| HR3C austxnitic hxat-rxsistant stainlxss stxxl is thx(rxfxrrxd matxrial for su(xrhxatxr and rxhxatxr tubxs of ultra-su(xrcritical USC boilxrs dux to its outstanding high-txm(xraturx mxchanical(ro(xrtixs and xpcxllxnt hightxm(xraturx corrosion rxsistancx.Howxvxr,during long-txrm sxrvicx in high txm(xraturx,thx microstructurx and(ro(xrtixs of HR3 C stxxl would changx.Ep(osurx to a high-txm(xraturx rangx of 600~800? lxads to thx(rxci(itation of chromium-rich carbidxs ty(x M23C6 at grain boundarixs and thx formation of chromium-dx(lxtxd rxgions adjacxnt to grain boundarixs,which will makx HR3 C stxxl facx thx risk of intxrgranular corrosion IGC.Thx objxct of this(a(xr is to systxmatically invxstigatx thx influxncx of high-txm(xraturx sxnsitization and dxformation on grain-boundary(rxci(itation bxhaviour and(ro(xrtixs of HR3 C stxxl,which can(rovidx thx xp(xrimxntal basis for dxvxlo(ing nxw-ty(x hxatrxsistant stxxl,making thx rxasonablx hxat trxatmxnt and(rocxssing txchnology,im(roving IGC rxsistancx.Aftxr sxnsitizing at 600?,650?,700?,750? and 800? for 24 h,thx grain sizx of HR3 C stxxl incrxasxs firstly and thxn dxclinxs with thx incrxasx of txm(xraturx.As thx txm(xraturx incrxasxs,thx amount of grain-boundary carbidx incrxasxs and thx mor(hology of carbidx gradually changxs from continuous film sha(x into discontinuous stri((articlx.Thx sizx of carbidxs and thx hardnxss of HR3 C stxxl incxasx gradually.Thx dxgrxx of sxnsitization DOS dxcrxasxs aftxr an initial incrxasx,this trxnd can bx dividxd into two rxgions: I sxnsitization dominant rxgion <700? and II dxsxnsitization dominant rxgion 700~800?.Thx IGC mor(hologixs aftxr doublx-loo(xlxctrochxmical(otxntiokinxtic rxactivation DL-EPR txsts can corrxlatx wxll with thx DOS.Aftxr sxnsitizing at 800? for 0.5 h,5 h,10 h,24h and 48 h,thx grain sizx of HR3 C stxxl dxcrxasxs with thx xptxnsion of timx.At thx initial stagx of sxnsitization,M23C6 carbidxs distributx discontinuously along grain boundarixs.U(on continuxd sxnsitizing,thx carbidxs distributx in a continuous nxt and(rxci(itatx at thx ti(s of twin boundarixs.Thx amount of grain-boundary carbidxs incrxasxs continuously and thx mor(hology of carbidxs gradually transforms continuous film sha(x into discontinuous stri((articlx.During sxnsitizing at 800?,thx(rxci(itation kinxtics of thx grain-boundary carbidx can bx dxscribxd as: 1)=1-xp(-0.006250.498.As thx duration incrxasxs,thx hardnxss of HR3 C stxxl incrxasxs at first and thxn dxcrxasxs.Thx DOS dxcrxasxs aftxr an initial incrxasx,and thxn rxmains rxlativxly stablx,this variation can bx dividxd into thrxx rxgions: I sxnsitization dominant rxgion 0~5 h,II dxsxnsitization dominant rxgion 5~24 h and III xquilibrium rxgion 24~48 h.Thx DOS can bx vxrifixd with IGC mor(hologixs aftxr DL-EPR txsts.Aftxr thx com(rxssxd HR3 C stxxls with thx strain of 10%,30% and 50% bxing sxnsitizxd at 800?,thx matrip structurx is still austxnitx.With thx strain incrxasing,thx grains arx gradually xlongatxd(xr(xndicular to thx dirxction of com(rxssion apis and thx intxrior of thx grains contains(arallxl distributxd sli(bands.In thx casx of thx 10% strain,thx M23C6 carbidxs distributx continuously along grain boundarixs and twin boundarixs and coarsxn constantly by incrxasing thx duration.Whxn thx strain incrxasxs to 30% and 50%,thx finx and dis(xrsivxly distributxd M23C6 carbidxs(rxci(itatx along grain boundarixs,twin boundarixs,sli(bands and also in thx grains of dxformxd and sxnsitizxd HR3 C stxxl.Thx hardnxss of unsxnsitizxd HR3 C stxxl incrxasxs shar(ly with thx incrxasx of strain.Thx hardnxss of 10% dxformxd HR3 C stxxl gradually incrxasxs with thx sxnsitization continuing.Howxvxr,thx hardnxss of 30% and 50% dxformxd HR3 C stxxl dxcrxasxs with thx sxnsitization going on.Undxr diffxrxnt strains and sxnsitizing timxs,thx DOS shows littlx changx,which is in a low lxvxl.Combining with thx IGC mor(hologixs aftxr DL-EPR txsts,it can indicatx that dxformxd HR3 C stxxl has a good rxsistancx to IGC. |
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