Effect of Rolling Oil Service Cycle on Stainless Steel Cold Rolled Surface
May 02, 2022
Case Overview: The customer was purchasing stainless steel hot-rolled NO.1 steel coil from a steel mill. During the cold rolling process, he found that there was suspected "iron oxide scale pressing" on the surface, and lodged a quality objection complaint with the steel mill. It is said that the purchased batch of strip rolls has bright spots on the side, which affects its subsequent processing. On-site observation of cold rolling production and physical objects: The physical surface inspection of the user's production process and the suspected "iron oxide scale pressing" after cold rolling of stainless steel (see the photo below)
According to the user's production process and the observation of the physical surface of the stainless steel, the rolling oil used by the user has been severely blackened and the color is dark brown. During the rolling process, the distribution of the impurity particles in the rolling oil sticks to the surface of the rolling piece, so that the surface of the strip after rolling is not bright, and the degreasing process is difficult to eliminate. In addition, a black serpentine band will appear on the surface of the cold-rolled steel coil during a long storage period, which directly affects the product quality of the terminal. Take rolling oil analysis: The dark brown rolling oil has poor oxidation resistance, high sulfur content, poor corrosion resistance and high viscosity, which affects the surface finish of the strip. Case Analysis: Obtaining high-quality cold-rolled stainless steel surface is the eternal pursuit of cold-rolling mills. Although hot-rolled stainless steel strip is produced during cold rolling in reversing or non-reversing mills, each pass is not the end surface of the finished product. But for stainless steel, the intermediate link of the rolling process directly affects the surface of the final product. At present, different types of cold rolling mills in my country generally use rolling oil, emulsion, water rolling + oil dripping mode. Rolling oil is generally composed of animal and vegetable fats + synthetic fats + special additives, and the commonly used concentration of emulsion is 5%. The use of rolling oil and emulsion is mainly determined according to the material and production process. Using rolling oil to roll stainless steel can reduce the friction coefficient and friction force on the contact arc surface between the rolling piece and the roll deformation zone. In high-speed rolling, it can reduce the wear of the rolls, and play the role of lubricating and cooling the rolling stock. Both the rolling oil and the emulsion have the same function as lubrication and cooling. The difference: the emulsion is a small mixture of oil, its cooling effect is stronger, and the lubricating effect is relatively poor. The low cost cannot be blindly pursued in the use of rolling oil. Adding appropriate synthetic esters in proper use can improve the lubricating performance of rolling oil. Adding phosphorus-containing compounds can improve the compressive and anti-wear properties of rolling oil, and adding anti-corrosion agent can improve the ability of rolling oil to protect the surface of strip steel. Recommended for users 1) For the current poor stainless steel surface caused by rolling oil, strengthen degreasing and degreasing. If the pickling solution and passivation solution cannot remove the grease, the grease existing on the surface will also directly affect the pickling passivation surface. 2) The surface quality problem is not the responsibility of the steel mill, and the quality objection will not be accepted.
