Ultra-Fine Grain Size by Dynamic Recrystallization in Strip Rolling of Nb Microalloyed Steel

2005 ◽  
pp. 141-144
Author(s):  
S.V. Subramanian ◽  
G. Zhu ◽  
Christian Klinkenberg ◽  
Klaus Hulka
Keyword(s):  
Grain Size ◽  
Dynamic Recrystallization ◽  
Microalloyed Steel ◽  
Strip Rolling ◽  
Fine Grain ◽  
Nb Microalloyed Steel

Ultra-Fine Grain Size by Dynamic Recrystallization in Strip Rolling of Nb Microalloyed Steel

2005 ◽  
Vol 475-479 ◽  
pp. 141-144 ◽  
Author(s):  
S.V. Subramanian ◽  
G. Zhu ◽  
Christian Klinkenberg ◽  
Klaus Hulka
Keyword(s):  
Grain Size ◽  
Dynamic Recrystallization ◽  
Large Strain ◽  
Quantitative Model ◽  
Temperature Deformation ◽  
Strain Accumulation ◽  
Strip Rolling ◽  
Fine Grain ◽  
Dynamic Recrystallisation ◽  
Nb Microalloyed Steel

The design of base chemistry and optimization of rolling schedule are the two important factors that influence large strain accumulation in multi-pass rolling in order to obtain ultra-fine grain size by dynamic recrystallization. A base chemistry of 0.03C-0.003N-0.08Nb-0.015Ti-1.8Mn (all in weight %) of HTP steel design was chosen in order to control the time evolution of strain induced precipitation of NbC and the strain accumulation through precipitate interaction with recovery and recrystallization at short inter-pass times characteristic of strip rolling. Experimental data on the critical strain for static and dynamic recrystallisation for HTP steel are used in a quantitative model to predict strain accumulation pass by pass and to achieve grain refinement by dynamic recrystallisation through large strain accumulation. The model is used to optimize the time-temperature-deformation schedule to prevent static recrystallization during the inter-pass times and to target ultra-fine grain size through dynamic recrystallization by large strain accumulation. The model predictions are validated by simulation of strip rolling of HTP steel on the thermo-mechanical simulator (WUMSI) to obtain a uniform ultra-fine ferrite grain size of about 1.5 micrometer diameter in final ferrite microstructure.

Processing and Oxidation of Nitride Stabilized 18Cr-20Ni Stainless Steel

1994 ◽  
Vol 362 ◽  
Author(s):  
C. S. McDowell ◽  
S. N. Basu ◽  
T. Ando
Keyword(s):  
Grain Size ◽  
Stainless Steel ◽  
High Temperature ◽  
Microalloyed Steel ◽  
Isothermal Oxidation ◽  
Spray Forming ◽  
Temperature Oxidation ◽  
Fine Grain ◽  
High Temperature Oxidation Behavior ◽  
Grain Boundary Pinning

AbstractThe present investigation explores the use of nitride precipitates for grain-size stabilization in a 18Cr-2ONi austenitic stainless steel for high temperature applications in oxidizing atmospheres. The potential for reductions in alloying contents of such steels has become a focus of research out of concern for the conservation of strategic alloying elements such as Cr. In order for the alloy to maintain superior oxidation resistance, it must sustain a fine grain size by virtue of effective grain boundary pinning by stable precipitates.Al and Ti microalloyed 18Cr-20Ni steels have been nitrided using rapid solidification processing (spray forming) and subjected to thermomechanical treatments to precipitate nitrides from the supersaturated solid solutions. The spray formed deposits were cold rolled to increase the density of dislocations, which act as sites for nucleation of nitride precipitates. The alloys were then annealed to nucleate and grow the precipitates, followed by cold rolling and recrystallization to generate a stable, fine grained microstructure. The Ti-microalloyed steel demonstrated high-temperature grain size stability by maintaining a grain size of≈7μm after 600h at 1000°C.The Ti-microalloyed steel has been subjected to isothermal oxidation in air at 900°C. The results of preliminary oxidation experiments are reported. The spray deposited and thermomechanically processed alloy demonstrated high-temperature oxidation behavior superior to conventionally processed (hot rolled and annealed) alloys.

Dynamic Recrystallization of Ferrite in a Low Carbon Nb-Microalloyed Steel

2005 ◽  
Vol 475-479 ◽  
pp. 149-152 ◽  
Author(s):  
Long Fei Li ◽  
Wang Yue Yang ◽  
Zu Qing Sun
Keyword(s):  
Dynamic Recrystallization ◽  
Hot Deformation ◽  
Microalloyed Steel ◽  
Phase Region ◽  
Ferrite Phase ◽  
Recrystallization Process ◽  
Low Carbon ◽  
Promoting Effect ◽  
Nb Microalloyed Steel ◽  
Average Size

The hot deformation behavior of a low carbon Nb-microalloyed steel is investigated by hot compression test in the ferrite phase region compared with a low carbon steel with similar compositions, and the effect of Nb on dynamic recrystallization of ferrite is analyzed. Results indicate that during hot deformation in the ferrite phase region, the effect of Nb solely depends on the size of NbC precipitates. Tiny particles which average size is about 7.5nm have a retarding effect on dynamic recrystallization process of ferrite, on the contrary, coarser particles which average size is about 30.6nm have a promoting effect and are of benefit to the refinement of recrystallized grains.

Effect of Rare Earth Addition on Dynamic Recrystallization and Precipitation Behavior of a Niobium-Containing Microalloy Steel

2013 ◽  
Vol 762 ◽  
pp. 189-193
Author(s):  
Hai Yan Wang ◽  
Hui Ping Ren ◽  
Hui Yang ◽  
S.D. Wang ◽  
D.X. Li
Keyword(s):  
Rare Earth ◽  
Dynamic Recrystallization ◽  
Dynamic Recovery ◽  
Microalloyed Steel ◽  
Carbon Activity ◽  
Precipitation Behavior ◽  
Rare Earth Addition ◽  
Transmission Electron ◽  
Nb Microalloyed Steel ◽  
Means Of Transmission

Hot compression experiments were carried out on rare earth (RE) added and RE-free Nb-containing steels by using a Gleeble simulator. Stress-strain curves obtained at various temperatures were analyzed to investigate the dynamic recovery and dynamic recrystallization softening behaviours. Morphology, size and number of precipitates in the both steels were examined by means of transmission electron microscopy (TEM). The results showed that, for the experimental Nb-containing steel, the grain size was fined by the RE addtion. In general, dynamic recrystallization cant occur in two steel under 40% deformation rates, and the deformation resistance of RE-containing steel is higher than that of RE-free steel in both the the austenite and ferrite temperatures range.While under the higher deformation rate, the dynamic recovery starting strains of the RE addition steel are higher than that of RE-free steel.It is also shown that the number of precipitate in the RE-containing steel more than that in the RE-free steel, which is due to the RE increasing nucleation rate and promoting Nb carbonitrides precipitation growth in the austenite region. Furthermore, the carbon activity may change by the RE addition, and thereby promote the precipitation strengthening of Nb-microalloyed steel.

Austenite Grain Size of Thin Slab and Its Influence on Direct Hot Strip Rolling of Nb Microalloyed Steel

2005 ◽  
Vol 500-501 ◽  
pp. 295-302 ◽  
Author(s):  
Hong Tao Zhang ◽  
Ganyun Pang ◽  
Rui Zhen Wang ◽  
Chengbin Liu
Keyword(s):  
Grain Size ◽  
Grain Refinement ◽  
Microalloyed Steel ◽  
Thin Slab ◽  
Hot Strip Rolling ◽  
Austenite Grain Size ◽  
Thick Slab ◽  
Rolling Pass ◽  
Austenite Grain ◽  
Nb Microalloyed Steel

In the production with thin slab casting a serious problem of insufficient grain refinement and microstructural inhomogeneity has been found. In this paper attention has been paid to the austenite grain size changes in thin slab of a high strength Nb microalloyed steel under as-cast conditions and after first rolling pass. For comparison, the conventional thick slab was also investigated. It was found that although as-cast thin slab shows a smaller average austenite grain size than that of as cast thick slab; the latter after reheating shows a much finer average austenite grain size. The first rolling pass at high temperature and with heavy reduction causes rapid recrystallization that contributes to austenite grain refinement.

Effect of Initial Austenite Microstructure on the Softening – Precipitation Interaction in a Low Nb Microalloyed Steel

2007 ◽  
Vol 550 ◽  
pp. 429-434 ◽  
Author(s):  
C. Iparraguirre ◽  
Ana Isabel Fernández-Calvo ◽  
Beatriz López
Keyword(s):  
Grain Size ◽  
Microalloyed Steel ◽  
Recovery Process ◽  
Precipitation Kinetics ◽  
Austenite Grain Size ◽  
Austenite Grain ◽  
Nb Microalloyed Steel ◽  
Niobium Microalloyed Steel ◽  
Softening Fraction

The influence of initial grain size on the softening-precipitation interaction in a low niobium microalloyed steel has been investigated. The study has revealed that for the largest initial grain size (1000 μm), the recrystallised fraction remains lower than the softening fraction until relatively long times are reached. In contrast, for the smallest initial grain size (166 μm) both magnitudes are similar. As a result, precipitation interacts with recrystallisation in the case of the finest austenite grain size, whereas for the coarsest one, since recrystallisation is significantly retarded, interaction with recovery process is observed. Apparently, the initial austenite grain size does not affect precipitation kinetics.

Sign in / Sign up

Export Citation Format

Share Document