Steel part having long rolling contact fatigue life and method for producing the same

Abstract

A steel part having a long rolling contact fatigue life and capable of further increasing the life of a bearing under severer using condition than usual conditions. The steel part includes steel having a composition containing 0.7% by mass to 1.1% by mass of C, 0.5% by mass to 2.0% by mass of Si, 0.4% by mass to 2.5% by mass of Mn, 1.6% by mass to 5.0% by mass of Cr, 0.1% by mass to less than 0.5% by mass of Mo, 0.010% by mass to 0.050% by mass of Al, less than 0.0015% by mass of Sb as an impurity, and the balance composed of Fe and inevitable impurities, the steel being hardened and tempered. In the steel structure of a portion from the surface to a depth of 5 mm, residual cementite has a grain diameter of 0.05 to 1.5 μm, prior austenite has a grain diameter of 30 μm or less, and the ratio by volume of the residual austenite is less than 25%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial sectional view showing a toroidal continuously variable transmission.

FIG. 2 is a schematic drawing showing a durability life test rig used in a rolling contact fatigue test.

Claims

1. A steel part having a long rolling contact fatigue life, comprising steel having a composition containing: C: about 0.7% by mass to about 1.1% by mass;Si: about 0.5% by mass to about 2.0% by mass;Mn: about 0.4% by mass to about 2.5% by mass;Cr: about 1.6% by mass to about 5.0% by mass;Mo: about 0.1% by mass to less than about 0.5% by mass;Al: about 0.010% by mass to about 0.050% by mass;less than about 0.0015% by mass of Sb as an impurity, and the balance composed of Fe and inevitable impurities, the steel being hardened and tempered, wherein a portion from the surface to a depth of about 5 mm has a steel structure in which residual cementite has a grain diameter of about 0.05 to about 1.5 μm, prior austenite has a grain diameter of about 30 μm or less, and the ratio by volume of the residual austenite is less than about 25%.

2. The steel part according to claim 1, wherein the steel further comprises at least one selected from the following: Ni: about 0.5% by mass to about 2.0% by mass;V: about 0.05% by mass to about 1.00% by mass; andNb: about 0.005% by mass to about 0.50% by mass.

3. A method for producing a steel part having a long rolling contact fatigue life, comprising: hot-working steel,spheroidizing annealing the steel by maintaining the steel at about 800° C. to about 850° C. for about 5 hours or more,cooling the steel to about 700° C. or less at a rate of about 0.01° C./s or less, andhardening and tempering the steel, wherein the steel has a composition comprising: C: about 0.7% by mass to about 1.1% by mass;Si: about 0.5% by mass to about 2.0% by mass;Mn: about 0.4% by mass to about 2.5% by mass;Cr: about 1.6% by mass to about 5.0% by mass;Mo: about 0.1% by mass to less than about 0.5% by mass;Al: about 0.010% by mass to 0.050% by mass; less than about 0.0015% by mass of Sb as an impurity, and the balance composed of Fe and inevitable impurities.

4. A method for producing a steel part having a long rolling contact fatigue life, comprising: hot-working steel,cooling the steel to about 200° C. at a cooling rate of about 0.5° C./s or less,spheroidizing annealing the steel by maintaining at about 750° C. to about 850° C.,cooling the steel to about 700° C. or less at a rate of about 0.015° C./s or less, andhardening and tempering the steel, wherein the steel has a composition comprising: C: about 0.7% by mass to about 1.1% by mass;Si: about 0.5% by mass to about 2.0% by mass;Mn: about 0.4% by mass to about 2.5% by mass;Cr: about 1.6% by mass to about 5.0% by mass;Mo: about 0.1% by mass to less than about 0.5% by mass;Al: about 0.010% by mass to about 0.050% by mass; less than about 0.0015% by mass of Sb as an impurity, and the balance composed of Fe and inevitable impurities.

5. The method according to claim 3, wherein the steel further comprises at least one selected from the following: Ni: about 0.5% by mass to about 2.0% by mass;V: about 0.05% by mass to about 1.00% by mass; andNb: about 0.005% by mass to about 0.50% by mass.

6. The method according to claim 4, wherein the steel further comprises at least one selected from the following: Ni: about 0.5% by mass to about 2.0% by mass;V: about 0.05% by mass to about 1.00% by mass; andNb: about 0.005% by mass to about 0.50% by mass.