A Microstructural Study of Compressive Plastic Pre-Strain Effects on Creep Damage Behaviour of Type 316H Stainless Steel

2011 ◽  
Author(s):  
Ali N. Mehmanparast ◽  
Catrin M. Davies ◽  
Mahmoud Ardakani ◽  
Kamran M. Nikbin
Keyword(s):  
Stainless Steel ◽  
Crack Growth ◽  
Mechanical Behaviour ◽  
Creep Crack Growth ◽  
Creep Damage ◽  
Tensile Creep ◽  
Compression Process ◽  
Creep Ductility ◽  
Crack Growth Behaviour ◽  
Creep Crack

Compressive plastic pre-strain induced at room temperature in type 316H stainless steel, significantly influences the tensile, creep deformation and crack growth behaviour of the material. It is known that the material is hardened after pre-strain to 8% plastic strain and thus exhibits little or no plasticity during loading of uniaxial or creep crack growth (CCG) tests. In addition pre-compression (PC) has been found to reduce the creep rupture time, creep ductility and accelerate creep crack growth rates compared to as-received (AR) (i.e. uncompressed) material. In order to understand pre-straining effects on mechanical behaviour of 316H, optical and scanning electron microscopy (SEM) studies have been performed on uncompressed and 8% pre-compressed material. Samples have been examined in three orientations (i.e. parallel and perpendicular to the pre-compression direction). Furthermore, the influence of cold pre-compression on local creep damage formation ahead of the crack tip on interrupted CCG tests on AR and PC material has been studied. The results are discussed in terms of intergranular and transgranular damage caused by the compression process and the importance of microstructural changes on the mechanical behaviour of the material in long term tests.

Estimation of Creep Crack Growth Properties Using Circumferential Notched Round Bar Specimen for 12CrWCoB Rotor Steel

2005 ◽  
Vol 297-300 ◽  
pp. 397-402
Author(s):  
Je Chang Ha ◽  
Joon Hyun Lee ◽  
Masaaki Tabuchi ◽  
A.Toshimitsu Yokobori Jr.
Keyword(s):  
Crack Growth ◽  
Axial Stress ◽  
Creep Crack Growth ◽  
Turbine Rotor ◽  
Rotor Steel ◽  
Creep Ductility ◽  
Crack Growth Behaviour ◽  
Creep Crack ◽  
Round Bar ◽  
Growth Properties

Most heat resisting materials in structural components are used under multi-axial stress conditions and under such conditions ductile materials often exhibit brittle manner and low creep ductility at elevated temperature. Creep crack initiation and growth properties are also affected by multi-axial stress and it is important to evaluate these effects when laboratory data are applied to structural components. Creep crack growth tests using circumferential notched round bar specimens are a simple method to investigate multi-axial stress effects without using complicated test facilities. Creep crack growth tests have been performed using a 12CrWCoB turbine rotor steel. In order to investigate the effects of multi-axial stress on creep crack growth properties, the tests were conducted for various notch depths at 650°C. The circumferential notched round bar specimen showed brittle crack growth behaviour under multi-axial stress conditions. Creep crack growth rate was characterized in terms of the C* parameter. A 12CrWCoB turbine rotor steel has been tested using circumferential notched round bar specimens with different multi-axiality. Circumferential notched round bar specimens show increased brittle creep crack growth behaviour due to the multi-axial stress condition. Creep crack growth properties could be predicted by allowing for the decrease of creep ductility under multi-axial conditions.

Compressive Pre-Strain Effects on the Creep and Crack Growth Behaviour of 316H Stainless Steel

2010 ◽  
Author(s):  
C. M. Davies ◽  
David W. Dean ◽  
A. N. Mehmanparast ◽  
K. M. Nikbin
Keyword(s):  
Stainless Steel ◽  
Crack Growth ◽  
Creep Crack Growth ◽  
Compact Tension ◽  
Growth Behaviour ◽  
Creep Ductility ◽  
Data Set ◽  
Crack Growth Behaviour ◽  
Constraint Effects

The effects of compressive plastic pre-strain on the creep deformation and crack growth behaviour of Type 316H stainless steel have been examined. Creep crack growth (CCG) tests have been performed on compact tension specimens of material which had been uniformly pre-strained by 4% and 8% in compression at room temperature. The CCG behaviour of the pre-compressed material has been interpreted in terms of the creep fracture mechanics parameter C* and compared with that of a significant data set of as-received (un-compressed) specimens and with CCG models. All creep testing has been performed at a temperature of 550 °C. High CCG rates, for a given value of C* have been observed for the pre-compressed material, compared with those of as-received material and these data follow the same trends as the long-term CCG data for as-received material. These observations are explained in terms of specimen constraint effects and variations in creep ductility.

Numerical Simulation of Creep Crack Propagation for Austenitic Stainless Steel 0Cr18Ni9 at 550°C

2011 ◽  
Vol 230-232 ◽  
pp. 596-599
Author(s):  
Li Jie Chen ◽  
Zun Qun Gong ◽  
Qi Zhao
Keyword(s):  
Stainless Steel ◽  
Austenitic Stainless Steel ◽  
Crack Propagation ◽  
Crack Growth ◽  
Elevated Temperatures ◽  
Creep Crack Growth ◽  
Tensile Creep ◽  
Computational Error ◽  
Propagation Length ◽  
Creep Crack

First, tensile creep curve and creep propagation tests are conducted for austenitic stainless steel 0Cr18Ni9, i.e. 304 stainless steel at 550°C. The corresponding time hardening creep law is given for stresses ranging from 240 to 320 Mpa and the creep crack propagation length under a tension load of 10kN is measured by using QUESTAR long focus microscope system. Second, with the commercial finite element (FE) code ANSYS, the critical crack tip opening displacement (CTOD) is considered as crack propagation criterion to simulate the creep crack growth in the standard compact tension (CT) specimen. The FE predictions of the creep crack length in the primary and secondary stages are found to agree reasonably with the experimental results. The maximum computational error between the predictions and the experiment results is within 10%. Hence, the critical CTOD is a feasible criterion for crack growth simulations at elevated temperatures.

Specimen Orientation and Constraint Effects on the Creep Crack Growth Behaviour of 316H Stainless Steel

2012 ◽  
Author(s):  
A. Mehmanparast ◽  
C. M. Davies ◽  
D. W. Dean ◽  
K. M. Nikbin
Keyword(s):  
Stainless Steel ◽  
Crack Growth ◽  
Creep Crack Growth ◽  
Compact Tension ◽  
Crack Growth Behaviour ◽  
Creep Crack ◽  
Uniaxial Creep ◽  
Microstructural Effects ◽  
Specimen Orientation ◽  
Constraint Effects

Pre-compression (PC) is found to have strong effects on the tensile, uniaxial creep rupture and creep crack growth (CCG) behaviour of type 316H stainless steel at 550 °C. In this work, blocks of 316H steel have been pre-compressed to 8% plastic strain at room temperature and compact tension, C(T), specimens are extracted from the pre-strained blocks with loading directions parallel and normal to the PC axis. The influence of specimen orientation and thickness on the CCG behaviour of the PC material is examined. The results are compared to short term and long term CCG behaviour of 316H steel at the same temperature. Higher CCG rates and shorter CCI times have been found in PC material with a loading direction normal to the PC axis compared to that parallel to the PC axis. These observations are discussed with respect to the microstructural effects.

Finite Element Damage Analyses for Predictions of Creep Crack Growth

2010 ◽  
Author(s):  
Chang-Sik Oh ◽  
Nak-Hyun Kim ◽  
Sung-Hwan Min ◽  
Yun-Jae Kim
Keyword(s):  
Experimental Data ◽  
Finite Element ◽  
Crack Growth ◽  
Damage Mechanics ◽  
Creep Crack Growth ◽  
Creep Damage ◽  
Simulation Method ◽  
Creep Tests ◽  
Creep Ductility ◽  
Creep Crack

This paper provides the virtual simulation method for creep crack growth test, based on finite element (FE) analyses with damage mechanics. Creep tests of smooth bars are used to quantify the constants of creep constitutive equation. The reduction of area resulting from creep tests of smooth and notched bar is adopted as a measure of creep ductility under multiaxial stress conditions. The creep ductility exhaustion concept is adopted for calculating creep damage, which is defined as the ratio of creep strain to the multiaxial creep ductility. To simulate crack propagation, fully damaged elements are forced to have nearly zero stresses using user-defined subroutine UHARD in the general-purpose FE code, ABAQUS. The results from 2D or 3D FE analyses are compared with experimental data of creep crack growth. It is shown that the predictions obtained from this new method are in good agreement with experimental data.

Predictions of Creep Crack Initiation Periods in Pre-Compressed 316H Stainless Steel

2013 ◽  
Author(s):  
K. M. Tarnowski ◽  
C. M. Davies ◽  
G. A. Webster ◽  
D. W. Dean
Keyword(s):  
Stainless Steel ◽  
Crack Initiation ◽  
Crack Growth ◽  
Crack Opening ◽  
Creep Crack Growth ◽  
Prediction Methods ◽  
Opening Displacement ◽  
Crack Growth Behaviour ◽  
Creep Crack ◽  
Significant Difference

Pre-compression of 316H stainless steel significantly alters its tensile, uniaxial creep and crack growth behaviour. It has previously been shown that reliable and conservative creep crack initiation predictions can generally be obtained for as-received 316H stainless steel using a variety of prediction methods. Given the changes in material behaviour caused by pre-compression, this paper applies similar prediction methods to pre-compressed 316H stainless steel at 550°C. Several procedures are available for estimating creep crack initiation time periods. The suitability of a procedure depends on the availability of the necessary material data. The procedures considered in this paper include the use of the creep fracture mechanics parameter C*, the crack opening displacement concept, the sigma-d approach and the time dependent failure assessment diagram. Creep crack growth tests have been performed on compact tension specimens manufactured from 316H stainless steel which was uniformly pre-compressed by 4% and 8% at room temperature. For each test, the time for creep crack initiation to occur was recorded. Predicted creep crack initiation times have been compared with the experimentally determined values. Comparisons with as-received material are also included. For pre-compressed material, conservative creep crack initiation predictions were only consistently achieved using steady state creep crack growth rates predicted from C*. This is a significant difference to as-received material for which conservative predictions were generally obtained by a variety of methods. At this time, there is only a limited set of pre-compressed data making it difficult to draw firm conclusions about the appropriateness of the various creep crack initiation prediction methods. The differences in the results between the pre-compressed and as-received material do however highlight the need for further tests on pre-compressed material.

Sign in / Sign up

Export Citation Format

Share Document