The precipitation characteristics of boron constituent appearing in the weld heat affected zone of boron treated T-1 type high tensile strength steel has been investigated. Following results are obtained: 1. The precipitatation of boron constituent is extremely little when the steel contains 0.002% of B but predominant in the steel containing 0.005% of B. 2. In the steel containing 0.002% of B, the precipitation characteristics of boron constituent varies with the cooling rate of heat affected zone. When the cooling condition of heat affected zone is such that the cooling time from 800°C to 500°C is 28.5 sec., there is no precipitation of boron constituent. When the choling time from 800°C to 500°C is more than 51.5 sec., slight precipitation of boron constituent has been observed. In case of the steel containing 0.005% of B, the precipitate has been observed in all the cooling conditions ranging from 10 sec. to 163.5 sec. in cooling time from 800°C to 500°C. 3. The precipitation characteristics of boron constituent can be deduced from the isothermal precipitation diagram by superimposing the cooling curve of heat affected zone on the diagram. And, the isothermal precipitation curve of boron constituent moves to the left as the austenitizing temperature is higher. It also moves to the left if the steel has more tendency to reveal the boron constituent in its heat affected zone. 4. The precipitation characteristics of boron constituent at different cooling condition can be more easily known by the observation of precipitate on the side of Jominy specimen, because each point at various distance from quenched end of this specimen represents various different cooling condition.
It has been usualy carried out to make the cotinuous cooling transformation diagram as one of the weldability tests of high tension steels. Up to the present, however, the diagram is often deferent depending upon experimental methods or investigaters because of the defficulty to discriminate each structure as pro-eutectoid ferrite, bainite or martensite. This report is the resullts if examination carried out to make clear these problems.
In the Petro-chemical industry, various equipments operating at low tempesatures are increasing, and generally Aluminum killed steel down to -46°C and 3.5% Nikel steel down to -101°C are used as low temperature service structural materials. For these low temperature materials including their weld metals, the properties specified in the relevant clauses of ASTM A-300 are to be satisfied. Detailed reports on the properties for Aluminum killed steel and 3.5% Nikel steel materials and on those of weld metals made reports were with coated electrode arc welding was published in the past, and also reports were made for the case of MIG welding. However, there are only few papers of submerged are welding which considered as most efficient among all automatic welding methods ever applied to this type of welding work. Therefore we experimentally processed several bonded fluxes intended for the specific use in a submerged arc welding method applicable to low temperature steels, and investigated various properties, particularly impact values, of such weld metals obtained with these bonded fluxes. The results of experiment are summarized as follows ; (1) In the case of Aluminum killed steels, weld metal made with either of B+H-540 or B+H-350 combination satisfies the low temperature specification of ASTM as these have good mechanical properties and low temperature impact values. (2) In the case of submerged arc welding, the low temperature properties of weld metal are affected greatly by flux compositions. Therefore, the use of flux having characteristics of a low hydrogen type with large amount of CaCO3 content is recommended. Also, the low temperature impact values obtained on the weld metal are better for multipass weldieg with a small current than single pass welding with a large current. (3) In the case of single pass welding for Aluminum killed steels with a large current, the H-525 flux to which Fe-Al and Ni are added is preferable, and the weld metal obtained on such well generally gives a good low temperature impact values. (4) 3.5% Nickel wire and H-350 flux combination gives a good results for 3.5% Nikel weld metal. Possible low temperature impact value can be improved by a weld made with a low hydrogen type flux and small diameter rod combination in comparison to one made with large size rods, since the former tends to have a higher deposit metal temperature rise which boosts up the weld metal cleanliness than the latter.
There are several advantages of electron beam welding as widely known and it is necessary to develop fully the application technique of this process, making good use of its merit. Some works on the applicability of the electron beam process to the welding of the nuclear fuel element and some heat resisting alloys were carried out. Discussion on the problem concerning the development work of the electron beam welding are also described. The conclusions obtained in this study are as follows. (1) From the experimental end-plug welding of nuclear fuel sheathing by electron beam, excellent joint design and weld penetration which are not expected by ordinary welding method were obtained. A smaller and simpler end-plug can be used for fuel element welding and this means a considerable widening of fuel element design. Weldability of such micro-welding was generally better by electron beam than by TIG method. (2) With electron beam, new joint design and welding procedure are applicable for various types of specimen. So it seems likely that the electron beam welding process has many fields of application in industries. (3) The results from the electron beam welding of some heat resisting alloys show a narrow and deep penetration in welds which reduces the heat affected zone and hardened area. Working efficiency on welding is rather superior with electron beam to that with ordinary arc welding.