Manufacturing method for hot rolled steel sheet

A method for the fabrication of a hot rolled steel comprising the steps of:

• providing a liquid metal comprising the following chemical composition with contents expressed by weight:
• 0.04%≤C≤0.08%;
• 1.2%≤Mn≤1.9%;
• 0.1%≤Si≤0.3%;
• 0.07%≤Ti≤0.125%;
• 0.05%≤Mo≤0.35%;
• 0.15%<Cr≤0.6% when 0.05%≤Mo≤0.11%;
• or
• 0.10%≤Cr≤0.6% when 0.11%<Mo≤0.35%;
• Nb≤0.045%;
• 0.005%≤Al≤0.1%;
• 0.002%≤N≤0.01%;
• S≤0.004%;
• and
• P<0.020%;
• a remainder including iron and unavoidable impurities,
• carrying out a vacuum or SiCa treatment, the chemical composition including, expressed by weight 0.0005%≤Ca≤0.005%, if a SiCa treatment is carried out;
• dissolving quantities of Ti and N in the liquid metal so as to satisfy (% [Ti])×(% [N])<6.10−4%2;
• casting the steel to obtain a cast semi-finished product;
• rolling the cast semi-finished product with an end-of-rolling temperature between 880° C. and 930° C., a reduction rate of the penultimate pass being less than 0.25, a reduction rate of the final pass being less than 0.15, a sum of these two rates of reduction being less than 0.37 and a start-of-rolling temperature of the penultimate pass being less than 960° C. to obtain a hot-rolled product, then
• cooling the hot rolled product at a rate between 20 and 150° C./s to obtain a hot rolled steel sheet;
• coiling the hot rolled product to obtain a hot rolled steel sheet;
• the hot rolled steel sheet having a thickness between 1.5 and 4.5 millimeters, a yield stress at least greater than 680 MPa in the direction transverse to the rolling direction and less than or equal to 840 MPa, a strength between 780 MPa and 950 MPa and an elongation at failure greater than 10%.