Strength of spot-welded steel sheets in corrosive environment

Stress Corrosion Cracking (SSC) is considered to be connected to the fragility through hydrogen phenomenon. The tests were made on samples of steel R510. On these, a circular weld seam was deposed. The samples were subdued to different thermal treatments and were maintained in a corrosive test environment. Stress Corrosion Cracking (SCC) is considered to be connected to the fragility through hydrogen phenomenon. This type of corrosion depends on the steel composition, on its structure, its mechanical properties, on the state of the steel tension, the state of the area and, last but not least, on the testing environment.

International Journal of Pressure Vessels and Piping, 2007

In order to gain the benefits of weldable high-strength steels in pressurized equipment applications, satisfactory toughness and crack properties of the welded joint, both in the weld metal and the heat-affected -zone (HAZ), are required. Experimental investigations of toughness and crack resistance parameters through static and impact tests of a high-strength, low-alloy steel (HSLA) with a nominal yield strength of 700 MPa and its welded joint, were performed on Charpy-sized specimens, V-notched and pre-cracked, of the parent metal, weld metal and HAZ. The selected electrode produced slight undermatching and enabled the welded joints to be manufactured without cold cracks. The impact energy and its parts responsible for crack initiation and propagation were determined by toughness evaluation. Crack sensitivity, defined as the ratio of the impact energy for V-notched and for pre-cracked specimens, enabled a comparison of the homogeneous microstructure of the parent metal and the weld metal, and of the heterogeneous microstructure of the heat-affected-zone (HAZ), which indicated a better crack toughness behaviour of the HAZ. The results obtained showed that the toughness and crack resistance of the weld metal were significantly lower than those of the parent metal and the HAZ. The fracture mechanics parameters, J Ic integral, and plane strain fracture toughness, K Ic , as well as J resistance curves expressed the degradation less. r

2003

The growing use of steel in civil, mechanical and nuclear constructions is justified by the reduction of labor time and costs due to assembly simplicity. Almost all steel structures and components are manufactured using welding processes, which can introduce some defects (cracks, for instance) on the structure or component. These defects must be evaluated and controlled within allowed levels indicated by the existing codes. Crack propagation resistance of welded joints, one of the major concerns, can be assessed through fracture tests. On these cases, the region next to the melted zone, denominated heat affected zone, is more sensitive to crack initiation and growth, which, means that the crack propagation resistance of this region is a critical parameter to be evaluated. On this work, the crack propagation resistance of the heat affected zone of USI-SAC-50 welded joints is experimentally evaluated on the longitudinal and transversal directions with respect to the weld bead, using t...

Welding in the World, 2012

N. den Uijl, T. Okada, T. Moolevliet, A. Mennes, E. van der Aa, M. Uchihara, S. Smith, H. Nishibata, K. Fukui: IIW-2162-11 (III-1573-10) Performance of resistance spot welded joints in advanced high strength steel in static and dynamic tensile tests. Welding in the World 7/8, 2012. The performance of resistance spot-welded joints in advanced high-strength steel sheets is critical for the application of these materials in safety-critical areas. To be able to predict the performance of such joints from available material data would be of great benefit to the automotive industry. This report starts with a review of literature about various aspects of spot weld performance in advanced high-strength steels. It then describes experimental work whereby a set of resistance spot-welded joints in various advanced high-strength steels was tested in lap shear and peel-type tensile testing. Testing was done both statically and dynamically. The steel sheet materials varied in microstructural and chemical compositions, strength and thickness. The goal of the tests was to investigate possible relations between material characteristics and performance of the welded joints. Therefore, the experimental results are related to several material parameters, i.e., sheet thickness, base metal yield and tensile strength, carbon content and various Carbon Equivalent numbers.

2007

Procedia Engineering, 2011

In this paper, fatigue tests are carried out on spot welded and spot weld-bonded joints of mild steel and ultra-high strength steel plates. The fatigue strength of the spot weld-bonded joints is higher than that of the spot welded joints. On the spot weld-bonded specimens, the strain distribution around the bonded area during fatigue tests is measured by using strain gauges to investigate the interfacial debonding behavior of adhesive bonding. According to the strain distribution measurement, the debonding initiates from the edge of the adhesive bonding, and propagates to the spot weld nugget. The fatigue strength is improved because the stress concentration of the nugget edge is considerably reduced in large part of fatigue life.

Metals, 2021

As the need for duplex stainless steel (DSS) increases, it is necessary to evaluate hydrogen stress cracking (HSC) in dissimilar welded joints (WJs) of DSS and carbon steel. This study aims to investigate the effect of the weld microstructure on the HSC behaviour of dissimilar gas-tungsten arc welds of DSS and carbon steel. In situ slow-strain rate testing (SSRT) with hydrogen charging was conducted for transverse WJs, which fractured in the softened heat-affected zone of the carbon steel under hydrogen-free conditions. However, HSC occurred at the martensite band and the interface of the austenite and martensite bands in the type-II boundary. The band acted as an HSC initiation site because of the presence of a large amount of trapped hydrogen and a high strain concentration during the SSRT with hydrogen charging. Even though some weld microstructures such as the austenite and martensite bands in type-II boundaries were harmless under normal hydrogen-free conditions, they had a neg...

This paper presents the analysis of the temperature and exploitation time impact on the resistant measure to brittle fracture of welded joint constituents of the new and exploited low-alloyed Cr-Mo steel A-387 Gr. B from the aspect of application of the parameters obtained by tensile testing and parameters obtained by fracture mechanics testing. The exploited parent metal is a part of the reactor mantle which has working for over 40 years and is in the damage repair stage, wherein it is being replaced with a new material. Basic characteristics of the material strength, as well as the stress-elongation curves required for stress analysis are obtained by tensile testing. The testing of plane strain fracture toughness is conducted in order to determine the critical stress intensity factor, KIc, that is, assessment of behavior of the new and exploited parent metal, welded metal and heat affected zone from the side of the new parent metal and from the side of the exploited parent metal in the

2014

In this study the residual stress distributions of spot welded advanced high strength steel (AHSS) sheets are examined. Resistance spot welded and gas tungsten arc spot welded DP 600 specimens are manufactured and tested for residual stresses. In the case of resistance spot welding (RSW) both single-pulse and two-pulse current are used. These measurements are utilized to validate coupled electrical-thermal-mechanical Finite Element Analysis (FEA) using MSC.Marc software. The analysis is performed on a two-dimensional axisymmetric finite element model. Different mechanisms occur during the welding e.g. electrode displacement, deformation of the weld nugget and distribution of the contact pressure at both sides and they are all taken into consideration. The cross-section macrostructures of the welded specimens are examined to compare the weld nugget and HAZ sizes to the predicted values. The simulated weld nugget sizes are in good agreement with the experimental results. The validated...

Materials Science and Engineering: A, 2020

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Welding in The World, 2021

This study deals with the fatigue strength of high-frequency mechanical impact (HFMI)-treated unprotected structural details made of mild steel S355 considering the influence of corrosive environmental conditions. The investigations are carried out on butt welded specimens with sheet thickness t = 15 mm and on transverse non-load-carrying attachment specimens with sheet thickness t = 25 mm. Two different methods were applied for the simulation of marine corrosive environment in the laboratory. Specimens first were deposited in a salt spray chamber and then tested subsequently dry at laboratory-air conditions considering the influence of corrosion on the crack initiation. Alternatively, and to cover the effects of corrosion on the crack growth, artificial seawater was used for pre-corrosion, and after a defined timespan, fatigue tests were performed simultaneously with the specimen resting in the corrosive medium. The corrosion fatigue tests were performed in as-welded and HFMI-treated conditions at a stress ratio R = 0.1 under axial tensile and 4-point bending cyclic loading. The test results are evaluated to determine the characteristic fatigue strengths for fixed slopes m = 3 and m = 5 according to IIW recommendations for the as-welded and for the HFMI-treated condition respectively. The results of the experimental investigations based on the nominal stress approach show that the fatigue strength of both specimen types could be significantly increased by the application of HFMI treatment compared to the corresponding specimens in the as-welded condition even if exposed to the investigated corrosive conditions. The comparison with the design proposals of IIW shows that for HFMI-treated butt welds, no reduction of the FAT class due to corrosion is required and the recommended FAT class is still valid. The results for the HFMI-treated transverse attachments are slightly below the design curve recommended by IIW and a proposal to consider corrosion is derived for this case. Additional numerical investigations by applying the effective notch stress (ENS) approach are performed to determine notch stress curves. It was found that for the corroded specimens in the as-welded condition, the FAT class according to IIW could not be reached and adjustments of the existing rules are necessary to consider corrosion effects. However, it can be concluded that the effective notch fatigue resistance recommended by IIW is still applicable in the case of corroded HFMI-treated structural details. Keywords Fatigue strength • Corroded welded joints • S355 • High-frequency mechanical impact (HFMI) treatment • Corrosion fatigue • Effective notch stress design Recommended for publication by Commission XIII-Fatigue of Welded Components and Structures * I.

Advances in Materials Sciences, 2013

Fracture evaluation of welded joints in high-strength steels, with bainitic and martensitic structures, is presented and cracking mechanisms discussed. Hot cracks or microcracks formed during welding are further expanded as cold cracks on cooling. The cause of cracking is shown to be low temperature of weld solidification and deformation-induced contraction. Hydrogen can also be an important factor in this cracking.

In this paper, behaviour of resistance spot welded joint was studied under tensileshear and coach-peel loading condition. Failure modes of resistance spot welds, pullout and interfacial, were investigated based on experimental observation. Optical micrographs of the cross sections of spot welds in shear-tensile and coach peel specimens before and after failure are examined to understand the failure mechanism. Results showed that there is a critical fusion zone size to ensure pullout failure mode. The experimental results showed that in pullout failure mode during shear-tensile test, necking is initiated at nugget circumference in the base metal and then the failure propagates along the nugget circumference in the sheet to final fracture, while pull out failure during coach peel test occurred by crack initiation and propagation near the weld nugget/HAZ boundary. The critical fusion zone size required to ensure pullout failure mode during tensile shear test was larger than that of during coach-peel test.

This project work is dedicated to study the influence of welding process on mechanical properties (such as ultimate tensile strength, hardness, and impact toughness) of welded structural steel component. In this work three grades of welded structural steel have been developed by using three different grades of electrodes such as E7016, E7018 and E7024. Comparative study has been made between the three grades of welded structural steel work pieces. Nondestructive test methods are used to find the quality of the weld. There after mechanical properties have been evaluated experimentally by preparing all specimens as per the ASTM standards. Based on the results of the tests carried out on the welded specimen using the three different grades of electrodes it is observed that the structural steel welded using E7016 grade exhibits better mechanical properties and hence crack resisting capability or fracture toughness . The stress intensity factor for the structural steel welded using E7016 has been evaluated by using the data obtained from the fracture toughness test. The stress intensity factor thus obtained is validated by using FEM. Finally, mini hydraulic excavator bucket has been taken for the static stress analysis in the welded region.

2007

In addition to the strength and toughness properties, the fatigue properties of welded joints are necessary for the design of high-strength steel structures exposed to variable loading. Wöhler curves were determined for smooth tensile specimens tested with variable loading. The fatigue behaviour of a welded joint can be improved by removing the overfill; however, the fatigue properties are still lower than the values for the parent metal. Tests with pre-cracked specimens have shown the difference in the fatigue-crack growth-rate properties to be less significant than other crack parameters.