Process for manufacturing a recovery annealed coated steel substrate for packaging applications and a packaging steel product produced thereby

A process for manufacturing a recovery annealed coated steel substrate for packaging applications, comprising the steps of:

• providing a steel slab or strip suitable for producing an ultra-low-carbon hot rolled strip having in weight percent:
• a carbon content of at most 0.003% and
• one or more of:
• a niobium content between 0.001% and 0.1%;
• a titanium content between 0.001% and 0.15%;
• a vanadium content between 0.001% and 0.2%;
• a zirconium content between 0.001% and 0.1%;
• a boron content between 5 and 50 ppm;
• for producing packaging steel by hot rolling at a finishing temperature higher than or equal to the Ar3 transformation point;
• wherein the steel substrate further comprises in weight percent:
• a nitrogen content of 0.004% or less;
• a manganese content between 0.05 to 0.5%;
• a phosphorous content of 0.02% or less;
• a silicon content of 0.02% or less;
• a sulphur content of 0.03% or less;
• an aluminium content of 0.1% or less;
• the remainder being iron and unavoidable impurities;
• cold-rolling the resulting steel strip to produce:
• single reduced steel substrate, or
• a double reduced steel substrate which was subjected to recrystallisation annealing between the first and second cold rolling step;
• electrodepositing a tin layer on one or both sides of the single reduced or double reduced steel substrate to produce a tin-coated steel substrate, wherein the coating weight of the tin layer or layers onto one or both sides of the substrate is at most 1000 mg/m2;
• heating the tin-coated steel substrate at a heating rate exceeding 300° C. followed by annealing the tin-coated steel substrate at a temperature Ta of between 513° C. and 645° C. for an annealing time ta:
• to convert the tin layer into an iron-tin alloy layer which contains at least 90 weight percent of FeSn, and
• to simultaneously obtain a recovered microstructure and wherein no recrystallisation of the single reduced substrate or double reduced substrate takes place;
• fast cooling the annealed substrate at a cooling rate of at least 100° C/s.