Flow Conditioning in Heat Treatment by Gas and Spray Quenching

Gas quenching has been known for centuries as a convenient, affordable method to heat treat ferrous alloys. Heated parts are taken out of the furnace and quenched at ambient pressure, casually using a blower to increase the heat exchange. Technical developments in the metal industry, over the last decades, have seen a constant improvement of the ratio of heat exchange, e.g. by using pressured chambers, specific blowers, and a variety of gases and gas mixtures. The current gas quenching technologies are adapted to heat treatable metals found in the automotive industry, requesting a minimum heat exchange ratio, also depending on the part geometry. Little has been however investigated concerning the quenched batch, defined as the arrangement of the heated parts onto a single- or multiple-layer charge carrier. The present work, through a combination of experimental and numerical techniques, provides guidelines to adapt the batch to a specific gas flow pattern (spatial fitting), and to adapt the gas flow pattern to the batch structure (temporal fitting). Measurement techniques have been developed to assess the flow patterns inside industrial quenching chambers. Evaluated flow structures have been converted to numerical boundary conditions for extended simulations tools. Simulations have helped implementing technical solutions for flow correction in industrial gas quenching chambers. Furthermore, simulations have served the design of batches of various geometries, to improve both quenching homogeneity and intensity. Both experimental and numerical results confirmed the advantages of gas quenching for the homogeneous heat treatment of automotive steel grades, and demonstrated the potential of various flow correcting devices, such as perforated plates and cylindrical flow ducts. Heat treatment gas and spray quenching has also been integrated into the forging and the turning process chains of single components, successfully optimizing the lean process flow (automation, quality, and time), for various high-performance materials and part geometries

Towards the simulation of the whole manufacturing chain processes with FORGE®

International audienceFollowing the metal composition and the microstructure evolution during the whole manufacturing chain is becoming a key point in the metal forming industry to better understand the processes and reach the increasing quality requirements for the parts. Thus, providing a simulation tool able to model the whole chain becomes critical. Physical phenomena occurring during the processes are nowadays better understood, providing always more relevant models for numerical simulation. However, important numerical challenges still exist in order to be able to run those simulations with the required accuracy. This article shows how FORGE® tackles those issues in order to provide highly accurate microstructure and surface treatments simulation features applied on real industrial processes

State of the Art of Laser Hardening and Cladding

In this paper an overview is given about laser surface modification processes, which are developed especially with the aim of hardness improvement for an enhanced fatigue and wear behaviour. The processes can be divided into such with and without filler material and in solid-state and melting processes. Actual work on shock hardening, transformation hardening, remelting, alloying and cladding is reviewed, where the main focus was on scientific work from the 21st century

Finding the edge: Net-shape surface sculpting during cold spray deposition

This thesis provides an overview of how a successful method for structuring cold spray deposition was developed, allowing the creation of defined surfaces from a previously uncontrolled deposition profile. When considering both additive and traditional manufacturing techniques, there remains a gap in the market for a high build rate, low-cost manufacturing system, capable of building net shape structures with good material properties from a range of difficult to work with engineering materials. A cold spray system had the potential to meet these requirements, and to provide additional benefits from being a solid-state fusion process, but the technique lacked the structural control capabilities required. The aim of this body of work was to develop methods for controlling the shape of depositing material, allowing the creation of three-dimensional structures, and determining an approach which would allow the creation of flexible manufacturing platform. A limited number of attempts had been previously made to control the deposition shape. These methods met with limited success, did not offer real control over the shape of the deposit during operation, and presented issues of accuracy, reliability, and repeatability. In this work, a series of concepts for shaping the deposition of the material were tested for the creation of flat vertical surfaces. Copper was used as the deposition powder as it readily deposits with cold spray under easily manageable conditions. The samples were investigated for shape conformity, surface roughness, porosity and build height, using optical microscopy and a white light interferometer. Successful shaping was delivered using masks, wide flow impeding backstops and thinner flow separating tools, provided the non-adhering powder had sufficient room to be cleared from the deposition zone. The thinner tool was further developed, as it allowed better positioning in smaller spaces for future systems. Computational fluid dynamics models were created to assist with the understanding of some inconsistencies in deposit quality. The results of these simulations showed minimal alteration to the particle trajectory was caused by the alteration of gas dynamics from the introduction of obstacles. The developed thin tool deposition concept was then successfully tested for robustness with deposition of further materials, and with the inclusion of laser irradiation of the substrate. It was demonstrated that the density, deposition efficiency and build heights are comparable with those expected from typical cold spray/supersonic laser deposition deposits. Following this, a range of building block structures were created, to further advance the shaping capabilities of the system, and demonstrate the freedom of deposition profile. Flat surfaces, thin walls, corners, curves, rings and overhangs were all shown to build efficiently without further complication. It is concluded that it is both possible to control the shape of the depositing material during cold spray, and possible to do so without adversely affecting the deposit characteristics that give cold spray manufacturing its specific advantages over other manufacturing methods. The next steps for this process are to create a more flexible system, automating the placement of the shaping tool and using a 5 or 6 axis bed and nozzle positioning setup. Further to that, precise control over the powder dosage, and the development of a known parameter space for select materials would progress the system to an additive capable platform

Light Weight Alloys: Processing, Properties and Their Applications

There is growing interest in light metallic alloys for a wide number of applications owing to their processing efficiency, processability, long service life, and environmental sustainability. Aluminum, magnesium, and titanium alloys are addressed in this Special Issue, however, the predominant role played by aluminum. The collection of papers published here covers a wide range of topics that generally characterize the performance of the alloys after manufacturing by conventional and innovative processing routes

Optimization of furnace residence time and ingots positioning during the heat treatment process of large size forged ingots

High-strength large size forgings which are widely used in the energy and transportation industries (e.g., turbine shaft, landing gears etc.) acquire significant mechanical properties (e.g., hardness) through a sequence of heat treatment processes, called Quench and Temper (Q&T). The heating process (tempering) that takes place inside gas-fired furnaces has a direct impact on the final properties of the product due to several major microstructural changes taking place at this step. Therefore, material properties are usually optimized by controlling the tempering process parameters such as time and temperature. A non-uniform temperature distribution around parts, as a result of thermal interactions inside the furnace or loading pattern, may result in the parts property variations from one end to another, changes in microstructure or even cracking. On the other hand, improvement of large products residence time inside the heat treatment furnace can minimize energy consumption and avoid undesirable microstructural changes. However, at the present time, the industrial production is mainly based on available empirical correlations which are costly and not always reliable. Accurate time-dependent temperature prediction of the large size forgings within gas-fired heat treatment furnaces requires a comprehensive quantitative examination of the heating process and an in-depth understanding of complex conjugate thermal interactions inside the furnace. Limitations in analytical studies and complexity and cost of experimentations have made numerical simulations such as computational fluid dynamics (CFD), effective methods in this field of study. However, among the rarely found studies on gas-fired furnaces, smallscale furnaces or those with shorter operation times were mainly considered (using different simplifications like steady-state calculations) because of complexity of the phenomena and large calculation times. Subsequently, there are very few studies on the improvement of the loading patterns of large-size steel parts inside the gas-fired furnaces and their relevant residence time optimization. Moreover, the limitation and strength of different numerical approaches to calculate thermal interactions in the turbulent reactive flow of the large size gas-fired batch type furnaces were addressed by few researchers in the literature. In this regard, the main objective of the present thesis is to provide a comprehensive quantitative analysis of transient heating and an understanding of thermal interactions inside the furnace so as to optimize the residence time and temperature uniformity of large size products during the heat treatment process. To attain this objective, the following milestones are pursued. The first part of this study provides a comprehensive unsteady analysis of large size forgings heating characteristics in a gas-fired heat treatment furnace employing experimentally measured temperatures and CFD simulations. A three-dimensional CFD model of the gasfired furnace, including heat treating chamber and high momentum natural gas burners, was generated. The interactions between heat and fluid flow consisting of turbulence, combustion and radiation were simultaneously considered using the k -ε , EDM and DO models, respectively. The applicability of S2S radiation model to quantify the effect of participating medium and radiation view factor in the radiation heat transfer was also assessed. Temperature measurements at several locations of an instrumented large size forged block and within the heating chamber of the furnace were performed for experimental analysis of the heating process and validation of the CFD model. Good agreement with a maximum deviation of about 7% was obtained between the numerical predictions and the experimental measurements. The results showed that despite the temperature uniformity of the unloaded furnace, each surface of the product experienced different heating rates after loading (single loading) resulting in temperature differences of up to 200 K. Analysis of the results also revealed the reliability of the S2S model and highlighted the importance of radiation view factor for the optimization purposes in this application. Findings were correlated with the geometry of the furnace, formation of vortical structures and fluid flow circulations around the workpiece. The experimental data and CFD model predictions could directly be employed for optimization of the heat treatment process of large size steel components. The second part of this study aims to determine the effect of loading pattern (in the multiple loading configurations) on the temperature distribution of large size forgings during the heat treatment process within a gas-fired furnace to attain more temperature uniformity and consequently homogenous mechanical properties. This part also focuses on the improvement of residence time of large size forged ingots within a tempering furnace proposing a novel hybrid methodology combining CFD numerical simulations and a series of experimental measurements with high-resolution dilatometer. Transient 3D CFD simulations validated by experimental temperature measurements were employed to assess the impact of loading patterns and skids on the temperature uniformity and residence time of heavy forgings within the furnace. Comprehensive transient analysis of forgings heating characteristics (including heat transfer modes analysis) at four different loading patterns allowed quantifying the impact of skids and their dimensions on the temperature distribution uniformity as well as products residence time. Results showed that temperature non-uniformities of up to 331 K persist for non-optimum conventional loading pattern. The positive influence of skids and spacers applications was approved and quantified using the developed approach. It was possible to reduce the identified non-uniformities of up to 32 % through changing the loading pattern inside the heat treatment furnace. This hybrid approach allowed to determine an optimum residence time of large size slabs improving by almost 15.5 % in comparison with the conventional non-optimized configuration. This approach was validated and it could be directly applied to the optimization of different heat treatment cycles of large size forgings. The third part of the study addresses the details of the numerical simulation of heat treatment process of large size forgings within real scale gas-fired furnaces. Specifically, assessment of chemical equilibrium non-premix combustion model for accurate temperature prediction of heavy forgings, as well as performance of six different RANS based turbulence models for predictions of turbulent phenomenon were discussed in this context. In this regard, thermal interactions at different locations of the forged block as well as critical regions such as burner area, stagnation and wake region were performed using a one-third periodic 3D model of the furnace and validated by experimental measurements. Results showed that the one-third periodic model with chemical equilibrium non-premix combustion is reliable for the thermal analysis of the heat treatment process with a maximum deviation of about 3% with respect to the experimental measurements. It was also revealed that the choice of the turbulence model has a significant effect on the prediction of combustion and heat transfer around the block. Prediction of ɛ/k ratio by different turbulence models showed a significant relation to the turbulent combustion (such as burner flame length) and block temperature predictions, around the stagnation region. Standard and realizable k - ɛ models, due to an unrealistic over prediction of turbulence kinetic energy (under-prediction of ɛ/k ratio), resulted in shorter flame length and under-prediction on the temperature of the forged block around the stagnation region; While, SST k - w model showed reasonable predictions in this region. RSM model was found as the most reliable turbulence model compared to the experimental measurements. Meanwhile, realizable k − ɛ model apart from some under-prediction on the stagnation region and flame length could effectively predict the overall temperature of the heavy forgings with reasonable accuracy with respect to the experimental data and RSM predictions

Experimental optimization of simulated ring rolling operation for heavy rail industry

“Industrially cast AISI 1070 steel wheel pre-forms from Amsted Rail Co. were experimentally hot rolled to simulate the conditions for industrial wheel rolling. Ring rolling of near net shape castings can improve location specific properties by decreasing segregation, closing porosity, and reducing grain size without the use of multiple forging operations in a traditional forging line. As-cast wheel sections were subjected to thermomechanical processing routes using a 2-high rolling mill in a temperature range of 830°C to 1200°C. The goal being to simulate the ring rolling process and optimize benefits of mechanical properties of the as-rolled steel. Charpy V- and U-notch impact tests were conducted at -20ºC and 20ºC, respectively, as a function of thermomechanical processing and notch orientation. Mitigation of cast defects such as inclusions and shrinkage porosity by hot rolling were quantified utilizing scanning electron microscopy and micro-computed X-Ray tomography. Microshrinkage porosity was shown to be virtually eliminated at a 66% reduction. A rolling temperature of 830°C resulted in a 114% increase in KCU at 20°C and 67% increase at -20°C in KCV for L-S impact properties through refinement of prior austenite grain size. Anisotropy related to MnS stringers in the rolling direction were the primary cause for reduction in impact toughness in the T-L orientation although grain texture also likely plays a role. Hot tensile tests performed between 830°C to 1200°C in strain rates of 0.1 to 10 s-1 were utilized to develop a Johnson-Cook Strength model. The experimental parameters determined from the Johnson-Cook model were used as inputs to develop a Finite Element Analysis model of the modified wheel rolling process utilizing FORGE NxT software”--Abstract, page iv

Advances in Design by Metallic Materials: Synthesis, Characterization, Simulation and Applications

Very recently, a great deal of attention has been paid by researchers and technologists to trying to eliminate metal materials in the design of products and processes in favor of plastics and composites. After a few years, it is possible to state that metal materials are even more present in our lives and this is especially thanks to their ability to evolve. This Special Issue is focused on the recent evolution of metals and alloys with the scope of presenting the state of the art of solutions where metallic materials have become established, without a doubt, as a successful design solution thanks to their unique properties