Duplex stainless steels are gaining greater interest due to their increasing amounts of application fields. Accordingly, there is a need for awareness of problems associated with improper microstructural distributions such as δ-ferrite (delta-ferrite), austenite and other important intermetallic phases that may form in these steel weldments. Since δ-ferrite versus austenite ratio profoundly influences corrosion and mechanical properties, optimum δ-ferrite ratios must be kept approximately within 35-65 vol % and balance austenite to maintain satisfactory corrosion and mechanical properties on welding of these steels. Cooling rates of welds and alloying elements in base metal are the major factors that determine the final microstructure of these steels. In this work, 3 mm thickness of 2205 duplex stainless-steel plates were TIG (Tungsten Inert Gas) welded with various amounts of nitrogen gas added to argon shielding gas. Specimens were joined within the same welding parameters and cooling conditions. As nitrogen is a potential austenite stabilizer and an interstitial solid solution hardener, the effects of nitrogen on mechanical properties such as hardness profiles, grain sizes and microstructural modifications are investigated thoroughly by changing the welding shielding gas compositions. Increasing the nitrogen content in argon shielding gas also increases the amount of austenitic phase while δ-ferrite ratios decreases. Nitrogen spherodized the grains of austenitic structure much more than observed in δ-ferrite. The strength values of specimens that welded with the addition of nitrogen gas into the argon shielding gas are increased more in both austenitic and delta-ferritic structure as compared to specimens that welded with plain argon shielding gas. The addition of 1 vol % of nitrogen gas into argon shielding gas provided the optimum phase balance of austenite and δ-ferrite in S32205 duplex stainless-steel TIG-welded specimens.

UNS S32205 duplex stainless steel plates with a thickness of 3 mm are arc stud welded by M8 × 40 mm AISI 304 austenitic stainless steel studs with constant stud lifts in order to investigate the effects of welding arc voltages on mechanical and microstructural behaviors of the joints. As the welding arc voltage increases starting from 140 V, the tensile strength of the weldment also increases but the higher arc values results in more spatters around the weld seam up to 180 V. Conversely, the lower arc voltages causes poor tensile strength values to weldments. Tensile tests proved that all of the samples are split from each other in the welding zone but deformation occurs in duplex plates during the tensile testing of weldments so that the elongation values are not practically notable. The satisfactory tensile strength and bending values are determined by applying 180 volts of welding arc voltage according to ISO 14555 standard. Peak values of micro hardness occurred in weld metal most probably as a consequence of increasing heat input decreasing the delta ferrite ratios. As the arc voltage increases, the width of the heat affected zone increases. Coarsening of delta-ferrite and austenite grains was observed in the weld metal peak temperature zone but it especially becomes visible closer to the duplex side in all samples. The large voids and unwelded zones up to approximately 1 mm by length are observed by macro-structure inspections. Besides visual tests and micro-structural surveys; bending and microhardness tests with radiographic inspection were applied to samples for maintaining the correct welding parameters in obtaining well-qualified weldments of these two distinct groups of stainless steel materials.

The usage of AISI/SAE 304L austenitic and 420 martensitic stainless steels is receiving greater interest especially in the defence and navy industries. 304L stainless steels exhibit excellent resistance to oxidizing media, while martensitic 420 alloy provides high strength values besides satisfactory corrosion properties at ambient atmospheres. In this work; 420 quality martensitic stainless steel is TIG (Tungsten Inert Gas) welded with 304L quality low carbon austenitic stainless steel plates. As filler metal dominantly determines the weld metals chemical compositions and final microstructures, 3 different TIG welding rods of ER312, ER316L ve ER2209 are used in welding operations in order to obtain 3 discrete weld metal contents under high purity argon shielding gas. Microstructural inspection, microhardness survey and Charpy V-notch impact tests are applied to all joints after welding operations. The specimen welded by ER2209 TIG welding rod executed the highest impact test results besides exhibiting the lowest micro-hardness profiles at heat affected zones and weld metals. All of the welded specimens weld region hardness profiles were determined to be lower than unwelded 420 martensitic stainless steel base metal.

Application fields for duplex stainless steels are drastically increasing. Industries producing and operating petrochemical process equipment, pipelines, bridges, pressure vessels, heat exchangers, rotors, and sea-water systems have a high demand for these steels. In this study, UNS S32205 duplex stainless steel plates of 3 × 40 × 145 mm were TIG welded with welding wires of W22 9 3 NL (2209). The main aim was to investigate the effects of various amounts of magnetic δ-ferrite and other important phases or intermetallic compounds that are formed during and after welding. The phase quantities differing by the welding conditions and argon shielding gas mixtures containing 0, 1, 3, 6, and 9 vol.-% N2 are studied. The investigations included Charpy V-notch impact tests, weight loss corrosion tests, and microstructural analyses according to ASTM A 923 and magnetic δ-ferrite measurements according to EN ISO 17655, and EN ISO 8249 as well as image analyses according to ASTM E-562, ASTM E 1245 for a comparision of the effect of the amounts of all phases. The differences with respect to the welding parameters were also identified.

Öz SAE/AISI 304L östenitik paslanmaz çelikler oksitleyici ortamlardaki korozyon dayanımları için tercih edilirken, SAE/AISI 420 martenzitik paslanmaz çelikler genel olarak atmosferik korozyona karşı dayanım amaçlı kullanılmaktadırlar. Martenzitik paslanmaz çelikler birçok alaşımlı çeliklere yakın değerlerde yüksek mekanik dayanım değerleri sergilerken bunun yanında östenitik paslanmaz çelikler yüksek ve düşük sıcaklıklarda yüksek tokluk değeri ortaya koyarlar. Bu iki farklı alaşım grubu ekonomik koşullar ve mekanik özellik yaklaşımlarından dolayı bir yapıda bir arada kullanılabilirler. Kaynaklı bağlantıların kaynak metalleri ve ısının tesiri altındaki bölgeleri, güvenilir bir kaynaklı bağlantı elde etmek için; penetrant, ultrasonik ve radyografik muayene yöntemleri gibi tekniklerle detaylıca incelenmelidir. Bu çalışmada; 3 mm kalınlıktaki SAE/AISI 304L östenitik paslanmaz çelik levha ile 3mm kalınlıkta SAE/AISI 420 martenzitik paslanmaz çelik levha TIG (Tungsten Asal Gaz) kaynak yöntemiyle saf argon koruyucu gazı altında ER312, ER316L, ER2209 olmak üzere 3 farklı ilave tel kullanılarak birleştirilmiştir. TIG kaynak teli bileşiminin kaynak metalinde oluşabilecek kusurlara etkileri incelenmiştir. Bu amaçla, numunelerin kaynak metallerinin tamamı x-ışınları radyografik muayenesi ile test edilmiştir. ER312 ve ER2209 TIG teli ile birleştirilen numunelere kıyasla, ER 316L TIG teli ile birleştirilmiş olan numunelerin kaynak metalinde, dolgu telinin en düşük krom ve en yüksek nikel içeriğine sahip oluşu neticesinde en düşük miktarda olduğu düşünülen gevrek karbürlere bağlı olarak en düşük oranda süreksizlik tespit edilmiştir.