Improvement of High Temperature Creep Strength of Conventional Grade 91 Steel by Thermomechanical Treatments

2019 ◽  
Author(s):  
Rebeca Hernández ◽  
Marta Serrano ◽  
Andrea García-Junceda ◽  
Elvira Oñorbe ◽  
Javier Vivas
Keyword(s):  
Thermomechanical Treatment ◽  
Creep Strength ◽  
Rupture Life ◽  
Constant Load ◽  
Creep Properties ◽  
The Matrix ◽  
The Common ◽  
Grade 91 ◽  
Different Levels ◽  
Grade 91 Steel

Abstract The study of the enhanced creep strength of conventional ferritic-martensitic (F/M) grade 91 steel by a thermomechanical treatment (TMT) to increase the precipitation of MX particles in the matrix was performed. Creep properties were evaluated by tests at constant load at temperatures that varied from 600 °C to 700 °C with different levels of stress for both steels: T91 and T91-TMT. The creep curves and main parameters for both steels in the different conditions were analysed. Results show a great improvement of creep strength of the T91 after the thermomechanical treatment in comparison with the conventional steel. T91-TMT presents a rupture life significantly higher than T91 and a decrease of the values of the minimum creep rate. An increase of the density of MX precipitates in the matrix of the T91-TMT due to the thermomechanical treatment in comparison with T91 can be also observed. A change in the fractography was also detected. T91-TMT specimens showed signs of brittle fracture instead of the ductile fracture, with the common necking effect detected in the T91.

Causes of heat-to-heat variation of creep strength in grade 91 steel

2017 ◽  
Vol 696 ◽  
pp. 104-112 ◽  
Author(s):  
K. Maruyama ◽  
J. Nakamura ◽  
N. Sekido ◽  
K. Yoshimi
Keyword(s):  
Creep Strength ◽  
Grade 91 ◽  
Grade 91 Steel

EPRI Guidelines for Fabrication of Components Manufactured From Grade 91 Steel

2012 ◽  
Author(s):  
Jonathan Parker ◽  
Kent Coleman
Keyword(s):  
Quality Assurance ◽  
Creep Strength ◽  
Ferritic Steels ◽  
Factors Affecting ◽  
Critical Information ◽  
Grade 91 ◽  
Recommended Guidelines ◽  
Grade 91 Steel

Over the last 10 years EPRI has been researching critical information on the factors affecting the performance of creep strength enhanced ferritic steels in general and Grade 91 steel in particular. This work has resulted in a major new report which provides recommended guidelines for fabrication and the associated quality assurance to ensure that component properties meet or exceed the minimum expectations of ASME design approaches. The present paper outlines the recommendations in the report and provides technical background for specific aspects of the guide.

Optimized Thermomechanical Treatment for Strong and Ductile Martensitic Steels

2007 ◽  
Vol 539-543 ◽  
pp. 4526-4531 ◽  
Author(s):  
Araz Ardehali Barani ◽  
Dirk Ponge
Keyword(s):  
Heat Treatment ◽  
Thermomechanical Treatment ◽  
Spring Steel ◽  
Martensitic Steels ◽  
Medium Carbon ◽  
Heat Treated ◽  
Conventional Heat Treatment ◽  
The Matrix ◽  
Different Levels ◽  
Strength And Ductility

In this study the effect of thermomechanical treatment on the microstructure of austenite and martensite and the mechanical properties of a medium carbon silicon chromium spring steel with different levels of impurities is investigated. Results are presented for conventional heat treatment and for thermomechanical treatment (TMT). Compared to conventionally heat treated samples austenite deformation improves strength and ductility. Thermomechanically treated samples are not prone to embrittlement by phosphorous. TMT influences the shape and distribution of carbides within the matrix and at prior austenite grain boundaries. It is shown that utilization of TMT is beneficial for increasing the ultimate tensile strength to levels above 2200 MPa and at the same time maintaining the ductility obtained at strength levels of 1500 MPa by conventional heat treatment. The endurance limit is increased and embrittlement does not occur.

Re-Evaluation of Long-Term Creep Strength of Welded Joint of ASME Grade 91 Type Steel

2016 ◽  
Author(s):  
Masatsugu Yaguchi ◽  
Kaoru Nakamura ◽  
Sosuke Nakahashi
Keyword(s):  
Creep Strength ◽  
Welded Joints ◽  
Rupture Strength ◽  
Creep Rupture ◽  
Base Metals ◽  
Rupture Data ◽  
Grade 91 ◽  
Term Creep ◽  
Grade 91 Steel

Creep rupture data of welded joints of ASME Grade 91 type steel have been collected from Japanese plants, milling companies and institutes, and the long-term creep rupture strength of the material has been evaluated. This evaluation of welded joints of Grade 91 steel is the third one in Japan as similar studies were conducted in 2004 and 2010. The re-evaluation of the creep rupture strength was conducted with emphasis on the long-term creep rupture data obtained since the previous study, with durations of the new data of up to about 60000h. The new long-term data exhibited lower creep strength than that obtained from the master creep life equation for welded joints of Grade 91 steel determined in 2010, then the master creep life equation was again reviewed on the basis of the new data using the same regression method as that used in 2010. Furthermore, the weld strength reduction factors obtained from 100000h creep strength of welded joints and the base metals are given as a function of temperature, where the master creep equations of the base metals are also redetermined in this study.

A Grain Size-Dependent Equation for Creep Rupture Life of Grade 91 Steel Verified Up To 233,000 Hours

2020 ◽  
Vol 142 (6) ◽  
Author(s):  
K. Maruyama ◽  
N. Sekido ◽  
K. Yoshimi ◽  
Y. Yamamoto
Keyword(s):  
Grain Size ◽  
Rupture Life ◽  
Creep Rupture ◽  
Life Assessment ◽  
Size Dependent ◽  
Grade 92 Steel ◽  
Grade 91 ◽  
Steam Pipes ◽  
Grade 91 Steel

Abstract Grade 91 steel is widely used as steam pipes in ultrasupercritical (USC) steam boilers. In residual creep life assessment of the pipes by calculation, one needs creep rupture life of the steel as a function of stress and temperature in a time range longer than 105 h. Four regions with different creep rupture characteristics appear in a stress versus creep rupture life diagram of the steel. Main steam pipes made of the steel are used in a long-term region with low values of stress exponent and activation energy for creep rupture life (referred to as region G in this paper). Creep rupture lives of the steel in this region vary from heat to heat depending on their prior austenite grain size. This paper proposes a grain size-dependent equation representing creep rupture life of the steel in region G. The equation is verified with creep rupture data up to 232,833 h at 600 °C. Region G is absent in some heats with a large grain size. The equation can rationalize the absence in the heats. In a stress versus creep rupture life diagram of grade 92 steel, there is the same long-term region G. In the region, a creep rupture life of each heat is dependent on its grain size as is the case in grade 91 steel. The proposed equation accords well with the creep rupture lives of the grade 92 steel in region G.

Effect of Aging on Creep Strength of Grade 91 Steel Weld Metal

2016 ◽  
Vol 2016 (0) ◽  
pp. J0310203
Author(s):  
Sosuke NAKAHASHI ◽  
Masatsugu YAGUCHI ◽  
Koji TAMURA ◽  
Yusuke MINAMI
Keyword(s):  
Weld Metal ◽  
Creep Strength ◽  
Steel Weld ◽  
Steel Weld Metal ◽  
Grade 91 ◽  
Grade 91 Steel

scholarly journals Creep Properties of Grade 91 Steel Steam Generator Tube at 923K

2013 ◽  
Vol 55 ◽  
pp. 70-77 ◽  
Author(s):  
D.P. Rao Palaparti ◽  
E. Isaac Samuel ◽  
B.K. Choudhary ◽  
M.D. Mathew
Keyword(s):  
Steam Generator ◽  
Steam Generator Tube ◽  
Creep Properties ◽  
Grade 91 ◽  
Grade 91 Steel

The creep strength of aberrant grade 91 steel

2021 ◽  
pp. 1-5
Author(s):  
Stephen James Brett ◽  
Alex Bridges ◽  
Daniel Purdy
Keyword(s):  
Creep Strength ◽  
Grade 91 ◽  
Grade 91 Steel

scholarly journals Estimation of Creep Strength of Grade 91 Steel Welded Joint in Time Region Over 100,000 Hours

2018 ◽  
Author(s):  
Masatsugu Yaguchi ◽  
Sosuke Nakahashi ◽  
Koji Tamura
Keyword(s):  
Creep Strength ◽  
Welded Joints ◽  
Welded Joint ◽  
Base Metals ◽  
Creep Life ◽  
Initial State ◽  
Creep Tests ◽  
Grade 91 ◽  
Grade 91 Steel

A creep strength of welded joint of ASME Grade 91 steel in a region exceeding 100,000 hours was examined in this work. Creep tests were conducted on the steel used at USC plants for long-term, and remaining creep life of the material for operating condition was calculated on a fitting curve using Larson-Miller parameter. Total creep life of the material, which means a creep life at initial state, was presumed to be a summation of the service time at the plants and the remaining creep life. The estimation was conducted for welded joints used at five plants for long-term, and all results lay within 99% confidential band by the creep life evaluation curve of the material proposed by Japanese committee in 2015, while a significant heat-heat variation of creep strength was found even in the region exceeding 100,000 hours. Creep tests on base metals related to each welded joint were also conducted, and the estimation results of the total creep life of the base metals were compared to those of the welded joints. It was suggested that the heat-heat variation of the welded joints eminently depends on the creep life property of the corresponding base metal.

scholarly journals Numerical Prediction of Creep Rupture Life of Ex-Service and As-Received Grade 91 Steel at 873 K

2021 ◽  
Vol 18 (3) ◽  
pp. 8845-8858
Author(s):  
IMAM UL FERDOUS ◽  
NASRUL AZUAN ALANG ◽  
Juliawati Alias ◽  
Suraya Mohd Nadzir
Keyword(s):  
Finite Element ◽  
Stress State ◽  
Creep Strain ◽  
Life Prediction ◽  
Rupture Life ◽  
Creep Rupture ◽  
Rupture Time ◽  
Damage State ◽  
Grade 91 ◽  
Grade 91 Steel

Infallible creep rupture life prediction of high  temperature steel needs long hours of robust  testing over a domain of stress and temperature. A substantial amount of effort has been made to  develop alternative methods to reduce the time  and cost of testing. This study presents a finite  element analysis coupled with a ductility based  damage model to predict creep rupture time  under the influence of multiaxial stress state of  ex-service and as-received Grade 91 steel at 873 K. Three notched bar samples with different  acuity ratios of 2.28, 3.0 and 4.56 are modelled in commercial Finite Element (FE) software,  ABAQUS v6.14 in order to induce different stress  state levels at notch throat area and investigate  its effect on rupture time. The strain-based  ductility exhaustion damage approach is  employed to quantify the damage state. The  multiaxial ductility of the material that is  required to determine the damage state is  estimated using triaxiality-ductility Cock and  Ashby relation. Further reduction of the ductility  due to the different creep mechanisms over a  short and long time is also accounted for in the  prediction. To simulate the different material conditions: ex-service and as-received material,  different creep coefficients (A) have been  assigned in the numerical modelling. In the case  of ex-service material, using mean best fit data  of minimum creep strain rate gives a good life  prediction, while for new material, the lower  bound creep coefficient should be employed to  yield a comparable result with experimental  data. It is also notable that ex-service material  deforms faster than as-received material at the  same stress level. Moreover, higher acuity  provokes damage to concentrate on the small  area around the notch, which initiates higher  rupture life expectancy. It also found out that,  the stress triaxiality and the equivalent creep  strain influence the location of damage initiation  around the notch area.

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