TW200538559A - The crank shaft excellent in bending fatigue strength - Google Patents

Abstract

The crankshaft disclosed exhibits a flexural fatigue strength superior to that of a conventional one. A crankshaft being excellent in flexural fatigue strength and having a quench hardened layer on the surface of a crank pin portion and a journal portion thereof, characterized in that it has a chemical composition, in mass%, that C: 0.40 to 0.51%, Si: 0.30 to 0.80%, Mn: 0.50 to 1.50%, Al: 0.040 % or less (including 0%), Ti: 0.005 to 0.06%, Mo: 0.15 to 0.50%, B: 0.0005 to 0.0030%, S:0.06 % or less, P: 0.02% or less, Cr: 0.2% or less, and the balance: Fe and inevitable impurities, the base material thereof has a bainite structure and/or a martensite structure in a total proportion of 10% or more, a surface-hardened layer after induction hardening has an old austenite grain diameter of 10 mum or less over the whole thickness of the hardened layer, and a fillet r part of the crank pin portion and the journal portion has a flexural fatigue strength of 800 MPa or more.

Description

200538559 IX. Description of the invention: [Technical field to which the invention belongs] The present invention relates to a crankshaft having a hardened layer obtained by induction hardening on the surface of a crank pin and a journal portion, and particularly for those who want to improve the bending fatigue strength. . [Prior art]

A crankshaft is a part that is used to change the reciprocating motion of a piston in an internal combustion engine (such as an automobile engine) into a rotary motion. As shown in FIG. 1, this crankshaft 1 includes a journal portion 2 provided for a cylinder, a crank pin portion 3, a crank arm portion 4, and a weight portion 5 which are bearing portions of a connecting rod for a piston. And the crank pin portion 3 is subjected to high frequency quenching in order to improve its fatigue strength. However, with the recent increase in the output of internal combustion engines, the crankshaft is required to be further strengthened, especially to increase the bending fatigue strength. Here, in order to improve the bending fatigue strength of the crankshaft, it is effective to increase the fatigue strength of the journal portion 2 and the crank pin portion 3 described above, especially to increase the fillet r portion 7 (that is, the journal portion 2 and the weight portion 5). Fatigue strength at the junction (the junction between the crank pin 3 and the crank arm 4). Because this part is part of the stress concentration in the shape, it is easy to become the starting point of the fatigue damage of the crankshaft. In order to improve the fatigue strength, it is effective to increase the grain boundary strength. Based on this viewpoint, for example, in Patent Document 1, a technique of using T i C dispersion to seek for miniaturization of the particle size of the old Voss field is proposed. The technology described in Patent Document 1 mentioned above is due to the use of 5 312XP / Invention Specification (Supplement) / 94-08 / 94] 12006

200538559 Fine T i C is dispersed in order to obtain the fine particle size of the old Voss field. T i C must be melted before quenching, and heated to a temperature above 110 ° C by hot pressure. Therefore, it is necessary to heat at a higher heating temperature, which causes a problem of poor productivity. Furthermore, even if the technology disclosed in the aforementioned Patent Document 1 is used, the requirements for improving the bending fatigue strength of the crankshaft are fully met. In addition, in Patent Document 2, a ratio of a zero hardened layer depth CD of a shaft structure for a mechanical structure to a radius R of a high-frequency quenched shaft component is limited to 0.3 to 0.7, and then the CD / R value and rf value (high The particle size of Vossian body crystals up to 1 mm in the surface), H f ί Fire-like (CD / R) = average Vickers hardness (W hardness) up to 0.1) and H c value (high frequency quenching) The value of A specified by the hardness of the central part of the subsequent shaft is controlled by the amount of C within the specified range with high torsional fatigue strength. However, this part does not take into account the full thickness of the hardened layer. Therefore, the bending fatigue strength expected by the present invention still cannot be obtained. In addition, Patent Document 3 proposes a high-frequency quenching after the forming process so that the particle size of the surface 7 is larger than the particle size of JISG 0 5 51, and the carbides are finely dispersed to improve the rotational fatigue strength. However, this technique is due to quenching. The depth of the hardened layer is shallow, etc., and a bending fatigue strength of a good degree expected by the present invention is obtained. Patent Document 1: Japanese Patent Laid-Open No. 2 0 0-1 5 4 8 1 9 (Scope, paragraph [0 0 0 8]) 312XP / Invention Specification (Supplement) / 94 · 08/941] 2〇〇 6 Miniaturization, so the delay time setting ^ can not be used, it is the rate (CD / R) after quenching L (Southern frequency 泮 icker's average Vickers), in order to improve the good process of the old Vo Paragraph No. 0 is a technology of 10 L. Patent 6 200538559 is still unavailable Patent Document 2: Japanese Patent Laid-Open No. 8-5 3 7 1 4 (Scope of Patent Application) Patent Document 3: Japanese Patent Laid-Open No. 7 -1 1 8 7 9 1 (Scope of patent application) [Contents of the invention]

The present invention has been developed in view of the above-mentioned circumstances, and its object is to propose a crankshaft that is superior in bending fatigue strength to conventional techniques. The inventors of this case have made intensive studies in order to effectively improve the bending fatigue strength of the crankshaft. The results are as follows, and the following understandings (i) to (iii) are obtained. When the chemical composition, microstructure of the crankshaft and the thickness of the hardened layer after quenching are optimized, the particle size of the old Voss field can be optimized. A crankshaft having excellent bending fatigue strength was obtained. (i) When quenching is applied to the necessary parts of the crankshaft adjusted with an appropriate chemical composition, and the particle size of the old Voss body in the full thickness of the quenched hardened layer is 1 0 # m or less (preferably 5 // m or less) Therefore, the bending fatigue strength is significantly increased. Specifically, regarding the chemical composition, especially when S i and M 0 are added in an appropriate range, the number of nucleation sites of the Voss field body during high-frequency quenching heating increases, and the growth of Voss field particles is suppressed. Effectively refine the particle size of the hardened layer, and significantly improve the bending fatigue strength. (ii) When the base material structure of the crankshaft, that is, the structure before quenching is set to a tissue containing the toughened tissue and / or Asada loose tissue at a specific rate, the toughened tissue or the Asada loose tissue is a ratio of fat particles. The iron-boronite structure is a finer dispersed carbide structure, which belongs to the core of Vossian body during quenching and heating 7 3] 2XP / Invention Specification (Supplement) / 94-08 / 94112006 200538559 The area of the iron / carbide interface increases, miniaturizing the resulting Voss field. As a result, the grain size of the hardened layer becomes finer, so the grain boundary strength is improved, and the bending fatigue strength is improved.

(iii) In addition, the necessary parts of the quenched part of the crankshaft were examined. As a result, under the operating environment of the crankshaft, stress is concentrated on the pin and the inner r portion of the journal, so it is necessary to fully ensure that part. The fact of the quenching depth. Then, in the case where the quenching depth (thickness of the hardened layer) of the part is less than 2.0 mm, the fact that the internal fatigue failure (early boundary between the hardened layer and the non-hardened layer) occurs at the beginning of the fatigue failure is prove. Therefore, it is particularly effective in improving the bending fatigue strength to suppress the early destruction of the internal starting point at a setting where the thickness of the hardened layer of the inner fillet r portion is 2.0 mm or more. The present invention is based on the above findings. That is, the gist of the present invention is as follows. (1) A crankshaft excellent in bending fatigue strength is a crankshaft having a hardened layer on the surface of a crank pin and a journal portion, which is characterized by containing C: 0 · 4 0 ~ 0 · 5 1 mass% , S i: 0.30 to 0.80% by mass, Μ η: 0.50 to 1.50% by mass, A 1 ·· 0 · 0 4 0% by mass or less (including 0), T i : 0 · 0 0 5 to 0. 0 6 mass%, Μ 〇: 0. 15 to 0. 5 0 mass ° / 〇, Β: 0 · 0 0 0 5 to 0. 0 0 3 0 mass%, S : 0.06 mass% or less, P: 0.02 mass% or less, and 8 3] 2XP / Invention Specification (Supplement) / 94-08 / 94112006 200538559 C plant 0.2 mass ° / ◦ or less,

The remaining part is composed of Fe and unavoidable impurities. The parent metal tissue has the deformed tissue and / or Asada loose tissue, and the total tissue score of these deformed tissue and Asada loose tissue is 10 Above, in addition, the particle size of the old Voss body of the surface hardened layer after induction hardening is maintained below 1 0 // m in the full thickness of the hardened layer, and the curvature of the r-round portion of the crank pin and the journal Those with a fatigue strength of 800 MPa or more. (2) In the above (1), the component composition of the steel material further contains Cu ·· 1.0% by mass or less, Ni: 3.5 · 5% by mass or less, C0: 1.0% by mass or less, N b: 0.1% by mass or less, and V: 0.5% by mass or less. One or two or more kinds are selected to have superior bending fatigue strength.

(3) In the above (1) or (2), the component composition of the steel material further contains T e: 0.2% by mass or less,

Se: 0.2% by mass or less, C a: (L 0 2% by mass or less, RE Μ: 0.30% by mass or less, Z r: 0.2% by mass or less, S η: 0.3% by mass or less, S b: 0.2% by mass or less, M g: 0.22% by mass or less, and 9 312XP / Invention Specification (Supplement) / 94-08 / 94112006 200538559 H f: 0.1% by mass or less A crankshaft excellent in bending fatigue strength composed of two or more types. (4) A crankshaft excellent in bending fatigue strength, which is a crankshaft having a hardened layer on the surface of the crank pin and the journal portion. It is characterized by containing C: 0.45 to 0.51 mass%,

S i: 0.4 .0 to 0.8 .80 mass ° / 〇, M η ·· 0.5 .0 to 0.7 .0 mass%, A 1: 0. 0 0 5 to 0 · 0 4 0 mass% or less , T i: 0. 0 0 5 to 0 · 0 3 0 mass ° / 〇, Μ 0: 0. 3 0 to 0. 5 0 mass%, Β: 0. 0 0 0 5 to 0 · 0 0 3 0 Mass ° / 〇, S: 0.06 mass. /. Below, P: 0.02 mass% or less, and

The remaining part is composed of Fe and unavoidable impurities. The parent metal tissue has the deformed tissue and / or Asada loose tissue, and the total tissue score of these deformed tissue and Asada loose tissue is 10 Above, in addition, the particle size of the old Voss body of the surface hardened layer after induction hardening is kept below 5 // m in the full thickness of the hardened layer, and the bending fatigue of the inner round corner r portion of the crank pin and the journal portion is fatigued. Those with a strength of 800 MPa or more. (5) In the above (4), the component composition of the steel material further contains Cu: 1.0% by mass or less, Ni: 3.5% by mass or less, 10 312XP / Invention Specification (Supplement) / 94- 08/94112006 200538559 C0: 1.0% by mass or less, Nb: 0.1% by mass or less, and V: 0.5% by mass or less of one or two or more selected from the group consisting of bending fatigue strength Excellent crankshaft. [Embodiment]

Hereinafter, the present invention will be specifically described. First, the reason for limiting the component composition of the crankshaft in the above range in the present invention will be explained. C: 0.4.0 to 0.51% by mass. C is the element that has the greatest effect on hardenability, that is, by increasing the hardness and depth of the hardened layer, it effectively contributes to the improvement of fatigue strength. However, if the content is less than 0.4 mass%, in order to ensure the required fatigue strength, the depth of quench hardening must be greatly increased. At this time, quench cracking occurs significantly, and the toughened structure is difficult to produce, so it is necessary to add 0. 40% by mass or more. On the other hand, if the content exceeds 0.51% by mass, the grain boundary strength is reduced, and consequently the bending fatigue strength is lowered. Further, the machinability, cold forgeability, and quench cracking resistance are also reduced. Therefore, the amount of C is limited to a range of 0.4% to 0.51% by mass. Pressing again, a more suitable range is 0.45 mass% or more. S i: 0.30 to 0.80 mass%

Si has the effect of increasing the number of nucleation sites of the Voss field during quenching and heating, while suppressing the particle growth of the Voss field, and miniaturizing the particle size of the hardened layer. Furthermore, it has a suppressing effect on the generation of carbides and the decrease in grain boundary strength caused by carbides. In addition, it is also a useful element in the production of the deformed body group 2 3 / 2XP / Invention Specification (Supplement) / 9108/94112006 200538559, and uses these effects to improve the bending fatigue strength.

As such, Si is a very important element in the present invention, and it must contain 0.3% by mass or more. This is because when the amount of S i is set to 0.30% by mass or more, fine particles having a particle diameter of 1 0 // m or less can be achieved in the entire thickness of the hardened layer. However, if the amount of S i exceeds 0.80% by mass, the solid solution of the ferrous grain iron hardens, which causes an increase in hardness, resulting in a decrease in machinability and cold forgeability. Therefore, the amount of Si is limited to a range of 0.3 to 0.8 mass%. Further, it is more suitable that the amount of Si is 0.40 mass% or more. Μ η: 0.50 to 1.50 mass ° / 〇Μ η is an indispensable component to improve the hardenability and ensure the hardening depth during quenching, so it needs to be actively added, but if its content is less than 0. 50 mass ° / 〇, the addition effect is lacking, so it is set to 0.5 mass% or more. On the other hand, if the amount of M η exceeds 1.5% by mass, hardening of the base material is caused, which is disadvantageous in terms of machinability. Therefore, the amount of M η is set to 1.5% by mass or less. A more suitable amount of M η is 0.70 mass% or less. A 1: 0. 0 4 mass% or less (including 0) A 1 is an element effective for deoxidation. In addition, based on the viewpoint of suppressing the particle growth of the Vossian body during quenching heating to achieve the miniaturization of the particle size of the quenched hardened layer, it is also a useful element, and may suitably contain 0.05 mass% or more as needed. However, if the content of A 1 exceeds 0.40% by mass, the effect will be saturated, and the fatigue strength may be reduced due to the increase in oxides. Therefore, the amount of A 1 is limited to 0.04 0 mass % Or less. T i: 0. 0 0 5 ～ 0 · 0 6 mass ° / 〇 12 3] 2XP / Invention Manual (Supplement) / 94-08 / 94112006

200538559 T i has the following effects: It is combined with the impurities of N which are inevitably mixed to prevent B from becoming BN (that is, to prevent the quenching effect of B from disappearing and make the effect of improving the quenchability of B fully exerted. The effect needs to contain at least 0.05% by mass, but if the amount exceeds 0.05% by mass, coarsening of T i N or the generation of oxides will be caused. These factors become the starting point of fatigue failure and cause bending The fatigue strength is significantly reduced, so the amount of T i is limited to a range of 0.05 to 0.6 mass%. A more suitable range is 0.030 mass% or less. Μ 0: 0 · 15 to 0.5 mass / ° M0 has the effect of promoting the production of toughened tissues so that the particle size of the Voss field body during quenching heat is reduced, and the particle size of the quenched hardened layer is reduced. It has the effect of suppressing the particle growth of the Voss field body during quenching and heating, and miniaturizing the particle size of the quenched hardened layer. In addition, MO is an element useful for improving the hardenability, so it is used to adjust the hardenability. In addition, , Mo is an effective resistance based on inhibiting the generation of carbides An element that reduces the grain strength caused by carbides. In this way, Mo is a very important element in the present invention. If the content is 0.15% by mass or more, no matter how the manufacturing conditions or quenching conditions are adjusted, the hardened layer cannot be completely cured. In the thickness, fine particles having a particle size of 10 # m or less are achieved. However, if the M0 content exceeds 0.50% by mass, the hardness of the rolled material is significantly high, resulting in a decrease in processability. Therefore, the M0 amount is limited to 0 · 15 ~ 0. In the range of mass%. A more suitable amount of M0 is in the range of 0.30 ~ 0.50% by mass. Β: 0. 0 0 0 5 ~ 0. 0 0 3 0 Mass% 312XP / Invention Specification (Supplement) / 94-08 / 94112006), with production and grains added, so that it is not evenly bounded. 50 liters 13 200538559 B has the effect of promoting the production of deformed tissues or loose field tissues . In addition, it has the effect of improving the hardenability by adding a small amount of B, and increasing the quenching depth during quenching, thereby improving the bending fatigue strength. In addition, B has the priority to precipitate out of the grain boundary to reduce the concentration of P precipitated to the grain boundary and increase the strength of the grain boundary, thereby also improving the bending fatigue strength. Therefore, in the present invention, it is necessary to actively add B, but if the content is less than 0.0005 mass%, the effect of addition is lacking, and when the content exceeds 0.0003 mass%, the effect is added. Saturation is reached, but the fatigue strength is reduced due to the increase of the single compound. Therefore, the amount of B is limited to the range of 0.005% to 0.30% by mass. S: 0.6 mass% or less S is a useful element for forming MnS in steel to improve machinability, but if the content exceeds 0.6 mass%, it will precipitate out of the grain boundary and reduce the strength of the grain boundary. The amount of S is limited to 0.6 mass% or less.

P: 0. 2 2 mass ° / ◦ or less P-based analysis decreases the grain boundary strength due to the grain boundary of the Voss field, and therefore reduces the bending fatigue strength. It also helps in the harm of quench cracking. Therefore, it is desirable to reduce the P content as much as possible, but it is allowable to 0.22% by mass. C r: 0.2% by mass or less

Cr stabilizes carbides and promotes the generation of residual carbides, resulting in lower grain boundary strength and lower bending fatigue strength. Therefore, it is desirable to reduce the content of C r as much as possible, but it is allowable to 0.2 mass%. Although the basic components have been described above, the present invention may appropriately contain the following elements. 14 312XP / Invention Specification (Supplement) / 94-08 / 94112006 200538559 C u: 1.0% by mass or less

Cu is effective in improving the hardenability. In addition, Cu can be solid-dissolved in ferrous iron, and this solid-solution strengthening is used to improve the bending fatigue strength. Furthermore, it can suppress the generation of carbides, thereby suppressing the decrease in grain boundary strength caused by carbides and improving the bending fatigue strength. However, if the content exceeds 1.0 mass%, cracks may occur during hot processing, so it is set to 1.0 mass%.

The following added strength. N i: 3.5 mass ° / ◦ or less N i is used to improve the hardenability because it is an element that improves the hardenability. In addition, Ni is an element which can suppress the generation of carbides, thereby suppressing the decrease in grain boundary strength caused by carbides and improving the bending fatigue strength. However, Ni is an extremely expensive element, and if its added amount exceeds 3.5 mass%, the cost of the steel will increase, so it is set to an added amount of 3.5 mass% or less. Furthermore, if the added amount is less than 0.05% by mass, both the effect of improving the hardenability and the effect of suppressing the decrease in the strength of the grain boundary are reduced, so it is desirable to contain the content of 0.05% by mass or more. Co: 1.0 mass ° /. The following C 0 is an element which can suppress the generation of carbides, and thereby suppress the decrease in grain boundary strength caused by carbides, and improve the bending fatigue strength. However, Co is an extremely expensive element. If the amount of Co added exceeds 1.0% by mass, the cost of the steel is increased. Therefore, the amount of Co is set to 1.0% by mass or less. Furthermore, if the added amount is less than 0.01% by mass, the effect of suppressing the decrease in grain boundary strength becomes small, so it is preferable to add 0.1% by mass or more. N b: 0.1% by mass or less 15 312XP / Invention Specification (Supplement) / 94-08 / 94112006 200538559

Nb not only has the effect of improving the hardenability, but also acts as a precipitation strengthening element in combination with C and N in steel. In addition, Nb is an element that improves the resistance to temper softening, and uses this effect to increase the bending fatigue strength. However, if the content exceeds 0.1% by mass, the effect is saturated, so the upper limit is set to 0.1% by mass. Furthermore, if the added amount is less than 0.05% by mass, the effect of improving the resistance to precipitation strengthening and temper softening will be small. Therefore, it is desirable to add 0.05% by mass or more. V ·· 0.5% by mass or less V is a combination of C and N in steel and acts as a precipitation strengthening element. Furthermore, V is an element that improves the resistance to temper softening, and this effect is used to improve the bending fatigue strength. However, if the content exceeds 0.5% by mass, the effect is saturated, so it is set to 0.5% by mass or less. Furthermore, if the added amount is less than 0.01% by mass, the effect of improving the bending fatigue strength becomes small, so it is preferable to add 0.01% by mass or more. With 0 · 0 3 ~ 0.3 mass. / G is preferred. D e: 0.2% by mass or less S e: 0.2% by mass or less

Te and Se combine with Mn to form MnTe and MnSe, respectively, which act as chip breakers to improve the machinability. However, when the contents are more than 0.2% by mass, the effects are saturated and the cost of ingredients is increased. Therefore, the contents are all set to 0.2% by mass or less. Again, the preferred range is 0.1% by mass or less. Furthermore, in order to improve the machinability, it is preferable that the Te content is 0.003 mass% or more, and the Se content is 0.003 mass% or more. C a: 0.2% by mass or less R E M: 0.03% by mass or less 16 312XP / Invention Specification (Supplement) / 94-08 / 94112〇06 200538559 Zr: 0.2% by mass or less

C a, R E M, and Z r each form a sulfide together with M n S to act as a chip breaker, thereby improving the machinability. However, when the contents of Ca, REM, and Z r each exceed 0.02% by mass, 0.33% by mass, and 0.2% by mass, the effect is saturated, and the cost of ingredients is increased. Therefore, the contents are set to the above ranges, respectively. A more suitable content is that Ca is 0.01% by mass or less, R E M is 0.015% by mass or less, and Z r is 0.1 · 1% by mass or less (in a range). Further, in order to improve the machinability, it is preferable that the content of C a is greater than or equal to 0.01% by mass, the content of REM is greater than or equal to 0.001% by mass, and the content of Zr is greater than 0.003% by mass. S η: 0.3% by mass or less S b: 0.2% by mass or less

Both Sn and Sb are elements that improve the machinability by using embrittlement. However, when the amount of S η exceeds 0.3% by mass and the amount of S b exceeds 0.2% by mass, the effect is saturated and the cost is increased, which is economically disadvantageous. Therefore, the contents are individually set to the above ranges. A more preferable range is S η: 0.15% by mass or less, and Sb: 0.1% by mass or less. Furthermore, in order to improve the machinability, it is preferable that the content of S η is greater than or equal to 0.05 mass%, and the content of Sb is greater than or equal to 0.05 mass%. M g: 0.2% by mass or less, H f: 0.1% by mass or less

Both Mg and Hf have the effect of not only acting as a deoxidizing element, but also acting as a stress concentration source to improve the machinability. Therefore, they can be added as needed. However, if it is excessively added, the effect will be saturated and the component cost will be increased. Therefore, the content is set to the above range. A more suitable content is that M g is 0.01 mass% or less, and H f is 0.05 mass% or less. And 17 312XP / Invention Specification (Supplement) / 94-08 / 94112006 200538559 Press, in order to improve the machinability, it is preferable that the M g content is more than 0. 0 0 0 1 mass%, and the Η f content is 0. Ο Ο 5 mass% or more. In the above, the range of the appropriate component composition has been described. However, in the present invention, limiting the component composition to the above range is not sufficient to meet the requirements, and the adjustment of the steel structure is also important. That is, in the present invention, it is necessary to set the parent metal structure of the crankshaft, that is, the structure before quenching (equivalent to the structure other than the hardened layer after high-frequency quenching) to have a toughened structure and / or a Mata loose structure, and The total tissue fraction of these deformed tissues and Asada's loose tissues is set to 10% or more by volume fraction (ν ο 1%). The reason is that the toughened tissue or Asada loose tissue is a finer dispersed carbide structure than the ferritic iron-wave body tissue, and it is the ferrous iron that belongs to the nucleation site of the Vostian body when it is quenched and heated. The increase in the area of the carbide interface has made the Vossian body miniaturized, which effectively contributed to the miniaturization of the particle size of the fire hardened layer. Then, as the particle size of the hardened layer becomes finer, the grain boundary strength is increased, and the bending fatigue strength is improved. Here, it is more appropriate that the total tissue fraction of the metaplasty tissue and the Mata loose tissue is more than 2 0 ν ο 1%. It is also required that the remaining tissues other than the metaplasty tissue or the Mata loose tissue may be fertilized iron, boron, etc., and there is no special requirement. In addition, regarding the miniaturization of the particle size of the hardened layer after quenching, Asada's loose structure has the same effect as the toughened structure, but from an industrial point of view, compared with Asada's loose structure, the alloy has a toughened structure. The addition amount of the element is small, and it may be generated at a low cooling rate, so it is advantageous in manufacturing. 18 312XP / Invention Specification (Supplement) / 94-08 / 94112006

200538559 In the crankshaft of the present invention, it is also important to adjust the field size of the hardened layer after induction hardening. That is, it is necessary for the stone j after high frequency quenching to maintain the particle size of the old Voss field body at 10 V m in its full thickness, because if the median particle size of the hardened layer after quenching exceeds 1 0 // m method Since sufficient grain boundary strength is obtained, it is impossible to expect to achieve improvement in Chengqu fatigue strength. According to another, the particle diameter is more preferably 5 // m or less and 2 // Π1 or less. Here, the particle size of the old Voss field in the entire thickness of the hardened layer is as follows. After the induction hardening, the crankshaft of the present invention has an Asta granular structure with an area ratio of 100% at the outermost surface layer after the induction hardening. Then, face to the inside, up to a certain depth, there are 100% of the Asada loose group area, and the area of the Asada loose tissue decreases sharply from a certain depth. In the present invention, regarding the part subjected to high frequency quenching, from The depth of the steel until the area ratio of the Mata interstitial structure decreases to 98% is defined as a hardened layer. Then, regarding this hardened layer, the average field particle size is measured from the surface to the hardened layer thickness position, 1/2 position, and 4/5 position. At any average old Voss field particle size, All cases are as follows, the old Vostian in the full thickness of the hardened layer is deemed to be 1 0 // m or less. Again, the measurement of the average particle size of the old Voss field is performed as follows ^ The optical microscope is used to scale from 400 times (the area of a field of view is 0 0 · 2 2 5 mm) to 100 times (1 The area of each field of view is 0 312XP / Invention Specification (Supplements) / 94-08 / 94112006 Old Voss t-layer, below., J | The leading area is 1/5 of the old surface, and the size of the old Voss is 1 0 // m. The size of the body is for official use. 2 5 mm X .1 0 mmx 19 200538559 0. 0 9 mm), observe 5 at each position The visual field area, and the average particle diameter was measured using an image analysis device. In addition, in the crankshaft of the present invention, it is necessary to make the bending fatigue strength of the crank pin portion and the journal portion of the journal portion of the crankshaft to reach 800 MPa or more. Because it can be used to achieve miniaturization or lightweight of the engine.

Omm 之间。 In order to make the flexural fatigue strength of the fillet r part reach more than 8 0 Μ Pa, it is necessary to set the thickness of the hardened layer of the fillet r part to 2. Omm or more. Fig. 2 is a sectional view schematically showing a pin portion or a journal portion, and the thickness of the hardened layer of the fillet r portion is shown in Fig. 2, which refers to the distance L from the fillet r portion 7 to the closest quenching boundary. . In the use environment of the crankshaft, stress is concentrated in the pin and the inner r portion of the journal, so it is necessary to fully ensure the quenching depth of this part. If the thickness of the hardened layer of the fillet r portion is less than 2.0 mm, it is difficult to ensure a bending fatigue strength of 800 MPa or more. In addition, it is necessary to ensure the thickness M of the hardened layer 8 of the pin smooth portion and the shaft smooth portion 8 of the journal portion to be 2.0 inm or more. This is because if the thickness of the hardened layer of the shaft smooth portion 8 is not sufficiently ensured, internal damage will occur from the quenched boundary of the shaft smooth portion 8. In addition, the thickness of the hardened layer of the shaft smooth part refers to the distance from the surface of the shaft smooth part to the closest to the quenching boundary. Next, the manufacturing conditions of the present invention will be described. In the present invention, the steel adjusted according to the specified composition is rolled into a round bar by hot rolling, and then cut to a specified length, followed by hot forging to form a crankshaft, and then the normalization of the steel is performed as required , And then apply cutting processing, followed by induction hardening / tempering treatment, and then apply final processing or shot peening as the product as required. 20 312XP / Invention Specification (Supplement) / 94-08 / 94112006

200538559 Set appropriate conditions for hot forging and subsequent cooling so that the above-mentioned microstructure, that is, the tissue before quenching, can have the toughened tissue and / or the Mata tissue, and the total score of these deformed tissues and the Mata loose tissue Rate to more than 10%. Set the hot forging temperature to 800 ° C or more, and after forging, cool at a cooling rate of 0.2 ° C / s or more. In addition, in order to achieve a particle size of the old Voss body of the hardened layer of 10 //, it is necessary to set the maximum reachable temperature during induction hardening to 80 0 to ° C and the heating rate to 2 0 0 ° C / s or more. If the maximum temperature is less than 800 ° C, the hardened layer cannot be formed by quenching. On the other side, if the highest temperature reached is more than 1050 ° C, or the heating rate is less than 200 ° C, the particle size of the old Voss field in the hardened layer will exceed 1 0 // m, and the fatigue strength cannot be determined. . Press again, it is more appropriate to set the maximum temperature during induction hardening to less than 950 ° C. When set to less than 950 ° C, the particle size of the old Voss field can be 5 // m or less. Ultra-fine hardened layer. [Examples] An iron material composed of the components shown in Table 1 was produced by melting using a converter, and cast pieces were made by continuous casting. The slab size is 400mm. The ball was rolled into a steel rod of 90 mm0 by heating. After this steel rod is cut to a specified length, it is heated to 12 0 ° C, and then bent to the completed hot forging to further remove the burrs. After the shaft shape is formed, it is about 0.7 ° C. / s to be cooled. Pressing again, the steel of No. C is also prepared as cold steel after forming at the condition of 0.08 t / s for comparison. Then, it is drilled into a crankshaft shape by oil hole drilling and final cutting. Press again, the completion temperature of the hot forging is based on the formation of the parent body of 312XP / Invention Specification (Supplement) / 94-08 / 94112006, which can reach the hot room m at a temperature of 1050, / s, and bend to reach the steel 3 0 0 x, set the line to a temperature of more than 9 0 ° C from the viewpoint of remembering the song and remembering the toughness. 21 200538559 Body tissue or Mata loose tissue.

Next, as shown in the cross-sectional view of the crankshaft, high-frequency hardening is performed on the surfaces of the crank pin and the journal portion of the crankshaft [heating speed 2 50 ° C / s, maximum heating temperature 890 ° C (Table 2 No. 1 ~ 33, 39 ~ 42) or 1030 ° C (No. 0.34 ~ 3 8 in Table 2), there is no holding time] to form the hardened layer 6, and then perform under a heating furnace Tempering at 1 70 ° C for 30 minutes, and then applying final processing as the product. Also, the depth of the hardened layer is adjusted by adjusting the output conditions of the high frequency. The results of investigations on the bending fatigue strength of the crankshaft thus obtained are shown in Table 2. Here, the bending fatigue strength of the crankshaft is evaluated as follows. That is, as shown in FIG. 4, a connecting rod is mounted on a crank pin portion of a crankshaft, and a endurance test is performed to make each connecting rod carry a certain repeated load while the end portion of the crankshaft is fixed. The number of repetitions until the pin or journal is damaged, and the upper limit of the unbroken stress more than 107 times is used as bending fatigue

Furthermore, regarding the bending strength, the load stress of the fillet r portion in the above-mentioned load state was obtained by analyzing the finite element method, and then the obtained value was used for evaluation. In addition, about the same crankshaft, the optical microscope was used to measure the thickness of the hardened layer of the base metal structure, the smoothed part of the shaft after quenching, and the fillet r part, and the average hardened layer particle diameter obtained from the full thickness of the hardened layer Stein body size). These results are also shown in Table 2. Here, as described above, the thickness of the hardened layer is set so as to decrease from the surface of the steel material to a depth of 98% of the area structure of the Asada granular structure. 22 312XP / Invention Manual (Supplement) / 94-08 / 94] 12006 200538559 In addition, the particle size of the hardened layer is from the surface to the 1/5 position, 1/2 position, and 4/5 position of the thickness of the hardened layer. At each of these positions, the average particle size of the old Voss field is measured, and it is expressed by the maximum value of these values.

Also, the measurement of the particle size of the hardened layer is about a section cut along the thickness direction of the hardened layer, so that bitterness is added by adding 11 g of dodecyl benzoate, 1 g of ferrous gas, and 1.5 g of oxalic acid. An acid solution (made by dissolving 50 g of picric acid in 50 g of water) acts as a corrosive solution, so that the old Vostian body grain boundary appears and is implemented.

23 312XP / Invention Specification (Supplement) / 94-08 / 94112006 200538559 Table 1

Steel symbol C Si Mn PS A1 Cr Mo Ti BN Cu Ni Co Nb V Other A 0.48 0.51 0.60 0.010 0.023 0.025 0.04 0.40 0.018 0.0017 0. 0044------Application example B 0.47 0.70 0.55 0.010 0.015 0.025 0.02 0.42 0.017 0.0014 0.0042 Suitable case C 0.49 0.78 0.65 0.008 0.020 0.027 0.03 0.41 0.016 0.0016 0. 0044 Suitable case D 0.48 0.62 0.65 0.009 0.038 0.025 0.03 0.38 0.019 0.0017 0. 0048 Suitable case E 0.48 0.75 0.60 0.012 0.020 0.024 0.18 0.38 0.020 0.0016 0. 0043 suitable Example F 0.48 0.75 0.59 0.012 0.020 0.024 0.04 0.38 0.019 0.0016 0. 0045------Suitable for case G 0.49 0.74 0.59 0.013 0.021 0.025 0.04 0.39 0.019 0.0017 0. 0044---0.05--Suitable for case II 0.46 0.70 0.60 0.012 0.020 0.024 0.04 0.40 0.020 0.0015 0.0050----0.21-fit case I 0.50 0.68 0.60 0.012 0.021 0. 024 0.04 0.38 0.020 0.0015 0. 0038 0.4-----fit case J 0.49 0.55 0.61 0.012 0.020 0.025 0.03 0.39 0.019 0.0016 0.0041-1.5----Suitable examples K 0.48 0.71 0.60 0.013 0.020 0.025 0.03 0.39 0.021 0.0018 0. 0040--0.45---Suitable example L 0.84 0.65 0.68 0.012 0.019 0.024 0.03 0.40 0.017 0.0018 0. 0040------Comparative example M 0.26 0.68 0.65 0.013 0. 022 0. 022 0. 03 0.42 0.018 0. 0022 0. 0044 Comparative Example N 0.46 0.06 0.67 0.012 0.023 0.025 0.01 0.34 0.018 0. 0021 0. 0032 Comparative Example 0 0. 50 0. 76 0. 65 0.018 0.019 0.022 0.0. 2-0.018 0. 0020 0. 0041--- ---Comparative Example P 0.49 0.58 0.65 0.013 0.014 0.022 0.04 0.38 0.020 0. 0045 0. 0037-Comparative Example Q 0.48 0.65 2.59 0.007 0.018 0.022 0.02 0.38 0.020 0. 0020 0.0056 Comparative Example R 0.47 0.60 0.64 0. 039 0.083 0. 022 0. 02 0.40 0. 021 0. 0018 0. 0049-One----Comparative Example S 0.47 0.59 0.63 0.008 0.015 0.070 0.02 0.41 0.022 0.0018 0. 0049-One----Comparative Example D 0.48 0.70 0.58 0.009 0.018 0.020 0.31 0.41 0.018 0.0019 0. 0045 Comparative Example U 0.48 0.72 0.64 0.012 0.018 0.018 0.03 0.37 0.080 0.0018 0. 0045--One---Comparative Example V 0.48 0.74 0.63 0.013 0.014 0.018 0.04 0.38 0. 004 0.0018 0. 0040--0040-- ----Than Example w 0.46 0.45 0.65 0.015 0. 040 0.002 0.01 0.38 0.030 0. 0020 0. 0045 Ca: 0.002 Suitable example X 0.47 0.47 0.70 0.018 0.035 0.001 0.01 0.35 0.040 0. 0021 0.0040 Te: 0. 05 Se: 0. 05 Sn: 0. 01 fit case Y 0.46 0.50 0.67 0.014 0.050 0.002 0.01 0.33 0.028 0.0018 0. 0047 Zr: 0. 02 REM: 0. 005 Sb: 0.005 fit case z 0.44 0.45 0.70 0.012 0.048 0.001 0.01 0.35 0.030 0. 0021 0.0046 Mg: 0.0020 Hf: 0. 05 fit case AA 0.44 0.51 0.68 0.015 0.038 < 0.001 0.01 0.38 0.025 0. 0022 0.0048 Ca: 0. 0018 fit case AB 0.41 0.32 1.30 0.015 0.030 0.003 0.01 0.18 0.056 0. 0022 0. 0048 0.05-1 -Ca: 0.0020 Suitable example 312XP / Invention specification (Supplement) / 94-08 / 94112006 24 200538559 Table 2

No. Steel Mark Toughened Tissue Fraction (vol%) Asa Intermediate Tissue Fraction (vol ° / 〇) Thickness of Hardened Layer on the Smooth Part of the Axis (Rec) Thickness of Hardened Layer on the Fillet of R (mm) Hardened Layer Particle size (㈣). Flexural fatigue strength (MPa) of the fillet r section Remarks 1 A 81 0 5.0 3.9 3.1 930 Invention Example 2 A 81 0 4.3 3.2 3.1 880 Invention Example 3 A 81 0 6.5 4.5 3.1 950 Invention Example 4 A 81 0 3.2 2.4 3.1 865 Invention Example 5 B 65 0 4.1 3.1 2.5 925 Invention Example 6 B 9 91 4.2 3.2 2.2 900 Invention Example 7 C 88 0 3.8 2.9 1.8 920 Invention Example 8 C 88 0 6.7 4.6 1.8 990 Invention Example 9 C 6 0 3.8 2.8 15.0 630 Comparative Example 10 D 28 0 4.0 3.0 3.8 880 Invention Example 11 E 63 0 4.0 2.9 3.8 890 Invention Example 12 F 63 0 4.2 3.2 3.6 890 Invention Example 13 G 61 0 3.8 3.0 2.9 900 Invention Example 14 H 64 0 3.8 2.8 3.8 .885 Invention Example 15 I 67 0 4.1 3.1 3.7 890 Invention Example 16 J 87 0 4.3 3.1 3.4 895 Invention Example 17 K 71 0 3.8 2.9 3.0 900 Invention Example 18 L 33 0 3.7 2.7 3.2 440 Comparative Example 19 M 8 0 4.0 3.0 14.0 420 Comparative example 20 N 35 0 4.2 2.8 13.5 580 Comparative example 21 0 12 0 3.8 2.7 13.7 550 Comparative example 22 P 7 0 4.0 2.9 4.4 620 Comparative example 23 Q 87 0 4.0 2.8 3.2 580 Comparative example 24 R 69 0 3.8 2.9 3.0 620 Comparative example 25 S 69 0 3.7 2.7 3.1 620 Comparative example 26 T 24 0 4.0 2.9 2.9 610 Comparative example 27 U 80 0 4.1 3.0 4.0 640 Comparative Example 28 V 7 0 4.0 3.0 15.3 620 Comparative Example 29 W 80 0 4.8 2.7 4.2 910 Invention Example 30 X 81 0 5.2 2.6 4.3 960 Invention Example 31 Y 80 0 4.7 2.6 4.8 905 Invention Example 32 Z 82 0 4.7 2.6 4.8 900 Invention Example 33 AA 80 0 4.9 2.7 4.2 910 Invention Example 34 W 80 0 5.5 2.7 5.5 860 Invention Example 35 X 81 0 5.1 2.6 7.2 850 Invention Example 36 Y 80 0 5.3 2.7 6.5 840 Invention Example 37 Z 82 0 5.5 2.7 5.8 855 Invention Example 38 AA 80 0 5.7 2.8 8.0 835 Invention Example 39 A 81 0 4.5 1.5 3.1 660 Comparative Example 40 A 81 0 1.9 2.9 3.1 665 Comparative Example 41 B 80 0 5.3 1.7 2.5 640 Comparative Example 42 B 82 0 1.9 3.0 2.5 655 Comparative Example 43 AB 80 0 5.2 3.0 4.8 945 Invention Example 25 312XP / Invention Specification (Supplement) / 94-08 / 94112006 200538559 It is apparent from Table 2 that the ingredients satisfying the requirements of the present invention are satisfied The composition range and organization of the crankshaft meet the hardened layer of old Vostian body particles In full thickness PICC 5 // m or less of the holding conditions, was able to be obtained by the stress in the fillet portion of r bending fatigue strength of more than 800 Μ P a is excellent in the bending fatigue strength.

In contrast, No. 9 is a comparative example in which the cooling rate after hot forging is reduced to 0.08 ° C / sec, and the total tissue fraction of the deformed tissue and the Mata loose tissue is less than 1 0%, which results in coarsening of the particle size of the hardened layer and low bending fatigue strength. Although No. 18 has a fine particle diameter of the hardened layer, since its C content is higher than the range of the present invention, the grain boundary strength is lowered, so its bending fatigue strength is inferior. No. 19, 20, and 21 respectively have C, Si, and Mo content lower than the appropriate range of the present invention, which results in coarsening of the particle size of the hardened layer and poor bending fatigue strength.

No. 22 with B content, No. 23 with Mη content, No. 24 with S and Pi content, No. 25 with A1 content, and No. 26 with Cr content each exceed the appropriate range of the present invention, and therefore all cause granulation The reduction of the boundary strength and the low bending fatigue strength. No. 27 shows that its Ti fatigue strength exceeds the appropriate range of the present invention, and its flexural fatigue strength is inferior. On the other hand, No. 28 has a low Ti content, which results in coarsening of the particle size of the hardened layer and poor flexural fatigue strength.

Nos. 39 and 41 show inadequate bending fatigue strength due to insufficient thickness of the hardened layer in the r-round portion, while No. 40 and 42 show bending fatigue strength due to insufficient thickness of the hardened layer in the shaft smooth portion. inferior. 26 312XP / Invention Specification (Supplement) / 94-08 / 94112006 200538559 [Industrial Applicability] In this way, according to the present invention, a crankshaft having a bending fatigue strength that is superior to that of a conventional person can be stably obtained. With the requirements of lightweight parts, excellent efficacy can be achieved. [Schematic description] Figure 1 is a schematic diagram of the crankshaft.

Fig. 2 is a schematic diagram for explaining the thickness of the hardened layer of the fillet r portion and the shaft smooth portion. Figure 3 is a map of the south frequency > the location of the fire of the non-curved car. Fig. 4 is a diagram showing an outline of a durability test according to the present invention. [Description of main component symbols] 1 Crankshaft 2 Journal neck 3 Crank pin

5 Counterweight section 6 Hardened layer 7 Fillet r section 8 Shaft smooth section 27 312XP / Invention manual (Supplement) / 94-08 / 94112006

Claims (1)

200538559 10. Scope of patent application: 1. A crankshaft with excellent bending fatigue strength, which is a crankshaft with a hardened layer on the surface of the crank pin and the journal portion, which is characterized by containing C: 0. 4 0 to 0 5 1% by mass, S i: 0.30 to 0.80% by mass, Μ η: 0.50 to 1 · 50% by mass, A 1 ·· 0 · 0 4 0% by mass or less (including 0), T i: 0. 0 0 5 to 0. 0 6 mass%, Μ 〇 ·· 0. 1 5 to 0 · 5 0 mass%, Β: 0 · 0 0 0 5 to 0 · 0 0 3 0 % By mass, S: 0.6% by mass or less, P: 0.22% by mass or less, and Cr: 0.2% by mass or less, The remaining part is composed of Fe and unavoidable impurities. The parent metal tissue has the deformed tissue and / or Asada loose tissue, and the total tissue score of these deformed tissue and Asada loose tissue is 10 Above, in addition, the particle size of the old Voss body of the surface hardened layer after induction hardening is kept below 10 m in the full thickness of the hardened layer, and the bending fatigue strength of the inner round corner r portion of the crank pin and the journal portion It is 800 MPa or more. 2. The crankshaft having excellent bending fatigue strength according to item 1 of the scope of patent application, wherein the component composition of the steel further contains Cu: 1.0% by mass or less, Ni: 3.5% by mass or less, C. : 1.0% by mass or less, 28 3] 2XP / Invention Specification (Supplement) / 94-08 / 94112006 200538559 N b: 0.1% by mass or less, and V ·. 0.5% by mass or less, choose one Or two or more. 3. If the crankshaft has excellent bending fatigue strength according to item 1 or 2 of the scope of patent application, wherein the component composition of the steel further contains from e: 0.2% by mass or less, S e: 0.2% by mass or less, Ca: 0.2% by mass or less, REM: 0.3% by mass or less, Zr: 0.2% by mass or less, Sη: 0.3% by mass or less, Sb: 0.2% by mass Below, M g: 0. ◦ 2% by mass or less, and H f: 0.1% by mass or less, Choose one or more. 4. A crankshaft having excellent bending fatigue strength, which is a crankshaft having a hardened layer on the surface of a crank pin and a journal portion, characterized in that it contains C: 0.45 to 0.51 mass%, S i: 0 · 4 0 ~ 0 · 80 mass%, Μ η: 0.5 0 ~ 0.70 mass ° / 〇, A 1: 0. 0 0 5 ~ 0. 0 4 0 mass. / ◦, T i: 0. 0 0 5 to 0 · 0 3 0 mass ° / 〇, Μ 0: 0 · 3 0 to 0. 5 0 mass%, Β ·· 0. 0 0 0 5 to 0. 0 0 3 0 mass ° / 〇, 29 312XP / Invention Specification (Supplement) / 94-08 / 94112006 200538559 S: 0.06 mass% or less, P: 0 · 0 2 mass% or less, and C r: 0 2 mass% or less, the remainder is composed of Fe and unavoidable impurities, and the parent metal tissue has a toughened tissue and / or Asada loose tissue, and the total amount of these deformed tissue and Asada loose tissue is The structure fraction is above 10%. In addition, the particle size of the old Voss body of the surface-hardened layer after induction hardening is kept below 5 // m in the full thickness of the hardened layer. The inner circle of the crank pin and the journal The bending fatigue strength of the corner r is 800 MPa or more. 5. The crankshaft having excellent bending fatigue strength according to item 4 of the scope of patent application, wherein the composition of the steel material further contains Cu: 1.0% by mass or less, Ni: 3.5% by mass or less, and C: 1.0 mass% or less, Among N b: 0.1% by mass or less, and V: 0.5% by mass or less, one or two or more kinds are selected. 30 312XP / Invention Specification (Supplement) / 94-08 / 94112006