Method of production of steel superior in machinability
AssigneeNippon Steel Corporation
InventorsMasayuki Hashimura, Atsushi Mizuno, Kenichiro Naito, Hiroshi Hagiwara, Kohichi Isobe, Hiroshi Hirata
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Abstract
The present invention provides steel superior in machinability comprised of, by wt %, C: 0.005 to 0.2%, Si: 0.001 to 0.5%, Mn: 0.2 to 3.0%, P: 0.001 to 0.2%, S: 0.03 to 1.0%, T.N: 0.002 to 0.02%, T.O: 0.0005 to 0.035%, and the balance of Fe and unavoidable impurities, said steel satisfying one or both of Mn/S in the steel being 1.2 to 2.8 or an area ratio of pearlite over a grain size of 1 μm in a microstructure of the steel being not more than 5%.
Claims4
A method of production of steel superior in machinability, said method of production of steel characterized by casting molten steel consisting of, by wt %:
- C:
- 0.005 to 0.2%,
- Si:
- 0.001 to 0.5%,
- Mn:
- 0.2 to 3.0%,
- P:
- 0.001 to 0.2%,
- S:
- 0.3 to 1.0%,
- T.N:
- 0.002 to 0.02%,
- T.O:
- 0.0005 to 0.035%,
- optionally, one or more of:
- V:
- 0.05 to 1.0%,
- Nb:
- 0.005 to 0.2%,
- Cr:
- 0.01 to 2.0%,
- Mo:
- 0.05 to 1.0%,
- W:
- 0.5 to 1.0%,
- Ni:
- 0.05 to 2.0%,
- Cu:
- 0.01 to 2.0%,
- Sn:
- 0.005 to 2.0%,
- Zn:
- 0.0005 to 0.5%,
- Ti:
- 0.0005 to 0.1%,
- Ca:
- 0.0002 to 0.005%,
- Zr:
- 0.0005 to 0.1%,
- Mg:
- 0.0003 to 0.005%,
- Bi:
- 0.005 to 0.5%,
- Pb:
- 0.01 to 0.5%, and
- Al:
- ≦0.015%, and
- a balance of Fe and unavoidable impurities,
- then cooling the molten cast steel at a cooling rate of 10 to 100° C./min at the time of cooling from the liquid phase line temperature to the solid phase line temperature in a billet thickness Q part, hot rolling, then cooling from a temperature of at least the A3 point to 550° C. or less at a cooling rate of at least 0.5° C./sec to provide an area ratio of pearlite grains of 1 μm or more of not more than 5%, wherein the balance of the area ratio is ferrite-pearlite or ferrite.
A method of production of steel superior in machinability, said method of production of steel characterized by casting molten steel consisting of, by wt %:
- C:
- 0.005 to 0.2%,
- Mn:
- 0.3 to 3.0%,
- S:
- 0.3 to 1.0%,
- optionally one or more of,
- V:
- 0.05 to 1.0%,
- Nb:
- 0.005 to 0.2%,
- Cr:
- 0.01 to 2.0%,
- Mo:
- 0.05 to 1.0%,
- W:
- 0.5 to 1.0%,
- Ni:
- 0.05 to 2.0%,
- Cu:
- 0.01 to 2.0%,
- Sn:
- 0.005 to 2.0%,
- Zn:
- 0.0005 to 0.5%,
- Ti:
- 0.0005 to 0.1%,
- Ca:
- 0.0002 to 0.005%,
- Zr:
- 0.0005 to 0.1%,
- Mg:
- 0.0003 to 0.005%,
- Bi:
- 0.005 to 0.5%,
- Pb:
- 0.01 to 0.5%, and
- Al:
- ≦0.015%, and
- a balance of Fe and unavoidable impurities,
- then cooling the molten cast steel at a cooling rate of 10 to 100° C./min at the time of cooling from the liquid phase line temperature to the solid phase line temperature in a billet thickness Q part, hot rolling, restricting a finishing temperature of the hot rolling to at least 1,000° C., then cooling from a temperature of at least the A3 point to 550° C. or less at a cooling rate of at least 0.5° C./sec to provide an area ratio of pearlite grains of 1 μm or more of not more than 5%, wherein the balance of the area ratio is ferrite-pearlite or ferrite.
Dependencies are inferred from the claim text.