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EP-4239085-B1 - ROLLING MEMBER AND ROLLING BEARING

EP4239085B1EP 4239085 B1EP4239085 B1EP 4239085B1EP-4239085-B1

Inventors

  • SATO, Miyu
  • MIWA, NORIAKI
  • YAMADA, MASAHIRO
  • OHKI, CHIKARA

Dates

Publication Date
20260506
Application Date
20211028

Claims (4)

  1. A rolling member formed of quenched steel having a contact surface, the rolling member including a superficial part (50) in a region up to a depth of 20 µm from the contact surface, the steel containing greater than or equal to 0.70 mass% and less than or equal to 1.10 mass% of carbon, greater than or equal to 0.15 mass% and less than or equal to 0.35 mass% of silicon, greater than or equal to 0.30 mass% and less than or equal to 0.60 mass% of manganese, greater than or equal to 1.30 mass% and less than or equal to 1.60 mass% of chromium, greater than or equal to 0.01 mass% and less than or equal to 0.50 mass% of molybdenum, and greater than or equal to 0.01 mass% and less than or equal to 0.50 mass% of vanadium, and the remainder of iron and inevitable impurities, a content of nitrogen in the superficial part (50) being greater than or equal to 0.2 mass% and less than or equal to 0.8 mass%, wherein in a sectional view that is orthogonal to the contact surface, a total of greater than or equal to 60 precipitates having a grain size of less than or equal to 0.50 µm exist per 100 µm 2 in the superficial part, and a total of area fractions of precipitates in the superficial part is greater than or equal to 1% and less than or equal to 10%, a volume fraction of retained austenite quantity at a position of 50 µm deep from the contact surface is greater than or equal to 20% and less than or equal to 40%, and hardness at a position of 50 µm deep from the contact surface is greater than or equal to 653 Hv and less than or equal to 800 Hv, wherein the hardness is measured as defined in JIS Z 2244:2009.
  2. The rolling member according to claim 1, wherein the steel contains greater than or equal to 0.90 mass% and less than or equal to 1.10 mass% of carbon, greater than or equal to 0.20 mass% and less than or equal to 0.30 mass% of silicon, greater than or equal to 0.40 mass% and less than or equal to 0.50 mass% of manganese, greater than or equal to 1.40 mass% and less than or equal to 1.60 mass% of chromium, greater than or equal to 0.20 mass% and less than or equal to 0.30 mass% of molybdenum, and greater than or equal to 0.20 mass% and less than or equal to 0.30 mass% of vanadium, and the remainder of iron and inevitable impurities, and the content of nitrogen in the superficial part (50) is greater than or equal to 0.3 mass% and less than or equal to 0.5 mass%.
  3. The rolling member according to claim 1 or claim 2, wherein in a sectional view that is orthogonal to the contact surface, a total of greater than or equal to 80 precipitates having a grain size of less than or equal to 0.50 µm exist per 100 µm 2 in the superficial part, and a total of area fractions of precipitates in the superficial part is greater than or equal to 2% and less than or equal to 7%, a volume fraction of retained austenite quantity at a position of 50 µm deep from the contact surface is greater than or equal to 25% and less than or equal to 35%.
  4. A rolling bearing (100) comprising: a raceway member (10, 20); and a rolling element (30) arranged in contact with the raceway member, at least either the raceway member (10, 20) or the rolling element (30) being the rolling member according to any one of claim 1 to claim 3.

Description

TECHNICAL FIELD The present invention relates to a rolling member and a rolling bearing. BACKGROUND ART Conventionally, rolling members such as a raceway ring and a rolling element of a rolling bearing have been formed of high-carbon chromium bearing steel (SUJ2, SUJ3 and so on) defined in JIS standard (JIS G 4805:2008). Also, in order to improve the durability in the surface of rolling members, superficial parts have been undergone a nitriding treatment. In recent years, use environments of rolling bearings are becoming more severe. Therefore, it is sometimes the case that sufficient durability is not obtained only by forming a rolling member of a common steel material such as SUJ2, SUJ3 or the like, and subjecting the superficial part to a nitriding treatment. In rolling bearings described in PTL 1 (JP 38 73 741 B2, Japanese Patent No. 3873741) and PTL 2 (JP 53 72 316 B2, Japanese Patent No. 5372316), an attempt is made to improve the abrasion resistance and the seizure resistance under the environment accompanying a sliding contact, and under the environment where lubricating oil is exhausted by forming a rolling member of a steel material to which a large quantity of silicon (Si) or manganese (Mn) is added. In a rolling bearing described in PTL 3 (JP 2000 282 178 A, Japanese Patent Laying-Open No. 2000-282178), penetration of hydrogen into steel is prevented by adding a large quantity of chromium (Cr) to the steel material for use in the rolling member and forming a passive state film on the surface. Moreover, PTL 4 (JP 2000 213 549 A) discloses that the material and surface hardness of a bearing ring after hardening and high-temperature tempering treatment are made stabilized under high temperature and excellent in a rolling fatigue characteristic and abrasion resistance, to ensure a long durable life even in a rotating shaft supporting device used under a high load and temperature environment, by forming the bearing ring of a pair of ball bearing, for supporting a rotor rotating shaft, of steel material containing a Si of 0.3% or more and 3.0% or less in mass % as an alloy element, and containing singly or compositely Ni of 0.1% or more and 3.0% or less, V of 0.05% or more and 1.0% or less, and Mo of 0.05% or more and less 0.25%, to make the surface hardness of the bearing ring Rockwell hardness HRC 58 or more. PTL 5 (WO 2013/156 091 A1) describes a steel alloy comprising: from 0.8 to 1.2 wt% carbon from 0.1 to 0.8 wt% manganese from 0.5 to 2.5 wt% chromium from 0.3 to 0.8 wt% vanadium optionally one or more of from 0 to 1.0 wt% silicon from 0 to 0.3 wt% molybdenum from 0 to 0.5 wt% copper from 0 to 3.5 wt% nickel from 0 to 0.1 wt% aluminium from 0 to 0.05 wt% phosphorus from 0 to 0.05 wt% sulphur from 0 to 0.1 wt% titanium from 0 to 0.1 wt% niobium from 0 to 0.1 wt% tantalum from 0 to 0.1 wt% tungsten from 0 to 0.1 wt% boron from 0 to 0.1 wt% nitrogen from 0 to 0.1 wt% oxygen from 0 to 0.1 wt% calcium from 0 to 0.1 wt% cobalt and the balance iron, together with unavoidable impurities. From PTL 6 (JP 2014 152 378 A) bearing components (an outer ring, an inner ring and a ball) are known, comprising: a steel containing 0.95 mass% or more and 1.10 mass% or less carbon; 0.35 mass% or less silicon; 0.50 mass% or less manganese; 1.30 mass% or more and 2.00 mass% or less chromium; and residual impurities, and a carbonitriding layer is formed on a surface layer part including traveling surfaces (an outer ring traveling surface, an inner ring traveling surface) or a rolling surface. The area ratio of a deposit in a region where the carbonitriding layer is not formed is 7% or less. The amount of retained austenite in the surface layer part is 20 vol% or more and 35 vol% or less, and the average amount of retained austenite in the whole bearing components (the outer ring, the inner ring and the ball) is 18 vol% or less. CITATION LIST PATENT LITERATURE PTL 1: JP 38 73 741 B2 (Patent No. 3873741)PTL 2: JP 53 72 316 B2 (Patent No. 5372316)PTL 3: JP 2000 282 178 A (Japanese Patent Laying-Open No. 2000-282178)PTL 4: JP 2000 213 549 APTL 5: WO 2013/156 091 A1PTL 6: JP 2014 152 378 A SUMMARY OF INVENTION TECHNICAL PROBLEM However, in consideration of recent demands for improvement in durability of rolling members, durability of rolling members can be insufficient depending on the application in rolling bearings described in PTL 1 to PTL 6. For example, in the rolling bearing according to PTL 3, carbide in steel can become coarse by addition of chromium to the steel material. The coarse carbide can become a stress concentration source, and can become an origin of early flaking. While the passive state film has the effect of preventing dispersion of hydrogen into steel, it also has the effect of promoting adsorption of hydrogen. When the rolling bearing according to PTL 3 is used intermittently, hydrogen is dissipated at the time of stoppage, so that delaying the penetration of hydrogen into steel by a passive state film