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Study of the effect of nano-sized precipitates on the mechanical properties of boron-added low-carbon steels by neutron scattering techniques.

Seong BS, Cho YR, Shin EJ, Kim SI, Choi SH, Kim HR, Kim YJ - J Appl Crystallogr (2008)

Bottom Line: In the BA steels, the number of boron precipitates, such as BN, Fe(3)(C,B) and MnS, surrounded by BN layers increased drastically at higher hot-rolling temperatures.The volume fraction of the fine precipitates of the BA steels was higher than that of the BF steels; this difference is related to the rapid growth of the BN layers on the MnS and CuS precipitates.Boron addition to low-carbon steels resulted in a reduction in strength and an improvement in elongation; this behaviour is related to the reduction of the solute carbon and the nitrogen contents in the ferrite matrix caused by the precipitation of BN, as well by the increase in the volume fraction of the cementites.

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ABSTRACT
Small-angle neutron scattering (SANS) and neutron powder diffraction (ND) techniques were used to study quantitatively the effect of nano-sized precipitates and boron addition on the mechanical properties of low-carbon steels. SANS was used to evaluate nano-sized precipitates, smaller than about 600 A in diameter, and ND was used to determine the weight fraction of the cementite precipitates. Fine core-shell structured spherical precipitates with an average radius of ~50 A, such as MnS and/or CuS, surrounded by BN layers were observed in the boron-added (BA) low-carbon steels; fine spherical precipitates with an average radius of ~48 A were mainly observed in the boron-free (BF) low-carbon steels. In the BA steels, the number of boron precipitates, such as BN, Fe(3)(C,B) and MnS, surrounded by BN layers increased drastically at higher hot-rolling temperatures. The volume fraction of the fine precipitates of the BA steels was higher than that of the BF steels; this difference is related to the rapid growth of the BN layers on the MnS and CuS precipitates. Boron addition to low-carbon steels resulted in a reduction in strength and an improvement in elongation; this behaviour is related to the reduction of the solute carbon and the nitrogen contents in the ferrite matrix caused by the precipitation of BN, as well by the increase in the volume fraction of the cementites.

No MeSH data available.


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Rietveld refinement results for the BF low-carbon steel with a rolling temperature of 1148 K. Inset shows the refinement results of minor cementite phases.
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fig1: Rietveld refinement results for the BF low-carbon steel with a rolling temperature of 1148 K. Inset shows the refinement results of minor cementite phases.

Mentions: In order to evaluate the total weight fraction of cementite in the BF and BA steels, ND was combined with Rietveld refinement. As an example of Rietveld refinement, the ND pattern of BF steel with a rolling temperature of 1148 K is shown in Fig. 1 ▶. The observed intensities are depicted by circles and the upper solid line represents the calculated fits. The three rows of small bars represent the Bragg reflection positions of the bcc phase (ferrite and bainite), the bainite–cementite phase in space group P6322 and the cementite phase in space group Pbnm. The lower solid line represents the differences between the observed and calculated intensities. The inset represents the Rietveld refinement result of some cementite peaks. Even though the cementite peaks are very weak, the calculated data seem to be in good agreement with the measured data. The refined lattice parameters of the cementite phase (Pbnm) are a = 4.65, b = 5.13 and c = 8.10 Å. As this c value is larger than that of c = 6.74 Å given in the literature (Cullity, 1978 ▶), it appears that a metastable phase forms during the hot-rolling process.


Study of the effect of nano-sized precipitates on the mechanical properties of boron-added low-carbon steels by neutron scattering techniques.

Seong BS, Cho YR, Shin EJ, Kim SI, Choi SH, Kim HR, Kim YJ - J Appl Crystallogr (2008)

Rietveld refinement results for the BF low-carbon steel with a rolling temperature of 1148 K. Inset shows the refinement results of minor cementite phases.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2553556&req=5

fig1: Rietveld refinement results for the BF low-carbon steel with a rolling temperature of 1148 K. Inset shows the refinement results of minor cementite phases.
Mentions: In order to evaluate the total weight fraction of cementite in the BF and BA steels, ND was combined with Rietveld refinement. As an example of Rietveld refinement, the ND pattern of BF steel with a rolling temperature of 1148 K is shown in Fig. 1 ▶. The observed intensities are depicted by circles and the upper solid line represents the calculated fits. The three rows of small bars represent the Bragg reflection positions of the bcc phase (ferrite and bainite), the bainite–cementite phase in space group P6322 and the cementite phase in space group Pbnm. The lower solid line represents the differences between the observed and calculated intensities. The inset represents the Rietveld refinement result of some cementite peaks. Even though the cementite peaks are very weak, the calculated data seem to be in good agreement with the measured data. The refined lattice parameters of the cementite phase (Pbnm) are a = 4.65, b = 5.13 and c = 8.10 Å. As this c value is larger than that of c = 6.74 Å given in the literature (Cullity, 1978 ▶), it appears that a metastable phase forms during the hot-rolling process.

Bottom Line: In the BA steels, the number of boron precipitates, such as BN, Fe(3)(C,B) and MnS, surrounded by BN layers increased drastically at higher hot-rolling temperatures.The volume fraction of the fine precipitates of the BA steels was higher than that of the BF steels; this difference is related to the rapid growth of the BN layers on the MnS and CuS precipitates.Boron addition to low-carbon steels resulted in a reduction in strength and an improvement in elongation; this behaviour is related to the reduction of the solute carbon and the nitrogen contents in the ferrite matrix caused by the precipitation of BN, as well by the increase in the volume fraction of the cementites.

View Article: PubMed Central - HTML - PubMed

ABSTRACT
Small-angle neutron scattering (SANS) and neutron powder diffraction (ND) techniques were used to study quantitatively the effect of nano-sized precipitates and boron addition on the mechanical properties of low-carbon steels. SANS was used to evaluate nano-sized precipitates, smaller than about 600 A in diameter, and ND was used to determine the weight fraction of the cementite precipitates. Fine core-shell structured spherical precipitates with an average radius of ~50 A, such as MnS and/or CuS, surrounded by BN layers were observed in the boron-added (BA) low-carbon steels; fine spherical precipitates with an average radius of ~48 A were mainly observed in the boron-free (BF) low-carbon steels. In the BA steels, the number of boron precipitates, such as BN, Fe(3)(C,B) and MnS, surrounded by BN layers increased drastically at higher hot-rolling temperatures. The volume fraction of the fine precipitates of the BA steels was higher than that of the BF steels; this difference is related to the rapid growth of the BN layers on the MnS and CuS precipitates. Boron addition to low-carbon steels resulted in a reduction in strength and an improvement in elongation; this behaviour is related to the reduction of the solute carbon and the nitrogen contents in the ferrite matrix caused by the precipitation of BN, as well by the increase in the volume fraction of the cementites.

No MeSH data available.


Related in: MedlinePlus