초록 ▼

Various inexpensive rolling elements for use under high interface pressure such as induction hardened gears are provided, which have improved seizure resistance at tooth flanks and a temper hardness of HRC 50 or more at 300 ° C. To this end, a rolling element is made from a steel material which

Various inexpensive rolling elements for use under high interface pressure such as induction hardened gears are provided, which have improved seizure resistance at tooth flanks and a temper hardness of HRC 50 or more at 300 ° C. To this end, a rolling element is made from a steel material which contains at least 0.5 to 1.5 wt % carbon and 0.2 to 2.0 wt % one or more alloy elements selected from V, Ti, Zr, Nb, Ta and Hf; and in which 0.4 to 4.0% by volume one or more compounds selected from the carbides, nitrides and carbonitrides of the above alloy elements and having an average particle diameter of 0.2 to 5 μm are dispersed. In such a rolling element, the soluble carbon concentration of a martensite parent phase of a rolling contact surface layer is adjusted to 0.3 to 0.8 wt %, the martensite parent phase having been subjected to induction hardening and low temperature tempering, and one or more of the above carbides, nitrides and carbonitrides are dispersed in an amount of 0.4 to 4.0% by volume within the martensite parent phase.

대표청구항 ▼

What is claimed is: 1. A rolling element which is made from a steel, the steel comprising 0.5 to 1.5 wt % carbon; 0.3 to 1.5 wt % Cr; and a total amount of 0.2 to 2.0 wt % of one or more alloy elements selected from the group consisting of V, Ti, Zr, Nb, Ta and Hf; wherein 0.4 to 4.0% by volume of

What is claimed is: 1. A rolling element which is made from a steel, the steel comprising 0.5 to 1.5 wt % carbon; 0.3 to 1.5 wt % Cr; and a total amount of 0.2 to 2.0 wt % of one or more alloy elements selected from the group consisting of V, Ti, Zr, Nb, Ta and Hf; wherein 0.4 to 4.0% by volume of carbides of said alloy elements having an average particle diameter of 0.2 to 5 μm are dispersed, wherein the rolling element has a rolling contact surface layer, the rolling contact surface layer has a quench hardened layer which has been subjected to induction hardening, the quench hardened layer has a martensite parent phase and the martensite parent phase has a soluble carbon concentration of 0.3 to 0.8 wt %, and said carbides in an amount of 0.4 to 4.0% by volume and cementite in an amount of 2 to 15% by volume are dispersed within the martensite parent phase, wherein the 2 to 15% by volume of the cementite contains 2.5 to 10 wt % Cr as an average composition. 2. The rolling element according to claim 1, wherein prior austenite grains in the quench hardened layer are refined to have a particle size equal to or greater than the level of ASTM No. 10 and wherein the amount of retained austenite is adjusted to 10 to 50% by volume. 3. The rolling element according to claim 1, wherein said steel further comprises 0.5 to 3.0 wt % Si, 0.20 to 1.5 wt % Al or 0.5 to 3.0 wt % (Si+Al), and one or more elements selected from the group consisting of Mn, Ni, Mo, Cu, W, B, and Ca, unavoidable impurity elements selected from the group consisting of P, S, N and O , and a balance of Fe. 4. The rolling element according to claim 3, wherein said steel further comprises 0.3 to 1.5 wt % Ni and 0.2 wt % or more Al. 5. The rolling element according to claim 4, wherein cementite and retained austenite are dispersed in the quench hardened layer. 6. The rolling element according to claim 3, wherein said steel further comprises one or more alloy elements selected from the group consisting of 0.2 to 1.5 wt % Mn; 0.5 wt % or less Mo; and 0.5 wt % W or less. 7. The rolling element according to claim 6, wherein cementite and retained austenite are dispersed in the quench hardened layer. 8. The rolling element according to claim 1, wherein the quench hardened rolling contact surface layer is formed by induction hardening of the steel such that rapid heating of the steel to a quenching temperature of 900 to 1050° C. higher than the Al temperature is carried out within 10 seconds from room temperature, or from a temperature equal to or lower than the Al temperature when the steel is preheated, and then rapid cooling is carried out. 9. The rolling element according to claim 8, which is a gear used under a slipping condition, wherein the quench hardened layer is formed along the contour of teeth of said gear by induction hardening. 10. The rolling element according to claim 9, which is a gear used under a slipping condition and wherein a compressive residual stress of at least 50 kgf/mm2 or more is generated at the roots of the teeth. 11. The rolling element according to claim 10, wherein the compressive residual stress is generated by shot peening. 12. A method of producing a rolling element from a steel, the steel comprising 0.5 to 1.5 wt % carbon; 0.3 to 1.5 wt % Cr; and a total amount of 0.2 to 2.0 wt % of one or more alloy elements selected from the group consisting of V, Ti, Zr, Nb, Ta and Hf, wherein 0.4 to 4.0% by volume of carbides of said alloy elements, and having an average particle diameter of 0.2 to 5 μm and 7.5 to 20% by volume of cementite are dispersed, the method comprising the following steps (a) to (c): (a) subjecting the steel to a Cr concentration treatment such that an average Cr concentration of the cementite dispersed in the steel is 2.5 to 10 wt %; (b) spheroidizing the cementite by heating the steel; and (c) subjecting said steel to induction hardening such that the rolling element has a rolling contact surface layer, the rolling contact surface layer has a quench hardened layer, the quench hardened layer has a martensite parent phase, wherein in the martensite parent phase, a soluble carbon concentration is adjusted to 0.3 to 0.8 wt %, 2 to 15% by volume of granular cementite having an average particle diameter of 1.5 μm or less is dispersed, and 10 to 50% by volume of retained austenite is formed. 13. The method of producing a rolling element according to claim 12, wherein said induction hardening of the rolling contact surface layer of the steel is performed such that rapid heating of the steel to a quenching temperature of 900 to 1050° C. higher than the Al temperature is carried out within 10 seconds from room temperature, or from a temperature equal to or lower than the Al temperature when the steel is preheated, and then rapid cooling is carried out. 14. The method of producing a rolling element according to claim 13, the rolling element being a gear used under a slipping condition, wherein said induction hardening is performed such that an induction-hardened-contour gear having a quench hardened layer formed along the contour of teeth of the gear is produced with a speed of heating at least from the A1 temperature to said quenching temperature being 150° C./sec or more. 15. The method of producing a rolling element according to claim 12, wherein a compressive residual stress at the rolling contact surface layer is generated by shot peening.