Samples of 6082-T6 aluminum alloy were subjected to bobbin tool friction stir welding (BT-FSW), and the joints were treated by postweld natural aging (PWNA) and postweld artificial aging (PWAA). The microstructure, mi...Samples of 6082-T6 aluminum alloy were subjected to bobbin tool friction stir welding (BT-FSW), and the joints were treated by postweld natural aging (PWNA) and postweld artificial aging (PWAA). The microstructure, microhardness, and tensile properties of the aged and as-welded specimens were investigated. Transmission electron microscopy (TEM) observations revealed that a large number of Guinier–Preston (GP) zones precipitated in the form of a network on the stir zone (SZ) after PWNA for 60 d, and a large number of β'' phases precipitated in the matrix for after PWAA for 6 h. As the aging time increased, the microhardness of the SZ and the thermomechanically affected zone (TMAZ) increased significantly, and the hardness of the SZ after PWAA for 6 h was close to that of the base metal (BM). With increasing PWNA time, the strength and strain increased slightly. When the PWAA time increased, the strength clearly increased, with a maximum value of 279.9 MPa after 6 h, while the strain decreased.展开更多
Local postweld heat treatment (PWHT)is usually performed when it is impractical to heat treat the whole vessel in a furnace, Many factors have an influence on PWHT procedures, such as size of the pipe,heated widths, ...Local postweld heat treatment (PWHT)is usually performed when it is impractical to heat treat the whole vessel in a furnace, Many factors have an influence on PWHT procedures, such as size of the pipe,heated widths, insulation conditions, heating rates soak temperatures and hold times, material composition etc,. However up to now the influences these factors have on PWHT are not very clearly understood and different criteria for sizing the parameters can be found in different codes. This study provides a direct method to assess the effectiveness of local PWHT.An axisymmetrical model was used based on the thermal-visco-elastic-plastic Finite Element Method with the consideration of creep phenomena. By using this method both temperature and stress distributions can be simulated during whole local PWHT history. The computation results of temperature distributions and the strain histaries during local PWHT are compared with the experiments, and good agreements are obtained, Investigations show that the thermal stresses induced by local PWHT are much affected by creep behavior and the changes of Young's Modulus. The study of stress relief history shows that the stresses decrease quickly in the heating stage, then decrease slowly according to creep law in the hold stage and then studdenly increase when the cooling stage starts. The study shows the possibility that through a series of computations the effects of many factors can be assessed and the optimum parnmeters can be found. Compared with the heated widths based apon some applicable codes, it is found that a heated area of 2.5 on either side of the weld seems more reasonable.展开更多
The microstructure of E911 deposited metal was observed and the effect of heat input and postweld heat treatment on microstructure and impact toughness was investigated. The microstructure consists of tempered martens...The microstructure of E911 deposited metal was observed and the effect of heat input and postweld heat treatment on microstructure and impact toughness was investigated. The microstructure consists of tempered martensite and residual δ- ferrite. The morphology of tempered martensite is columnar and the residual δ-ferrite is polygonal. With the increase in heat input, the width of columnar martensite grain and the size of residual δ-ferrite increased, whereas the volume fraction of residual δ-ferrite varied slightly. The impact toughness decreased as heat input increased. The result reveals that coarsening columnar martensite grain and δ-ferrite have greater effect on impact toughness than volume fraction of residual δ-ferrite. As the time of postweld heat treatment is exceeded 8h, aggregation of M23 C6occurs in some grain boundaries or lath interfaces. The partial aggregation of M23 C6 results in the decrease in impact toughness.展开更多
铬钼钢高频焊翅片管在石油化工管式炉、锅炉等设备中应用广泛。在联合企业标准(由15家国际翅片管制造商共同签署的企业标准International Standard for Dimensions,Tolerances and Tests of High Frequency Resistance Welded Fins)和...铬钼钢高频焊翅片管在石油化工管式炉、锅炉等设备中应用广泛。在联合企业标准(由15家国际翅片管制造商共同签署的企业标准International Standard for Dimensions,Tolerances and Tests of High Frequency Resistance Welded Fins)和国内部分行业标准中,未明确要求在翅片管制造过程中翅片和基管焊接后需要进行热处理,这与ASME(美国机械工程师学会)标准中铬钼钢焊后应热处理的要求不符。对比铬钼钢翅片管的热处理试件和未经热处理试件的性能,结合高频电阻焊特点分析,认为铬钼钢高频电阻焊翅片管焊接工艺可靠,不需要进行焊后热处理,既可降低生产成本,也可避免因热处理工艺不成熟对翅片管性能带来的其他影响。展开更多
文摘Samples of 6082-T6 aluminum alloy were subjected to bobbin tool friction stir welding (BT-FSW), and the joints were treated by postweld natural aging (PWNA) and postweld artificial aging (PWAA). The microstructure, microhardness, and tensile properties of the aged and as-welded specimens were investigated. Transmission electron microscopy (TEM) observations revealed that a large number of Guinier–Preston (GP) zones precipitated in the form of a network on the stir zone (SZ) after PWNA for 60 d, and a large number of β'' phases precipitated in the matrix for after PWAA for 6 h. As the aging time increased, the microhardness of the SZ and the thermomechanically affected zone (TMAZ) increased significantly, and the hardness of the SZ after PWAA for 6 h was close to that of the base metal (BM). With increasing PWNA time, the strength and strain increased slightly. When the PWAA time increased, the strength clearly increased, with a maximum value of 279.9 MPa after 6 h, while the strain decreased.
文摘Local postweld heat treatment (PWHT)is usually performed when it is impractical to heat treat the whole vessel in a furnace, Many factors have an influence on PWHT procedures, such as size of the pipe,heated widths, insulation conditions, heating rates soak temperatures and hold times, material composition etc,. However up to now the influences these factors have on PWHT are not very clearly understood and different criteria for sizing the parameters can be found in different codes. This study provides a direct method to assess the effectiveness of local PWHT.An axisymmetrical model was used based on the thermal-visco-elastic-plastic Finite Element Method with the consideration of creep phenomena. By using this method both temperature and stress distributions can be simulated during whole local PWHT history. The computation results of temperature distributions and the strain histaries during local PWHT are compared with the experiments, and good agreements are obtained, Investigations show that the thermal stresses induced by local PWHT are much affected by creep behavior and the changes of Young's Modulus. The study of stress relief history shows that the stresses decrease quickly in the heating stage, then decrease slowly according to creep law in the hold stage and then studdenly increase when the cooling stage starts. The study shows the possibility that through a series of computations the effects of many factors can be assessed and the optimum parnmeters can be found. Compared with the heated widths based apon some applicable codes, it is found that a heated area of 2.5 on either side of the weld seems more reasonable.
基金Acknowledgements The authors acknowledge gratefully to the financial support for this work from National Natural Science Foundation of China and Baosteel （No. 50734004） and the assistance of Welding Laboratory of Baosteel Group.
文摘The microstructure of E911 deposited metal was observed and the effect of heat input and postweld heat treatment on microstructure and impact toughness was investigated. The microstructure consists of tempered martensite and residual δ- ferrite. The morphology of tempered martensite is columnar and the residual δ-ferrite is polygonal. With the increase in heat input, the width of columnar martensite grain and the size of residual δ-ferrite increased, whereas the volume fraction of residual δ-ferrite varied slightly. The impact toughness decreased as heat input increased. The result reveals that coarsening columnar martensite grain and δ-ferrite have greater effect on impact toughness than volume fraction of residual δ-ferrite. As the time of postweld heat treatment is exceeded 8h, aggregation of M23 C6occurs in some grain boundaries or lath interfaces. The partial aggregation of M23 C6 results in the decrease in impact toughness.
文摘铬钼钢高频焊翅片管在石油化工管式炉、锅炉等设备中应用广泛。在联合企业标准(由15家国际翅片管制造商共同签署的企业标准International Standard for Dimensions,Tolerances and Tests of High Frequency Resistance Welded Fins)和国内部分行业标准中,未明确要求在翅片管制造过程中翅片和基管焊接后需要进行热处理,这与ASME(美国机械工程师学会)标准中铬钼钢焊后应热处理的要求不符。对比铬钼钢翅片管的热处理试件和未经热处理试件的性能,结合高频电阻焊特点分析,认为铬钼钢高频电阻焊翅片管焊接工艺可靠,不需要进行焊后热处理,既可降低生产成本,也可避免因热处理工艺不成熟对翅片管性能带来的其他影响。
