Influence of process variables on development of camber during hot rolling of strip steel

Abstract

Experimental design techniques have been used to study the effects of variations in horizontal scale breaker process parameters in relation to camber generation during the early reduction stages in a hot strip mill. A fractional factorial experiment was designed and performed to identify which process variables are most influential to camber generation. The parameters which emerge from this analysis as being significant are: slab wedge, temperature differentials across the strip width, the deviation of the slab from the mill centreline, and mill tilt. A full factorial experiment was then designed and performed to further investigate these significant process parameters to determine where to set influential and controllable variables so that camber is minimised. The results show that none of the process parameters is significant to camber generation when acting alone; however, they are all significant when combined with one or two other process parameters. This study has enabled a predictive equation to be developed which is able to predict camber to within ±4 mm. This equation may be used in conjunction with mill tilting strategies to reduce camber in the early reduction stages of a hot strip mill.     

A constitutive equation for hot deformation range of 304 stainless steel considering grain sizes

A general constitutive equation based on the framework of invariant theory by consideration of hot deformation key variables and also the properties of the material such as initial grain size is presented in the current work. Soundness of the considered parameters to be used in the developed formula was initially verified based on the important axioms such as objectivity, entropy principle, and thermodynamics stability. To access the prediction ability of the method, the formula was simplified for the simple hot compression test. To evaluate the simplified formula, single-hit hot compression tests were carried out at the temperature range of 900–1100 °C under true strain rate of 0.01–1 s⁻¹ on a AISI 304 stainless steel. The capability of proposed formula for reproducing the variation of flow stress with strain and the strain hardening rate with stress for the resultant flow stress data was examined. The good agreement between model predictions and actual results signified the applicability of this method as a general constitutive equation in hot deformation studies.     

Additively manufactured 316L stainless steel: An efficient electrocatalyst

In the quest of finding an economical, yet efficient material, the idea of fabricating 316L stainless steel using additive manufacturing technology was explored to produce material with refined sub-granular structure. The surface of the stainless steel was further chemically treated with an etching solution to expose the grain boundaries. The grain boundary enriched surface resulted in more active sites for the oxygen evolution reaction (OER) in additively manufactured treated (AM-T) 316L stainless steel. AM-T sample manifests enhanced catalytic activity for OER with an overpotential of 310 mV to draw a 10 mA/cm² current density, along with a lower Tafel slope of 42 mV/dec compared to AM and wrought samples. These features were validated from the increased double-layer capacitance of AM-T and approximately 1.5 times larger electrochemically effective surface area of AM-T due to etching treatment compared to the wrought sample. Furthermore, AM-T also possesses stable activity retention for 100 h at a current density of 10 mA/cm².     

Effect of N and C on stress corrosion cracking susceptibility of austenitic Fe18Cr10Mn-based stainless steels

Stress corrosion cracking (SCC) susceptibility of austenitic Fe18Cr10Mn alloys with 0.3N, 0.6N and 0.3N0.3C was investigated in aqueous chloride environment using a slow strain rate test method. The SCC susceptibility of Fe18Cr10Mn alloys in 2 M NaCl solution at 50 °C under constant anodic potential condition decreased with increase in N content from 0.3 to 0.6 wt%, and with addition of 0.3 wt% C to the Fe18Cr10Mn0.3N alloys. The present study strongly suggested that the beneficial effects of N and C on the SCC behavior of Fe18Cr10Mn alloys would be associated with the resistance to pitting corrosion initiation and the repassivation kinetics.     

Active screen plasma nitriding of 316 stainless steel for the application of bipolar plates in proton exchange membrane fuel cells

Proton exchange membrane fuel cell (PEMFC) has attracted considerable interest because of its superb performance, and many researches are focused on the development of high-performance, long-life bipolar plates. Stainless steel bipolar plates offer many advantages over the conventional graphite bipolar plates, such as low material and fabrication cost, excellent mechanical behaviour and ease of mass production. However, the insufficient corrosion resistance and relatively high interfacial contact resistance (ICR) become the major obstacles to the widespread use of stainless steel bipolar plates. In this work, active screen plasma nitriding (ASPN), a novel plasma nitriding technique, was used to modify the surface of 316 austenitic stainless steel. A variety of analytical techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), glow discharge optical emission spectrometer (GDOES), were employed to characterize the nitrided samples. The results reveal that a nitrogen supersaturated S-phase layer has been successfully produced on the surface of all nitrided 316 stainless steel samples. The interfacial contact resistance (ICR) value can be decreased dramatically after ASPN treatment and the corrosion resistance can also been improved. In addition, better corrosion resistance can be achieved by active screen plasma nitriding with a stainless steel screen than with a carbon steel screen. This technique could be used to improve the performance and lifespan of bipolar plates for fuel cells.     

Evaluation of material flaws identified during fabrication leak testing of 304L containment vessel

Abstract

Savannah River National Laboratory has designed the bulk tritium shipping package as a replacement for the UC609 which was designed in the early 1970s. In the course of prototype package fabrication four components of the containment vessel boundary failed helium leak testing due to material flaws in the base material. Leak testing was being performed in accordance with ANSI N14·5, ‘Radioactive materials-leak tests on packages for shipment’. This paper addresses the ASME Section III test requirements for components and the failure mode of the base material. Additionally, the paper discusses the process used to correct the flaws for this application and recommendations for eliminating this potential in future applications.     

Structural performance of cold-formed lean duplex stainless steel columns

The structural performance of cold-formed lean duplex stainless steel columns was investigated. A wide range of finite element analysis on square and rectangular hollow sections and other available data, with a total number of 259 specimens, were considered. An accurate finite element model has been created to simulate the pin-ended cold-formed lean duplex stainless steel columns. Extensive parametric study was carried out using the validated finite element model. The column strengths predicted from the parametric study together with the available data are compared with the design strengths calculated from various existing design rules for cold-formed stainless steel structures. It is shown that the existing design rules, except for the ASCE Specification as well as the stub column and full area approach, are conservative. Modifications are proposed for the AS/NZS Standard, EC3 Code, and direct strength method. Reliability analysis was performed to assess the existing and modified design rules. It is also shown that the modified design rules are able to provide a more accurate and reliable predictions for lean duplex stainless steel columns. In this study, it is suggested that the modified design rules in the AS/NZS Standard and the modified direct strength method to be used in designing cold-formed lean duplex stainless steel columns.     

Single medium microbial fuel cell: Stainless steel and graphite electrode materials select bacterial communities resulting in opposite electrocatalytic activities

A graphite electrode and a stainless steel electrode immersed in exactly the same medium and polarised at the same potential were colonised by different microbial biofilms. This difference in electroactive microbial population leads stainless steel and graphite to become a microbial cathode and a microbial anode respectively. The results demonstrated that the electrode material can drive the electrocatalytic property of the biofilm opening perspectives for designing single medium MFC.This new discovery led to of the first demonstration of a “single medium MFC.” Such a single medium MFC designed with a graphite anode connected to a stainless steel cathode, both buried in marine sediments, produced 280 mA m^?2 at a voltage of 0.3 V for more than 2 weeks.     

Characterization of stainless steel parts by Laser Metal Deposition Shaping

Laser Metal Deposition Shaping (LMDS) is a new rapid manufacturing technology, which can build fully-dense metal components directly from the information transferred from a computer file by depositing metal powders layer by layer with neither mould nor tool. Typically, performed with stainless steel (SS) 316 powder, the orthogonal experiments combining with the ideal overlapping model were applied to ascertain the optimal processing parameters. Then the characteristics of microstructure, composition and phase of as-deposited cladding layers were analyzed through Scanning Electron Microscope (SEM) and X-ray diffraction (XRD), as well as relative model. Furthermore, the cooling rate and the solidification velocity during LMDS were evaluated based on empirical method. With the optimal parameters, some parts were fabricated without obvious defects, and then the mechanical properties of them were tested. Finally, the influencing regularities of critical parameters on microstructure and properties were concluded by comparison. The results prove that the microstructure of SS 316 deposits is composed of the slender dendrites growing epitaxially from the substrate, the mechanical properties are favorable and anisotropic, and the composition is uniform. Besides, the microstructure morphology and the mechanical properties are affected by the varied processing parameters at different degrees. Among them, the scanning speed shows the most remarkable effects on microstructure morphology, characteristic microscale, mechanical properties, as well as geometric shape of as-deposited parts.     

The sulphidation of alloys used in a fluidized bed combustor

The results of an investigation of the sulphidation behaviour of lncoloy BOOH and AISI 310 stainless steel in coal combustion conditions at temperatures between 650°C and 900°C are presented. Laboratory tests were carried out in controlled environments in the presence of solids representative of fluidized bed combustor operation. The morphology and composition of scale formed during sulphidation was examined and compared with that from tube samples removed from test rigs operated by the National Coal Board. The results have shown that at 900°C a gas mixture corresponding to the equilibrium conditions close to the coexistence point for CaS0₄, CaO and CaS on the phase stability diagram is sufficient to induce sulphidation. However, at lower temperatures an interaction between the deposit and the protective oxide is necessary and in some cases the presence of typical contaminants found in coals is an added requirement. The morphology of the corrosion products found in practice can be reproduced under controlled conditions in laboratory tests. The results are interpreted in terms of likely mechanisms of the processes involved.