Effect Of Carbon Content On Microstructure And Properties Of Food-grade Tinplate Steel Sheets

Tinplate steel sheets are widely used for containers,food packaging,packaging materials and stamping products,because of its excellent overall properties,such as non-toxic,high strength,and corrosion resistance.Nowadays,tinplate steel sheets are recognized as green environmentally friendly packaging materials.However,with the rise of plastic and paper packaging materials,and the development and application of aluminum and tin-free(chrome-plated,nickel-plated)plates,tin-plated plates face great challenges in the packaging market,such as the need to reduce costs by reducing the thickness of plates and increasing its strength levels.Therefore,developing the extremely thin food-grade tinned steel plates for two-piece cans and its fabrication technologies has become an effective way to raise the core competitiveness of enterprises.In this study,two kinds of tinplate steel sheets(0.03/0.05C-0.02Si-0.19Mn,wt.%)were used to investigate the effects of carbon content,cold rolling reduction and annealing parameters on the microstructure,mechanical properties and formability.The main factors influencing the microstructure and properties of the extremely thin food-grade tin plate sheets were further discussed.The main research results are as follows:(1)The influcen of carbon content on the microstructure and mechanical properties of hot-rolled tinplate sheets was studied.The results show thatas carbon content increases from 0.03%to 0.05%,the ferrite grain size was refinied slightly to 14.6?m,and the ultimate tensile strength increased slightly by 16MPa,together with the reduction in total elongation from 45%to 36.2%as well as the product strength and elongation(PSE)from 15.6 to 13.2GPa·%.(2)The influence of carbon content on the microstructur and properties of cold-rolled tinplate sheets(total rolling reduction:84%).The results show that increasing carbon coentent raises the tensile strength,but decreases the total elongation,PSE vaule and the formability index(e.g.Er,n and r values).Prior to tensile deformation,the 0.05C steel exhibits the weaker{111} but stronger {101} texture.The strengths of both the rolling texture {112}<110>and the cubic texture ?001}<110>become weakened,and the 0.05C steel samples after failure.The fracture morphologies show that the 0.05C steel exhibits less and shallower dimples than the 0.03C steel.(3)The influence of cold rolling reduction on microstructur and properties of the 0.03C tinplate steel sheets:as the rolling reduction increases from 78%to 88%,the grain size of ferrite in the annealed state drops,and the ultimate tensile strength increases,along with the reduced total elongation and the PSE and formability indicators.(4)As the annealing temperature rises from 680 to 710?,the 0.03C steel samples exhibit deeper and more evenly dimples after tensile failure and cupping tests.The fraction of high angle grain boundaries increases,impying further recrystallization.The {102} orientation texture gradually becomes weakened,but the the cubic texture {001}<110>is gradually replaced by the fibre texture {111}<112>.(5)When the cold rolling reduction is 84%and annealing at 710? for 25s,the 0.03C steel sheets exhibit excellent comprehensive properties:UTS=382.1MPa,EL=31.6%,PSE=12.1GPa·%,forming performance indicators:n=0.2,r=1.4,Er=7.8mm.