Method of manufacturing Martensitic steel and a Martensitic steel thereof

A method of manufacturing a composite coil comprising the following successive steps:

• providing a prime steel in form of a non-heat treated cold rolled steel sheet;
• de-coiling at least the first two outer windings of the non-heat treated cold rolled steel sheet;
• preparing a leading end of the decoiled windings of the non-heat treated cold rolled steel sheet for welding;
• welding a first stringer having carbon content less than the non-heat treated cold rolled steel sheet to the prepared end of the non-heat treated cold rolled steel sheet to define a welded cold rolled steel sheet;
• spooling-back the welded cold rolled steel sheet to bring the un-welded end as the outer windings;
• de-coil at least first two outer winds of the welded cold rolled steel sheet;
• preparing the de-coiled end of welded cold rolled steel sheet for welding;
• welding a second stringer steel having carbon content less than the non-heat treated cold rolled steel sheet to the de-coiled end of welded cold rolled sheet;
• and
• coiling the welded cold rolled steel sheet to obtain a composite coil;
• where the prime steel comprises the following elements, expressed in percentage by weight:
• 0.1%≤C≤0.4%;
• 0.2%≤Mn≤2%;
• 0.4%≤Si≤2%;
• 0.2%≤Cr≤1%;
• 0.01%≤Al≤1%;
• 0%≤S≤0.09%;
• 0%≤P≤0.09%;
• 0%≤N≤0.09%;
• And optionally one or more of the following elements:
• 0%≤Ni≤1%;
• 0%≤Cu≤1%;
• 0%≤Mo≤0.1%;
• 0%≤Nb≤0.1%;
• 0%≤Ti≤0.1%;
• 0%≤V≤0.1%;
• 0.0015%≤B≤0.005%;
• 0%≤Sn≤0.1%;
• 0%≤Pb≤0.1%;
• 0%≤Sb≤0.1%;
• 0%≤Ca≤0.1%;
• a remainder composition being composed of iron and unavoidable impurities caused by processing;
• where the first stringer and the second stringer comprise the following elements, expressed in percentage by weight:
• 0.001%≤C≤0.25%;
• 0.2%≤Mn≤2%;
• 0.01%≤Si≤2%;
• 0.01%≤Cr≤1%;
• 0.01%≤Al≤1%;
• 0%≤S≤0.09%;
• 0%≤P≤0.09%;
• 0%≤N≤0.09%;
• And optionally one or more of the following elements:
• 0%≤Ni≤1%;
• 0%≤Cu≤1%;
• 0%≤Mo≤0.1%;
• 0%≤Nb≤0.1%;
• 0%≤Ti≤0.1%;
• 0%≤V≤0.1%;
• 0.0015%≤B≤0.005%;
• 0%≤Sn≤0.1%;
• 0%≤Pb≤0.1%;
• 0%≤Sb≤0.1%;
• 0%≤Ca≤0.1%;
• a remainder composition being composed of iron and unavoidable impurities caused by processing.