Austenite grain growth behaviour of HSLA steel during reheating treatment

Wang, Fei (2017). Austenite grain growth behaviour of HSLA steel during reheating treatment. University of Birmingham. Ph.D.

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Abstract

The grain growth behaviour during reheating between 950 ºC and 1300 ºC of as-cast Al-Nb steel (containing 0.019 wt% Nb and 0.057 wt% Al) and rolled Nb-containing steel (containing 0.028 wt% Nb and 0.031 wt% Al) have been investigated. In particular the role of microalloying element segregation during casting and, hence the spatial distribution of microalloying precipitates, on grain boundary pinning during reheating has been considered. The Al-Nb containing steel has been examined in separate initial conditions, including as-cast (segregated structure), homogenised and forged (reduced separation of segregated bands) samples. It was found that microalloy segregation occurred between the dendritic and interdendritic regions, where the secondary dendrite arm spacing (SDAS) was 150 ± 50 μm. Nb showed strong segregation into the interdendritic regions resulting in a higher number density of Nb(C,N) precipitates (2.64 × 104 /mm2) compared to the dendritic region (0.73 × 104 /mm2). However, Al did not show strong segregation resulting in relatively well-distributed AlN precipitates in the matrix (1.29× 104 /mm2 in the interdendritic region and 1.89× 104 /mm2 in the dendritic region). After forging, the separation between the segregated bands was reduced to 65 ± 10 μm from the previous 150 ± 50 μm in the as-cast sample. The increased Nb content in the rolled Nb-containing steel compared to the Al-Nb steel gave a greater extent of segregation in the solute-enriched regions resulting in a larger number density of Nb(C,N) present (5.9× 104 /mm2), whilst the separation between in the segregated bands in the as-rolled Nb-containing steel was 35 ± 10 μm.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

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