Development Study Of Welding Rod For The Purpose Of T91/P91 Heat Resistant-steel

With the development of electric power in our country, thermal power units with high quantity and high capacity are more and more useful, which promotes the use of T91/P91 heat resistant-steel. However, compared with industrially developed country, the weldability of the electrode for T91/P91 steel made in china is a little worse, and the microstructure and mechanical property of the weld are not stable. At present, all most welding metals for T91/P91 steel rely on imports. So, it is valuable to develop the electrode with high quality for T91/P91 steel.A lot of work has been done in the study. The influence of the constituent of the coating on the usability of the electrode has been investigated by the orthogonal experimental, and the optimal proportion of the constituent, marble, fluorite, quartz, etc, is confirmed. On this basis, the content of the other materials in the coating was slightly adjusted to get the electrode with excellent usability for T91/P91 steel. A little rare-earth elements were added in the coating with the optimal proportion. The influence of the rare-earth elements on the shape, size and distribution of non-metallic inclusion in deposited metal, and the promotion on grain refinement has been investigated. The organization and structure of deposited metal were analysed by using OM, SEM, EDS and XRD, and the mechanical property was tested by using Vickers, tensile testing machine and impact testing machine.The research shows:during the experiments, the content of marble has a big influence on weld spatter, detachability and form of the weld; the content of fluorite has a big influence on weld spatter; the content of quartz has a big influence on form of the weld. The experiments show that using the electrode made with the optimal proportion makes a good result with little spatter, good detachability and a good form. As the content of REE in the coating increases, the size of the grain of deposited metal is reducing, and the amount and the size of the inclusion are reducing, too. When the content is 2.0%, the size of the grain is the least and most of the inclusions are Al2O3, which are fined and uniformly distributes and disperses. The content has less effect on the hardness of deposited metal.After high temperature tempering, the structure of deposited metal is tempered martensite, and observed by using metallographic microscope, the orientation of the old marten lath is no longer obvious. It can be sure that the structure of deposited metal made by 55# electrode is tempered martensite by using XRD and SEM, and tiny carbide of Cr uniformly disperses in martensite, especially fasten on the interface of martensite.In all of the experiments, the usability of 55# electrode is the best:the grain of deposited meta is the fined; Al2O3 inclusion uniformly disperses in the whole weld layer, and the size is smallest; after high temperature tempering, the structure is tempered martensite, and tiny carbide of Cr uniformly disperses in martensite; the hardness is appropriate and the mechanical property is qualified. As a result, the 55# electrode is the best.