The thermal efficiency of oxy-acetylene flame have not been determined by the researchers of gas welding fields. It is necessary, however, to the fundamental study of oxy-acetylene welding and allied processes. Authers have measured the value experimentary with simple apparatus. The skelton diagram of heating apparatus was shown in Fig. 1. The heated specimen of mild steel plate 100 x 100 mm (3.2, 4.6, 6.5 and 10.3 mm in thickness) was inserted into the calorimeter as shown in Fig. 2. The thermal efficiency was defined as follow ; thermal effciency=received heat quantity of specimen/total heat combustion of oxy-acetylene flame ×100% In this experiment, if the plate thickness and tip distance (L) were varied, relations between the thermal efficiency and mixed ratio O2/C2H2 were shown as Fig. 5-8. Effects of heating time and tipangles to the thermal efficiency were shown in Fig. 13 and Fig. 14. The test results can be described as follows ; 1) The thermal efficiency of oxy-acetylene flame is 45-75%. But in case the plate surface is melted, it is about 45-55%. 2) The thermal efficiency is gradually increased according to the decrease of the tip distance. 3)The thermal efficiency is increased according to the increase of the mixed ratio. 4) In case the plate surface is. not melted, the thermal efficiency is slightly increased according to the increase of plate thickness even if the same heating time is used. And in case the plate of same thickness are used, the thermal efficiency is decreased according to the increase of heating time. 5) In case the heating is -done until the plate surface, just below the white cone only, is melted, the thermal efficiency is increased according to decreases of plate thickness and mixed ratio. 6) The thermal efficiency is increased according to the increase of the tip angle.
The effect of heating duration on the properties of oil quenched high steels was investigated comparing the long heating in usual heat treatment with the short heating in welding. The short heating and quenching which was impractical in a furnace, was realized on a bar specimen with a reproducing apparatus for rapid thermal cycles. V-Charpy impact test hardness measurment and examination of microstructure were made for two high strength steels, manganese-silicon and manganese-vanadiumtitanium, and the following conclusions were obtained; (1) The specimen with the weld thermal cycle reproduced in it was found to be satisfactory for the test purpose. The short heated and quenched microsructures were very similer to those in welding. (2) The transition temperature, hardness and microstructures of short heated specimen were considerably different from those of long heated one, thus resulting in a conclusion that the usual heat treatment such as Jominy test may not be adequate to evaluate the properties of welded steels. (3) The effect of vanadium and titanium addition to the composition of steel was not so effective in reducing the maximum hardness in the heat affected zone.
As the first step of producing high tensile structural steels (H. T. 60) with tensile strength over 60 kg/mm2 and good weldability, five laboratory heats prepared by adding Ni, Cr, Mo, V and Ti, to the Si+Mn type usually adopted for making a high tensile steel with tensile strength below 60 kg/mm2 were melted and tested. From this experiment it is deduced that by decreasing C and Mn contents and adding V and Ti, the ductility transition temperature and the maximum hardness in H. A. Z. can be lowered, keeping tensile strength above 60 kg/mm2. But the plates as rolled would be attended with the danger that elongation may not be high enough and ductility transition temperature lowered. In case of normalizing plates, however, the tensile strength will be lowered and the ductility can be considerably improved. And it is learned that replacing Mo with V and Ti, better weldability can be achieved as H. T. 60 plates.
As the first part of studies on the weld hardening of heat affected zone in high tensile steels, the effects of various factors on the cooling rate at the bond of a long bead were investigated experimentally by measuring the heating and cooling thermal cycle with thermocouples. The accuracy and the reproducibility of measurement were first discussed, and the studied factors included the location of thermocouple, size and thickness of specimen, initial plate temperature, heat input (welding current and welding speed), as well as the type of electrode coating. The effects of various factors, namely temperature (T), initial plate temperature (T0), welding current (I), welding speed (v), and plate thickness (t) on the cooling rates at the bond of a long bead welded on a plate were found to be summarized with an experimental parameter, P: P=(T-T0/I/v)1.7×(1+2/π tan-1t-t0/α) to, α: constant.
In the previous report, authors investigated the influence of finish roll temperature of three project high tensile steel plates, 22 mm thick. During the course of that work it became evident that further information was desirable concerning the mechanical properties and notch sensitivity in thickness direction (Z direction). This report was intended to furnish information about the influence of each of the finish roll temperatures on the mechanical properties and notch toughness of Z direction in a series of the same project steels as the above-mentioned. Suitable testing methods to measure these properties are as follows: (1) V-Charpy impact test in Z direction (the specimens were taken from cross joint of double bevel grooves with fillet welds). (2) Tension test in Z direction using the test piece of cross joint. (3) Micro tension test in X, Y and Z directions. As a result, it was concluded that marked difierences of mechanical properties and notch toughness was observed in the specimen of Z directions as compared to those of X and Y directions, but these anisotropic properties were the common among the three project steel plates, and steel "C" showed rather better performance even in Z direction.
On the occassion of cutting of mild steel plate by oxyacetylene gas torch, it is well-known that the longitudinal distortion occurs along the cutting edge and it spoils the straightness of cutting. Many reports have been made on this problem, but most of them were only measurements of the experimental f acts. Longitudinal distortion is an outgrowth of the permanent set of the longitudinal strain caused from the constrained thermal expansion. One analytical approach to this problem was prepared by the author to explain, the mecanism of longitudinal distortion, and it was shown that the theoretical value was in good accord with, the experimental data.