Abstract: Microstructure evolution and tensile properties were studied in a bainitic pipeline steel grade by performing a number of physical simulations on samples machined out of an industrially produced transfer bar. In these simulations, the cooling interval between roughing and finishing stages (tV) was varied from 5 s to 180 s. The austenite status after this cooling interval, regarding the prior austenite grain size and precipitates, simulates the condition of austenite before entering the finishing mill. The finishing parameters and the subsequent cooling strategy were kept unchanged throughout all the applied simulation processes. The gradual increase in tV resulted in a gradual increase of the granular bainite phase on the expense of the aciculare ferrite. This resulted in an incremental decrease in ultimate tensile strength and yield strength with increasing tV. However, this behavior approached a steady state condition after which the tV has limited/insignificant effect on the ultimate-and yield strength. This saturating value of tV is process parameter dependent.
Abstract: Due to the exploration of gas and oil sources in remote regions with harsh environment, the pipe line designers are faced with the challenging conditions. Especially in the cases where displacement-controlled loads are the predominant design condition, such as ground movement, strain-based design is applied instead of stress-based design to build safer pipelines and to assure the integrity of the lines along their lifetimes. It requires steels to have a large strain hardening capacity, long uniform elongation, and good toughness to achieve a well-defined and sufficient plastic deformation. In order to fulfil the requirements, all the processing steps are supposed to be well designed, for example, the chemical composition, microstructural design, thermo-mechanical controlled process (TMCP) and heat treatment, etc. In general pipe line steel has a low carbon, high manganese content combined with a certain amount of micro-alloying elements as Nb, Ti and sometimes B. Using Thermo-mechanical rolling and cooling schedules excellent combinations of strength and toughness can be established. To successfully produce steel plates for strain based design pipe lines the actual heating rolling and cooling technologies must be developed further as well as the equipment to produce such steel. The paper gives an overview about modern plate mill equipment and new setup strategies for the production of heavy plates X70 to X100 as well as thethermo-dynamic simulations used during the development.
Abstract: In this paper the microstructure evolution of an iron-silicon alloy with 3.2 wt.% silicon throughout the manufacturing stages hot rolling, cold rolling and annealing is presented. Starting with a 35 mm thick feedstock, which was hot rolled to 1 mm, with different cooling conditions, the material was cold rolled to a final thickness of 0.3 mm and final annealed under same conditions to show the influence of the hot rolling on the texture and microstructure of the final annealed material.
Abstract: In the scope of the optimization of multi phase steels, e.g. for the automotive industry, control of the microstructure is essential to tailor the mechanical properties. In this study, two cold rolled steels varying in carbon content were annealed and cooled under different laboratory conditions. The microstructure is investigated using optical and electron microscopy and EBSD. The results are correlated to the mechanical properties obtained from tensile, hole expansion and bending test. It is found that tensile strength and elongation are mainly dependent on martensite volume fraction, while yield strength is less affected by chemical composition or annealing treatment. In contrast, hole expansion capacity and maximum bending angle are significantly improved by the homogenization of the microstructure which is independent of strength and elongation. The microstructure homogeneity is expressed by analyzing the Lorenz curves derived from the kernel average misorientation from EBSD measurements.
Abstract: The production of hot-rolled sheets of high-strength and wear-resistant special structural steels by direct quenching from the rolling heat is a cost effective and energy-saving alternative to traditional production via downstream quenching the previously cut-to-length plates. Reaching the required strength and toughness parameters in combination with best flatness of the sheets requires strict compliance with the pre-set rolling and cooling conditions over the entire strip width. Using two high-strength low-alloyed steels, plant trials have been carried out to study the effect of the cooling conditions and the coiling temperature on mechanical properties, impact toughness and flatness of cut-to-length sheets made of hot-rolled strip. The results showed that by applying optimized cooling pattern and low coiling temperatures, high-strength steel sheets with outstanding mechanical properties and good flatness can be produced.
Abstract: The paper focuses on experimental and numerical investigations of own designed, casted and then hot rolled martensitic steel. In order to understand the effect of the thermo-mechanical rolling parameters on the formation of the microstructure and resulting mechanical properties many tests and experiments have been performed. Martensitic steels offer satisfied balance of cost production, light weight and mechanical properties. These characteristics are achieved by using low alloy steel as a basis, and strict control of rolling conditions, strain rate, cooling rate and coiling temperature.
Abstract: After 5 years from start-up, Arvedi ESP Technology has achieved outstanding performances in terms of production, products and quality. The technology has proved particularly suitable for the production of thin gauge strips (< 2 mm). This paper presents the experiences in the production of high strength and advanced high strength steels, such as micro-alloyed S550MC, dual phase DP600 and ferritic bainitic HR60 in thin gauge strips on the ESP line of Acciaieria Arvedi S.p.A. in Cremona. Some aspects of the industrial production process for these steel grades are highlighted on the basis of casting and rolling parameters and microstructural and mechanical investigation.
Abstract: Magnesium alloys containing rare earth elements have better properties in terms of of formability, strength and corrosion resistance. Due to the tight supply situation these elements should be partially or complete substituted, for example by calcium. Microstructural studies of casted alloys of new compositions, and the influence of various heat treatments on their microstructure are investigated. The mechanical properties of the rolled materials are also presented and discussed. The works presented in this paper are results of the ongoing BMBF project SubSEEMag.
Abstract: Magnesium alloys containing rare earth elements offer excellent strength at room temperature as well as at elevated temperatures and are distinguished by a high ignition-resistance. However, with regard to cost efficiency and the conversation of resources, these alloys are not suitable for commercial industrial applications. Therefore, the research project SubSEEMag at the Institute of Metal Forming/Technische Universität Bergakademie Freiberg focusses on the development of alternative alloy compositions, which meet the requirements on materials properties of magnesium alloys for industrial applications and production costs. Several magnesium alloys containing zinc, aluminum, manganese and calcium were poured in cylindrical molds at the Helmholtz-Zentrum Geesthacht. The characterization of the as-cast condition was carried out by light and scanning electron microscopy. Phase compositions were determined using EDX analysis. The Mg alloys were homogenized at different temperatures. Afterwards, hot rolling to a final thickness of 2.7 mm was conducted. The influence of temperature and time of the annealing on the microstructure and the mechanical properties of the hot rolled condition have been investigated. The results were discussed in comparison to commercial available Mg-RE alloys.