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B. C. Kim

Bio: B. C. Kim is an academic researcher. The author has contributed to research in topics: Charpy impact test & Brittleness. The author has an hindex of 2, co-authored 2 publications receiving 178 citations.

Papers
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TL;DR: In this article, a correlation between the microstructure and the local brittle zone (LBZ) phenomena in high-strength low-alloy (HSLA) steel welds was investigated by means of simulated heat-affected zone (HAZ) tests as well as welded joint tests.
Abstract: This study is concerned with a correlation between the microstructure and the local brittle zone (LBZ) phenomena in high-strength low-alloy (HSLA) steel welds The influence of the LBZ on toughness was investigated by means of simulated heat-affected zone (HAZ) tests as well as welded joint tests Micromechanical processes involved in microvoid and cleavage microcrack formation were also identified using notched round tensile tests and subsequent scanning electron microscopy (SEM) analyses The LBZ in the HAZ of a mUltipass welded joint is the intercritically reheated coarse-grained HAZ whose properties are strongly influenced by metallurgical factors such as an effective grain size and high-carbon martensitic islands: The experimental results indicated that Charpy energy was found to decrease monotonically with increasing the amount of martensitic islands, confirming that the martensitic island is the major microstructural factor controlling the HAZ toughness In addition, microvoids and microcracks were found to initiate at the interface between the martensitic island and the ferrite matrix, thereby causing the reduction in toughness These findings suggest that the LBZ phenomena in the coarse-grained HAZ can be explained by the morphology and the amount of martensitic islands

146 citations


Cited by
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Journal ArticleDOI
TL;DR: In this article, the authors examined acicular ferrite, bainite, and martensite microstructures observed in three low-alloy steels and used electron backscattering diffraction (EBSD) to assess crystallographic features.
Abstract: This study deals with acicular ferrite, bainite, and martensite microstructures observed in three low alloy steels. Electron backscattering diffraction (EBSD) was used to assess crystallographic features of these microstructures. In each area studied by EBSD mapping, ‘crystallographic packets’ defined as clusters of points sharing the same crystallographic orientation were compared with ‘morphological packets’ observed in the corresponding light micrograph. Microtexture studies suggested that acicular ferrite and upper bainite grow with Nishiyama– Wassermann relationships with the parent austenite phase, whereas lower bainite and martensite consist of highly intricate packets having Kurdjumov–Sachs relationships with the parent phase. In all cases three highly misoriented texture components were found within each former austenite grain. Electron backscattering diffraction also gave information about the cleavage and intergranular reverse temper embrittlement fracture mechanisms of these steels. In...

399 citations

Journal ArticleDOI
TL;DR: In this article, the authors investigated the austenite to bainite phase transformation in a low alloy structural steel after simulated welding heat treatment, by means of light microscopy, electron backscatter diffraction and transmission electron microscopy.

284 citations

Journal ArticleDOI
TL;DR: In this paper, the effect of welding cycle on the fracture toughness properties of high-strength low alloy (HSLA) steels is examined by means of thermal simulation of heat-affected zone (HAZ) microstructures.
Abstract: The effect of the welding cycle on the fracture toughness properties of high-strength low alloy (HSLA) steels is examined by means of thermal simulation of heat-affected zone (HAZ) microstructures. Tensile tests on notched bars and fracture toughness tests at various temperatures are performed together with fracture surface observations and cross-sectional analyses. The influence of martensite-austenite (M-A) constituents and of “crystallographic” bainite packets on cleavage fracture micromechanisms is, thus, evidenced as a function of temperature. Three weakest-link probabilistic models (the “Master-curve” (MC) approach, the Beremin model, and a “double-barrier” (DB) model) are applied to account for the ductile-to-brittle transition (DBT) fracture toughness curve. Some analogy, but also differences, are found between the MC approach and the Beremin model. The DB model, having nonfitted, physically based scatter parameters, is applied to the martensite-containing HAZ microstructures and gives promising results.

257 citations

Journal ArticleDOI
TL;DR: In this paper, the authors used tensile, crack opening displacement (COD), blunt notch, and charpy impact tests to investigate cleavage initiation in the intercritically reheated coarse-grained heat affected zone (IC CG HAZ) of three steels.
Abstract: Tensile, crack opening displacement (COD), blunt notch, and Charpy impact tests were used to investigate cleavage initiation in the intercritically reheated coarse-grained heat-affected zone (IC CG HAZ) of three steels. The steels were chosen to provide different distributions and morphologies of MA (high-carbon martensite with some retained austenite) particles within the IC CG HAZ structure. Observation of minimum impact toughness values for the IC CG HAZ was found to be associated with a particular microstructure containing a near-connected grain boundary network of blocky MA particles, the MA particles being significantly harder than the internal grain microstructure. The initiation mechanism for this structure was determined to be from a combination of an overlap of residual transformational induced stress fields, due to the formation of the MA particles, between two closely spaced particles and stress concentration effects resulting from debonding of the particles.

237 citations

Journal ArticleDOI
TL;DR: In this paper, the effects of alloying elements on microstructural factors of six high speed steel (HSS) rolls manufactured by centrifugal casting method were made, focusing on the role of hard carbides located along solidification cell boundary and the type of the martensite matrix.
Abstract: A study was made of the effects of alloying elements on microstructural factors of six high speed steel (HSS) rolls manufactured by centrifugal casting method. Particular emphasis was placed on the role of hard carbides located along solidification cell boundary and the type of the martensite matrix. Microstructural observation, X-ray diffraction analysis, and hardness measurement were conducted on the rolls to identify carbides. Various types of carbides were formed depending on the contents of strong carbide forming elements. In the rolls containing the high Cr content, MC carbides inside cells and M 7 C 3 carbides along cell boundaries were primarily formed, while in the rolls containing the high W and Mo contents, MC carbides inside the cells and fibrous M 2 C carbides in the intercellular regions were dominantly formed. The most important microstructural factor affecting overall roll hardness was the intercellular carbides and their distribution. The effects of alloying elements were analyzed on the basis of the liquidus surface diagram, suggesting that the proper contents of carbon, tungsten, molybdenum, chromium, and vanadium were 1.9–2.0, 3–4, 3–4, 5–7, and 5–6%, respectively.

195 citations