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원자로압력용기장 용접열영향부의 미세조직 변화가 Magnetic Barkhausen Noise 거동에 미치는 영향
김주학,윤의박,문종걸,박덕근,홍준화 韓國非破壞檢査學會 1998 한국비파괴검사학회지 Vol.18 No.4
최근 자기적 특성의 변화가 재료의 미세조직적 상태에 민감하다는 보고가 있다. 재료의 미세조직은 상(phase), 결정립의 크기, 석출물 등의 다양한 인자로 구성되며, 본 연구에서는 이러한 인자들을 이용하여 재료의 특성과 Barkhausen noise(BN)의 관계를 연관시키기 위한 시도를 하였다. ASTM A 508 Gr.3 원자로압력용기강을 대상으로 용접열영향부의 미세조직적인 변화를 일곱가지 대표적인 영역으로 구분하였고, 각 영역에서의 미세조직과 기계적특성의 변화를 파악한 후, 각 조건별로 BN을 측정하였다. 통상의 보자력이나 잔류자화 같은 자기적 성질은 큰 변화가 없었지만, BN은 미세조직의 상태에 따라 현격한 변화를 보였다. 결정립과 석출물의 크기가 증가함에 따라 BN은 증가하였고, tempered martensite 보다는 tempered bainite 조직에서 높은 BN을 나타냈다. Recent study has demonstrated that some magnetic properties are sensitive to the microstructural state of material. The ASTM A 508 Gr. 3 reactor pressure vessel steel has various microstructural changes including martensitic and bainitic phases, and various sizes of grain and precipitates in the weld heat-affected zone (HAZ). To correlate the microstructural state with Barkhausen noise (BN), specimens were prepared through simulating various weld thermal cycles using a thermal simulator. The conventional magnetic properties, i.e. coercive force, remanence and maximum induction, did not change significantly. whereas the BN amplitude and energy during a magnetization cycle changed markedly with microstructural state. The BN increased with increasing grain and carbide sizes, and the tempered bainite structure showed higher BN parameter than tempered martensite.
용접열 사이클 최고 온도가 원자로 압력용기강 IRHAZ 의 미세조직과 기계적 특성에 미치는 영향
이창희,홍준화,김주학,문종걸 대한금속재료학회(대한금속학회) 1999 대한금속·재료학회지 Vol.37 No.8
The microstructure and mechanical properties in the intercritically-reheated heat-affected zone (IRHAZ) of an SA 508 Cl.3 Mn-Mo-Ni reactor pressure vessel (RPV) steel have been investigated systematically using the welding thermal cycle simulated specimens. The double thermal cycles with varying peak temperatures(T_(p1), T_(p2)) in the range 700-800℃ were applied to simulate the various IRHAZs using a Gleeble 1500 thermal simulator. The effect of post-weld heat treatment (PWHT) was also studied. The microstructures of the IRHAZs were mainly composed of bainite, martensite and tempered bainite. But the specimens subjected to T_(p1)=T_(p2)=750℃ (before PWHT) and subjected to T_(p1)=T_(p2)=700℃ (after PWHT) showed lowest toughness. The microstructural factors affecting toughness were discussed with reference to the fraction of high carbon martensite for the specimen before PWHT, and to they coarsened carbide and softened matrix for the specimen after PWHT.
원자로 압력용기강 용접열영향부의 천이영역 파괴인성과 미세조직 변화
홍준화,김주학,정인상,신학수,문종걸 대한금속재료학회(대한금속학회) 1999 대한금속·재료학회지 Vol.37 No.10
The fracture toughness of the thermal cycle simulates weld HAZ (heat-affected zone) of SA 508 Cl.3 RPV (reactor pressure vessel) steel was evaluated in the ductile-brittle transition region. Reference temperature(T_0), and master curve for each region in the weld HAZ were determined from the three point bending tests at low temperatures, by using the Weibull's statistical method as described in ASTM E1921. Most specimens were conformed to validate at the test temperatures. It was shown that the new test method, which evaluates the fracture toughness in the transition region, was effectively applicable to the weld HAZ. The fracture toughness test results indicated that the coarse grained HAZ region near the weld fusion line possesses relatively good fracture toughness. In contrast, the minimum toughness value was noted at the subcritically reheated HAZ region adjacent to the base metal. The volume fraction of tempered martensite, mean sizes of grains and precipitates were quantitatively analysed as microstructural factors, a discussion on the effects of these factors on fracture toughness of the weld HAZ is presented.