Soft Sensors for Property‑Controlled Multi‑Stage Press Hardening of 22MnB5

In multi-stage press hardening,the product properties are determined by the thermo-mechanical history during the sequence of heat treatment and forming steps.To measure these properties and finally to control them by feedback,two soft sensors are developed in this work.The press hardening of 22MnB5 sheet material in a progressive die,where the material is first rapidly austenitized,then pre-cooled,stretch-formed,and finally die bent,serves as the framework for the development of these sensors.To provide feedback on the temporal and spatial temperature distribution,a soft sensor based on a model derived from the Dynamic mode decomposition(DMD)is presented.The model is extended to a parametric DMD and combined with a Kalman filter to estimate the temperature(-distribution)as a function of all process-relevant control vari-ables.The soft sensor can estimate the temperature distribution based on local thermocouple measurements with an error of less than 10°C during the process-relevant time steps.For the online prediction of the final microstructure,an artificial neural network(ANN)-based microstructure soft sensor is developed.As part of this,a transferable framework for deriving input parameters for the ANN based on the process route in multi-stage press hardening is presented,along with a method for developing a training database using a 1-element model implemented with LS-Dyna and utilizing the material model Mat248(PHS_BMW).The developed ANN-based microstructure soft sensor can predict the final microstructure for specific regions of the formed and hardened sheet in a time span of far less than 1 s with a maximum deviation of a phase fraction of 1.8%to a reference simulation.

Improving mechanical properties and high-temperature oxidation of press hardened steel by adding Cr and Si

This work investigated the effect of Cr and Si on the mechanical properties and oxidation resistance of press hardened steel.Results indicated that the microstructure of the Cr-Si micro-alloyed press hardened steel consisted of lath martensite,M_(23)C_(6)carbides,and retained austenite.The retained austenite and carbides are responsible for the increase in elongation of the micro-alloyed steel.In addition,after oxidation at 930℃for 5 min,the thickness of the oxide scales on the Cr-Si micro-alloyed press hardened steel is less than 5μm,much thinner than 45.50μm-thick oxide scales on 22MnB5.The oxide scales of the Cr-Si micro-alloyed steel are composed of Fe_(2)O_(3),Fe_(3)O_(4),mixed spinel oxide(FeCr_(2)O_(4)and Fe_(2)SiO_(4)),and amorphous SiO_(2).Adding Cr and Si significantly reduces the thickness of the oxide scales and prevents the generation of the FeO phase.Due to the increase of spinel FeCr_(2)O_(4)and Fe_(2)SiO_(4)phase in the inner oxide scale and the amorphous SiO_(2)close to the substrate,the oxidation resistance of the Cr-Si micro-alloyed press hardened steel is improved.

Improving hydrogen embrittlement resistance of a modified press hardening steel by introducing retained austenite as hydrogen trap

The effect of retained austenite(RA)with higher mechanical stability on hydrogen embrittlement resistance of a modified 22MnB5(C 0.22,Si 0.8,Mn 1.5,B 0.002,Fe balance,in wt.%)press hardening steel(PHS)has been studied.One-step quenching and partitioning(Q&P)treatment was applied to PHS,and around 6 vol.%ultra-fine RA was obtained.The ultra-fine RA was found to act as stronger hydrogen trap than dislocations and grain boundaries in martensitic matrix and can decrease the apparent diffusion coefficient of hydrogen from 5.97×10^(-7) to 3.83×10^(-7) cm^(2) s^(-1),which was verified by the combination of thermal desorption spectroscopy analysis and hydrogen permeation test.The higher mechanical stability of the ultrafine RA assures enough stability of the hydrogen trap,which results in better hydrogen embrittlement resistance in Q&P-treated PHS than the conventional directly quenched PHS.

Deep Drawing with Local Hardening on Digital Multi-axis Servo Press

The paper discusses a new drawing technology, based on a synchronized movement of ram and cushion with multiple bending operations in alternating directions called ＂bi-directional deep drawing（BDD）.＂ The goal is to avoid local thinning by strengthening the weak point using local hardening. BDD operations are realized before the conventional deep drawing process. This results in a local strain hardening at the weak point of the workpiece, which is usually located at the bottom punch radius. Two major aspects have to be given attention due to the high number of process parameters. On the one hand, for process design, it is helpful to have a tool by means of which it is possible to simultaneously create both the machine program for the servo press and the initial configuration for the process simulation. From the authors＇ point of view, this complexity can only be represented by a numerical analysis method, on the other hand. Consequently, both aspects are given attention in this paper.

Reverse metallurgical engineering towards sustainable manufacturing of vehicles using Nb and Mo alloyed high performance steels

Steel is the dominant construction material for most industrial goods such as equipments, structures, buildings or vehicles. Although there have been great advances in steel technology over the last 4 decades, the industry currently faces serious sustainability challenges with regard to energy conservation, reduction of CO2 emission and a generally more efficient use of resources. The principal connotation in this respect is increasing steel strength allowing to reduce component weight. However, it is also necessary considering in how far the modified steel properties interfere with typical manufacturing techniques established in the processing chain. A feasible method in this sense is a reverse approach starting from detailed knowledge of the manufacturing process and translating it back into the most suitable metallurgical and microstruc- tural design of steel. Modifying steels towards better manufacturing performance typically involves innovative alloying and metallurgical processing concepts. Niobium and molybdenum are two of the most powerful alloying elements in helping to adapt microstructures and properties with regard to downstream manufacturing processes. This paper will highlight several examples how a reverse met- allurgical engineering approach can be successfully applied to optimize the efficiency of subsequent manufacturing processes with a focus on the automotive industry.

Molybdenum alloying in high-performance flat-rolled steel grades

Considerable progress in developing flat-rolled steel grades has been made by the Chinese steel industry over the recent two decades.The increasing demand for high-performance products to be used in infrastructural projects as well as in production of consumer and capital goods has been driving this development until today.The installation of state-of-the-art steel making and rolling facilities has provided the possibility of processing the most advanced steel grades.The production of high-performance steel grades relies on specific alloying elements of which molybdenum is one of the most powerful.China is nearly self-sufficient in molybdenum supplies.This paper highlights the potential and advantages of molybdenum alloying over the entire range of flat-rolled steel products.Specific aspects of steel property improvement with respect to particular applications are indicated.