Thick Stainless Steel Plate Research Articles

Productivity improvement in butt joining of thick stainless steel plates through the usage of activated TIG welding

Activated tungsten inert gas (A-TIG) welding is one variant of conventional TIG welding where a thin layer of suitable activating flux is deposited on the parent components prior to constituting the arc in order to harness enhanced penetration. Despite several benefits, industries are still reluctant in overwhelmingly using this new variant. This article attempts to highlight the productivity benefits in employing A-TIG welding either together with or superseding TIG welding during butt joining of 10-mm-thick AISI-316L austenitic stainless steel components. Initially, three single-component fluxes (Cr2O3, Fe2O3, and SiO2) are tested in forehand welding technique under varying currents but with straight polarity. Filler rod having similar metallurgical composition is also delivered during homogeneous welding. The extent of capability of each of the three fluxes is analysed by comparing the weld bead geometrical parameters (penetration, puddle width, and reinforcement) with the same obtained in conventional TIG welding under similar set of parameters. While Fe2O3 and SiO2 fluxes are found capable in enhancing penetration and reducing puddle width and heat affected zone, Cr2O3 flux failed to exhibit better performance. The article further demonstrates the time saving that can be obtained by adopting flux-assisted TIG for joining 10-mm-thick plates. When joining from both the faces is allowed, about 70% less time is desired if a combination of A-TIG and TIG is employed rather than using only TIG welding. If joining from only one face is allowed, then also usage of flux can reduce welding time by 33%.

Investigations on the effect of surface coatings on the weldment properties on chromium manganese stainless steel gas tungsten arc welded plates

This paper reports the enhancements for the effects of specific fluxes such as Tungsten Carbide and Chromium Oxide on the weldment properties such as micro hardness, weld bead geometry and tensile strength obtained with Gas Tungsten Arc Welding Process (GTAW) applied to 6 mm thick Chromium Manganese stainless steel plates. The significant expense of Nickel has made Chromium Manganese stainless steel as an option for conventional 300 arrangement stainless steel. The two fluxes tungsten carbide and chromium oxide were utilized in powdered structure. The tensile test, micro hardness test and corrosion resistance test was conducted to reveal the effect of fluxes on the weldment properties. Results of tensile shows that considerable enhancement in tensile strength and elongation of about 20% increase in case of Chromium Oxide coated samples and 10% increase in case of Tungsten Carbide samples when compared to uncoated specimen. In case of microhardness, 10% increase is exhibited for coated samples compared with uncoated samples. The corrosion rate of coated samples found to be highly resistant for coated samples, which sums to be 300% more than that of uncoated samples. The effect of corrosion rate on the specimens was seen by conducting SEM analysis after the corrosion test. The SEM analysis uncovered that the coating covers the limits encompassing the inclusions and encloses dendrites which reduce the pitting corrosion of the parent metal.

Evaluation of through-thickness residual stresses in conventional and narrow grooved stainless steel welds

Thick AISI 304L stainless steel plates were welded using the gas metal arc welding process, and through-thickness residual stresses were evaluated by finite element simulation and the deep hole drilling technique. 3D moving heat source-based thermo-mechanical models were implemented to evaluate through-thickness residual stresses. The effects of the weld groove geometries and external restraints on the pattern of through-thickness residual stresses were studied. The maximum magnitude of locked-in residual stresses was recorded beneath the top surface, at a depth of around 6 mm. In comparison to conventional weld groove, the narrow weld groove configuration exhibited a 20–40% reduction in peak residual stresses. A significant rise in residual stresses was observed in constrained welds. The effect of the yield strength of the filler material on the evaluation of the through-thickness residual stress distribution in the course of finite element modeling was illustrated. The evolution of through-thickness residual stresses was also assessed concerning each weld pass.

Understanding root humping in high-power laser welding of stainless steels: a combination approach

High-power laser welding is an efficient way for joining the thick plates in the industries. However, full penetration laser welding of thick plates is prone to form weld imperfections such as undercuts, root humps, and porosity. In this paper, numerical simulation and laser welding experiments are combinedly carried out to investigate the dynamics of the keyhole and molten pool and understand the formation mechanism of root humping during full penetration fiber laser welding of thick stainless steel plates. Besides, the microstructure of the welded joint is analyzed. Good agreements are obtained between the numerical simulation and experimental results. The results indicate that recoil pressure, surface tension, and gravity are the main driving forces for the formation of root hump. The melt flow driven by the recoil pressure near the bottom of the keyhole is an initial and direct formation cause of the root hump. Welding speed is an important factor for the growth of root hump. Local solidification of the rear weld pool path is a hinder for the continuous growth of root hump and can cause a periodic root humping weld.

Design and application of multifunctional physical model test device for movement and accumulation process of rapid long-runout landslide

There are many factors affecting the movement and accumulation process of rapid long-runout landslide. During the developing the physical model test device, it is necessary to meet the needs of multi-factors, so as to achieve multi-functional purposes. The device is 3.40 m long, 0.56 m wide and 1.35 m high in initial state (vertical angle=20° and horizontal angle=0°). The design includes three modules: volume adjustment of slide body, slope adjustment of upper slide groove and horizontal angle adjustment of horizontal slide groove. Two kinds of materials, 3 mm thick stainless steel plate and 8 mm thick tempered glass, are used as the processing raw materials, leading to good durability. Moreover, the universal wheel is installed in the form of component assembly to facilitate the handling of the experimental instrument. Based on sand and pebble granular materials, the physical model tests with respect to the movement and accumulation process of rapid long-runout landslide are preliminarily carried out by using the developed device. The effects of slope, horizontal angle, height of sliding body and base material on sliding distance are briefly analyzed.

Microstructure and mechanical properties of dissimilar Ti/Nb/Cu/steel laser joints

The absence of intermetallic phases in Fe/Cu, Cu/Nb and Nb/Ti binary systems opens the possibility to obtain reliable joints between titanium alloys and steels by using a multimaterial copper/niobium insert. Continuous Yb:YAG laser welding of 1 mm thick titanium and 316L stainless steel plates through niobium/copper multimaterial insert was performed. The use of a 100 µm laser beam allowed producing isolated molten zones and thus completely avoiding the formation of brittle intermetallic phases, according to SEM and XRD analysis. The effect of energy per unit length applied to the niobium/copper welds on the mixing process and mechanical properties of the joints was investigated. A ductile fracture systematically occurred in the unmelted copper zone of the joints at maximal average UTS of 250 MPa.

Experimental investigation on thermal insulation performance of air interlayer under an impinging jet at high temperature

Air interlayers are widely used in building envelope to reduce heat transfer between indoor and outdoor environments. However, it is less common to apply to industrial processes in confined spaces, especially when the heating source is at high temperature with high velocity. In this paper, a special structure with air interlayer between two plates for thermal insulation was derived from an industrial manufacturing application. The effects of the interlayer on heat transfer was investigated under an impinging jet at high temperature. An experimental mock-up was designed to produce high temperature (∼ 500 °C) impinging gas jet with relative stable high velocity (∼56 m/s) at the nozzle exit. The impingement surface of the test structure was covered with a 2mm thick stainless-steel plate at a distance of 5mm, which formed a horizontal air insulation layer. Benchmark test was also conducted after the removal of the stainless-steel layer. In each case, a standard procedure within a duration of 30 min was applied to minimize the variations of testing conditions. The temperatures at both inner and outer surfaces of the structure, as well as the temperatures from inside and outside the air interlayer, were measured by thermocouples. In addition, an analytical model to account for the effects of air insulation was proposed to compared with experiments. The results showed that, the air interlayer can reduce the highest temperatures for about 48 °C. The temperature difference at the end of the experiment was about 30 °C. The analytical model was in good agreement with the experimental data and the maximum difference was ∼6.5 °C.

A Feasibility Study of CFETR 1/8 Sector Vacuum Vessel Mock-Up

The vacuum vessel (VV), one of the important components for the Chinese Fusion Engineering Test Reactor (CFETR) superconducting magnet tokamak, can provide an ultrahigh vacuum and clean environment for plasma operation. The CFETR VV was preliminarily designed to be a torus with a D-shaped cross section, eight upper vertical ports, eight equatorial ports, and eight lower ports. In order to verify the design and key technologies to be used in the future, a 1/8 VV sector mock-up has been designed and fabricated at the Institute of Plasma Physics, Chinese Academy of Sciences (abbreviated ASIPP). In this paper, the mock-up is used to demonstrate thick austenitic stainless steel plate hot forming, welding, cutting, part segment assembly, and other technologies and developments. The design considerations and criteria of the 1/8 sector mock-up are discussed in detail. Based on these considerations, the main design parameters and characteristics of the 1/8 VV sector mock-up are described, including the inner shells, outer shells, and stiffening ribs between them and the straight line, arcs, and the tangential joint between them. Finally, the research and development of technologies for the mock-up manufacture that has been carried out at ASIPP is discussed.

Underwater cutting of 50 and 60 mm thick stainless steel plates using a 6-kW fiber laser for dismantling nuclear facilities

Underwater cutting of 50 and 60 mm thick stainless steel plates with a 6-kW fiber laser was performed as a fundamental study for application to dismantling nuclear facilities. For this purpose, an underwater cutting head was developed by upgrading our previously developed in-air cutting head. A waterproof function was added while the optical design of the in-air cutting head was maintained. In the developed head, a single supersonic minimum length nozzle was applied without any complicated nozzle features because it was enough to make a local-dry-zone. With this head, cutting tests were performed for pierced and non-pierced specimens. The pierced specimen showed a slightly better cutting performance than the non-pierced specimen. However, the cuttings were adequate for both types of specimens with thicknesses of 50 and 60 mm. In the cutting results for the non-pierced specimens, the maximum cutting speeds were 80 mm/min for the 50 mm thickness and 40 mm/min for the 60 mm thickness. To the best of our knowledge, the results from this study show the best cutting performance in terms of speed and thickness for the same laser power among the reported results of underwater laser cutting. The kerf width was also measured for each cutting. As in ordinary laser cutting, the kerf widths were narrow. For the cutting at each maximum speed, the kerf widths for the 50 mm thickness were 1.6 mm for the front surface and 0.7 mm for the rear surface, and the kerf widths for the 60 mm thickness were 1.5 mm for the front surface and 1.2 mm for the rear surface. It is expected that the results of this study will contribute to the continued development of underwater cutting research for dismantling nuclear facilities.

Spray cooling of hot steel plate using aqueous solution of surfactant and polymer

In the current work, authors have performed extensive spray cooling experiments on a 6 mm thick hot stainless steel plate (>900 °C). The work has been separated into two distinctive parts. The first part involves optimization of water flow rate and spray impingement height based on maximum surface cooling rate and heat flux value. The highest cooling rate and heat flux of 133.7 °C/s and 2.21 MW/m2 were attained for a water flow rate of 16 lpm and impingement height of 6 cm. In the second part, different surfactants (cationic, CTAB; anionic, SDS; non-ionic, Tween 20), and polymer (PVP, water soluble) were added in to the water to study its impact on heat transfer parameters such as surface cooling rate, heat flux, and heat transfer coefficient. Amongst all the additives, the maximum enhancement in cooling rate and critical heat flux was achieved for non-ionic (Tween 20) based water solution which is 25.6% (168.2 °C/s) and 19.91% (2.65 MW/m2) higher than what had been attained by water spray. High speed photography was used at a lower temperature to visualize a single droplet impact and to understand the effect of surface tension and underlying physics on the heat transfer phenomenon. This study revealed that upon impingement, surfactant and polymer added drops disintegrate into multiple drops, increasing the overall contact area, and thereby enhancing the heat transfer rate.

Influence of welding current on bead profile and mechanical properties of double sided submerged arc welding of AISI 304 austenitic stainless steel

Abstract Submerged arc welding is a high productivity process for joining thick sections of steels, used particularly in ship building, pipe welding, construction applications and surfacing. In the present work double sided submerged arc welded was performed on 12 mm thick austenitic stainless steel plates to determine the effect of welding current on bead profile and mechanical properties. As the welding current increases, reinforcement height, reinforcement area, penetration depth and area, bead overlap area are found to show improvement in almost linear fashion. The welding current doesn’t much influence the weld bead width. The average bead contact angle decreased with increase in welding current. The tensile properties were found to increase steeply with increase in welding current. Two different morphologies of δ ferrite namely, skeletal and lathy structures were observed in the fusion zone.

Study of Microstructure 304L Austenitic Stainless Steel Weld Deposited by GTAW for Root Pass and SMAW for Filler Passes

In the present experimentation, a 10mm thick austenitic stainless steel plate type 304L is welded using single V-joint configuration and approaching the joint from one side. Back purging has been employed to protect the rear side of the root pass weld metal against oxidation. The root pass has been deposited by gas tungsten arc welding (GTAW) process. The filler passes are deposited by shielding metal arc welding (SMAW) process at 90A and 120A welding currents giving heat inputs of the order of 0.679 and 0.933 kJ/mm respectively while the speed of weld deposition was kept practically constant. The results of experimentation show that the micro-hardness of weld metal and heat affected zone (HAZ) of weldments produced at lower heat input is higher whereas impact toughness value of weld metal and HAZ is lower than that of joints produced at higher heat input. The microstructure of weld metal and heat affected zone developed at lower weld heat input has been observed finer in comparison to that resulted at higher heat input. This has primarily happened due to a higher rate of cooling at low heat input.

Experiments on formation mechanism of root humping in high-power laser autogenous welding of thick plates with stainless steels

Deep penetration laser welding is an efficient and effective way to produce the heavy section structure. Deep penetration can be achieved by high-power autogenous laser welding; however, it poses a significant challenge in obtaining good quality of welds, which are free of imperfects such as root hump, under-fill, and collapse. It is partially attributed to a lacking of understanding on the formation of imperfects. In this paper, we looked into the formation mechanism of root humping experimentally. The laser autogenous welding were implemented using a 10 kW fiber laser on thick stainless steel plates. A high-speed imaging system was applied to observe the metallic vapor and molten pool flow during the welding process. The formation mechanism of root humping with different focal positions were analyzed and discussed. The results showed that the most important welding parameter was the focal position; it had a strong effect on the formation of root hump; it affected the penetration mode of laser keyhole welding. The root hump had a large volume and were generated periodically when a positive defocus was applied. When a negative defocus was applied, the root hump had a small volume and with no obvious periodicity. On the other hand, the welding speed could be optimized to suppress root hump only when a negative defocus was applied. Finally, applying a bottom shielding gases played a positive role in reducing root hump. The results from our study provides the evidences to develop the strategies to suppress root hump during high-power laser autogenous welding on thick metal plates.

Cutting performance of thick steel plates up to 150 mm in thickness and large size pipes with a 10-kW fiber laser for dismantling of nuclear facilities

The cutting performance of thick steel plates and large size pipes with a 10 kW fiber laser was studied for the dismantling of nuclear facilities. First, thick steel plates of up to 100 mm were tried to be cut at a high speed. For the thickness of 100 mm, both stainless steel and carbon steel plates were cut at maximum cutting speeds of ∼30 mm/min. And narrow kerf widths of less than 5 mm were obtained for all cutting tests. Second, a 150-mm thick stainless steel plate near the cutting thickness limit was attempted to be cut. The specimen was able to be cut even with a low cutting speed of 3 mm/min. To the best of our knowledge, this thickness is the largest among the published reports with a laser power of 10 kW. And this corresponds to a cutting capability in which most thick structures in a nuclear reactor can be cut. In addition, large size stainless steel pipes were also attempted to be cut. For a 165 mm diameter pipe, it was possible to be cut at high speed by one scan at a speed of 50 mm/min and round trip scan at a speed of 100 mm/min. This result implies that high-speed cutting was also possible for most pipe-type components inside the nuclear reactor. As a result, our 10-kW laser cutting system showed very efficient cutting performance in terms of the cutting speed and thickness. Moreover, the cuttings showed narrow kerf widths of less than 5 mm even for very thick steel of up to 150 mm in thickness. In the future, it is expected that the results of this work will contribute to cutting thick metal structures as basic research data in the dismantling of nuclear facilities using a laser. In addition, it is also expected that this work will contribute to other industrial fields requiring a thick steel cutting technique.

Mechanisms for Improvement of Weld Appearance in Autogenous Fiber Laser Welding of Thick Stainless Steels

High-power fiber laser welding is an efficient and effective way to produce heavy section structures. However, there is a significant challenge in producing the welds with free of imperfections such as nail-head-shaped welds, spatters, and root sagging. This is partially due to a lack of understanding of the welding mechanism of high-power fiber laser. In this paper, we were especially interested in the mechanism to improve the appearance of welds, and we focused on the autogenous laser welding on thick stainless steel plates by a 10 kW fiber laser. To look into the relations of process parameters and the quality of welds, a high-speed imaging system was applied to observe the molten pool flow and vapor plume during the welding process. The appearances of welds subjected to different welding conditions were analyzed. The results showed that (1) nail-head-shaped welds were suppressed by using a gas jet during laser welding process. (2) In the forward welding, a gentle upwelling molten metal flow on the rear keyhole wall, a deeper weld pool and a weaker vapor plume resulted in no spatter. (3) The gravity affected the formation of underfills and root sagging significantly during autogenous laser welding of thick plates. (4) When the workpiece was placed vertically in the transverse position, the welding process was stable without an aggregation of molten melt at the back surface. Moreover, the mechanisms of forming root sagging and humps were different at the top surface.

A new approach to increase the subsurface flaw detection capability of pulsed eddy current technique

In this paper, the detection of subsurface flaws by pulsed eddy current (PEC) technique has been studied. Experiments have been carried out on an 8.0 mm thick stainless steel plate with subsurface flaws located at different depths below the surface by varying the excitation rise time (Er). The conventional PEC signal parameters like peak amplitude (Vp), time-to-peak (Tp) and rise time (tr) are influenced by noise and could not be effectively used to detect flaws located beyond 4.0 mm below surface. In this context, a new approach based on fitting the PEC response pulse to a modified inductor current equation has been proposed. Based on this approach, two parameters viz. time constant (τ) and voltage parameter (V1/V0) have been derived and used for detection and separation of flaws. The study shows that the two parameters derived from the proposed approach can be used to detect flaws located 6.0 mm below the surface with improved sensitivity. The advantage of the proposed approach is that, it does not require subtraction from reference signal to detect flaws. The derived parameters are also able to differentiate the subsurface and surface flaws.

The influences of welding parameters on the metal vapor plume in fiber laser welding based on 3D reconstruction

Fiber laser has significant advantages in the welding of moderately thick stainless steel plates. However, the influences of welding parameters on interaction behavior are still not fully understood. The metal vapor, as process product of fiber laser welding, carries abundant information of interaction behavior. A novel three-dimensional reconstruction technique was used to establish spatial structure of metal vapor during fiber laser welding. The spatial field of temperature and electron density were computed based on the 3D distribution of radiation intensity, as well as the relative spectral intensity method. Experimental results showed that the temperature of the metal vapor was generally at about 4000–5500 K. Defocusing amount had a significant influence on metal vapor and its energy interaction process in fiber laser welding.

Investigation on the Effect of Activating Flux on Tungsten Inert Gas Welding of Austenitic Stainless Steel Using AC Polarity

Tungsten Inert Gas (TIG) welding is a popular joining process due to its inherent capability in producing superior quality welding in a wide range of materials. However, lower productivity of it paves the way for introduction of a number of variants of TIG welding, including Flux Bounded TIG (FB-TIG) welding and Activated TIG (A-TIG) welding. In this paper, variations of weld morphology and characteristics with heat input in AC A-TIG welding of both bead-on-plate and butt joining of 6mm thick 316L stainless steel plates using TiO 2 , Cr 2 O 3 and Fe 2 O 3 as activating flux and a stainless steel filler material are investigated. Results are also compared with that obtained in conventional TIG welding. Variations of various weld characteristics viz. depth of penetration, width of weld bead, reinforcement, Reinforcement Form Factor (RFF), and Penetration Shape Factor (PSF) against change in heat input are analyzed and compared. It is observed that TiO2 and Fe 2 O 3 fluxes effectively enhance the penetration due to increase in fluidity and wettability of molten metal and, at the same time, reduce the width of weld bead; whereas, Cr 2 O 3 flux gives inferior results as it reduces penetration instead of increasing it as compared to conventional TIG welding.

Improvement of cutting performance for thick stainless steel plates by step-like cutting speed increase in high-power fiber laser cutting

A study was conducted to improve the cutting performance of a 60-mm thick stainless steel plate using a 6-kW fiber laser. Two techniques for improving the initial cutting performance were evaluated by preheating the work piece with a waiting time and step-like cutting speed increase. Both techniques showed improved cutting results compared to constant speed cutting. Among them, the method with a step-like cutting speed increase showed the better result in terms of cutting performance. As a result, a 60-mm thick stainless steel plate was cut at a maximum cutting speed of 72 mm/min with a preheating cutting speed of 24 mm/min. In order to confirm the effect of preheating, an additional experiment was performed to measure the temperature variation during the cutting process. Through this experiment, preheating temperature conditions were found to allow the specimen to be cut. It is expected that the results of this work will contribute to improving the cutting performance of thick metal structures in various industrial fields, as well as the dismantling of nuclear facilities using lasers in the future.

Detection of fastener loosening in simple lap joint based on ultrasonic wavefield imaging

Joints in aero-mechanical structures are critical elements that ensure the structural integrity but they are prone to damages. Inspection of such joints that have no prior baseline data is really challenging but it can be possibly done using the Ultrasonic Propagation Imager (UPI). The feasibility of applying UPI for detection of loosened fastener is investigated in this study. A simple lap joint specimen made by connecting two pieces of 2.5mm thick SAE304 stainless steel plates using five M6 screws and nuts has been used in this study. All fasteners are tightened to 10Nm but one of them is completely loosened to simulate the damage. The wavefield data is processed into ultrasonic wavefield propagation video and a series of spectral amplitude images. The spectral images showed noticeable amplitude difference at the loosened fastener, hence confirmed the feasibility of using UPI for structural joints inspection. A simple contrast maximization method is also introduced to improve the result.