Advanced High Strength Steels IV: Poster Session
Sponsored by: TMS Structural Materials Division, TMS: Steels Committee
Program Organizers: Ana Araujo, Vesuvius USA; Mary O'Brien, Los Alamos National Laboratory; Tilmann Hickel, Bam Federal Institute For Materials Research And Testing; Amy Clarke, Los Alamos National Laboratory; Kester Clarke, Los Alamos National Laboratory; C. Tasan, Massachusetts Institute of Technology; MingXin Huang, University of Hong Kong

Tuesday 5:30 PM
February 25, 2020
Room: Sails Pavilion
Location: San Diego Convention Ctr


J-1: Electrochemical Characterization of Advanced High Strength Steel DP 780 MPa: Abraham Escalona Gómez1; Marisol Delgado Espino1; Maria del Refugio Lara Banda1; Facundo Almeraya Calderón1; 1Universidad Autonoma de Nuevo Leon
     Nowadays, with the increase of environmental problems, car safety became the major priority for the automotive industry. This is why advanced high strength steels were implemented instead of conventional steels. DP steels are part of this group, due to their excellent combination of mechanical properties. The objective of this work is to study the corrosion behavior in a double-phase steel with a tensile strength of 780 MPa, in the presence of chlorides, applying electrochemical techniques obtaining parameters such as corrosion rate, type of corrosion, density of corrosion current and corrosion potential. To know the chemical composition of the material, the X-ray fluorescence technique was used, at the end of the tests a stereoscope was used to see its morphology. As electrolytes were used: water (H2O), magnesium chloride (MgCl2), sodium chloride (NaCl) and calcium chloride (CaCl2) at 3.5 wt.% and was evaluated using electrochemical techniques of potentiodynamic polarization curves (PP) and electrochemical noise (EN), using a three-electrode cell. The results indicated activation in the anodic branch, in addition there is pitting corrosion in the material under study mostly in the presence of magnesium chloride.Keywords: AHSS, corrosion, pitting, electrochemical

J-2: Excellent Strength-ductility Combination of Austenitic-hadfield/martensitic-hot-press-forming Clad Steel Sheet: Min Cheol Jo1; Jaeyeong Park1; Seok Su Sohn2; Taejin Song3; Hyoung Seop Kim1; Sunghak Lee1; 1Pohang Inst of Sci & Tech (POSTECH); 2Korea University; 3POSCO
    An austenitic Hadfield steel shows excellent tensile strength and ductility as well as highly-sustained strain hardening, but its yield strength is relatively low. In order to overcome this shortcoming, a multi-layer clad steel sheet was fabricated by the hot-roll-bonding with martensitic hot-press-forming (HPF) steels. Carburized and decarburized layers were formed near Hadfield/HPF interfaces by the C diffusion from the high-C Hadfield (1.2%) to low-C HPF (0.23%) layers. This clad sheet was fractured right after the yielding because the intergranular fracture appeared in the carburized layer. The tempering at 200 °C was adopted for relieving residual stress and the 200 °C-tempered clad sheet showed dramatically improved tensile properties over the non-tempered clad sheet. This simultaneous enhancement of strength and ductility was explained by a multi-layer effect induced from populated twin formation, generation of geometrically necessary dislocations, and increase of back stress inside thin interfacial layers.

J-4: Producing a 1200 MPa Complex-phase Advanced High Strength Steel: Renan Lima1; Kester Clarke2; Amy Clarke2; F.T.F Tolomelli3; Fernando Rizzo1; 1Pontifícia Universidade Católica do Rio de Janeiro (PUC-RIO); 2Colorado School of Mines; 3Companhia Siderúrgica Nacional, Rodovia
    Safety, environmental preservation and cost effectiveness are important driving factors for innovation in the automotive industry. Together, they drive the demand for higher strength structural metallic alloys with low production costs for the creation of parts with reduced weight. This demand is being answered by the development of Advanced High Strength Steels (AHSS) with novel alloying and processing strategies. The present work investigates the processing of AHSS steel with focus on the production of a Complex Phase (CP1200) steel, with tensile strengths greater or equal to 1200 MPa and mixed microstructures that may contain small amounts of martensite, retained austenite, and pearlite within a ferrite/bainite matrix. Continuous cooling transformation (CCT) diagrams were developed from microstructures produced by thermal treatments performed with a DIL805 quenching dilatometer. Samples were characterized by optical and electron microscopy, and mechanical properties were determined from hardness measurements of laboratory and industrial scale samples.

J-5: Solutions to Hydrogen Embrittlement of Ultra-high Strength Press-hardened Steel for Automotive Application: Lawrence Cho1; P.E. Bradley1; Matthew Connolly1; M.L. Martin1; D.S. Lauria1; Frank Delrio1; A.J. Slifka1; E.J. Seo2; K.R. Jo3; S.W. Kim4; 1National Institute of Standards and Technology; 2Colorado School of Mines; 3Pohang University of Science and Technology; 4POSCO
    Improved safety standards and reduced automotive body-in-white weight have led to a strong interest in ultra-high strength press-hardened steels (PHS). However, the martensitic PHS is particularly sensitive to the hydrogen embrittlement. An atmospheric corrosion of the steel or Al-Si coating by water vapor in the furnace atmosphere of hot stamping lines produces hydrogen, leading to the hydrogen uptake of the steel. This hydrogen uptake causes a hydrogen-induced fracture of the PHS during tensile straining. The present contribution reports three methods to address the PHS hydrogen-induced fracture. The first method involves post-bake hardening treatment, which partially removes the diffusible hydrogen in the PHS. Second, use of Zn-coated steel for the hot stamping application reduces the risk of hydrogen embrittlement. Finally, vanadium additions into the steel composition cause an increased density of hydrogen-trapping sites and considerably reduce the negative impact of hydrogen uptake on the mechanical properties of the PHS.

J-6: The effect of alloy elements on the peritectic range of Fe-C-Mn-Si steels: Qing-Qiang Ren1; Tao Liu2; Sung Il Baik1; Zugang Mao1; Bruce Krakauer3; David Seidman1; 1Northwestern University; 2Chongqing University; 3AO Smith Coorporate
    The occurrence of peritectic reaction remains a big challenge in the modern production of widely applied Fe-C-Mn-Si steels, hence it is of vital importance to determine the peritectic range to avoid such reactions. However, the effect of alloy elements on the peritectic range is not clear especially for steel composition designs in a large compositional space. Herein, we studied the effect of alloy elements on the peritectic range in the common composition ranges of Fe-C-Mn-Si steels by a combination of experimental measurements and thermodynamic modelling. The phase transition sequences and temperatures at high-temperature range of two model Fe-C-Mn-Si steels are experimentally investigated by differential scanning calorimetry (DSC) and high-temperature confocal laser scanning microscope (HTCLSM), the results of which are in good agreement with the thermodynamic modelling by Thermo-Calc and the TCFE9 databases. The database is then utilized to calculate 1680 phase diagrams for the information of peritectic ranges to explore the common composition ranges. The contour plots of the results reveal the complex interactions rather than single-element effect of Mn, Si, and Ti on the peritectic ranges. Regression equations are also derived based on the thermodynamic modelling, and these equations are utilized to establish links with casting practices.

J-7: Transformation Kinetics in a Trip Steel during the Plastic Deformation by Tension and Compression: Jose Pacheco1; Pedro Garnica2; Yadira Solana2; Lesliee Espino3; Jorge Navarro2; 1DICIM UASLP; 2TecNM, Instituto Tecnológico de Morelia, División de Estudios de Posgrado e Investigación; 3TecNM, Instituto Tecnológico de Morelia, Departamento de Ingeniería en Materiales
     The transformation kinetics of the retained austenite (RA) of a TRIP steel was determined during the plastic deformation by tension and compression, the tests were carried out at room temperature at different deformation percentages. In the induction furnace, a commercial steel was melted, to which ferroalloys were added, obtaining 0.21% C, 1.22% Mn, 2.16% Si. An intercritical annealing and isothermal treatment was carried out. Tension test tubes (ASTM-E8) were machined, as well as specimens to be laminated at room temperature.The micrographs show the presence of: ferrite, bainite, RA/martensite. By means of XRD the RA was identified and quantified (15.6%), this was reduced to 7.1% after the stress test. The evaluation of the RA after each rolling pass shows that before 20% of deformation the volume of RA was reduced by 47%, and in the tension test the RA volume is reduced by 59% with the same plastic deformation.