Brief study on δ-ferrite characterization: A review

Heat-affected zone (HAZ) of welding joints critical to the equipment safety service are commonly repeatedly welded in industries. Thus, the effects of repeated welding up to six times on the microstructure and mechanical properties of HAZ for AISI 304N austenitic stainless steel specimens were investigated by a Gleeble simulator. The temperature field of HAZ was measured by in situ thermocouples. The as-welded and one to five times repeated welding were assigned as-welded (AW) and repeated welding 1–5 times (RW1–RW5), respectively. The austenitic matrices with the δ-ferrite were observed in all specimens by the metallography. The δ-ferrite content was also determined using magnetic and metallography methods. The δ-ferrite had a lathy structure with a content of 0.69–3.13 vol.%. The austenitic grains were equiaxial with an average size of 41.4–47.3 μm. The ultimate tensile strength (UTS) and yield strength (YS) mainly depended on the δ-ferrite content; otherwise, the impact energy mainly depended on both the austenitic grain size and the δ-ferrite content. The UTS of the RW1–RW3 specimens was above 550 MPa following the American Society of Mechanical Engineers (ASME) standard. The impact energy of all specimens was higher than that in ASME standard at about 56 J. The repeated welding up to three times could still meet the requirements for strength and toughness of welding specifications.

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Microstructure and Mechanical Properties of Modern 11%Cr Heat-Resistant Steel Weld Joints

Materials ◽

10.3390/ma14123430 ◽

2021 ◽

Vol 14 (12) ◽

pp. 3430

Author(s):

Grzegorz Golański ◽

Jacek Słania ◽

Marek Sroka ◽

Paweł Wieczorek ◽

Michał Urzynicok ◽

...

Keyword(s):

Mechanical Properties ◽

Welded Joints ◽

Martensitic Steel ◽

Base Material ◽

Hardness Measurement ◽

Power Industry ◽

Strength Properties ◽

Typical Structure ◽

Δ Ferrite ◽

The Impact

In addition to good high-temperature creep resistance and adequate heat resistance, steels for the power industry must have, among other things, good weldability. Weldability of such steels is one of the criteria determining whether or not the material is suitable for applications in the power industry. Therefore, when materials such as martensitic steel Thor 115 (T115) are introduced into the modern power industry, the quality and properties of welded joints must be assessed. The paper presents the results of metallographic and mechanical investigations of T115 martensitic steel welded joints. The analysis was carried out on joints welded with two filler metals: WCrMo91 (No. 1) and EPRI P87 (No. 2). The scope of the investigations included: microstructural investigations carried out using optical, scanning and transmission electron microscopy and mechanical testing, i.e., Vickers microhardness and hardness measurement, static tensile test and impact test. The macro- and microstructural investigations revealed correct structure of the weld, without welding imperfections. The microstructural investigations of joint No. 1 revealed a typical structure of this type of joint, i.e., the martensitic structure with numerous precipitates, while in joint No. 2, the so-called Nernst’s layers and δ-ferrite patches were observed in the weld fusion zone as well as the heat affected zone (HAZ). The mechanical properties of the test joints met the requirements for the base material. A slight influence of the δ-ferrite patch on the strength properties of joint No. 2 was observed, and its negative effect on the impact energy of HAZ was visible.

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The effects of morphology of ferrite and non-metallic inclusions on corrosion behaviour of as-cast 304 stainless steel

CORROSION ◽

10.5006/3763 ◽

2021 ◽

Author(s):

Danbin Jia ◽

Liangcai Zhong ◽

Jingkun Yu ◽

Zhaoyang Liu ◽

Yuting Zhou ◽

...

Keyword(s):

Stainless Steel ◽

Corrosion Resistance ◽

Corrosion Behaviour ◽

Solidification Process ◽

Inclusion Size ◽

304 Stainless Steel ◽

Experimental Conditions ◽

Quenching Temperature ◽

Δ Ferrite ◽

Metallic Inclusions

The effects of morphology of ferrite and non-metallic inclusions on corrosion resistance of as-cast 304 stainless steel (304 SS) were investigated. With the decrease in quenching temperature from 1723 K to 1648 K, the different microstructures of the as-cast 304 SS were obtained as the following series: austenitic-lathy δ ferrite, austenitic-colony δ ferrite and austenitic-blocky δ ferrite, and the average inclusion size increased. The electrochemical results show that the sample with the microstructure of austenitic- lathy δ ferrite and smaller size inclusions had a higher corrosion tendency and the lower pitting resistance. Furthermore, the effect of morphology and content of ferrite on corrosion resistance was greater than that of inclusion size under the current experimental conditions. Therefore, a promising method was developed to improve the corrosion resistance of as-cast 304 SS by changing the solidification process.

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The Effect Of δ-Ferrite Upon the Low Temperature Mechanical Properties of Centrifugally Cast Stainless Steels

Austenitic Steels at Low Temperatures ◽

10.1007/978-1-4613-3730-0_14 ◽

1983 ◽

pp. 221-242 ◽

Cited By ~ 1

Author(s):

K. S. Lee ◽

David Dew-Hughes

Keyword(s):

Mechanical Properties ◽

Low Temperature ◽

Stainless Steels ◽

Centrifugally Cast ◽

Δ Ferrite

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Microstructure Optimization in δ-TRIP Steels with Al and Nb

Materials Science Forum ◽

10.4028/www.scientific.net/msf.930.501 ◽

2018 ◽

Vol 930 ◽

pp. 501-506

Author(s):

Eustáquio de Souza Baêta Júnior ◽

Ramón Alves Botelho ◽

Leonardo Sales Araújo ◽

Luiz P. Brandão ◽

Sergio Neves Monteiro

Keyword(s):

Chemical Composition ◽

Alloying Elements ◽

Eutectoid Temperature ◽

Transformation Induced Plasticity ◽

Trip Steels ◽

Plasticity Effect ◽

Δ Ferrite ◽

Areas Of Interest ◽

Thermocalc Software ◽

Strength And Ductility

δ-TRIP steel is a recent concept and has been developed over the last ten years aiming to combine good mechanical strength and ductility. This class of steels is multiphase and contains δ and α ferrites, as well as austenite, bainite and/or martensite. The TRIP (Transformation Induced Plasticity) effect is influenced by those phases proportion, which depends on alloying contents. This paper investigates a chemical composition that allows adequate proportion among the phases, optimizing the microstructures by means of computational methods. These microstructures are designed to contain between 10 to 50% austenite, 10 to 70% α-ferrite and 20 to 80% δ-ferrite at the eutectoid temperature. The ThermoCalc Software [1] was used to predict the fractions of the microconstituents, producing graphs describing areas of interest of microconstituents as function of alloying elements variations that leads to the desired microstructure. Results indicate that the designed volume of the phases can be found for certain proportions among the alloying elements, higher concentrations of Al and Nb combined with C allow or not the occurrence of carbides and other phases in smaller quantities.

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Effects of Chemical Compositions of Welding Rods on J-R Fracture Resistances and Tensile Properties of Type 347 Welds

Materials Science Forum ◽

10.4028/www.scientific.net/msf.539-543.4105 ◽

2007 ◽

Vol 539-543 ◽

pp. 4105-4110

Author(s):

Ji Hyun Yoon ◽

Bong Sang Lee ◽

Eui Pak Yoon

Keyword(s):

Tensile Properties ◽

Arc Welding ◽

Fracture Resistance ◽

Chemical Compositions ◽

High Fracture ◽

Carbon And Nitrogen ◽

Gas Tungsten Arc ◽

Weld Metals ◽

Δ Ferrite ◽

Nitrogen Contents

The objective of this investigation was to correlate the chemical composition of welding rods for gas tungsten arc welding with the fracture resistance and tensile properties of type 347 welds through the systematic tests and microstructural analyses. Five weld metals which differed in contents of carbon, nitrogen and niobium each other and a high δ-ferrite containing weld metal were deposited by the six different welding rods. J-R fracture resistance and tensile properties were evaluated for the type 347 welds. The microstructural examinations were performed to relate key microstructural features to mechanical properties. It was found that the contents of Nb(C,N) precipitates in type 347 welds were determined by the mixed function of carbon and nitrogen and niobium contents in welding rods. The strengths of type 347 welds were in direct proportion to the contents of Nb(C,N) and J-R fracture resistances were inversely proportional to the contents of Nb(C,N). It was concluded that the type 347 weld with high fracture resistance and adequate strength was obtainable by controlling the sum of carbon and nitrogen contents near 0.1wt% and a limitation of the carbon content below 0.04 wt% in welding rod.

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