Low density hot rolled steel, method of production thereof and use of such steel to produce vehicle parts

A method for producing a low density hot rolled steel comprising the following steps:

• feeding a slab having a composition of:
• 0.12%≤carbon≤0.25%,
• 3%≤manganese≤10%,
• 3.5%≤aluminum≤6.5%,
• 0%≤phosphorus≤0.1%,
• 0%≤sulfur≤0.03%,
• 0% nitrogen 0.1%,
• and optionally one or more of the following elements
• 0%≤silicon≤2%,
• 0.01%≤niobium≤0.03%,
• 0.01%≤titanium≤0.2%,
• 0%≤molybdenum≤0.5%,
• 0%≤chromium≤0.6%,
• 0.01%≤copper≤2.0%,
• 0.01%≤nickel≤3.0%,
• 0%≤calcium≤0.005%,
• 0%≤boron≤0.01%,
• 0%≤magnesium≤0.005%,
• 0%≤zirconium≤0.005%,
• 0%≤cerium≤0.10%,
• a balance including iron and unavoidable impurities;
• reheating the slab at a temperature above 1000° C. and hot rolling the slab with a final rolling temperature of at least 750° C.;
• cooling the hot rolled steel from finishing of hot rolling to a coiling temperature range from 620° C. to 740° C. at a cooling rate CR1 from 1° C./s to 150° C./s;
• thereafter, coiling the hot rolled steel at a temperature from 620° C. to 740° C.;
• then cooling the hot rolled steel from the coiling temperature to room temperature at a cooling rate CR2 from 1° C./h to 50° C./h to obtain a low density hot rolled steel,
• the low density hot rolled steel sheet having a microstructure comprising, in area fraction, ferrite from 60% to 80%, 10% to 35% kappa carbides (Fe,Mn)3AICx, where x is lower than or equal to 1 and austenite from 0% to 10%, more than 45% of grains of the microstructure having a nano-hardness less than 4 GPa and less than 10% of the grains of the microstructure grains having a nano-hardness of more than 5 GPa.