Advanced Steel Metallurgy: Miscellaneous
Program Organizers: Chirag Mahimkar, Big River Steel; Justin Raines, SSAB Americas; Kip Findley, Colorado School of Mines; Alla Sergueeva, NanoSteel Company Inc; Daniel Branagan, The NanoSteel Co
Wednesday 2:00 PM
November 4, 2020
Room: Virtual Meeting Room 39
Location: MS&T Virtual
2:00 PM
Digital Innovative Design (DID) for Reliable Casting Performance of Steel Castings: Maria Diana David1; David Poweleit1; Raymond Monroe1; 1Steel Founders' Society of America
Steel castings have been designed using legacy, heuristic approach with workmanship quality standards. The Digital Innovative Design (DID) for Reliable Casting Performance aims to provide design tools that will support engineers design steel castings more reliably. Two design strategies are being developed: (1) a design allowable code-based process with embedded Non-Destructive Testing (NDT) and (2) a lower bound modeling-based practice with quantitative NDT. This presentation will go over the research being done to support these new methodologies. Statistical analysis of mechanical properties of common cast steel grades is being done similar to MMPDS approach in determining A and B design allowables. The effect of indications on properties is evaluated using fracture mechanics. Quantitative NDT that are related to performance are being developed.
2:20 PM
Strain Aging Embrittlement of Structural Steel
: Morimichi Kimura1; Kazutoshi Ichikawa1; Tomohiko Omura1; Masaki Mizoguchi2; 1Tohoku University; 2Nippon Steel Corporation
There is a great industrial concern that toughness of strained part of building structural steels, such as press columns, is deteriorated by strain aging. Strain ageing is a time-dependent phenomenon caused, even at ambient temperature, by diffusion of interstitial solute atoms (e.g., nitrogen) to vicinities of dislocations of plastically deformed steel. In this research, deformation at room temperature and aging were performed on the steel plates and changes in absorbed energy of Charpy impact tests were examined to evaluate toughness of steels. The effects of microstructures on strain age-hardening were then investigated by nanoindentation. Effects of steel manufacturing process (as-rolled and thermos-mechanical controlled processes), magnitude of strain, aging process and contribution of each microstructural (ferrite and pearlite) component were thoroughly quantitatively identified.
2:40 PM
Double-Twist Torsion Testing to Assess Partial Recrystallization in Microalloyed Steels: Trevor Ballard1; John Speer1; Kip Findley1; Emmanuel De Moor1; 1Advanced Steel Processing and Products Research Center, Colorado School of Mines
The non-recrystallization temperature (Tnr) represents an important parameter in the development of controlled rolling schedules for processing microalloyed steels. Tnr has been used to define the transition from complete to incomplete austenite recrystallization, although multiple and slightly varying definitions exist. Controlled rolling usually involves deformation at higher temperature to refine the austenite via recrystallization above Tnr, with finishing at a lower temperature where recrystallization is fully suppressed to enable austenite “pancaking.” Thus, Tnr is important since knowledge of the temperatures where transitions in austenite recrystallization behavior occur is required for effective microstructural control in the final product A double-twist torsion test has been applied here to a Fe 0.065C 0.060Nb 0.021V (wt pct) microalloyed steel for experimental determination of the temperature region where partial recrystallization occurs. The double-twist torsion test allows the effect of multiple deformation and recrystallization cycles on Tnr to be assessed while maintaining a link to the austenite microstructure via measurements of fractional softening. Pairs of isothermal torsional deformation steps with a true strain of 0.2 per pass and a shear strain rate of 5 s-1 separated by an interpass time of 5 s were applied to a single specimen in the range of 1200 to 800 ˚C in 50 ˚C decrements. The extent of recrystallization in the austenite was estimated from the extent of softening that occurred during the interpass time. Three methods used to determine fractional softening were applied to the experimental data and compared. The temperature region of partial recrystallization was estimated from the fractional softening measurements and compared to Tnr determined using traditional methods of double-hit compression and multi-step hot torsion testing.
3:00 PM
Effect of Coiling and Annealing Temperature on Nb precipitation, Microstructure and Mechanical Properties of HSLA: Lei Cui1; Wenjun Wang2; Deshun Chen1; Yonggang Liu1; 1Ma Steel; 2Citic Metal Co., Ltd
High Strength Low Alloyed(HSLA) steel has found its worldwide use in multiple industries such as automobile, oil and gas. Nb is usually introduced in the automotive HSLA grade with yield strength exceeding 300MPa. However, variation of yield strength tends to increase as Nb addition is above than 0.04%. To address this scattering, dual micro-alloying strategy with Nb and Ti was applied on galvanized HS420LA grade. The effect of annealing and coiling temperatures on microstructure and precipitation of Nb-rich particles were systematically studied using optical microscope, scanning electron microscope and transmission electron microscopy. Mechanical properties of the Nb+Ti micro-alloyed HSLA420 were compared with that of the Nb-alloyed counterpart. Optimized process with appropriate annealing and coiling temperature results in a significant narrowing of single-coil variation in yield strength, the ratio of steel coil yield strength variation above 20 MPa from 28.7% to 1.5% based on industrial production data
3:20 PM
Silicide Strengthened Ferritic Alloy - A New Method of Wear Protection in Nuclear Environments: Rahul Unnikrishnan1; David Bowden2; Michael Preuss1; 1The University of Manchester; 2UK Atomic Energy Authority
Cobalt-based alloys have been traditionally used for hard facing applications in pressurized water reactors. There has been an interest in developing cobalt-free hard facing alloys as cobalt wear debris transported to reactor core becomes reactive 60Co, increasing radiation levels. A high-hardness intermetallic phase, named π-ferro-silicide, was recently discovered in a stainless steel hard facing alloy. This study involves developing cobalt and carbon-free silicide based hard facing alloys. Two high strength silicide based alloys, one with a duplex ferrite/silicide and other with a triplex ferrite/austenite/silicide phase has been developed. These high strength alloys can accommodate more than 20% of compressive strain while showing maximum strengths of 1.5-1.75 GPa. The high strength is a result of uniformly distributed fine precipitates of silicide phase in ferrite matrix achieved by thermo-mechanical processing. Also, the orientation relationship between silicide and ferrite interface make these alloys promising material for wear-resistant applications.
3:40 PM
Triple Nano-precipitate Strengthened Austenitic Steel: Colin Stewart1; Richard Fonda2; Keith Knipling2; 1National Research Council Associate at the U.S. Naval Research Laboratory; 2U.S. Naval Research Laboratory
FCC austenitic steels lack the ability to achieve significant solid solution strengthening, thus precipitate phases may instead be employed to achieve alloy strengthening upon ageing. A cost-effective Mn-stabilized austenitic steel has been engineered via an ICME approach, which demonstrates precipitation of three nano-scale phases: (i) insoluble Cu (FCC) particles; (ii) ordered intermetallic β-NiAl (B2) precipitates; and (iii) carbides. The evolution and interaction of these precipitates has been investigated across ageing times by atom probe tomography (APT) in combination with transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD). These techniques help elucidate the mechanisms of particle formation, as well as the crystallographic relationships between platelet-shaped β-NiAl odered BCC precipitates and the FCC matrix. Results are discussed in the context of refining computational models for an efficient ICME alloy design approach.