Stress Corrosion Cracking Characteristics Research Articles

The characteristics of hydrogen diffusion and concentration around a crack tip concerned with hydrogen embrittlement

Previously, we proposed a physical model for hydrogen diffusion and accumulation around the crack tip and performed accurate numerical analysis which takes account of the effects of both hydrogen diffusion and accumulation due to the stress gradient. Based on this analysis, the characteristics of hydrogen accumulation around the crack tip were clarified. Since the characteristics of stress corrosion cracking and corrosion fatigue are dominated by chemical anodic reaction, hydrogen embrittlement and dislocation mechanism, to perform the analysis on the competitive phenomenon by these mechanism and to relate the sensitivity of hydrogen embrittlement to the characteristics of corrosion fatigue, it is necessary to construct a exact physical law on the characteristics of hydrogen diffusion and concentration and to formulate the characteristics as a simple function such as diffusion constant, D, yield stress σ ys, and stress intensity factor, K. The effect of stress field such as plane strain and plane stress on the hydrogen embrittlement is necessary to be clarified as the effect of specimen thickness on the hydrogen embrittlement. In this paper, based on this view point, the effect of D, σ ys, and K on hydrogen embrittlement were investigated and formulated. A quantitative parameter which characterize hydrogen embrittlement was proposed for both cases of plane strain and plane stress conditions as the effect of specimen thickness on the hydrogen embrittlement.

K-0510 窒化ケイ素における表面き裂の応力腐食割れ特性に及ぼす環境の影響(G03-5 環境強度)(G03 材料力学部門一般講演)

Crack growth characteristics of stress corrosion cracking were investigated for an Si_3N_4 ceramic using an indentation pre-crack. The effect of test environment on the crack growth was studied. The small surface pre-crack and the macro through pre-crack was prepared and being experimented.

F07-(3) ウォータージェットピーニングによる耐応力腐食割れと疲労強度の改善

F07-(3) ウォータージェットピーニングによる耐応力腐食割れと疲労強度の改善

Cavitation erosion of duplex and super duplex stainless steels

Owing to their excellent corrosion resistance, stainless steels are widely used both in the marine, urban water, chemical and food industries. In addition to the corrosive environment, high fluid flow speeds are always encountered for components used in these industries. The cavitation characteristics of S30400 and S31600 austenitic stainless steels and duplex stainless steels were studied in detail by a number of authors. It was generally agreed that S30400 has higher cavitation erosion resistance than that of S31600 due to higher tendency of strain induced martensitic transformation under high impulse of stress. A considerable number of results on stress corrosion cracking characteristics of SDSS and duplex stainless steels have been published but data concerning their cavitation erosion property are extremely rare.

Fractal characteristics of stress corrosion cracking in SNCM 439 steel having different prior-austenite grain sizes

An approach by fractal geometry was examined for the SCC problem on a NiCrMo steel. Stress corrosion tests were conducted in 3.5% NaCI solution by using SNCM439 steel specimens. These specimens had different prior-austenite grain sizes due to variations in heat treatment. After summarizing the results of analysis, we explain the profiles of stress corrosion cracks having fractal characteristics. The relevant fractal dimension D was about 1.05 for the region where the intergranular cracking was predominant, while D was about 1.10 for the region having mixed fracture of intergranular and transgranular cracking. The fractal analysis concluded that the crack growth rate da dt depends on the grain size d, but not stress intensity factor K. The investigations of crack growth phenomena were seen to be an important factor to explain the mechanism.

Effect of Ga on Stress Corrosion Cracking Characteristics of Al-9 mass%Mg Alloys

In the present investigation, precipitation behavior of a secondary phase by aging treatment, mechanical properties and time to stress corrosion cracking failure were measured and examined, for the purpose of determining the effect of Ga content on the stress corrosion cracking behaviors of Al-9 mass%Mg alloys in a mixed solution of 1 x 10 -2 kmol/m 3 HCl + 5 x 10 -1 kmol/m 3 NaCl including 3 x 10 -2 kmol/m 3 K 2 Cr 2 O 7 as an oxidizing agent. The principal conclusions are summed up as follows: (1) Stress corrosion cracking fracture resistance deteriorates with increasing Ga concentration in the alloys. Especially when the Ga component exists in the form of a solid solution, its effect is strong. The failure from stress corrosion cracking of the specimens in this investigation is primarily intergranular cracking. However, the aging treatment and the Ga content do not have considerable effects on the mechanical properties of the specimens. (2) The secondary phase precipitated in the specimens by the aging treatment consists of the Al 3 Mg 2 compound. However, in the specimens containing Ga, in addition to the Al 3 Mg 2 compounds, Ga compounds such as Mg2Ga and MgGa2 also precipitate. However, during the aging time shorter than 76.8 ks no no precipitation of the Ga compound was observed and the Ga component exists in the matrix as a solid solution.

Stress Corrosion Cracking Characteristics of a Range of Pipeline Steels in Carbonate-Bicarbonate Solution

Abstract Stress corrosion cracking (SCC) characteristics of a range of pipeline steels immersed in a carbonate-bicarbonate solution were studied in terms of the deleterious effects of small-amplitude cyclic loading on threshold stress, together with the increase of crack nucleation and the decrease of average crack growth rates with increasing test times. Data were reported on conditions for coalescence or otherwise of adjacent cracks in terms of spatial separation. The time dependence of crack nucleation rates and crack growth in laboratory tests varied with stress. The laboratory rates for crack nucleation and growth likely are applicable in high-pressure gas transmission pipelines in service, but values of the constants in the power law expressions for those rates differed for service conditions. The data showed service condition calculations can be guided by empirically assigning ranges of values for the constants by imposing boundary conditions that relate to service experience. Ranges of values also...

The role of carbon level on the stress corrosion cracking characteristics of steel

The present study examined the interrelated effects of bulk carbon level, 0.4% to 0.8%, and yield strength on the threshold stress intensity value, K ISCC , of steels in a sea water environment. Significant effects of these parameters on K ISCC were demonstrated. At constant yield strength, the true effect of carbon level was evident, viz., with increasing C level up to 0.4% K ISCC values were dramatically reduced. Above this value, however, K ISCC values again increased up to 0.8% C. This trough in the K ISCC -% C relationship was tentatively explained in terms of microstructural changes. A review of the various SCC models in hydrogen producing environments illustrated that the Nair - Tien approach exhibited excellent commonality with the present data and reported data in the literature. Finally, abrupt changes in the SCC failure mode were evident in the 0.4% steel. Such failure mode changes were readily explained in terms of Hydrogen Assisted Cracking model for SCC phenomena.

高強度黒鉛材ＩＧ‐１１の破壊力学的特性の評価

Fracture toughness and crack growth characteristics of stress corrosion cracking and fatigue were investigated for an isotropic fine grain size graphite, IG-11, one of the candidates for the core components of High Temperature Gas Cooled Reactors. The results obtained are summarized as follows:(1) The fracture toughness and the fracture resistance were reasonably described by using the stress intensity factor. Introduction of the J-integral as a parameter did not bring an increase in accuracy.(2) The plain strain fracture toughness KIc values for the fatigue precracked specimens were 0.93-1.00MPa√m. Without fatigue precracking, 10-20% decrease in fracture toughness was observed. In both cases, further crack growth brought an increase in the fracture resistance KR up to 1.05-1.25MPa√m.(3) The stress corrosion cracking did not occur in the material tested. On the other hand, the fatigue crack growth below KIc was observed although the crack growth mechanism is quite different from that for conventional metallic materials.

腐食環境下での疲労き裂成長速度に及ぼす応力上昇時間，保持時間，下降時間効果の定量的評価

The corrosion fatigue tests were carried out for Cr-Mo steel (SCM440) by varying the stress rising time (tR), holding time (tH) and descending time (tD). In the present paper, for the case of symmetrical stress wave (tR=tH), the constitutive equation of corrosion fatigue crack growth rate, da/dN|CF, was derived explicitly in terms of tR and tH as follows:da/dN|CF=Dda/dN|air, D=1/1-dtRetHfΔKbexp{a(lnΔK)2+c} (1)where da/dN|air is the fatigue crack growth rate in air, ΔK is the range of stress intensity factor, a, b, c, e, and f are constants. The acceleration coefficient with holding time D(=[D]tH) is this equation was derived by the following method; First, the acceleration coefficient under the condition without holding time, [D]tH=0 was obtained as:[D]tH=0=a(lnΔK)2+blnΔK+c (2)Next, under the condition with holding time, the holding time effect was estimated by the following equation, [D]tH-[D]tH=0/[D]tH=dtRetHf (3)The experimental results of corrosion fatigue crack growth rate under various stress rising and holding time conditions were found to be well expressed by eq. (1). On the other hand, this equation does not satisfy the critical condition that da/dN should be proportional to 1/tH for tH→∞, which is characteristics of stress corrosion cracking. Thus a more satisfied constitutive equation was derived as the equation of the following type: da/dN=F0(ΔK, tR, 2tR+tH). From this equation, it can be found that the corrosion fatigue crack growth rate is affected by f=1/(2tR+tH)) which concerns the time dependent effect and tR which concerns the fatigue effect under the symmetrical stress wave condition.Furthermore, it was deduced that the mechanism of the tR process is controlled by the fatigue effect coupled with the time dependent effect controlling the tH process, while the tD process is controlled mainly by the time dependent effect although it includes some fatigue effect.

Stress corrosion cracking of nuclear pressure vessel steels in pressurized high temperature waters.

The quantitative evaluation of the subcritical crack growth behavior of nuclear pressure vessels and piping steels in pressurized high temperature water has been receiving extensive attention to ensure the structual integrity of nuclear pressure vessels and piping. Recent research progress in this field suggests the significance of the sulfur content of steels in assessing susceptibility to environmentally assisted cracking of these steels in high temperature water from the view point of solution chemistry at a crack tip, where dissolution of MnS, non-metallic inclusion, results in an enrichment of S anion, such as SO42-. Hence, it is neccesary to simulate the solution which has been commonly used as a useful tool to see stress corrosion cracking characteristics in a short time. In this material/environments systems are examined quantitatively as a function of temperature, sulfur content in steels and also SO42- contents in solution, simulating crack tip solution chemistry. Cracking potential showed a lower value of about 250°C, rather than 288°C. Sulfur content of steel and SO42- concentration in solution can drastically influence the cracking potential and some amount of sulfur in steels or SO42- anion at a crack tip make it possible to crack at a BWR or PWR condition.

Near-threshold corrosion fatigue crack growth behavior of type 422 stainless steel at controlled maximum stress intensities

The Kmax-controlled near-threshold fatigue crack growth behavior was investigated on 422 stainless steel in a boiling NaCl solution. During the test, there was a transition from corrosion fatigue to stress corrosion cracking. The transition occurred at very high load ratios (R=-0.91) and at very lowAK levels (≤2.1 MPa√m). The characteristics of stress corrosion cracking (SCC) were manifested by time-based crack growth rather than cycle-based crack growth, by crack extension under static loading, and by change in fracture mode. In corrosive environments, the small ripple loading imposed on structural materials should be recognized for engineering designs and failure analyses.

SUS 310S鋼単結晶のH<SUB>2</SUB>SO<SUB>4</SUB>-NaCl溶液中における応力腐食割れ

The characteristics of stress corrosion cracking (SCC) of type 310 S steel single crystal were investigated in H2SO4-NaCl solution with reference to faceting dissolution and a crystallographic plane of the fracture surface in the two potential zones: I (near the corrosion potential) and II (active-passive transition region). Kinds of facets change in the order of {100}→{100}+{111}→{111} in 2.5 kmol/m3-H2SO4+0.2 kmol/m3-NaCl and 2.5 kmol/m3-H2SO4+0.5 kmol/m3-NaCl solutions, and change in the order of {100}→{110}→{111} in 2.5 kmol/m3-H2SO4+0.8 kmol/m3-NaCl solution with an increase in potential from the corrosion potential to the active-passive transition potential. There are many cracks on the {100} specimen surface at the potential of {100} faceting dissolution, and are many cracks on the {110} specimen surface at the potential of {110} faceting dissolution compared with other crystallographic planes. Cracking occurs as the result of a competition process between the dissolution rate on the surface (Ih) and the crack growth rate (\Dot{C}), and the upper critical potential corresponds to a potential to give a relation, Ih\simeq\Dot{C}. At the potentials of zone I in every solution, a crystallographic plane {hkl} of the fracture surface corresponds to the slowest dissolution plane {hkl} under every given condition. On the other hand, at the potentials of zone II {111} faceting dissolution occurs over all specimen surfaces. These results imply an important relationship between SCC and {hkl} faceting dissolution.

304鋼単結晶のH<SUB>2</SUB>SO<SUB>4</SUB>-NaCl溶液中における応力腐食割れ

The characteristics of stress corrosion cracking (SCC) of type 304 steel single crystal were investigated in H2SO4-NaCl solution with reference to faceting dissolution and the crystallographic plane of the fracture surface in the two potential zones: I (near the corrosion potential) and II (active-passive transition region). The kinds of facet change in the order of {100}→{100}+{111}→{111} in 1N-H2SO4+0.5M-NaCl solution, and change in the order of {110}→{110}+{100}→{100}+{110}+{111} in 5N-H2SO4+0.5M-NaCl solution with an increase in potential from the corrosion potential to the active-passive transition potential. At the potential of zone I in 5N-H2SO4+0.5M-NaCl solution, cracks are found mainly to initiate at the traces of {110} with large normal stress (σ) and shear stress (τ), and to propagate along {110} in the crystal. On the other hand, at the potential of zone I in 1N-H2SO4+0.5M-NaCl solution, cracks mainly nucleate at the traces of {110} with large σ and τ, and propagate along {100} in the crystal. At the potential of zone II in both solutions, {111} faceting dissolution occurs over all specimen surfaces, and cracks are rarely found. Since the crystallographic plane {hkl} of the fracture surface in zone I corresponds to the slowest dissolution plane {hkl} under the above condition, there is an important relationship between SCC and {hkl} faceting dissolution.

The fracture toughness and stress corrosion cracking characteristics of an anhydride‐hardened epoxy adhesive

AbstractThe toughness and stress corrosion cracking characteristics of an epoxy resin (DER 332) hardened with hexahydrophthalic anhydride (HHPA) were investigated. The epoxy was studied in both the bulk and bond form, and its properties were compared with an amine‐hardened (tetraethylene pentamine, TEPA) system. The toughness, 𝒢Ic, of the anhydride system varied less as a function of ratio of hardener‐to‐resin content and postcure temperature than it did in the TEPA‐hardened system. Like the latter, however, its toughness in the bulk and bond forms could not be correlated, but 𝒢Ic of the joints was dependent on tensile modulus and/or yield strength of the bulk epoxy. Both systems were also toughened in the vicinity of the crack tip by water for short‐time loading, but their long‐time load carrying capability was reduced by a water environment. The anhydride hardened system was more sensitive to strength loss in water than the amine system. The fracture morphology for the two systems was the same, i.e., fast cracking occurred cohesively near the center of the bond, and slow cracking occurred at the interface.