Studies were made on the effects of adding Ti and B on Timken 16-25-6 alloy, heat-resisting steel for gas turbine materials. In this report, the influence of the addition of Ti and B to 16-25-6 alloy on the phecipitation phenomena were examined.
There were four grades of samples of chemical compositions (See Table 1). Based on 16-25-6 alloys, two of them included Ti, one of them included B, and another alloy contained both Ti and B.
Samples were melted in high-frequency electric furnace, cast into moulds, and forged to bars. Solution-treatment was operated at 1150°C or 1200°C for 1 hour.
Specimens after solution-treatment were aged at four degrees of temperature, 700°C, 750°C, 800°C, and 850°C, from 1 hour to 500 hours. Aged specimens were tested for hardness, and observed through microscope. Microstructure was prepared by (HCl, HNO3, glycerine) etching solution and other selective-etching reagent.
With the sample #D1 (0.7% Ti) and #D2 (1.8 Ti), precipitation-hardening speed increased with rise of the aging temperature from 750°C to 850°C, but softening began at 850°C after about 75 hours aging. Maximum hardness appeared at 750°C aging. In aging process, precipitated particles, which appeared in the case of standard commereial 16-25-6 alloy's aging, and TiC would also be precipitated.
With the sample #D3 (0.085% B), precipitation-hardening velocity was lower than the sample #D1 and #D2, and it yet continued to harden after 500 hours even at 850°C. Fe2B was found and other precipitated particles, which were similar to particles of commereial 16-25-6 alloy, were also found.
In sample the #D4 (0.19% Ti and 0.03% B), precipitation process ranked between #D1 or #D2 and #D3. Variaties of microstructure during aging were found as cqmbinations of #D1 or #D2 group and #D3 group.