Factors influencing fatigue crack propagation behavior of austenitic steels

In order to develop a method of gas nitriding of austenitic stainless steels without chemical treatment such as pickling, three types of steels, sus304, sus316 and sus310, were pretreated under various mechanical processes ascut with resinoid blade, polishing with emery papers, grinding with cbn wheel, and shot peening, followed by nitriding in nh 3 gas with a flow rate of 2. Marquette university, 2016 this thesis presents the study of fatigue crack propagation in a low carbon steel astm a36 and two different weld metals aws a5. Effect of carburizing on fatigue behaviour in a type 316. Fatigue crack propagation in martensitic and austenitic steels. This allows a correction to elastic analysis to be performed in place of a full elasticplastic analysis. There are many factors influencing the fatigue crack initiation such as material microstructure grain size, microscopic flaws at grain boundaries, twin boundaries and inclusions and loading conditions such as sequence and path effects multiaxial fatigue, variable amplitude problem etc 916.

The nearthreshold fatigue crack propagation fcp behavior, as represented by the. If tensile residual stresses are high, kmin is greater than kop throughout the load cycle. The crack path and fractographic analyses suggested that the nearthreshold fcp behavior of these austenitic steels was largely influenced by the degree of slip planarity, as determined by stacking. Srawleywide range stress intensity factor expressions for astm e399. Fatigue crack growth threshold of austenitic stainless steels. Estimation of fatigue strainlife curves for austenitic. Factors influencing fatigue crack propagation behavior of austenitic steels. These deformation twins in an austenite matrix interrupt dislocation gliding and act. Strength gradient enhances fatigue resistance of steels. Mechanical behavior of pack carburized aisi 316l steel desmond edem fiawoyife page i.

The influence of load ratio on propagation behavior was analyzed by. The main parameters which affect the corrosion fatigue crack growth rate are stress intensity factor range, load ratio, electrochemical. The fatigue crack propagation fcp behavior of fe25mn and fe16mn2al austenitic steels was investigated at 298 and 110 k, and the results were compared with the reported results of fe24mn2cr steel. Austenitic stainless steel grade uns s31035 sandvik sanicro 25 has been developed for the next generation of 700c ausc power plant. In real engineering components and structures many accidental failures occur due to unexpected or additional loadings, such as additional bending or torsion. Fatiguecrack propagation behavior of several pressure. Crack growth rates were related to the stress intensity factor range. Corrosion fatigue crack growth and threshold stress intensity.

The aim of the present investigation is to characterise cyclic deforma. Factors influencing fatigue crack propagation behavior of austenitic. Microstructural modeling of fatigue crack initiation in. Effects of material composition on corrosion fatigue crack. This requires a careful examination of all factors influencing material fatigue behavior. Highalloy steels 4 austenitic manganese steel 4 stainless steels 414 heatresisting steels 415 tool steels 415. Investigations have shown that the microstructure,grain size,load ratio,loading frequency and test temperature have a great effect on the fatigue crack growth threshold,and the impact of the laws and influence mechanisms will vary with different materials.

Figure 3 temperature effect on the fatigue behavior of 304l a. Prediction of crack initiation in lowcycle fatigue in an. Recent work has shown that significant environmental enhancement of growth rates can occur in this environment, especially for some long rise time loading cycles. Laboratory studies on austenitic stainless steels in pwr primary coolant environments have shown that the asme xi procedures used to assess fatigue crack growth of reactor components may not always be conservative. It is widely believed that fatigue crack nucleation and early crack growth are caused by. The existing fatigue en data are analyzed to define key material, loading, and environmental parameters that influence the fatigue lives of these steels. There are many factors influencing the fatigue crack paths, such as the material type microstructure, structural geometry and loading path. Abstract for applications under dynamic loads in aqueous, hot chloride containing media, austenitic stainless steels are often used. Reviews on factors affecting fatigue behavior of highmn steels. The mechanism and estimation of fatigue crack initiation in. Cyclic deformation behaviour of austenitic steels at ambient and elevated temperatures th nebel and d eifler institute of materials science, university of kaiserslautern, p.

In the present study, the fatigue crack propagation fcp behaviors of austenitic single phase steels, including sts304, fe18mn and fe22mn with different grain sizes ranging from 12. Fatiguecrack propagation behavior of several pressure vessel. Many studies have revealed that fatigue crack growth fcg rate of austenitic stainless steels is accelerated in light water reactor environment compared to that in air at room temperature. Steels are heavily used in infrastructure and the transportation industry, and enhancing their fatigue resistance is a major challenge in materials engineering.

More importantly, the morphology of damage has a great influence on service life. In the presented work the influence of microstructure on fatigue crack growth behavior was evaluated in annealed and cold rolled austenitic stainless steels in thin specimen under positive stress ratio. Fatigue crack propagation resistance of sintered stainless steels was investigated according to e647 astm standard, using a computer controlled instron 8501 100 kn servohydraulic testing machine in constant load amplitude conditions. Effect of mechanical pretreatment on gas nitriding behavior. Nearthreshold fatigue crack propagation behavior of. Fatigue behaviour of welded austenitic steels, international. Chai 9 observed subsurface nondefect fatigue crack origins in experiments with a nonpredeformed martensiteaustenite steel at cycles higher than 10. Local strains that lead to the thermomechanical fatigue of thickwalled pressure vessels 20 september 2014. Fatigue crack growth threshold of austenitic stainless. Results from sour fatigue crack growth behaviour fcgr tests on cmn pipeline steel specimens containing shallow initial flaws are reported.

Especially the lifetime limiting factor of environmentally assisted fatigue eaf is being discussed. The presence of a reversed cyclic plastic zone within the monotonic plastic zone was. Fatigue strainlife behavior of carbon and lowalloy. Corrosion fatigue crack initiation behavior of stainless. The fatigue crack propagation behaviour of annealed type 316 stainless steel was. Fatigue crack propagation 176 fatigue crack failure 176. Fatiguecrack propagation behavior of several pressure vessel steels and weldments fatiguecrack growth rates in an air environment tend to increase with increasing test temperature, althoughat a given temperaturethere is very little difference in the crack growth of several pv steels from 75 to 800 f and only minor differences at f. The material was solution treated at 53 k for 1 h followed by oil cooling, from which the following fatigue specimens were machined. The tests were intermitted at every crack half length increment of.

However, eaf is only one influencing parameter in terms of transferability from laboratory conditions to plant like conditions. Factors influencing the measurement of ferrite content in austenitic stainless steel weld metal using. Analysis of fatigue crack propagation in welded steels. A recent development in creepfatigue testing 20 september 2014. Asme iii nb3200 provides a method for carrying out fatigue calculations using a simplified elasticplastic analysis procedure. Fatigue crack propagation behaviour of type 316 stainless steel at. Fatigue monitoring of austenitic steels with electromagnetic acoustic transducers emats 28 february 2015. The material was solution treated at 53 k for 1 h followed by oil cooling.

Fatigue performance of austenitic stainless steel is a topic of international activities. Effect of mechanical pretreatment on gas nitriding. The asme boiler and pressure vessel code design fatigue curves for structural materials do not explicitly address the effects of reactor coolant environments on fatigue life. Many factors affecting corrosion fatigue behavior have been studied, such as solution temperature, average stress, surface mechanical grinding treatment, heat treatment, grain boundary characteristic distribution and grain size. Moreover test samples are ground to obtain a surface finish rougher than all that could be found in nuclear power plants.

Fatigue strength reduction factor of crack initiation life. N behavior of cast cf8 and cf8m ss is similar to that of wrought austenitic sss. However, the effect of tensile properties on the fcp behavior of steel, particularly in low and intermediate. The metallurgical factors influence the initiation and propagation behaviors of fatigue by altering the characteristics of slip that is prerequisite for fatigue damage accumulation. The fatigue strength represents a limit value below which short macro crack does not initiate, and the mechanism for the improved fatigue strength of steel with increasing tensile strength, and arguably yield strength, has been well established. Innovation stainless steel, florence, italy, 1114 oct, 1993, vol. Influence of prestrain and carbon content on delayed. Fcgr data are also compared with sour fatigue endurance data. The mechanism and estimation of fatigue crack initiation. Crack initiation and propagation i three stages of fatigue failure. However, austenitic stainless steels show tremendous resistance to brittle. The fatigue strength reduction factor k f of fatigue crack initiation life n c basis was previously proposed by one of the authors as a function of the elastic stress concentration factor k t and work hardening constants in the cyclic hysteresis loop. Corrosion fatigue investigations on austenitic stainless. Influence of the strain rate on the low cycle fatigue life of.

The influence of these factors has been the subject of. Tests performed at matched loading conditions in air and water provided a direct comparison of the relative crack growth rates over a wide range of test conditions. Nearthreshold fatiguecrack propagation in steels berkeley lab. Fatigue crack growth behavior of ferritic and austenitic steels at elevated temperatures 20 september 2014. Fatigue crack growth in a metastable austenitic stainless steel d. The validity of the fundamental relation was shown mainly through the experimental investigations using mild steel, high strength steel and. Understanding fatigue crack growth behavior at low frequencies for a mnnicr steel in 3. Fatiguecrack propagation in steels initial defect size often taken as the. Nearthreshold fatigue crack propagation behavior of austenitic highmn steels daeho jeong, wongyu seo, hyokyung sung, sangshik kim. The main parameters which affect the corrosion fatigue crack growth rate are stress intensity factor range, load ratio, electrochemical potential, environment, cycle frequency 1. Fatigue strainlife behavior of carbon and lowalloy steels. Factors influencing solid solubility 310 formation of intermediate phases and compounds 316.

The authors have studied the corrosion fatigue crack initiation and propagation of different types of steels. Fatigue crack growth rate vs stress intensity factor range at different load ratios a in the stable. For some researchers, the key to understanding the hydrogeninduced, fcg acceleration lies in the hydrogendislocation interaction in the vicinity of a crack tip, especially in relatively low or moderatestrength steels with ts of less than mpa e. A model combining the energy density and the critical plane method was used in order to quantify the fatigue damage. Mechanical behavior of pack carburized aisi 316l steel desmond edem fiawoyife page ii abstract austenitic stainless steels are widely used in the chemical, petrochemical and food. Cyclic deformation behaviour of austenitic steels at ambient. In the case of polycrystal ferritic steels, the recent work by. Many other factors have a direct influence on the kinetics such as the strain, the strain level, the stress s tate, and the temperature. Influence of the strain rate on the low cycle fatigue life. Exploring factors controlling precorrosion fatigue of. Major driving factors in the acceleration of fcg rate are stress ratio, temperature and stress rise time. Hydrogenenhanced fatigue crack growth in steels and its. In metallic materials, their accumulation leads to crack initiation in grains at the surface, usually at the interface between a persistent slip band psb. Analysis of fatigue crack propagation in welded steels roberto a.

Microhardness measurements were used to determine the plane strain plastic zone sizes as a function of. K and to evaluate the cyclic flow stress of the material near the crack tip. The influence of metallurgical factors on corrosion fatigue strength of. Corrosion fatigue strength of stainless steels is controlled by tangled. Corrosion fatigue crack growth and threshold stress. With increase in temperature the rate of crack growth for a given.

Overview of influencing factors of fatigue crack growth. Department of materials engineering and convergence technology, recapt, gyeongsang national university, jinju 52828, republic of korea. K th value, of highmn steels was examined with the emphasis on the effect of stacking fault energy sfe, grain size, twinning and tensile properties. Austenitic stainless steels are difficult to carburise due to the tenacious cr 2 o 3. The level of cyclic plastic strain is very high in lowcycle fatigue. Tests performed under increasing k conditions at high r to measure nearthreshold data. The material used is a type 316 austenitic stainless steel of 16 mm diameter whose chemical composition wt. Recent test data indicate a significant decrease in fatigue lives of austenitic stainless steels sss in light water reactor. Fatigue crack growth behavior of 316ln stainless steel with. In austenitic steels and in titanium, high fatigue resistance in welds has been attributed to the occurrence of rough fracture surfaces and a reduced crack tip stress intensity factor of due to. In the present study, the fatigue crack propagation fcp behaviors of austenitic single phase steels, including sts304, fe18mn and fe22mn.

The metallurgical factors influence the initiation and propagation behaviors of. Highmn austenitic steels utilizing twip twinning induced plasticity effect have excellent combination of tensile strength and ductility. The material behavior under cyclic loading was modeled using lemaitrechaboches law which includes the concept of. This report provides an overview of fatigue crack initiation in austenitic stainless steels sss in lwr coolant environments. Fatigue crack growth rates were measured in an annealed and in an aged maraging steel and in three different austenitic steels. To reach a full and stable austenitic lattice, two different alloying concepts are commonly used. The microscope observations show crack initiation and microcrack propagation are dependent on crystallographic orientations, indicating the need for such modeling approach. Fatigue crack propagation rates for notched 304 stainless. Mendez, low cycle fatigue behavior of a type 304l austenitic stainless steel in air or in vacuum, at 20 degrees c or at 300 degrees c.

Cyclic deformation behaviour of austenitic steel 191 s a a,p stress amplitude s m mean stress e a,t total strain amplitude e a,p plastic strain amplitude e m,t total mean strain e m,p plastic mean strain total strain nominal stress e m,t s m e m,p e s m 2 e 2e a,t s. Very high cycle fatigue behaviour of austenitic stainless. Fatigue abstracts fatigue behaviour of austenitic stainless steel sheets for rnllcars. The fatigue crack propagation fcp behavior of fe25mn and fe16mn2al austenitic steels was investigated at 298 and 110 k, and the results were compared with the. Factors influencing fatigue crack propagation behavior of. In metallic materials, their accumulation leads to crack initiation in grains at the surface, usually at the interface between a. Microstructure influence on fatigue crack propagation in. Fatigue crack propagation tests were made at maximum stress levels of. Understand the factors and accompanying interactions that influence crack propagation of stainless steel due to eaf when exposed to cyclical stresses in high temperature water factors that influence the crack propagation or retardation. Table 3 mechanical properties of austenitic stainless steels 304l at room temperature. Statistical models have been developed for estimating the effects of the various service. Cyclic deformation behaviour of austenitic steels at.

Fatigue crack propagation behavior of type 316 american. Fatigue crack growth in a metastable austenitic stainless steel. Crack initiation and growth path under multiaxial fatigue. The role of corrosion pit in the corrosion fatigue crack initiation process of martensitic, ferritic, austenitic, duplex and precipitationhardening stainless steels is briefly summarized. Fatigue crack growth characteristics of several austenitic. Figure 5 shows the rdependence of fatigue crack growth behavior in the present sus 304 steel. Study of fatigue crack propagation in the austenitic. Where possible, effects are contrasted with crackpropagation behaviour. Effect of structural orientation on the susceptibility of. This paper will mainly focus on the study of low cycle fatigue behavior and damage mechanisms of the material at room temperature, 600c to 700c by using electron back scatter diffraction and electron channeling contrast image techniques. Thus, for highly tensile residual stresses, fatigue life of aswelded components is governed by the total stress. Low cycle fatigue behavior and mechanism of newly developed.