Grain Boundary Strengthening in Austenitic Nitrogen Steels

Gavriljuk, V.G.; Berns, Hans; Escher, C.; Glavatskaya, N.I.; Sozinov, A.; Petrov, Yu. N.

doi:10.4028/www.scientific.net/msf.318-320.455

Cited by 13 publications

(6 citation statements)

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“…For high manganese steel and high nitrogen steel, the NES of different solute atoms during quenching process had been previously reported [24,25]. Combined with the above discussions, it can be deduced that the transformation of the NES state of the solute atoms at the grain boundaries leads to the AGG in the HAZ of the joint for the present steel during the whole FSW process and the subsequent heat treatment.…”

Section: Discussionsupporting

confidence: 60%

Abnormal Grain Growth in the Heat Affected Zone of Friction Stir Welded Joint of 32Mn-7Cr-1Mo-0.3N Steel during Post-Weld Heat Treatment

et al. 2018

Metals

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The abnormal grain growth in the heat affected zone of the friction stir welded joint of 32Mn-7Cr-1Mo-0.3N steel after post-weld heat treatment was confirmed by physical simulation experiments. The microstructural stability of the heat affected zone can be weakened by the welding thermal cycle. It was speculated to be due to the variation of the non-equilibrium segregation state of solute atoms at the grain boundaries. In addition, the pressure stress in the welding process can promote abnormal grain growth in the post-weld heat treatment.

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Section: Discussionsupporting

confidence: 60%

Abnormal Grain Growth in the Heat Affected Zone of Friction Stir Welded Joint of 32Mn-7Cr-1Mo-0.3N Steel during Post-Weld Heat Treatment

et al. 2018

Metals

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“…12) However, each mechanism was only demonstrated indirectly in a certain kind of steel, and there are also counterarguments for each mechanism. Although we have never reached a consensus, the most frequently used idea, including nonferrous materials, would be the (3) grain boundary segregation theory.…”

Section: Change In Hall-petch Coefficient By Grainmentioning

confidence: 99%

“…8,10) (2) Planar slip of dislocations promoted by nitrogen enhances the grain refinement strengthening. 8,[11][12][13] (3) Grain boundary segregation of nitrogen atoms stabilizes the ledge structure of grain boundary working as a dislocation source.…”

Section: Change In Hall-petch Coefficient By Grainmentioning

confidence: 99%

Effect of Interstitial Elements on Hall–Petch Coefficient of Ferritic Iron

et al. 2008

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Here, on the assumption that the classical grain boundary segregation theory would be applied to the case of this study, namely, carbon in ferritic steel, the Hall-Petch coefficient was compared with the concentration of carbon at grain boundary. According to the MacLean's theory, 17) solute carbon concentration segregated at ferrite grain boundary at 973 K is calculated by following equation:In this equation, [at%C], Q and R are the total carbon concentration in solid solution, the activation energy of carbon for grain boundary segregation and the gas constant, respectively. As for the value of Q, 78 kJ/mol estimated by Grabke 18) was taken. Figure 6 shows relationship between k y and segregated carbon content calculated by Eq. (3). k y value tends to increase linearly with increasing segregated carbon content, which suggests that grain boundary segregation of interstitial alloy elements significantly prevents the yielding of ferritic steel. Only 60 ppm carbon causes marked grain boundary segregation to 80 at%, resulting in the enlargement of the k y from 100 (in IF-steel) to 550 MPa · mm 1/2 . The solubility of carbon was reported to be approximately 60 ppm even at ambient temperature 19) in Fe-C binary alloy. Therefore, it could be understood that the similar k y values, around 600 MPa · mm 1/2 , have been reported in lots of previous studies on grain refinement strengthening of ferritic steels except for IF-steels. On the other hand, it is known that nitrogen has less tendency to cause grain boundary segregation in steel, as compared to carbon. [20][21][22] This agrees well with the experimental results that k y is hardly influenced by nitrogen. The enlarged k y by nitrogen mentioned above might be due to the large amount of solute nitrogen in austenite matrix leading to the high concentration of nitrogen at grain boundary even though the segregation coefficient is small. Conclusions(1) IF-steel has a low Hall-Petch coefficient of approximately 100 MPa · mm 1/2 . The Hall-Petch coefficient of ferritic iron monotonously increases with increasing solute carbon content, and it levels off at 550-600 MPa · mm 1/2 when the solute carbon content reaches 60 ppm. On the other hand, the solute nitrogen hardly affects the Hall-Petch coefficient.(2) The increase in Hall-Petch coefficient by solute carbon seems to be derived from the grain boundary segregation of carbon atoms. The small effect of solute nitrogen on Hall-Petch coefficient could be explained by the less tendency of nitrogen atoms to cause grain boundary segregation. ISIJ, Tokyo, Japan, (1991), 762. 12) V. G. Gavriljuk, H. Berns, C. Escher, N. I. Glavatskaya, A. Sozinov and Yu. N. Petrov: Mater. Sci. Forum, 318-320 (1999)

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“…* The change in hardness and normalized nitrogen concentration successfully coincide at any solution nitriding time in both of the plate and the wire materials. Since the hardness of austenite matrix is proportional to the solute nitrogen concentration up to 0.7 % in nitrogen-bearing austenitic stainless steels, 7) this result indicates the validity of the profile of normalized nitrogen concentration which has been calculated.…”

Section: Methodsmentioning

confidence: 66%