The thermal conductivity of AISI 304L stainless steel

A compilation and critical analysis of the thermal conductivity () of AISI 304 stainless steel (SS) between 100 and 1707 K has been given in the literature. The author represented his recommended values of by an inflection in the A versus temperature relationship between 300 and 500 K. Because a physical mechanism had not been identified that would produce such a temperature dependence in of 304 SS, interest was generated in the possible existence of an as yet undiscovered phenomenon that might cause such an inflection. Consequently, experimental verification of the inflection was sought. The present paper presents recent measurements of , the electrical resistivity, and the absolute Seebeck coefficient of 304L SS from 300 to 1000 K and of the thermal diffusivity () from 297 to 423 K. The values computed from the a measurements were within ± 1.6% of the directly measured An inflection was not observed in the temperature dependence of between 300 and 500 K. After careful evaluation and because a physical mechanism still has not been identified which would produce such an inflection, the authors conclude that the inflection in the vs T relationship reported in the literature was caused by the data analysis technique.     

Fracture failure analysis of AISI 304L stainless steel shaft

Fracture failure analysis of an agitator shaft in a large vessel is investigated in the present work. This analysis methodology focused on fracture surface examination and finite element method (FEM) simulation using Abaqus software for stress analysis. The results show that the steel shaft failed due to inadequate fillet radius size and more importantly marking defects originated during machining on the shaft. In addition, after visual investigation of the fracture surface, it is concluded that fracture occurred due to torsional–bending fatigue during operation.     

The effect of grain size and martensitic transformation on the wear behavior of AISI 304L stainless steel

In the present study, a combination of cold rolling and subsequent annealing was used to produce an AISI 304L stainless steel with different grain sizes (650 nm, 3 μm and 12 μm). Wear behavior of the steel was subsequently examined using dry sliding wear test under different loads of 10 N, 20 N and 30 N. Different microstructural characterizations were conducted on the samples. The results demonstrated that the ultra-fine grained steel (650 nm grain size) had better wear resistance under normal loads of 10 N and 20 N, whereas under the normal load of 30 N, it showed weak wear resistance as compared to the steel with larger grain size (3 μm and 12 μm). This behavior can be attributed to the amount of induced martensitic transformation formed during the wear test. This transformation was evaluated using XRD analysis and quantified by Ferritescope measurements. Wear mechanism was recognized as delamination in the early stages of the wear test and the mixture of delamination and abrasion for higher distances.     

Fretting wear of nitrogen-implanted AISI 304 stainless steel

Fretting wear resistance of nitrogen-implanted AISI 304 stainless steel was measured and compared to that of unimplanted steel. After 5 × 10³ cycles, unimplanted steel revealed severe damage on non-slip area and adhesive-type wear on microslip region whereas nitrogen-implanted stainless steel was still undamaged. The improved fretting wear resistance is explained to be due to the increased load carrying capacity and decreased adhesion of nitrogen-implanted steel.     

Evolution of dynamic recrystallisation in AISI 304 stainless steel

Abstract

The nucleation and development of dynamic recrystallisation (DRX) has been studied via hot torsion testing of AISI 304 stainless steel. The DRX behaviour was investigated with microstructural analysis and slope changes of flow stress curves. The characteristics of serrated grain boundaries observed by SEM, electron backscattered diffraction and TEM indicated that the nucleated DRX grain size was similar to that of the bulged part of the original grain boundary. The DRX of the alloy was nucleated and developed by strain induced grain boundary migration and by the necklace mechanism. Before the steady state in the flow curve at 1000 ° C and 0.5 s^-1, the dynamically recrystallised grains did not remain a constant size and gradually grew to the size of fully DRX grains at steady state (30 μm). The calculation of the grain size was based on X _DRX (volume fraction of dynamically recrystallisation) under the assumption that the nucleated DRX grains grow to the steady state continuously. It was found that the calculated grain size of the alloy was good agreement with that of the observed grain size. It is expected that a fine grained steel can be obtained by controlling hot deformation conditions on the basis of newly developed equations for predicting DRX behaviour.     

Effects of martensite formation and austenite reversion on grain refining of AISI 304 stainless steel

The austenite–martensite transformation followed by annealing for austenite reversion in AISI 304 stainless steel has been investigated in order to study the effect of this thermo-mechanical process on grain refinement. In particular the effect of cold reduction, annealing temperature and annealing times have been analysed. After getting ultrafine grains the effect of the grain size on the hardness and on the tensile properties has been evaluated, showing a Petch-Hall dependency in the fully analysed range (down to 0.8 m grain size).     

Predicting recrystallized grain size in friction stir processed 304L stainless steel

A major dilemma faced in the nuclear industry is repair of stainless steel reactor components that have been exposed to neutron irradiation. When conventional fusion welding is used for repair, intergranular cracks develop in the heat-affected zone(HAZ). Friction stir processing(FSP), which operates at much lower peak temperatures than fusion welding, was studied as a crack repair method for irradiated 304 L stainless steel. A numerical simulation of the FSP process in 304 L was developed to predict temperatures and recrystallized grain size in the stir zone. The model employed an Eulerian finite element approach,where flow stresses for a large range of strain rates and temperatures inherent in FSP were used as input. Temperature predictions in three locations near the stir zone were accurate to within 4%, while prediction of welding power was accurate to within 5% of experimental measurements. The predicted recrystallized grain sizes ranged from 7.6 to 10.6 μm, while the experimentally measured grains sizes in the same locations ranged from 6.0 to 7.6 μm. The maximum error in predicted recrystallized grain size was about 39%, but the associated stir zone hardness from the predicted grain sizes was only different from the experiment by about 10%.     

The edge-cracking of AISI 304 stainless steel during hot-rolling

The hot-rolled plates of AISI 304 stainless steel, containing edge cracks of different intensities, were examined. The austenitic matrix of the steel contained small amounts of ferrite inhomogeneously distributed across the width and the thickness of the plate. A correlation was found between ferrite content and edge cracking: the higher the ferrite content the longer the edge cracks. Among the chemical elements present in the steel, the most critical effect on ferrite content was exerted by carbon and nitrogen. The longest edge cracks were observed for plates with the lowest content of carbon and nitrogen. A possible contribution of steel chemistry and heating temperature to changes in the steel phase composition and the probability of edge cracking is discussed.     

Friction stir welding of AISI 304 austenitic stainless steel

The objective of this work is to demonstrate the feasibility of friction stir welding (FSW) AISI 304 austenitic stainless steels. The tool used was formed of a tungsten‐based alloy. The specimens were welded on an 11 kW vertical milling machine. Defect‐free welds were produced on 2.5 mm plates of hot‐rolled AISI 304 austenitic stainless steels at travel speeds ranging from 40 to 100 mm/min with a constant rotating speed of 1000 rpm. Tensile strengths and hardness values of the weld interface were determined and microstructure features of these samples were investigated.     

Analysis of the recrystallization and grain growth processes in AISI 316 stainless steel

A theoretical and experimental study on the recrystallization and grain growth processes on AISI 316 stainless steel is here reported. Experimental data are analyzed according to a mathematical model based on statistical assumptions able to describe simultaneously recrystallization and grain growth in metals. Taking into account the classical constitutive equations of the Taylor's theory, the model adopts two parameters: the dislocation density and the initial number of nuclei. The predictions of the model are in good agreement with experimental results. As cross check of the model predictions, the independent parameter dislocation density is found to properly correlate to the mechanical properties of the steel, to X-ray diffraction measurements and to transmission electron microscopy measurements. A comparison with an analogue study on AISI 304 stainless steel is also reported, enhancing the effect of molybdenum in inhibiting recrystallization and grain growth.     

Strain-rate effect on high temperature low-cycle fatigue deformation of AISI 304L stainless steel

The effect of strain rate on the behaviour of high temperature low-cycle fatigue is investigated for AISI 304L stainless steel. Regardless of the test temperature of 873 or 973 K, the fatigue life is saturated in the strain-rate range of slower than 4 × 10^–3 sec^–1. Also it is interesting to note that serrated flow, which is evidence of the occurrence of dynamic strain ageing, is clearly observed in the load-elongation hysteresis loops for strain rates that are slower (at 873 K) and faster (at 973 K) than 4 × 10^–3 sec^–1. Since the combination of temperature and strain rate is concerned with the phenomenon of dynamic strain ageing, it is considered that the above-mentioned saturated fatigue life at 873 K is caused by dynamic strain ageing and that the hardening effect due to dynamic strain ageing abnormally increases the fatigue life. However, even though the behaviour of fatigue life under strain rates slower than 4 × 10^–3 sec^–1 at 973 K has nothing to do with the dynamic strain ageing, it has been found that the failure life is also saturated in this slower strain-rate range. This behaviour is considered to be caused by the effect of creep, because the deformation under the low strain-rate activates the recovery process and as a result it causes saturation of the inelastic strain range.     

Stress induced martensite transformation texture in AISI 304 austenitic stainless steel

Abstract

The phenomenological theory of martensitic transformation was applied to a tension induced martensitic transformation in an AISI 304 austenitic stainless steel in order to estimate the transformation texture. Input data were obtained from the published literature. Calculated pole figures were constructed assuming a variant selection process based on Patel and Cohen’s theory, which emphasises that a mechanical component of free energy is the driving force for martensitic transformation at temperatures above martensite start M_s. The results showed a remarkably good match between the calculated and published measured data.     

Low-cycle fatigue behaviour of notched AISI 304 stainless steel specimens

Low-cyclic fatigue tests were conducted on semi-circle notched and V-notched specimens made of AISI 304 stainless steel. Extensive scanning electron microscopic examination of the fracture surface was also carried out to correlate the microscopic fracture surface features with the macroscopic fatigue loading parameter for this steel. The elastic-plastic fatigue test results indicated a noticeable cyclic hardening phenomenon and also a great influence of the maximum cyclic stress, the mean stress and the notch geometry on both the fatigue life and the fatigue behaviour process. Using careful sensitivity and regression analysis correlations between the macroscopic fatigue parameters on the one hand and the macroscopic and the microscopic fracture surface features on the other, these correlations are presented and clearly documented and discussed for the two notch geometries investigated.     

Sensitization evaluation of the austenitic stainless steel AISI 304L, 316L, 321 and 347

This work presents a systematic investigation of the influence of time and temperature in the sensitization of stainless steel AISI 304L, AISI 316L, AISI 321 and AISI 347 pipes used in petroleum refining plants. The sensitization was assessed by Scanning Electron Microscopy (SEM) according to ASTM A-262 and by the Double Loop Electrochemical Potentiokinetic Reactivation test (DLEPR). The results showed that all steels did not present sensitization at operating temperature (380°C) in the desulfurizers process, but the temperature of 500°C was critical to the appearing of sensitization for the both low carbon stainless steels and AISI 321 SS, while for the AISI 347 the critical temperature was 550°C. The stabilized steels confirmed to be more resistant to sensitization than the low carbon stainless steels, and niobium showed to be more efficient stabilizing agent than titanium.     

Microstructural investigation on strengthening mechanisms of AISI 304L austenitic stainless steel during cryogenic deformation

Abstract

In the present paper, microscopy techniques and mechanical tests were used to investigate in detail the strengthening mechanisms of an AISI 304L austenitic stainless steel during cryogenic deformation. The strain hardening rate–strain response of the alloy indicated three distinct regimes of hardening, being very similar to that previously reported for other low stacking fault energy alloys. The hardening rate initially decreased up to a strain of ～6% (stage I). Then, a second stage of increasing hardening rate began (stage II). At strains larger than ～25%, stage III with decreasing hardening rate followed. It was suggested that the formation of ?-martensite and α′-martensite together is responsible for the appearance of stage II. The high strain hardening values of the alloy in stage II were related to the increased fraction of α′-martensite and dislocation pile-ups behind the Lomer–Cottrell locks. The appearance of stage III was attributed to the difficulty of α′-martensite nucleation and ease of dislocation cross-slip at higher strains.     

Corrosion behaviour of amorphous Ni–Si thin films on AISI 304L stainless steel

Abstract

Nanoscale Ni – Si thin films are widely used in commercial microelectronic devices because of their promising electrical properties as well as their chemical stability. However, their application in corrosive environment has not been frequently addressed in the literature. In this study, amorphous Ni_0.66Si_0.33, Ni_0.40Si_0.60, and Ni_0.20Si_0.80 thin films are prepared on AISI 304L stainless steel by means of ion-beam sputter (IBS) deposition and their corrosion behaviour is studied using potentiodynamic polarisation measurements. The electrochemical measurements were conducted in 0.05M HCl solution at room temperature. By means of optical interferometer, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), the surface morphology and chemical composition of the thin films were examined before and after the electrochemical measurement. The evaluated results showed that the Ni–Si thin films may exhibit improved corrosion resistance over the 304L substrate provided that Si content is high enough to facilitate the formation of a Si-rich passive film.     

Selective dissolution of austenite in AISI 304 stainless steel by bacterial activity

Selective attack in an AISI 304 stainless steel weld metal has been developed after three months in service in well water. Welding zones showed a severe corrosive attack that in some cases led to the steel perforation. Optical and scanning electron microscopy (SEM/EDX) revealed a selective attack. An in-depth analysis showed indications of microbiological activity which could be responsible of the severe attack.