Hot rolled steel sheets and method of producing the same

A hot rolled steel sheet comprising C:

• 0.001-0.20 wt %, Si:
• 0.01-0.50 wt %, Mn:
• 0.05-2.0 wt %, P:
• not more than 0.05 wt %, S:
• not more than 0.05 wt %, sol.Al:
• 0.01-0.10 wt %, N:
• not more than 0.020 wt %, one or two of Ti:
• not more than 0.10 wt % and Nb:
• not more than 0.10 wt % and the balance being Fe and inevitable impurities, and having an average surface scale thickness of not more than 4 .mu.m and a surface roughness (Ra) of not more than 0.8 .mu.m developed after rough rolling at a completing temperature of (Ar.sub.3 point+100.degree. C.)-(Ar.sub.3 point+50.degree. C.) and super-high pressure descaling at a liquid quantity density of not less than 0.002 liter/cm.sup.2 under a jetting pressure of not less than 25 kgf/cm.sup.2 and then subsequent finish rolling.

A hot rolled steel sheet comprising C:

• 0.001-0.20 wt %, Si:
• 0.01-0.50 wt %, Mn:
• 0.05-2.0 wt %, P:
• not more than 0.05 wt %, S:
• not more than 0.05 wt %, sol.Al:
• 0.01-0.10 wt %, N:
• not more than 0.020 wt %, B:
• not more than 0.0100 wt % and the balance being Fe and inevitable impurities, and having an average surface scale thickness of not more than 4 .mu.m and a surface roughness (Ra) of not more than 0.8 .mu.m developed after rough rolling at a completing temperature of (Ar.sub.3 point+100.degree. C.)-(Ar.sub.3 point+50.degree. C.) and super-high pressure descaling at a liquid quantity density of not less than 0.002 liter/cm.sup.2 under a jetting pressure of not less than 25 kgf/cm.sup.2 and then subsequent finish rolling.

A hot rolled steel sheet comprising C:

• 0.001-0.20 wt %, Si:
• 0.01-0.50 wt %, Mn:
• 0.05-2.0 wt %, P:
• not more than 0.05 wt %, S:
• not more than 0.05 wt %, sol.Al:
• 0.01-0.10 wt %, N:
• not more than 0.020 wt %, one or two of Ti:
• not more than 0.10 wt % and Nb:
• not more than 0.10 wt %, B:
• not more than 0.0100 wt % and the balance being Fe and inevitable impurities, and having an average surface scale thickness of not more than 4 .mu.m and a surface roughness (Ra) of not more than 0.8 .mu.m developed after rough rolling at a completing temperature of (Ar.sub.3 point+100.degree. C.)-(Ar.sub.3 point+50.degree. C.) and super-high pressure descaling at a liquid quantity density of not less than 0.002 liter/cm.sup.2 under a jetting pressure of not less than 25 kgf/cm.sup.2 and then subsequent finish rolling.

A method of producing a hot rolled steel sheet, which comprises heating a starting material of steel comprising C:

• 0.001-0.20 wt %, Si:
• 0.01-0.50 wt %, Mn:
• 0.05-2.0 wt %, P:
• not more than 0.05 wt %, S:
• not more than 0.05 wt %, sol.Al:
• 0.01-0.10 wt %, N:
• not more than 0.020 wt % and the balance being Fe and inevitable impurities to not lower than Ac.sub.3 point, completing rough rolling within a temperature range of (Ar.sub.3 point+100.degree. C.).about.(Ar.sub.3 point+50.degree. C.), conducting super-high pressure descaling under conditions satisfying a jetting pressure of not less than 25 kgf/cm.sup.2 and a liquid quantity density of not less than 0.002 liter/cm.sup.2, starting finish rolling at a rolling reduction of not less than 80% above Ar.sub.3 point of rolling complete temperature within 5 seconds and coiling up below 700.degree. C.

A method of producing a hot rolled steel sheet, which comprises heating a starting material of steel comprising C:

• 0.001-0.20 wt %, Si:
• 0.01-0.50 wt %, Mn:
• 0.05-2.0 wt %, P:
• not more than 0.05 wt %, S:
• not more than 0.05 wt %, sol.Al:
• 0.01-0.10 wt %, N:
• not more than 0.020 wt %, one or more of Ti:
• not more than 0.10 wt %, Nb:
• not more than 0.10 wt % and B:
• not more than 0.0100 wt % and the balance being Fe and inevitable impurities to not lower than Ac.sub.3 point, completing rough rolling within a temperature range of (Ar.sub.3 point+100.degree. C.).about.(Ar.sub.3 point+50.degree. C.), conducting super-high pressure descaling under conditions satisfying a jetting pressure of not less than 25 kgf/cm.sup.2 and a liquid quantity density of not less than 0.002 liter/cm.sup.2, starting finish rolling at a rolling reduction of not less than 80% above Ar.sub.3 point of rolling complete temperature within 5 seconds and coiling up below 700.degree. C.