The detrimental impact of argon bubbles on caster mold fluid flow and slab defect formation is well known among hot metal circles. Casters around the world struggle with argon flow optimization to minimize mold level fluctuations and slab defects.
Argon injection is required to protect aluminum-killed liquid steel from coming in direct contact with air to minimize the risk of creating new alumina inclusions by re-oxidation. The gas also protects the refractory channel from clogging. The liquid steel jet entering the mold through the SEN (submerged entry nozzle) ports and circulating argon bubbles create turbulent fluid flow conditions inside the mold.
Trials were conducted at the No. 1 continuous caster at Hamilton, Ontario-based ArcelorMittal Dofasco (AMD) to optimize argon injection through the refractory stack (stopper rod, tundish upper nozzle, plate and SEN]). Results were inconclusive.
Taking a fresh approach, AMD used computational fluid dynamic modeling (CFD), experimental water modeling, and caster trials to understand the issue and solve the problem, focusing initially on argon injection through the upper nozzle. The argon flow study lasted about 18 months. Research on other components continues.
Researchers found that removing argon injection through the tundish upper nozzle for a short period reduced the biased flow conditions in the mold during a caster trial. CFD model results revealed that argon gas bubbles exit the tundish upper nozzle inner surface from both the circumferential and vertical channels, causing the argon injection to be biased toward the vertical channel.
That biased argon injection was found to be the source of biased fluid flow conditions in the mold, even though the SEN ports were unclogged. Based on those findings, the vertical argon channel in the tundish upper nozzle was sealed. Improvements in argon back pressure signal and mold level deviation were observed during the trials.
This design change has been permanently implemented at both casters at AMD.
ArcelorMittal Cleveland was asked by an automotive customer to develop and produce a new, advanced high-strength steel (AHSS) grade offering improved strength and formability.
Working with the parent companys Global Research & Development team, ArcelorMittal Cleveland developed GA DP 1180; the number represents the minimum tensile strength of the steel in megapascals. The new steel has qualified for six different car parts for one vehicle. Commercial production of that vehicle is set to begin this summer, ramping up to 30,000 units a month.
Although ArcelorMittal Clevelands hot-dip galvanizing line is well suited to produce the new steel, it had not yet actually processed the material. To produce DP 1180, a new set of processing logistics had to be developed to maintain the materials microstructure throughout the process. Commercial production began in January.
To meet the customers schedule requirements, ArcelorMittal could not allot the time typically required to follow a traditional development cycle in qualifying GA DP 1180. Instead, the new steel was developed and tested in existing production facilities not in the lab on an accelerated timeframe.
Pursuing such an approach, required unprecedented collaboration between Global R&D and Clevelands operations teams. In an industry beset with persistent organizational silos, the research and production groups formed a team to address problems in steelmaking, casting, hot rolling, cold rolling, and galvanizing.
For example, the Cleveland plant struggled early on to achieve uniform hardness across the steel strip during the cold-reduction phase. That caused problems downstream for the galvanizing line and ultimately for the customer.
To address that challenge, the team had to completely re-think the traditional process flow and subsequently introduced a new batch-anneal step to homogenize the products properties before cold rolling. Operating technicians on the shop floor worked with quality specialists and R&D engineers to test several annealing cycles until they achieved the desired properties and uniform hardness.
There is no scarcity of potential hazards overhanging North Americas highways and the same holds true in the context of the metals industry, where the dangers inherent in securing and covering loads on flatbeds can prove dangerous or worse and intensify in bad weather.
Canada is notorious for its harsh weather, and when staff at Gerdau Steels plant in Whitby, Ontario, outside Toronto found commercial safety systems for drivers securing loads to be unsatisfactory, they decided to develop their own.
The result is a custom system designed to protect truck drivers accessing flatbed trailers four feet high or taller. To meet the local needs at Whitby, Gerdau pulled together members of its safety, engineering, logistics, maintenance, and procurement teams. Together, they developed a cantilever design which prevents snow, ice, and slush from interfering with the systems platforms.
The system had to be designed to accommodate a variety of flatbed trailer sizes and heights. Whitbys tarping building is located a short drive from the warehouse. To keep loads dry, the previous practice called for truck drivers to install temporary protection over their loads. The solution was a 60-foot long stretch of thin plastic that each driver can easily apply.
The long-term solution was to build a 13,000-square-foot tarping building as well as a landscaped earth berm using excavation spoils to control traffic flow and eliminate offsite soil disposal. The new Truck Tarping Fall Prevention System (TTFPS) was designed to be easy to operate. To ensure its effective use, the implementation team developed training that could be completed quickly, on site, and available in English, French, and Spanish.
The TTFPS operates in extreme climates ranging from -30C to +30C and allows for snow accumulation and plowing. It does not affect truck time on site. The TTFPS is automated, sequenced, and operates in a way that minimizes the potential for unsafe practices or situations.
Gerdau Whitby invested C$ 1.5-million in its Truck Tarping Fall Prevention System (TTFPS), and similar systems have already been installed at other Gerdau sites.
U.S. Automotive Materials Partnership LLC
The United States Automotive Materials Partnership (AMP) is a part of the U.S. Council of Automotive Research, a collaborative automotive technology development joint venture formed by Fiat Chrysler, Ford, and General Motors.
AMP applied an integrated computational materials engineering approach to develop lightweight Third Generation Advanced High Strength Steels (3GAHSS) specifically for application in vehicle sub-assemblies. The team developed and produced two new 3GAHSS materials exhibiting high strength, and exceptional ductility that met U.S. Department of Energy (DoE) requirements.
Production of the two 3GAHSS was expanded from small laboratory heats of approximately one pound used to generate coupons, to larger heats of approximately 450 pounds from which small scale T-shaped components were formed that emulate a critical part of an automotive B-pillar.
A new experimental method was also developed to measure the non-homogenous in-situ transformation of meta-stable retained austenite to martensite as a function of strain and strain path. The method uses stereo digital image correlation coupled with high-energy, synchrotron x-ray diffraction at Argonne National Laboratory. The collaborative approach involved academia, national laboratories, and industrial resources.
Team members developed, calibrated, and implemented a 3GAHSS model in the commercial simulation software LS-DYNA. Included were crystal plasticity for micro-structure based modeling, as well as a homogenized (state variable) constitutive model approach for implementation into commercial codes. That will also facilitate forming material models.
The model substituted 3GHASS for AHSS in an automotive side structure and optimized the design to achieve a performance-neutral design and 29-percent mass savings with material gauges below 1.0 mm. A state-of-the-art data model was developed for curating relevant theoretical and experimental data using the institutional repository application at the National Institute of Standards Technology in Gaithersburg, Maryland. Metadata development was included.
DoE targets for a high-strength, exceptional-ductility steel are 1,200 MPa ultimate tensile strength, 30-percent total elongation; for exceptional-strength, high-ductility steel targets are 1,500 MPa ultimate tensile strength, 25-percent total elongation.
Arkansas Steel Processing
Pipe and tube strength levels continue to increase from grade X70 to grade X80, with the next generation of grade X100 already in development. Along with that has come a growing demand for new coil-slitting capability to handle heavier, thicker, and stronger coil steels.
Arkansas Steel Processing (ASP) has developed a five-cut slitting line that it claims is unique among North American service centers. The company has been cutting steel on the line since late 2016 and says initial response from customers has been positive.
It comes as no surprise to industry insiders that coils shipped for slitting are not always the flattest and smoothest. Nor do they need to be. Center buckle is irrelevant for strips measuring just a few inches. ASPs objective was to slit the heaviest, thickest, strongest material available in coil on a high-production basis.
By offering a heavy-tension leveler on a slitter, which is new in North American service centers, Arkansas says it can now supply flatter slit steel and increase productivity in high-volume stamping and roll-forming applications. ASP is targeting wider cuts where the tension leveler provides a competitive advantage. The company anticipates that the new line will meet the needs of the pipe and tube market over the next 10 years.
The line is capable of slitting up to 5/8-inch Grade X100 with five cuts. The tension leveler, within the slitting line, can handle up to ¼-inch Grade X60 and improve shape. To avoid the potential of surface issues, the slitting line features all alternating-current, high-torque, vector drives with excellent speed and torque control.
The ability to handle 100,000-pound coils, the largest in a North American service center, increases productivity, reduces changeover and splices in tubing, and decreases scrap generation in heavy stamping and roll-forming.