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Tham khảo tài liệu 'smithells metals reference book part 18', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Fusion welding 33-25 Chromium munaent 7.Crfr 7 Mo -r 15 7.5i 0 5 7.Nbi Figure 33.3 Modified Schaeffler diagram for Cũỉiĩtiĩuĩiữỉĩ of sỉíiinỉess sieel weld ifieial. matrix with a consequent reduction in corrosion resistance and susceptibility to intercrystalline attack or weld decay The problem is normally avoided by the use of material cither with carbon contents below 0 03 or containing strong Carbide forming elements such as niobium or titanium. Such stabilized1 Steels arc not immune to intercrystalline attack under all circumstances and heat treatment within the sensitizing range 500-900 C can induce sensitization to intercrystalline corrosion. If post-weld heat treatment is carried out the temperature should be above 900 C. For practical purposes intercrystalline attack due to arc welding is unlikely to be encountered in unstabilized molybdenum-free material of 0.06 carbon and below provided that the arc energy per unit length of weld metal is below 2 kJ mm l although service in highly oxidizing media should be regarded with caution. Austenitic Steels may suffer HAZ liquation cracking during welding. The problem is minimized by the use of low arc energy welding conditions and with wrought material by avoiding grain sizes coarser than about ASTM 3-4 In castings cracking can often be suppressed by using material containing above 5 ferrite. The liquation cracks are of the order of 0.5 mm tong and arc not generally significant in service. In welds of high restraint however they can form initiation points for reheat cracking during elevated temperature service or post-weld heat treatment. Al elevated temperature intragranular strain-induced precipitation occurs in the HAZ. This causes a loss of creep ductility and if joint restraint is high enough intergranular cracking results. All common grades of austenitic stainless Steel are susceptible to reheat cracking with the exception of the l8 Cr 12 Ni 3 Mo types provided that these do not contain residual carbide .
