Using the physically based constitutive model and processing maps to understand the hot deformation behavior of 2304 lean duplex stainless steel

RESEARCH DATA : The research data for this article are available on the University of Pretoria Bahr Dilatometer machine and the SEM post-processing machine, available on request.Please read abstract in the article.Mintek.https://link.springer.com/journal/11661hj2023Materials Science and Metallurgical Engineerin

Tracking the railway line in-service behaviour through metallurgical and mechanical property characterisation

Wear, contact-impact, fatigue and corrosion properties are important factors initiating rail track degradation and are composition dependent. This work focuses on the effect of chromium content on the metallurgical and mechanical properties of the the rail steels. Two medium steel railway tracks differing in their chromium content, alloy MS02 with 0.02 wt% Cr and alloy MS03 containing 0.72 wt% Cr, were characterised in order to predict their in-service performance as a function of their chemical composition. The microstructural analysis revealed in MS02 a relatively coarser grain size, consisting of pearlite and grain boundary ferrite. MS03 showed a fully pearlitic structure with no grain boundary ferrite. The average distance between cementite lamella in rail MS03 is shorter than that in MS02. The Rockwell C hardness values of MS02 were lower than those of MS03 which is in agreement with the microstructural analysis. As expected, a finer pearlitic structure observed in rail MS03 resulted in a superior tensile and impact properties as compared to MS02. These data indicate that MS03 with a fully pearlitic structure gives a better wear resistance and higher strength than MS02 and, it is anticipated to give a better corrosion and oxidation resistance due to higher chromium content.http://www.satnt.ac.zaam2022Materials Science and Metallurgical Engineerin

The effect of soaking time on mechanical properties of roll-bonded AA3003 and AA4045 used for heat exchangers

Due to the rising need for energy saving, high-performing automotive heat exchangers, demand has significantly grown in recent years. As a result, effective fin-tube heat exchangers are becoming more popular. These tubes are typically made by rolling flat strips of AA3003 aluminum alloys that have either one or both sides coated with AA4xxx alloys. The AA3003 type of alloy is typically used as the core, which is then covered in either AA4045 or AA4343, which melts during the brazing process to adhere the fins to the tubes. To maintain the optimal size and distribution of manganese (Mn)-containing precipitates, preheating parameters are carefully controlled. Then, longer soaking times or higher soaking temperatures result in larger precipitates, which cause the final product to exhibit poor mechanical properties. Therefore, it is crucial to optimize the different manufacturing steps, such as homogenization, soaking time, and brazing in order to achieve a high quality product. Studies on the impact of homogenization temperature and time on the microstructure of AA3xxx aluminum alloys have been conducted. However, there has been little research on the impact of soaking (reheating) time on AA3003 cladded alloys. Hence, the effects of isothermal soaking time on the microstructure and mechanical properties of AA3003 cladded with AA4045 alloy were investigated in this work. Optical microscopy (OM) and scanning electron microscopy (SEM) were used to characterize the microstructure and identify intermetallic phases. The final microstructure in terms of grain structure at various homogenization times was characterized by electron backscattered diffraction (EBSD). After the hot-rolling and cold-rolling of the as-received material, large particles of intermetallic (mainly in the form of Chinese script morphology consisting of Fe-Mn-Si) were broken into smaller particles with an increased Fe, Mn, and Si content, indicating the formation of an α-Al(Fe,Mn)Si phase. The α-Al(Mn,Fe)Si was found to be a dominant dispersoid precipitate in the modified AA3003 core. Coarsening of the Al(Mn,Fe)Si dispersoids at 505 °C was only observed at a 45 h homogenization time. The hardness trend with homogenization time was found to be similar to that after homogenization, cold working, and annealing, with exception of an increase in hardness in the latter possibly due to strain hardening (from cold-rolling).The Department of Science and Innovation (DSI)—Advanced Materials Initiative (AMI), through the Ferrous Materials Development Network (FMDN), and the Department of Minerals, Resources, and Energy (DMRE) through State Grant and Mintek.https://www.mdpi.com/journal/metalsMaterials Science and Metallurgical EngineeringSDG-07:Affordable and clean energySDG-09: Industry, innovation and infrastructur

Study of one-step and two-step quench and partition heat treatments on a medium carbon high silicon alloy using dilatometry

This study evaluated the microstructural evolution in a medium carbon high silicon steel during one-step, and two-step quench and partition (Q&P) processes using dilatometry experiments. The two-step Q&P process was carried out using different quench temperatures ranging from 180 to 260 oC. In the one-step process, Q&P heat treatment samples were held isothermally for ten minutes after quenching at specified temperatures ranging between 200 and 450oC. The two-step Q&P process yielded a higher fraction of retained austenite than a one-step Q&P process. During the isothermal hold step, the volume expansion due to carbon partitioning and austenite decomposition behavior was interpreted by experimentally determined strain values. For the one-step Q&P process, the austenite decomposition kinetics above and below the Ms temperature differed, as evidenced by the JMAK parameters. The TTT diagram generated for the one-step Q & P process showed a “swing back” at a temperature of around 355oC.Ferrous Metal Development Network (FMDN).http://www.satnt.ac.za/index.php/satntam2022Materials Science and Metallurgical Engineerin

Effect of hot rolling parameters on recovery mechanism in 436 (17%Cr, Nb-Mo) ferritic stainless steel

Ferritic stainless steel (FSS) grades are widely used for applications that require high strength and corrosion resistance. Their cost and versatility in the steel market have attracted a lot of interest from both industry and academic research. Despite their desirable properties, these steels grades experience surface defects as a result of microstructural evolution that evolves due to softening mechanism. The current study simulated the roughing hot rolling processes of AISI 436 (17%Cr, Nb-Mo) FSS to study the effects of inter-pass time and strain on the precipitation behaviour and the softening mechanisms in 436 FSS. The softening mechanisms and the resulting microstructures were investigated using SEM-EBSD technique. The results revealed Particle Stimulated Nucleation of new grains during the simulated roughing rolling which promoted recrystallisation due to strain accumulation. Stored deformation energy was found to increase with an increase in interpass time and strain.University of Pretoria; MINTEK and Columbus Stainless Steel (Middleburg).http://www.satnt.ac.za/index.php/satntMaterials Science and Metallurgical Engineerin

Study of wear performance of wheel and rail steels under dry sliding conditions

The demand for efficient railway services has significantly increased in the past years due to an increased demand for the high-speed transportation of goods with high loads. The increase in loads and velocities has resulted in increased problems associated with rolling contact fatigue (RCF), rolling and sliding wear on the wheel and rail materials causing a reduction of service life of wheel/rail systems. Rail operating companies spend significant funds in maintenance and replacing damaged rails and wheels caused by wear. In addition, unscheduled maintenance due to wear and RCF often lead to poor availability of railway networks. For this study, dry sliding wear was investigated on wheel and rail steels using RTEC Multi-Function Tribometer. The results demonstrated that the rig was successful in simulating sliding wear, and that the fractions of the wear components could be varied, and it also provided instrumentation. Information on coefficient of friction against sliding distance and applied force were obtained which were used to compare sliding wear performance of both wheel and rail steels. The wheel was found to perform better than the rail under the same conditions due to its high initial hardness values and smaller interlamellar spacing.Mintekhttp://www.satnt.ac.za/index.php/satntam2022Materials Science and Metallurgical Engineerin

Effects of lubrication on wear and rolling contact fatigue behavior of class B wheel steels against R350HT rail steels using a twin-disc wear simulator

Wear and rolling contact fatigue (RCF) are major causes of delays and unavailability of rail systems. The presence of lubricants at the rail and wheel interface influences wear and RCF. Lubricants include naturally occurring types, such as water from rain and leaves from trees next to rail lines, and materials applied on purpose to help improve adhesion and friction, such as friction modifiers, greases, and traction gels. The aim of this work was to study the wear behavior of AAR class B wheel versus R350HT rail materials in the presence of water and oil in comparison with the dry condition. There is currently a lack of knowledge regarding the combination of these materials in a twin-disc simulator, and this work provides information on their impact on RCF and wear performance for use by the rail industries. It was found that wear was much lower when water or oil was introduced at the wheel–rail interface compared to dry conditions, for all slip ratios. When water was used, the main cause of RCF was found to be fluid crack pressurization. The RCF cracks were also observed under dry contact.Mintek South Africa.http://www.tandfonline.com/loi/utrb202024-06-08hj2024Materials Science and Metallurgical EngineeringSDG-09: Industry, innovation and infrastructur

A study of smart materials for roofbolts application in the mining industry

M.Tech.This dissertation details the research performed into the development of a smart material for roofbolt application in the mining industry. It describes the methodology and research done to design a smartbolt using a metastable austenitic stainless steel. A number of measuring devices were used to study the properties and structure of this smartbolt alloy. These devices include a Ferritescope and a Krautkramer USM 25 DAC ultrasonic sound velocity measuring instruments. The dissertation details the development, processing, laboratory and field testing of the smartbolt alloy. The designed alloy was found to have much stronger workhardening effect, causing it to have a relatively low ductility. Therefore, the threads on the roofbolts produced from this alloy were machined instead of thread rolled. It was also found that the incubation strain of the smartbolt alloy to be a' transformation in the smartbolt alloy loaded in uniaxial and biaxial tension. It was found that the von Mises effective strain criterion gives a reasonable correlation of transformation kinetics. Using the modelling method, it was found that the failure strains for the rock are not the same as those for the smartbolt alloy. All the smartbolts installed in the haulage tunnel (level 94 of mineshaft) showed a pattern of increasing longitudinal ultrasonic velocity (load) with time. This was due to the fact that mining was taking place above the area (in level 93 of the mineshaft)