다중회귀분석을 이용한 페라이트-펄라이트 조직 아공석강의 충격인성에 미치는 미세조직적 인자의 민감도 해석

이승용 ( Seung-yong Lee ),이상인 ( Sang-in Lee ),황병철 ( Byoung Chul Hwang ) 대한금속재료학회(구 대한금속학회) 2016 대한금속·재료학회지 Vol.54 No.9

In this study, the effect of microstructural factors on the impact toughness of hypoeutectoid steels with ferrite-pearlite structure was quantitatively investigated using multiple regression analysis. Microstructural analysis results showed that the pearlite fraction increased with increasing austenitizing temperature and decreasing transformation temperature which substantially decreased the pearlite interlamellar spacing and cementite thickness depending on carbon content. The impact toughness of hypoeutectoid steels usually increased as interlamellar spacing or cementite thickness decreased, although the impact toughness was largely associated with pearlite fraction. Based on these results, multiple regression analysis was performed to understand the individual effect of pearlite fraction, interlamellar spacing, and cementite thickness on the impact toughness. The regression analysis results revealed that pearlite fraction significantly affected impact toughness at room temperature, while cementite thickness did at low temperature.(Received March 2, 2016; Accepted April 8, 2016)

항복강도 390 MPa급 가공열처리강 대입열용접열영향부 충격인성 및 연화현상

방국수,안영호,정홍철 대한금속·재료학회 2018 대한금속·재료학회지 Vol.56 No.11

The Charpy impact toughness of the heat affected zone (HAZ) of electro gas welded 390 MPa yield strength grade steel, manufactured by a thermo mechanically controlled process, was investigated. The effects of added Nb on the toughness of the steel and the factors influencing scatter in toughness are discussed in the present work. It was observed that adding Nb to the steel led to the deterioration of HAZ toughness. The presence of soluble Nb in the HAZ increased its hardenability and resulted in a larger amount of low toughness bainitic microstructure. Microstructural observations in the notch root area revealed the significant role of different microstructures in the area. In the presence of a larger amount of bainitic microstructures, the HAZ exhibited a lower Charpy toughness with a larger scatter in toughness. A softened zone with a lower hardness than the base metal was formed in the HAZ. However, theoretical analysis revealed that the presence of the zone might not be a problem in a real welded joint because of the plastic restraint effect enforced by surrounding materials.

Improvement of Low Temperature Toughness of Ferritic Mn Steels by Alloy Modification

이일철,하유미,K. H. Kwon,이학철,김낙준 대한금속·재료학회 2015 METALS AND MATERIALS International Vol.21 No.3

A study has been made on the effects of Mn content and addition of Al on the microstructure and mechanical properties of (4-6)Mn steels, with the aim of developing ferritic Mn steels having good combination of tensile properties and impact toughness. It has been shown that the reduction of Mn content to 6 wt% and lower from 8-12 wt% of conventional steels can effectively prevent the occurrence of intergranular fracture, which has been a major problem of (8-12)Mn steels with poor toughness at cryogenic temperature. While increasing Mn content in the binary (4-6)Mn steels results in an increase in strength and a decrease in impact toughness, the addition of 1Al to (4-6)Mn steels results in improvements in both strength and impact toughness as compared to those of the binary (4-6)Mn steels and the best impact toughness has been obtained in the as-rolled 1Al added 4Mn steel, whose microstructure consists of fine acicular ferrite grains.

Experimental Investigations on Impact Toughness and Shear Strength of Lead Free Solder Alloy Sn–0.5Cu–3Bi–xAg

S. Jayesh,Jacob Elias 한국전기전자재료학회 2020 Transactions on Electrical and Electronic Material Vol.21 No.2

Lead is banned in alloy making citing toxicity concerns and environmental legislations. Researchers around the world were in search of new lead free solder alloys which could replace the old Sn–Pb alloy. Solder alloys are important electronic material used in electronics package industries. In this study, shear strength and impact toughness tests were conducted on Sn–0.5Cu–3Bi when different amounts of Ag (0.25, 0.5, 0.75, 1 wt%) is added. Shear strength test is done using micro force test system. Impact toughness test is done using Charpy impact test set up by fi nding the energy diff erence before and after impact. Ultimate shear stress is found to be increased from 17.3 to 23 MPa. Yield strength is found to be increased from 23.4 to 28 MPa. Impact toughness of the alloys increased from 10.4 to 11.3 J. EDAX analysis and mapping of the Sn–0.5Cu–3Bi–1Ag is also obtained Sn–0.5Cu–3Bi–1Ag is found to be having good improved shear strength and impact toughness than Sn–0.5Cu–3Bi.

초고강도 베이나이트강의 미세조직과 기계적 성질에 미치는 탄소함량과 항온열처리 온도의 영향

황보승,이홍범,송영범,함진희,김홍규,서동우 대한금속·재료학회 2019 대한금속·재료학회지 Vol.57 No.6

The effect of carbon content and isothermal heat treatment conditions on the microstructure evolution and mechanical properties of ultra-high strength bainitic steels was investigated. A reduction in carbon content from 0.8 wt% to 0.6 wt% in super-bainite steel with typical chemistry effectively improved not only the Charpy impact toughness but also the strength level. This suggests that reducing the carbon content is a very promising way to obtain better mechanical balance between strength and impact toughness. The higher Charpy impact toughness at a lower carbon content of 0.6 wt% is thought to result from a reduction in austenite fraction, and refinement of the austenite grain. The coarse austenite grains have a detrimental effect on impact toughness, by prematurely transforming to deformation-induced martensite during crack propagation. Mechanical properties were also affected by the isothermal treatment temperature. The lower isothermal temperature enhanced the formation of bainitic ferrite with a refined microstructure, which has a beneficial influence on strength, but reduces impact toughness. The lower impact toughness at lower isothermal temperature is attributed to the sluggish redistribution of carbon from the bainitic ferrite into the surrounding austenite. Higher solute carbon in the bainitic ferrite contributes to an increase of strength, but at the same time, encourages a propensity to cleavage fracture.

페라이트-펄라이트 조직 아공석강의 상온 및 저온 충격 인성에 미치는 미세조직적 인자의 영향

이승용,정상우,황병철,Lee, Seung-Yong,Jeong, Sang-Woo,Hwang, Byoungchul 한국재료학회 2015 한국재료학회지 Vol.25 No.11

This paper presents a study on the room- and low-temperature impact toughness of hypoeutectoid steels with ferrite-pearlite structures. Six kinds of hypoeutectoid steel specimens were fabricated by varying the carbon content and austenitizing temperature to investigate the effect of microstructural factors such as pearlite volume fraction, interlamellar spacing, and cementite thickness on the impact toughness. The pearlite volume fraction usually increased with increasing carbon content and austenitizing temperature, while the pearlite interlamellar spacing and cementite thickness mostly decreased with increasing carbon content and austenitizing temperature. The 30C steel with medium pearlite volume fraction and higher manganese content, on the other hand, even though it had a higher volume fraction of pearlite than did the 20C steel, showed a better low-temperature toughness due to its having the lowest ductile-brittle transition temperature. This is because various microstructural factors in addition to the pearlite volume fraction largely affect the ductile-brittle transition temperature and low-temperature toughness of hypoeutectoid steels with ferrite-pearlite structure. In order to improve the room- and low-temperature impact toughness of hypoeutectoid steels with different ferrite-pearlite structures, therefore, more systematic studies are required to understand the effects of various microstructural factors on impact toughness, with a viewpoint of ductile-brittle transition temperature.

입열량에 따른 FCAW용접부 파괴인성에 미치는 미세조직의 영향

신용택,강성원,김명현,Shin, Yong-Taek,Kang, Sung-Won,Kim, Myung-Hyun 대한용접접합학회 2008 대한용접·접합학회지 Vol.26 No.3

This paper is to evaluate fracture characteristics of API 2W Gr.50 TMCP steel weldment typically applied for offshore structures, with the focus on the influence of heat input arising from flux cored arc welding. Based on the results and insights developed from this study, it is found that the toughness for both CTOD and impact exhibits a tendency to decrease as the weld heat input increases. The reheated zone of weldmetal exhibit lower hardness than solidified zone and microstructure that are liable to affect the toughness are acicular ferrite and martensite-austenite constituents (M-A). In particular, M-A is a more effective micro-phase for CTOD toughness than impact toughness.

Effects of Chemical Composition on the Microstructure and Mechanical Properties of FCAW-S Weld Metal Containing 2% Ni

방국수,Woong Kil,Woong-Seong Chang 대한금속·재료학회 2013 METALS AND MATERIALS International Vol.19 No.2

In this study the effects of alloying elements on the microstructure and mechanical properties of 600MPa grade FCAW-S weld metals containing 2% Ni were examined. Carbon, manganese and aluminum contents were varied in the ranges of 0.075%-0.101%, 1.19%-1.69%, and 0.66%-1.49% respectively. Regardless of the Al content, all of the weld metals showed a bainite dominant microstructure with no δ-ferrite. This indicates that when a weld metal contains 2% Ni, the Al content can be increased up to around 1.5% without concern about the deterioration of impact toughness due to the presence of δ-ferrite. The tensile strength of the weld metals varied from 595 MPa to 702 MPa dependent upon the chemical composition. Multiple regression analysis showed that while C and Mn have strong influences on the tensile strength, Al has little influence. Therefore, the Pcm index of weld metals could be used as an indication of their tensile strength. Impact toughness of the weld metals was influenced most by tensile strength and showed that the 50J transition temperature increased by 36 °C when the tensile strength was increased by around 100 MPa. Therefore, an excessive increase of the tensile strength should be avoided to attain higher impact toughness. Even when inclusion mean diameters were increased from 0.588 μm to 0.708 μm with an increase of the Al content from 0.66% to 1.49%, the size difference showed little influence on the impact toughness of the weld metals in this experiment.

Nb 첨가에 따른 저탄소강의 충격 특성에 미치는 변태 온도의 영향

이상인,강준영,황병철,Lee, Sang-In,Kang, Jun-Young,Hwang, Byoungchul 한국재료학회 2016 한국재료학회지 Vol.26 No.11

In this study, six kinds of low-carbon steel specimens with different ferrite-pearlite microstructures were fabricated by varying the Nb content and the transformation temperature. The microstructural factors of ferrite grain size, pearlite fraction, interlamellar spacing, and cementite thickness were quantitatively measured based on optical and scanning electron micrographs; then, Charpy impact tests were conducted in order to investigate the correlation of the microstructural factors with the impact toughness and the ductile-brittle transition temperature (DBTT). The microstructural analysis results showed that the Nb4 specimens had ferrite grain size smaller than that of the Nb0 specimens due to the pinning effect resulting from the formation of carbonitrides. The pearlite interlamellar spacing and the cementite thickness also decreased as the transformation temperature decreased. The Charpy impact test results indicated that the impact-absorbed energy increased and the ductile-brittle transition temperature decreased with addition of Nb content and decreasing transformation temperature, although all specimens showed ductile-brittle transition behaviour.

Quantitative analysis of microstructural and mechanical behavior for Fe-0.1C-(V, Nb) steels as a function of the final rolling temperature

Kang, N.,Lee, Y.,Byun, S.,Kim, K.,Kim, K.,Chung, J.,Cho, K. Elsevier Sequoia 2009 Materials science & engineering. properties, micro Vol.499 No.1

The microstructure, tensile property and impact toughness of Fe-0.1C steel were investigated as a function of the final rolling temperature (FRT: 950 or 860<SUP>o</SUP>C) and microalloying contents: Fe-V steel, Fe-V-Nb steel, and Fe-Nb steel. Microstructural features (ferrite volume fraction and grain size) were correlated with mechanical properties (hardness, tensile strength, and impact toughness). Specifically, the mixed grain size of ferrite was quantitatively and statistically analyzed to explain the level of toughness. For FRT 860<SUP>o</SUP>C, the impact toughness of Fe-Nb steel deteriorated due to the inhomogeneity of ferrite grain size, although its ferrite grain size was mostly the same or slightly smaller than the Fe-V steel. However, Fe-V-Nb steel showed the smallest average and the narrowest distribution of ferrite grain size, which produced comparable impact toughness with Fe-V steel with a minimum loss of the tensile property.