Advanced High-Strength Steels Design
For the past decades, the automobile industry has been improving fuel efficiency, passenger safety, and reduction in greenhouse gas emission by adopting advanced high strength steels (AHSS) with both high strength and high ductility. In general, AHSS is classified as the first-generation AHSS (1st-G AHSS), the second-generation AHSS (2nd-G AHSS), and the third-generation AHSS (3rd-G AHSS).
The 1st-G AHSS, such as dual-phase (DP), complex-phase (CP), and transformation-induced plasticity (TRIP) steels, possesses the high strength of over 600 MPa but the relatively low ductility of below 20%. This low ductility restricts the application of the 1st-G AHSS to automobile parts with complex shapes. The 2nd-G AHSS, such as high Mn TRIP and twinning-induced plasticity (TWIP) steels, shows a remarkable combination of high strength of over 700 MPa and large uniform ductility exceeding 50%. The extraordinary tensile properties of the 2nd-G AHSS result from the high strain hardening rate due to the formation of strain-induced martensite or mechanical twins in the austenite phase during plastic deformation. However, the 2nd-G AHSS has difficulties in mass production, material cost, and welding, which are caused primarily by a lot of alloying elements greater than approximately 17 wt.%. Therefore, nowadays, the 3rd-G AHSS, such as lightweight steel, quenching and partitioning (Q&P) processed steel and medium Mn steel has been attracted because it has a good trade-off between material cost and mechanical properties.
One of the objectives of ASML is to investigate the next generation AHSS showing better mechanical properties than 3rd-G AHSS even maintaining reasonable materials cost. This concept is based on optimal using of various strengthening mechanisms simultaneously.
Advanced Alloys Design
We also have a lot of attention to investigate multi-functional alloys such as self-healing alloy, multi-component alloy (high entropy alloy), Ti alloy, and cost-effective superplastic alloy. The objective of the research scheme is to develop not only alloys with excellent sustainability for extreme environments but also unraveled phenomena of alloys to suggest novel routes for the application such as hydrogen-storage metal, nuclear material, and thermoelectric material.
Hydrogen is known to be one of the most harmful elements in steel because the presence of that in steels might cause a detrimental effect on mechanical properties. The hydrogen can permeate in steels from the production process (e.g. pickling, electroplating, and welding), product assembling, and service environment exposure. Even a very low concentration of hydrogen (less than 1 ppm) can cause a significant decrease in ductility and premature failure of steels and this phenomenon is the so-called hydrogen embrittlement (HE). It is known that the diffusible hydrogen is the suspect causing HE, and there are several proposed mechanisms for HE, such as internal pressure model, hydrogen-enhanced decohesion (HEDE), hydrogen-enhanced local plasticity (HELP) and hydrogen-enhanced strain-induced vacancy (HESIV).
Our lab.`s objective is to clarify the HE mechanism of alloys with various microstructures and showing various deformation mechanism like TRIP and TWIP through the state-of-the-art analyses by thermal desorption analysis (TDA), scanning Kelvin probe microscope (SKPFM) and post-mortem microstructural analysis such as electron backscattered diffractometer (EBSD) and electron channeling contrast imaging (ECCI) method. Through our research, we expect to reveal the reason for HE in steels.
With decreasing the environment`s temperature, the alloy`s fracture mode sometimes changes from ductile fracture to brittle fracture, and this phenomenon is so-called as ductile to brittle transition. The various factors could affect the ductile to brittle transition behavior such as crystal structures, lattice defects, and element segregations.
Our lab.`s objective is to clarify the low-temperature embrittlement mechanism of alloys and suggest the solution for improved mechanical responses through post-mortem analyses using combined EBSD/ECCI techniques and segregation engineering using STEM-EDXS and 3D atom probe tomography (APT).
Thermo-Mechanical Process Design
The microstructure of alloys and steels could be controlled by the material`s synthesis. Generally, alloys are subjected to various hot and cold rolling or forging and annealing with various conditions for the productions. This procedure is called as a thermo-mechanical process. The different microstructures which are characterized by various thermo-mechanical process give a lot of effort on material`s properties such as mechanical properties.
Our lab`s goal is to try and apply the various thermo-mechanical process on various alloys and steels to optimize the mechanical properties.
Multi-Scale Microstructure Analysis
Revealing interrelation between microstructure and mechanical properties is the essential topic of the metallurgical engineering. Multi-scale microstructural analysis from bulk scale to atomic scale could give a clear information of the component of steel and alloys, thus it could facilitate the successful alloy design and reveal the secret of interrelation.
Our lab uses state-of-the-art microstructural analysis techniques such as not only general X-ray diffraction (XRD) and electron microscope (SEM, TEM), but also high-performance electron backscatter diffraction (EBSD), electron channeling contrast imaging (ECCI) and 3D atom probe tomograph (APT).
01. June. 2020 - 28. February. 2023
ASML is selected as a laboratory for "Basic Research (기본연구)" of NRF. The research theme is "Ultrahigh strength lightweight maraging armor steel". Our goal of this project is to design bullet-proof maraging steel by rendering of nanolaminate morphology and dynamic strengthening mechanisms.
01. February. 2020 - 31. July. 2020
ASML is funded by Korea Shipbuilding & Offshore Engineering from February. 2020 to July. 2020. The research theme is the investigation of medium-Mn steel with excellent cryogenic impact toughness.
01. January. 2020 - 31. December. 2021
ASML is funded by POSCO TJ Park Foundation from January. 2020 to December. 2021. The research theme is designing new-era steel to overturn a conventional physical metallurgy theory.
01. March. 2018 - 28. February. 2023
ASML is selected as a laboratory for "Workforce Training for Alloys and Steels (고부가 금속소재 전문인력양성사업)" of MOTIE. The project period is from Mar. 2018 to Feb. 2023 and research theme is discovering new concepts of alloy design for next-generation high strength steels, the special phenomenon of steels (e.g., hydrogen embrittlement, low-temperature toughness, etc.).
01. June. 2018 - 31. May. 2019
ASML is funded by Hyundai Steel from June. 2018 to May. 2019. The research theme is related to the mechanical response of advanced high strength steels.
01. March. 2018 - 31. December. 2018
ASML is selected as a laboratory for "Research Funding for Cooperative Research" of KBSI. The project period is from Mar. 2018 to Dec. 2018 and research theme is "Unravelling reverse transformation mechanism and deformation behavior at a high temperature of medium Mn steel".
01. March. 2017 - 28. February. 2020
ASML is selected as a laboratory for "Research Funding for Starting Professor (신진연구자지원사업)" of NRF. The project period is from Mar. 2017 to Feb. 2020 and research theme is "Investigation on Multifunctional Medium Mn Lightweight Steels with Giga Strength". Our goal of this project is to design cost-effective modern AHSS with lightweightness, high resistance to hydrogen embrittlement and low-temperature embrittlement.