Optimal Control of a Cooling Line for Production of Hot Rolled Dual Phase Steel

Self Cite

The rate model inherited from Leblond and Devaux's concept has been applied to multiphase transformations in hot-rolled TRIP steel. The phase fraction is collected from different laboratory scale process simulations, both multi-pass rolling for repeated recrystallization and single-pass cycles. The latter is also investigated by in situ synchrotron X-ray diffraction (XRD) to acquire instantaneous data for the phase fraction and carbon content. The different cycles allow different austenite conditioning inputs for the model to enlarge the range of thermomechanical parameters. Bainite transformation model is a function of the instantaneous average carbon content in the remaining austenite, which is measured from the shift in the 1-dimensional diffraction peaks. The modeling can map different process windows for a specific required microstructure of TRIP steel. The bainite formation is remarkably favored by low carbon content. But, the promotion of ferrite formation in the former step increases the carbon content dramatically and yields smaller bainite fraction that consequently larger fraction of retained austenite is allowed. A modified Koistinen-Marburger equation has been established from the in situ XRD data to model the martensite formation during the final cooling to reveal the stability of austenite. Above an average carbon content of 1.475 mass%, the retained austenite becomes stable.

Section: Discussionmentioning

confidence: 99%

Modeling Bainite Transformation and Retained Austenite in Hot Rolled TRIP Steel by Instantaneous Carbon Enrichment

Suwanpinij

Prahl

et al. 2017

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“…Therefore, much effort was focused to set the proper cooling strategy that ensured the adjustment of the targeted DP microstructure on the run out table immediately after the last deformation pass. The conventional SC strategy consists of accelerated cooling and isothermal holding for ferrite formation followed by rapid cooling . The accelerating cooling implies lowering of A r3 and decreases the transformation time due to the increase in undercooling and hence the increase of the nucleation rate .…”

Section: Discussionmentioning

confidence: 99%

Development of a New Concept for Hot‐Rolled Weathering–DP Steel: Thermo‐mechanical Simulation, Microstructure Adjustment, and Mechanical Properties

Allam

Bleck

2015

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A new alloying concept is proposed to develop a hot‐rolled weathering steel with a dual‐phase microstructure in order to combine good anticorrosion and good forming properties. The chemical composition in wt% comprises 0.11C, 0.5 Si, 1.52 Mn, 0.055 P, 0.4 Cr, 0.3 Ni, and 0.3 Cu. The phase transformation behavior is investigated by means of continuous cooling transformation diagrams. Different cooling strategies are applied in thermo‐mechanical simulation experiments for proper adjustment of the dual‐phase microstructure. The laboratory‐scale processing parameters are transferred to a pilot hot rolling plant. The hot‐rolled sheets are characterized by tensile testing and quantitative metallography. The produced hot‐rolled steel sheets consist of a microstructure with 71 vol% ferrite, 2 vol% pearlite, and 27 vol% martensite achieving average mechanical properties of 375 MPa for Rp0.2, 740 MPa for Rm, and 14% for A50. A delayed ferrite transformation makes step cooling unnecessary and enables easy processing by continuous cooling after hot rolling. The tendency to microstructural banding decreases as the cooling rate increases.

“…We first establish an appropriate mathematical setting for the model‐based optimization of slab shapes in hot rolling processes that takes industrial specifications and technical limitations into account. Similar problems have been discussed in the context of different applications, such as shape optimization, parameter identification, or material optimization . As we want to apply fast gradient‐based methods to solve the resulting optimization problem, we need to compute derivatives of cost functional and constraints .…”

Section: Introductionmentioning

confidence: 99%

Model‐Based Optimization of Short Stroke Control in Roughing Mills

Werner

Kurz²,

Stingl

et al. 2017

Automatic width control is one key issue in hot strip rolling and the main actuator for width control is the vertical draft (edging) applied to slabs in the roughing sequence. In order to compensate for the occurring strip necking, a variable edger gap is applied in the edging process. This paper introduces a comprehensive mathematical optimization approach for the fully automatic generation of the associated edger roll trajectories, which is based on a nonlinear dynamic simulation model for the material flow in the roughing mill. Due to the complexity of this simulation model, gradient-based methods are applied to solve the resulting optimization problem in reasonable time. Hence, derivatives of cost functional and constraints must be provided, which entails computing sensitivity information from the underlying simulation model. Finally, numerical results for real-world examples are discussed to illustrate the capability of the presented approach. In particular, this paper examines the influence of characteristic parameters such as the slab width or the maximum edger screw in velocity onto the optimization results.[ Ã ] Dr.