軟鋼のろう付強度におよぼす表面状態の影響

Abstract

This investigation has been conducted to determine the impact strentgh of brazed (or soldered) joint of mild steel. To obtain some experimental data as to the effects of roughness of base metal, specimens of mild steel (SS41, 12×12×28 mm) were prepared according to the design of Fig. 1(a). The two abutt-ing surface of each specimens were identically finished by emery papers (No. 60, 120, 240, 400, 600), or other mechanical process such as milling, grinding, supper finishing and electrolytic polishing. These specimens were then brazed with BAG-8 filler metal using a resistance furnace (35 KW) operated in hydrogen atmosphere, or soldered by Pb-Sn alloy in the small resistance soldering bath (0.3 KW). Each specimens were machined according to the design of Fig. 1(b). The impact test of these specimens were carried out by 30 Kg-m charpy testing machine. The charpy test of these specimens gave the result shown as follows :(a) On the brazing by BAg-8(1) Impact strength of specimen polished by emery paper No. 120 was excellent, its value being 1.501 KG-m/cm2, and also that of one machined by milling cutter was very high. But impact strength of specimen polished by emery paper No. 600 was poor, its value being about 1.27 KG-m/cm2.(2) Impact strength of specimens with narrow joint clearance (t<0.1 mm) were very low, but that of one with wide joint clearance (t=0.4-0.55 mm) were very high.(3) All specimens were failured at filler metal zone as shown Photo. 4, 5.(b) On the soldering by Pb-Sn Alloy.(1) Impact strength of specimens polished by large grain size emery powder (No. 60, 120) showed about 0.3-0.35 Kg-m/cm2, but that of one polished by small grain size emery powder (No. 400, 600) were about 0.45-0.5 Kg-m/cm2.(2) Most of specimens were fractured at interface of joint, but a few of them were fractured at filler metal zone as shown Photo. 7.