Inhibition Effect of Ti on the Formation of Martensite Lath in 14Cr Oxide Dispersion Strengthened Steel

Three model powders defined as MP powders (milled pre-alloyed powders), mixed powders (MX, 50 wt.% MP powders + 50 wt.% Oxide-Dispersion Strengthened powders) and Oxide Dispersion Strengthened (ODS) powders (alloyed pre-alloyed powders with the addition of Ti and Y2O3) are obtained under identical ball milling parameters. These powders are then consolidated under same sintering condition by spark plasma sintering (SPS) in order to investigate the formation mechanism of martensite lath in the MP steel and the effect of Ti on the stability of ferrite. The results indicate that the addition of Y2O3 and Ti powders can act as friction material during the mechanical alloying process, thus promoting the refinement effect. The formation of martensite lath in the MP steel is attributed to the local Cr depletion resulted from the large amounts of M23C6 precipitation. Ti possesses a strong affinity to C and long range diffusion ability, which efficiently prevents the martensite lath formation and local Cr depletion. Present study supports the conclusion that the lack of martensite in the MX and ODS steel is due to the addition of Ti. Secondary phases in these steels are identified and analyzed as well.

Download Full-text

Joining of Oxide Dispersion-Strengthened Steel Using Spark Plasma Sintering

Metals ◽

10.3390/met10081040 ◽

2020 ◽

Vol 10 (8) ◽

pp. 1040

Author(s):

Foad Naimi ◽

Jean-Claude Niepce ◽

Mostapha Ariane ◽

Cyril Cayron ◽

José Calapez ◽

...

Keyword(s):

Spark Plasma Sintering ◽

Oxide Dispersion Strengthened ◽

Tensile Tests ◽

Control Surface ◽

Oxide Dispersion ◽

Simultaneous Application ◽

Ods Steel ◽

Plasma Sintering ◽

Spark Plasma ◽

Welding Processes

Difficulties with joining oxide dispersion-strengthened (ODS) steels using classical welding processes have led to the development of alternative joining techniques such as spark plasma sintering (SPS). SPS, which is classically employed for performing sintering, may also be used to join relatively large components due to the simultaneous application of electrical pulsed current and uniaxial charge. SPS technology was tested by joining two ODS steel disks. The preliminary tests showed that it is necessary to control surface roughness before joining. Furthermore, the use of ground and lapped surfaces seemed to improve the quality of the interface. Tensile tests on two ODS cylinders joined using SPS were performed at 750 °C without any additives. Failure occurred away from the interface with a total elongation close to 50% and an ultimate stress of 110 MPa.

Download Full-text

Effect of Small Variations in Zr Content on the Microstructure and Properties of Ferritic ODS Steels Consolidated by SPS

Metals ◽

10.3390/met10030348 ◽

2020 ◽

Vol 10 (3) ◽

pp. 348 ◽

Cited By ~ 3

Author(s):

Andrea García-Junceda ◽

Eric Macía ◽

Dariusz Garbiec ◽

Marta Serrano ◽

José M. Torralba ◽

...

Keyword(s):

Mechanical Properties ◽

Oxide Dispersion Strengthened ◽

Oxide Dispersion ◽

Heating Rates ◽

Ultrafine Grains ◽

Ods Steel ◽

Plasma Sintering ◽

Final Microstructure ◽

Spark Plasma ◽

Ods Steels

Two different zirconium contents (0.45 and 0.60 wt.%) have been incorporated into a Fe-14Cr-5Al-3W-0.4Ti-0.25Y2O3 oxide dispersion-strengthened (ODS) steel in order to evaluate their effect on the final microstructure and mechanical properties. The powders with the targeted compositions were obtained by mechanical alloying (MA), and subsequently processed by spark plasma sintering (SPS) at two different heating rates: 100 and 400 °C·min−1. Non-textured bimodal microstructures composed of micrometric and ultrafine grains were obtained. The increase in Zr content led to a higher percentage of Zr nano-oxides and larger regions of ultrafine grains. These ultrafine grains also seem to be promoted by higher heating rates. The effective pinning of the dislocations by the Zr dispersoids, and the refining of the microstructure, have significantly increased the strength exhibited by the ODS steels during the small punch tests, even at high temperatures (500 °C).

Download Full-text