Analysis of Boron Segregation in Medium Carbon Steel
EMSL Project ID
50904
Abstract
Medium-carbon steels have been widely used for gas and oil pipelines, and their excellent combination of strength and toughness favorably contributes to construction, heavy equipment and automobile industries. Since the 1970's, B has been added to these steels to improve the hardenability due to the ready segregation of B atoms at prior austenite grain boundaries (PAGBs), which may reduce the grain-boundary energy, thereby preventing the austenite to ferrite transformation and rendering bainite or martensite formation more favorable. The B segregation at PAGBs in martensitic steels has been analyzed by using particle tracking autoradiography (PTA), electron energy loss spectroscopy (EELS), atom probe tomography (APT), and secondary ion mass spectrometry (SIMS). These techniques, except EELS and APT, are advantageous for large-scale (up to several hundred micrometers) investigations, and provide overall distributions of grain-boundary B atoms or B-containing precipitates. Only ATP tracks individual atoms at an atomic scale, and delivers accurate information on solute distribution at grain boundaries, interfaces, and within the matrix or other phases. APT can be limited because only a very small region can be analyzed, although it is possible to perform quantitative analysis. In the present work, investigation of B segregation on a greater length scale is also desired. Recently, B-segregation behavior has been studied by using a Nano-SIMS, which is capable of larger length scales than APT and also provides quantitative analysis. The spatial resolution of the SIMS mainly depends on the primary ion-beam spot size. With a coaxial objective and extraction lens, a lateral resolution of a few tens of nanometers, together with an extremely high sensitivity for all elements from hydrogen to plutonium, can be achieved by Nano-SIMS. The depth resolution is limited to 10~15 nm due to the atomic mixing effect, but we do not consider that to be of concern in the present study. At EMSL, we would like to investigate B segregation by using Nano-SIMS, which provides better resolution than the TOF-SIMS instrument recently installed at Colorado School of Mines. As mentioned earlier, we believe that Nano-SIMS may provide the best way to quantitatively analyze the B-segregation behavior on the length scales of interest.Project Details
Project type
Limited Scope
Start Date
2019-07-01
End Date
2019-08-31
Status
Closed
Released Data Link
Team
Principal Investigator