Materials Week '97: Tuesday AM Session

Focusing on physical metallurgy and materials, Materials Week '97, which incorporates the TMS Fall Meeting, features a wide array of technical symposia sponsored by The Minerals, Metals & Materials Society (TMS) and ASM International. The meeting will be held September 14-18 in Indianapolis, Indiana. The following session will be held Tuesday morning, September 16.

FERROUS METALLURGY: General Abstract Session

Session Chair: Long-Qing Chen, University of Pennsylvania, Philadelphia, PA

ON LINE MEASUREMENT OF STRAND DISPLACEMENT AND ITS EFFECT ON INTERNAL QUALITY OF STEEL SLAB DURING CONTINUOUS CASTING: J.D. Lee, C.H. Yim, Technical Research Laboratories, Iron & Steel Making Research Team, POSCO, Pohang P.O. Box 36, 1, Koedong-dong, Nam-ku, Pohang-ski, Kyungbuk, 790-785, South Korea

Strand bulging is presumed to play a major role in the formation of internal cracks and centerline segregation in continuous casting. Meanwhile, the other factors such as roll displacement, which are due to ferrostatic force, roll bending and wear in the mechanical system, have not yet been investigated in detail. In the present paper, strand behavior at various positions of caster has been monitored during casting and its deformation has been discussed. Slab and roll displacement, which affects internal quality of slab, has been studied in relation to such casting conditions as pinch roll pressure, casting speed etc. Variation of slab displacement with pinch roll pressure at inlet of straightening may leads to quality defects and has been optimized by on-line monitoring of strand. It was also concluded that roll displacement control, which is based on on-line measurement during casting, specially around crater end should be emphasized for internal quality and effective maintenance of machine. In addition, dynamic bulging analysis considering strain accumulation has been performed to predict the critical strain for internal cracks and compared with experimental data.

8:50 am

HOT WORKING AND MICROSTRUCTURE DEVELOPMENT IN 409 FERRITIC STAINLESS STEEL: H.J. McQueen, E.V. Konopleva, N.D. Ryan, R. Zaripova*, Mech. Eng., Concordia University, 1455 de Maisonneuve Blvd. W., H-549-34, Montreal, Quebec, Canada

As continuously cast and homogenized 409 steels were deformed by torsion in the T range of 600-1200°C with strain rates of 0.01-5s^-1 to different strains (0.5 1, 2, 4 ) and to fracture. Flow curves exhibited peaks at 800-1200°C and gradual softening which was higher at higher stresses, thus due to deformation heating. At 600 and 700°C with =0.01 s¹, failure occurred at or just after the peak. The activation energy and strength were lower than those of 430 and 434 steels. In the as-cast segregated austenite, appearing at grain boundaries and within grains, raised the strength and diminished the nearby substructure recovery, causing some recrystallized nuclei. After testing at 600°C, deformed grains show little trace of recovery. At 700-1000°C, elongated grains contain substructure which is more developed at higher T and and lower . While the homogenization has eliminated the stringers, microprobe examination confirmed that there were small differences in composition between elongated grains which affect subgrain sizes and etching. There is no evidence of dynamic recrystallization in the range studied.

9:10 am

MÖSSBAUER EFFECT STUDY OF PHASE TRANSFORMATION & TRANSITION STATE IN MECHANICALLY ALLOYED Fe-Zn CUBIC MATERIALS: O.N.C. Uwakweh*, A. Jordan, Z. Liu, University of Cincinnati, Department of Materials Science and Engineering, Cincinnati, OH 45221-0012

The Mössbauer Effect measurement of Fe₂₅Zn₇₅ alloy corresponding to the mixed phase +₁ cubic phase reveals the presence of four distinct Fe-sites with quadrupole splitting (QS) of 1.10, 0.241, 0.0773 and 0.0772 mm/s. After aging at 130°C for 30 min., a new site with QS of 1.5 mm/s, and relative abundance of 5% is observed. At stable equilibrium following aging at 400°C for 1 hr., Fe-sites corresponding to the single phases of and ₁ are observed, with their total abundance in line with equilibrium compositions as determined by the lever rule. Comparison with the single phases show that this transient stage at 130°C aging is unique in the mixed phase composition and is detected for the first time in this system. X-ray diffraction (XRD) measurements confirm the existence of this stage.

9:30 am

KINETICS & TRANSFORMATION OF BALL-MILLED Fe-Zn-Al MATERIALS: Oswald N.C. Uwakweh, Zhentong Liu, Department of Materials Science and Engineering, 578 Engineering Research Center (ERC) Building, University of Cincinnati, Cincinnati, OH 45221-0012

Fixed ratios of Fe and Zn corresponding to -(Fe₃Zn₁₀), _l-(Fe₅Zn₂₁), -(FeZn₇) and -(FeZn₁₃) with the addition of 5% A1 (wt.) were ball milled in an argon gas atmosphere Non-isothermal kinetic analyses of the mechanically alloyed materials, based on DSC measurements revealed two diffusion controlled processes during the evolution of the + 5% Al and + 5% Al compositions with activation energies of 2272 kJ/mole, and 1591 kJ/mole respectively. Also endothermic and exothermic reactions detected are consistent with respect to the formation of the Fe₃Al, Fe₂Al₅, and -FeZn₇ phases. Based on FeA1₂ formation at 440°C for the + 5% Al, the revision/re-evaluation of the Fe-ZnAl equilibrium phase diagrams is proposed. The + 5% Al, and _l + 5% Al materials evolved similarly, except at 400°C where the former consisted of -Fe+ +, while the later was without the phase.

9:50 am

PHASE IDENTIFICATION IN ULTRA-LOW CARBON STEEL WELDMENTS: Richard W. Fonda, Naval Research Laboratory, Code 6324, Washington, DC 20375

While identification of phases is well established for medium and high carbon steels, the proper identification of phases in low and ultra-low carbon steels is still a problem which has not been adequately addressed. In this study, the decomposition of austenite in ultra-low carbon steels is examined by a combination of dilatometry, optical microscopy, and transmission electron microscopy. Samples cored out of an advanced ultra-low carbon steel weldment were thermally cycled at different cooling rates to simulate a wide variety of wading conditions. Dilatometric analysis is used to independently determine the volume fraction of each microconstituent present. These various samples are then examined by optical microscopy to determine the efficacy of different etchants in revealing and differentiating the various phases. Characteristics of these phases, both at the optical and the transmission electron microscopy levels of resolution will be discussed.

10:10 am BREAK

10:20 am

THE STUDY OF METASTABLE TO STABLE EQUILIBRIUM TRANSFORMATION OF MECHANICALLY ALLOYED Fe-Zn-Si MATERIALS: O. Uwakweh, Z. Jordan, P. Maziasz*, University of Cincinnati, Materials Science and Engineering Department, Cincinnati, OH 45221-0012; ^*Metals & Ceramics Division, Oak Ridge Natinal Lab (ORNL), Oak Ridge, TN

The ball-milling of elemental powders corresponding to (Fe₃Zn₁₀) + 0.12 Si; ₁ (Fe₅Zn₂₁) + 0.12 Si; (FeZn₇) + 0.12 Si; and (FeZn_l3) + 0.12 Si mechanically alloy to crystalline states. Differential scanning calorimetry (DSC) measurements show that they evolve through characteristic stages. The activation energies for these stages are 120 ± 0.32 kJ/mole, and 130 ± 0.99 kJ/mole ( + 0.12 Si); 161 ± 0.16 kJ/mole (₁ + 0.12 Si) respectively. Three stages with activation energies of 131 kJ/mole, 167 ± 0.2 kJ/mole and 244 ± 3.21 kJ/mole are observed for the + 0.12 Si alloy. Evolution of the + 0.12 Si alloy, exhibits two stages with activation energies of 96 ± 2.08 kJ/mole and 641 ± 0.45 kJ/mole, while the peak at 420 ± 3°C depicts the eutectic reaction in Zn-Si, and the melting of Zn in Fe-Zn binary systems.

10:40 am

METASTABLE TRANSFORMATION OF BALL-MILLED Fe-Zn-Si ALLOYS IN EQUILIBRIUM PHASE EVALUATION: O. Uwakweh, A. Jordan, 578 Engineering Research Center (ERC) Building, Materials Science & Engineering Department, University of Cincinnati, Cincinnati, OH 45221-0012

Fe-Zn intermetallics with the addition of 0.12 wt % Si corresponding to an isocomposition line in the ternary system is investigated with respect to FeSi formation. The mechanically alloyed -(Fe₃Zn₁₀) + 0.12 % Si; ₁(Fe₅Zn₂₁) + 0.12 % Si; (FeZn₇) + 0.12 % Si; and (FeZn₁₃) + 0.12 % Si, and the intermediate compositions (i.e., mixed phase alloys) yield metastable crystalline materials through ball-milling of pure elemental powders. DSC measurements in the 200-600°C temperature range indicate the presence of characteristic stages during their structural change. An invariant reaction occurring at 420-423°C is identified in the (FeZn₇) + 0.12 % Si and + + 0.12 % Si composition range. This reaction explains the phenomenon associated with the Zn coating of Si bearing steels, otherwise known as the Sandelin Effect. 2-D representation of the domain of FeSi boundaries is constructed from DSC and XRD measurements.

11:00 am

ANALYSIS ON THE INTERLAMELLA SPACING OF HYPEREUTECTOID PEARLITIC STEELS: Kyung-Tae Park, Sam-Kyu Cho, Jong-Kyo Choi, POSCO Technical Research Lab., P.O. Box 36, Pohang, Korea

Unless proeutectoid cementite exists, pearlitic cementite thickness would be a primary factor influencing the brittleness of hypereutectoid steels. In the present study, the variation of pearlitic cementite thickness with carbon content was analyzed by using a simple carbon mass conservation relation during austenite/pearlite transformation. The analysis revealed that pearlitic ferrite thickness always decreased with increasing carbon content while cementite thickness either increased or decreased with increasing carbon content. The critical condition for the variation of cementite thickness with carbon content was examined and the result was compared to the interlamellar spacing measurement data reported previously.

11:20 am

TOUGHNESS OF THIN COATED STEELS WITH HARDENED SUBSTRATE: T. Arai, Arvin TD Center, 2020 15th St., Columbus, IN 47201

Impact test and static bending tests made clear the fracture behavior of hardened steels coated mainly by TRD, as well as PVD and CVD. Impact strength and transverse rupture stress are more susceptible to the fracture behaviors of the hardened substrates rather than that of the coatings. In the case of brittle substrates, high-alloyed tool steels tempered at the low temperature, cracking will precede in the substrates, leading to failure. Cracking in the coatings preceding cracking in the tough steel substrates, tempered at the high temperature, usually does not induce the fractures of specimens. In some steels tempered at the low temperature cracking in the coatings induces cracking in the substrate simultaneously or at higher stress level. As a result, the coated steels are inferior in toughness to uncoated hardened steels.

11:40 am

DEFORMATION AND AGING BEHAVIORS OF Fe-Mn-Al-Cr-C DUPLEX ALLOY: M. Hadji, M. Temmar, T. Sahraoui, S. Zidelmel, Institute of Mechanical Engineering, University of BLIDA, P.O. Box 270, route de soumaa BLIDA 09000, ALGERIA

The microstructural changes which occur during aging of cold rolled Fe-Mn-Al-Cr-C duplex alloy have been studied. Typical laminate microstructures were developed during the first and second cycle of deformation. It was observed that at room temperature deformation the austenite deformed by the formation of deformation twins. The age hardening behaviors is observed to occur in four stages: a) very fine precipitation in ferrite with formation of precipitation free-zones (PFZ); b) significant homogeneous and heterogeneous precipitation in the deformation twins within the ferrite matrix; c) coursening of precipitation in ferrite and at grain boundaries, d) precipitation of secondary equiaxed ferrite within the austenite. A correlation between the mechanical properties and the microstructures is discussed.