Wear, defined as deterioration due to use, of water wheel at a hydroelectric power station is caused primarily by three factors, namely corrosion, abrasion and cavitation. It is the purpose of this paper to study on abrasion resistance of various materials against sand in a rapid current of water and their hardface-welding method, and to analize some of the aspects of abrasion mechanism. Abrasion testing apparatus, method and results are described together. As an abrasion phenomenon is very complicated, homogeneous C-steel pieces were chosen for analizing abrasion mechanism. Harder material is not always more abrasion resistant and high C-steeil as quenched is not more abrasion resistant than that tempered at 400° 500°C.
Classifying weldability in the five classes, the authors made weldability tests on low manganese high tensile-strength steels and found the following reuslts. (1) It is recognized in each steel-plates under test that the close-relation respectively exists among Ceq, hardness in the vicinity of water-quenched end in Jominy test, max. hardness of heat-affected zone during welding, and bead-bend angles. When Ceq is located above 0.5%, weldability is apt remarkably to become worse. (2) The higher welding current, the lower welding speed, max hardness at the heat-affected zone is decreased and bend angle is increased propotionally. In the case of hardness below 300Hv, no measurable differences of bend angles are exhibited. (3) Using the low-hydrogen type electrode, satisfactory results are obtained in weldability. (4) With regard to influence upon elapsing time for bend angle of longitudial bead-bend test after welding, bend angle is found to be very small immediately after welding, in spite of various type of electrodes. When the low-hydrogen type electrode is used, bend angle is rapidly increased within following 24 hrs. However, the high cellulose type electrode is sluggish, concering increase in bend angle as compared with the former. It may be assumed that causes as above are due to effect of both hydrogen content absorbed during welding and residual hydrogen content retained after welding.
Corrosion test against boiling 65% nitric acid and saturated salt solution have been made on the parent metal and welded specimen of three grades of 18Cr steel plates, one grade of 13Cr and two grades of 18-8 Cr-Ni. Microscopic observations of the corrosion of heat-affected zones in them have been carried out with the following conclusions: 1) Corrosion in 18Cr steel welds occur in the coarsened crystal grain area of heat-affected zone in the vicinity of beads. Boiling 65% nitric acid and saturated salt solution present considerably differing conditions. of corrosion. 2) In the case of nitric acid, the heat-affected zone is found less susceptible to corrosion when there is coexistence of martensite and ferrite than when there is ferrite alone. In the case of salt solution, intergranular corrosion at martensite-ferrite boundary is conspicuous. 3) For both cases, addition of Ti to 18Cr steel aggravates corrosion in the heat-affected zone; liberal addition of Mo besides Ti tends to make it mild. 4) General corrosion of 13 Cr steel is worse than those of other grades, but no intergranular corrosion appears in both cases. 5) The varying degrees of corrosion in the heat-affected zone between 18 Cr and 13 Cr steel may be reasonably ascribed to different extents of carbide precipitation at intergranular boundary.
This paper reports the effects on the Acetylene pressure in the weleing. In this experiments, Acetylene pressure has been investigated as a factor affecting weld qualities in the welding. The results were as follows; In Carbon steel and Brass welding, when used Acetylene higher pressure, Elongation of the Vee Butt welded join is higher. In Aluminum welding, welded quality in the Vee butt Joint is not so affected by the acetylene pressure. The extent of softening which takes place in higher pressure is Closed to welded Joint.
In this report, the author has investigated the spot welding of light alloy and points out the difference of heating under high load from free conditions. The results obtained are as follows. 1) Under high load, current path increases as temperature rises, and current density decreases during welding. 2) Current path is affected with mechanical pressure and temperature. So it is possible to control heat generation by pressure or current wave. 3) Heat generation is controlled by following factors, electrode Material and its shape, too.
When low chromium steel bars (C 0.43%, Cr 0.99%) are flash-butt-welded, the weld metal and heat affected zone show coarse structure containing martensite and troostite. The degree of decarburization of weld metal is smaller than that of low manganese steel bar. If these parts are postheated at about 800°C with an electric furnace, the very hard microstructure in these parts, martensite, disappears and fine sorbite or granular cementite appear. Accordingly the improvement of mechanical properties are observed. In the case of postheating with a flash-butt-welder, the postheating at about 800°C is also suitable.
Penetrations of bead-on specimens (200×200 mm, 6, 10, 15 and 20 mm thick) of plain carbon steel were measured for, various welding conditions. (see Fig. 1 and Table 1).Penetration and bead width were presumed by theoretical calculation of temperature distribution near the weld. (see Fig. 2). These are shown-in Figs. 3, 4 and 5, where Q: heat input per unit time (cal/sec), λ: thermal conductivity (cal/cm.sec°C), k: temperature diffusivity (cm2/sec), θ1: melting temperuture (°C), W: width of'heat source (cm). From this calculation, penetration (d) and bead width (b) are expressed by equations (3) and (4). Constants m1, m2, n1, n2 and K are given in Table 3 for the typical electrode "A" in Japan. The change of arc length (or arc voltage) little affect the penetration as shown in Fig.7. The effect of welding current (I amp.) and welding speed (v cm/sec) on penetration is shown in Figs. 8 and 9 respectively. The effect of electrode size is shown in Fig. 10.