JP4970811B2 - High surface pressure parts and manufacturing method thereof - Google Patents

Description

  The present invention relates to parts made of steel for machine structures subjected to high surface pressure (hereinafter referred to as “machine structure parts”), such as gears and CVTs produced by quenching, carburizing, carbonitriding and the like. The present invention relates to a machine structural component having excellent pitting resistance and wear resistance used in a pressure component and a method for manufacturing the same.

  Machine structural parts, such as parts that receive high surface pressure, such as gears, are formed by forming a steel material into a part shape by hot forging, cold forging, cutting, or the like, followed by carburizing. Low alloy case-hardened steels such as JIS-SCM420 and JIS-SCr420 are mainly used as steel materials for such parts. For example, a method for producing a high surface pressure component made of such a low alloy case-hardened steel is already known (see, for example, Patent Document 1 and Patent Document 2).

  However, in recent years, with the improvement in performance and size and weight of machinery and equipment that use parts made of these steel materials, the use conditions become severe and the load on the parts increases, so the pitting resistance and wear resistance of the parts are increased. There is a demand for further improvement in fatigue and fatigue strength.

  As a means effective for such a requirement, high-concentration carburizing for members can be cited. In this high-concentration carburizing method, the carbon concentration in the surface layer of the carburized material is 1.0 to 1.5% by mass where C is higher than about 0.8% by mass of the conventional C, and carbide is added to the martensitic structure on the surface of the carburized material. This is a surface treatment method for dispersion (see, for example, Non-Patent Document 1). However, this method requires a long heat treatment, which increases the cost. Moreover, it is necessary to control the carbide in a spherical shape. This is because when the net-like carbide is precipitated, the pitting resistance and fatigue strength of the parts are reduced.

Japanese Patent No. 3033349 Japanese Patent No. 3219167 “Heat Treatment Technology” Vol. 26, No. 2, April 1986, “Technology of High Carbon Carburization”, Takeshi Uchino, p. 157-162

  The problem to be solved by the present invention is to overcome the above-described problems without increasing the carbon concentration of the surface layer of the carburized material by conventional high-concentration carburization such that C is 1.0 to 1.5 mass%, The object is to provide a machine structural component excellent in pitting resistance, wear resistance, fatigue strength, and impact resistance, particularly a component for high surface pressure, and a manufacturing method thereof.

In order to achieve the above object, according to the first aspect of the present invention, in the invention of claim 1, C: 0.15 to 0.60% (preferably 0.20 to 0.45%), Si: 0 0.01 to 2.00% (preferably 0.30 to 1.00%), Mn: 0.01 to 2.00% (preferably 0.30 to 1.50%), Al: 0.003 to 0 0.050% (preferably 0.003 to 0.050%), N: 0.005 to 0.100% (preferably 0.0080 to 0.0200%), Cr: 1.50 to 6.00% ( Preferably 2.00 to 5.50%), Mo: 0.01 to 3.00% (preferably 0.01 to 1.50%), and Cr + 2Mo: 2.00 to 8.00% (Preferably 2.00 to 6.00%), made of steel consisting of the balance Fe and inevitable impurities, The carbide having a square root of the product of the major axis and the minor axis (hereinafter referred to as “√ (major axis × minor axis)”) of 2 μm or more has an area ratio of 2% or less, and the C concentration of the carburized surface layer is 0.60. It is a part for high surface pressure which is excellent in pitting resistance and wear resistance, characterized by being -0.80% .

In the second aspect of the invention, the high surface pressure component is, in addition to the steel component of the means of the first aspect, in mass%, Ni: 0.1 to 2.0%, B: 0.0001 to 0 Contains one or more selected from 0020%, V: 0.01 to 0.50%, Nb: 0.01 to 0.20%, Ti: 0.01 to 0.20%, and the balance It consists of steel consisting of Fe and inevitable impurities, and in the carburized surface layer, the carbide whose square root of the product of the major axis and the minor axis is 2 μm or more is 2% or less in area ratio, and the C concentration in the carburized surface layer is 0.60 to 0.80. % , It is a part for high surface pressure excellent in pitting resistance and wear resistance.

In the invention of claim 3, the high surface pressure component is, in addition to the steel component of the means of claim 1 or 2, mass%, S: 0.001 to 0.030%, Pb: 0.01 ~ 0.20%, Bi: contains one or more selected from 0.01 ~ 0.20%, consists of steel consisting of the remainder Fe and inevitable impurities Carbide having a square root of 2 μm or more has an area ratio of 2% or less, and the C concentration of the carburized surface layer is 0.60 to 0.80%. High surface excellent in pitting resistance and wear resistance It is a pressure component.

In invention of Claim 4, with respect to the part for high surface pressure which consists of the steel component of the means of any one of Claims 1-3, heating temperature is 930-1050 degreeC, C concentration of carburizing surface layer is 0.60-0. It is a method for producing a high surface pressure part characterized by performing carburizing quenching, tempering treatment or carbonitriding quenching, and tempering treatment while controlling the quenching temperature to 850 to 900 ° C.

Furthermore, in the invention of claim 5, after tempering in the method for producing a high surface pressure component of the means of claim 4, the high surface pressure component is finish-polished, and further shot peening, hard shot peening, fine particle shot peening Any one or two or more kinds of surface hardening treatments are performed .

  As described above, in comparison with the parts of the conventional material carburized the low alloy case-hardened steel, the parts of the means of the present invention use high Cr-Mo steel, and the material of the parts for high surface pressure is coarse. By carburizing, tempering, or carbonitriding and quenching, and tempering that do not generate tempered carbides, (1) strengthening the matrix by high Cr-Mo conversion, and (2) preventing coarse carbides that reduce pitting resistance Increases wear resistance, pitting resistance, impact resistance and fatigue strength.

In addition, if necessary, the high surface pressure parts that have been tempered are polished , shot peened, surface carburized abnormal layers are removed, and compressive stress is applied to improve wear resistance, pitting resistance, impact resistance, and fatigue strength. It is increasing.

The reasons for limiting the steel components and the processing conditions for the high surface pressure parts of the present invention will be described below. In addition,% described below is mass%.

Cr: 1.50 to 6.00%, preferably 2.00 to 5.50%
Cr is one of the most important elements in the present invention, like Mo described later. Cr dissolves in martensite, thereby significantly improving wear resistance and pitting resistance. In order to obtain the effect, Cr needs to be 1.50% or more. However, if Cr exceeds 6.00%, the workability deteriorates and a net-like carbide is generated to reduce the pitting resistance. Therefore, Cr is 1.50 to 6.00%, preferably 2.00 to 5.50%.

Mo is 0.01 to 3.00%, preferably 0.01 to 1.50%
Mo, like Cr, is one of the most important elements in the present invention. Mo is an element effective for improving wear resistance and pitting resistance and ensuring hardenability. In order to obtain the effect, Mo needs to be 0.01%. However, if Mo exceeds 3.00%, workability deteriorates and costs increase. Therefore, Mo is 0.01 to 3.00%, preferably 0.01 to 1.50%.

Cr + 2Mo: 2.00 to 8.00%, preferably 2.00 to 6.00%
Cr + 2Mo needs to be at least 2.00% to improve wear resistance. However, if there is too much Cr + 2Mo, the workability deteriorates. Therefore, Cr + 2Mo is 2.00 to 8.00%, preferably 2.00 to 6.00%.

√ (major axis × minor axis): 2 μm or more of carbide is 2% or less in area ratio √ (major axis × minor axis) of carbide having 2 μm or more lowers pitting resistance. Below 2%, the decrease is in an acceptable range. Therefore, √ (major axis × minor axis): Carbide of 2 μm or more is 2% or less in terms of area ratio.

C: 0.15 to 0.60%, preferably 0.20 to 0.45%
C is an element necessary for ensuring the hardness of the core of the high surface pressure component. For that purpose, C is required to be 0.15% or more. However, when there is too much C, workability will deteriorate. Therefore, C is 0.15 to 0.60%, preferably 0.20 to 0.45%.

Si: 0.01 to 2.00%, preferably 0.30 to 1.00%
Si is an element necessary for deoxidation, and is also an element effective for improving temper softening resistance. For that purpose, Si needs to be 0.01% or more. However, when there is too much Si, the effect of the temper softening resistance is saturated, and further, the hardness is increased and the workability is deteriorated. Therefore, Si is 0.01 to 2.00%, preferably 0.30 to 1.00%.

Mn: 0.01 to 2.00%, preferably 0.30 to 1.50%
Mn is an element necessary for ensuring hardenability, and for that purpose, 0.01% or more is necessary. However, when there is too much Mn, hardness will rise and workability will deteriorate. Therefore, Mn is 0.01 to 2.00%, preferably 0.30 to 1.50%.

Al: 0.003 to 0.050%
Al is an element necessary for deoxidation, and deoxidation is insufficient at 0.003% or less. However, if there is too much Al, non-metallic inclusions are generated and the fatigue strength decreases. Therefore, Al is made 0.003 to 0.050%.

N: 0.005 to 0.100%, preferably 0.008 to 0.020%
N forms Al and AlN to prevent coarsening of crystal grains during carburization. However, if N is less than 0.005%, the effect is small, and if it exceeds 0.100%, the effect of preventing the coarsening of crystal grains is saturated. Therefore, N is 0.005 to 0.100%, preferably 0.008 to 0.020%.

Ni: 0.1 to 2.0%
Ni is an element effective for improving toughness. However, Ni is less effective at less than 0.1%. On the other hand, if Ni is more than 2.0%, the workability is deteriorated and the cost is increased. Therefore, Ni is set to 0.1 to 2.0%.

B: 0.0001 to 0.0020%
B is an element effective for improving hardenability. However, if B is less than 0.0001%, the effect is not obtained. On the other hand, even if B exceeds 0.0020%, the effect is saturated. Therefore, B is set to 0.0001 to 0.0020%.

V: 0.01 to 0.50%
V is an element effective for grain refinement. However, when V is less than 0.01, there is no effect. On the other hand, even if V exceeds 0.50%, the effect of crystal grain refinement is saturated, resulting in an increase in cost. Therefore, V is set to 0.01 to 0.50%.

Nb: 0.01-0.20%
Nb is an element effective for grain refinement. However, if Nb is less than 0.01, the effect is not obtained. On the other hand, even if Nb exceeds 0.20%, the effect of crystal grain refinement is saturated and the cost increases. Therefore, Nb is set to 0.01 to 0.20%.

Ti: 0.01-0.20%
Ti is an element effective for grain refinement. However, when Ti is less than 0.01, there is no effect. On the other hand, even if Ti exceeds 0.20%, the effect of crystal grain refinement is saturated and workability deteriorates. Therefore, Ti is Ti: 0.01 to 0.20%.

S: 0.001 to 0.030%, preferably 0.003 to 0.020%
S is an effective element for ensuring machinability, and the effect is effective at 0.001% or more. However, when S is too much, the pitting resistance and fatigue strength deteriorate. Therefore, S is 0.001 to 0.030%, preferably 0.003 to 0.020%.

Pb: 0.01-0.20%
Pb is an effective element for ensuring machinability, and the effect is effective at 0.01% or more. However, when there is too much Pb, pitting resistance and fatigue strength deteriorate. Therefore, Pb is set to 0.01 to 0.20%.

Bi: 0.01-0.20%
Bi is an effective element for ensuring machinability, and the effect is effective at 0.01% or more. However, when there is too much Bi, pitting resistance and fatigue strength deteriorate. Therefore, Bi is set to 0.01 to 0.20%.

Carburizing heating temperature: 930-1050 ° C, preferably 950-1000 ° C
When the carburizing heating temperature is lower than 930 ° C., a large amount of reticulated carbide is generated. On the other hand, when the carburizing heating temperature exceeds 1050 ° C., the coarsening of crystal grains occurs during carburizing, leading to a decrease in fatigue strength. Therefore, the carburizing heating temperature is 930 to 1050 ° C, preferably 950 to 1000 ° C.

C concentration of carburized surface layer: 0.60 to 0.80%
The C concentration of the carburized surface layer needs to be 0.60% or more in order to ensure the surface hardness required for high surface pressure parts. However, if the C concentration in the carburized surface layer is too higher than 0.80%, a large amount of reticulated carbide is generated. Therefore, the C concentration of the carburized surface layer is set to 0.60 to 0.80%.

Quenching temperature: 850-900 ° C
If the quenching temperature is less than 850 ° C., a large amount of reticulated carbide is generated. On the other hand, if the quenching temperature exceeds 900 ° C., the strain after quenching increases and cracking is likely to occur during quenching. Therefore, the quenching temperature is set to 850 to 900 ° C.

  By using the means of the present invention, mechanical structural parts subjected to high surface pressure, for example, gears manufactured by quenching, carburizing, carbonitriding, etc., and parts for high surface pressure such as CVT require long-time heat treatment. In addition, the present invention is excellent in pitting resistance and wear resistance, improves the quietness of automobiles that increase the load on parts under severe use conditions, and enables weight reduction at low cost. Excellent effect.

  BEST MODE FOR CARRYING OUT THE INVENTION The best mode for carrying out the present invention will be described through tests of invention examples and comparative examples of the following examples.

  First, the manufacturing process of the test piece applied to this experiment is demonstrated. From a steel obtained by melting steel containing chemical components shown in Table 1 in a 100 kg vacuum melting furnace, a round bar having a diameter of 32 mm was manufactured by hot forging.

In the component example of the present invention, a roller pitching test piece, a Charpy impact test piece, and an Ono-type rotary bending test piece were produced from a round bar of φ32 mm produced by the above hot forging by machining. Subsequently, after carburizing and diffusing at carburizing temperature conditions: 920 to 1050 ° C., quenching was performed in oil at 60 ° C. from 830 to 900 ° C., and tempering was performed at 180 ° C. After tempering, the test piece was finished by polishing the surface with 0.1 mm. The atmosphere in the carburizing furnace was controlled so that the surface layer after carburizing was 0.60 to 1.00%, and then tempered at 180 ° C. On the other hand, for the comparative component examples, roller pitching test pieces, Charpy impact test pieces, and Ono-type rotary bending test pieces were manufactured by machining from the φ32 mm round bar by the above hot forging, and carburizing conditions: 920 ° C. After carburizing and diffusing, the steel was quenched in oil from 830 ° C. to 60 ° C. and tempered at 180 ° C. After tempering, the test piece was finished by polishing the surface with 0.1 mm. Table 2 shows the carburizing conditions and the area ratio of carbides having a √ (major axis × minor axis) of 2 μm or more from the surface to 0.5 mm. The measurement area is 0.25 mm ² . Further, √ (major axis × minor axis) of the present invention example: the area ratio of carbides of 2 μm or more was 2% or less.

Using these test pieces, a roller pitching test was first performed under the following conditions. In addition, the amount of wear was measured in the same test. The amount of wear was measured by measuring the dent depth of the sliding portion of the roller pitching test piece at a contact pressure of 3440 MPa, a slip rate of −40%, an oil temperature of 80 ° C., and a rotation speed of 1 × 10 ⁶ times. The amount of wear was evaluated. In addition, Charpy impact test and Ono type rotary bending test were conducted. The test piece used was a 10 RC notch with a 10 mm square in the Charpy impact test, and a notched rotary bending fatigue test piece with a parallel portion of φ8 mm in the Ono type rotary bending fatigue test. Table 3 shows the results obtained by these tests.

  As shown in Table 3, it can be seen that the inventive examples are superior in wear resistance, pitting resistance, fatigue strength, and impact resistance compared to the comparative examples. In particular, it was found that the components of the present invention are extremely superior in abrasion resistance as compared with Comparative Examples 5 and 6 which are Comparative Components 1 and 2.

  Next, after finish polishing, shot peening, hard shot peening, and fine particle shot peening under the conditions specified in Table 4 were performed.

They were subjected to a roller pitching test under the following conditions. Furthermore, the amount of wear was measured in the same test. The amount of wear was measured by measuring the dent depth of the sliding portion of the roller pitching test piece at a contact pressure of 3440 MPa, a slip rate of −40%, an oil temperature of 80 ° C., and a rotation speed of 1 × 10 ⁶ times. Evaluated as a quantity. In addition, Charpy impact test and Ono type rotary bending test were conducted. Table 5 shows the results obtained by these tests.

  In Table 5, those not subjected to various shot peening in Table 4 and those subjected to various shot peening are compared in Invention Example 1, Invention Example 8, Invention Example 11, Invention Example 3, and further shot peening is performed. Comparative example 5 which is not applied is shown in comparison. Inventive Example 3 shows a comparison with the case where both hard shot peening and fine particle shot peening were performed. From Table 5, it was found that the fatigue strength is particularly improved by performing various shot peening. On the other hand, it can be seen that Comparative Example 5 is particularly inferior in wear resistance.

Claims (5)

In mass%, C: 0.15 to 0.60%, Si: 0.01 to 2.00%, Mn: 0.01 to 2.00%, Al: 0.003 to 0.050%, N: 0.005 to 0.100%, Cr: 1.50 to 6.00%, Mo: 0.01 to 3.00%, and Cr + 2Mo: 2.00 to 8.00%, the balance It consists of steel consisting of Fe and inevitable impurities, and in the carburized surface layer, the carbide whose square root of the product of the major axis and the minor axis is 2 μm or more is 2% or less in area ratio, and the C concentration in the carburized surface layer is 0.60 to 0.80. % High surface pressure components with excellent pitting resistance and wear resistance. In addition to the steel components according to claim 1 , Ni: 0.1 to 2.0%, B: 0.0001 to 0.0020%, V: 0.01 to 0.50% in mass%. Nb: 0.01 to 0.20%, Ti: One or more selected from 0.01 to 0.20%, made of steel consisting of the remainder Fe and unavoidable impurities, the major axis in the carburized surface layer The carbide having a square root of 2 μm or more of the product of the minor axis and the area ratio is 2% or less, and the C concentration of the carburized surface layer is 0.60 to 0.80%. High surface pressure parts with excellent wear resistance. In addition to the steel component according to claim 1 or 2, in mass%, S: 0.001 to 0.030%, Pb: 0.01 to 0.20%, Bi: 0.01 to 0.20% 1 or 2 or more types selected from the above, and the balance is 2% or less of the carbide having a square root of the product of the major axis and the minor axis in the carburized surface layer of 2 μm or more. A component for high surface pressure having excellent pitting resistance and wear resistance, wherein the C concentration of the carburized surface layer is 0.60 to 0.80% . The heating temperature is 930 to 1050 ° C., the C concentration of the carburized surface layer is 0.60 to 0.80%, and the quenching temperature is set for the high surface pressure component made of the steel component according to claim 1. A method for producing a part for high surface pressure, characterized by performing carburizing and quenching, tempering or carbonitriding and quenching, and tempering by controlling the temperature to 850 to 900 ° C. After performing the tempering process in the manufacturing method of the part for high surface pressure of Claim 4, it finish-polishs, Furthermore, any 1 type, or 2 or more types of surface hardening processes of shot peening, hard shot peening, and fine particle shot peening are performed. A method for producing a high surface pressure component, comprising: