LI Hua-bing
,
JIANG Zhou-hua
,
FENG Hao
,
MA Qi-feng
,
ZHAN Dong-ping
钢铁研究学报(英文版)
The solution-treated (ST) condition and aging precipitation behavior of 18Cr-16Mn-2Mo-1.1N high nitrogen austenitic stainless steel (HNS) were investigated by optical microscope (OM), scanning electron microscope (SEM), and transmission electron microscope (TEM). The results show that the ST condition of 18Cr-16Mn-2Mo-1.1N HNS with wN above 1% is identified as 1100 ℃ for 90 min, followed by water quenching to make sure the secondary phases completely dissolve into austenitic matrix and prevent the grains coarsening too much. Initial time-temperature-precipitation (TTP) curve of aged 18Cr-16Mn-2Mo-1.1N HNS which starts with precipitation of 0.05% in volume fraction is defined and the “nose” temperature of precipitation is found to be 850 ℃ with an incubation period of 1 min. Hexagonal intergranular and cellular Cr2N with a=0.478 nm and c=0.444 nm precipitates gradually increase in the isothermal aging treatment. The matrix nitrogen depletion due to the intergranular and a few cellular Cr2N precipitates induces the decay of Vickers hardness, and the increment of cellular Cr2N causes the increase in the values. Impact toughness presents a monotonic decrease and SEM morphologies show the leading brittle intergranular fracture. The ultimate tensile strength (UTS), yield strength (YS) and elongation (El) deteriorate obviously. Stress concentration occurs when the matrix dislocations pile up at the interfaces of precipitation and matrix, and the interfacial dislocations may become precursors to the misfit dislocations, which can form small cleavage facets and accelerate the formation of cracks.
关键词:
solution-treated condition
,
aging precipitation behavior
,
time-temperature-precipitation curve
,
high nitrogen austenitic stainless steel
,
mechanical property
JIANG Zhou-hua
,
LI Shuang-jiang
,
LI Yang
钢铁研究学报(英文版)
A phase diagram was drawn through thermodynamic calculation to understand the equilibrium conditions of 2MgO·SiO2, MgO·Al2O3, 3Al2O3·2SiO2, and 2MgO·2Al2O3·5SiO2 formation in Mg-Al-Si-O system of 430 stainless steel melts at 1873 K. Further, the thermodynamic formation and transformation conditions of MgO·Al2O3 inclusion were discussed. The following results are obtained when wSi=026% and wO=10×10-5 in molten steel. The uniphase cordierite inclusion is difficult to exist stably; MgO·Al2O3 inclusion cannot be formed in case of wAl being less than 1×10-6; 3Al2O3·2SiO2 would change to MgO·Al2O3 and 2MgO·SiO2 in turn with increasing the Mg content when wAl is above 17×10-6; with the formation of MgO·Al2O3 inclusion, Al content increases with increasing Mg content when wMg is over 17×10-9. For equilibrium condition and calculated steel composition, 2MgO·SiO2 inclusion would be formed ultimately and MgO·Al2O3 is almost inexistent.
关键词:
phase diagram
,
thermodynamic calculation
,
MgO·Al2O3 inclusion
,
430 stainless steel
