In order to evaluate the effect of secondary cold reduction rate on the drawing performance of double reduction tinplate and explain the mechanism, a detailed investigation into the microstructural characterization, dissolved carbon atoms, texture characterization by an X-ray powder diffractometer (XRD) and electron backscatter diffraction (EBSD), and earing behavior were carried out with different secondary cold reduction rates of 15%, 20% and 25% for double reduction tinplate. The experimental results indicate that 15% secondary cold reduction rate could obtain a better drawing performance because there are no holes and cracks at the microstructure, and the content of dissolved carbon atom is relatively low; at the same time, it has a better texture distribution and low earing coefficient.

In order to make a comprehensive comparison between ultra-thin hot rolled low carbon steel (LC) and extra low carbon steel (ELC) produced by endless roll technology and explain the differences, a detailed investigation into the microstructural characterization, characteristics of cementite and precipitates, mechanical properties, internal friction peaks, texture characterization by an X-ray powder diffractometer and electron backscatter diffraction, and formability including earing behavior, hole expanding ratio and V-shaped bending properties was carried out with different carbon content for 1.0 mm thickness ultra-thin hot rolled strip produced in endless strip production line. The experimental results indicate that the microstructure of both is composed of multi-layer areas with different grain sizes and thicknesses, the strength and elongation of LC are higher than that of ELC, but the content of solid solution carbon atoms and r of ELC are higher than that of LC, at the same time, the formability of ultra-thin strip ELC is better than that of LC mainly related to the content of {hkl} and {111} of ELC was higher than those of LC. The mechanical and formability properties of ultra-thin hot rolled strip by endless roll technology can meet the requirements of replacement cold rolled strip by hot rolled strip.

The warm stamping technology is a promising technology to meet the needs of car weight reduction and energy conservation. In order to compare with the mechanical properties of the traditional hot-stamped boron-alloyed steel 22MnB5, a new warm-stamped niobium-alloyed steel 22Mn3SiNb was designed and tested. The optimal heating parameters for warm forming process were explored through mechanical tests, and the process of their microstructure evolution was investigated by scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray diffraction (XRD), etc. The experimental results indicate that the optimal heating parameters for the niobium-alloyed steel 22Mn3SiNb are a heating temperature of 800 °C and a soaking time of 5 min. Compared to the hot-stamped boron-alloyed steel 22MnB5 under their respective optimal heating parameters, the properties and microstructure characteristics of 22Mn3SiNb are greatly improved, and nearly no decarburized layer is found on the surface of the niobium-alloyed steel 22Mn3SiNb. In addition, the addition of Nb produces the effects of grain refinement and precipitation strengthening due to the introduction of plenty of nano-precipitated particles and dislocations. In the end, it can be predicted that the new warm-stamped niobium-alloyed steel will replace the conventional hot-stamped boron-alloyed steel.

EffEct of final Rolling tEmpERatuRE on micRostRuctuRE, pRopERtiEs and tExtuRE of Hot RollEd stRip by nEw EndlEss RollEd linE Donghua steel continuous casting-rolling (DSCCR) line is a new endless rolling line in which tunnel heating furnace is added before and after roughing mills to change the temperature field of slab and intermediate slab, but this change will affect the microstructure and properties of hot rolled plate. Therefore, the microstructure evolution, mechanical properties, texture analysis, hole expanding and earing test of 2.0 mm thick hot rolled plate produced by DSCCR line at different final rolling temperature of 860°C, 840°C and 820°C are studied. The results show that with the decrease of final rolling temperature, there is an obvious layered microstructure distribution along the thickness direction, and the surface coarse grain area gradually expands inward, at the same time the morphology of cementite also changed from large multi domain lamellar pearlite and long rod cementite to small single domain lamellar pearlite and short rod cementite. The engineering stress-strain curves have discontinuous yield with the yield elongation of 4-5% and the elongations are more than 35%. eBSD analysis shows that small angle grain boundaries and deformed grains increase significantly with the decrease of final rolling temperature, and are mainly distributed in fine grain area. hole expanding and earing tests show that with the decrease of final rolling temperature, the earing performance decreased but the limiting hole expanding ratio is similar.