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.     

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.     

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.     

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.     

Abnormal grain growth in AISI 304L stainless steel

The microstructural evolution during abnormal grain growth (secondary recrystallization) in 304L stainless steel was studied in a wide range of annealing temperatures and times. At relatively low temperatures, the grain growth mode was identified as normal. However, at homologous temperatures between 0.65 (850 °C) and 0.7 (900 °C), the observed transition in grain growth mode from normal to abnormal, which was also evident from the bimodality in grain size distribution histograms, was detected to be caused by the dissolution/coarsening of carbides. The microstructural features such as dispersed carbides were characterized by optical metallography, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, and microhardness. Continued annealing to a long time led to the completion of secondary recrystallization and the subsequent reappearance of normal growth mode. Another instance of abnormal grain growth was observed at homologous temperatures higher than 0.8, which may be attributed to the grain boundary faceting/defaceting phenomenon. It was also found that when the size of abnormal grains reached a critical value, their size will not change too much and the grain growth behavior becomes practically stagnant.     

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.     

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.     

Characterization of cyclic plastic bending of austenitic AISI 304 stainless steel

Steels used in chemical, nuclear and power industries are usually subjected to repeated loads that may induce significant inelastic deformations. Successful assessment of a component life places a great demand on understanding of material behaviour under strain histories involving cyclic plasticity under bending conditions.

This work is concerned with an experimental study of low-cycle fatigue behaviour under both load and deflection controlled conditions. The tests were conducted on AISI 304 stainless steels with the objective of determining strain cycling properties under cyclic plastic bending. These properties are characterized by the cyclic stress-strain hysteresis responses obtained.

The cyclic bending plasticity behaviour is investigated for beams with circular cross-section at two conditions of the material, under constant strain and under constant stress. Hysteresis loops for five different strain ranges of ±0.4%, ±0.82%, ±1.1%, ±1.33% and ±1.55% were obtained and also for different stress ranges of 730, 800, 870 and 940 MPa. The material exhibits cyclic hardening in its virgin state, the rate of hardening is very rapid at first but diminishes quickly as the stabilized condition is approached. The cyclic hardening for the constant strain condition is higher than the constant load condition.

The results also confirm the applicability of the reference stress method for predicting the cyclic moment-curvature curve for beams with circular cross-sections. The observed strain values are higher in the lower strain range and lower in the higher strain. However, the correlation obtained is considered quite satisfactory in view of the nonlinearity of the problem.     

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.     

Load relaxation of stainless steel Type AISI 304 near 563 K

Load relaxation data reported by Anciaux, near 563 K, on mill-annealed Type AlSl 304 stainless steel are interpreted in terms of a general expression which describes stress relaxation as thermally activated dislocation motion over precipitates. Several physical parameters are obtained from the stress-strain rate curves and it is shown that for some stress relaxation curves the internal stress does not remain constant during the relaxation.     

Economical and ecological cryogenic machining of AISI 304 austenitic stainless steel

 While it is a clean alternative to conventional machining using environmentally polluting cutting oils and emulsions, cryogenic machining using liquid nitrogen has been reported to increase cutting forces and shorten tool life when cutting AISI 304 austenitic stainless steel. This paper presents improved results by using an economical cryogenic cooling approach designed after studying the cryogenic properties of the stainless steel material. By injecting a small amount of liquid nitrogen to the chip–tool interface, but not to the workpiece, this approach yielded a 67% tool-life improvement at 3.82 m/s and a 43% improvement at the medium speed of 3.40 m/s when compared with conventional emulsion cooling. It improved machining productivity and reduced production cost. In this study, different cryogenic machining approaches were compared in the machining test using commercial carbide inserts. The results show the cooling approach is crucial in attaining the benefits of cryogenic machining in cutting stainless steel. Received: 7 February 2000 / Accepted: 30 April 2000     

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.     

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.     

Growth behaviour of small surface fatigue cracks in AISI 304 stainless steel

A series of axial tensile fatigue tests (R = 0.1) was carried out to investigate the initiation and the growth behaviours of very small surface fatigue cracks under two different surface conditions (viz. smooth and pitted surfaces) of AISI 304 stainless steel at room temperature. This paper deals with both of the two approaches regarding the analysis of fatigue: the approach based on the concept of fracture mechanics and low cycle fatigue. In particular, both the initiation and growth of cracks and the coalescence of small cracks by fatigue in the specimen have been investigated by the methods of surface replicas and photomicrographs. Quantitative information such as the initiation period, growth and coalescence behaviours of small cracks, and crack growth properties were systematically obtained. The results show that the accurate determination of these parameters is critical for the application of fracture mechanics to fatigue life assessment.     

Investigation of the influential parameters of machining of AISI 304 stainless steel

Austenitic stainless steels are hard materials to machine, due to their high strength, high ductility and low thermal conductivity. The last characteristic results in heat concentration at the tool cutting edge. This paper aims to optimize turning parameters of AISI 304 stainless steel. Turning tests have been performed in three different feed rates (0.2, 0.3, 0.4 mm/rev) at the cutting speeds of 100, 125, 150, 175 and 200 m/min with and without cutting fluid. A design of experiments (DOE) and an analysis of variance (ANOVA) have been made to determine the effects of each parameter on the tool wear and the surface roughness. It is being inferred that cutting speed has the main influence on the flank wear and as it increases to 175 m/min, the flank wear decreases. The feed rate has the most important influence on the surface roughness and as it decreases, the surface roughness also decreases. Also, the application of cutting fluid results in longer tool life and better surface finish.