Pan American Materials Congress: Steels: Poster Session
Sponsored by: Third Pan American Materials Congress Organizing Committee
Program Organizers: Omar Garcia-Rincon, TERNIUM Mexico SA de CV; Andre Costa E Silva, EEIMVR - Universidade Federal Fluminense

Tuesday 5:30 PM
February 28, 2017
Room: Poster Area
Location: Marriott Marquis Hotel

PAN-60: Effect of Titanium Sulfide Precipitates on Grain Size in Low Carbon Steel: Yuan Wu1; 1Shanghai University
    The effect of titanium sulfide particles on the grain size characteristic of low carbon steel was analyzed. Optical microscope (OM), scanning electron microscope (SEM) were used to characterize the grain size and particles. The result showed that grain size increased from 19.95 μm to 60.56 μm after heat treatment. The particles were mainly titanium sulfide in the size range of 0.2-0.8 μm and the volume fraction decreased significantly from 0.0084% to 0.0023%. The thermodynamic calculation resulted that these particles were dissolved during heat treatment. The pinning force of grain boundary and the driving force of grain growth were calculated. Based on experimental results and theoretical calculations, titanium sulfide particles with diameter from 0.2 μm to 0.8 μm and volume fraction of 0.0084% would be sufficient to inhibit the ferrite grain growth.

PAN-61: Hydrogen Gaseous Embrittlent Effect over Mechanical Properties of a Heat Treated Experimental Microalloyed Steel with Different Cooling Rates: Julio Villalobos1; Edgar Lopez2; Octavio Vazquez3; Sergio Serna1; Bernardo Campillo4; 1CIICAP; 2Universidad del Istmo, Campus Tehuantepec; 3Instituto Tecnológico de Morelia; 4ICF-UNAM, FQ-UNAM
    The aim of this work is to determine the hydrogen gaseous embrittlement susceptibility and the effect on the mechanical properties of an experimental microalloyed steel subjected to heat treatments with different cooling rates. The microalloyed steel in its initial condition was heated at 900°C and cooled in water spray, pressurized air and an oil-10% water mixture; and heated at 820°C, cooled in oil. Tensile tests in-situ were carried out in a hydrogen gas atmosphere at pressures of 150, 600 and 1000 psi. The results showed high hydrogen gaseous embrittlement susceptibility as the hydrogen gas pressure increases, reducing their yield strength and ultimate tensile strength in all conditions; the less susceptible condition was the sample cooled in pressurized air, showing a lower embrittlement index. In order to determine the diffusion coefficients, permeability tests were performed. The results showed that a higher cooling rate had a higher susceptibility to hydrogen embrittlement.

PAN-62: Influence of Oxide Size and Composition on MnS Formation in Continuous Casting Slab of Low Carbon Steel: Fangjie Li1; 1Shanghai University
    To avoid the precipitate of pure MnS during the solidification and cooling process of slab, MnS formation on oxide nuclei was researched. The composition and size of inclusions in three different areas from continuous casting slab of low carbon steel were performed by using scanning electron microscopy (SEM) equipped with energy dispersive spectrometry (EDS). The results showed that the number of inclusions smaller than 10 µm was varied in different areas. The main component of oxide was identified as aluminum silicate, and that of the sulfide was MnS. The manganese sulfide was inclined to nucleate at silicon-rich oxide. By analyses of different size of inclusions, the sulfides were prone to precipitate at the surface of smaller size inclusions (1-3 µm) compare with inclusions bigger than 3 µm.

PAN-63: Kinetic Study of the Austenite Decomposition during Continuous Cooling in a Welding Steel: Octavio Vázquez-Gómez1; Edgar López-Martínez2; Alexis Gallegos-Pérez3; Heber Santoyo-Avilés4; Héctor Vergara-Hernández3; Bernardo Campillo5; 1Instituto Tecnologico de Morelia - CONACyT; 2Universidad del Istmo; 3Instituto Tecnológico de Morelia; 4Ternium México; 5Universidad Nacional Autónoma de México
    The kinetics of austenite decomposition during the continuous cooling in a low-carbon welding steel was determined by dilatometric analysis. Based on the measurements, the transformation critical temperatures of austenite decomposition were determined in ferrite and pearlite. The cooling conditions were established from the Stelmor® controlled cooling process for the manufacturing of wire rod. It was observed that the critical temperatures decrease while time was reduced as a result of the cooling rate in an interval of 600 to 900 °C. Using the decomposition temperatures, a continuous cooling transformation CCT diagram was created and it is observed that austenite decomposition occurs in two steps. The kinetic parameters for each step were determined and compared with the Johnson-Mehl-Avrami-Kolmogorov diffusive model. The final microstructure was analyzed using an optical microscope and evaluated by nanoindentation to determine the effect of the cooling rate on the nanohardness of each phase.

PAN-64: Study of Ductile Austemperized Iron Alloyed with V, Mo AND Cr: Fatima Alicia de la Rosa Castañeda1; 1IPN - UPIIZ
    Nodular Iron is one of the most widely used materials in the automotive industry since it presents many advantages in comparison to gray iron such as higher resistance to fatigue, higher tolerance to wear and tear, higher resistance to traction and better manufacturing performance apart from its low fabrication cost. Due to its strength, it is being used in the manufacture of parts subjected to fatigue cycles since the crystalline structure it possesses inhibits the development and propagation of cracks. In the following work, different types of nodular iron alliyed with V, Mo y Cr under an austempering process are studied to determine the effect they have on the homogenization time as well as the thermal treatment effect for different thicknesses. To validate this effect, studies were conducted on the microstructure using an optical microscope. In order to relate it to its mechanical properties, tension and microhardness testing were conducted.

PAN-66: Tempering Response of Bainitic and Martensitic Microstructures: Igor Vieira1; Emmanuel De Moor1; 1Colorado School of Mines
    The tempering response of fully martensitic microstructures has been well characterized. However, bainitic microstructures may also be found in quenched industrial materials and the present study investigates the tempering response of fully martensitic and fully bainitic microstructures. Specific thermal cycles were developed to generate both microstructures in a boron added 0.17 wt pct carbon steel. The tempering response was assessed through dilatometry and microstructural characterization was conducted using scanning electron microscopy and Mössbauer spectroscopy. The dilatometric analysis of the tempering response of the martensitic microstructures provided information about retained austenite decomposition and cementite precipitation whereas bainitic microstructures showed a less sensitive dilatometric response during tempering likely due to the low amount of carbon in solution and absence of retained austenite as measured by Mössbauer spectroscopy.

PAN-67: Using CCT and TTT Diagrams Obtained by Simulation for Developing AHSS: Jose Pacheco1; Jose Cruz2; Pedro Garnica3; Jose Lopez3; Josè Gutierrez4; Jose Quezada1; 1DICIM UASLP; 2Facultad de Ingenieria UASLP; 3Instituto Tecnologico de Morelia; 4Instituto de Metalurgia UASLP
    Advanced high-strength steels (AHSS) was developed to be used by the automotive industry, because favoring weight reduction and thus economic and environmental benefits can be obtained. In this work TTT and CCT diagrams were used to design the processing route to obtaining a dual-phase (DP) and a multiphase (MP) steels. CCT and TTT diagrams were obtained using JMat-Pro software. The base steel was melted in an induction furnace from commercial AISI-1018 steel. The steel was heat treated following two routes. One route resulted in a DP structure composed of Ferrite+Martensite. The other showed a microstructure of Ferrite+Untransformed Austenite+Bainite+Martensite. Tensile specimens were prepared to evaluate the strength. Average strength obtained for DP Steel was 1067 MPa and elongation 7.65%, the MP steel strength was 897 MPa and elongation 30.75%. These results show the usefulness of the CCT and TTT diagrams obtained by simulation on the processing routes development for AHSS steels.