Nitrided or soft nitrided part with excellent wear resistance and pitting resistance, and nitriding and soft nitriding method
A nitrided part and soft nitrided part with excellent wear resistance and pitting resistance and a nitriding method and soft nitriding method are provided, specifically, a nitrided part or soft nitrided part made by a steel material comprising, by mass %, C: 0.05 to 0.3%, Si: 0.05 to 1.5%, Mn: 0.2 to 1.5%, P: 0.025% or less, S: 0.003 to 0.05%, Cr: 0.5 to 2.0%, Al: 0.01 to 0.05%, and N: 0.003 to 0.025% and having a balance of Fe and impurities, wherein, the surface layer comprises a compound layer containing iron, nitrogen, and carbon and a nitrogen diffusion layer positioned below the compound layer, the compound layer comprises an ε single phase, the ε single phase has a thickness of 8 to 30 μm and a Vicker's hardness of 680 HV or more, and the ε single phase has a volume ratio of pores of less than 10%.
1. A nitrided part or soft nitrided part made of a steel material comprising, by mass %,
C: 0.05 to 0.3%,
Si: 0.05 to 1.5%,
Mn: 0.2 to 1.5%,
P: 0.025% or less,
S: 0.003 to 0.05%,
Cr: 0.5 to 2.0%,
Al: 0.01 to 0.05%, and
N: 0.003 to 0.025% and
having a balance of Fe and impurities,
wherein,
the surface layer comprises a compound layer containing iron, nitrogen, and carbon and a nitrogen diffusion layer positioned below the compound layer,
said compound layer consists of an ε single phase,
said ε single phase has a thickness of 8 to 30 μm and a Vicker's hardness of 680HV or more, and
said ε single phase has a volume ratio of pores of less than 10%.
2. The nitrided part or soft nitrided part according to claim 1 , wherein said compound layer includes, by atm %, (C+N)=22% or more.
3. A method of nitriding a part comprising a steel material having the components according to claim 1 , comprising heating the part in a gas atmosphere comprising NH 3 , H 2 , and N 2 to 550 to 620° C. for 1.0 to 10 hours, wherein a nitriding potential K N obtained by the following (formula 1) is 0.3 to 2.0 in minute 0 to 50 in said nitriding time and is 0.70 to 1.50 from minute 50 on:
K N =(NH 3 partial pressure)/[(H 2 partial pressure) 3/2 ] (formula 1).
4. A method of soft nitriding a part comprising a steel material having the components according to claim 1 , comprising heating the part in a gas atmosphere comprising NH 3 , H 2 , N 2 , and CO 2 to 550 to 620° C. for 1.0 to 10 hours, wherein a nitriding potential K N obtained by the following (formula 1) is 0.3 to 2.0 in minute 0 to 50 in said soft nitriding time and is 0.70 to 1.50 from minute 50 on:
K N =(NH 3 partial pressure)/[(H 2 partial pressure) 3/2 ] (formula 1).
5. The nitrided part or soft nitrided part according to claim 1 , further containing, by mass %, one or both of Mo: 0.01 to less than 0.50% and V: 0.01 to less than 0.50%.
6. The nitrided part or soft nitrided part according to claim 5 , further containing, by mass %, one or both of Cu: 0.01 to less than 0.50% and Ni: 0.01 to less than 0.50%.
7. The nitrided part or soft nitrided part according to claim 5 , wherein said compound layer includes, by atm %, (C+N)=22% or more.
8. A method of nitriding a part comprising a steel material having the components according to claim 5 , comprising heating the part in a gas atmosphere comprising NH 3 , H 2 , and N 2 to 550 to 620° C. for 1.0 to 10 hours, wherein a nitriding potential K N obtained by the following (formula 1) is 0.3 to 2.0 in minute 0 to 50 in said nitriding time and is 0.70 to 1.50 from minute 50 on:
K N =(NH 3 partial pressure)/[(H 2 partial pressure) 3/2 ] (formula 1).
9. A method of soft nitriding a part comprising a steel material having the components according to claim 5 , comprising heating the part in a gas atmosphere comprising NH 3 , H 2 , N 2 , and CO 2 to 550 to 620° C. for 1.0 to 10 hours, wherein a nitriding potential K N obtained by the following (formula 1) is 0.3 to 2.0 in minute 0 to 50 in said soft nitriding time and is 0.70 to 1.50 from minute 50 on:
K N =(NH 3 partial pressure)/[(H 2 partial pressure) 3/2 ] (formula 1).
10. The nitrided part or soft nitrided part according to claim 1 , further containing, by mass %, one or both of Cu: 0.01 to less than 0.50% and Ni: 0.01 to less than 0.50%.
11. The nitrided part or soft nitrided part according to claim 10 , wherein said compound layer includes, by atm %, (C+N)=22% or more.
12. A method of nitriding a part comprising a steel material having the components according to claim 10 , comprising heating the part in a gas atmosphere comprising NH 3 , H 2 , and N 2 to 550 to 620° C. for 1.0 to 10 hours, wherein a nitriding potential K n obtained by the following (formula 1) is 0.3 to 2.0 in minute 0 to 50 in said nitriding time and is 0.70 to 1.50 from minute 50 on:
K N =(NH 3 partial pressure)/[(H 2 partial pressure) 3/2 ] (formula 1).
13. A method of soft nitriding a part comprising a steel material having the components according to claim 10 , comprising heating the part in a gas atmosphere comprising NH 3 , H 2 , N 2 , and CO 2 to 550 to 620° C. for 1.0 to 10 hours, wherein a nitriding potential K N obtained by the following (formula 1) is 0.3 to 2.0 in minute 0 to 50 in said soft nitriding time and is 0.70 to 1.50 from minute 50 on:
K N =(NH 3 partial pressure)/[(H 2 partial pressure) 3/2 ] (formula 1).