Hot Flat Product Rolling, Rolls, Safety & Health
Variation in strength along the length of hot-rolled strip presents the challenge of complying with gauge tolerances at the cold mill. Such strength variation, however, is typically manifested only when cold rolling begins and can lead to strip breaks, especially while rolling advanced high-strength steel (AHSS) grades. Charts of the thickness variation along the length of hot-rolled strip provide no indications of the variable strength. This is because the sources of the variable strength are located further downstream from the finishing stands, i.e., in the laminar cooling section and in the method that the hot-rolled coils are stored in the coil yard.
The heat-affected zone (HAZ) of the weld joint of low-carbon microalloyed steel has a complex microstructural configuration. The microhardness and microstructure of industrial samples of a 150-mm welded joint of ABS EH36 Z35 offshore steel heavy plates after the normalizing process and additional post-weld heat treatment (PWHT) were investigated. This paper presents the positive effect of the post-weld heat treatment on the decreasing of local microhardness and the increasing of the low-temperature resistance to brittle fracture of the grain-coarsened HAZ of the tested type of welded joint.
Laminar cooling is a critical process that, unless perfectly regulated, can have a detrimental impact on the finished product in terms of flatness and shape while still achieving the desired microstructure and metallurgical properties. To overcome this, together with SSAB Borlänge and Vinnova (Sweden’s innovation agency), Shapeline has developed an optical flatness gauge system, designed to collect relevant flatness and shape data before and after the laminar cooling process. This paper explains the measurement principle and how the system operates. It will also provide some insight into the specific project after having been in operation for almost one year.
Hot rolling thin gauges without cold rolling reduces production costs tremendously. With Arvedi ESP (Endless Strip Production) lines achieving exit thickness down to 0.6 mm, the requirements for tension and thickness control of finishing mills have increased. A new control concept for hot rolling thin gauges with existing instrumentation is based on the cold rolling control concept successfully used in tandem cold rolling mills. The concept is based on fast roll gap change to control entry strip tension. Results from the Arvedi ESP No. 4 line at Rizhao Iron and Steel Co. have shown excellent strip tension and thickness performance.
A data-driven feedforward compensation method based on system identification was applied for coiling temperature control in a hot strip mill. System identification is a statistical method to build mathematical models of dynamic systems from measured input-output data, and it is expected to be one of the most useful methods of modeling for big data. By using system identification, the dynamics of coiling temperature fluctuation in bar was predicted on-line, and it was compensated for by feedforward control. As a result, the accuracy of coiling temperature control was successfully improved. This presentation will explain the basic idea and actual results in the paper.
Oxide dust generated from the rolling process is a problem for most rolling mills, especially those rolling high-silicon or high-carbon products. This dust is troublesome and there have been many attempts to control it. A system has been developed and installed to effectively control the oxide dust from the rolling operations. Effective control of the oxide dust results in significantly reduced oxide dust-related defects to the strip. The system utilizes an air/water mixture with specifically proportioned design to encapsulate and control dust particles without affecting cooling or quality of the rolled product. This paper will explore the subject of rolling oxide dust suppression and discuss key factors that must be recognized and controlled for proper results from the suppression system.