304 오스나이트계 스테인리스강에 Nb/C가 4-11의 범위가 되도록 Nb를 0.3-0.7wt% 첨가하여 합금을 제조한 후, 이를 용체화 및 예민화처리 하여 기계적성질과 입계부식을 조사하였고 이 재료를 용접하여 용접부, 열영향부 및 기지별로 나누어 입계부식을 비교하였다. 1) Nb의 함량이 증가함에 따라 □-ferrite상의 양이 증가하고 경도, 항복강도 및 ...
304 오스나이트계 스테인리스강에 Nb/C가 4-11의 범위가 되도록 Nb를 0.3-0.7wt% 첨가하여 합금을 제조한 후, 이를 용체화 및 예민화처리 하여 기계적성질과 입계부식을 조사하였고 이 재료를 용접하여 용접부, 열영향부 및 기지별로 나누어 입계부식을 비교하였다. 1) Nb의 함량이 증가함에 따라 □-ferrite상의 양이 증가하고 경도, 항복강도 및 인장 강도는 증가하지만 연신율은 감소하였다. 2) 10% 옥살산에서의 입계부식시험결과 Nb함량이 증가함에 따라 용체화처리한 경우 입계침식이 깊게 나타난 반면 예민화처리한 경우는 입계침식이 감소하는 경향을 보였다. 3) 0.1M H₂SO₄+ 0.01M KSCN용액에서 측정한 결과 예민화처리한 경우는 재료의 Nb함량에 따라 활성화전류밀도(Ia)는 거의 변화가없고 비슷하지만 재활성화전류밀도(Ir)는 크게 감소하였다. 4) 용착부는 주로 오스데나이트상과 □-ferrite상이 혼합된 수지상조직이고 Nb함량이 감소될수록 기지에는 석출물이 형성되지 않고 열영향부의 입계에 석출물이 형성되고 쌍정이 나타났다. 5) 용접부의 경도는 열영향부, 용착부, 기지순으로 증가하며 Nb함량이 많아질수록 경도가 높아졌다. 6) EPR곡선 측정결과 Nb함량이 증가될수록 용접부위의 재활성화전류밀도(Ir) 및 활성화전류밀도(Ia)가 용착부, 기지, 열영향부 순으로 감소하며 열영향부에서 입계가 심하게 부식되는 현상을 보였다.
304 오스나이트계 스테인리스강에 Nb/C가 4-11의 범위가 되도록 Nb를 0.3-0.7wt% 첨가하여 합금을 제조한 후, 이를 용체화 및 예민화처리 하여 기계적성질과 입계부식을 조사하였고 이 재료를 용접하여 용접부, 열영향부 및 기지별로 나누어 입계부식을 비교하였다. 1) Nb의 함량이 증가함에 따라 □-ferrite상의 양이 증가하고 경도, 항복강도 및 인장 강도는 증가하지만 연신율은 감소하였다. 2) 10% 옥살산에서의 입계부식시험결과 Nb함량이 증가함에 따라 용체화처리한 경우 입계침식이 깊게 나타난 반면 예민화처리한 경우는 입계침식이 감소하는 경향을 보였다. 3) 0.1M H₂SO₄+ 0.01M KSCN용액에서 측정한 결과 예민화처리한 경우는 재료의 Nb함량에 따라 활성화전류밀도(Ia)는 거의 변화가없고 비슷하지만 재활성화전류밀도(Ir)는 크게 감소하였다. 4) 용착부는 주로 오스데나이트상과 □-ferrite상이 혼합된 수지상조직이고 Nb함량이 감소될수록 기지에는 석출물이 형성되지 않고 열영향부의 입계에 석출물이 형성되고 쌍정이 나타났다. 5) 용접부의 경도는 열영향부, 용착부, 기지순으로 증가하며 Nb함량이 많아질수록 경도가 높아졌다. 6) EPR곡선 측정결과 Nb함량이 증가될수록 용접부위의 재활성화전류밀도(Ir) 및 활성화전류밀도(Ia)가 용착부, 기지, 열영향부 순으로 감소하며 열영향부에서 입계가 심하게 부식되는 현상을 보였다.
In order to investigate effects of Nb on the mechanical properties and intergranular corrosion behaviors of the welded AISI 304 stainless steels, the stainless steels containing Nb up to 0.7wt% were melted by using a vacuum furnace and hot rolled at 1100℃ into 12mm thickness and then solutionized fo...
In order to investigate effects of Nb on the mechanical properties and intergranular corrosion behaviors of the welded AISI 304 stainless steels, the stainless steels containing Nb up to 0.7wt% were melted by using a vacuum furnace and hot rolled at 1100℃ into 12mm thickness and then solutionized for 1hr at 1050℃. Some of them were sensitized for 5hrs at 650℃ in argon atmosphere. The samples were welded by MIG method. The microstructures and phases were investigated by using optical microscope, SEM and XRD for the solutionized, sensitized and welded samples before and after corrosion. The micro-vickers hardness and tensile test were carried out for the solutionized, sensitized and welded samples. Intergranular corrosion behavior of the samples were examined through DL-EPR(double loop electrochemical potentiokinetic reactivation) tests in 0.5M H₂SO₄+ 0.01M KSCN and 10% oxalic acid solutions at 25℃. The experimental results are as follows; 1) As Nb content increased the amount of □-ferrite as a second phase increased, and consequently the hardness, yield strength and tensile strength were increased whereas elongation decreased. 2) The corrosion test in 10% oxalic acid showed that the intergranular corrosion was severe in the solutionized samples with increasing Nb content but in the sensitized samples it decreased. 3) The EPR curves measured in 0.1M H₂SO₄+ 0.01M KSCN solution showed that the activation current density(Ia) for the sensitized samples were not changed significantly, however, the reactivation current density(Ir) decreased with increasing Nb content. 4) The microstructure of the welded zone was dendritic structure constituted of austenites and □-ferrites, but in HAZ the □-ferrites were precipitated at grain boundaries and there was no □-ferrite in the matrix. The amount of the □-ferrite increased with Nb content. 5) The hardness of the welded samples increased with Nb content and were high in the order of welded zone, HAZ and matrix. 6) It was found from the EPR curves that the reactivation(Ir) and the activation(Ia) current densities decreased with increasing Nb content and were low in the order of the welded zone, matrix and HAZ implying the most severe intergranular corrosion in HAZ.
In order to investigate effects of Nb on the mechanical properties and intergranular corrosion behaviors of the welded AISI 304 stainless steels, the stainless steels containing Nb up to 0.7wt% were melted by using a vacuum furnace and hot rolled at 1100℃ into 12mm thickness and then solutionized for 1hr at 1050℃. Some of them were sensitized for 5hrs at 650℃ in argon atmosphere. The samples were welded by MIG method. The microstructures and phases were investigated by using optical microscope, SEM and XRD for the solutionized, sensitized and welded samples before and after corrosion. The micro-vickers hardness and tensile test were carried out for the solutionized, sensitized and welded samples. Intergranular corrosion behavior of the samples were examined through DL-EPR(double loop electrochemical potentiokinetic reactivation) tests in 0.5M H₂SO₄+ 0.01M KSCN and 10% oxalic acid solutions at 25℃. The experimental results are as follows; 1) As Nb content increased the amount of □-ferrite as a second phase increased, and consequently the hardness, yield strength and tensile strength were increased whereas elongation decreased. 2) The corrosion test in 10% oxalic acid showed that the intergranular corrosion was severe in the solutionized samples with increasing Nb content but in the sensitized samples it decreased. 3) The EPR curves measured in 0.1M H₂SO₄+ 0.01M KSCN solution showed that the activation current density(Ia) for the sensitized samples were not changed significantly, however, the reactivation current density(Ir) decreased with increasing Nb content. 4) The microstructure of the welded zone was dendritic structure constituted of austenites and □-ferrites, but in HAZ the □-ferrites were precipitated at grain boundaries and there was no □-ferrite in the matrix. The amount of the □-ferrite increased with Nb content. 5) The hardness of the welded samples increased with Nb content and were high in the order of welded zone, HAZ and matrix. 6) It was found from the EPR curves that the reactivation(Ir) and the activation(Ia) current densities decreased with increasing Nb content and were low in the order of the welded zone, matrix and HAZ implying the most severe intergranular corrosion in HAZ.
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