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朴準龜 서울産業大學校 1980 논문집 Vol.13 No.1
White layer appears in the interface between the built up edge and the tool when cutting medium carbon steels, It is reported that the tendency to white layer formation increases with the decrease in cobalt content of tool and cobalt acts as an inhibitor, In this study, the formation of White layer is examined for various kind of material cut using three kinds of typical high-speed steel tool with different content of cobalt and vanadium and carbon. The test results show that white layer is formed only in case of carbon steels and low alloyed steels and dose not depend upon the cobalt contents in tools, low carbon steel, pure iron and armco iron, Inclusions contained in work materials cause micro and macro cracks which propagate along the maximum shear stress direction, The surface finish is damaged by fracture phenomena of various types depending on the relative position of the inclusions to that of the cutting tip
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.
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.
朴準龜 서울産業大學校 1984 논문집 Vol.20 No.1
The influence of fatigue accumulation given by pulsating tensile stress (bending) on the delayed fracture crack initiation was studied with notched specimens of Ni-Cr-Mo steel quenched and tempered at 200 or 400℃. The results obtained are as follows. 1) When tempering temperature is 200℃, the time to crack initiation in delayed fracture decreases as the fatigue accumulation stress and the amount of the fatigue accumulation are increased, but the critical stress below which no crack initiation occurs is not changed by the fatigue accumulation. 2) When tempering temperature is 400℃, both the time to crack initiation and the critical stress are decreased by the fatigue accumulation. 3) The crack initiation time in delayed fracture is decreased to greater extent by the superposition of small repeating stress as the stress amplitude or the repeating frequency is increased. 4) The lower limit stress under which no delayed fracture occurs is markedly decreased by the superposition of small repeating stress,