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한준희,황농문,김종집,문한규 ( J . H . Hahn,N . M . Hwang,J . J . Kim,H . G . Moon ) 한국열처리공학회 1989 熱處理工學會誌 Vol.2 No.2
In order to improve hardness uniformity of standard-hardness blocks, exprimental procedure was designed using Taguchi Method. For this purpose the following factors were studied : austenitizing temperature, tempering condition, grinding condition, subzero treatment, lapping time, 15㎛ polishing time, final polishing time. These factors were processed and then ten hardness values were measured on each specimen, SN (signal to noise) ratio for each condition was calculated with standard variations of these values. Finally, from the calculated value of ANOVA on SN ratios, the lapping time was found to be the main factor. Better uniformity with longer lapping time implies that residual stress that was formed after quenching is a dominent parameter that affects on the unformity of hardness. Therefore, step-quenching method was adapted to minimize the residual stress. By this modification of quenching procedure, the hardness uniformity was improved remarkably and the yield ratio was increased from 55% to 88%.
남승훈,전승범,김종집 ( S . H . Nahm,S . B . Jeon,J . J . Kim ) 한국열처리공학회 1990 熱處理工學會誌 Vol.3 No.2
For the accurate measurements of hardness in a material, it is necessary to have a thorough understanding of the effects of test variables on the accuracy of hardness value. For the rebound hardness test, major test variables are the radius of hammer ball tip, type of backing materials, size and roughness of the specimen. In this study, effects of these variables on Equo-Tip hardness value were investigated. Hardness measurements were carried out using WC balls with various sizes of worn-ot zone. The sample materials chosen for the experiments were commercial standard hardness blocks and SM45C steel bars subjected to either normalization or quench and temper treatments. As backing materials, aluminum, steel and rubber plates were used in all the experiments. Experimental results show that for the accurate measurements of Equo-tip hardness, it is necessary to use the hammer ball with a worn-out zone parameter of less than 0.23, and the recommended minimum thickness and width of the specimen are 25㎜ and 70㎜, respectively. Further for the surface preparation, the specimens need to be polished with an emery paper of No. 400 or finer, and for the backing matrials, it is recommended to use steels or rubbers.
가스침탄 처리한 AISI 8620강에서 급냉제가 표면잔류응력에 미치는 영향
장충길,한준희,황농문 ( C . G . Jang,J . H . Han,N . M . Hwang ),김종집 ( J . J . Kim ),임병수 ( B . S . Lim ) 한국열처리공학회 1989 熱處理工學會誌 Vol.2 No.2
The effect of quenchant temperature on the surface residual stress was studied for AISI 8620 steel. Specimens were carburized at 900℃ in all case type furnace using a gas-base atmosphere of methanol cracked and liquefied petroleum gas, and then subjected to single reheat quenching in oil or salt bath in the temperature range of 60℃ to 300℃. After carburizing and reheat quenching, residual stress was measured by the hole drilling method. Experimental results showed that the surface residual stress was increased as the quenchant temperature was raised. This is in contrast to the fact that the formation of phase of low transformation strain such as bainite results in lower surface compressive stress. The greater compressive stress observed in specimens quenched at higher temperature may be attributed to the shifting of the transformation start point farther from the surface, as was reported in other carburizing steels.
뜨임처리가 AISI 403 스테인레스강의 Kiscc 에 미치는 영향
김종집,장현구,한범석,문한규 한국부식학회 1989 Corrosion Science and Technology Vol.18 No.1
The plane strain stress corrosion threshold stress intensity factor, K_(ISCC), has been determined for a martensitic stainless steel, AISI 403, in quenched and tempered conditions. The specimens were tempered at three different temperatures of 390℃, 520℃ and 610℃, and tested in 3.5 percent NaCl solution. The measured K_(ISCC) values varied remarkably depending on the tempering temperature: the highest value of 72.3 MPa◎m for 610℃ and the lowest value of 13.3 MPa◎m for 520℃. Fractographic study revealed that the intergranular fracture was dominant after stress corrosion cracking in all the specimens investigated.
부하 방식이 마르텐사이트계 스테인리스강의 응력 부식 특성에 미치는 영향
장현구,한범석,김종집,문한규 대한금속재료학회(대한금속학회) 1989 대한금속·재료학회지 Vol.27 No.7
The response of a martensitic stainless steel, AISI 403, to stress corrosion cracking (SCC) under Mode Ⅰ and Mode Ⅲ loading has been investigated. SCC tests were conducted in 3.5 % NaCl solution using precracked specimens, tempered at 390℃, 520℃ and 610℃. Average crack propagation rates at various stress intensity levels were measured and compared for each mode. Experimental evidence indicates that Mode Ⅰloading exhibits higher crack propagation rate or stronger susceptibility to SCC than Mode Ⅲ loading under all the tempering conditions, which suggests that hydrogen embrittlement is involved in SCC. Furthermore, fractographic study reveals that SCC under both of the loading mode occurs on the notch plane with a predominant mode of intergranular fracture in all of the aforementioned tempering conditions.