scholarly journals The Significance of Coherent Transformation on Grain Refinement and Consequent Enhancement in Toughness

Materials ◽  
2020 ◽  
Vol 13 (22) ◽  
pp. 5095
Author(s):  
Xiucheng Li ◽  
Jingxiao Zhao ◽  
Lili Dong ◽  
R. Devesh Kumar Misra ◽  
Xuemin Wang ◽  
...  
Keyword(s):  
Electron Backscattered Diffraction ◽  
Block Boundary ◽  
Austenite Grain ◽  
Different Temperatures ◽  
Ductile To Brittle Transition ◽  
Austenite Grain Boundary ◽  
Key Aspects ◽  
Quenching And Tempering ◽  
Misorientation Angles ◽  
Prior Austenite Grain

Coherent transformation is considered to be an effective approach to refine the microstructure and enhance toughness of structural steels. However, there are gaps in the knowledge on the key aspects of microstructure that govern toughness. In this regard, a low alloyed experimental steel with lean chemistry was subjected to a simple heat treatment involving austenitization at different temperatures, followed by quenching and tempering to obtain bainitic microstructures with different boundary composition. The microstructure of the four experimental steels was characterized by electron backscattered diffraction and mechanical properties were determined. The study indicated that the density of high angle grain boundaries does not adequately reflect the change of ductile-to-brittle transition temperatures (DBTT) of the experimental steels. Thus, we propose here a new mechanism on reducing DBTT from the perspective of misorientation of boundary, which takes into consideration these aspects in defining DBTT. One is inhibition effect on cleavage fracture by boundaries with high {100}-plane misorientation angles, and the other is ductility improvement by boundaries with high {110}-plane misorientation angles. Furthermore, the contribution of prior austenite grain boundary, packet boundary, block boundary, and sub-block boundary on toughness is also analyzed.

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.

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.

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.

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.

Influence of Repeated Quenching-Tempering on Fisheye Cracks around Tin and Al2O3 Inclusions in SAE 52100 Steel

2013 ◽  
Vol 300-301 ◽  
pp. 1298-1303 ◽  
Author(s):  
Koshiro Mizobe ◽  
Takashi Honda ◽  
Hitonobu Koike ◽  
Edson Costa Santos ◽  
Takuya Shibukawa ◽  
...  
Keyword(s):  
High Strength ◽  
Bearing Steel ◽  
Rolling Contact ◽  
High Carbon ◽  
Austenite Grain Size ◽  
Repeated Heating ◽  
Austenite Grain ◽  
Prior Austenite Grain Size ◽  
Quenching And Tempering ◽  
Prior Austenite Grain

Martensitic high-carbon high-strength SAE 52100 bearing steel has been widely used as the main alloys for rolling contact applications, and also at the components under bending and tension-compression. In order to enhance the material’s strength, refining the prior austenite grain size through repeated heating has been investigated. In this work, the microstructure of repeatedly quenched-tempered Ti, N-rich SAE 52100 steel was investigated. The material was melted by an electric furnace and formed by continuous casting and forging, and the crack origin on the fracture surface was investigated. It was found that repeated furnace quenching and tempering effectively refined the martenstic structure.

scholarly journals EFFECT OF AUSTENITIC GRAIN SIZE ON THE PHASE TRANSFORMATION OF A NOVEL 6.5% Cr STEEL FOR FORGED COMPONENTS

2021 ◽  
Vol 25 (1) ◽  
pp. 18-23
Author(s):  
Andrea Di Schino
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Chemical Elements ◽  
Austenite Grain Size ◽  
Cr Content ◽  
Austenite Grain ◽  
Prior Austenite Grain Size ◽  
Quenching And Tempering ◽  
Austenitic Grain Size ◽  
Prior Austenite Grain

In this paper the effect of quenching and tempering (Q&T) thermal treatment on mechanical properties of a novel 6.5% Cr steel for forged components is studied. The main innovation is in the increased hardenability following the higher Cr content with respect to the more common 5% Cr steel allowing to lower the content of other chemical elements aimed to achieve the target mechanical properties. Following to the high intrinsic hardenability of such steel based on the Cr content a poor effect of prior austenite grain size should be expected after quenching. Aim of this work is to evaluate such effect and to analyse the dependence of mechanical properties on it.

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