scholarly journals Influence of Tempering and Cryogenic Treatment on Retained Austenite and Residual Stresses in Carbonitrided 18CrNiMo7-6 Low Alloy Steel

2019 ◽  
Vol 38 (1) ◽  
pp. 71-82
Author(s):  
Richard J. Katemi ◽  
Jeremy Epp
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Alloy Steel ◽  
Retained Austenite ◽  
Cryogenic Treatment ◽  
Thermal Stabilization ◽  
Gas Analysis ◽  
Low Alloy Steel ◽  
Mass Percent ◽  
Carbon And Nitrogen Content

This work investigated the influence of tempering conditions coupled with cryogenic treatment on thermal stabilization of retained austenite and residual stress distributions in carbonitrided 18CrNiMo76 low alloy steel samples. The carbonitriding conditions were set to enable attaining surface carbon and nitrogen content of 0.87 and 0.34 mass.-percent respectively. After carbonitriding, some of the samples were subjected to varying tempering conditions followed by cryogenic treatment at -120 °C using nitrogen gas. Analysis of both retained austenite and residual stresses was conducted using X-ray diffraction. In the as-quenched state, carbonitrided samples contained 52 mass.-percent. Samples that were directly subjected to the cryogenic treatment after quenching retained only about 20 mass.-percent of austenite. Samples subjected to variant tempering conditions coupled with cryogenic treatment retained at least 30 masses.-percent of austenite. A thermal stabilization of retained austenite which increases with increasing temperature was identified. On tempering at 240°C for 14 hours retained austenite becomes unstable and decomposes to bainite leading to the low initial amount of retained austenite before cryogenic treatment. It can be concluded that the tempering process coupled with cryogenic treatment leads to an increasing hardness, to higher compressive residual stresses as well as to a shift of the location of maximum compressive residual stress toward the surface.

scholarly journals Influence of carbonitriding conditions on phase composition and residual stresses for 20MnCr5 low alloy steel

2021 ◽  
Vol 47 (2) ◽  
pp. 790-799
Author(s):  
Richard J Katemi ◽  
Jeremy Epp
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Alloy Steel ◽  
Retained Austenite ◽  
Case Depth ◽  
Martensite Phase ◽  
Stress Distributions ◽  
Low Alloy Steel ◽  
The Core ◽  
Core Hardness

This paper reports an investigation of the influence of carbonitriding conditions for 20MnCr5 low alloy steel. Three gaseous carbonitriding conditions were investigated based on different carbon and nitrogen potentials to attain varying levels of carbon between 0.62 and 0.93% mass, whereas for nitrogen between 0.19 and 0.26% mass at the surface. Analysis of retained austenite and residual stress distributions was conducted using X-ray diffraction technique. The effective case depth varied between 900 and 1200 µm. The case microstructures were characterized by varying proportions of retained austenite and martensite, while the core contained essentially bainitic microstructures. The maximum amount of retained austenite which occurred at a depth of 50 µm from the subsurface ranged between 30 and 70% mass and significantly influenced the level of surface micro-hardness whereas the core hardness remaining relatively constant at 450 HV1. High values of residual stresses in martensite phase were observed. The signs, magnitudes, distributions and location of maximum compressive residual stresses were highly influenced by the maximum fraction of retained austenite. Retained austenite of 30%, 50% and 70% mass at the surface lead to peak compressive residue stresses of -280, -227, and -202 MPa at depths of 555, 704, and 890 μm, respectively. Keywords: Carbonitriding, retained austenite, martensite, residual stress, XRD.

scholarly journals Investigations of Residual Stress Distributions in Retained Austenite and Martensite after Carbonitriding of a Low Alloy Steel

2014 ◽  
Vol 996 ◽  
pp. 550-555
Author(s):  
Richard J. Katemi ◽  
Jeremy Epp ◽  
Franz Hoffmann ◽  
Matthias Steinbacher
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Alloy Steel ◽  
Retained Austenite ◽  
Stress Distributions ◽  
Low Alloy Steel ◽  
X Ray Diffraction ◽  
Carbon And Nitrogen ◽  
Stress States ◽  
Nitrogen Contents

Specimens of low alloy steel were carbonitrided under different conditions to attain varying levels of carbon and nitrogen contents. The residual stress depth distribution was evaluated in martensite and retained austenite by X-ray diffraction. Beside standard evaluations, triaxial residual stress states with σ33≠0 in both phases were also considered. High values of residual stresses in both phases were observed. The sign, magnitude and location of maximum compressive residual stresses were greatly influenced by the level of carbon and nitrogen contents.

Study on Residual-Stress Redistributions During the Process of Manufacture of a Vessel Penetration Set-On Joint

2009 ◽  
Author(s):  
Nobuyoshi Yanagida ◽  
Kazuo Ogawa ◽  
Koichi Saito ◽  
Ed Kingston
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Alloy Steel ◽  
Steel Plate ◽  
Three Dimensional ◽  
Hole Drilling ◽  
Low Alloy Steel ◽  
Butt Weld ◽  
Control Rod ◽  
Inner Surface

The stress-redistribution phenomenon in a vessel penetration set-on joint due to post-weld heat treatment (PWHT) was studied using finite element (FE) analyses and mocked-up experiments. The mocked-up consisted of a nickel-based alloy (NCF600) tube welded onto an alloy-82 cladded, low-alloy steel plate (SQV2A) using an alloy-182 butt weld. The angle of the tube to the plate surface was 45 degrees, simulating a side hill, a control rod drive (CRD), and a stub-tube nozzle attachment used in boiling-water reactor (BWR) plants. PWHT at a temperature of 625 °C was conducted after welding and then the inner surface of the tube was machined. Three-dimensional FE modeling was performed to simulate the cladding, the butt weld, the PWHT, and the inner-surface machining of the tube. Thermal elasto-plastic and thermal elasto-plastic creep analyses were conducted to simulate the process of residual-stress build up and its redistribution by PWHT. To validate the FE analysis, the residual stresses in the mocked-up specimen were experimentally measured using the deep-hole-drilling (DHD) and sectioning methods. The analytical and experimental results revealed that residual-stress redistributions in the mocked-up specimen were different in circumferential positions. High-residual stresses in the low-alloy steel plate were particularly mitigated during the PWHT. The stress relief in the low-alloy steel plate primarily controlled the global stress balance between the cladding, the weld metal, and the stub tube.

Effect of Ausforming Temperature on Bainite Transformation of High Carbon Low Alloy Steel

2015 ◽  
Vol 817 ◽  
pp. 454-459 ◽  
Author(s):  
Jian Guo He ◽  
Ai Min Zhao ◽  
Huang Yao ◽  
Chao Zhi ◽  
Fu Qing Zhao
Keyword(s):  
Low Temperature ◽  
Alloy Steel ◽  
Retained Austenite ◽  
Volume Fraction ◽  
Transformation Rate ◽  
Low Alloy Steel ◽  
High Carbon ◽  
Bainite Transformation ◽  
Electron Backscattered Diffraction ◽  
In Situ Experiments

The effect of ausforming temperature on bainite transformation of high carbon low alloy steel was studied by in situ experiments using a Gleeble 3500 thermal and mechanical testing system. Morphology and crystallography of ausforming bainite were examined by scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD). It has been found that deformation at all temperatures range from 230°C to 600°C can accelerate low temperature bainite transformation, and transformation rate increased with deformation temperature reduced. Quantitative X-ray analysis shows that the volume fraction of retained austenite was about 35.84% after deformation and isothermal transformation for 20 hours, it was approximately the same amount with austempering bainite transformation process (no strain) which austenite volume fraction was about 32.01%. Low temperature bainite formation can be accelerated with a smaller increase amount of retained austenite by deformation at a low temperature range of 230~600 oC.

scholarly journals Martensitic Transformation of Retained Austenite in Ferrite Matrix for Low Alloy Steel

2018 ◽  
Vol 59 (5) ◽  
pp. 712-716
Author(s):  
Takayuki Yamashita ◽  
Norimitsu Koga ◽  
Osamu Umezawa
Keyword(s):  
Martensitic Transformation ◽  
Alloy Steel ◽  
Retained Austenite ◽  
Ferrite Matrix ◽  
Low Alloy Steel

Study on Evaluation Procedure for Calculating the Stress Intensity Factor of Flaws Beneath RPV Cladding During Pressurised Thermal Shock Events by FE Analysis

2016 ◽  
Author(s):  
Hiroyuki Sakamoto ◽  
Takatoshi Hirota ◽  
Naoki Ogawa
Keyword(s):  
Residual Stress ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Thermal Shock ◽  
Alloy Steel ◽  
Fe Analysis ◽  
Welding Residual Stress ◽  
Low Alloy Steel ◽  
Elastic Plastic

Elastic-plastic finite element (FE) analysis is performed to determine the plastic behavior of the reactor pressure vessel (RPV) inner surface caused by rapid cooling during pressurized thermal shock (PTS) events. However, as the J-integral is not path-independent for elastic-plastic material in the unloading process, it is necessary to apply a suitable correction method using elastic material. In addition, it is also necessary to consider the effect of the welding residual stress appropriately. Therefore, we investigated the stress intensity factor derived from FE analysis based on a model consisting of elastic-plastic cladding and linear elastic low-alloy steel with subsequent plastic zone correction, since the stress level of low-alloy steel remains within the elastic region except the crack front during a PTS event. Furthermore, we examined whether the stress mapping method is applicable for reflecting the effect of welding residual stress in FE analysis, even though the plastic strain generated during welding is ignored.

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