Structural steel final mechanical properties of strength and ductility are predominately generated by the final ferrite grain size/packet size and homogeneity of that ferrite grain size/packet size through the cross-sectional area. Forty to seventy percent of the strength components comes from how fine of a final cross-sectional ferrite grain size/packet size that can be realized. All the ductility properties of structural steels for a given microstructure are driven by how fine the final cross-sectional ferrite grain size/packet size AND how homogenous of a cross-sectional final ferrite grain size/packet size that can be developed. One key ductility property of structural steels used in construction and energy transmission applications is fatigue. Both low and high cycle fatigue can be realized in these end applications, however low cycle fatigue is typically the predominate mechanism. In construction applications the environment for fatigue is typically air, such as in wind towers or high-rise building construction. In energy applications, there is an interest in gaseous hydrogen as an alternative fuel source to fossil fuels. In these applications, economical transportation of gaseous hydrogen is typically done in pressure vessels or pipelines and requires operating pressures in the 800-3000 psi range. Various structural steel microstructures primarily related to API grade pipeline steels have been fatigue tested and published in both hydrogen and air over the past 10 years by NIST and other US National Laboratories. NIST in particular has developed a unique multi specimen fatigue testing device with capability for both air and high pressure gaseous hydrogen atmosphere hence allowing for capabilities to significantly increase productivity of the fatigue test. One of the microstructures fatigue tested by NIST is a production produced API X60 HIC Sour Service plate grade consisting of a predominately pure microstructure of polygonal ferrite with a low carbon (0.03%), higher Nb content (0.085%) allowing for higher temperature processing (HTP). This microstructure has performed well in both 800 and 3000 psi hydrogen pressure fatigue testing. However, one of the questions that has risen from this testing was while the overall microstructure performed well in fatigue testing what would happen to the fatigue performance if the same alloy design and same predominate pure microstructure of polygonal ferrite had variability in cross-sectional final ferrite grain size homogeneity. To study the fatigue performance of a common microstructure with different cross-sectional final ferrite grain size homogeneity, laboratory produced plate trials were developed duplicating the original API X60 HIC Sour Service alloy design but designing the rolling process to create two different cross-sectional final ferrite grain size/homogeneity situations in the laboratory produced plates. One design utilized a properly optimized rolling strategy to generate an optimum Type I Static Recrystallization behavior and Type II No-recrystallization behavior for the niobium content. The second rolling design strategy was a non-optimized strategy for Type I Static Recrystallization and Type II No-recrystallization behaviors. This “optimized” and “non-optimized” resulted in distinct differences in the cross-sectional final ferrite grain size and homogeneity. Since ductility properties are significantly controlled by high angle grain boundaries (HAGB, >15°), microstructural characterization of the laboratory produced plates of both low angle grain boundaries and high angle grain boundaries was performed. The goal of creating similar microstructures in the two laboratory plates with distinctly different cross-sectional final ferrite grain size/homogeneity was realized. The microstructure in both the optimized and non-optimized plates was predominately polygonal ferrite. The optimized produced plates had an average cross-sectional HAGB ferrite grain size of 3.2 µm with 20% of the cross-sectional HAGB > 8.5 µm. The non-optimized produced plates had an average cross-sectional HAGB ferrite grain size of 4.5 µm with 20% of the cross-sectional HAGB >16.5 µm. Both will be fatigued tested in air and high-pressure gaseous hydrogen to determine the effect the cross-sectional average and homogeneity has on final fatigue performance. This will be compared to the original production produced grade. In addition, austenite grain size evolution modeling with MicroSim® will be done utilizing the processing parameters from the laboratory rolling for comparison to the final polygonal microstructure characterized.

Mathematical models for rolling force calculation during hot rolling are crucial for both automatic mill operation and prediction of steel behavior and of mill capacity, especially for development of new steel grades and improvement of the existing ones. In literature, the models are based usually on the calculation of steel mean flow stress (MFS), firstly, followed by a force model based on MFS. This approach was applied to a large volume of industrial data of coils produced at Usiminas’ plant in Ipatinga, rendering unsatisfactory results. Then, the empirical model developed by Schultz was applied to calculate directly the force, with further fine tuning the model with a linear regression taking into account steel chemical composition. This approach led to force prediction capability better than the traditional models based on the binomial MFS-force presented in literature, markedly for plain CMn steels and IF steels. In such cases, more than 90% of force predictions were inside the ±10% error margin, considering the front stands of hot strip mill.

Abstract: The corrosion behavior of three kinds of medium-Cr rolled steel pipeline steels in carbon dioxide collecting and transporting environment at different temperatures was studied. The results shew that the 5Cr sample was most affected by temperature. When the temperature rised from 30 °C to 90 °C, the corrosion rate increased from 0.1201 mm/a to 1.8698 mm/a, which was increased 15.6 times. The corrosion rate of 7Cr steel at 30 °C was similar to that of 5Cr steel. However, as the temperature increased, the corrosion rate rised slowly, which was increased 2.4 times at 90 °C. The corrosion rate of 9Cr steel was not obvious with temperature, and it was always below 0.06 mm/a. The thickness of the corrosion product film of the three samples gradually increased below 70 ° C, and suddenly increased above 70 ° C. This was related to the negative temperature coefficient of the solubility of FeCO3, and the thickening of the product film also affected the ion exchange of the cathodic reaction. An increase in the Cr content contributed to grain refinement and increased the proportion of the small-angle grain boundaries. More fine grains mean an increase in the total length of the grain boundaries, which could provide a diffusion channel for the free Cr element; on the other hand, the low-angle grain boundary structure was more orderly, with a lower free volume and lower interface energy. Under the combined effect of both, 9Cr steel and 7Cr steel had smaller micro-area potential difference and better corrosion resistance.

Optimized CAPEX, OPEX, yield and product quality and introducing of new products in new process equipment as well as by upgrading of existing facilities are the key factors for success and profitable operation.
For this, innovation in processes and design is crucial. Danieli is supporting these customer and market demands by offering innovative and well-thought-out process equipment and upgrade solutions.

In 2019, Danieli has put into operation a complete cold processing complex in Turkey, which includes a new continuous pickling tandem mill featuring latest generation of market oriented technologies.
In this line, dedicated to run a broad range of size and grades (IF to AHSS as DP1000), the highly efficient Turboflo® pickling process was selected. This technology already proved its efficiency and ability in former applications handling ultra-thin gauges at speeds even exceeding 400 m/min in the pickling tanks.
The 5-stand 6-high OSRT tandem mill features important developments, like actuators to improve significantly strip flatness and a special air knife arrangement on the tandem mill exit side to generate perfect strip surface cleanliness.
Fast startup and thin gauge rolling already short time after production start are further proves for the technological superiority of this innovative mill design.

In dis-continuous operating rolling mills, the Danieli Yield Boost technology is the right answer to significantly increase material yield with limited CAPEX. As an example, the usual way to operate a cold reversing mill for strip threading and tail-out is to open the roll gap. Danieli developed a method for already partial strip thickness reduction during threading in and tail out phases. Operating results at a two-stand reversing mill show an impressive increase in material yield. Depending on specific conditions, this technology can create annual savings in six or even seven-digit US Dollar figures.

In the last 10 years, Danieli has supplied most of the worldwide construction and high speed galvanizing plants. In those lines, the zinc pot is the most effective area to reduce costs in operation and consumables and increase the product quality.
Danieli has spent significant efforts in developing most advanced technology for the wiping process. A fully integrated system solution has been designed to perform a wiping process with high quality, economy, accuracy and productivity.
Center part is the newly developed X-Jet / Compact X-Jet air knife. Its innovative design creates highly stable static pressure with direct impact on the shear effect, and extremely accurate pressure along the strip width. The new generation electromagnetic stabilizer is cutting down strip vibrations and improves strip flatness, leading to further increase in wiping process.
Robotic systems are supporting to reduce human intervention and health risks in the zinc pot area.

These technological packages are ideal also for upgrade of existing lines, typically generating a return of investment in less than 1 year, proven in latest revamp installations.
On top, Danieli has developed advanced automation systems including L2 and L1 controls to achieve outstanding product performances.

The steel sheets coated with Zinc and their alloys are widely used in the automotive industry due they exhibit excellent corrosion resistance, together with good performances of formability and weldability. The corrosion resistance property is acquired through the galvanizing process; the coating layer protects the metal against direct contact with the corrosive environment.
Among the largely range of steels in the market, the most important are galvanized, called GI. The GI coating can be divided into two main layers, the first composed of intermediate intermetallic phases of iron-aluminum-zinc, called the intermetallic layer. Its formation and composition may vary according to the characteristics of the substrate used (steel grade and surface texture), the chemistry of the zinc bath and the process parameters used during its production. The second layer is formed mainly by the zinc itself.
The characteristics and properties of the GI coating have a direct relationship with the intermetallic layer formation, which is responsible for providing a dial between the metal substrate and the zinc layer, affecting the anchoring of the zinc layer itself. Thus, the intermetallic layer characterization becomes extremely important to the final characteristics of the total GI coating layer in the set.
The study aims to present differentiated metallographic preparation techniques used to characterize intermetallic layers in steel samples of GI coated produced by hot dip. The samples were collected at coils produced with two different steel grades. The different chemistries studied were: IF (Interstitial Free) and TRIP780 (Transformation Induced Plasticity) steels. Due a significant difference in their chemical composition (addition of alloying elements), this grades were chosen for evaluating the substrate composition influence of the intermetallic layer formation. The TRIP steels present higher complexity chemistry due to the addition of high levels of alloying elements, such as Si, Al, Cr and Mn.
The intermetallic layers were characterized for their morphology using different techniques of dissolution of the zinc layer. For the surface analyzes, it was used the immersion process in different chemical solutions, ultrasonic cleaning and metallographic procedures. For the section analyzes, were employed techniques based on different positions and angles during the bakelite preparation, providing greater amplitude of the field of vision of the interest region. The images were analyzed using a scanning electron microscope, and their chemical compositions were obtained by the energy dispersive X-ray spectrometer (SEM / EDS).