Effect of Tempering on Microstructure and Mechanical Properties of Boron Containing 10%Cr Steel

Abstract

The effect of heat treatment on the microstructure and the mechanical properties of a 10%Cr steel with 0.008% boron was examined. The microstructure and the mechanical properties of this steel subjected to the normalizing were studied after tempering under different conditions. The layers of retained austenite are located along the lath boundaries. The formation of M23(B·C)6 phase having film-like shape takes place on interface boundaries of retained austenite/martensite during tempering at 525°C. As a result, the steel exhibits brittle fracture with a low value of Charpy V-notch impact toughness of 6 J/cm 2 . Particles of the M23(B·C)6 phase are highly resistant against the spheroidizing. The tempering at 770°C only leads to the coagulation of these particles; when the fraction of M23(B·C)6 phase significantly decreases while the fraction of M23C6 carbides increases. The tempered at 770°C steel exhibits a high value of Charpy V-notch impact toughness of 260 J/cm 2 . The effect of boron additives on the phase composition and the brittleness of high-chromium steels is discussed.

Evolution of Lath Substructure and Internal Stresses in a 9% Cr Steel during Creep

“…29,33) A tempering treatment of high Cr steels affects slightly their dislocation structure, 29,[34][35][36] which retains high dislocation density ( Fig. 10(a)).…”

Low Cycle Fatigue Behavior of a 10% Cr Martensitic Steel at 600°C

“…The precipitates of the M 23 C 6 and MX phases, which effectively stabilized the TMLS for long-term aging or creep conditions in low N steel 3,4,23) due to suppressing the lath boundary migration and dislocation rearrangements, are ineffective under cyclic stress conditions. The cyclic softening effect is correlated to the dislocation density decrease and subgrain coarsening.…”

“…Slight improvements of fatigue life can be observed at small strain amplitudes less than ± 0.3%. 6) Therefore, modifications in the carbide and carbonitride distribution due to decreasing the nitrogen content and increasing the boron content 3,4,23) does not influence the resistance of the high Cr steels to cyclic softening.…”

“…2,3) Superior creep strength of this steel is attributed to the high coarsening resistance of M 23 C 6 located at the lath/(sub)grain boundaries and uniformly distributed MX precipitates during long-term aging and under creep conditions. 3,4) This dispersion of secondary phase particles effectively stabilizes the tempered martensite lath structure (TMLS) under exploitation conditions. 3) Steam turbine components are often subjected to pulsating centrifugal forces and repeated temperature gradients, which generate strong fatigue conditions and can lead to low cycle fatigue (LCF) damage.…”

Prospects for Martensitic 12 % Cr Steels for Advanced Steam Power Plants

“…2. The results indicate that this steel could reach the creep strength target of 100 MPa for 10 5 h at 650°C [31][32][33]. Alloy design is based on the TOS 110 steel earlier developed at Toshiba [34], but the composition has been altered with reduced Nitrogen and addition of Titanium.…”