There are many variables which affect impact resistance of weld metals. In this report we have attempted to obtain quantitative effects of silicon on the notch toughness of pearlitic weld metals. By varying ferro-silicon amounts of welding flux we can adjust the amounts of silicon of the weld metals. Ten specimens thus obtained were investigated. During deoxidizing process is continuing, silicon raises maximum energy, and shifts transition curves to lower temperature by reducing oxygen contents of weld metals. Then after the completion of deoxidation addition of silicon reqularly raises transition temperature, lowers maximum energy and widens transition range.
For the steel DT containing low carbon, Ni, Mo, V and B, of which ultimate tensile strength is about 90 kg/mm2 in the state quenched from 930°C and water cooled after tempering for 1hr at 630°C, as well as USS "T-1" steel, the continuous cooling transformation diagram in case of maximum heating temperature 1350°C was constructed. Then this continuous cooling transformation diagram was compared with that obtained in case of maximum heating temperature 1093°C by Nippes, Savage and Allio. The following results were obtained : 1. The A3-transformation point of steel DT is extremely low. In the continuous cooling transformation diagram, the time at the Ac3 temperature 833°C was adopted as 0 sec of a datum point. 2. Critical cooling times of steel DT are determined as follows ; Cz'=6 sec, Cf'=18 sec, Cp'=56 sec, Ce'>2000 sec. The cooling time corresponding to 50% martensite is 18.5 sec, namely, near the value of Cf'. 3. The positions of the beginning curves and the ending curves of each consitituents of microstructures in the authors' continuous cooling transformation diagram in case of maximum heating temperature 1350°C, remove to the longer cooling time and lower temperature side, compared with those in the continuous cooling transformation diagram in case of maximum heating temperature 1093°C constructed by Nippes, Savage and Allio. 4. In the author's continuous cooling transformation diagram, critical cooling time Cz', Cf', Cp', 50% martensite cooling time and others are determined, but in that diagram by Nippes, Savage and Allio, Cz' critical cooling time was only determined and 4.6 sec of the value is smaller than 6 sec of the author's value.
The hot-start has been thought to have the two functions, i. e., (1) easy arc striking and (2) deep penetration. In addition, the authors have found the third function, (3) elimination of blow holes. From the X-ray results of many short bead tests, optimum hot-start conditions are concluded as follows ; (a) boosted current is between 1.5 and 2 times of rated welding current and (b) the duration time of hotstart is between 1 and 2 seconds. The reasons why the hot-start can eliminate blow holes are explained by (a) rapid shutoff of air into arc by easy arc striking and (b) increased heat input into base metal. A hot-start circuit without relays is achieved by using a magnetic amplifier with time delay characteristics.
In the study of oxy-acetylene gas cutting of low alloy high strength steel, the relation between crack sensitivity of heat affected zone and following subjects are researched applying bending tests. Gas cutting speed Pre-heating temperature Post-heating temperature Hardness of mother steel Condition of cutting surface Composition of steel etc. Experiments are made in this study, in order to know the metallergical nature of heat affected zone and its effect for weldability of mother steel. Following results are shown by these experiments. 1. Increase of bending angle in bending test and decrease of maximum hardness at heat affected zone show that 100°C pre-heating gives remarkable effect to improve the crack sensitivity of steel. 2. 200°C or over 400°C post-heating gives effect for the decreasing of crack sensitivity value, through 100°C pre-heating gives better effect. 300°C post-heating which belongs to the range of temper brittleness should be avoidable. 3. Less cutting speed gives better bending effect generally. 4. Less hardness by high tempering temperature gives better bending effect to mother steel, just same as the effect of post-heating temperature. 300°C tempering gives less bending effect. 5. Removing of cutting carf makes bending effect a little better, despite removing of heat affected zone gives remarkable effect. 6. Value of bending test of rolled steel is far higher than cast steel. 7. X-ray spectrochemical analysis and michro-structure proof the increase of Ni, Cu, Mo content and the decrease of C, Cr, Mn content on the gas cutting surface. 8. It is suposed that the cementite zone and the high carboned zone inside made by carbon defusion out of mother steel. 9. It became clear that the application of suitable gas cutting is quite effective for the welding edge of low alloy high strength steel.
In this paper, we have studied the characteristics of spot weld in 1mm stainless steels, being applied to faying surfaces with a sealer before spot welding. We investigated the spot weld results in contact resistance, shear strength, shear strength consistency, internal structure and radiograph by changing some welding conditions of three phase frequency converter type machine. Results obtained are as follows : (1) Applied to faying surfaces, contact resistance increased to some degrees. (2) Normal weld characteristics were little influenced by sealer applications. (3) Shear strength consistency resulted very excellent. (4) Spattering and burning to be feared has not revealed.
On the welding of rail joints by non-pressure thermit welding, breaking load over 80 ton and deflection at breaking over 20 mm are obtained with a thermit mixture and a sand mold made in our laboratory, and with sufficient preheat. When postheat is done, bend deflection of this joint is over 30mm.