Ferritic Grades Research Articles

Effect of rhenium on the microstructure and mechanical behavior of Fe–2.25Cr–1.6W–0.25V-0.1C bainitic steels

A new ferritic creep resistant steel has been developed by eliminating Nb and adding 1.5 mass % Re to a ferritic steel grade T/P23 with the aim of enhancing its mechanical properties at high temperature. Cast ingots of both steels, new grade and ASTM T/P 23, were hot rolled at 900°C and then submitted to a thermal treatment consisting of solubilization at 1050°C and tempering at 700°C. Tempered bainitic microstructures obtained contain second phases reinforcing carbide particles, mainly M6C and M23C6 at the boundaries of both, prior austenite grains and bainitic ferrite laths, as well as MC within the grains. Mechanical properties at temperatures ranging from 540 to 600°C were studied by strain-rate-change tests in compression at strain rates between 10−7 and 10−4s−1. These tests showed high stress exponents (n≥20) and activation energies (Q≈400kJ/mol) for both alloys, which were associated with a dislocation movement mechanism with a strong interaction between dislocations and precipitates. On the other hand, a creep exponent of 5 was derived for the stress dependence of minimum creep rate from conventional-type creep tests at 600°C. Although this stress exponent is usually related to a dislocation climb controlled creep mechanism, remarkable microstructural degradation observed with increasing creep time makes difficult to elucidate the true deformation mechanism controlling creep.

Effects of surface preparation on tribological behaviour of a ferritic stainless steel in hot rolling

Some defects on the surface of carbon steel do not need to be removed before hot rolling because the surface will be vigorously oxidised in a reheating environment. Thus the defects can be minimised by oxidising and then removed by the de-scaling process. The defects on the surface of ferritic stainless steels, however, are not easily removed by oxidation when a high chromium concentration is used. In this paper, a ferritic stainless steel grade 445 was selected as a research material. The effects of different surface features on oxidation and tribological behaviour in the hot rolling process were investigated. Three surface states were prepared, namely, smooth surface, surface with 45° grinding marks and surface with oscillation marks. The samples were put into an electric furnace at 1100°C for reheating. Hot rolling tests were carried out on a 2-high Hille 100 experimental rolling mill. Rolling forces were measured, and the coefficient of friction was calculated and compared under various rolling parameters. It was found that the original surface profiles with grinding marks were still maintained during oxidation. The original oxide scale on the surface with oscillation marks caused the formation of irregular oxide nodules and the spallation of the oxide scale. Surface morphology and the reduction in thickness had a significant impact on the oxide scale integrity and coefficient of friction in the hot rolling process.

Experimental simulation of dissimilar weld metal of high manganese steels by arc melting technique

This paper presents an arc melting technique that allows simulating dissimilar weld metal of high manganese steels with ferritic and martensitic steel grades. The objective of this initial study was to conceive a melting technique that produces dissimilar metal welds using a GTA process in a water-cooled copper crucible under welding adequate cooling conditions and with homogeneous mixing. For this purpose, the sample size, the shape of the crucible, and the melting parameters have been optimized. Using the developed arc melting technique avoids the time-consuming and expensive process of iteratively producing actual welds. It is demonstrated that the dissimilar weld metal microstructure and properties can be easily evaluated for a wide range of dilutions. For an industrially relevant material combination of an austenitic high manganese steel and a ferritic low-alloy steel, the effect of dilution on the weld metal microstructure, the hardness, and the measured ferrite number are shown utilizing the developed arc melting technique. Determining the effect of dilution for a wide range material combination is the basis for the development of a constitutional diagram and will be part of a subsequent paper.

Formation of Al2O3/FeAl coatings on a 9Cr-1Mo steel, and corrosion evaluation in flowing Pb-17Li loop

Iron aluminide coating layers were formed on a ferritic martensitic grade 9Cr-1Mo (P 91) steel using pack aluminizing process. The formation of different aluminide compositions such as orthorhombic-Fe2Al5, B2-FeAl and A2-Fe(Al) on the pack chemistry and heat treatment conditions have been established. About 4–6 μm thick Al2O3 scale was formed on the FeAl phase by controlled heat treatment. The corrosion tests were conducted using both the FeAl and Al2O3/FeAl coated specimens in an electro-magnetic pump driven Pb-17Li Loop at 500 °C for 5000 h maintaining a flow velocity of 1.5 m/s. The detailed characterization studies using scanning electron microscopy, back-scattered electron imaging and energy dispersive spectrometry revealed no deterioration of the coating layers after the corrosion tests. Self-healing oxides were formed at the cracks generated in the aluminide layers during thermal cycling and protected the base alloy (steel) from any kind of elemental dissolution or microstructural degradation.

Integranular corrosion susceptibility analysis in austeno-ferritic (duplex) stainless steels

Abstract: Austenitic-ferritic stainless steels combine the favorable properties of ferrite and austenite, showing both high mechanical properties and very good corrosion resistance. These steels are characterized by the precipitation of many secondary phases, carbides and nitrides for tempering temperatures between 200 and 1050°C. This phenomenon implies a high susceptibility to localized corrosion, however better than austenitic and ferritic grades. In this work, the susceptibility to intergranular corrosion in of two duplex stainless steel characterized by analogous ferrite/austenite volume fraction was investigated. A “standard” duplex stainless steel SAF 2205 and a “super” duplex stainless steel SAF 2507 were investigated by means of potentiostatic reactivations tests. In addition, chronoamperometric tests and light optical microscope observations of the specimens surfaces were performed in order to analyze the evolution of the corrosion morphologies.

Surface Integrity, Surface Finish and Corrosion Characteristics of Stainless Steels in Saline Water Medium

The surface roughness of austenitic (304), martensitic (410) and ferritic (430) grades of stainless steels have been measured after fine emery paper grinding. The surface integrity of the ground samples were further examined in SEM. Metal removal during emery paper grinding occurred by rubbing, ploughing, micro cracking and gouging out of metal grains. The rate of corrosion/year, as determined through potentiostat test in 0.9 N NaCl solution, increased with surface roughness but it was insignificant in case of the metallographically polished samples of all the stainless steels. Corrosion progressed fast from the grinding pits on the stainless steel sample surfaces.

Analysis of Mechanical Behaviour of Heat Affected Zone on Ferritic Side of Bimetallic Welds under Thermal Fatigue Conditions

In this paper the effect of thermal fatigue on mechanical behaviour of the heat affected zone on ferritic side of bimetallic weld was investigated. The bimetallic weld coupons between ferritic steel SA516 Grade 70 and stainless steel 304L were fabricated using TIG (Tungsten Inert Gas) welding process. In this investigation, an experimental test rig was developed and used to simulate the thermal fatigue conditions at laboratory scale. The thermal fatigue factors selected were heating time, notch radius and number of cycles.

Web crippling strength of cold-formed stainless steel lipped channel-sections with web openings subjected to interior-one-flange loading condition

In cold-formed stainless steel lipped channel-sections, web openings are becoming increasingly popular. Such openings, however, result in the sections becoming more susceptible to web crippling, especially under concentrated loads applied near the web opening. This paper presents the results of a finite element parametric study into the effect of circular web openings on the web crippling strength of cold-formed stainless steel lipped channelsections for the interior-one-flange (IOF) loading condition. This involves a bearing load applied to the top flange of a length of member, away from the end supports. The cases of web openings located centred beneath the bearing load (i.e. beneath the bearing plate delivering the load) and offset to the bearing plate, are considered. Three grades of stainless steel are considered: duplex EN1.4462, austenitic EN1.4404 and ferretic EN1.4003. In total, 2218 finite element models were analyzed. From the results of the parametric study, strength reduction factors for load bearing capacity are determined, where these reduction factors are applied to the bearing capacity calculated for a web without openings, to take account the influence of the web openings. The strength reduction factors are first compared to equations recently proposed for cold-formed carbon steel lipped channel-sections. It is shown that for the case of the duplex grade, the strength reduction factor equations for cold-formed carbon steel are conservative but only by 2%. However, for the cases of the austentic and ferritic grades, the cold-formed carbon steel equations are around 9% conservative. New strength reduction factor equations are proposed for all three stainless steel grades.

A micro-mechanical analysis of thermo-elastic properties and local residual stresses in ductile iron based on a new anisotropic model for the graphite nodules

In this paper, the thermo-elastic behavior of the graphite nodules contained in ductile iron is derived on the basis of recent transmission electron microscopy investigations of their real internal structure. The proposed model is initially validated by performing a finite element homogenization analysis to verify its consistency with the room-temperature elastic properties of ductile iron measured at the macro scale. Subsequently, it is used to investigate the formation of local residual stresses around the graphite particles by simulating the manufacturing process of a typical ferritic ductile iron grade, and the results are compared with preliminary measurements using synchrotron x-rays. Finally, the obtained accurate description of the stress & strain field at the micro scale is used to shed light on common failure modes reported for the nodules and on some peculiar properties observed in ductile iron at both micro and macro scale.

Metallurgical response of weld metal to different filler metal and joint design combinations of laser-arc hybrid welded lean duplex and novel ferritic stainless steels

Laser and laser-arc hybrid welding of duplex and ferritic stainless steels is demanding, because microstructure of the welds tends to be highly ferritic. Therefore, filler metal must be used for maintaining corrosion and mechanical properties of the welds. In this study, different filler metals including duplex, basic, and overalloyed austenitic grades were used with laser-arc hybrid method to weld lean duplex 1.4162 and novel ferritic stainless steels grades 1.4622 and 1.4509. Several sets of joint design and welding parameter combinations were used to adjust the amount of filler metal in the weld. The purpose of the trials was to evaluate whether weld metal microstructures (grain morphology, austenite/ferrite balance, etc.) can be modified by using an applicable joint preparation and an “overmatched” filler metal addition. Weld characterization included several research methods such as: Macro- and microscopic examination using light microscope¸ cross-sectional dilution ratio determination from the metallographic cross sections, electron backscatter diffraction method in order to assess austenite, and ferrite phase proportions in the test welds. The effects of used groove geometry, filler metal composition, and content on resulting metallurgical features of the welds are discussed in detail.

Effect of Heat Treatment on the Microstructure and Mechanical Properties of a Welded AISI 410 Martensitic Stainless Steel

2 Abstract: Although martensitic stainless steel materials are not used in large quantities compared to austenitic and ferritic grades, they play a huge and often unseen part in our modern world due to their combination of strength, toughness and moderate corrosion resistance. However, after welding the martensitic stainless steel tend to lose their mechanical/microstructural integrity. In this study, the microstructures and mechanical properties of a welded AISI 410 martensitic stainless steel after different heat treatments were studied, with aims to restore the hardness and improve grain refinement of the materials. The results show that the structures of the steel after austenitizing treatment at 1020°C are of lath martensite mixed with a small amount of retained austenite. Apart from TP2 specimen, where martensite phase was transformed into ferrite structure, the structures of the tempered steel are mixtures of tempered martensite, carbides and reversed austenite dispersed in the martensite matrix. The result indicated that the tempering regimens (500, 600 and 700°C) carried out improved the hardness and grain refinement leading to the existence of finely distributed carbides in the materials. TheTP3 specimen experienced secondary hardening phenomenon, displays the best comprehensive mechanical properties and has the highest hardness value of 370.7 HV close to the parent metal after tempering at 700 °C.

On the synergy of diffusible hydrogen content and hydrogen diffusivity in the mechanical degradation of laboratory cast Fe-C alloys

The present work investigates the influence of hydrogen on the mechanical properties of generic Fe-C alloys by tensile tests on notched samples. Different microstructures, such as pearlite, bainite and martensite are generated in a 0.2%C Fe-C alloy by an appropriate heat treatment. “Pure” iron is used as a reference material and a variation in the carbon content up to 0.4% is established for the bainitic grade. The effect of hydrogen is demonstrated by mechanical tests on both in-situ hydrogen charged and uncharged specimens. At high cross-head deformation speed (5mm/min), the results indicate a considerable, though variable hydrogen effect for different microstructures. The bainitic and martensitic materials both show ductility drops of about 20%, whereas the pearlitic and ferritic grades display a higher sensitivity to hydrogen embrittlement (HE) with a ductility loss of approximately 50%. In order to evaluate the role of the diffusible hydrogen, tensile tests are performed at a lower cross-head deformation speed (0.05mm/min) as well. Next to the correlation between the amount of diffusible hydrogen and HE, the distance over which hydrogen can diffuse during a tensile test, determined by hydrogen diffusion coefficient, seems to play a crucial role as well.

On the isotropic elastic constants of graphite nodules in ductile cast iron: Analytical and numerical micromechanical investigations

A comprehensive description of the mechanical behavior of nodules in ductile iron is still missing in the published literature. Nevertheless, experimental evidence exists for the importance of such graphite particles during macroscopic material deformation, especially under compressive loading. In the present paper, the nodules’ elastic properties are thoroughly investigated by means of both analytical and numerical techniques. The analysis takes into account the influence of several non-linear phenomena, as local residual stresses arising during solid-state cooling, interface debonding and limited particle strength. It is shown that if the nodule internal structure is considered, the traditional isotropy assumption leads to the definition of a domain of admissible values for the effective elastic constants. However, micromechanical calculations indicate that values within the domain do not provide mesoscopic moduli in agreement with Young's modulus and Poisson's ratio recorded for common ferritic ductile iron grades. This suggests that graphite nodules may not be considered isotropic at the microscopic scale, at least from a mechanical viewpoint.

Experimental study on ferritic stainless steel RHS and SHS beam-columns

Ferritic stainless steels, with their lower nickel content, supplement the desirable features offered by different stainless steel grades with a more controlled and lower initial investment requirements, which have encouraged the use of these materials in construction. The nonlinear behaviour of stainless steel grades is not usually considered when extending design expressions codified for carbon steel to these alloyed materials, leading to overconservative design approaches and the applicability of the different design expressions initially developed for carbon steel needs to be adjusted for every stainless steel grade. The study of stainless steel elements subjected to combined flexural buckling and bending moment loading conditions only covers the most usual austenitic, duplex and lean duplex grades, but experimental results on ferritic grades are still necessary to complete the analysis. Hence, an experimental programme on ferritic stainless steel RHS and SHS pin-ended elements has been conducted where the flexural buckling and beam-column behaviour of these elements has been investigated. Furthermore, the assessment of the different design approaches for flexural buckling and interaction expressions for combined loading has been derived from the obtained experimental results, and current specifications provided in Standards have been found to be, in general, safe but overconservative.

Dubleks Paslanmaz Çeliklerde Sigma Fazının Korozyon Dayanımına Etkileri

800x600 Normal 0 21 false false false TR X-NONE X-NONE MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Normal Tablo"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman",serif;} Duplex stainless steels consistsof approximately half austenitic and half δ-ferritic phases and are preferred due to applications demanding both satisfactory corrosion and strength properties versus solely ferritic and austenitic grades. In this work; deleterious sigma phase that may form in microstructures of S32205 (2205) duplex stainless steel plates was intended to be quantified after various thermal conditions such as heat treatments, welding and service life and also the effects of sigma phase on microstructural and corrosion properties were investigated. Sigma phase was formed in two distinct raw material by applying heat treatments, and microstructural and corrosion states were analyzed. For this purpose; 800°C was adjusted as heat treatment temperature and two seperate specimens were heated through 5,5 and 16 hours of duration time in consequenceof the most rapidly formation rate of sigma phase at this temperature.

Experimental Study on Ferritic Stainless Steel RHS and SHS Cross-sectional Resistance Under Combined Loading

The excellent corrosion resistance presented by all stainless steel grades, together with their appropriate mechanical properties, aesthetic appearance and easy maintenance, makes these metallic alloys perfect for sustainable structural performances. However, their nonlinear stress–strain behaviour, together with their strong strain hardening features, makes them different from carbon steel and makes the development of some specific guidance necessary. Although the compressive and flexural behaviour of stainless steel Rectangular and Square Hollow Sections (RHS and SHS) has been widely analysed and advanced design approaches considering strain hardening have been developed, more general loading conditions such as combined axial compression and bending moment loading conditions still need to be investigated. Within this scenario, this paper presents an experimental programme on several ferritic RHS and SHS stub column tests subjected to concentric and eccentric compression. The objective is to extend the recent research on austenitic and lean duplex stainless steel RHS under combined loading to ferritic grades by assessing the applicability and accuracy of the interaction expressions currently codified in EN1993-1-4 and those proposed in the literature.

Very High Cycle Fatigue of Two Ductile Iron Grades

Two ductile iron grades, EN‐GJS‐600‐3 a ferritic–pearlitic grade, and EN‐GJS‐600‐10 a silicon strengthened ferritic nodular iron grade, are studied in the very high cycle fatigue range using a 20 kHz ultrasonic test equipment. Fatigue strengths and SN‐curves are achieved, and fracture surfaces and microstructures are investigated. The ferritic grade with higher ductility displays a lower fatigue strength at 108 load cycles than the ferritic–pearlitic grade, 142 and 167 MPa, respectively. Examination of fracture surfaces shows that fatigue failures are controlled by micropores in both of the ductile iron grades, while the graphite nodule distributions do not seem to influence the difference in fatigue strengths. Prediction of the fatigue strengths, using a model for ductile iron proposed by Endo and Yanase, indicates a large potential for improvement in particular for the ferritic grade.

Reliability analysis of structural stainless steel design provisions

Since the establishment of the Eurocode design provisions for structural stainless steel, a considerable amount of both statistical material data and experimental results on structural elements has been generated. In light of this, the current partial resistance factors recommended in EN 1993-1-4 for the design of stainless steel elements are re-evaluated. First, following an analysis of material data from key stainless steel producers, representative values of the over-strength and the coefficient of variation (COV) of the material yield strength and ultimate tensile strength were established. For yield strength, over-strength values and COVs of 1.3 and 0.060 for austenitic, 1.1 and 0.030 for duplex and 1.2 and 0.045 for ferritic stainless steels were determined. For the ultimate tensile strength, an over-strength value of 1.1 was found to be suitable for all stainless steel grades, and COV values of 0.035 for the austenitic and duplex grades and 0.05 for the ferritic grade were proposed. For the variability of the geometric properties, a COV value of 0.05 was recommended. Analysis of available experimental results based on the First Order Reliability Method (FORM), set out in EN 1990 Annex D, and utilising the derived statistical material parameters, revealed that the current recommended partial resistance factors in EN 1993-1-4 (γM0=γM1=1.1 and γM2=1.25) cannot generally be reduced, and in some cases, modified design resistance equations are required, if the current safety factors are to be maintained.

Duplex and ferritic stainless steel sheet linings versus weld overlay and other metallic corrosion-resistant barriers

Sheet linings made from stainless steel can protect carbon steel substrates at lower initial direct cost for installation and subsequent direct inspection than weld overlay and thermal sprayed coating. Closely matched thermal expansion coefficients of ferritic and duplex stainless steel grades with carbon steel allow large “tile pieces” in reliable, leak-proof linings compared to linings from austenitic grades, simplifying and speeding installation. Sheet linings with ferritic and duplex grades typically have lower unit costs than weld overlay and thermal sprayed coatings. Ferritic and lean duplex grades resist corrosion and stress corrosion cracking in most alkaline pulping and liquor recovery environments. Super-duplex grades can replace acid-resistant brick linings in D-stage bleaching equipment, including pre-retention tubes and towers. Carefully specified sheet linings of ferritic and duplex stainless steels, professionally installed in accordance with longstanding industry standards, are reliable and economical protective barriers, especially compared with weld overlay, in many applications in modern pulp

Considerations in development of CCT diagrams for complex ferritic materials

A recent literature review of available data for the bainitic creep strength enhanced ferritic steel grade 23 revealed significant variations among available continuous cooling transformation (CCT) diagrams. Substantial differences in these diagrams were noted with respect to the observed transformation products, reported transformation temperatures and the data provided with the CCT diagram. While it is recognised that grade 23 is a complex material exhibiting up to three transformations on-cooling from austenitisation, there does not seem to be a standardised or uniform procedure for the development of CCT diagrams for such metallurgically diverse materials. This paper details development of a CCT diagram for this material through integration of results from thermal analysis, hardness measurements and microstructural observations.