Effect of Hydrogen on the Apparent Yield Stress—Research on the Cause of Hydrogen Induced Delayed Plasticity

CORROSION ◽  
1981 ◽  
Vol 37 (9) ◽  
pp. 514-521 ◽  
Author(s):  
Wu-Yang Chu ◽  
Shi-Qun Li ◽  
Chi-Mei Hsiao ◽  
Shur-Yahn Ju
Keyword(s):  
Plastic Deformation ◽  
Tensile Strength ◽  
Yield Stress ◽  
Test Temperature ◽  
Stress Reduction ◽  
Stress Gradient ◽  
Tensile Specimen ◽  
Low Alloy Steels ◽  
Wide Range ◽  
Alloy Steels

Abstract The effect of hydrogen on the apparent yield stress, which is a necessary exterior stress to cause the local macroscopic plastic deformation, was investigated for various carbon and low alloy steels with a wide range of tensile strength. Smooth tensile, bent beam, and precracked WOL specimens were used. The results show that the effect of hydrogen on the yield strength of a smooth tensile specimen is insignificant. However, for the smooth bent beam or precracked specimens with a stress gradient, hydrogen decreases the apparent yield stress considerably if the strength of steel and the amount of hydrogen entering into the specimen exceed critical values. This is the cause of hydrogen induced delayed plastic deformation and then hydrogen induced delayed cracking. The apparent yield stress of the charged specimen decreases with increasing tensile strength and the amount of hydrogen in the steel. It depends evidently on the strain rate and test temperature and is reversible, but is not related to the prestrain condition. The variation of the apparent yield stress of the charged specimens with the test temperature is not monotonous, there is a minimum near room temperature. According to these results, a possible mechanism of hydrogen induced apparent yield stress reduction has been suggested.

Mechanism of Stress Corrosion Cracking of Low Alloy Steel in Water

CORROSION ◽  
1981 ◽  
Vol 37 (6) ◽  
pp. 320-327 ◽  
Author(s):  
Wu-Yang Chu ◽  
Tian-Hua Liu ◽  
Chi-Mei Hsiao ◽  
Shi-Qun Li
Keyword(s):  
Plastic Deformation ◽  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Cathodic Polarization ◽  
Optical Microscope ◽  
Corrosion Cracking ◽  
Low Alloy Steels ◽  
Wide Range ◽  
Alloy Steels ◽  
Loaded Crack

Abstract For four low alloy steels with a wide range of tensile strengths, the dynamical processes of the nucleation and propagation of stress corrosion cracking (SCC) in water with various polarization conditions and in a inhibitor solution were traced with an optical microscope. The results show that if the tensile strength of the steel is higher than a critical value, which is different in the different polarization conditions, and KI>KISCC, the plastic zone in front of a loaded crack tip is enlarged with time, i.e., the delayed plastic deformation occurs in all the environments used. The nucleation and propagation of SCC will follow when this delayed plastic deformation develops to a critical condition. Neither anodic and cathodic polarization nor the inhibitor can change the feature of the delayed plasticity and the nucleation and propagation of SCC in water. In all the environments used, the KISCC is increased and da/dt is decreased with decreasing strength of the steel. Anodic polarization and the addition of the inhibitor make KISCC increase and da/dt decrease. But cathodic polarization is just opposite.

A Model for the Conductivity and Compliance of Unpropped and Natural Fractures

SPE Journal ◽  
2017 ◽  
Vol 22 (06) ◽  
pp. 1893-1914 ◽  
Author(s):  
Weiwei Wu ◽  
Mukul M. Sharma
Keyword(s):  
Plastic Deformation ◽  
Yield Stress ◽  
Young’S Modulus ◽  
Correlation Length ◽  
Young's Modulus ◽  
Heterogeneous Surfaces ◽  
Natural Fractures ◽  
Wide Range ◽  
Fracture Closure ◽  
Deformation Interaction

Summary Fluid flow in unpropped and natural fractures is critical in many geophysical processes and engineering applications. The flow conductivity in these fractures depends on their closure under stress, which is a complicated mechanical process that is challenging to model. The challenges come from the deformation interaction and the close coupling among the fracture geometry, pressure, and deformation, making the closure computationally expensive to describe. Hence, most of the previous models either use a small grid system or disregard deformation interaction or plastic deformation. In this study, a numerical model is developed to simulate the stress-driven closure and the conductivity for fractures with rough surfaces. The model integrates elastoplastic deformation and deformation interaction, and can handle contact between heterogeneous surfaces. Computation is optimized and accelerated by use of an algorithm that combines the conjugate-gradient (CG) method and the fast-Fourier-transform (FFT) technique. Computation time is significantly reduced compared with traditional methods. For example, a speedup of five orders of magnitude is obtained for a grid size of 512 × 512. The model is validated against analytical problems and experiments, for both elastic-only and elastoplastic scenarios. It is shown that interaction between asperities and plastic deformation cannot be ignored when modeling fracture closure. By applying our model, roughness and yield stress are found to have a larger effect on fracture closure and compliance than Young's modulus. Plastic deformation is a dominant contributor to closure and can make up more than 70% of the total closure in some shales. The plastic deformation also significantly alters the relationship between fracture stiffness and conductivity. Surfaces with reduced correlation length produce greater conductivity because of their larger apertures, despite more fracture closure. They have a similar fraction of area in contact as compared with surfaces with longer fracture length, but the pattern of area in contact is more scattered. Contact between heterogeneous surfaces with more soft minerals leads to increased plastic deformation and fracture closure, and results in lower fracture conductivity. Fracture compliance appears not to be as sensitive to the distribution pattern of hard and soft minerals. Our model compares well with experimental data for fracture closure, and can be applied to unpropped or natural fractures. These results are obtained for a wide range of conditions: surface profile following Gaussian distribution with correlation length of 50 µm and roughness of 4 to 50 µm, yield stress of 100 to 1500 MPa, and Young's modulus of 20 to 60 GPa. The results may be different for situations outside this range of parameters.

Proposal of Fatigue Life Equations for Carbon and Low-Alloy Steels and Austenitic Stainless Steels as a Function of Tensile Strength

2013 ◽  
Author(s):  
Hiroshi Kanasaki ◽  
Makoto Higuchi ◽  
Seiji Asada ◽  
Munehiro Yasuda ◽  
Takehiko Sera
Keyword(s):  
Tensile Strength ◽  
Fatigue Life ◽  
Stainless Steels ◽  
Room Temperature ◽  
Austenitic Stainless Steels ◽  
Low Alloy Steels ◽  
Strength Based ◽  
Fatigue Data ◽  
Current Design ◽  
Alloy Steels

Fatigue life equations for carbon & low-alloy steels and also austenitic stainless steels are proposed as a function of their tensile strength based on large number of fatigue data tested in air at RT to high temperature. The proposed equations give a very good estimation of fatigue life for the steels of varying tensile strength. These results indicate that the current design fatigue curves may be overly conservative at the tensile strength level of 550 MPa for carbon & low-alloy steels. As for austenitic stainless steels, the proposed fatigue life equation is applicable at room temperature to 430 °C and gives more accurate prediction compared to the previously proposed equation which is not function of temperature and tensile strength.

Investigation of Dynamic Strain Ageing Effects of Low Alloy Steels 15Kh2MFA and 15Kh2NMFA

2005 ◽  
Vol 482 ◽  
pp. 367-370
Author(s):  
Miroslava Ernestová
Keyword(s):  
Strain Rate ◽  
Tensile Tests ◽  
Dynamic Strain ◽  
Low Alloy Steels ◽  
Strain Rates ◽  
Dynamic Strain Ageing ◽  
Strain Ageing ◽  
Lower Strain ◽  
Wide Range ◽  
Alloy Steels

The paper summarizes results of tensile tests in low alloy steel (LAS) specimens (steels 15Kh2MFA and 15Kh2NMFA). Slow Strain Rate Tensile tests (SSRT) were performed in air at temperatures from 22 to 325°C over a wide range of strain rates from 2.5×10-6 to 1.67×10-3 s-1. The possible effect of strain rate and temperature to mechanical properties of tested LAS is searched for. The dynamic strain ageing (DSA) was observed within certain temperature ranges at lower strain rates tested and its hardening effect in terms of the maximum strengthening stress decreased linearly with the increase of log strain rate. It has been found that the occurrence of susceptibility to environmentally assisted cracking (EAC) of tested steels in high temperature water (HTW) is corelated to the DSA behavior. The result suggest that DSA reduces ductility of reactor pressure vessel (RPV) steel and its role in enhancing the EAC of RPV steels should not be neglected, in view of the coincidence with susceptibility zones for DSA and EAC in terms of strain rate and temperature. A reasonable coincidence was observed between the susceptibility to DSA exhibited by SSRT in air and with the EAC behavior observed in laboratory experiments.

scholarly journals STUDYING THE IMPROVEMENT OF TENSILE STRENGTH OF LOW ALLOY HIGH STRENGTH STEEL WELDS USING AN ECONOMICAL TECHNIQUE

2018 ◽  
Vol 18 (3) ◽  
pp. 498-505
Author(s):  
Abdul Sameea J Jilabi
Keyword(s):  
Tensile Strength ◽  
Weld Joint ◽  
Copper Wire ◽  
High Strength Steels ◽  
High Strength ◽  
Low Alloy Steels ◽  
Joint Efficiency ◽  
Comparison Results ◽  
Alloy Steels ◽  
Welding Processes

Low alloy steels are particularly used in manufacturing several parts in the heavyengineering industries, agricultural equipment and dies which may be subject to servicefailure, and thus may need to be repaired by one of the welding processes. The weldabilityof steels is determined by their sensitivity to cracks that can be prevented by the use ofspecial welding procedures which are often expensive and difficult to use. Manual metal arcwelding of low alloy high strength steels was done firstly, using a cheap electrode (OK46.00), followed by the use of an economical technique which depends on coiling copperwires with different diameters around the cheap electrode. The expensive electrode (OK73.68) was also used for comparison. Results showed an increase in the tensile strength (712MPa) and weld joint efficiency (83.8%) when the expensive iron powder low hydrogencovering electrode (OK 73.68) was used. On the other hand, the tensile strength wasdecreased to (206 MPa) and the weld joint efficiency to (24.2%) when the cheap electrode(OK 46.00) was used. Coiling a (0.6 mm) dia. copper wire around the (OK 46.00) electrodeincreased the tensile strength and weld joint efficiency to (510 MPa) and (60%) respectively.

scholarly journals Technical condition of welded load-bearing metal structures of operated agricultural hoisting cranes

2020 ◽  
Vol 175 ◽  
pp. 11005
Author(s):  
Alexander Scherbakov ◽  
Anna Babanina ◽  
Ivan Kochetkov ◽  
Pavel Khoroshilov
Keyword(s):  
Plastic Deformation ◽  
Metal Structure ◽  
Technical Condition ◽  
Technical Diagnostics ◽  
Low Alloy Steels ◽  
Low Carbon ◽  
Load Bearing ◽  
Metal Structures ◽  
Elastic Plastic ◽  
Alloy Steels

The paper considers the methodology for assessing the technical condition of welded load-bearing metal structures of operated agricultural hoisting cranes. In the course of the study, the relationship between structural, mechanical and magnetic parameters was established during cyclic elastic-plastic deformation of low-carbon and low alloy steels. Based on the analysis, it was concluded that the dependence of the minimum values of the magnetic parameter on the acting stresses Нр(σ) is influenced by the metal structure and its chemical composition. It has been established that the coarser-grained structure of the studied steels under elastic-plastic deformation contributes to a shift in the minimum values of Нр towards lower acting stresses; an increase in the strength characteristics of steels shifts the minimum of Нр toward large values of s, which must be taken into account when conducting technical diagnostics of the elements of the operating metal structures of hoisting cranes. Based on the results of the study, a method for determining the acting stresses in the elements of the metal structures of hoisting cranes was developed, which, by the nature and magnitude of the change in the residual magnetization of the scattering field during their stepwise loading (unloading), allows judging the magnitude of the acting stresses. The work also presents a methodology for assessing the technical condition of welded load-bearing metal structures of hoisting cranes based on the integrated use of passive flux-gate and other control methods, which allows determining the acting stresses used in strength calculations in the identified hazardous zones of concentration of stresses in the elements of metal structures.

Stress Corrosion Cracking of Mild and Low Alloy Steels in CO-CO2-H2O Environments

CORROSION ◽  
1976 ◽  
Vol 32 (10) ◽  
pp. 395-401 ◽  
Author(s):  
MASAMICHI KOWAKA ◽  
SABURO NAGATA
Keyword(s):  
Mild Steel ◽  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Laboratory Tests ◽  
Corrosion Cracking ◽  
Low Alloy Steels ◽  
Wide Range ◽  
Alloy Steels ◽  
Increasing Temperature ◽  
Co2 Environment

Abstract This paper is related to the new stress corrosion cracking phenomenon of mild and low alloy steels in a CO/CO2 environment. The incidents of cracking are described and these were reproduced by laboratory tests. The results obtained are as follows: (1) No stress corrosion cracking of mild steel was found to occur in water containing just CO or CO2. (2) The transgranular stress corrosion cracking occurred only in CO/CO2 environment with water. (3) Stress corrosion cracking occurred in a wide range of CO/CO2 ratios in water. (4) The susceptibility to stress corrosion cracking of mild steel decreases with increasing temperature. (5) No stress corrosion cracking was found to occur on 18Cr-10Ni stainless steel. (6) From the study of electrochemical measurements, the mechanism has been proposed that this form of cracking is stress corrosion cracking rather than hydrogen embrittlement. (7) Prevention of stress corrosion cracking in these environments is discussed.

scholarly journals Study Deformability Ecological Steel (41Cr4)

2018 ◽  
Vol 55 (3) ◽  
pp. 357-360
Author(s):  
Carmen Otilia Rusanescu ◽  
Marin Rusanescu ◽  
Florina Violeta Anghelina ◽  
Ileana Nicoleta Popescu
Keyword(s):  
Heat Treatment ◽  
Plastic Deformation ◽  
Minimum Degree ◽  
Low Alloy Steels ◽  
Continuous Cast ◽  
External Market ◽  
Degree Of Deformation ◽  
Resistance To Deformation ◽  
Alloy Steels ◽  
Low Alloyed Steel

In this paper is studied the hot plastic deformability (plasticity and resistance to deformation) for the low-alloyed steel of heat treatment for mechanical engineering in two ways: compression and tension. Groups of low alloy steels is very important in terms of quality and quantity, the products of these steels have developed internal and external market. The plasticity variation were plotted with the temperature and it was established that the plasticity of the steel increases in the range 700-12000C, then decreases as a result of the firing of the grain boundaries, for the bars obtained from ingot and continuous cast blown it was noticed that the plasticity values are very close. Deformation resistance decreases as the temperature increases. The finest granulation was obtained for a final plastic deformation temperature of 8000C and a minimum degree of deformation of 45%.

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