scholarly journals Evaluation of Mechanical Properties and Microstructures of Direct‐Quenched and Direct‐Quenched and Tempered Microalloyed Ultrahigh‐Strength Steels

2020 ◽  
pp. 2000451 ◽  
Author(s):  
Jaakko Hannula ◽  
Antti Kaijalainen ◽  
David A. Porter ◽  
Mahesh C. Somani ◽  
Jukka Kömi
Keyword(s):  
Mechanical Properties ◽  
Ultrahigh Strength ◽  
Ultrahigh Strength Steels

scholarly journals The Effect of Electroslag Remelting on the Microstructure and Mechanical Properties of CrNiMoWMnV Ultrahigh-Strength Steels

Metals ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 262
Author(s):  
Mohammed Ali ◽  
David Porter ◽  
Jukka Kömi ◽  
Mamdouh Eissa ◽  
Hoda El Faramawy ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Laser Scanning ◽  
Electron Backscatter Diffraction ◽  
Laser Scanning Confocal Microscopy ◽  
Electroslag Remelting ◽  
Scanning Confocal Microscopy ◽  
Ultrahigh Strength ◽  
Microstructure And Mechanical Properties ◽  
Considerable Impact ◽  
Ultrahigh Strength Steels

The effect of electroslag remelting (ESR) with CaF2-based synthetic slag on the microstructure and mechanical properties of three as-quenched martensitic/martensitic-bainitic ultrahigh-strength steels with tensile strengths in the range of 1250–2000 MPa was investigated. Ingots were produced both without ESR, using induction furnace melting and casting, and with subsequent ESR. The cast ingots were forged at temperatures between 1100 and 950 °C and air cooled. Final microstructures were investigated using laser scanning confocal microscopy, field emission scanning electron microscopy, electron backscatter diffraction, electron probe microanalysis, X-ray diffraction, color etching, and micro-hardness measurements. Mechanical properties were investigated through measurement of hardness, tensile properties and Charpy-V impact toughness. The microstructures of the investigated steels were mainly auto-tempered martensite in addition to small fractions of retained austenite and bainite. Due to the consequences of subtle modifications in chemical composition, ESR had a considerable impact on the final microstructural features: Prior austenite grain, effective martensite grain, and lath sizes were refined by up to 52%, 38%, and 28%, respectively. Moreover, the 95th percentiles in the cumulative size distribution of the precipitates decreased by up to 18%. However, ESR had little, if any, the effect on microsegregation. The variable effects of ESR on mechanical properties and how they depend on the initial steel composition are discussed.

Microstructures and Mechanical Properties of Tough Ductile Ultrahigh-Strength Steels Processed through Direct Quenching and Partitioning

2018 ◽  
Vol 941 ◽  
pp. 468-473 ◽  
Author(s):  
Pekka K. Kantanen ◽  
Mahesh C. Somani ◽  
David A. Porter ◽  
Jukka I. Kömi ◽  
Devesh K. Misra
Keyword(s):  
Mechanical Properties ◽  
Lath Martensite ◽  
Controlled Rolling ◽  
Processing Route ◽  
Direct Quenching ◽  
Ultrahigh Strength ◽  
Microstructures And Mechanical Properties ◽  
Hot Strip Mills ◽  
Low Temperature Impact Toughness ◽  
Ultrahigh Strength Steels

Using a novel TMR-DQP processing route, two ultrahigh-strength steels have been developed with yield strengths up to 1100 MPa combined with good uniform and total elongations and low-temperature impact toughness. Processing involved thermomechanically controlled rolling including significant reductions below the recrystallization stop temperature (RST), subsequent direct quenching to desired quench stop temperatures between Ms and Mf and finally partitioning of carbon from the supersaturated martensite to the untransformed austenite in a furnace at the quench stop temperature. Samples were cooled slowly in the furnace over 50 hours to simulate the cooling of coiled strips on industrial hot strip mills. The approach used was to utilize a suitable 0.3C steel composition based on high silicon and/or aluminium contents. Detailed metallographic studies using LOM, FESEM-EBSD, TEM and XRD showed that the desired martensite-austenite microstructures were achieved. The advantage of strained austenite in respect of refinement of martensite packets/blocks was clearly evident. Austenite was finely divided between martensite laths and only an insignificant amount of austenite existed as pools. The fine lath martensite structure with narrow interlath retained austenite films enabled the achievement of excellent combinations of mechanical properties. Promising results in respect of microstructures and mechanical properties indicate that there are possibilities for developing tough ductile structural and abrasion-resistant steels through the TMR-DQP route.

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