 28 mm, and the root 16 to the tip 17 of the wall portion 14. The length L is 40 mm.

  Next, with reference to FIG. 3, the gas quenching method of the component 12 of a present Example is demonstrated.

  First, in a vertical posture such that the front surface (generally U-shaped surface on the front side in FIG. 2) 12a of the component 12 is a bottom surface on the tray 6 and the connecting portion 13 stands vertically from the flat surface 6a of the tray 6. The component 12 is placed on the rectangular tray 6. At this time, the groove 15 of the component 12 is open to the near side in FIG.

  The tray 6 has a plurality of rectangular openings 18 and has a lattice shape when viewed from a direction perpendicular to the plane 6 a of the tray 6.

  Then, a rectangular frame-shaped jig 23 having four plate portions 19, 20, 21, and 22 is disposed on the tray 6 so as to surround the component 12 on the tray 6. The jig 23 is integrally formed in a cylindrical shape by four plate portions 19, 20, 21, and 22. The inner dimension of the jig 23 corresponds to the outer dimension of the component 12.

  Alternatively, the jig 12 may be first arranged on the tray 6 and then the component 12 may be arranged in the jig 23.

  In a state where the component 12 is surrounded by the jig 23, the inner side surface 19 b of the plate portion 19 covers the opening surface 15 a of the groove 15 of the component 12, and the two plate portions 20 and 21 on both sides of the plate portion 19 are inside. The side surfaces 20b and 21b are in close contact with the outer surfaces 14a and 14a of the pair of wall portions 14 and 14, respectively, and the inner side surface 22b of the remaining plate portion 22 is in close contact with the outer surface 13a of the connecting portion 13. Yes. At this time, the opening surface 15a of the groove 15 is closed, and this groove 15 becomes a passage through which nitrogen gas flows during gas quenching. In a state where the part 12 is surrounded by the jig 23, the part 12 is held on the tray 6 by the jig 23.

  The jig 23 is made of a material having a relatively high thermal conductivity and thermal emissivity, for example, a carbon composite.

  In the present embodiment, an example in which the jig 23 has four plate portions 19, 20, 21, and 22 has been disclosed, but the jig 23 has at least three plate portions 19, 20, and 21, It is sufficient to enclose at least three surfaces of the component 12, that is, the opening surface 15a of the groove 15 and the outer surfaces 14a, 14a of the pair of walls 14,14. When the jig 23 has three plate portions 19, 20, 21, the jig 23 is generally U-shaped.

  Then, after heating the component 12 to a gas quenching temperature, for example, 850 ° C., the tray 6 is placed in the gas quenching furnace 1 together with the component 12 and the jig 23 so as to be orthogonal to the gas flow direction G. At this time, the pair of wall portions 14 of the component 12 are arranged in parallel with the gas flow direction G. Note that the gas quenching furnace 1 may be provided with a heating mechanism to heat the component 12 inside the gas quenching furnace 1. The metal structure of the heated part 12 is austenite.

  While the component 12 is surrounded by the jig 23 on the tray 6, the component 12 is rapidly cooled with nitrogen gas, that is, gas quenching is performed. This gas quenching is performed by circulating and supplying nitrogen gas toward the component 12 through the gas passage 9 by driving the cooling fan 11 (FIG. 1). As an example, the temperature of nitrogen gas is room temperature, and the cooling pressure is 1 MPa. Furthermore, the flow rate of nitrogen gas is 19 m / second, and the cooling time is 120 seconds. The metal structure of the part 12 after gas quenching is martensite.

  As described above, in this embodiment, using the jig 23 having high thermal conductivity and thermal radiation rate, the opening surface 15a of the groove 15 of the component 12 and the outer surfaces 14a, 14a of the pair of wall portions 14, 14 are used. Is surrounded. By surrounding the component 12 with the jig 23, nitrogen gas flows in the groove 15 in which the opening surface 15a is closed. Accordingly, the inner side surfaces 14 b and 14 b of the pair of wall portions 14 and 14 of the component 12 are reliably cooled by the nitrogen gas flowing through the groove 15. In addition, heat is transmitted from the pair of wall portions 14 and 14 to the plate portions 20 and 21 of the jig 23 through the two outer surfaces 14 a and 14 a, and the periphery of the jig 23 is transmitted from these plate portions 20 and 21. It is cooled by being further transmitted to the flowing nitrogen gas. Thereby, since the difference between the cooling rate of the inner side surface 14b by nitrogen gas and the cooling rate of the outer side surface 14a by nitrogen gas and the jig 23 is reduced, the distortion generated between the inner side surface 14b and the outer side surface 14a is Get smaller. Further, by controlling the cooling rate of the outer surfaces 14a and 14a by changing the thickness of the wall portion 14, adjusting the thermal conductivity of the jig 23, adjusting the thermal radiation rate of the jig 23, etc., the inner side surface 14b And the cooling rate difference between the outer surface 14a and the distortion of the wall portion 14 can be further reduced.

  Further, in this embodiment, when the parts 12 and the tray 6 are arranged in the gas quenching furnace 1, the pair of wall portions 14 and 14 are made parallel to the gas flow direction G, so that the nitrogen gas is the wall portion. 14 and 14 flows parallel to the inner side surfaces 14b and 14b. Therefore, the cooling rate of the inner surface 14b by nitrogen gas becomes stable Newtonian cooling proportional to the flow rate of nitrogen gas, and stable cooling can be performed even when the part 12 is repeatedly quenched during mass production.

  FIG. 4 shows a gas quenching method of a comparative example for this embodiment. In the comparative example, the component 12 having the same shape and material as in the present embodiment is in a posture (outside surface of the component 12 shown in FIG. 2) in which the outer surface 13a of the connecting portion 13 is the bottom surface of the tray 6, and the jig 23 It is arrange | positioned on the tray 6 without using. At this time, the groove 15 is opened to face the gas flow direction G. During gas quenching, the nitrogen gas that has flowed into the groove 15 from the opening surface 15a side of the groove 15 flows at a lower speed than the nitrogen gas that flows around the part 12, particularly outside the walls 14.

  In FIG. 5, the test result regarding the distortion of the wall part 14 when gas quenching of the components 12 is performed by the gas quenching method of the comparative example and the gas quenching method of the present embodiment is shown. As illustrated, in the gas quenching method of the comparative example that does not use the jig 23, the amount of change in the distance D between the pair of wall portions 14 and 14 was 0.03 to 0.18 mm. In contrast, in the gas quenching method of the present example using the jig 23, the amount of change in the distance D was 0.04 to 0.12 mm. Therefore, the amount of change in the distance D between the two wall portions 14 and 14 during gas quenching can be reduced by the gas quenching method of the present embodiment.

  FIG. 6 shows a lower link 24 used in, for example, a multi-link piston crank mechanism as a component having other steel parts to which the present invention is applied. The lower link 24 connects an upper link having one end connected to a piston pin and a crank pin of a crankshaft as disclosed in, for example, JP-A-2015-42849, and is shown in FIG. Thus, a pin boss for the upper pin has a cylindrical crank pin bearing hole 25 fitted in a crank pin (not shown) at the center and at positions almost 180 ° opposite to each other with the crank pin bearing hole 25 interposed therebetween. A portion 26 and a control pin pin boss portion 27 are provided. The lower link 24 has a parallelogram shape close to a rhombus as a whole, and a lower link upper 24A including an upper pin pin boss portion 26 and a control pin for a split surface 28 passing through the center of the crank pin bearing hole 25. The lower link lower 24B including the pin boss portion 27 is divided into two parts. As illustrated, the lower link 24 includes an upper surface 29, a lower surface 30, and a pair of side surfaces 31, 31 orthogonal to the dividing surface 28. The lower link upper 24A and the lower link lower 24B are fastened to each other by a plurality of bolts (not shown) after the crank pin bearing hole 25 is fitted into the crank pin.

  In the second embodiment, the lower link upper 24A is quenched as a steel part suitable for the gas quenching method of the present invention. The lower link upper 24A includes a thick portion 32 extending between the side surfaces 31 and 31 along the arc of the dividing surface 28 and the crank pin bearing hole 25, and a pair of plate-like pin bosses rising vertically from the thick portion 32. Wall portions 26a, 26a. A groove 33 is formed between the pair of pin boss wall portions 26a, 26a. The pin boss wall portions 26a and 26a are provided with upper pin holes 34 and 34, respectively, which are fitted with upper pins (not shown).

  Next, the gas quenching method of the second embodiment will be described with reference to FIG.

  First, the lower link upper 24A is arranged on the tray 6 in a vertical posture such that the side surface 31 of the lower link upper 24A becomes the bottom surface on the tray 6 and the dividing surface 28 rises vertically from the flat surface 6a of the tray 6. .

  And the jig | tool 23 which has high heat conductivity and heat radiation rate is arrange | positioned so that the lower part of the lower link upper 24A may be enclosed on the tray 6. FIG. The jig 23 has a rectangular frame shape, as in the embodiment of FIG. The jig 23 includes rectangular plate portions 19 and 22 and rectangular plate portions 20 and 21 that are larger than the plate portions 19 and 22. The lengths of the long sides of the rectangles of the plate portions 19 and 22 correspond to the thickness of the lower link upper 24A (the length between the outer side surfaces 36 and 36). The length corresponds to the length between the dividing surface 22 and the curved portions 37, 37 (FIG. 6) in the vicinity of the upper pin holes 34, 34 of the pin boss wall portions 26a, 26a. The length of the rectangular short side (height along the gas flow direction G) of the plate portions 19, 20, 21, and 22 is set to be higher than the position of the upper pin hole 34 along the gas flow direction G. Has been.

  In a state where the lower portion of the lower link upper 24 </ b> A is surrounded by the jig 23, the inner side surface 19 b of the plate portion 19 covers a part of the groove 33. At this time, a part of the inner side surface 19b of the plate portion 19 is in contact with the curved portions 37, 37 of the pin boss wall portions 26a, 26a. The inner side surfaces 20b and 21b of the plate portions 20 and 21 are formed on the outer surface 36 of the pin boss wall portions 26a and 26a at the lower portion of the lower link upper 24A, except for the inclined upper surface 29 and the portion of the crank pin bearing hole 25 that is in the arc. , 36 is in contact. Here, the upper pin hole 34 is covered with the plate portions 20 and 21 from the outside of the pin boss wall portions 26a and 26a. The inner side surface 22b of the plate part 22 is in contact with the dividing surface 28 of the lower link upper 24A at the lower part of the lower link upper 24A except for the upper part of the inner side surface 22b. Thus, in a state where the lower link upper 24 </ b> A is disposed in the jig 23, the lower link upper 24 </ b> A is appropriately held on the tray 6.

  If gas quenching is performed without using the jig 23, the lower link upper 24A expands due to the martensite transformation and the pin boss wall portion 26a is distorted, so the distance between the pair of pin boss wall portions 26a, 26a. D changes. In order to prevent this, as in the second embodiment, at the lower part of the lower link upper 24A, the opening surface 33a of the groove 33 of the lower link upper 24A and the outer surfaces 36, 36 of the pair of pin boss wall portions 26a, 26a. Is surrounded by a jig 23. Thereby, similarly to the first embodiment, nitrogen gas flows in the groove 33 with the opening surface 33a closed, and the inside of the groove 33, in particular, the inner side surfaces 35 and 35 are reliably cooled. Further, as in the first embodiment, the outer surfaces 36 and 36 are configured such that heat is transmitted from the pair of pin boss wall portions 26 a and 26 a to the plate portions 20 and 21 of the jig 23, and from here, the periphery of the jig 23. It is cooled by being further transmitted to the nitrogen gas. In this manner, as in the first embodiment, the inner side surfaces 35, 35 and the outer side surfaces 36, 36 are located below the pin boss wall portions 26a, 26a (in the vicinity of the upper pin holes 34, 34) that are easily deformed during gas quenching. The cooling rate balance can be controlled by the jig 23. Accordingly, the difference between the cooling rate of the inner side surface 35 by nitrogen gas and the cooling rate of the outer side surface 36 by nitrogen gas and the jig 23 is reduced, so that the distortion generated between the inner side surface 35 and the outer side surface 36 is reduced. Become.

  Further, by not enclosing the remaining portion of the lower link upper 24A by the jig 23, the lower link upper 24A can be taken out without deteriorating workability after gas quenching.

  In each of the above embodiments, the example in which the lower link upper 24A is quenched is disclosed. However, the present invention is also suitable for quenching the lower link lower 24B having a similar shape to the lower link upper 24A, and quenching various other parts. It is possible to apply to.

  Further, in each of the above embodiments, an example in which the part 12 and the lower link upper 24A are quenched using nitrogen gas is disclosed, but the refrigerant may be another gas, and further, a liquid such as oil or water. Also good.

DESCRIPTION OF SYMBOLS 1 ... Gas quenching furnace 6 ... Tray G ... Gas flow direction 12 ... Part 13 ... Connection part 14 ... Wall part 15 ... Groove 19, 20, 21, 22, ... -Plate part 23 ... Jig 24 ... Lower link 24A ... Lower link upper 26a ... Pin boss wall part 33 ... Groove 34 ... Upper pin hole

Claims (4)

This is a method in which a steel part having a U-shaped cross section having a pair of wall portions is arranged on a tray capable of flowing refrigerant, and the steel part is cooled and quenched by supplying the refrigerant toward the tray. And
Place the above steel parts on the tray so that the U-shaped surface of the steel parts becomes the bottom surface on the tray,
Using a jig having at least three surfaces surrounding the steel part and having thermal conductivity, one surface of the jig covers the opening surface of the U-shaped steel part and 2 of the jig. One surface is brought into close contact with the outer surfaces of the pair of wall portions of the steel part,
A quenching method in which a coolant is supplied toward the tray in a state where the steel part is surrounded by the jig.   The quenching method according to claim 1, wherein the pair of wall portions are arranged in parallel with the flow direction of the refrigerant.   The quenching method according to claim 1 or 2, wherein the refrigerant is nitrogen gas.   The quenching method according to claim 1, wherein the jig has a quadrangular frame shape having four plate portions.

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