DMR-249 A is an indigenously developed high strength low alloy steel for Indian ship building industry for making ship-hull and is extensively used in the construction of war ships and submarines. Welding electrodes c...DMR-249 A is an indigenously developed high strength low alloy steel for Indian ship building industry for making ship-hull and is extensively used in the construction of war ships and submarines. Welding electrodes conforming to SFA 5.5 AWS E8018 C1 has been indigenously developed for welding of this steel using shielded metal arc welding process. In the present study, susceptibility to hydrogen assisted cracking of DMR-249 A steel welds made using this electrode has been assessed using implant test. Implant tests were conducted using this electrode at two different levels of diffusible hydrogen, measured using gas chromatography technique. It is observed that both the steel and the welding consumable are not susceptible to hydrogen assisted cracking even with a high diffusible hydrogen level of 9 m L/100 g of weld metal. In implant tests, specimen did not fracture even after loading to stress levels higher than the yield strength of the base metal. The good resistance of this steel and the welding consumable, even with high levels of diffusible hydrogen, is attributed to absence of a susceptible microstructure in both the weld metal and heat affected zone. Hence, this study shows that, in the absence of a susceptible microstructure, hydrogen assisted cracking is unlikely to occur even if hydrogen level is high. It also confirms that in welding of DMR-249 A with indigenously developed E8018 C1 electrode, hydrogen assisted cracking is not a concern and no preheating is required to avoid it during welding.展开更多
In the present study an attempt has been made to investigate the relationship between the variations in the fouling assemblage and corrosion behaviour of HSLA steel at three coastal locations in the Gulf of Mannar, In...In the present study an attempt has been made to investigate the relationship between the variations in the fouling assemblage and corrosion behaviour of HSLA steel at three coastal locations in the Gulf of Mannar, India, over a period of 24 months. Oyster fouling was dominant in the Tuticorin open sea, while barnacles were the major foulants in the Tuticorin harbour and Mandapam. The fouling load in the Tuticorin waters was higher when compared to the Mandapam waters. The corrosion rates decreased progressively with the immersion time at all three test locations. In the Tuticorin open sea, the corrosion rates were higher when compared to the other two locations throughout the study period. The surface of the coupons was characterized by crevices beneath the hard foulers in the Tuticorin harbour and Mandapam, whereas in the Tuticorin open sea, the coupons experienced crevices of a tunneling nature. The percentage of the loss of the tensile strength increased with time at all the test locations.展开更多
An experinientally quantitative inveetisation has been made on the precipitationand coarsening behaviors of niobium carbide in a high strength low alloy(HSLA) steel. The results suggest that the static coarsening proc...An experinientally quantitative inveetisation has been made on the precipitationand coarsening behaviors of niobium carbide in a high strength low alloy(HSLA) steel. The results suggest that the static coarsening processes duringisothermal reaction in (α+γ) two phase region and during isothermal stay aftercertain amount of deformation of austenite are principally controlled by thediffusion of niobium atoms along dislocation pipes, and the volume fraction ofthe precipitates exerts sisnificant influence on the coarsening processes.Whereas the dynamic coarsening process during hot deformation of austeniteappoars to be dominated by the carbide/matrix interphase reaction.展开更多
文摘DMR-249 A is an indigenously developed high strength low alloy steel for Indian ship building industry for making ship-hull and is extensively used in the construction of war ships and submarines. Welding electrodes conforming to SFA 5.5 AWS E8018 C1 has been indigenously developed for welding of this steel using shielded metal arc welding process. In the present study, susceptibility to hydrogen assisted cracking of DMR-249 A steel welds made using this electrode has been assessed using implant test. Implant tests were conducted using this electrode at two different levels of diffusible hydrogen, measured using gas chromatography technique. It is observed that both the steel and the welding consumable are not susceptible to hydrogen assisted cracking even with a high diffusible hydrogen level of 9 m L/100 g of weld metal. In implant tests, specimen did not fracture even after loading to stress levels higher than the yield strength of the base metal. The good resistance of this steel and the welding consumable, even with high levels of diffusible hydrogen, is attributed to absence of a susceptible microstructure in both the weld metal and heat affected zone. Hence, this study shows that, in the absence of a susceptible microstructure, hydrogen assisted cracking is unlikely to occur even if hydrogen level is high. It also confirms that in welding of DMR-249 A with indigenously developed E8018 C1 electrode, hydrogen assisted cracking is not a concern and no preheating is required to avoid it during welding.
基金Supported by the Ministry of Environment and Forests,New Delhi for the Financial Support(Project Grant No.19-26/2003-RE)
文摘In the present study an attempt has been made to investigate the relationship between the variations in the fouling assemblage and corrosion behaviour of HSLA steel at three coastal locations in the Gulf of Mannar, India, over a period of 24 months. Oyster fouling was dominant in the Tuticorin open sea, while barnacles were the major foulants in the Tuticorin harbour and Mandapam. The fouling load in the Tuticorin waters was higher when compared to the Mandapam waters. The corrosion rates decreased progressively with the immersion time at all three test locations. In the Tuticorin open sea, the corrosion rates were higher when compared to the other two locations throughout the study period. The surface of the coupons was characterized by crevices beneath the hard foulers in the Tuticorin harbour and Mandapam, whereas in the Tuticorin open sea, the coupons experienced crevices of a tunneling nature. The percentage of the loss of the tensile strength increased with time at all the test locations.
文摘An experinientally quantitative inveetisation has been made on the precipitationand coarsening behaviors of niobium carbide in a high strength low alloy(HSLA) steel. The results suggest that the static coarsening processes duringisothermal reaction in (α+γ) two phase region and during isothermal stay aftercertain amount of deformation of austenite are principally controlled by thediffusion of niobium atoms along dislocation pipes, and the volume fraction ofthe precipitates exerts sisnificant influence on the coarsening processes.Whereas the dynamic coarsening process during hot deformation of austeniteappoars to be dominated by the carbide/matrix interphase reaction.
