304 스테인리스강의 열영향부에 미치는 탄소 함량과 용접 입열량의 영향

오은종 부경대학교 2017 국내석사

As a result of welding 304 stainless steel which has a high carbon content containing 0.074wt.%C with an heat input of minimum 60kJ/in to investigate the effect of carbon content and welding heat input on the heat affected zone of austenitic stainless steels, a variety of tests to identify characteristics such as nondestructive properties, mechanical properties, chemical compositions, delta ferrire contents and structure observation satisfied all the requirements, but the intergranular corrosion by ASTM A262 test was observed at a specific location of the heat affected zone. The sensitization phenomena according to intergranular corrosion of the heat affected zone was confirmed by the temperature distribution analysis using SYSWELD 2014 program. However, as a result of welding 304 stainless steel which has a carbon content containing 0.064wt.%C with an heat input of minimum 60 kJ/in, the resistance to intergranular corrosion was confirmed in the heat affected zone. Therefore, it is deemed necessary to limit the maximum 0.65wt.%C of carbon content and maximum 60kJ/in of welding heat input to be applied to industrial field welding to ensure corrosion resistance of 304 series stainless steel in a corrosive environment.

316L 스테인리스강의 機械的 性質과 減衰能

권민기 부경대학교 대학원 2014 국내박사

The interrelation between mechanical properties and damping capacity of 316L stainless steel has been investigated and two factors, mechanical properties and damping capacity of 316L stainless steel with two phase of martensite and austenite, were also studied. Furthermore the effect of thermo-mechanical treatment on the mechanical properties and damping capacity of 316L stainless steel was studied to obtain good combination of mechanical properties and damping capacity. The results obtained from this study are as follow: The and -martensite were formed with surface relief, specific direction, and intersection by deformation. With increasing degree of deformation, the volume fraction of ε-martensite increased and then subsequently decreased, while -martensite rapidly increased. With increasing degree of deformation, tensile strength was increased, and elongation was decreased, however damping capacity increased and then subsequently decreased. Tensile strength and elongation were affected by the -martensite and damping capacity was influenced greatly by -martensite. Thus, there was no proportional relationship among strength, elongation, and damping capacity. The two phase structures of deformation induced martensite and reverse austenite were obtained by deformation and reverse annealing treatment at given temperatures between 500℃ and 700℃. Austenite with ultra fine grain less than 0.5㎛ was obtained by reverse annealing treatment. Volume fraction of reverse austenite increased with an increase of annealing temperature and time. With an increase of volume fraction of reverse austenite, strength was decreased rapidly, while elongation was rapidly increased, and damping capacity was slowly decreased. Strength, elongation, and damping capacity of 316L stainless steel with two phases of martensite and austenite were strongly affected by reverse austenite. Dislocation, martensite, and stacking faults were formation by thermo- mechanical treatment. The and -martensite were formed by deformation, but only -martensite was formed by thermo-mechanical treatment. Volume fraction of stacking faults and ε-martensite were increased with increasing number of cycle of thermo- mechanical treatment. With an increase number of thermo-mechanical treatment, hardness, strength and damping capacity increased, while elongation decreased. With increasing volume fraction of martensite formed by thermo-mechanical treatment, hardness and strength were rapidly increased, but elongation was rapidly decreased. Thus, hardness, strength, and elongation were influenced greatly by martensite. Damping capacity of thermo-mechanical treated 316L stainless steel was increased with an increase of stacking faults formed by thermo-mechanical treatment. Thus, damping capacity of thermo-mechanical treated 316L stainless steel was strongly affected by stacking faults. The results confirmed that the good combination of strength and damping capacity was obtained from thermo-mechanical treatment.

가공열처리한 Fe-20Mn-12Cr-3Ni-3Si 합금의 강도와 감쇠능의 상호관계

오동석 부경대학교 대학원 2019 국내석사

This study was processed to investigate the co-relationship between the mechanical properties and damping capacity of thermo-mechanical treated Fe-20Mn-12Cr-3Ni-3Si alloy. αʹ and ε-martensite were formed by deformation and thermo-mechanical treatment. With the increasing cycle number of thermo-mechanical treatment, volume fraction of ε-martensite was increased, and then decreased, whereas dislocation and αʹ-martensite were slowly increased. In 5-cycle number thermo-mechanical treated specimens result showed more than 10% of the volume fraction of ε-martensite and less than 3% of the volume fraction of αʹ-martensite. With the increasing number of thermo-mechanical treatment, the strength rapidly increased, but the damping capacity was slowly decreased, and results of damping capacity was the opposite to tendency for a metal with deformation induced martensite transformation. The damping capacity was decreased with the strength increasing, these results was opposite to tendency for metal with deformation induced martensite transformation. The strength was affected to formation of martensite and dislocation, grain refining by thermo-mechanical treatment, damping capacity was affected formation of dislocation and grain refinement.

오스템퍼드 구상흑연주철의 기계적 성질과 감쇠능의 관계

이병락 부경대학교 산업대학원 2014 국내석사

This study was carried out to investigate the relationship of tensile properties and damping capacity in austempered ductile cast iron. The results obtained from this study are as follow . Tensile strength an elongation of ductile cast iron increased by austempering treatment, but strength and elongation decreased with on increase of austempering temperature. Damping capacity of ductile cast iron decreased by austempering treatment, and damping capacity was affected by austempering temperature. Mechanical properties of austempered ductile cast iron was controlled by bainite and retained austenite structure, but damping capacity was controlled by transformation from ferrite to bainite. Damping capacity un-changed with increasing of tensile strength and elongation. Thus, there was no propertional relationship between damping capacity and strength, elongation in austempered ductile cast iron.

Elbow의 인장 성질에 미치는 제조공정의 영향

김학철 부경대학교 2019 국내석사

The following conclusions have been reached by evaluating and comparing microstructure, tensile properties of each part of Elbow, which is manufactured through the cold and the hot-expanding forming using 304Lseamless and welded pipe. Hot-expanding formed specimen showed the presence of austenite single-phase, while the cold displayed the presence of some martensite in austenite structure. This result was obtained from 304L Elbow before heat treatment. Heat treated Elbows after the cold and the hot-expanding forming also consist of austenite single-phase. It can be well known that martensite produced by cold forming is all inversely transformed into austenite, and therefore there is no difference in microstructure of specimens regardless of heat treatment and forming methods. Grains of the cold formed specimen are larger than that of hot-expanding, which is mainly attributed to a growing of grain. The growing of grain was caused by heat treatment after the cold and hot-expanding forming. The cold formed specimen displayed higher strength but lower elongation than hot-expanding specimen before heat treatment. This is clearly attributed to transformation of some austenite into martensite, dislocation, and vacancy generated during heat treatment. The Elbows subjected to the heat treatment after the cold and the hot-expanding forming exhibit no significant difference in tensile strength, elongation regardless of forming methods. Microstructures remained unchanged regardless of forming methods. The Elbows manufactured using the Seamless Pipe and the Welded Pipe display no significant difference in tensile strength, while elongation have a tendency to be lowered in the Welded Pipe than in the Seamless, but the difference can be negligible by heat treatment. No significant difference in strength is not located in both the Seamless Pipe and the Welded before and after heat treatment. However, elongation is slightly lower in the Welded than the Seamless before heat treatment, after which the difference is negligible. In conclusion, it can be found that there is no significant difference in structures and tensile properties between the Elbows produced the cold and the hot-expanding forming.

피로손상된 Fe-22Mn-12Cr-3Ni-4Co-2Si 제진합금의 기계적 성질

이명수 부경대학교 2018 국내석사

This study was carried out to investigate the effect of fatigue stress on the tensile properties in Fe-22Mn-12Cr-3Ni-4Co-2Si damping alloy. The results obtained from this study are as follows. αʹ and ε-martensite were formed by damaged fatigue stress in Fe-22Mn-12Cr-3Ni-4Co-2Si damping alloy. The martensite was formed with the specific direction and surface relief by fatigue stress. With the increasing degree of fatigue stress, volume fraction of αʹ-martensite and ε-martensite was increased. With an increasing of fatigue stress, the yield and tensile strength was increase by volume fraction of αʹ-martensite and ε-martensite was increasing, while elongation was decreased. Tensile properties of damaged Fe-22Mn-12Cr-3Ni-4Co-2Si damping alloy under fatigue stress was strongly affected by the volume fraction of martensite formed by fatigue stress.

고 Mn 오스테나이트계 스테인리스강의 가공유기 마르텐사이트 변태 및 역변태에 관한 연구

허태영 부경대학교 대학원 2012 국내박사

Cr과 Ni의 양을 낮추는 대신에 Mn이 많이 첨가된 오스테나이트계 스테인리스강은 내식성, 인성, 가공성 등이 우수한 기존 오스테나이트계 스테인리스강이 갖는 가격이 높은 문제를 해결하기 위해 개발된 강이지만 이 또한 항복강도가 낮아 여러 산업 분야에서 구조용 재료로서는 다양하게 사용되지 못하고 있다. 이러한 강에서 강도를 향상할 수 있는 방법으로서는 합금원소 첨가에 의한 고용강화법 등을 생각 할 수 있지만[, 합금원소 첨가에 따른 용접성 등과 같은 또 다른 문제가 발생되기 때문에 적절한 방법이 되지 못한다. 때문에 합금원소를 첨가하지 않고 강도를 향상 시킬 수 있는 방법이 강구 되어야 하고, 그러한 방법으로서 결정립을 미세화 시켜 강도를 향상하는 방법이 이상적이라 판단된다. 그러나 이 강은 상온에서 오스테나이트 조직이기 때문에 가열과 냉각과정에서 상변태가 일어나지 않아 결정립을 미세화시켜 강인화 하는 것 또한 어렵다. 때문에 가공에 의해 오스테나이트 조직을 마르텐사이트 조직으로 변태 시킨 후 이를 가열하여 오스테나이트 조직으로 역변태 시켜 결정립을 미세화 하는 방법을 생각 할 수 있다. 상온에서 오스테나이트 조직을 갖는 강에서 역변태를 이용하여 결정립을 미세화 시켜 강인화 하는 방법에 대해서는 많은 연구가 수행되었다. 그러나 Cr과 Ni의 양을 낮추는 대신에 Mn이 많이 첨가되면 이들 함금원소의 양이 달라지는데 기인되어 오스테나이트의 안정도가 달라지게 되고, 그 결과 가공에 의한 마르텐사이트의 변태거동과 역변태 거동도 달라지게 될 뿐만 아니라 이에 따른 기계적 성질도 달라질 것으로 판단된다. 하지만 이러한 강에서 역변태 거동과 기계적성질을 연관시켜 연구한 논문은 없다. 따라서 본 연구는 Cr과 Ni의 양을 낮추는 대신에 가격이 낮은 Mn이 많이 첨가된 강을 가공에 의해 오스테나이트 조직을 마르텐사이트 조직으로 가공유기 변태시킨 다음 이를 가열하여 오스테나이트 조직으로 역변태 시켜 역변태 거동과 이에 따른 기계적 성질 변화를 조사하였다. The transformation behavior of martensite caused by deformation of high manganese austenitic stainless steel, which has lower content of 14wt.% Cr, 5wt.% Ni, and higher content of 6wt.% Mn compared with an conventional austenitic stainless steel, was investigated. In addition, the effect of grain size for deformation induced martensite transformation behavior and the reversed transformation behavior related to solve lower yield strength was investigated. The results obtained from this study are as follows: The a'-martensite was formed by a cold rolling , and it was formed with surface relief and with specific direction or crossing each other. With increasing degree of cold rolling, the volume fraction of martensite was increased quickly and than, was rose gradually. With increasing degree of cold rolling, the hardness and tensile strength were linearly increased, while elongation was rapidly decreased in the early stage of deformation, and than decreased slowly. The hardness and tensile strength were greatly influenced by deformation induced martensite, but the elongation was influenced by transformation behavior of deformation induced martensite. With increasing of grain size, the volume fraction of deformation induced martensite was increased. With increasing of grain size, hardness, tensile strength and elongation were decreased. The hardness and tensile strength were more highly influenced by grain size than the volume fraction of martensite induced by plastic deformation. But the elongation was greatly influenced by both grain size and volume fraction of martensite induced by deformation. The rate of reversed transformation was quickly increased with increasing of annealing temperature over 550℃, but significant change of reversed transformation was not observed over 700℃. In addition, the rate of reversed transformation was quickly increased with increasing of annealing time, and it was virtually completed after 10 minutes. The hardness and tensile strength were rapidly decreased with increasing of annealing temperature over 550 ℃, while significant change of the elongation was not observed as increasing temperature, but the change of elongation was quickly increased over 600 ℃. The hardness and tensile strength were rapidly decreased with increasing treating time of transformation, but they were not changed over 10mins. The the elongation was quickly increased with increasing treating time of reversed transformation, but hardness and tensile properties were not changed significantly over 10 min.. The ultra-fine grain size of less then 0.2 ㎛, could be obtained by reverse-transformed austenite, which means that it was possible to strengthen the high manganese austenitic stainless steel.

Incoloy 825 합금의 고온소성변형과 기계적 성질에 관한 연구

박영태 부경대학교 2018 국내박사

In this study, effects of the high temperature precipitation behavior and precipitate on the high temperature deformation stability were investigated by heat treatment and high temperature compression tests on incoloy 825 alloy. The effects of mechanical properties and microstructural changes were investigated according to hot forging ratio and heat treatment temperature and aging time after hot forging. The results obtained from this study were as follows : Cr23C6 carbide was precipitated under 950℃, but was not detected over 1,000℃. Most of the precipitate consist of Cr23C6 carbide. Strain-rate sensitivity was the highest in 0.01s-1 and the lowest in 10s-1. Strain-rate sensitivity was decreased sharply below 950℃. In the temperature between 850℃∼1,150℃, plastic instable area did not exist. It showed the lowest Ziegler Parameter value of 0.06. Ziegler Parameter was the lowest as 0.06 at 850℃ with 10s-1 of strain. The highest Ziegler Parameter value(0.43) was found in plastic deformation at 1,050℃ with 0.01s-1 of strain. It tends to have an higher resistance to the high temperature deformation under 950℃, due to the precipitate. Hot forging was carried out at the forging ratio of 0%, 60% and 90% respectively in a range of 900℃∼1,140℃ and followed solution treatment was conducted at 1,000℃ for 1 hr. In all the specimens of hot forged of 0%, 60% and 90%, precipitates were not observed. The average grain size of 0% specimen is 82㎛ and that of 60% and 90% is 56㎛ and 31㎛, respectively. The range of grain size in the 0% specimen is uneven in 182㎛ to 31㎛, but the grain size of 90% specimen is uniform. With increasing hot forging ratio, the mechanical properties such as tensile strength, elongation, hardness increased and impact toughness increased by grain refinement. With increasing solution treatment temperature, the grain size increased and the volume fraction of total precipitates decreased, and the precipitates disappeared at 1,000℃. With increasing aging time at 700℃, the volume fraction of precipitate increased and the precipitates size increased. Most of the precipitates consist Cr23C6 carbide, and a small amount of TiC carbide was also observed. With decreasing solution treatment temperature and increasing aging time, tensile strength and hardness increased, and the elongation and impact value decreased. With increasing aging time, the impact value decreased sharply by the increased of the precipitate size.

Fe-26Mn-3Co-2Al-3Si 제진합금의 인장성질에 미치는 미세조직의 영향

공주원 부경대학교 2018 국내석사

The tensile properties of Fe-26Mn-3Co-2Al-3Si damping alloy have been investigated for the development of new materials with high strength and damping capacity. The results obtained from this study are as follows : Austenite structure was transformed to the α’ and ε martensite structure by cold working, and α’ and ε martensite was formed with the surface relief and specific direction. phaseation in Fe-26Mn-3Co-2Al-3Si damping alloys have the microstructure that were α’ and ε martensite phase, Increasing the degree of cold rolling, the volume fraction of ε martensite decreased after rising to maximum value at specific level of cold rolling, the volume fraction of α’ martensite slowly increased and then dramatically increased from the point of decreasing ε martensite volume fraction. The tensile strength increased to a straight line relationships and the elongation rapidly decreases in initial stage and than slowly decreased with increasing the degree of cold rolling. Tensile strength and elongation is strongly affected by the content of α΄ martensite, but ε martensite is not, actually exhibit little effect on damping capacity.

Incoloy 825 합금의 기계적 성질에 미치는 열간 단조비와 용체화 온도의 영향

김도훈 부경대학교 대학원 2019 국내석사

This study was carried out to investigate the effect of hot forging ratio and solution treatment temperature on the mechanical properties of incoloy 825 alloy. With an increasing of the hot forging ratio, grain size and range of grain size was decreased. With an increasing of the solution treatment temperature after 90% forging, grain size and range of grain size was increased. Cr carbides and Ti nitrides was precipitated at below 900℃ and volume fraction of precipitate was increased with an decreasing of the solution treatment temperature. With an increasing of the hot forging ratio, hardness, tensile strength and elongation, toughness was increased. With an increasing of the solution treatment temperature after 90% forging, hardness and strength was increased, elongation and toughness was decreased by grain refinement. With an increasing of the forging ratio, effect of solution treatment temperature on the hardness, strength and elongation was small, but on the toughness was large.