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| Study on microstructure and properties of high boron stainless steel with 3.29%
boron content |
| PEI YanBin1,2,3，WANG TieJun4，GE QiLu1，CHEN Jin3，QU XuanHui2 |
| 1. Central Iron & Steel Research Institute，Beijing 100081，China；2. Institute forAvanced Materials and
Technology，The University of Science and Technology Beijing，Beijing 100083，China； 3.Antai-heyuan
Nuclear Energy Technology & Materials Co.，Beijing 100094，China；4. Advanced Technology & Materials Co.，
Ltd.，Beijing 100081，China |
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Abstract The objective of the study was to prepare the borated stainless steel (BSS) containing with 3.29% boron,
to test BSS powder morphology and eutectic melting points, and observe phases, microstructure, elemental distribution
and mechanical properties of BSS alloy. These characteristics were compared with two grades of BSS alloy
with lower boron content (0.29% and 1.86%) which correspond to standard A887 304B and 304B7 respectively issued
by American Society of Testing Materials (ASTM). The Fe-Cr-Ni austenite steel powder with boron was obtained
by atomization equipment. Fe-B, Fe-Cr and other raw materials were put into the melting furnace to melt and
then were ejected to make the powder. The morphology of the BSS powder was observed by scanning electron microscope
(SEM) and the eutectic melting point was analyzed by differential scanning calorimetry (DSC). The gas atomization
powder obtained was passed through the 74 μm sieve. The powder was placed in the capsules. Filled with
BSS powder, the capsules were heated to 500 °C in the atmospheric oven and degassed to 10?3 Pa to reduce oxidation
of the powder. The capsule was placed in the hot isostatic pressing (HIP) furnace and then heated up, elevated
pressure and held at sintering temperature and maximum pressure (110 MPa) for 2 h. Coupons of three BSS alloys
were evaluated by quantitative X- ray diffraction (XRD) phase analysis. Microstructures were observed by
SEM and energy-dispersive spectroscopic (EDS) analysis. Strength and ductility of specimens were tested according
to Chinese Standard GB/T 228.1. The eutectic liquid phase point of BSS with 3.29% boron occurs at 1 181.4 °C tested by DSC. The BSS alloy with 3.29% boron prepared by PM comprised two main phases: the cubic austenite
phase is 66 %; the orthorhombic Fe1.1Cr0.9B0.9 boron phase is 34 %. The boron phase grains of BSS with 3.29%
boron have irregularly shaped grains, many of which are already in contact and joined together, while the grains of
the low content boron BSS alloys have the regular shape and are separated from each other. The element boron fluctuates
between 9.0% and 16.6% in the boron-containing phase of BSS, so the boron distribution of BSS is uneven.
The BSS containing 3.29% boron have the tensile strength of 900 MPa and the elongation of only 1.0%, while
304B7 BSS have tensile strength of 720 MPa and elongation of 13.0% and 304B sample have tensile strength of
770 MPa and elongation of 20.5%. The tensile strength of BSS with lower boron content below 2.25% is similar,
but elongation decreases with the increase of boron content; however, the strength of BSS with 3.29% boron is greater
than that of low boron alloys by more than 100 MPa, but elongation decreases to only 1%. BSS alloys consist of
two phases, the boron-containing phase content increases as the boron content of the alloy increases. As the boron
content increases, the grains of the boron-bearing phase become irregular and the connections between grains
increase. The BSS alloy containing 3.29% boron is brittle material.
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Received: 09 April 2021
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2022, Vol. 32 
