Tham khảo tài liệu 'navfac p-433 welding materials handbook_4', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | PRESSifc 6 and Split Unregistered Version Table 2-1 shows recommended preheat temperatures for welding. Temperatures higher than those indicated on this chart are sometimes required when hard-facing depending on the size and shape of the part and the type of hard-facing alloy to be applied. WELDING ON CAST IRON Rebuilding and hard-facing of cast iron is not generally recommended since it is extremely crack sensitive. However some cast iron parts primarily those subject to straight abrasion are being successfully hard-faced. Under any circumstances cast iron parts require high preheat temperatures from 1000- 1200 F dull red and must be slow cooled after welding. Weld deposits on cast iron should be peened to help relieve stresses. BUILDUP MATERIALS AND BASE METALS Considerable differences exist between welding materials used to buildup worn equipment and those used for hard-facing overlays. 2-3 - http Prior to hard-facing badly worn parts must be restored with an appropriate buildup material to within 2 16 -3 8 in. of their finished size. The buildup material must have sufficient mechanical strength to sustain structural requirements. It must resist cold flowing mushing under high compressive loads and plastic deformation under heavy impact. If the buildup material doesn t possess these properties a hard-facing overlay which has comparatively little ductility will span for lack of support. In addition to these mechanical requirements a buildup material must be compatible with the base metal and the hard-facing overlay. Use electrode on page 1-24 as the primary source and electrodes on pages 1-5 and 1-3 in that order as alternate sources to rebuild carbon steel parts prior to overlaying with hard-facing electrodes. When hard-facing with the high alloy group apply the recommended hard-facing material before placing it in service and do not allow it to wear more than 1 4 in. two layers before hard-facing. If carbon steel parts BUI iẸrt ỉj6 Erè ístérfeQ
