Tham khảo tài liệu 'handbook of workability and process design part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 74 Workability Testing Techniques temperature tested 1230 C or 2250 F and at the PDT 1120 C or 2050 F where hot-tensile ductility is extremely high the fracture appearance is ductile and dynamic recrystallization occurs leading to an equiaxed grain structure. At the higher temperature a coarser grain structure results from grain growth which accounts for the drop in ductility. At the opposite end of the hot-working temperature range 842 C or 1548 F the elongated grain structure reveals that dynamic recrystallization does not occur and the fracture surfaces indicate a -less-ductile fracture mode. The correlation among fracture appearance microstructure and hot-tensile ductility was even more evident for a developmental solid-solution-strengthened cobalt-base superalloy Fig. 11 . At the PDT 1150 C or 2100 F dynamic recrystallization occurs fracture was primarily transgranular and the fracture appearance was ductile. At the ZDT 1200 C or 2200 F both static recrystallization and grain growth were obvious but incipient melting was not evident in the microstructure. Microstructural evidence of in- cipient melting at the ZDT is observed for some alloys but not for others Ref 13 . An example of the sensitivity of the hot- tensile Gleeble test is shown in Fig. 12 iron nickel-base superalloy Alloy 901 Ref 14 . A small amount of lanthanum added to one heat top curve was sufficient to reduce the analyzed sulfur content to the 1 to 5 ppm range. This resulted in a small improvement in the hot-tensile ductility according to Gleeble hot-tensile data. Test temperature F Isothermal Hot-Tension Test Data From the isothermal hot-tension test information can be obtained about a number of material parameters that are important with regard to metalworking process design. These include plastic-flow stress-strain behavior plastic anisotropy tensile ductility and their variation with the test temperature and the strain rate. Stress-Strain Curves Material Alloy type Nominal composition wt .