A method for producing spheroidized or non-lamellar microstructure steels

A method for producing high strength hot rolled steel, the method comprising:

• casting, a steel slab of a composition, comprising in weight %:
• carbon (C) of about 0.45 wt. %-1.2 wt. %,
• manganese (Mn) of about 0.0-1.0 wt. %,
• silicon (Si) of about 0.0-0.5 wt. %,
• niobium (Nb) up-to 0.03 wt. %,
• sulphur (S) up-to 0.05 wt. %,
• phosphorous (P) up-to 0.05 wt. %,
• nitrogen (N) 0.002 wt. %-0.012 wt. %,
• balance being Iron (Fe) optionally along with incidental elements;
• heating, the steel slab to an austenitizing temperature for a first pre-determined time;
• hot rolling, the steel slab at a temperature ranging from Ae3 to Ae3+100° C., wherein Ae3 is the temperature at which transformation of austenite to ferrite starts at equilibrium and strain accumulation takes place during at least two strands of hot rolling;
• cooling, the steel to a coiling temperature at a cooling rate of 5° C./s-40° C./s;
• and
• coiling, the steel at the coiling temperature and retaining the steel at an ambient temperature for 1-24 hr to obtain high strength hot rolled steel,
• wherein, the high strength hot rolled steel comprises 75-95% spheroid microstructure and 5-25% pearlite microstructure.

A high strength hot rolled steel, comprising:

• composition of:
• carbon (C) of about 0.45 wt. %-1.2 wt. %,
• manganese (Mn) of about 0.0-1.0 wt. %,
• silicon (Si) of about 0.0-0.5 wt. %,
• niobium (Nb) up-to 0.03 wt. %,
• sulphur (S) up-to 0.05 wt. % of S,
• phosphorous (P) up-to 0.05 wt. %,
• nitrogen (N) 0.002 wt. %-0.012 wt. %,
• balance being Iron (Fe) optionally along with incidental elements;
• wherein, the high strength hot rolled steel comprises 75%-95% spheroid microstructure and 5%-25% pearlite microstructure.