Effect of Tempering Temperature on Microstructure Evolution and Hardness of 9Cr1. 5Mo1CoB(FB2) Steel

Herein, it is proposed to obtain a favorable combination of microstructure and mechanical properties of martensitic stainless steel 14Cr14Co13Mo5 by prenitriding method before carburizing and appropriate heat treatment processes. The result indicates that the effective hardened layer depth is increased by 32% to 0.66 mm, and the hardness is significantly improved by prenitriding. The confocal laser scanning microscope and electron backscattered diffraction show that the prenitriding can effectively refine the martensite substructure of the carburized layer after quenching due to the refinement of prior austenite grain. In addition, plenty of second‐phase particles M2N with finer size appear at the same case layer depth instead of coarse M23C6 in the specimen prenitrided, which optimize the microstructure of the case layer.

σ_{normalp}

) also could reflect the difference in contribution of precipitation to hardness of microstructure for martensitic steels.…”

Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

The Impact of Prenitriding on the Microstructure and Mechanical Properties of the Carburized Surface Layer in a Martensitic Stainless Steel

Tian

Song

Wang

et al. 2022

“…[ 1,2 ] The 9–12% chromium ferritic/martensitic steels are ideal for constructing advanced USC power plants because of their enhanced thermophysical properties, high creep strength, and low cost. [ 3,4 ] The microstructure of 9–12% chromium martensitic steels is complex. The steels are composed of prior‐austenite grains, martensitic laths and blocks, and several precipitated phases.…”

Section: Introductionmentioning

confidence: 99%

“…

Fossil power plants operating at ultrasupercritical (USC) temperatures must be constructed with enhanced heat-resistant materials with creep strengths that can withstand temperatures above 600 C. [1,2] The 9-12% chromium ferritic/martensitic steels are ideal for constructing advanced USC power plants because of their enhanced thermophysical properties, high creep strength, and low cost. [3,4] The microstructure of 9-12% chromium martensitic steels is complex. The steels are composed of prior-austenite grains, martensitic laths and blocks, and several precipitated phases.

…”

mentioning

confidence: 99%

“…The steels are composed of prior-austenite grains, martensitic laths and blocks, and several precipitated phases. [3,4] Their strength is attributed to their high-density dislocations and solution strengthening using molybdenum (Mo), niobium (Nb), and tungsten (W). Their strength is also ascribed to boundary strengthening and dispersion strengthening with M 23 C 6 (where M is Cr or Fe), M 2 X, and MX (here, M is niobium or vanadium and X is carbon or nitrogen).…”

mentioning

confidence: 99%

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Plastic Flow Behavior of an Advanced 9Cr Martensitic Heat‐Resistant Steel at High Temperatures

Gao

Zhang

2021

Advanced 9Cr–1.5Mo–1Co–VNbBN martensitic steel is used for thick castings under ultra‐supercritical conditions. The microstructure, including martensitic laths, dislocations, and precipitations, is observed before and after deformation by transmission electron microscope. Steady‐state flow behavior and deformation mechanisms are investigated by analyzing strain‐rate jump test data at 600–650 °C. Results show that the plastic flow behavior of 9Cr steel is well characterized by a stress power law whose apparent stress exponent n is between 20.5 and 27.0 for the three test temperatures. The apparent activation energy of 621 kJ mol is estimated for the plastic flow of this steel, and the stress exponent and apparent activation energy are particularly high. The analysis incorporates the effect of a threshold stress, which is associated with the pinning effect of particles on dislocations. The truly modified stress exponent n0 is 4.6 at all test temperatures after removing the threshold stress, which is close to that of dislocation‐climb deformation, indicating the deformation of this steel can be described as a lattice diffusion‐controlled dislocation‐climb mechanism. Transmission electron microscopy observation is conducted to characterize the interaction of dislocation–precipitate to provide structural evidence for specific deformation mechanisms.

Mobile Induction Heat Treatment of Large‐Sized Spur Gear—The Effect of Scanning Speed and Air Gap on the Uniformity of Hardened Depth and Mechanical Properties

Saputro

Chen

Jheng³

et al. 2023

Prematurely fractured teeth of SCM440 large‐sized spur gear are commonly found among gears of a mechanical press machine. The macroscopic inspection and microstructure examination of a fractured tooth are established to show that the previous induction hardening process produced two serious issues; insufficient hardening in the root areas and nonuniform hardened depth along the tooth circumference. The numerical simulation is executed to replicate the previous induction hardening process, which consists of simulations for tooth‐to‐tooth mobile induction heating, water spray quenching, and the tempering process. This study highlights the influence of most adjustable parameters, such as the scanning speed of the inductor coil and air gap, to collect beneficial insights for further improvements. Experimental and numerical results are compared to validate the numerical model used. The adjustment of scanning speed and air gap highly affects the magnitude and uniformity of hardened depth along the tooth profile. Promising improvements can be achieved by slower, smaller scanning speeds and thinner air gaps, where the distortion is still in the allowed allowable range. This research provides a method and insights for future explorations to deal with relevant issues in the tooth‐to‐tooth mobile induction hardening process.