Steel with excellent delayed fracture resistance and tensile strength of 1801 MPa class or more, and its shaped article
View Patent ↗Steel and steel shaped articles with an excellent delayed fracture resistance and a tensile strength of the 1600 MPa class or more, containing, by mass %, C: 0.20 to 0.60%, Si: 0.50% or less, Mn: over 0.10% to 3%, Al: 0.005 to 0.1%, Mo: over 3.0% to 10%, and, as needed, one or more of W: 0.01 to 10%, V: 0.05 to 1%, Ti: 0.01 to 1%, Nb: 0.01 to 1%, Cr: 0.10 to 2%, Ni: 0.05 to 1%, Cu: 0.05 to 0.5%, and B: 0.0003 to 0.01%, and a balance of Fe and unavoidable impurities and, further, a method of production comprising shaping the above steel to a desired shape (for example, a bolt shape), quenching it, then tempering it at 500 to 750° C. in temperature range.
1. A steel with an excellent delayed fracture resistance and a tensile strength of the 1801 MPa class or more consisting essentially of, by mass %,
C: 0.20 to 0.60%,
Si: 0.50% or less,
Mn: over 0.10% to 3%,
Al: 0.005 to 0.045%, in an amount effective to deoxidize and form nitrides to make pre-austenite grains finer,
Cu: 0.05 to 0.30%, in an amount effective to improve corrosion resistance,
Mo: over 3.0% to 10%, and
further consisting essentially of a quenched and tempered microstructure, treated by tempering at 600% to 750° C., containing fine Mo carbide precipitates, and a balance of Fe and unavoidable impurities.
2. The steel with an excellent delayed fracture resistance and a tensile strength of the 1801 MPa class or more as set forth in claim 1 , further consisting essentially of, by mass %, one or more of
W: 0.01 to 10%,
V: 0.05 to 1%,
Ti: 0.01 to 1%, and
Nb: 0.01 to 1%.
3. The steel with an excellent delayed fracture resistance and a tensile strength of the 1801 MPa class or more as set forth in claim 1 , further consisting essentially of, by mass %, one or more of
Cr: 0.10 to 2%,
Ni: 0.05 to 0.70%,
Cu: 0.05 to 0.30%, and
B: 0.0003 to 0.01%.
4. A steel, having an excellent delayed fracture resistance and a tensile strength in the 1801 MPa class or more, in accordance with claim 1 , wherein the steel is shaped to a steel shaped article by a process comprising the steps of shaping the steel to a desired shape, then quenching it, and thereafter tempering it in temperature range of 600° to 750° C.
5. A steel, having an excellent delayed fracture resistance and a tensile strength in the 1801 MPa class or more, in accordance with claim 2 , wherein the steel is shaped to a steel shaped article by a process comprising the steps of shaping the steel to a desired shape, then quenching it, and thereafter tempering it in temperature range of 600° to 750° C.
6. A steel, having an excellent delayed fracture resistance and a tensile strength in the 1801 MPa class or more, in accordance with claim 3 , wherein the steel is shaped to a steel shaped article by a process comprising the steps of shaping the steel to a desired shape, then quenching it, and thereafter tempering it in temperature range of 600° to 750° C.
7. A bolt produced from the steel in accordance with claim 1 , having an excellent delayed fracture resistance and a tensile strength in the 1801 MPa class or more.
8. A bolt produced from the steel in accordance with claim 2 , having an excellent delayed fracture resistance and a tensile strength in the 1801 MPa class or more.
9. A bolt produced from the steel in accordance with claim 3 , having an excellent delayed fracture resistance and a tensile strength in the 1801 MPa class or more.