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朴準龜 서울産業大學校 1981 논문집 Vol.15 No.1
In order to obtain a better understanding of fracture of Spheroidal graphite cast lron, Cracks appearing on the Surface of bending Specimens were fully traced by means of 100 magnification optical microscope, Testing Several Specimens With Variation in microscopic Structure, espicially in the ratio of pearlite and ferrite the following behaviors of cracks were Confirmed. In pearlite rich Structures, most cracks in the matrix initiate On the ferrite-pearlite boundary(F/P boundary) and propagate through pearlite to rest on the opposite F/P boundary, After the crack rests, another crack propagates in the Same way in another pearlite, By and by cracks initiate on the F/P boundary and propagate through ferrite So as to link graphites and/or pearlite, and or the influence of silicon Content on mechanical and anti-oxidation properties of theiron was investigated, The Specimens Containing from 2.4%∼5.0% Siwere heated at 700°C and 850°C for 100hrs, then the amount of oxides eliminated by means of Shot blast treatment were measured, On the other hand, tensile Strength, elongation and hardness from room temperature to 700°C and impact Value form -70°C to 200°C were measured, The γeasons why adding si Contributes to improvement of anti-oxidationare Considered to be that Fe₂Sio₄ Content increases in the Oxide layer, and that decarburization γeaction in accelerated as the upper point of eutectoid transformation temperature rises, The higher the temperature, the Samaller the effect of Si Content on the tensile Strengthis, Adding si is not effective in improving the Strength over 500°C, As the elongation at 500°C abruptly declines at 4.7% si in the annealing Specimens and 4.4% Si in the as-cast specimens, improved etongation is detained by annealing, The relation between Strength and hardness is drawn by a straight line fram room temperature to 300°C.
熔接構造綱의 막대기 熔接이음에 있어 疲勞强度에 對한 硏究
박준구 서울産業大學校 1991 논문집 Vol.33 No.1
This paper is concerned with the effect of the reinforcement on the fatique strength of butt welded joints. Since the fatique strength of butt welded joint is strongly influenced by the geometrical conditions of reinforcement, it has been pointed out that the flank angle and the root radious of weld toe responsible for the fatique strength. However, the fatique limit of butt welded joint of SM50 Steel plates is nearly independent of the root radious of weld toe. This result is explained from the characteristics of fatique behavior of notched speciments made of the same materials.
高張力鋼 熔接이음 融合境界領域의 組織과 靭性評價에 對한 硏究
朴準龜 서울産業大學校 1987 논문집 Vol.26 No.1
The fracture toughness in a high tension welded steel-has been examined with particular reference to HAZ microstructures. It is show that a wide variety of structure in the HAZ adjacent to fusion boundary through thickness is produced by Virtue of the different thermal histories experienced by each part in a multipass welded high tension steel. The HAZ microstructures can be classified into seven distinct kinds (named A, B, C, D, E, F and G) according to the microscopic constituent and grain size. Fracture toughness dependence on the HAZ microstructures is demonstrated by instrumented charpy dynamic ?? and static COD test on small specimens taken from the full thickness welded plate, the slit tip is carefully located in the HAZ adjacent to fusion boundary. The results make it clear that static COD test is more available for assessing fracture toughness dependence on the HAZ microstructues than instrumented charpy impact test. The martensite-bainitic HAZ microstructures (A, B and C) which are localized in the Vinicity of the weld toe fusion boundary impair most significantly of all the HAZ microstructures Furthermore, the emphasis must be placed upon the fact that martensitic-bainitic HAZ microstructure G tempered at relative high temperature during following welding process has excellent toughness, although the microstructure G seems to be similar to the microstructure of weld toe HAZ.