Effects of Grain Refinement and Predeformation Impact by Severe Plastic Deformation on Creep in P92 Martensitic Steel

Abstract

Creep testing is conducted on an advanced martensitic‐ferritic creep‐resistant P92 steel (ASME Grade 92) to evaluate the effects of grain refinement and the predeformation impact after processing by severe plastic deformation (SPD), namely, by high‐pressure torsion and high‐pressure sliding. Constant‐load tensile creep tests are carried out in an argon atmosphere at 600 °C and under an applied stress ranging from 50 to 200 MPa. The results show that under the same creep loading conditions, the ultrafine‐grained (UFG) microstructure states after SPD processing exhibit higher minimum creep rate trueϵ˙m and creep fracture plasticity ϵf, but significantly shorter creep lives in comparison with the coarse‐grained (as‐received) state of the steel. These distinct differences between the coarse‐grained and UFG states are explained by the different deformation mechanisms that operate; creep behavior in a coarse‐grained state is controlled by the intragranular climb of dislocations, while creep in UFG states can be interpreted as the synergistic action of the dynamic recovery of free dislocations at high‐angle grain boundaries and grain boundary‐mediated deformation processes.

高圧スライド法を用いたTi同素変態のその場放射光X線解析

“…(HPS: High-Pressure Sliding) 加工 55) と呼ばれ，粉末の固化 60) をはじめ，多くの金属材料 [56][57][58][59] に利用されている．この HPS プロセスは棒状試料 [61][62][63][64] やパイプ状試料 65) にも適用可能であ ることが示されている．さらに，試料の逐次送りと組み合わ V i e w せることで，SPD 処理面積が拡大できることも示されてい る 66,67) ．このような開発は，SPD プロセスの実用化を目指し たもので，最近のレビュー論文 68) でも詳しく解説されてい る．本研究では，HPS プロセス装置はむしろ小型にして，シ ンクロトロン光施設における高圧高温下でのその場 X 線解析 に使用する． HPT や HPS プロセスによる特性向上は，プロセス中に発 生する高密度の格子欠陥に起因している [69][70][71] ．このような格 [72][73][74] やマルチアンビル装置 75,76) を用いて行われ ることが多い．これらは主に静水圧条件下で使用されるが， DAC の場合，Bridgman のアイデアに沿って，一方のダイヤ モンドアンビルを他方に対して回転させることで意図的に塑 性変形を導入できる 13) ．Blank らは DAC を用いてせん断ひず みを導入した最初であり 77,78) ，Levitas らは DAC でひずみ導 A d v a n c e…”

Effect of severe plastic deformation on creep behaviour and microstructure changes of P92 at 923 K

“…Constant load tensile creep tests were conducted at 923 K in a protective argon atmosphere using flat specimens with a gauge length of 10 mm and a crosssection of 3 × 1 mm 2 . The tested HPT-processed specimen for the creep testing were manufactured from the disc region with an equivalent strain of about 20-30 [20,21]. Microstructure investigations were performed using a scanning electron microscope (SEM, Tescan Lyra 3 equipped with NordlysNano EBSD detector operating at accelerating voltage of 20 kV with specimen tilted at 70 • ).…”

Creep of High-Strength Steel Coated with Plasma Sprayed Self-Fluxing Alloy

“…The grain size of a polycrystalline material results from several manufacturing processes, such as thermal and mechanical treatments. It is generally accepted that the creep rate decreases as the grain size increases [5]. Protective coatings are often applied to steels to enhance their performance under more severe conditions, including wear and corrosion.…”