Microalloyed steel

About: Microalloyed steel is a research topic. Over the lifetime, 2183 publications have been published within this topic receiving 33586 citations.

The Microstructure Evolution of Nb, Ti Complex Microalloyed Steel during the CSP Process

Abstract: The development of microstructure of Nb,Ti-bearing microalloyed steel during the CSP process was studied. Three samples were taken from the as-cast slab prior to tunnel furnace, intermediate bar after stand F2 and the hot band, respectively. In the as-cast slab, the average austenite grain size is 654 µm with a large size range from 150 to 2000 µm. In the intermediate bar after stand F2, the austenite grains are remarkably refined, but are heterogenous due to the incomplete recrystallization, which are in the size range of 23 to 116 µm. In the hot band is mainly non-polygonal ferrite. Microstructural heterogeneity exists in the hot band. It is attributed to the heterogeneous austenite grain size in the intermediate bar and the less rolling reduction after stand F2. With regards to precipitation, cubic TiN and fine precipitates less than 20nm are commonly observed in the as-cast slab and the intermediate bar. Some complex (Ti,Nb)(C,N) precipitates with a slightly larger size also exist. In the hot band, most particles are complex (Ti,Nb)(C,N) precipitates, in a shape of irregular or cruciform. The fine precipitates which can strengthen the ferrite matrix are seldom seen. These results are in good agreement with the size distribution of the precipitates determined using small angle X-ray scattering method. The chemical phase analysis reveals that 45%Nb of the total and 43%Ti of the total are still in solution in ferrite of the hot band.

Hot ductility trough elimination through single cycle of intense cooling and reheating for microalloyed steel casting

Abstract: Surface transverse cracking, especially corner cracking, is prone to generate in continuously cast slabs of microalloyed steels The method of surface structure control (SSC) was supposed to the best way to avoid the detrimental defects However, the mechanism of improving hot ductility by SSC and the specific parameters to control the process are still unclear for the reasonable adoption in production In the present work, the impact of cooling rate, holding temperature and holding time on austenite decomposition, and the austenite grain size before and after intense cooling were investigated by thermal simulation method With the increase of cooling rate, it is observed that the phase is transformed from austenite → grain boundary film-like alltromorph ferrite → Widmanstatten ferrite plates (or intragranular ferrite plates) → bainite+martensite Mostly important, the film-like ferrite can be eliminated through intense cooling and the following reheating, but the austenite grain size is not observed to b

Determination of no-recrystallisation temperature in Nb-V-Ti microalloyed steel and discussion of its definition

Abstract: Using torsion tests, the no-recrystallisation temperature Tnr was determined for two cooling rates in a Nb-V-Ti microalloyed steel. The same tests made it possible to deduce the Ar3 phase transformation temperature. When Tnr is known, it is possible to establish approximately the conditions for which the strip rolling or plate rolling of this steel must be performed to obtain the appropriate microstructure. With the aid of a recrystallisation model and the results obtained in other work, a discussion is made of the concept of Tnr the conclusion being that it represents the temperature above which the fraction recrystallised between consecutive passes reaches a value close to 50% and not 100%. This parameter, and the value of Ar3, can be determined at minimal cost and in a relatively short time. Both economic and time aspects are of interest to any steel manufacturer producing hot rolled microalloyed steels.

Effect of Retained Strain on the Microstructural Evolution during the Austenite to Ferrite Transformation

Abstract: In the present work the transformation behaviour of a C-Mn-Nb steel deformed by torsion at temperatures both above and below the non recrystallisation temperature for this steel has been studied in detail. After deformation, specimens were cooled at a constant cooling rate of 1°C/s, and interrupted quenching from different temperatures was used to observe different stages of transformation. In the case of transformation from deformed austenite, in addition to the austenite grain boundaries, the deformation bands and twin boundaries act also as preferential nucleation sites for the ferrite. It has been observed that in all the cases when impingement becomes important, the number of grains per unit volume decreases significantly during transformation denoting that ferrite coarsening is taking place.

Microstructure and mechanical properties of laser surface treated 44MnSiVS6 microalloyed steel

Abstract: Fatigue property improvement for automotive components such as crankshafts can be achieved through material selection and tailored surface design. Microalloyed steels are of high interest for automotive applications due to their balanced properties, excellent hardenability and good machinability. Lasers facilitate efficient and precise surface processing and understanding the laser-material-property interrelationships is the key to process optimisation. This work examines microstructural development during laser surface treatment of 44MnSiVS6 microalloyed steel and the r esulting mechanical properties. Laser beam shaping techniques are employed to evaluate the impact of beam shaping on the process. It revealed that ferrite structures remain in the treated area surrounded by martensite due to insufficient heating and dwell time of carbon diffusion.