JP5224969B2 - Rolling parts with long life in a hydrogen environment - Google Patents

Description

  The present invention relates to a bearing and other rolling parts having a long life in a hydrogen environment by heat-treating a part produced from a steel material for the rolling part.

  In recent years, power transmission parts such as automobile parts are required to be reduced in size and weight in order to reduce the environmental load. Furthermore, these parts are also required to have characteristics that can cope with conflicting problems such as harsh use environments and maintenance-free. In particular, in rolling parts such as bearings, hydrogen penetrates into the rolling parts when used in an environment where water infiltrates into the lubricating oil or when hydrogen is generated by decomposition of the lubricating oil. Then, it is known that the rolling parts are separated in a short time. Therefore, extending the life of rolling parts in a hydrogen intrusion environment is an important issue.

  As a conventional technique for this problem, a large amount of Ti or Al is added to disperse and deposit Ti carbide / carbonitride and Al nitride near the surface of the part, thereby extending the rolling life under foreign matter lubrication and clean lubrication. (For example, refer to Patent Document 1). In addition, there is a technique in which Ti carbide and Ti carbonitride are precipitated by solutionizing Ti-added steel at 1150 to 1350 ° C. to extend the rolling life under foreign matter lubrication and clean lubrication (for example, , See Patent Document 2). These techniques are based on the fact that finely precipitated Ti and Al carbides and carbonitrides serve as hydrogen trap sites, and these carbides and carbonitrides reduce the austenite crystal grains and increase the hardness. Improved wear and long life.

  However, in the thing of the patent document 1 of the 1st case mentioned above, based on C: 0.65-1.20% high carbon steel, Ti: 0.26-0.40% or Al: 0.11 It is made of steel containing at least one of ~ 0.40%, and in addition to Ti or Al fine carbides and carbonitrides effective for extending the life, large-scale carbides and carbonitrides are produced in large quantities, Since hot workability deteriorates, it adversely affects the workability when rolling steel and forging parts. Furthermore, there is a problem that the tool life when cutting parts is reduced. The same applies to the second patent document 2. Furthermore, since both of the first patent document 1 and the second patent document 2 have a retained austenite amount of 20% or less, the foreign matter is less compared with the case-hardened steel containing a larger amount of retained austenite. There was a problem that the rolling life when mixed was short.

Japanese Patent No. 3591236 Japanese Patent No. 3728887

  The problem to be solved by the present invention is to provide a rolling part, for example, a bearing part, which achieves a long life in a hydrogen intrusion environment in consideration of the manufacturability of steel and rolling parts.

The means of the present invention for solving the above-mentioned problem is that, in the invention of claim 1, in mass%, C: 0.10 to 0.35%, Si: 0.35 to 1%, Mn: 0.2 -1.6%, P: 0.03% or less, S: 0.03% or less, Cr: 1.5-3%, N: 0.004-0.025%, the balance is Fe and inevitable impurities A rolling part produced from a steel material comprising a former austenite grain size number of 12 or more after carburization or carbonitriding and at least two quenching steps following the treatment, and 0.03 containing Cr A rolling part excellent in life under a hydrogen environment, characterized in that there are at least 15 carbides / carbonitrides of ˜1 μm / 100 μm ² or more.

In invention of Claim 2, in mass%, C: 0.10-0.35%, Si: 0.35-1%, Mn: 0.2-1.6%, P: 0.03% or less, S: 0.03% or less, Cr: 1.5-3%, N: 0.004-0.025%, Nb: 0.01-0.2%, B: 0.0001-0. 005%, Ti: 0.01 to 0.05%, V: 0.01 to 0.5%, Ni: 0.2 to 2%, Mo: 0.05 to 0.3%, one or two The remainder is a rolling part manufactured from a steel material comprising Fe and inevitable impurities, and the former austenite grain size number is 12 after carburizing or carbonitriding and at least two quenching steps following the treatment. It exists, and the carbides or carbonitrides of 0.03~1μm containing Cr is at least 15/100 [mu] m ² or more than It is rolling part having excellent life under hydrogen environment characterized by.

  The reasons for limiting the components of the steel material in the present invention will be described below. In addition,% in each component shows the mass%.

C: 0.10 to 0.35%
C is an element necessary for imparting strength, but if it is less than 0.10%, the core strength after carburizing cannot be ensured, and if it exceeds 0.35%, toughness decreases. At the same time, the hardness of the material increases and the workability deteriorates. Therefore, C is set to 0.10 to 0.35%, preferably 0.14 to 0.27%.

Si: 0.35 to 1%
Si is an element effective for deoxidizing steel, and is an element effective for imparting the necessary hardenability to the steel and increasing the strength. In addition, it is an element effective for rolling life in a poorly lubricated state in order to improve temper softening resistance. However, if it is less than 0.35%, the effect of improving the strength cannot be secured, and if it exceeds 1%, the toughness decreases. Furthermore, the material hardness increases and the workability deteriorates. Therefore, Si is 0.35 to 1%, preferably 0.40 to 0.80%.

Mn: 0.2 to 1.6%
Mn is an element that improves the hardenability of the steel. However, if it is less than 0.2%, it cannot secure the hardenability and deteriorates the productivity. As a result, the workability deteriorates. Therefore, Mn is set to 0.2 to 1.6%.

P: 0.03% or less P is an element that segregates at grain boundaries to lower toughness and fatigue strength, thereby reducing component strength. Therefore, P is set to 0.03% or less.

S: 0.03% or less S, when added, forms MnS effective for machinability, but MnS is an element that deteriorates cold workability and toughness. Therefore, S is set to 0.03% or less.

Cr: 1.5-3%
Cr is an element effective for refinement of prior austenite crystal grains because it gives hardenability and strength improvement to steel, and further produces fine carbide or carbonitride containing Cr during repeated quenching. Further, this fine carbide or carbonitride is extremely effective as a hydrogen trap site. If Cr is less than 1.5%, these effects cannot be sufficiently obtained. If it exceeds 3%, the hardness is increased and the workability is deteriorated. Therefore, Cr is 1.5 to 3%, preferably 1.8 to 2.5%. In addition, by adding 1.5% or more of Cr, it becomes possible to precipitate fine Cr carbide or carbonitride during the second quenching. On the other hand, when the Cr content is less than 1.5%, fine carbides or carbonitrides are not deposited even if repeated quenching is performed. Further, the number of Cr carbides or carbonitrides is required to be 15/100 μm ² or more in order to obtain the prior austenite grain refinement effect and the hydrogen trap effect. The size of Cr carbide or carbonitride is 0.03 to 1 μm. This is because when the size is less than 0.03 μm, the above effect cannot be obtained sufficiently, and when the size exceeds 1 μm, the number of Cr carbides or carbonitrides cannot be secured.

N: 0.004 to 0.025%
N is an effective element for producing Nb and carbonitride, making the grain refinement and detoxifying diffusible hydrogen, but if less than 0.004%, the effect cannot be obtained, and 0.025% If it exceeds, the effect is saturated. Therefore, N is set to 0.004 to 0.025%. However, in the case of adding B, which will be described later, if N is present, BN is generated and the effect of adding B is lost, so the upper limit of N is made 0.015%.

Nb: 0.01 to 0.2%
Nb forms fine Nb carbides and carbonitrides to suppress coarsening of austenite crystal grains during carburization, and further contributes to refinement of prior austenite crystal grains after repeated quenching. Further, Nb carbides and carbonitrides are effective elements for trapping diffusible hydrogen and detoxifying hydrogen. However, if Nb is less than 0.01%, these effects are not sufficient, and Nb is less than 0.1%. If it exceeds 2%, the carbide and carbonitride of Nb are coarsened, the effect of suppressing the coarsening of crystal grains is lowered, and the cost is increased. Therefore, Nb is set to 0.01 to 0.2%.

B: 0.0001 to 0.005%
B is an effective element for ensuring the effect of improving the strength and hardenability, but the effect is not sufficient when B is less than 0.0001%, and the effect is saturated even when it exceeds 0.005%. To do. Therefore, B is set to 0.0001 to 0.005%.

Ti: 0.01 to 0.05%
Ti forms fine Ti carbides and carbonitrides, suppresses grain coarsening during carburizing, and contributes to crystal grain refinement after quenching. In addition, Ti carbide and carbonitride are effective in detoxifying hydrogen by trapping diffusible hydrogen. Furthermore, since Ti forms free N and nitrides in steel, when B is added, Ti is an effective element for ensuring the effect of improving the strength and hardenability of B by preventing BN formation. In order to ensure these effects, Ti is required to be 0.01% or more, but if it exceeds 0.05%, Ti sulfide is generated and MnS effective for machinability is reduced, and a larger size is required. Ti carbides and carbonitrides are produced, resulting in deterioration of workability such as machinability and forgeability. Therefore, Ti is set to 0.01 to 0.05%.

V: 0.01 to 0.5%
V is an element that forms fine V carbides and carbonitrides to trap diffusible hydrogen, and is also effective in detoxifying hydrogen. However, if V is less than 0.01%, these effects are sufficient. If it exceeds 0.5%, the effect is saturated and the cost is increased. Therefore, V is set to 0.01 to 0.5%.

Ni: 0.2-2%
Ni is an element effective for improving the hardenability and toughness of steel. If Ni is less than 0.2%, these effects are not sufficient, and if it exceeds 2%, the hardness of the material is excessively increased and the workability is increased. This will further increase the cost. Therefore, Ni is 0.2 to 2%.

Mo: 0.05-0.30%
Mo is an element effective for improving the hardenability and toughness of steel. If Mo is less than 0.05%, these effects are not sufficient, and if it exceeds 0.30%, the hardness of the material increases too much. The workability is deteriorated and the cost is further increased. Therefore, Mo is set to 0.05 to 0.30%.

  Nb, B, Ti, V, Ni, and Mo can be selectively contained in the above-mentioned other steel components in the range of each of the above components.

One of the reasons for suppressing the short-lived peeling at the time of hydrogen intrusion into the steel material in the present invention is that the fine carbide containing Cr present after the second quenching treatment in the heat treatment of the rolling parts made of steel material is hydrogen. It works as an effective trap site. Further, the Cr carbide acts as a nucleation site for austenite transformation in the temperature raising stage of the second quenching treatment, and the austenite crystal after the second quenching is suppressed in order to suppress the austenite grain growth by the pinning effect. The grains can be refined and controlled to 12 or more by the crystal grain size number. As a result, it is possible to reduce the length of needle-like cracks that occur near the surface of rolling parts due to rolling fatigue in a hydrogen intrusion environment, and to suppress the connection, resulting in a significant increase in life until peeling. It becomes possible to extend to. In the present invention, after the second quenching, the presence of at least 15/100 μm ^{2 of} 0.03-1 μm carbides and carbonitrides containing Cr further ensures the above effect.

  Of course, precipitation of carbides and carbonitrides such as Nb, Ti, and V in steel according to conventional knowledge, regardless of the size and number of carbides and carbonitrides containing Cr described above, is a hydrogen trap or crystal. It is effective for grain refinement, and the effect is further enhanced when these are used in combination.

  The quenching process may be performed twice in total. For example, when the steel is slowly cooled after carburizing, it is necessary to perform the quenching process twice thereafter. In the case of carrying out, it is only necessary to carry out one quenching process thereafter.

  In addition, the quenching treatment is more advantageous in crystal grain refinement three times than two times, but the effect is hardly saturated and improved even if it is carried out four times or more. Therefore, from the economical viewpoint, the total number of times of quenching is sufficient. As a heating means for the quenching treatment, a sufficient effect can be obtained by a method using a heating furnace. However, when induction hardening is used, further refinement of crystal grains is possible, which is more effective.

  By employing the above means, the rolling component according to the present invention, for example, a bearing, in a hydrogen environment in which when the hydrogen enters the steel of the rolling component made of a conventional steel material, the rolling material is separated from the steel material. The part does not cause separation even when hydrogen enters the steel, and thus has a long life, and the steel material in the present invention has good machinability, so the wear amount of the carbide tool is small, The present invention has an unprecedented effect such as excellent workability.

  Embodiments of the present invention will be described below. A steel (hereinafter referred to as “Example Steel”) and a comparative steel (hereinafter referred to as “Comparative Example Steel”) according to an embodiment of the present invention containing each component having the chemical composition shown in Table 1 are vacuumed at 100 kg. It was made into steel by melting in a melting furnace. Next, these steels were hot-forged at 1250 ° C. to produce 32 mm diameter steel bars, held at 925 ° C. for 90 minutes, then air-cooled and subjected to a normalizing treatment. In addition, it has shown that the shaded part of the comparative example steel of Table 1 remove | deviates from the component range of the Example steel of this invention. Furthermore, in description of each component element of Example steel of Table 1, the value of the range which is less than the composition range of the component element of steel in this invention is contained as an unavoidable impurity on actual operation.

  Thereafter, the steel bar was processed into the shape of a thrust type rolling fatigue test piece 1 having a thickness D of 5.8 mm, an outer diameter of φ60 mm, and an inner diameter of φ20 mm shown in FIG.

  The thrust type rolling fatigue test piece 1 of this machined shape is heated to 930 ° C. as shown in FIG. 2 (a), soaking at the same temperature for 0.5 hours, carburizing for 3.0 hours, and 2. After diffusion for 5 hours, lowering to 830 ° C., holding at the same temperature for 0.5 hour, and then carburizing and quenching conditions (OQ) in oil to 60 ° C., the surface carbon concentration is 0.8-0. Carburizing and quenching aiming at 9%, holding at 840 ° C for 0.5 hours under the quenching conditions shown in Fig. 2 (b), then re-quenching in oil to 60 ° C and carburizing and quenching The prepared thrust type rolling fatigue test piece 1 was prepared.

  Further, the thrust type rolling fatigue test piece 1 is heated to 930 ° C. as shown in FIG. 2C, soaking at the same temperature for 0.5 hours, carburizing for 3.0 hours, and spreading for 2.5 hours. The temperature is lowered to 830 ° C., subjected to carbonitriding treatment at the same temperature for 0.5 hour, and then subjected to carbonitriding / quenching conditions of quenching in oil at 60 ° C., aiming for a surface carbon concentration of 0.8 to 0.9% After carbonitriding and quenching, it was further heated to 840 ° C. and held for 0.5 hours, and then re-quenched thrust type rolling fatigue test piece 1 shown in FIG. Got ready.

  Furthermore, after performing carburizing and quenching aiming at a surface carbon concentration of 0.8 to 0.9% under the carburizing and quenching conditions shown in FIG. 2A, thrust type rolling fatigue subjected to re-quenching by induction quenching. A test piece 1 was prepared.

  Furthermore, for comparison, a thrust type rolling fatigue test piece 1 which was not carburized and quenched as shown in FIG. 2A and was not re-quenched as shown in FIG. 2B was prepared.

  Thereafter, all of the prepared thrust type rolling fatigue test pieces 1 are tempered by holding at 180 ° C. for 1.5 hours, polished as a finishing process, and finished into thrust type rolling fatigue test pieces 1. It was.

  In order to simulate the hydrogen intrusion environment, the thrust type rolling fatigue test piece 1 before the rolling test was charged with hydrogen. The hydrogen charging condition was that the thrust type rolling fatigue test piece 1 was held for 48 hours in an ammonium thiocyanate solution having a concentration of 20% at a specific solution of 250 ml / sheet and 50 ° C. Immediately after hydrogen charging, the thrust type rolling fatigue test piece 1 is washed and the corrosion products on the test surface are removed by buffing, and then the thrust type rolling fatigue test is performed at a maximum contact surface pressure of 5.3 GPa. The number of cycles of the rolling fatigue test until peeling from the surface of the test piece was determined by a machine. The number of carbides and carbonitrides containing Cr in the thrust type rolling fatigue test piece 1 was obtained by SEM, photographing 10,000 fields of view for each condition, and analyzing the images.

Hardness in the vicinity of the surface of these thrust type rolling fatigue test pieces 1 and the prior austenite grain size number (GS), the number of 0.03-1 μm carbides and carbonitrides containing Cr, and rolling fatigue Tool: Carbide JIS P20, Cutting edge R: 0.4 mm, Peripheral speed: 150 m / min, Cutting depth: 0 after L ₅₀ life by test and after 10 minutes of cutting in the normal state before carburizing or carbonitriding Table 2 shows the amount of wear of the turning tool under the conditions of 0.5 mm, feed: 0.25 mm / rev, and cutting oil: none. In Table 2, the shaded portions are those of carbides and carbonitrides containing Cr having a size of 0.03 to 1 μm in the prior austenite grain size number (GS) of less than # 12. The number of pieces is less than 15 pieces / 100 μm ² , and the rolling type fatigue life L ₅₀ of the hydrogen-charged thrust type rolling fatigue test piece 1 is less than 15 × 10 ⁶ cycles, and the wear amount of the carbide tool exceeds 0.10 mm for 10 minutes. is there.

Therefore, from Table 2, No. of the example steel. A-No. I has a long life and machinability because the L ₅₀ life is more than 15 × 10 ⁶ cycles and the wear amount of carbide tool is 0.10 mm or less. doing. In addition, even if the composition range of the example steel of the present invention has a component, No. B and No. The number of times of quenching in C is one when the austenite grain size number G.I. S. Is less than No. 12, the number of carbides and carbonitrides containing Cr is less than 15/100 μm ² , and the L ₅₀ life is less than 15 × 10 ⁶ cycles. The effect of the lifetime has not been obtained, and it was shown in the remarks that it is outside the scope of the present invention. Moreover, No. of Example steel. A and No. In E, the carbonitriding and quenching performed for the first time gave an L ₅₀ life equal to or greater than the other carbonitriding and quenching performed for the first time. No. of Example Steel As shown by C, even when induction quenching was performed as the second quenching, an L ₅₀ life equal to or higher than that of normal quenching was obtained.

Comparative Example Steel No. J-No. For S, no. N and No. Except for O, the L ₅₀ life reached peeling at a low cycle of less than 15 × 10 ⁶ cycles. Those that have come off are either the prior austenite grain size number less than 12 or the number of carbides / carbonitrides containing Cr of 0.03 to 1 μm is less than 15/100 μm ^2. However, it is described as not subject to the present invention in the remarks. Furthermore, No. of comparative example steel. N and No. O is excellent in L ₅₀ life, but has a large amount of carbide tool wear, that is, the machinability is poor, which causes problems in the part machining process. .

The shape of a thrust type | mold rolling fatigue test piece is shown, (a) is a front view, (b) is a side view. The heat processing pattern is shown, (a) is carburizing + quenching, (b) is re-quenching, and (c) is carbonitriding + quenching.

Explanation of symbols

  1 Thrust-type rolling fatigue test piece

Claims (2)

In mass%, C: 0.10 to 0.35%, Si: 0.35 to 1%, Mn: 0.2 to 1.6%, P: 0.03% or less, S: 0.03% or less , Cr: 1.5 to 3%, N: 0.004 to 0.025%, the balance is a rolling part manufactured from a steel material composed of Fe and inevitable impurities, carburizing or carbonitriding, and the treatment The prior austenite grain size number after at least two quenching steps subsequent to is 12 or more, and 0.03 to 1 μm carbide or carbonitride containing Cr is present at least 15/100 μm ² or more. Rolling parts with excellent service life in a hydrogen environment. In mass%, C: 0.10 to 0.35%, Si: 0.35 to 1%, Mn: 0.2 to 1.6%, P: 0.03% or less, S: 0.03% or less Cr: 1.5 to 3%, N: 0.004 to 0.025%, Nb: 0.01 to 0.2%, B: 0.0001 to 0.005%, Ti: 0. 01-0.05%, V: 0.01-0.5%, Ni: 0.2-2%, Mo: 0.05-0.3% 1 type or 2 types or more are included, The remainder is It is a rolling part manufactured from a steel material consisting of Fe and inevitable impurities, and the former austenite grain size number after carburizing or carbonitriding and at least two quenching steps following the treatment is 12 or more, and contains Cr water carbide or carbonitride of 0.03~1μm which is characterized by the presence of at least 15/100 [mu] m ² or more Rolling parts having excellent life under environment.

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