The Influence of a Novel Inorganic-Polymer Lubricant on the Microstructure of Interstitial-Free Steel during Ferrite Rolling

A novel polyphosphate lubricant was used and evaluated during hot (ferrite) rolling of an interstitial-free (IF) steel. The texture evolution of these rolled IF steels have been examined by means of X-ray diffraction (XRD) and electron backscatter diffraction (EBSD) measurements. The polyphosphate lubricant shows an improved lubrication performance in terms of the texture optimization compared with lubricating oil and with unlubricated conditions. The γ-fiber texture is enhanced, and less shear texture is produced. This microstructure is responsible for enhanced drawability of ferrite rolled IF steels. The very high thermal stability of the polyphosphate enabled its use at very high temperatures (from 700 to 800 °C). Rolling temperature exerted limited influence on the resulting rolling texture evolution. The polyphosphate lubricant stabilizes the surface texture and reduces the gradient of shear texture through the thickness. The in-grain shear bands are reduced significantly (48.5%) compared with the unlubricated condition. Measured grain orientations indicate that the favorable texture of {111}<112> along the γ-fiber is developed while the undesired α-fiber texture of {001}<110> is effectively suppressed.

Simulation Experimental Study on Ferrite Rolling Process of Low-Carbon Steels

In this paper, the Steel Plate Heat Commercial (SPHC) that produced by RiZhao Steel’s Endless Strip Production (ESP) line was taken as the research object. The phase transition points under different cooling rates were measured by DIL805A thermal expansion instrument and then the static Continuous Cooling Transformation (CCT) curve was plotted. The rolling process of ferritic zone was simulated by Gleeble-3800 hot compression tester. The microstructure evolution of SPHC under different temperatures and different strain rates were analyzed, and the hot compression deformation behavior was studied. The experimental result has shown that when the cooling rate of low carbon steel is lower than 15 °C·s-1, the microstructure is mainly composed of ferrite and a small amount of pearlite and tertiary cementite. The experimental material showed a mixed crystal phenomenon when the deformation reached 50% at 780 °C. The fitting calculation has shown that the deformation activation energy of the ferrite zone rolling is 112 kJ·mol-1, and the relationship between the deformation energy storage and the temperature compensation strain rate factor was established. Subsequently, the above experimental results were verified in the RiZhao Steel’s ESP line, which laid the experimental foundation for the use of ferrite rolling technology for endless strip production.

Effects of Lubrication in Ferrite Rolling of Interstitial Free Steel

Ferrite rolling of interstitial free steel strip in the temperature range 650-850°C can effectively reduce furnace costs and scale formation as a result of lower strip reheating temperatures. Different lubrication conditions of lubricating oil, solid lubricant and dry condition were used during ferrite rolling tests of thin interstitial free steel strip on a 2-high Hille 100 experimental rolling mill. Different rolling speed, rolling temperature and reductions were applied to the rolling process. The rolling force and roll roughness were affected by the lubrication conditions and rolling parameters. Solid lubricant indicated an improved performance in terms of the roll roughness, as well as the oxidation property of the strip surface during ferrite rolling.