• Journal of Welding and Joining
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• v.26 no.1
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• pp.76-82
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• 2008

The effect of Nb addition on the precipitation and precipitate coarsening behavior was investigated in Ti and Ti + Nb steel weld HAZ. A dilatometer equipped with a He-quenching system was used to simulate the weld thermal cycle. Compared to $TiC_yN_{1-y}$ precipitate in a Ti containing steel, $Ti_xNb_{1-x}C_yN_{1-y}$ complex particle with addition of Nb is precipitated in a Ti + Nb containing steel. Meanwhile, precipitate coarsening occurred more easily in Ti + Nb steel, which may be because the high temperature stability of $Ti_xNb_{1-x}C_yN_{1-y}$ complex particle is deteriorated by the Nb addition.

• Transactions of Materials Processing
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• v.3 no.4
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• pp.415-426
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• 1994

Multistage deformation behavior of Nb-microalloyed steel and carbon steel was studied by torsion test with declining temperature T, constant pass strain $\varepsilon_i$, interrupt time $(t_i)$, and varying strain rate $(\.{\varepsilon})$. In the range of $1000^{\circ}C~790^{\circ}C$ and 4.00/sec~0.38/sec, the flow stress at each pass was correlated to the deformation variables. As the finished deformation temperatures are decreased to the range of $790^{\circ}C~900^{\circ}C$, Nb precipitates play an important role on the grain refinement of Nb-microalloyed steel. the flow stress of Nb-microalloyed steel was higher than the carbon steel's while the grain size of Nb-microalloyed steel was smaller than carbon steel below the temperature of $900^{\circ}C$.

• Korean Journal of Materials Research
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• v.2 no.5
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• pp.343-352
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• 1992

The high temperature deformation behavior of microalloyed hot forging steels has been examined as a function of the temperature, the strain rate, and the alloying element by using high temperature compression test. The high temperature deformation mechanism, which was obtained by analyzing the flow stress-strain curve and microstructure, could be considered to dynamic recrystallization. The peak stress of Nb-V-Mo steel was more increased and the dynamic recrystallization of Nb-V-Mo steel was faster than those of Nb-V steel. The peak stress of 1.2Mn-0.09Nb steel was more increased and the dynamic recrystallization of 1.2Mn-0.09Nb was delayed a little bit than those of 1.0Mn-0.05Nb. The peak stress of C-Nb-V steel was more increased and the dynamic recrystallization of C-Nb-V steel was delayed than those of C-steel. The constitutive equation of high temperature deformation had a power law type. The grain size of dynamic recrystallization was refined as the Zener-Hollomon parameter was increased. The relation of the dynamic recrystallization grain size and Zener-Hollomon parameter could be quantified to power law.

• 한국신재생에너지학회:학술대회논문집
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• 2006.11a
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• pp.324-324
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• 2006

Nb and Ti were added to 316 stainless steel, and then heat-treatments and surface treatments were performed on the 316 stainless steel and the Nb- and Ti-added alloys. All samples indicated enhanced electrical conductivity after surface treatments, whereas they showed low electrical conductivity before surface treatments due to the existence of non-conductive passive film on the alloy surface. In particular, the Hb- and Ti-added alloys showed remarkable enhancement of electrical conductivity compared to the original alloy, 316 stainless steel. Surface characterization revealed that small carbide particles formed on the alloy surface after surface treatments, while the alloys indicated flat surface structure before surface treatments. $Cr_{23}C_6$ mainly formed on the 316 stainless steel, and NbC and TiC mainly formed on the Nb- and Ti-added alloys, respectively. We attribute the enhanced electrical conductivity after surface treatments to the formation of these carbide particles, possibly acting as a means of electro-conductive channel through the passive film. Furthermore, NbC and TiC are supposed to be more effective carbides than $Cr_{23}C_6$ as electro-conductive channels of stainless steel

• Journal of Korea Foundry Society
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• v.21 no.5
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• pp.280-285
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• 2001

Nb-containing austenitic stainless steel is widely used as exhaust frame and diffuser assembly in power plant. However, this steel is known to be difficult to produce by the continuous casting process due to the surface cracks. Therefore, the continuous casting technology was developed for the prevention of the surface cracks on CC slabs. Precipitates and the analysis of heat trasfer in a slab were investigated in order to find out the formation mechanism of surface cracks on cc slabs It was found that surface cracks are occurred due to the NbC precipitates, which are formed along the grain boundaries around $800^{\circ}C$. The secondary cooling pattern has been developed to produce the defect free CC slabs of Nb-containing austenitic stainless steel.

• Korean Journal of Materials Research
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• v.3 no.2
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• pp.131-139
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• 1993

Abstract Alloying elements such as AI, Ti, Nb and B in the extra low carbon AI-killed steel precipitate as nitrides or carbides and change the recrystallization texture structure of the steel during heattreatment with the result of strong effects on the deep drawability of the steel sheet. In this study the effects of fine precipitates such as nitrides and carbides on the texture of extra low carbon steels into which Ti, Nb, B, P, Si and Mn were added as alloying elements were investigated by means of TEM, SEM and optical microscopic analyses. Fine N$b_2$C and T$i_2$AIN precipitates are mainly observed in the steel containing both Nb and Ti, while fine AIN and coarse BN precipitates are observed in the Nb~containing steel and coarse T${i_4}{N_3}$ and ${N_10}{N_22}$/T$i_68$ precipitates are observed in the Ti-containing steel. The grain size of the Ti containing steel is larger than that of the Nb containing steel and that of the one containing both Nb and Ti.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.217-218
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• 2006

More and more applications or demands for machine parts etc are expected for AISI 440C (hereinafter referred to as "440C") Stainless Steel because of its characteristic features, i.e. high-strength as well as high-corrosion resistance. This research has enabled us to obtain sintered products with good quality even under a wide range of temperature by utilizing the pinning effect of NbC, improving the relevant sintering feature of 440C Stainless Steel in the MIM method.

• Korean Journal of Materials Research
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• v.3 no.1
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• pp.43-49
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• 1993

Excellent deep drawability and strain aging rsistance are obtained by the addition of alloying elements such as Ti and Nb which can form carbide and nitride easily into Al killed extra low carbon steel. Recrystallization textures and mechanical properties of the three different extra low carbon steels with B containing Nb only, Ti only, and both Nb and Ti, respectively, along with have been compared. Inverse pole figure shows that (100) and (111) texture intensities of Nb containing steel changed a lot during the annealing treatment and the degree of texture-structural change in the steel containing both Nb and Ti is about the same as that in the Ti-containing 5teel. After annealing the pole figure shows that the {Ill} < 110 > and {112} < 110> textures are the strongest in the cold rolled state and the annealed state, respectively. However, there is little difference in texture structure among the three kinds of steels. There is a tendency that the steel containing both Nb and Ti the grain size of which is the smallest is the highest in hardness. Nb-containing steel is the next and Ti -containing steel is the last in hardness.

• Journal of the Korean Society for Heat Treatment
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• v.16 no.2
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• pp.83-89
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• 2003

As a research for developing fine-grained high strength low carbon steels, the effects of austenitization temperature and hot deformation on microstructure was investigated in 0.15 wt.% carbon steels with microalloying elements such as Nb and Ti. When the steels were reheated at $1250^{\circ}C$, Nb containing steel showed very coarse austenite grain size of $200{\mu}m$ whereas Nb-Ti steel did fine one of $70{\mu}m$ because Ti carbonitrides could suppress the austenite grain growth. In case of 50% reduction at $850^{\circ}C$, the austenite grains in the Nb steel partially recrystallized while those in the Nb-Ti steel fully recrystallized probably due to finer prior austenite grains.For the Nb-Ti steel, ferrite grain size was not sensitively changed with austenitization temperature and compression strain and, severe deformation of 80% reduction was not essentially necessary to refine ferrite grains to about $3{\mu}m$ which could be obtained through lighter deformation of 40% reduction.

• Journal of the Korean institute of surface engineering
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• v.49 no.3
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• pp.274-279
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• 2016

Stainless steel is widely used in various industries due to its excellent anti-corrosion characteristics. However, if the stainless steel is exposed to high speed fluid flow and chloride ion in the marine environment, corrosion and cavitation damage occurred on the surface easily. Therefore, to prevent these problems, stabilzed stainless steel is applied to offshore and shipbuilding industries. In this study, stabilized stainless steel specimen was made by 19%Cr-9%Ni with different Nb contents (0.29%, 0.46% and 0.71%). And then, their cavitation characteristics were investigated. As a result, the characteristics of cavitation resistance of stainless steel could be improved by increasing Nb contents.