Stress corrosion cracking behaviour of stainless steels with respect to their use in architecture,part 2: corrosion in the passive state

Unexpected failures of 18/10 CrNi and 17/12/2 CrNiMo steels in indoor swimming pool atmospheres made it necessary to reinvestigate chloride stress corrosion cracking of stainless steels with respect to their use in arcitecture. A preceding paper presented inwestigations into stress corrosion cracking (SCC) in the active state of corrosion; the present paper deals with SCC In the passive state. The investigations showed that – in contrast to general opinion – stress corrosion cracking in the passive state can occur at temperatures well below 50°C in 18/10 CrNi and 17/12/2 CrNiMo steels, provided the corrosive medium has an extremely high chloride concentration. Other factors such as stress level, pH value or type of kation only exert a subordinate influence. Especially the high alloy austenitic steels 1.4439 and 1.4539 proved SCC-resistant under such conditions at ambient temperatures. Electrolytes with critical chloride concentrations may develop when deposits containing chlorides of sufficiently high solubility (e.g. MgCI₂, CaCl₂) are exposed to an atmoshere with critical, i.e. comparatively low humidity. Such conditions are evidently met only under very specific circumstances such as may occur in indoor swimming pools. In other structures where stainless steels have been used for decades without such damage having occurred to date, these critical conditions appear generally not to be reached.     

Stress corrosion cracking behaviour of stainless steels with respect to their use in architecture,part 1: corrosion in the active state

Unexpected failures on 18/8 CrNi and 17/12/2 CrNiMo steels in indoor swimming pool atmospheres made it necessary to reinvestigate chloride induced stress corrosion cracking (SCC). SCC in the active state was investigated on stainless steels 1.3974, 1.4301, 1.4303, 1.4439, 1.4462, 1.4522, 1.4539 and 1.4571 by testing under constant load at temperatures up to 50°C. Selected tests were performed on the material with the highest SCC susceptibility, 1.4301, in solutions with different concentrations of hydrochloric acid and sodium chloride. SCC was only observed in critical ranges of hydrogen-ion concentration and only in conjunction with pronounced general corrosion. In a solution with c(HCl) = 1.0 mol/l and c(NaCl) = 0.5 mol/l, which had proved to be highly SCC-inducing, the effects of different parameters on SCC behaviour were studied. Temperature, stress level and degree of cold deformation exerted only a secondary influence, in contrast to alloy composition: austenitic steels containing about 10% nickel (1.4301, 1.4303, 1.4571) exhibited very pronounced SCC. The other materials with nickel contents distinctively higher or lower proved, respectively, to be less susceptible or resistant to SCC. Thus, the same effect of nickel content was observed as is known for resistance to chloride induced SCC in the passive state. All materials were prone to pronounced general corrosion. The corrosion phenomena observed were completely different from the swimming pool failures reported.     

On the application of linear elastic fracture mechanics to hard steels

The fracture toughness of a high speed steel (M3-2PM) and a tool steel (AISI 01) was assessed by the application of LEFM in a nonconventional manner. The point of fracture initiation in bend test specimens was identified in a scanning electron microscope and the shape of the inclusion sites found was approximated by ellipses to allow a critical stress intensity factor to be calculated. In this way an assessment of the fracture initiating inclusion size as well as the matrix toughness was attained. The toughness results obtained for the M3-2PM steel were on average 18.0 MNJm^3/2 and for the AISI 01 steel 13.5 MNJm^3/2 both of which somewhat deviate from previously reported values in the hardness range 65 and 61 HRC respectively. The deviation falls within 30 pct in both cases.     

Fracture of steels containing pearlite

The relative effects of pearlite and spherodite on ductile, cleavage, and fatigue failure are summarized. Neither the cleavage strength nor the fatigue endurance limit appear to depend directly on cementite contentper se. Spherodized steels cleave less readily than ferrite/pearlite steels. Ductile fracture resistance is lowered considerably by both types of cementite, pearlite being more deleterious. Ferrite/pearlite steels appear to exhibit slower fatigue crack growth rates at low stress intensity levels than high strength steels. At high stress intensity levels the behavior is reversed. Slip-incuded cracking of carbide lamellae appears easier than that of spherodized carbides. In ductile fracture situations the crack spreads progressively through a pearlite colony via preferential cracking of carbides and rupture of the intervening ferrite accompanied by large local shear strains. Fatigue fracture proceeds with formation of frequent branches, preferentially along the pearlite colony interface. This paper is based on a presentation made at a symposium on “The Cellular and the Pearlite Reactions,” held at the Detroit Meeting of The Metallurgical Society of AIME, October 20, 1971, under the sponsorship of the IMD Heat Treatment Committee.     

Fracture mechanics and the nuclear industry

Fracture mechanics provides a methodology which can be used in the evaluation of the integrity and safety of structural components used in nuclear power plants. In return, the nuclear industry has provided a major driving force for the development of the technology. This includes defining the direction for new developments in fracture mechanics and identifying the important problems for implementing these new developments, as well as supplying much of the financial support for research efforts. Many of the new developments in fracture mechanics throughout the past three decades were generated in response to specific needs of the nuclear industry. This paper takes a historical perspective in looking at the relationship between fracture mechanics and the nuclear industry. Individual subject areas include basic development of linear elastic fracture mechanics, developments in elastic-plastic fracture and ductile instability, testing and standards, and some of the newest problem areas. This paper is based on a presentation made in the symposium “Irradiation-Enhanced Materials Science and Engineering” presented as part of the ASM INTERNATIONAL 75th Anniversary celebration at the 1988 World Materials Congress in Chicago, IL, September 25–29, 1988, under the auspices of the Nuclear Materials Committee of TMS-AIME and ASM-MSD.     

Fracture mechanics and the nuclear industry

Fracture mechanics provides a methodology which can be used in the evaluation of the integrity and safety of structural components used in nuclear power plants. In return, the nuclear industry has provided a major driving force for the development of the technology. This includes defining the direction for new developments in fracture mechanics and identifying the important problems for implementing these new developments, as well as supplying much of the financial support for research efforts. Many of the new developments in fracture mechanics throughout the past three decades were generated in response to specific needs of the nuclear industry. This paper takes a historical perspective in looking at the relationship between fracture mechanics and the nuclear industry. Individual subject areas include basic development of linear elastic fracture mechanics, developments in elastic-plastic fracture and ductile instability, testing and standards, and some of the newest problem areas. This paper is based on a presentation made in the symposium “Irradiation-Enhanced Materials Science and Engineering” presented as part of the ASM INTERNATIONAL 75th Anniversary celebration at the 1988 World Materials Congress in Chicago, IL, September 25–29, 1988, under the auspices of the Nuclear Materials Committee of TMS-AIME and ASM-MSD.     

The flow behaviour of structural steels at large plastic zones with respect to a geometry-independent presentation

Experiments with 2CT specimens of a structural steel St 37-2 with different ratios a/W. Dependence of the normalized crack tipdisplacement σ_gy/a?_gy at general yielding on a/W and comparison with theoretical results. Shape of the normalized flow curve (σ/σ_gy)² versus σ/σ_gy on the basis of the present results and of experimental and theoretical results from the literature. Conclusions for the calculation of the load-displacement curves by use of the geometric parameters and the uniaxial yield stress.     

Fracture resistance of various carburized steels

Fracture toughness and fatigue studies were conducted on various grades of car-burizing steels. The results indicate that similar or superior mechanical performance can be achieved using the alternate EX grades (EX24, EX29, and EX55) compared to the more commonly used grades (SAE 8620, SAE 4320, and SAE 4817). During the study of fatigue properties, various trends on the influence of surface carbon (re-tained austenite) and carbon gradient (hardness profile and case depth) were observed: 1) increasing the surface carbon to the extent that the hardness profile indicated a max-imum at 0.02 in. (0.5 mm) below the surface severely reduced the endurance limit, 2) changing the hardness profile such that the maximum hardness occurred within 0.010 in. (0.25 mm) of the surface improved the endurance limit, but lowered the impact fracture stress, and 3) increasing the case depth improved the endurance limit. This paper is based on a presentation made at a symposium on “Carburizing and Nitriding: Fundamentals, Processes and Properties” held at the Cincinnati Meeting of The Metallurgical Society of AIME, November 11 and 12, 1975 under the sponsorship of the Heat Treatment Committee.     

Fracture mechanics approach to hydrogen-assisted microdamage in eutectoid steel

A fracture mechanics approach to hydrogen-assisted microdamage in eutectoid steel is presented. Fractographic analysis revealed micromechanical effects of hydrogen in the form of tearing topography surface (TTS). The progress of this microdamage is modeled as a macroscopic crack that extends the original fatigue precrack and involves linear elastic fracture mechanics principles. In this case, the change from hydrogen-assisted microdamage (TTS) to cleavagelike topography takes place when a critical stress intensity factor (K _H) is reached, and this value depends on the amount of hydrogen which penetrated the vicinity of the actual crack tip (the fatigue precrack plus the TTS area). It is shown that the value K _H depends on experimental variables—mainly on the fatigue precracking regime—and its value may be associated with a characteristic level of stress intensity factor in the crack growth kinetics curve.     

The fracture behaviour of structural steels at large plastic zones with respect to a criterion for the validity of the COD concept

Fracture tests with 2CT specimens of a structural steel St 37-2 with different ratios a/W. Independence of the fracture stress intensity K_f on a/W in the K_Ic range, but dependence at larger plastic zones. Normalized fracture stress σ_f/σ_gy and normalized crack tip displacement δ_f/δ_gv versus test temperature Tand discussion of the lower and upper boundaries of the scatter bands for the different values of a/W. Agreement of the normalized fracture curve (σ_f/σ_gy)² versus δ_f/δ_gy with the normalized flow curve. Criterion for the validity of the COD concept by comparison of the curves σ_f/σ_gy and δ_f/δ_gy versus T for different geometries and confirmation of it by examples.     

Fracture mechanics of a new blister test with stable crack growth

A new blister test is proposed to measure the specific work of adhesion W between a thin flexible film on a rigid substrate. In contrast to the conventional blister loaded by constant fluid pressure which leads to catastrophic crack propagation, the new test is driven by an internal expansion of a fixed mass of working gas which leads tostable crack growth. The new technique is demonstrated by measuring W of an interface with a commercial sticky tape serving as the thin film and aluminium as the rigid substrate.     

Fracture toughness of powder forged Cr-Mn alloy steels

Metallurgical and Materials Transactions A - The fracture characteristics of a powder forged Cr-Mn alloy steel have been evaluated by plane strain fracture toughness tests. The toughness values...     

Influence of the microstructure of higher carbon steels on fracture mechanics properties

By varying the cooling rate in the region of the γ-α-transformation different parameters of pearlite microstructure, such as interlamellar spacing and pearlite colony size, were adjusted in a pearlitic steel with 0.79% C. Refinement of the microstructure improved the mechanical properties and the fracture mechanical properties, expressed by the J_R-curve. Partial spheroidization of pearlite was achieved by deformation just after the pearlite formation (at the deformation temperature of 600°C). Investigations on ferritic-pearlitic steels with 0.19, 0.35 and 0.45% C, thermomechanically treated in such a way, showed a significant influence of the change in pearlite morphology on the fracture properties, especially with a pearlite fraction larger than about 80%.     

Balancing respect for autonomy with competing values with the use of principle-based ethics.

Psychologists sometimes find themselves in situations in which they need to balance respect for patient autonomy with other competing values and neither the laws nor ethics codes provide clear direction on how they are to do so. With the use of a model from principle-based ethics, this article recommends a strategy for resolving those dilemmas in a manner that promotes patient autonomy as much as possible, even when respect for autonomy may be temporarily trumped by other values. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Structure/activity relationship of adenine-modified NAD derivatives with respect to porcine heart lactate dehydrogenase isozyme H4 simulated with molecular mechanics

Using a significantly simplified modification procedure, four charged analogues of the coenzyme NAD, N(1)- and N6-(2-hydroxy-3-trimethylammoniumpropyl)-NAD, N(1)- and N6-(3-sulfopropyl)-NAD were prepared. The kinetic parameters of these derivatives and N(1)-(2-aminoethyl)-NAD, N6-(2-aminoethyl)-NAD and tricyclic 1,N6-ethanoadenine-NAD, all with alterations to the adenine moiety, were determined for porcine heart lactate dehydrogenase isoenzyme H4. The coenzyme activity depends on both position and charge of the introduced groups. Modification of the N6-position leads to a 25-250-fold increase of the kcat/Km value compared to the related N(1) derivative. The kcat/Km value for 1,N6-ethanoadenine-NAD is in the range between that of N(1)-(2-aminoethyl)-NAD and N6-(2-aminoethyl)-NAD. In the case of both N(1) and N6 functionalization, the Km values increase from (3-sulfopropyl)-NAD, with a negatively charged substituent at the adenine, over (2-amino-ethyl)-NAD to (2-hydroxy-3-trimethylammoniumpropyl)-NAD with an uncharged and positively charged substituent, respectively, at the adenine. All N6 derivatives are analogues like NAD with respect to Km and/or Vmax and kcat/Km. The conformation of NAD and its derivatives was calculated and their interaction in the active site of lactate dehydrogenase was simulated using the molecular mechanics program AMBER. The significant differences in activity in correlation to porcine heart lactate dehydrogenase isoenzyme H4 could be rationalized by modelling the three-dimensional structure of the NAD site.