Microstructures and stress rupture properties of pulse laser repaired Inconel 718 superalloy after different heat treatments

The effect of a prior short-term ageing on mechanical and creep properties of P92 steel

The mechanical behavior of a P92-type steel was studied by tension and Charpy impact tests in the temperature range of 77–293 K. The yield stress (YS) and uniform elongation increase concurrently with decreasing temperature because the steel exhibits work-hardening behavior. Transgranular dimpled fracturing remains the primary fracture mechanism under tension down to 193 K. Brittle fracture takes place at lower temperatures. At 77 K, the steel exhibits a well-defined yield plateau. Impact tests demonstrate that the ductile-brittle transition (DBT) occurs at 210 K. At 193 K, the energy absorption of 110 J/cm 2 at high impacts is attributed to extended areas of crack initiation and a stable crack propagation; the fast fracture load also has a high value. The steel becomes completely brittle at 77 K, at which temperature the absorbed energy falls to 6 J/cm 2 .

Ductile-brittle transition in a 9% Cr heat-resistant steel

The effect of increasing tungsten content from 2 to 3 wt % on the creep rupture strength of a 3 wt % Co-modified P92-type steel was studied. Creep tests were carried out at a temperature of 650 °C under applied stresses ranging from 100 to 220 MPa with a step of 20 MPa. It was found that an increase in W content from 2 to 3 wt % resulted in a +15% and +14% increase in the creep rupture strength in the short-term region (up to 103 h) and long-term one (up to 104 h), respectively. On the other hand, in the long-term creep region, the effect of W on creep strength diminished with increasing rupture time, up to complete disappearance at 105 h, because of depletion of excess W from the solid solution in the form of precipitation of the Laves phase particles. An increase in W content led to the increased amount of Laves phase and rapid coarsening of these particles under long-term creep. The contribution of W to the enhancement of creep resistance has short-term character.

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Effect of Tungsten on Creep Behavior of 9%Cr–3%Co Martensitic Steels

The effect of temperature on the impact toughness and fracture behavior of a 10% Cr-2% W-0.7% Mo-3% Co-0.05% Nb-0.2% V-0.008% B-0.003% N (all in wt%) steel was studied. The ductile-brittle transition (DBT) occurs at 10 °C. At the DBT temperature (DBTT), the onset of unstable crack propagation occurs at the maximum load. The embrittlement is attributed to the onset of unstable crack propagation at stresses below the general yielding. A decrease in nitrogen content and an increase in boron content lead to the formation of chains of closely spaced M23C6 carbides at lath boundaries. The formation of numerous voids at carbide-matrix boundaries results in the appearance of crack with critical dimension after stable crack propagation over a very short distance. As a result, the energy of the stable crack propagation is low and the embrittlement takes place at relatively high temperature.

Impact toughness of a 10% Cr steel with high boron and low nitrogen contents

Laves phase has been widely accepted to cause the impact brittleness of 9–12Cr martensitic heat-resistant steels after long time aging at elevated temperatures. However, in the present research, the impact toughness of the already brittle P92 steel aged at 600 °C for 2035 h could be restored to the original level by reheating at 700 °C for 1 h, with Laves phase barely changed. This interesting result strongly indicated that the presence of Laves phase might not be the real reason for the impact brittleness.

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Xu Yang

Papers

Relationship between Laves phase and the impact brittleness of P92 steel reevaluated