Temperature Dependence of Austenite Nucleation Site on Reversion of Lath Martensite

2010 ◽  
Vol 638-642 ◽  
pp. 3424-3429 ◽  
Author(s):  
Nobuo Nakada ◽  
Toshihiro Tsuchiyama ◽  
Setsuo Takaki ◽  
Naoki Miyano
Keyword(s):  
Grain Boundary ◽  
Temperature Dependence ◽  
Elastic Strain ◽  
Prior Austenite ◽  
Nucleation Site ◽  
Lath Boundary ◽  
Austenite Grain ◽  
Austenite Grains ◽  
Austenite Grain Boundary ◽  
Prior Austenite Grain

The temperature dependence of austenite nucleation behavior within lath martensitic structure was investigated in an ultralow carbon 13%Cr-6%Ni martensitic stainless steel partially reversed at (austenite + ferrite) two phase region. The shape and nucleation site of the reversed austenite grains were varied depending on the reversion temperature; fine acicular austenite grains frequently formed along the lath boundaries at a temperature lower than 915 K, while the granular ones tended to nucleate mainly on the prior austenite grain boundaries at a higher temperature. In order to explain the temperature dependence of nucleation site transition, the difference in energetics of austenite nucleation between the lath boundary and the prior austenite grain boundary was discussed on the basis of the classical nucleation theory and FEM analysis. The calculation of the changes in interfacial energy and elastic strain for austenite nucleation suggested that the lath boundary acts as more preferential nucleation sites for austenite rather than the prior austenite grain boundary to reduce the increment of elastic strain when the reversion temperature is low.

Cavitation control in steels of high residual element content

1980 ◽  
Vol 295 (1413) ◽  
pp. 305-305 ◽  
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Prior Austenite ◽  
Low Alloy Steels ◽  
Boundary Zone ◽  
Austenite Grain ◽  
Alloy Steels ◽  
Austenite Grain Boundary ◽  
Prior Austenite Grain ◽  
Transverse Boundary

The cavitational mode of failure of prior austenite grain boundaries in bainitic creep-resisting low alloy steels is now well established as a principal factor in the high incidence of cracking problems which has developed on modern power plant in recent years. The microstructural features dominating the cavitation process at the reheat temperature in a ½CMV bainitic steel of high classical residual level have been determined. The prior austenite grain boundaries become zones of comparative weakness ca . 1 pm thick at 700 °C and are incapable of sustaining significant shear loads. Deformation is therefore initiated by a relaxation of load, through a process of prior austenite grain boundary zone shear, from inclined to transverse boundaries such that a concentration of normal stress develops across the latter. The overall deformation is thereafter determined by cavitation of the transverse boundary zones, the necessary inclined boundary displacements being accommodated by further grain boundary zone shear. Transverse boundary cavitation is shown to be an essentially time-independent process of localized ductile microvoid coalescence resulting from the plastic deformation of the boundary zone.

Prior austenite grain boundary embrittlement of low alloy steel by boron

1980 ◽  
Vol 295 (1413) ◽  
pp. 298-298
Keyword(s):  
Grain Boundary ◽  
Prior Austenite ◽  
Alloying Element ◽  
Reheat Cracking ◽  
Austenite Grain ◽  
Segregation Effect ◽  
Commercial Steel ◽  
Grain Boundary Embrittlement ◽  
Austenite Grain Boundary ◽  
Prior Austenite Grain

A previous study of reheat cracking in a CrMoV steel (Ducol W-30), in which the fracture toughness of the coarse grain size region of the h.a.z. was measured as a function of temperature, revealed a large decrease in toughness at 600 °C accompanied by prior austenite grain boundary (p.a.g.b.) fracture (Ritter & McPherson 1974). This severe embrittlement was eliminated if the steel was heated to 680 °C before testing at 600 °C suggesting that the effect may have been associated with a p.a.g.b. segregation effect. This hypothesis has been examined by comparing the degree of embrittlement at 600 °C of specimens with stimulated h.a.z. microstructures prepared from laboratory heats, with the same alloying element composition as the commercial steel used previously, but doped with the trace elements, S, P, As, Sb, Sn, Gu, A1 and B, singly or in various combinations.

Effects of V and Carbides on the Temper Embrittlement of the 2.25Cr-1Mo Steel

2006 ◽  
Author(s):  
Jeong Tae Kim ◽  
Byung Hoon Kim ◽  
Byeong Ook Kong ◽  
Dong Jin Kim
Keyword(s):  
Transition Temperature ◽  
Grain Boundary ◽  
Prior Austenite ◽  
Temper Embrittlement ◽  
Aging Treatment ◽  
Atomic Ratio ◽  
Fracture Appearance Transition Temperature ◽  
Austenite Grain ◽  
Austenite Grain Boundary ◽  
Prior Austenite Grain

The characteristics of temper embrittlement and carbides precipitated in 2.25Cr-1Mo and 2.25Cr-1Mo-V steels which were aged up to 50,000h at 454∼515°C were investigated. The temper embrittlement susceptibility was evaluated as the shift of 54 Joule transition temperature (vTr54) and 50% fracture appearance transition temperature (FATT50) by the Charpy v-notch impact tests. The shift of vTr54 and FATT50 in the 2.25Cr-1Mo steel rapidly increased with the aging time up to 10,000h and then slowly saturated. Peak ΔvTr54 and ΔFATT50 in the 2.25Cr-1Mo-V steel were obtained up to 30,000h aging at 454°C. The distribution of phosphorus in the 2.25Cr-1Mo-V steel and 2.25Cr-1Mo steel after aging treatment was different. Phosphorus in the conventional 2.25Cr-1Mo steel was mainly observed at the prior austenite grain boundary, however, phosphorus in the 2.25Cr-1Mo-V steel was observed at the prior austenite grain boundary and the interfaces between carbide and matrix. The type and composition of carbides were changed to the stable Mo-rich ones, the carbide of M6C type was manifestly precipitated in both steels, and the new type of M4C3 carbides in the 2.25Cr-1Mo-V steel were finely distributed within grain and the atomic ratio of M4C3 was changed from (Fe0.08Cr0.21Mo2.61V1.10)C3 in the PWHT state to (Fe0.22Cr0.20Mo2.78V0.80)C3 with aging.

scholarly journals Reconstruction and Size Prediction of Prior Austenite Grain Boundary (PAGB) using Artificial Neural Networks

2020 ◽  
Vol 58 (12) ◽  
pp. 822-829
Author(s):  
Bong-Kyu Kim ◽  
Nam Hoon Goo ◽  
Jong Hyuk Lee ◽  
Jun Hyun Han
Keyword(s):  
Neural Networks ◽  
Grain Size ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Detection Rate ◽  
Prior Austenite ◽  
Data Sets ◽  
Austenite Grain ◽  
Austenite Grains ◽  
Prior Austenite Grain

To automatically reconstruct the prior austenite grains from as-quenched martensitic structure, we applied a deep learning algorithm to recognize the prior austenite grains boundaries hidden in the martensitic matrix. The FC-DenseNet architecture based on FCN (fully convolutional networks) was used to train the martensite and ground truth label of the prior austenite grain boundaries. The original martensite structures and prior austenite grain boundaries were prepared using different chemical etching solutions. The initial PAGS detection rate was as low as 37.1%, which is not suitable for quantifying the basic properties of the microstructure such as grain size or grain boundary area. By changing the weight factor of the neural net loss function and increasing the size of the data set, the detection rate was improved up to 56.1%. However, even when the detection rate reached 50% or more, the quality of the reconstructed PAGS was not comparable to the analytically calculated results based on EBSD measurements and crystallographic orientation relationships. The prior austenite grain size data sets were obtained from martensite samples via the FCDenseNet method, and had a linear correlation with the mechanical properties measured in the same samples. In order to improve the accuracy of the detection rate using neural networks, it is necessary to increase the number of neural networks and data sets.

scholarly journals Exploring the Difference in Bainite Transformation with Varying the Prior Austenite Grain Size in Low Carbon Steel

Metals ◽  
2018 ◽  
Vol 8 (12) ◽  
pp. 988 ◽  
Author(s):  
Liangyun Lan ◽  
Zhiyuan Chang ◽  
Penghui Fan
Keyword(s):  
Grain Size ◽  
Prior Austenite ◽  
Low Carbon Steel ◽  
Low Carbon ◽  
Bainite Transformation ◽  
Austenite Grain Size ◽  
Austenite Grain ◽  
Austenite Grains ◽  
Prior Austenite Grain Size ◽  
Prior Austenite Grain

The simulation welding thermal cycle technique was employed to generate different sizes of prior austenite grains. Dilatometry tests, in situ laser scanning confocal microscopy, and transmission electron microscopy were used to investigate the role of prior austenite grain size on bainite transformation in low carbon steel. The bainite start transformation (Bs) temperature was reduced by fine austenite grains (lowered by about 30 °C under the experimental conditions). Through careful microstructural observation, it can be found that, besides the Hall–Petch strengthening effect, the carbon segregation at the fine austenite grain boundaries is probably another factor that decreases the Bs temperature as a result of the increase in interfacial energy of nucleation. At the early stage of the transformation, the bainite laths nucleate near to the grain boundaries and grow in a “side-by-side” mode in fine austenite grains, whereas in coarse austenite grains, the sympathetic nucleation at the broad side of the pre-existing laths causes the distribution of bainitic ferrite packets to be interlocked.

Contribution of Z-Phase Precipitation to Recovery of Martensitic Structure in High Chromium Creep Resistant Steel

2007 ◽  
Vol 539-543 ◽  
pp. 3000-3005 ◽  
Author(s):  
Kota Sawada ◽  
Hideaki Kushima ◽  
Kazuhiro Kimura
Keyword(s):  
Phase Formation ◽  
Prior Austenite ◽  
Martensitic Structure ◽  
Number Density ◽  
Austenite Grain ◽  
Nb Content ◽  
Lath Structure ◽  
Austenite Grain Boundary ◽  
Martensitic Lath ◽  
Prior Austenite Grain

The precipitation site, main metallic composition and number density of Z phase have been investigated in T91 in order to clarify the influence of Z phase formation on recovery of martensitic structure and creep strength degradation. The Z phase particles were mainly present around prior austenite grain boundaries and/or packet boundaries in the steels crept at 550oC and 600oC. The Z phase particles were found in specimens crept at 550oC to 650oC. There was no indication of Z phase formation up to about 62475.0 h at 500oC and 14106.5 h at 700oC. The Nb content of Z phase observed at 550oC was lower than that at 600oC. The number density of Z phase measured at 550oC was lower that that at 600oC, indicating that the preferential recovery of martensitic lath structure around prior austenite grain boundary is not remarkable at 550oC in contrast with 600oC.

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