Advancements in Steel Structural Refinement: Session I
Sponsored by: AIST Metallurgy — Processing, Products & Applications Technology Committee
Program Organizers: Emmanuel De Moor, Colorado School of Mines; Jose Rodriguez-Ibabe, RIcon; Charles Enloe, Steel Dynamics
Tuesday 8:00 AM
October 11, 2022
Room: 406
Location: David L. Lawrence Convention Center
Session Chair: Emmanuel De Moor, Colorado School of Mines; Charles Enloe, CBMM
8:00 AM
Effect of Nb Microalloying on the HAZ Grain Growth Kinetics and Precipitation Dissolution during Welding: Iņigo Iturrioz1; Nerea Isasti1; Jose Rodriguez-Ibabe1; Pello Uranga1; Nobuyuki Ishikawa2; Daichi Izumi2; Douglas Stalheim3; David Jarreta4; David Martin4; 1CEIT and TECNUN (University of Navarra); 2JFE Steel Corporation; 3DGS Metallurgical Solutions, Inc.; 4CBMM Asia
Low carbon Nb microalloyed steels, combined with thermomechanically controlled rolling, are usually employed for producing modern high strength/high toughness linepipe steels. Property control in the welds is usually a critical point in these applications. Therefore, alloy design and hot rolling strategy must be carefully defined to avoid austenite grain size coarsening in the heat affected zone (HAZ) and to achieve an optimum combination between strength and toughness. In order to analyze the effect of Nb on the competition between austenite grain growth and dissolution of precipitates during welding, laboratory heat treatment simulations reproducing the heating cycle were carried out for different low carbon Nb microalloyed steels. The initial precipitation state in the plates was also modified by different hot rolling strategies. The interaction between austenite grain growth and precipitation is modeled, in order to predict the evolution of the microstructure in the HAZ after welding.
8:20 AM
Phase Transformation Behavior of Fe-10wt.% Ni Steel Weld Metal: Daniel Bechetti1; Jennifer Semple1; Matthew Sinfield1; 1Naval Surface Warfare Center, Carderock Division
Researchers at the Naval Surface Warfare Center, Carderock Division and Carpenter Technology Corporation have collaborated to develop a high-strength steel solid wire welding electrode based on the Fe-10wt.% Ni metallurgical system (dubbed ‘10Ni steel’). As development of the 10Ni steel welding consumable progressed, a more granular understanding of its on-heating and on-cooling transformation behavior was needed to explain microstructural and mechanical property observations and to provide data for increasing the accuracy of computational models. This presentation reports the results of Gleeble-based dilatometry testing of 10Ni steel gas metal arc (GMA) weld metal and use of the resulting data to explain effects of chemistry and heat affected zone (HAZ) peak temperature on martensite transformation behavior, effects of heating rate on recrystallization, the development of residual stresses during weld fabrication, and the importance of recrystallization to mechanical properties.
8:40 AM
Intercritical Annealing of HY Steel to Improve Impact Toughness: John Galuardi1; Emmanuel De Moor1; Kip Findley1; 1Colorado School of Mines
New heat treatments are being investigated to reduce the reject rate of large section-size castings of High Yield (HY) steel. Intercritical annealing (IA) has been used historically to improve impact toughness properties of nickel-bearing ferrous alloys by lowering the ductile-to-brittle transition temperature (DBTT) to cryogenic operating conditions. This shift in the DBTT is attributed to retained austenite (RA) films, which are stabilized to cryogenic temperatures through enrichment of Ni into austenite during IA. To explore the tenability of IA improving the impact toughness of HY steel, CALPHAD modeling, dilatometry, mechanical testing, scanning electron microscopy (SEM), and X-ray diffraction (XRD) have been performed to determine the phase fraction of RA in HY-80 and examine the joint effect of IA and tempering treatments on mechanical properties and microstructure.
9:00 AM
The Effect of Adding Minor Alloying Elements in Reducing the Prior Austenite Grain Size in High Yield Strength (HY) Steels: Aphrodite Strifas1; Matthew Frichtl1; Sreeramamurthy Ankem1; 1University of Maryland
High yield (HY) steels are primarily alloyed with carbon, nickel, chromium, and molybdenum to achieve enhanced yield strength, provide corrosion resistance, and desired formability. The present work reports on the prior austenite grain size refinement due to micro-alloying additions to a baseline HY-80 (with a minimum yield strength of 80 kilo-pounds per square inch) composition. Tensile and Charpy V-Notch testing showed an improvement in mechanical properties due to the micro-alloying addition. Grain refinement was observed using microscopic analysis, following a representative heat treatment path typically used in HY-80 steels. The advantages of a finer prior austenite grain size in regard to processing and mechanical property improvements will be discussed.Acknowledgement: This research is partly sponsored by the DLA-Troop Support, Philadelphia, PA and the Defense Logistics Agency Information Operations, J68, Research & Development, Ft. Belvoir, VA.
9:20 AM
High Cycle Fatigue Behavior of Nano-bainitic Steels: A Detailed Crack Initiation and Grain Boundary Study: Blessto B1; Avanish Kumar2; Aparna Singh1; 1Indian Institute of Technology, Bombay; 2Indian Institute of Technology (ISM) Dhanbad
A range of refined nano-bainitic steels was developed by varying the austempering temperature (2500C, 3000C and 3500C). These steels' tensile and fatigue strength were investigated and linked to their microstructural features. Fractography showed that the fatigue failure has occurred primarily due to surface-induced crack initiations. The steel with the most cycles to failure has a greater tendency for transformation-induced plasticity. The plastic region transforms to martensite, which increases the fatigue life of steels in these conditions, thus delaying crack nucleation. The bainitic block width determined from EBSD analysis was correlated with the mechanical properties. The bainitic block boundary plays a predominant role as a microstructural barrier for fatigue crack growth.
9:40 AM
In-situ Measurement of Surface Relief Effect during Displacive Transformation of Low-carbon Steel: Ruogu Hou1; Junya Inoue1; 1The University of Tokyo
In-situ observation of surface relief development during displacive transformation was conducted by a digital holographic microscope (DHM) to probe into the process of martensite and bainite transformation. Based on high-resolution signal processing, quantitative measurement of surface relief is achieved. Surface relief of typical variant pair(VP) such as V1/V8 for upper bainite is clarified as well as correlated with prior austenite deformation and inclination of variants. The sequence of variant growth over cooling time is observed as well, indicating that change of variant growth pattern changes with driving force such as transformation temperature. Combining phenomenological theory of martensite crystallography (PTMC) calculation, measured value by DHM are verified, and the reason for the deviation between theoretical value and measured value will be discussed.