Steel, steel sheet having excellent workability and method of producing the same by electric furnace-vacuum degassing process

A mild steel having excellent workability, produced by an electric furnace-vacuum degassing process, said steel having a composition which comprises:

• C:
• 0.0050 wt % or less
• Si:
• 0.2 wt % or less
• P:
• 0.10 wt % or less
• Al:
• 0.10 wt % or less
• O:
• 0.010 wt % or less
• Mn:
• 0.5 wt % or less
• S:
• 0.020 wt % or less
• N:
• from 0.0040 to 0.0090 wt %
• Ti:
• from 0.014 to 0.10 wt %,
• wherein the contents of Ti, N, S and Mn meet the condition of:
• Ti/48-(N/14+S*/32).gtoreq.C/12
• where
• S*=32(S/32-0.3Mn/55) said composition further containing:
• Cu:
• 0.02 to 0.96 wt %
• Ni:
• 0.02 to 0.88 wt %,
• wherein the contents of Cu and Ni meet the condition of:
• 0.0015.ltoreq.Cu/64+Ni/59.ltoreq.0.0150.
• 9.

In a method of producing steel having excellent workability, the steps which comprise:

• performing electric furnace degassing using as the main ferrous material iron scrap alone or iron scrap with addition of molten iron, the steps which comprises:
• adjusting the steel composition in said electric furnace to a composition comprising about:
• C:
• from 0.03 to 0.10 wt %
• Cu:
• 0.02 to 1.5 wt %
• Ni:
• 0.02 to 2.0 wt %
• S:
• 0.020 wt % or less
• N:
• from 0.0040 to 0.0150 wt %
• discharging said molten steel from said electric furnace at a temperature not lower than about 1580.degree. C.;
• and vacuum degassing said molten steel while adding necessary alloy components to form a steel composition which comprises about:
• C:
• 0.0050 wt % or less
• Si:
• 1.5 wt % or less
• Mn:
• 1.5 wt % or less
• P:
• 0.10 wt % or less
• Al:
• 0.10 wt % or less
• S:
• 0.020 wt % or less
• O:
• 0.01 wt % or less
• Cu:
• 0.02 to 1.5 wt %
• Ni:
• 0.02 to 2.0 wt %
• Ti and/or Nb:
• from 0.001 to 0.10 wt % and
• N:
• from 0.0040 to 0.0090 wt %, and
• recovering the steel so produced.

In a method of producing steel having excellent workability, the steps which comprise:

• performing electric furnace degassing using as the main ferrous material iron scrap alone or iron scrap with addition of molten iron, the steps which comprise:
• adjusting the steel composition in said electric furnace to comprise about:
• C:
• from 0.03 to 0.10 wt %
• Cu:
• 0.02 to 1.5 wt %
• Ni:
• 0.02 to 2.0 wt %
• S:
• 0.020 wt % or less
• N:
• from 0.0040 to 0.0150 wt %
• discharging said molten steel from said furnace at a temperature not lower than about 1580.degree. C.;
• degassing said molten steel in a vacuum while adding alloy components in amounts to obtain a steel composition which comprises about:
• C:
• 0.0050 wt % or less
• Si:
• 1.5 wt % or less
• Mn:
• 1.5 wt % or less
• P:
• 0.10 wt % or less
• Al:
• 0.10 wt % or less
• O:
• 0.010 wt % or less
• S:
• 0.020 wt % or less
• N:
• from 0.0040 to 0.0090 wt %
• Ti:
• from 0.014 to 0.10 wt %
• Cu:
• 0.02 to 0.96 wt %
• Ni:
• 0.02 to 0.88 wt %
• wherein the adjusted composition also meets the conditions of about:
• Ti/48-(N/14+S*/32).gtoreq.C/12
• where
• S*=32(S/32-0.3Mn/55);
• and 0.0015.ltoreq.Cu/64+Ni/59.ltoreq.0.0150;
• continuously casting said molten steel of said adjusted composition into a slab;
• heating said slab to a temperature of from about 900.degree. to about 1300.degree. C.;
• subjecting said heated slab to hot rolling conducted at a total rolling reduction of about 70% or higher and to a rolling finish temperature of about 600.degree. C. or higher;
• taking up said hot-rolled steel at a temperature of about 800.degree. C. or lower;
• subjecting said hot-rolled steel to cold rolling conducted at a rolling reduction of about 50% or higher;
• and
• subjecting said cold-rolled steel to annealing conducted at a temperature of about 600.degree. C. or higher for a period of about 5 seconds or longer.

In a method of producing steel having excellent workability, the steps which comprise:

• performing electric furnace degassing using as the main ferrous material iron scrap alone or iron scrap with addition of molten iron, the steps which comprise:
• adjusting the steel composition in said electric furnace to comprise about:
• C:
• from 0.03 to 0.10 wt %
• Cu:
• 0.02 to 1.5 wt %
• Ni:
• 0.02 to 2.0 wt %
• N:
• from 0.0040 to 0.0150 wt %
• discharging said molten steel from said electric furnace at a temperature not lower than about 1550.degree. C.;
• said method further comprising effecting ladle refining of said molten steel discharged from said electric furnace in a manner to adjust the S content in said molten steel to about S:
• 0.020 wt % before subjecting said molten steel to said degassing;
• and vacuum degassing said molten steel while adding necessary alloy components to form a steel composition which comprises about:
• C:
• 0.0050 wt % or less
• Si:
• 1.5 wt % or less
• Mn:
• 1.5 wt % or less
• P:
• 0.10 wt % or less
• Al:
• 0.10 wt % or less
• S:
• 0.020 wt % or less
• O:
• 0.01 wt % or less
• Cu:
• 0.02 to 1.5 wt %
• Ni:
• 0.02 to 2.0 wt %
• Ti and/or Nb:
• from 0.001 to 0.10 wt % and
• N:
• from 0.0040 to 0.0090 wt %, and
• recovering the steel so produced.

In a method of producing steel having excellent workability, the steps which comprise:

• performing electric furnace degassing using as the main ferrous material iron scrap alone or iron scrap with addition of molten iron, the steps which comprise:
• adjusting the steel composition in said electric furnace to comprise about:
• C:
• from 0.03 to 0.10 wt %
• Cu:
• 0.02 to 1.5 wt %
• Ni:
• 0.02 to 2.0 wt %
• N:
• from 0.0040 to 0.0150 wt %
• discharging said molten steel from said electric furnace at a temperature not lower than about 1550.degree. C.;
• said method further comprising effecting ladle refining of said molten steel discharged from said electric furnace in a manner to adjust the S content in said molten steel to about S:
• 0.020 wt % before subjecting said molten steel to said degassing;
• and vacuum degassing said molten steel while adding necessary alloy components to form a steel composition which comprises about:
• C:
• 0.0050 wt % or less
• Si:
• 1.5 wt % or less
• Mn:
• 1.5 wt % or less
• P:
• 0.10 wt % or less
• Al:
• 0.10 wt % or less
• O:
• 0.01 wt % or less
• S:
• 0.020 wt % or less
• N:
• from 0.0040 to 0.0090 wt %
• Ti:
• from 0.014 to 0.10 wt %
• Cu:
• 0.02 to 0.96 wt %
• Ni:
• 0.02 to 0.88 wt %
• wherein the adjusted composition also meets the conditions of about:
• Ti/48-(N/14+S*/32).gtoreq.C/12
• where
• S*=32(S/32-0.3Mn/55);
• and 0.0015.ltoreq.Cu/64+Ni/59.ltoreq.0.0150;
• continuously casting said molten steel of said adjusted composition into a slab;
• heating said slab to a temperature of from about 900.degree. to about 1300.degree. C.;
• subjecting said heated slab to hot rolling conducted at a total rolling reduction of about 70% or higher and to a rolling finish temperature of about 600.degree. C. or higher;
• taking up said hot-rolled steel at a temperature of about 800.degree. C. or lower;
• subjecting said hot-rolled steel to cold rolling conducted at a rolling reduction of about 50% or higher;
• and
• subjecting said cold-rolled steel to annealing conducted at a temperature of about 600.degree. C. or higher for a period of about 5 seconds or longer.