Shushi Kinoshita

Effect of the Amount and Shape of Inclusions on the Directionality of Ductility in Carbon-Manganese Steels

The present work has been made to elucidate the quantitative effects of the amount and shape of inclusions in carbon-manganese steel plates on the tensile and impact ductilities in connection with test directions. The influence of rolling conditions on ductility can be expressed as a function of the shape parameter of the inclusions in terms of the aspect ratio of elliptical manganese sulfide on the polished surface. Tensile and impact ductilities in transverse and through-thickness directions were improved by rare earth metal (REM) additions to such an extent that the ductilities of REM-treated steel specimens were nearly the same as those of the REM-free steel specimens, although the inclusion content of the former was as much as two or three times more than that of the latter. Efforts were made to express ductility in one parameter regardless of the inclusion shape and test directions, and it was found that the ductility was closely related to an inclusion area fraction on the ductile fracture surface.

Mechanical Properties of Vacuum Carbon-Deoxidized Thick-Wall 2¼Cr-1Mo Steel Forging

The effect of postweld heat treatment on the susceptibility to temper embrittlement of 2 1 / 4 Cr-1Mo steel forgings which have various silicon contents has been investigated. Then, to verify the validity of low-silicon 2 1 / 4 Cr-1Mo steel for an actual forging, the mechanical properties and the susceptibility to temper embrittlement of a 296-mm (11.7-in.)-thick forged ring made from a 100-ton ingot with silicon content reduced to below 0.10 percent by the vacuum carbon deoxidation (VCD) process have been tested. The results are as follows: (I) the through-thickness mechanical properties of the forging meet the requirements of ASME SA-336. F22; (2) silicon content has no significant effect on the creep-rupture strength at least to IS 000 h at 550°C (1022°F) and 600°C (1112°F); and (3) the susceptibility to embrittlement is very low, as the shift in 50 percent fracture appearance transition temperature is 14°C (25°F) for step cooling and 22°C (40°F) for isothermal treatment at 475°C (887°F) for 5000 h.

Manufacture of Differentially Heat-Treated Turbine Rotor Forgings

Using modified Cr-Mo-V steel with small additions of nickel and niobium and reduced silicon, four integral high pressure (HP) and low pressure (LP) combination turbine rotor forgings with 1240-mm maximum barrel diameter were manufactured. To obtain improved toughness in the LP portion and sufficient creep strength in the HP portion, the rotor forgings were differentially heat-treated; HP portions were austenitized at high temperatures and LP portions at low temperatures, followed by forced air cooling in the HP portions and by water spray quenching in the LP portions. Evaluation of the manufactured rotor forgings revealed that the toughness and the creep strength were sufficient in the LP and HP portions, respectively, the residual stress was sufficiently low, and the heat indication testing results were satisfactory in spite of the differential heat treatment.