常亮
,
张伟
,
杨超
,
陈湘茹
,
华勤
,
翟启杰
上海金属
利用图像分析软件定量分析了铌对球墨铸铁石墨球形态和铸态组织的影响.研究结果表明,添加铌能够使石墨化程度和球化率降低,圆度和石墨球大小增加,石墨球数量显著降低,但少量铌对球墨铸铁的石墨化、球化率、圆度、石墨球大小等影响不大.少量铌能显著增加珠光体数量.
关键词:
球墨铸铁
,
铌
,
石墨球
,
珠光体
Song XIANG
,
Guoquan LIU
,
Yang LI
,
Changrong LI
,
ong WANG
,
null
,
null
,
null
,
null
,
null
材料科学技术（英文）
Microalloying element Nb in low carbon steels produced by compact strip production (CSP) process plays an important role in inhibiting recrystallization, decreasing the transformation temperature and grain refinement. With decreasing the rolling temperature, dislocations can be pinned by carbonitrides and the strength is increased. Based on the two sublattice model, with metal atom sublattice and interstitial atom sublattice, a thermodynamic model for carbonitride was established to calculate the equilibrium between matrix and carbonitride. In the steel produced by CSP, the calculation results showed that the starting temperature of precipitation of Ti and Nb are 1340℃ and 1040℃, respectively. In the range of 890-950℃, Nb rapidly precipitated. And the maximum of the atomic fraction of Nb in carbonitride was about 0.68. The morphologies and energy spectrum of the precipitates showed that (NbTi) (CN) precipitated near the dislocations. The experiment results show that Nb rapidly precipitated when the temperature was lower than 970℃, and the atomic fraction of Nb in carbonitride was about 60%-80%. The calculation results are in agreement with the experiment data. Therefore the thermodynamic model can be a useful assistant tool in the research on the precipitates in the low carbon steels produced by CSP.
关键词:
Compact strip production
,
strip
,
production
,
niobium
,
low
,
car
J.Rassizadehghani
,
H.Najafi
,
M.Emamy
,
G.Eslami-Saeen
材料科学技术（英文）
The influence of microalloying additions on the mechanical properties of a low-carbon cast steel containing combinations of V, Nb, and Ti in the as-cast condition was evaluated. Tensile and hardness test results indicated that good combinations of strength and ductility could be achieved by V and Nb additions. While the yield strength and UTS (ultimate tensile strength) increased up to the range of 378–435 MPa and 579–596 MPa, respectively in the microalloyed heats, their total elongation ranged from 18% to 23%. The presence of Ti, however, led to some reduction in the strength. Microstructural studies including scanning electron microscopy (SEM) and optical microscopy revealed that coarse TiN particles were responsible for this behavior. The Charpy impact values of all compositions indicated that microalloying additions significantly decreased the impact energy and led to the dominance of cleavage facets on the fracture surfaces. It seems that the increase in the hardness of coarse ferrite grains due to the precipitation hardening is the main reason for brittle fracture.
关键词:
Cast steel
,
null
,
null
,
null
,
null
Yating Shan
材料科学技术（英文）
The grain structures and the precipitates in the solidification microstructure of the ultra pure 17 wt% Cr ferritic stainless steels with different Ti and/or Nb micro-alloying were investigated both experimentally and theoretically. It was found by the grain structure observation that the addition of Ti or Nb to the steel
reduced the grain size (D) and elongation factor (E), and improved the equiaxed grain proportion (P) and globularity factor (ζ). Among the four steels studied, the minimum grain size and maximum equiaxed grain proportion were obtained by jointly adding both Ti and Nb to the steel. The SEM observation indicated that several kinds of precipitations, such as TiN, MC (rich in Nb), Laves phase (Fe2Nb) and so on, formed in the corresponding steels. In addition, the results calculated using the Thermo-Calc software illustrated that TiN precipitates in the liquid at proper Ti and N contents. Meanwhile, the solidification interval (?T) was enlarged by the addition of Ti or Nb, and the effectiveness of Nb was stronger than Ti. Based on the experimental and calculation results, the mechanisms of grain refinement and increment in equiaxed grain proportion were
discussed.
关键词:
Ultra pure ferritic stainless steel
