Steel In Corrosive Environment Research Articles

Roles of precipitates on corrosion fatigue crack growth of high-strength steels in corrosive environments: Hamano, R. J. Mater. Sci. Feb. 1989 24, (2), 693–697

The growth of the professions is traced from their origins in the growth of scientific knowledge, stemming from the Renaissance. The first professional institution was that of civil engineering, and other professionals have learned from the success of the engineers' methods. This success is based on scientific knowledge and analytical techniques. It is argued that the knowledge and techniques of the engineer produce original art and design, and that there should be more sharing of methods between the professions—and with clients—in order to produce objects of better value to more people.

Roles of precipitates on corrosion fatigue crack growth of high-strength steels in corrosive environments

The effect of microstructures on resistance to corrosion fatigue cracking and fracture surface morphology for age-hardened steels were investigated in a 3.5% NaCl aqueous solution under a cathodic potential of −0.85 V (Ag/AgCl). The free corrosion was about −0.63 V (Ag/AgCl). The resistance to corrosion fatigue cracking of materials containing coherent precipitates in the matrix (underaged conditions) was less than that of materials containing incoherent precipitates (reheated conditions) at equal strength levels. Accelerated fatigue crack growth rates of the underaged material in the aqueous solution were followed by cracking along prior-austenite grain boundaries, due to hydrogen embrittlement, while the overaged material did not show accelerated fatigue crack growth rates and had fracture surfaces similar to those in air. The difference in the fracture surfaces of both materials in air and in the aqueous solution was considered to depend on the ease of diffusion of hydrogen to the prior-austenite grain boundaries. It is concluded that incoherent precipitates in the matrix made hydrogen accumulation at prior-austenite grain boundaries much slower than for coherent precipitates.

A study on the characteristics of part-through crack growth of low-alloy steel in corrosive environment.

In order to investigate the characteristics of surface crack growth behavior, the fatigue test and potential measurement using a simulated surface crack specimen for low-alloy steel (STS-42) were achieved in pure water at a temperature of 50°C and an oxygen content of 2 ppm. The potential observed in the surface crack plane showed that the differences depended on the crack depth. With time, the potential around the. crack surface showed more noble values than at the deepest tip of crack This reason could be explained by the difference in oxygen content along the crack plane due to the effect of water flow and crack shape. The mechanism of the generation of the hydrogen-assisted intergranular fracture mode observed at crack surface was also discussed based on an electrochemical aspect.

面取りを施したステンレス鋼と施してないステンレス鋼の作用応力下における孔食形成

Pitting corrosion, which affects the fracture of stainless steel in corrosive environments, is an electrochemical phenomenon. There are still many unanswered questions with respect to the pitting corrosion and, furthermore, there is no well-established inhibition method for the pitting corrosion at present. Stainless steel was adopted as the testing material in this experiment, and the state of formed pits was examined on the rectangle section specimen and the chamfering specimen in deaerated 3%NaCl solution under various constant loads by changing the holding time of pitting potential which was determined from the anodic polarization curve. The results obtained are as follows.(1) The formation of pits proceeded gradually and led to deep pits with increasing holding time of pitting potential, and it was expressible as a function of time. The process of deep pit formation differed from SUS 304 and SUS 430. The pitting formation was promoted and accelerated by the presence of stress. Deeper pits were formed under the applied stress above the yield point in particular and this phenomenon became more pronounced at high setting potentials.(2) The number of pits changed with increasing holding time of pitting potential and applied stress. The appearance of pitting corrosion on SUS 304 was different from that on SUS 430. The pits on SUS 304 were distributed all over the specimen surface, and they were numerous and shallow. But the pits on SUS 430 were localized in a certain area of specimen surface, and they were small in number and deep.(3) The chamfering specimen had a tendency to inhibit the pitting formation to a certain extent. In addition, the surface condition (roughness) seemed to be the major factor on the pitting formation.

Effect of Loading History on Fatigue Crack Propagation Behavior of High Strength Steel in Corrosive Environment

The effects of loading history and corrosive environment on the retardation in crack growth were investigated in rotating bending. The material used was 200°C tempered SNCM439. Tests were made at two-step varying loading, K1→K2, in room air and in 1%NaCl solution. The stress intensity was estimated by K=σmax√πa/2 for convenience sake, where σmax is the stress amplitude and a is the crack length measured circumferentially on the surface.The results obtained are as follows:(1) The number of retardation cycles was influenced by the environment, K2, and the intermediate treatment (ex. hydrogen charge) during the change in K from K1 to K2.(2) The retardation crack length was determined by K1, irrespective of environment.(3) The relationship between the number of retardation cycles and a parameter of varying load, (K1-K2)/K2, was derived for each environment. The number of retardation cycles increased linearly with (K1-K2)/K2.(4) The crack propagation rate in retardation period decreased with an increase in K1 and increased with an increase in K2.

定電位のもとで孔食を起しつつあるステンレス鋼のクリープ挙動

The pitting corrosion, which affects the fracture of stainless steel in corrosive environments, is the electrochemical phenomenon, occurring in the specified electrode potential region. When halogen ions, especially chloride ions in a corrosive solution exceed a critical amount, the pitting corrosion occurs inevitably. In this study aimed to elucidata the relation between the pitting phenomena and mechanical properties, the fundamental experiments were carried out in deaerated 3% NaCl solution. For this purpose, the changes in the creep curve and the time to fracture under various potentials controlled potentiostatically above the critical potential for pitting corrosion as well as the magnitude of the applied stress that did not lead to any fracture of the material by the pitting during a specified period (104sec.) were determined. Observations of the specimen surface were also performed. The results obtained were as follows.(1) The controlled potentials within the pitting corrosion region influenced the creep fracture time, the applied stress that could not cause fracture in the material by pitting corrosion in 104sec., and the fracture process. Even though the applied stress was 352.8MPa (plastic region), the controlled potential below+0.1V could not cause fracture in SUS 430. When the controlled potential was raised to a higher value such as +0.2V, the applied stress of 196.0MPa (elastic region) was enough to cause fracture in SUS 430. On the other hand, for SUS 316, the applied stress of 450.8MPa was not enough to cause fracture at the low controlled potential below +0.5V. When the pitting potential was controlled at a high value such as +1.0V, a lower applied stress caused fracture in the material.(2) The change in the appearance of pitting corrosion caused by applied stress was also reflected in the change in the current. The current observed on SUS 316 was higher than that on SUS 430. This difference was remarkable at higher controlled potentials. When the applied stress was in the range from 548.8MPa to 588.0MPa and the controlled pitting corrosion potential was such a higher value as +1.0V, the difference was considerably large, and the creep strain dropped remarkably. Therefore, this difference was thought to be caused by the fast rate of pitting corrosion compared with the creep strain rate.(3) The appearance of pitting corrosion on SUS 430 was different from that on SUS 316. The pits on SUS 430 were localized in a certain area of the specimen surface, and they were small in number and deep. But the pits on SUS 316 were distributed all over the specimen surface, and they were numerous and shallow. This difference influenced their creep fracture properties. In SUS 430, the crack began to form from the large and deep pits grown at the side of the specimen and propagated very slowly. Such a phenomenon could not be observed on SUS 316.

Wear of Metals in Corrosive Environments

The wear of carbon steel in corrosive environments has been observed under the potential controlled conditions, and the mechanism of wear and friction in corrosive environments is discussed. In the wear of metals in corrosive environments, the fracture of adhesion points, the fracture by thermal fatigue, the rubbing off of corroded layer and the damage by corrosion fatigue are observed in accordance with the variety of corrosive agents, the corrosion intensity, the type of friction, the rubbing velocity and the contact load. In the oxidizing neutral media, the lubrication due to the corrosion products plays an important role in the behavior of wear, the minimum wear rate being obtained under the mild corrosiveness in the type of face contact. In the reducing acid media, the lubrication of corrosion products is not found because of their dissolution. In the corrosive wear of metals, the wear rate is much affected by the dissolution rate of metals because of the great effect of corrosion fatigue. The cathodic potential sufficient to protect the static corrosion is not adequate to the members under friction in corrosive environments, owing to the increase of the surface activity of metals. However, the protection from corrosion is not always expected to decrease the wear rate as is mentioned above.

Effect of Heat Treatment, Composition and Microstructure on Corrosion of 18Cr-8Ni-Ti Stainless Steels in Acids

Abstract Titanium additions to 18Cr-8Ni steels can effectively eliminate susceptibility to intergranular attack associated with the precipitation of chromium carbides. However, these additions also drastically reduce the grain size of these steels and promote the formation of sigma phase. Both of these factors modify the behavior of titanium-stabilized steels in corrosive environments. A detailed investigation of the influence of heat treatment and microstructure on the corrosion resistance of four titanium-stabilized, AISI 321, heats is described. Incomplete stabilization of carbon by titanium leads to precipitation of chromium carbides on heating in the range of 800 F to 1600 F. This type of susceptibility is readily detected in the oxalic acid etch test, the nitric-hydrofluoric acid test, the copper sulfate-sulfuric acid test, the ferric sulfate-sulfuric acid test, and in the nitric acid test. A second type of susceptibility to intergranular attack is associated with the formation of sigma phase, which may precipitate in a sub-microscopic form during heating in the range of 1150 to 1550 F. It is detected only in the nitric acid test and, to a lesser extent, in the ferric sulfate-sulfuric acid test. The action of various acid solutions on titanium-stabilized stainless steels are compared by means of metallographic studies of microstructures and of progressive corrosion, and by measurements of weight loss and change in electrical resistance of corroding specimens. The data obtained are used to explain the action of acids on these steels and to recommend procedures for evaluation testing.