砷对70/30黄铜在1N NaNO_2水溶液中应力腐蚀开裂的抑制作用

INHIBITIVE EFFECTS OF ARSENIC UPON THE STRESS CORROSION CRACKING OF 70/30 BRASS IN AQUEOUS SODIUM NITRITE SOLUTION

一、前言黄铜的应力腐蚀开裂(SCC)是延性合金环境敏感脆裂的典型。早期,曾以为只有氨或氨的衍生物介质才能导致黄铜发生 SCC。然而,现已发现黄铜在十多种非氨介质中均有 SCC 现象,其中又以在亚硝酸根水溶液中的开裂尤为敏感。

By using slow strain rate tests (SSRT),inhibitive effects of arsenic additions in brass and of additions of As-containing anions into solution upon the susceptibility to stress cor- rosion cracking (SCC)of 70/30 brass in LV NaNO_2 were studied respectively.The results indicated that arsenic contents from ca.0.03 to 0.1 (wt%) in the brass gave rise to cer- tain inhibition of SCC and the inhibitive effect became more pronounced with the increase of applied potential ranging from-100 to+100mV (SCE)where the alloy is normally susceptible to SCC.But.such contents were unable to suppress cracking completely.On the contrary,excessive arsenic addition in the brass,e,g.reaching 0.45% As,caused dele- terious effect on SCC.In contrast,additions of arsenical anions into nitrite solution were considerably effective on inhibiting the SCC of brass.The comparison made between the effects of arsenite and arsenate additions at identical arsenic concentration,i.e.1g/l As, showed that the relative effects of arsenite and arcenate on the inhibition varied with the variation of applied potential,the former anion being more effective than the latter at the potential of-100mV(SCE) but reversed order of the effects of those two anions being observed at the potential above-50mV(SCE).Increasing arsenic concentration from 0. 1 to 10g/l in the solution enhanced the inhibitive effect.At applied potional of-100mV (SCE),1g/l of arsenic,as added with arcenite,made the brass totally immune in 1N NaNO_2.hnmune potential could be further promoted up to-50mV(SCE)when the ar- senic concentration reached 10g/l.Experimental evidence proved that arsenic addition in either brass (in effective amount)or nitrite solution not only had an effect on slowing down the crack propagation rate,but also on increasing stress level for crack initiation.