Recent Developments in Steel Processing: Thermal and Thermomechanical Processing
Program Organizers: Amy Clarke, Los Alamos National Laboratory
Monday 2:00 PM
October 8, 2012
Room: Room 407
Location: David L. Lawrence Convention Ctr
Session Chair: Ron Radzilowski, Severstal North America; Amy Woods, Steel Dynamics Inc. - Flat Rolled Division
2:00 PM
The Alloy Design and Processing of High Strength Dual-Phase Steels for Production on Continuous Galvanizing Lines: Anthony Deardo1; Calixto Garcia1; 1University of Pittsburgh
Ultra-high strength DP steels are being developed to help the automotive industry achieve better fuel efficiency and improved crash worhiness. These DP steels now contain low carbon content for spot weldability; high Mn, plus Cr and Mo for hardenability; and Nb and V. This paper will present recent research conducted on these kinds of steels. It will be shown that the choice of intercritical annealing temperature is important in microalloyed DP steels, and the rates of cooling throughout the CGL simulation are also important. Furthermore, the role of microalloying, especially V, in suppressing softening at or near the zinc pot temperature of 460°C has been shown to be important. The physical metallurgy of producing ultra-high strength steels on CG lines will be presented and discussed.
2:20 PM
On the Decomposition of Austenite in a High-Silicon Steel during Quenching and Partitioning: Mahesh Somani1; David Porter1; Leo Karjalainen1; Devesh Misra2; 1University of Oulu; 2University of Louisiana at Lafayette
Using a Gleeble thermomechanical simulator, a high-silicon steel (Fe-0.2C-1.5Si-2.0Mn-0.6Cr) was austenitized and quenched into the Ms-Mf range, retaining 15-40% austenite, and held for 10-1000 s at or above the quench-stop temperature (QT) in order to better understand the mechanisms operating during partitioning. Dilatometer measurements, transmission electron microscopy and calculations showed that besides carbon partitioning, isothermal martensite and bainite form at the partitioning temperature. The appearance of bainite after certain hold times depends on the partitioning temperature and seems to follow TTT diagram predictions. The formation of small fractions of bainite and martensite on cooling from the partitioning temperature was in accord with the final fractions of retained austenite measured using X-ray diffraction.
2:40 PM
Interstitial Hardening of 316L Austenitic Stainless Steel by Low Temperature Gaseous Nitrocarburizing: Dandan Wu1; Harold Kahn1; Gary Michal1; Frank Ernst1; Arthur Heuer1; 1Case Western Reserve University
Low temperature interstitial hardening of 316L austenitic stainless steel involving diffusion of both nitrogen and carbon atoms either simultaneously or consecutively, leads to a hardened “case” containing a “colossal” supersaturation of both interstitial species. Following a standard “activation” procedure developed by Swagelok Company to remove the passivating Cr2O3-rich native oxide, nitrocarburizing was done in a gas mixture of NH3/CO/H2/N2. The formation of the so-called “expanded” austenite was confirmed by Boltzmann–Matano XRD analysis. Auger Electron Spectroscopy (AES) and nano-indentation were employed to determine the composition and hardness depth profile of the hardened layer, respectively.
3:00 PM
Recrystallization Kinetic Behaviour of Copper-Bearing Strip Cast Steel: Prabhukumar Sellamuthu1; Nicole Stanford1; Peter Hodgson1; 1Deakin University
In the present study, copper-bearing low carbon steels were produced by direct strip casting (DSC) method on a pilot scale. The effects of copper on mechanical, microstructural and recrystallization behaviour were investigated. As-cast microstructure mainly consists of polygonal ferrite and Widmanstatten ferrite. The increase in Cu increases the amount of Widmanstatten ferrite and induces the formation of bainite in the as-cast condition. It was found that copper increases strength and hardness by precipitation hardening and that the increment is significant above 1% Cu. Six different compositions were selected for recrystallization study. All the samples were cold rolled to 70% reduction and annealed at three different temperatures, 600, 650 and 700°C for various times. Recrystallization responses were strongly dependent on initial microstructure and Cu content and the effect is dramatic between 1 to 2% Cu.
3:20 PM
Operational Metallurgy Practices to Minimize Abnormal Austenite Grain Growth during the Reheat Furnace Process: Steven Jansto1; 1CBMM-Reference Metals Company
The integration of the process metallurgical effects upon the physical metallurgy of the heated slab or billet in actual practice is rarely reported. This relationship between the reheat furnace operation, condition and efficiency closely relates to the propensity for the initiation of abnormal austenite grain growth prior to the hot rolling step of the production process. Inhomogeneous furnace heating of slabs and billets results in variations in the prior austenite grain size and hence, variability in the final grain size and mechanical properties. Often laboratory studies attempt to simulate actual furnace conditions and the influence of different microalloys on the austenite pinning effect, but the technical transfer of these laboratory results to the mill is quite difficult and often inaccurate due to simulation incongruence with the actual furnace operation. Key reheat furnace process parameters are reviewed which directly influence the austenite grain size during the reheat process.
3:40 PM Break
4:00 PM
Modification of Microstructure of 100CrMn6 Steel by Accelerated Carbide Spheroidisation Process: Daniela Hauserova1; Jaromir Dlouhy1; Zbysek Novy1; 1COMTES FHT a.s.
Processing of high-carbon chromium steels often includes an annealing stage, at which initial lamellar pearlite should be transformed into ferrite with globular carbides. The purpose of such treatment is to enhance machinability of the material or to condition the microstructure for subsequent hardening. Carbide spheroidising occurs through diffusion, which is a long-term and energy-demanding process. The holding times, sometimes up to tens of hours make soft annealing one of the most expensive heat treatment processes. The process was newly designed at the company COMTES FHT shortens carbide spheroidising several times and therefore delivers considerable time and cost savings. The purpose of this annealing process is to obtain globular carbides uniformly distributed in the matrix and to achieve overall softening. The present paper explores the effect of the newly-designed thermal schedules on the carbide spheroidisation behaviour, on the decrease in hardness in bearing steel grade 100CrMn6 and on processing times.
4:20 PM
Heat Treatment of Reactor Vessel Steel 08CH18N10T: Pavel Podany1; Petr Martinek1; Jan Nachazel2; Martin Balcar3; 1COMTES FHT a.s.; 2CVUT Praha; 3ZDAS a.s.
Article deals with the heat treatment of austenitic stainless steel 08CH18N10T used in reactor vessels. Experiment is focused on influence of heat treatment and thermomechanical processing on the microstructure and especially on the morphology and distribution of titanium carbo/nitrides. Three experimental heats with various amounts of carbon, titanium and boron were prepared and subjected to different heat treatment regimes. Also different solution annealing after forging was applied. Microstructure of the samples was analysed by means of optical and scanning electron microscopy with EDS. Numerical simulation in DEFORM 3D software was used for simulation of cooling after forging.
4:40 PM
Development of Technology for the Production of HIC Resistant Slabs for Sour Service Applications at ArcelorMittal Lazaro Cardenas, Mexico: Jorge Nieto1; Tomas Elias1; German Lopez1; Gustavo Campos2; Francisco Lopez1; Ruben Garcia1; Amar De3; 1ArcelorMittal Lazaro Cardenas; 2ArcelorMittal International; 3ArcelorMittal Global R&D
ArcelorMittal Steelmaking facility at Lazaro Cardenas (AMLC), Mexico has recently implemented key steelmaking and casting technologies for production of sound, ultra clean slabs with least centerline segregation catering to the growing API linepipe and off-shore markets for sour service applications. State of the art Steelmaking with use of residual-free Direct-reduced iron (DRI) and continuous casting with dynamic soft reduction were introduced for the production of slabs with minimum centerline segregation. Introduction of controlled cooling of slabs for hydrogen control has enabled production of slabs suitable for high quality HIC resistant plate and hot rolled coil. Substantial tonnages of slabs were produced for subsequent processing of various API grade HR coils and plates. Stringent quality control at each stage of steelmaking, casting and slab inspection ensured slabs with excellent internal quality resulting in successful HIC resistance in various final products.
5:00 PM
High Strength Dual-Phase Steel Structure Evolution during Hot Rolling: Yuriy Bezobrazov1; Anton Naumov1; Nikolay Kolbasnikov1; 1Saint Petersburg State Polytechnical University
The influence of continuous mill 2000 hot rolling parameters on the high strength dual-phase steel structure evolution was investigated. Computer simulation of structure and mechanical properties formation was realized with the help of Hot Strip Mill Model (HSMM), ThermoCalc, AusEvol+ programs. Physical simulation of metal thermomechanical treatment was made by Gleeble-3800. Varying the thermomechanical treatment parameters the ferrite-martensitic (FM) dual-phase steels are received.
5:20 PM
Heat Transfer during Cooling of a Hot Stationary Steel Plate with a Planar Water Jet: Amir Hossein Nobari1; Vladan Prodanovic1; Matthias Militzer1; 1The Centre for Metallurgical Process Engineering, The University of British Columbia, Vancouver, BC, Canada
Accelerated cooling on the run-out table of a hot rolling mill plays a key role to tailor microstructure and properties of steel products. In order to develop a heat transfer model for predicting the temperature evolution of steel plates during run-out table cooling, systematic experimental studies have to be carried out to determine the effect of various processing parameters on heat extraction. In the present study, a series of experiments was conducted using a planar water nozzle to study the effect of water flow rate (100 to 250 L/min) and temperature (10 to 40°C) on the heat transfer rate for stationary plates. Temperature data were recorded at different locations from the stagnation line using intrinsic thermocouples and heat fluxes at the top surface were subsequently calculated. These experimental results provide the basis to develop heat extraction relationships as an upper limit for slow moving plates.
5:40 PM Cancelled
Applications of Microstructure and Mechanical Properties Prediction Technology on CSP Line: Wen Tan1; 1Research and Development Center of Wuhan Iron and Steel (Group)Corp.
Microstructure and mechanical properties prediction technology has been developed for few years. Its main applications include optimizing processing parameters for improving mechanical properties, reducing scatter of mechanical properties and assisting developing new grade steel. In present paper, mathematical models originally developed on conventional hot rolling line for describing austenite evolution during rolling and cooling process have been applied to CSP process. The work include three aspects: upgrading 345MPa grade C-Mn steel to 420MPa grade or even higher strength steel , optimizing laminar cooling processes to produce economical C-Si-Mn DP(dual phase) steel and designing the optimal rolling schedule for improving microstructure homogeneity of Nb containing steel. Integrating with SQL database, Off-line software for modeling and predicting microstructure evolution has been developed.