Rolling member and producing method thereof

1. A rolling member comprising:

a first quench hardened layer which is formed on a surface layer of the rolling member and has a parent phase taking the form of martensite phase containing carbon of 0.35 to 0.8 wt %; and

a second quench hardened layer which is formed at a deeper layer under said first quench hardened layer and has a parent phase containing at least either one of martensite phase or bainite phase containing carbon of 0.07 to 0.3 wt % and has a cementite dispersed therein a content of 2 to 20% by volume,

wherein said rolling member is made of a steel containing carbon of 0.4 to 1.5 wt % and Cr of 2 wt % or less, and

wherein said steel contains one or more elements of Mn of 0.1 to 2 wt %, Si+Al of 0.05 to 1.5 wt %, Mo of 0.7 wt % or less, W of 1.4 wt % or less, V of 2 wt % or less, Al of 1 wt % or less, Ni of 3 wt % or less, B of 0.01 wt % or less, Ti+Nb+Zr of 1 wt % or less and S of 1.0 wt % or less.

2. A rolling member according to claim 1 , further comprising an unquenched portion which is formed at a deeper portion under said second quench hardened layer and has a structure in which cementite is dispersed in ferrite.

3. A rolling member according to claim 1 , further comprising an intermediate layer between said first and second quench hardened layers, in which said intermediate layer has a hardness value that is between a hardness value of said first quench hardened layer and a hardness value of said second quench hardened layer.

4. A rolling member according to claim 1 ,

wherein said first and second quench hardened layers are formed by an induction hardening process.

5. A rolling member according to claim 1 ,

Wherein said steel contains Cr of 0.3 to 2 wt %, and said cementite dispersed in said steel contains Cr of 3-12 wt %.

6. A rolling member according to claim 1 ,

wherein said rolling member is made of a steel containing carbon of 0.5 to 1.5 wt % and Cr of 0.5 to 2 wt %,

said first quench hardened layer contains cementite dispersed therein in a content of 2 to 17% by volume, and

said second quench hardened layer contains cementite dispersed therein in a content of 4 to 20% by volume.

7. A rolling member according to claim 1 ,

wherein said first quench hardened layer contains retained austenite dispersed therein in a content of 10 to 50% by volume.

8. A rolling member according to claim 1 ,

wherein said first quench hardened layer contains one or more compounds dispersed therein selected from the group consisting of V 4 C 3 , TiC, NbC and ZrC.

9. A rolling member according to claim 1 ,

Wherein said steel contains Si+Al of 0.5 to 1.5wt % and further one or more elements of Mn of 0.1 to 2 wt %, Ni of 3 wt % or less, Mo of 9.05 to 0.7 wt %, V of 0.2 to 1 wt %, and Ti+Nb+Zr of 0.1 to 0.5 wt %.

10. A rolling member according to claim 1 ,

wherein said rolling member is a gear having teeth and a circular pitch, said rolling member being formed with said first quench hardened layer having a depth within 0.15 to 0.6 times a module of said gear on the circular pitch and said second quench hardened layer having Vickers hardness of Hv260 to 500 at a deeper portion under said first quench hardened layer or at a center internal portion of the teeth.

11. A rolling member according to claim 1 ,

wherein said rolling member is a bearing or a cam shaft.

12. A rolling member according to claim 1 ,

wherein said first quench hardened layer or both of said first and second quench hardened layers are tempered at 100 to 350° C.

13. A rolling member according to claim 1 ,

wherein said first quench hardened layer is worked at a surface layer thereof so as to provide compressive retained stress of 50 kgf/mm 2 or more thereto.