JP2012207247A - Carburizing member, steel for carburizing member and method for producing carburizing member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carburizing member enabling to improve wear resistance without accompanying massive cost increase, steel for the carburizing member being a semi-finished product thereof, and a method for producing the carburizing member.SOLUTION: This carburizing member contains the chemical components, by mass, of 0.10-0.30% C, 0.50-2.00% Si, 0.30-1.50% Mn, 0.035% or less P, 0.035% or less S, 1.35-3.00% Cr, 0.020-0.060% Al, and 0.0080-0.0250% N, and the balance Fe and inevitable impurities. The sliding surface has no carburizing abnormal layer, the surface carbon concentration is in the range of 0.7-0.9 mass%, and the troostite areal rate in the tissue from the top surface to 50 μm depth is 1% or less. Carbon potential at the carburizing period of carburization process is 1.3% or more.

Description

  The present invention relates to a carburized member, steel for carburized member, and a method for manufacturing a carburized member.

  Depending on the purpose of use, the steel material may be used with only the surface being hard and wear-resistant, while the central portion is rich in flexibility and toughness. As an application of such a steel material, for example, there is a CVT sheave constituting a pulley of a belt type continuously variable transmission (hereinafter referred to as “belt type CVT”). This type of CVT sheave has a sliding surface that always slides with the metal belt, and the sliding surface is required to have high wear resistance.

  Conventionally, carburizing and quenching is known as a surface hardening method for steel materials. The carburizing and quenching process is a process of increasing the amount of carbon in the surface layer and quenching and hardening only the surface layer after machining low carbon steel with good workability. In the past, carburizing and quenching has been performed to impart wear resistance to steel members such as the CVT sheave.

  In addition, in order to improve wear resistance, after the above carburizing and quenching treatment, a technique that further adds shot peening treatment to improve surface hardness and residual stress, and a structure that fine carbide is dispersed by high concentration carburizing treatment A technique for improving the surface roughness to a state suitable for wear resistance by devising a general improvement technique or a polishing method has been proposed (Patent Documents 1 to 4).

JP-A-6-73523 JP 2000-176586 A JP 2000-130527 A JP 2009-68609 A

  However, the prior art has problems in the following points. That is, additional processing such as shot peening involves an increase in cost. Therefore, there is a demand to improve the wear resistance of the carburized member without performing this kind of additional processing. In particular, CVT sheaves, which are one of automotive parts, have severe demands for cost reduction. Therefore, there is a demand for a method for improving the wear resistance of the sliding surface without adding a special surface treatment in addition to the carburizing and quenching treatment.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a carburized member capable of improving the wear resistance without significantly increasing the cost. Moreover, it is going to provide the steel for carburized members which is a semi-finished product of the said carburized member. Moreover, it is going to provide the manufacturing method of the said carburized member.

The first invention is a carburized member having a sliding surface,
Chemical component is mass%, C: 0.10 to 0.30%, Si: 0.50 to 2.00%, Mn: 0.30 to 1.50%, P: 0.035% or less, S : 0.035% or less, Cr: 1.35 to 3.00%, Al: 0.020 to 0.060%, and N: 0.0080 to 0.0250%, the balance being Fe and inevitable Consisting of impurities,
The sliding surface has no carburized abnormal layer, the surface carbon concentration is in the range of 0.7 to 0.9 mass%, and the troostite area ratio of the structure at a depth of 50 μm from the outermost surface is 1% or less. It is in the carburized member characterized by being (claim 1).

2nd invention has a sliding surface, this sliding surface has no carburizing abnormal layer, surface carbon concentration exists in the range of 0.7-0.9 mass%, and depth from outermost surface. A carburized member steel used for producing a carburized member having a structure troostite area ratio of up to 50 μm of 1% or less,
Chemical component is mass%, C: 0.10 to 0.30%, Si: 0.50 to 2.00%, Mn: 0.30 to 1.50%, P: 0.035% or less, S : 0.035% or less, Cr: 1.35 to 3.00%, Al: 0.020 to 0.060%, and N: 0.0080 to 0.0250%, the balance being Fe and inevitable It is in the steel for carburized members which consists of impurities (Claim 4).

According to a third aspect of the invention, there is provided a carburizing process including a carburizing period in which carbon enters a steel member and a diffusion period in which carbon invading the steel member is diffused, and quenching the steel member that has undergone the carburizing process. A carburized member manufacturing method comprising:
The steel member has a chemical composition of mass%, C: 0.10 to 0.30%, Si: 0.50 to 2.00%, Mn: 0.30 to 1.50%, P: 0.00. 035% or less, S: 0.035% or less, Cr: 1.35 to 3.00%, Al: 0.020 to 0.060%, and N: 0.0080 to 0.0250%, The balance consists of Fe and inevitable impurities,
The carbon potential in the carburizing period is 1.3% or more.

  The carburized member of the first invention has the above-mentioned specific chemical component, the sliding surface has no carburized abnormal layer, and the surface carbon concentration is in the range of 0.7 to 0.9% by mass. The troostite area ratio of the structure at a depth of 50 μm from the surface is 1% or less. For this reason, the wear resistance of the sliding surface is excellent even without additional processing such as shot peening with a significant cost increase.

  The steel for carburized member of the second invention is steel used for producing the carburized member and has the specific chemical component. Further, in the method for producing a carburized member of the third invention, when carburizing the steel member composed of the steel having the specific chemical component, the carbon potential in the carburizing period at the time of carburizing is set to 1.3. % Or more.

  When the Si and Cr contents are increased, the carburizing property is hindered, and thus such a steel material is unsuitable as a carburized member steel. However, even when the Si content is 0.50% or more and the Cr content is 1.35% or more, the carbon potential in the carburizing period during the carburizing process is 1.3% or more. If it does so, wear resistance can be improved, suppressing generation | occurrence | production of troostite in the carburizing surface layer of a carburizing member by ensuring carburizing property. Further, the softening resistance due to heat is increased by increasing the Si content to 0.50 to 2.00%, and further, the carburized surface layer is increased by increasing the Cr content to 1.35 to 3.00%. The generation of troostite is suppressed, and the wear resistance can be improved accordingly. If steels with the above-mentioned specific chemical components are used, and carburized parts are manufactured with a carbon potential at the carburizing stage of carburizing treatment of 1.3% or more, the resistance to sliding surfaces and the like will not increase significantly. It has been derived for the first time by the completion of the present invention that it becomes possible to improve the wear resistance of a part requiring wear.

  Thus, according to the present invention, there are provided a carburized member capable of improving wear resistance without significant cost increase, a steel for carburized member which is a semi-finished product thereof, and a method for manufacturing the carburized member. be able to.

It is explanatory drawing which shows the structure of a belt type continuously variable transmission (belt type CVT). It is explanatory drawing which shows the method of the abrasion test in an experiment example.

  The chemical components in the carburized member, the steel for carburized member, and the method for producing the carburized member are, as described above, mass%, C: 0.10 to 0.30%, Si: 0.50 to 2.00. %, Mn: 0.30 to 1.50%, P: 0.035% or less, S: 0.035% or less, Cr: 1.35 to 3.00%, Al: 0.020 to 0.060% And N: 0.0080 to 0.0250%, with the balance being Fe and inevitable impurities. Moreover, the said chemical component can contain Mo: 0.80% or less arbitrarily (Claim 2, Claim 5, Claim 7). Below, the reason for limitation of each component is demonstrated. In addition, the said chemical component is a chemical component of the base material in the steel inside except a carburized surface layer part.

C: 0.10 to 0.30%
C is a basic element for ensuring strength, and is added in an amount of 0.10% or more in order to ensure sufficient internal hardness in a carburized member such as a CVT sheave. If the amount added is too large, the machinability and cold forgeability are lowered, so the upper limit of the C content is 0.30%.

Si: 0.50 to 2.00%
Si is an element effective for enhancing the resistance to softening by heat, and 0.50% or more is added in order to ensure the characteristics. If the Si content is too high, toughness and workability deteriorate, so the upper limit of the Si content is 2.00%. The upper limit of the Si content is preferably 1.50%.

Mn: 0.30 to 1.50%
Mn is an element effective for improving the strength, and is added in an amount of 0.30% or more in order to ensure sufficient internal hardness in a carburized member such as a CVT sheave. If the amount of Mn added is too large, the machinability may decrease or the hardness may decrease due to an increase in retained austenite. Therefore, the upper limit of the Mn content is set to 1.50%.

P: 0.035% or less P is segregated at the grain boundaries to reduce fatigue strength, so the upper limit of the P content is 0.035%. P is an element inevitably contained as an impurity in production, but it is preferable to reduce it as much as possible by refining.

S: 0.035% or less S is an optional element that is effective in improving machinability, but does not need to be particularly positively added. If the S content is too large, it becomes a fatigue fracture starting point and causes a decrease in strength. Therefore, the upper limit of S content is 0.035%.

Cr: 1.35 to 3.00%
Cr is an element effective for improving the strength, and helps to ensure sufficient internal hardness in a carburized member such as a CVT sheave. In addition, by setting the carbon potential in the carburizing period during the carburizing process described above to 1.3% or more and ensuring a sufficient carburizing concentration in the carburized surface layer, generation of troostite in the carburized member is suppressed, and wear resistance is improved. It is effective for. Therefore, 1.35% or more of Cr is added. If the amount of Cr added is too large, the hardness increases and the workability decreases, so the upper limit of the Cr content is 3.00%. The upper limit of the Cr content is preferably 2.00%.

Al: 0.020 to 0.060%
Al is an element that is not only necessary for the deoxidation treatment but also effective for obtaining the effect of preventing the coarsening of the crystal grains after the carburizing treatment. To obtain this effect, 0.020% or more is added. If the Al content is excessively increased, the effect is saturated and the fatigue strength is reduced due to an increase in oxide inclusions. Therefore, the upper limit of the Al content is set to 0.060%.

N: 0.0080 to 0.0250%
N is an element that is inevitably contained in the production, but, like Al, it is effective in preventing the coarsening of crystal grains. Therefore, in order to obtain this effect, N is adjusted to contain 0.0080% or more. To manufacture. If the N content is excessively increased, the effect is saturated and the nitride increases to cause a decrease in fatigue strength. Therefore, the upper limit of the N content is set to 0.0250%.

Mo: 0.80% or less Mo is an element that can be optionally contained in the chemical component. Mo is an element effective for improving the strength and toughness, but is expensive, so the upper limit is suppressed to 0.80%. The Mo content is preferably about an impurity from the viewpoint of resource saving and cost reduction.

Next, the carburized member has a sliding surface that slides with other members. Examples of this type of carburized member include CVT sheaves, outer / inner races, gears, and the like. Preferably, the carburized member is a CVT sheave (claim 3).
. More preferably, it is a CVT sheave having a sliding surface with a metal belt. The CVT sheave is a member that is highly demanded for cost reduction and that requires high wear resistance on the sliding surface. Therefore, in this case, the wear resistance of the sliding surface can be improved without significantly increasing the cost, and the effects of the present invention can be sufficiently exhibited.

  Further, the carburized member does not have a carburized abnormal layer on its sliding surface. The carburizing abnormal layer is a layer that can be introduced during the quenching process after the carburizing process, and is a layer that reduces the wear resistance. The carburized member may not have an abnormal carburization layer by selecting the optimum carburizing conditions, and even if an abnormal carburization layer occurs during the quenching process, a finishing process is performed thereafter, thereby carburizing the carburizing member. The abnormal layer may be removed so that there is no carburized abnormal layer. The latter is preferred. This is because the carburized abnormal layer is surely removed, the effect of improving the wear resistance is great, and the reliability is also increased.

  When a finishing process is included after the quenching process as the manufacturing process, examples of the finishing process include cutting and polishing. These can be carried out by one or a combination of two or more. The finishing process is preferably a process for removing the sliding surface after quenching in the range of 50 μm to 300 μm. When the finishing amount is 50 μm or more, it is possible to sufficiently remove the carburized abnormal layer, and when it is 300 μm or less, the hardened layer obtained by carburizing treatment is obtained. This is because there is less possibility that the surface hardness will be reduced by removing too much. When such a finishing process is performed, the sliding surface is a surface after the finishing process of cutting and / or polishing.

  The carburized member has a surface carbon concentration in the range of 0.7 to 0.9 mass%. When the surface carbon concentration is less than 0.7% by mass, it is difficult to suppress the occurrence of troostite on the sliding surface. On the other hand, when the surface carbon concentration exceeds 0.9% by mass, carbides are precipitated at the grain boundaries with the Cr content, and the strength tends to decrease. The surface carbon concentration can be measured by EPMA.

  The carburized member has a troostite area ratio of 1% or less in the structure up to a depth of 50 μm from the outermost surface of the sliding surface. When the area ratio of troostite exceeds 1%, a sufficient effect of improving wear resistance cannot be obtained. The area ratio of the troostite can be calculated by observing a cross section up to a depth of 50 μm from the outermost surface of the sliding surface and analyzing the image.

  Next, the method for manufacturing the carburized member includes a carburizing period in which carbon enters the steel member and a diffusion period in which carbon invading the steel member is diffused, and a steel member that has undergone the carburizing process. A quenching process for quenching. As the steel member to be subjected to the carburizing treatment, for example, a steel material having the above-described chemical components shaped into a desired shape by forging (hot forging, cold forging), machining, or the like can be suitably used. For example, when finishing is performed after quenching, a steel material having the above-described chemical components as the steel member previously rough-processed into a rough shape can be preferably used.

  Here, in the manufacturing method of the carburized member, the carbon potential (hereinafter, also referred to as “CP”) in the carburizing period during the carburizing process is set to 1.3% or more. When the CP in the carburizing period is less than 1.3%, troostite is likely to be generated on the carburized surface layer on the sliding surface or the like, and the wear resistance is likely to be reduced. On the other hand, the upper limit of the CP of the carburizing period is not particularly limited, but if the CP of the carburizing period becomes excessively high, it becomes difficult to lower the surface carbon concentration to a desired level during the diffusion period, It becomes easy to invite boundary precipitation. Therefore, the upper limit of CP during the carburizing period is preferably 2.0%.

  In the carburized member manufacturing method, the carbon potential in the diffusion period during the carburizing process is preferably 0.8% or more. When the CP in the diffusion period is 0.8% or more, the surface carbon concentration on the sliding surface or the like of the carburized member is easily contained within the range of 0.7 to 0.9% by mass. On the other hand, the upper limit of the CP during the diffusion period is not particularly limited, but if the CP during the diffusion period becomes excessively high, the strength of the member tends to be impaired due to precipitation of grain boundary carbides. Therefore, the upper limit of CP in the diffusion period is preferably 0.90%.

  As other conditions in the carburizing process, for example, a carburizing temperature of 900 ° C. to 1000 ° C., a carburizing period of 1 h to 4 h, a diffusion period of 1 h to 4 h in gas carburizing or vacuum carburizing, etc. It can be illustrated.

  In addition, after the carburizing treatment step, for example, after holding at 800 ° C. to 900 ° C., various quenching such as oil quenching and gas cooling can be performed. Furthermore, after the above quenching, a tempering treatment or the like can be performed as necessary. Examples of conditions for the tempering treatment include a temperature of 130 ° C. to 160 ° C. and a holding time of 1 h to 1.5 h. Furthermore, after the quenching or tempering, finishing processing such as cutting and polishing can be performed as necessary.

  In the method for manufacturing the carburized member, the steel member has a sliding surface, and the sliding surface after the final step has a surface carbon concentration within a range of 0.7 to 0.9 mass%. In addition, the troostite area ratio of the structure up to a depth of 50 μm from the outermost surface is preferably 1% or less (claim 8).

  In this case, a carburized member having a sliding surface with excellent wear resistance can be obtained. Examples of the final process include the quenching process, the tempering process, and the finishing process.

  Hereinafter, the manufacturing method of the carburized member which concerns on an Example, the steel for carburized members, and the carburized member is demonstrated.

  In this example, a belt type CVT sheave was assumed as the carburized member. That is, as shown in FIG. 1, the belt-type CVT 1 includes an input pulley 201, an output pulley 202, and a metal belt 3 wound around the input pulley 201 and the output pulley 202. The input pulley 201 and the output pulley 202 are configured by combining two sheaves 2 each having a conical sliding surface 21. The sliding surface 21 of the sheave 2 is used in such a state that it always slides with the metal belt 3 constituted by a large number of elements 31 engaged with the steel band 32. The tension applied to the metal belt 3 is high, and the sliding surface 21 that comes into contact with the metal element 31 is used in a state where it is easily worn while repeatedly receiving a very high surface pressure. For this reason, the sliding surface 21 of the sheave 2 is required to have high wear resistance.

(Preparation of material steel)
Various steels having chemical components shown in Table 1 were produced as the raw material steel.

  Next, each carburized test piece is made from each material steel, and carburized, quenched, and finished with different carburizing CPs for each pre-carburized test piece, and each post-carburized test piece is made. did.

(Preparation of test specimen before carburization)
Each material steel was melted in a 30 kg melting furnace, and the steel ingot was forged at 1200 ° C. Next, each forged product obtained was annealed under the condition of holding it at 900 ° C. for 1 hour and then cooling it in the furnace. Next, each of the obtained annealed products was cut to prepare each cylindrical pre-carburization test piece having an outer diameter of 26.4 mm.

(Carburizing, quenching, tempering, finishing)
Each pre-carburized specimen was carburized, quenched, tempered, and finished. Specifically, first, each carburized test piece was heated and heated, and gas carburizing treatment was performed at a temperature of 950 ° C. for 6 hours. At this time, in the carburizing process, the CP of the carburizing period was as shown in Table 2 described later, and the time of the carburizing period was 3 hours. The diffusion period CP was as shown in Table 2 described later, and the diffusion period time was 3 hours.

  Next, after the carburizing treatment, the temperature was lowered to 850 ° C. and held for 1 hour, and oil quenching was performed at 130 ° C. Next, after the oil quenching, tempering was performed at a temperature of 160 ° C. for 1 hour. Next, after the tempering, cutting and polishing finishing with a machining allowance of 200 μm were applied to the surface to remove the carburized abnormal layer. As described above, columnar post-carburized test pieces having an outer diameter of 26.0 mm were produced.

  Next, the surface carbon concentration, the troostite area ratio, and the wear amount were measured and evaluated for each of the obtained carburized test pieces.

(Surface carbon concentration)
The surface carbon concentration of each specimen after carburization was measured by EPMA.

(Area ratio of troostite)
A cross section from the surface of each test piece after carburization (surface after finishing) to a depth of 50 μm was observed, and the area ratio of troostite was measured using image analysis software.

(Abrasion test)
As shown in FIG. 2, the abrasion test was performed by a two-roller contact test using a test piece 5 after carburizing and a counterpart roller 6 having an outer diameter of 130 mm. This test is a test in which the peripheral speeds of the test piece 5 and the counterpart roller 6 after carburizing are set to different speeds, sliding contact and load are applied, and the sliding surface is worn. The test conditions were as follows: the test piece 5 after carburizing was rotated at 2000 rpm, the contact surface pressure was 1250 MPa, the slip rate was -5%, and the lubricating oil was CVT fluid. This test was evaluated based on the amount of wear on the sliding surface, and when the amount of wear was 10 μm or less, it was determined that the wear resistance was excellent.
Table 2 below shows various test results together with the carburizing conditions.

  Table 2 shows the following. That is, in the comparative example, the CP in the carburizing period at the time of carburizing treatment is 1. even if the chemical composition of the material steel subjected to carburizing is outside the specified range of the present invention or the chemical component is within the specified range of the present invention. Less than 3%. Therefore, it can be seen that the surface carbon concentration of the test piece after carburization is less than 0.7% by mass, or the area ratio of troostite exceeds 1%, the wear amount is large, and the wear resistance is inferior.

  On the other hand, in the examples, the chemical composition of the material steel subjected to carburization is within the specified range of the present invention, and the CP in the carburizing period during the carburizing process is 1.3% or more. Therefore, the surface carbon concentration of the test piece after carburization is in the range of 0.7 mass% to 0.9 mass%, the area ratio of troostite is 1% or less, the wear amount is small, and the wear resistance is excellent. You can see that

  From the above, according to the present invention, it is possible to provide a carburized member excellent in wear resistance such as a sliding surface without significant cost increase, a steel for carburized member which is a semi-finished product thereof, and a method for manufacturing the carburized member. I understand.

  Although the embodiments have been described above, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the present invention.

1 Belt type continuously variable transmission (Belt type CVT)
2 CVT sheave 21 Sliding surface 201 Input pulley 202 Output pulley 3 Belt 31 Element 32 Steel band

Claims (8)

A carburized member having a sliding surface,
Chemical component is mass%, C: 0.10 to 0.30%, Si: 0.50 to 2.00%, Mn: 0.30 to 1.50%, P: 0.035% or less, S : 0.035% or less, Cr: 1.35 to 3.00%, Al: 0.020 to 0.060%, and N: 0.0080 to 0.0250%, the balance being Fe and inevitable Consisting of impurities,
The sliding surface has no carburized abnormal layer, the surface carbon concentration is in the range of 0.7 to 0.9 mass%, and the troostite area ratio of the structure at a depth of 50 μm from the outermost surface is 1% or less. A carburized member characterized by being. The carburized member according to claim 1,
The carburized member, wherein the chemical component further contains Mo: 0.80% or less.   The carburized member according to claim 1 or 2 is a CVT sheave. The sliding surface has no abnormal carburization layer, has a surface carbon concentration within a range of 0.7 to 0.9 mass%, and has a structure with a depth of 50 μm from the outermost surface. It is a steel for carburizing member used for manufacturing a carburized member having a tight area ratio of 1% or less,
Chemical component is mass%, C: 0.10 to 0.30%, Si: 0.50 to 2.00%, Mn: 0.30 to 1.50%, P: 0.035% or less, S : 0.035% or less, Cr: 1.35 to 3.00%, Al: 0.020 to 0.060%, and N: 0.0080 to 0.0250%, the balance being Fe and inevitable A steel for carburized members, characterized by comprising impurities. In the carburized member steel according to claim 4,
The carburized member, wherein the chemical component further contains Mo: 0.80% or less. A carburized member having a carburizing process in which carbon enters the steel member and a diffusion period in which carbon that has entered the steel member is diffused, and a quenching process in which the steel member that has undergone the carburizing process is quenched. A manufacturing method of
The steel member has a chemical composition of mass%, C: 0.10 to 0.30%, Si: 0.50 to 2.00%, Mn: 0.30 to 1.50%, P: 0.00. 035% or less, S: 0.035% or less, Cr: 1.35 to 3.00%, Al: 0.020 to 0.060%, and N: 0.0080 to 0.0250%, The balance consists of Fe and inevitable impurities,
A method for producing a carburized member, wherein a carbon potential in the carburizing period is 1.3% or more. In the manufacturing method of the carburized member of Claim 6,
The said chemical component contains Mo: 0.80% or less further, The manufacturing method of the carburized member characterized by the above-mentioned. In the manufacturing method of the carburized member according to claim 6 or 7,
The steel member has a sliding surface, and the sliding surface after the final process has a surface carbon concentration in the range of 0.7 to 0.9 mass%, and a depth from the outermost surface to 50 μm. A method for producing a carburized member, wherein the troostite area ratio of the structure is 1% or less.

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