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

A low density hot rolled steel comprising by weight:

• 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≤0.1%,
• a balance including iron and unavoidable impurities;
• the steel sheet having a microstructure comprising, in area fraction, ferrite from 55% to 80%, 15% to 50% austenite and martensite from 0% to 10%, more than 45% of grains of the microstructure having a nano-hardness less than 4 GPa and less than 22% of the grains of the microstructure grains having a nano-hardness of more than 5 GPa

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

• feeding a slab having a composition by weight 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≤0.1%,
• 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 380° C. to 480° C. at a cooling rate CR1 from 10° 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 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.