Effects of high concentration hydrogen during GMA welding of duplex stainless steel

In our research the effects of high concentration hydrogen (argon + 13.5 % to 15.0 % hydrogen) in the shielding gas was compared to pure argon in case of gas metal arc welding of LDX 2404 lean duplex stainless steel. The hydrogen in the shielding gas increased the weld bead width, penetration depth and the average arc voltage too. In the microstructure and hardness distribution no significant differences were observed with the addition of hydrogen in the argon shielding gas

Prediction of the Shear Tension Strength of Resistance Spot Welded Thin Steel Sheets from High- to Ultrahigh Strength Range

The tensile strength of newly developed ultra-high strength steel grades is now above 1800 MPa, and even new steel grades are currently in development. One typical welding process to join thin steels sheets is resistance spot welding (RSW). Some standardized and not standardized formulas predict the minimal shear tension strength (STS) of RSWed joints, but those formulas are less and less accurate with the higher base materials strength. Therefore, in our current research, we investigated a significant amount of STS data of the professional literature and our own experiments and recommended a new formula to predict the STS of RSWed high strength steel joints. The proposed correlation gives a better prediction than the other formulas, not only in the ultra-high strength steel range but also in the lower steel strength domain

Global Approach on the Shear and Cross Tension Strength of Resistance Spot Welded Thin Steel Sheets

Several correlations from the professional literature describing the shear and cross tension strength (STS and CTS) of resistance spot welded (RSWed) thin steel sheets were investigated. Some of them need chemical composition or weld nuggets strength hardness as input parameters, making them hardly applicable in the planning stage of the joints. Using STS and CTS data collected from over 250 papers, selected correlations were tested, whether they are applicable to predict the STS and CTS of the RSWed joints at the planning stage to help designers plan their static-loaded welds strength. Most correlations had limitations in the applicable base materials' tensile strength range. Therefore, new equations for STS and CTS are proposed, which can be used to plan in the 300–18900 MPa base metals tensile strength range for similar and dissimilar RSWed joints of thin steel sheets

A hőkezelés hatása duplex acél hegesztési varratainak szövetszerkezetére

A duplex acélok szövetszerkezete általában 50% ferritből, a fennmaradó rész pedig ausztenitből épül fel. A ferrit fázisban 700 °C alatt jelentősen csökken az ötvözőként használt nitrogén oldhatósága, ami króm-nitrid-kiválásokat okoz. Kutatásaink során azt találtuk, hogy elektrokémiai maratással kimutathatók a króm-nitrid-kiválások. További eredményként azt kaptuk, hogy a nitridkiválások a szekunder ausztenit nukleációs helyeiként működnek

Effect of Heat Treatment on the Microstructure of Duplex Stainless Steel Welds

Duplex stainless steels (DSS) are gaining in popularity due to their characteristic features, excellent mechanical properties, and corrosion resistance. The microstructure of DSSs consists of ferrite up to 50 %, and the rest is built up from austenite. The ferritic microstructure can cause chromium-nitride precipitation because the nitrogen solubility in the ferrite phase is very low below 700 °C. Our research showed that electrochemical etching is an acceptable process for revealing chromium-nitrides. Additionally, our research points out that chromium-nitride acts as a secondary austenite nucleation site

High Heat Input Welding of NSSC 2120 Type Lean Duplex Steel

Duplex stainless steels offer a high strength alternative to stainless steel, while providing excellent corrosion resistance, due to their dual-phase microstructure. This microstructure can be significantly influenced during welding, thus the maximum recommended heat input is usually 2.5 kJ/mm. In this research, we inspected the high heat input (3 kJ/mm) weldability of NSSC 2120 lean duplex stainless steel, which is designed and developed specifically for this purpose. The welds were evaluated by metallographic techniques and corrosion tests. It was found the NSSC 2120 grade can be welded with high heat input without deterioration in the phase balance and microstructure

Physical and Theoretical Modeling of the Nitrogen Content of Duplex Stainless Steel Weld Metal: Shielding Gas Composition and Heat Input Effects

Duplex stainless steels (DSSs) are gaining more and more attention in corrosion-resistant applications and also in the transport and automotive industry. The outstanding mechanical and corrosion properties of DSSs highly depends on the austenite-to-ferrite phase balance (A/F). This phase ratio can shift in a large scale during welding. Thus, the heat input and the shielding gas composition should be optimized. Nitrogen addition to argon shielding is frequently used in DSS welding, because it is a potent austenite former. The dissolved nitrogen content in the heat-affected zone and the weld metal (WM) predetermines the A/F. To determine the effect of heat input and nitrogen content in shielding gas, two different heat inputs and six different gas compositions were used in autogenous tungsten inert gas welding. An improved theoretical model was established in order to simulate theWMdissolved nitrogen content, which calculates it with less error than the initial models. The correlation between nitrogen content and arc voltage was also determined. This improved model delivers the basics for shielding gas selection and the subsequent weld design for optimal A/F for industrial applications

Az anyagátviteli mód és a nagy hidrogén tartalmú védőgáz hatásai duplex korrózióálló acél hegesztett kötéseire

Kutatásaink során nagy hidrogén tartalmú védőgázkeverék (Ar + 15 térf.% H2) hatásait vizsgáltuk 2101-es sovány duplex acél, huzalelektródás védőgázos hegesztéssel készített varrataira. A hegesztési varratokat rövidzárlatos ívvel és kis hőbevitellel járó (CMT; cold metal transfer) eljárásváltozattal is meghegesztettük. Hidrogén hatására mindkét eljárás esetében nőtt a varratszélesség (max. 40 %) és a beolvadási mélység (max. 141 %). A korrózióállóság CMT eljárás esetén a H2 hatására romlott (~36 %)