Control of Retained Delta Ferrite in Type 410 Stainless Steel

2017 ◽  
Author(s):  
David J. Stone ◽  
Boian T. Alexandrov ◽  
Jorge A. Penso
Keyword(s):  
Stainless Steel ◽  
Weld Metal ◽  
Cooling Rate ◽  
Elevated Temperatures ◽  
Low Cost ◽  
Corrosion Cracking ◽  
Delta Ferrite ◽  
Ferrite Formation ◽  
Sulfide Corrosion ◽  
Alloying Compositions

Type 410 stainless steel is used in petro-chemical refineries for its high resistance to halide stress corrosion cracking, sulfide corrosion cracking, and sulfur attack at elevated temperatures. Along with its adequate corrosion resistance 410SS also exhibits low cost and hardenability making it an ideal material for hydro-processing applications. Problems related to meeting toughness and hardness code requirements within the weld metal and heat effected zone (HAZ) have been experienced during fabrication of 410SS welded components. The loss of toughness has been related to excessive amounts of delta ferrite in the weld metal and HAZ. The objective of this study was to quantify the effect of cooling rate and alloying compositions within ASTM and AWS specifications for 410SS on delta ferrite formation. C, Cr, Ni, and Mo, were used as factors in a model-based design of experiment (DOE) within CALPHAD based software DICTRA™ to simulate the effects of composition and cooling rate on delta ferrite formation. Based on the DOE results, a predictive model for quantification of retained delta ferrite in 410SS welds was developed along with evidence for cooling rate effect on retained delta ferrite. Optical metallography was also used to demonstrate possible ferrite content within the 410 composition range.

Review of Ferrite Number (FN) Requirements and Proposed Changes to Code Case N-504-4 and Nonmandatory Appendix Q

2019 ◽  
Author(s):  
Steven L. McCracken ◽  
David Segletes
Keyword(s):  
Stainless Steel ◽  
Weld Metal ◽  
Carbon Content ◽  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Nuclear Power ◽  
Nuclear Regulatory Commission ◽  
Corrosion Cracking ◽  
Delta Ferrite ◽  
Ferrite Number

Abstract ASME Section XI Nonmandatory Appendix Q and Code Case N-504-4 are routinely used to install full structural weld overlays in the nuclear power industry for repair or mitigation of stress corrosion cracking in austenitic stainless steel weldments. Both Appendix Q and N-504-4 specify a Ferrite Number (FN) and carbon content requirement for the stainless steel weld metal used for the weld overlay to ensure acceptable resistance to stress corrosion cracking. The Ferrite Number (FN) is used in the ASME Code for establishing the delta ferrite content in the deposited weld metal. Field experience indicates there is often confusion and differing opinion concerning how the Ferrite Number and carbon content requirements of Appendix Q and N-504-4 are satisfied. This is in part due to unavailability of the original technical basis for these requirements. This paper provides a background for the delta ferrite and carbon content requirements, information on influence of delta ferrite and carbon content on stress corrosion cracking and U.S. Nuclear Regulatory Commission (NRC) guidance on the issue. Finally, this paper details a proposed revision of Nonmandatory Appendix Q and N-504-4 to clarify the FN and carbon content requirements.

Delta Ferrite Formation in Austenitic Stainless Steel Castings

2012 ◽  
Vol 730-732 ◽  
pp. 733-738 ◽  
Author(s):  
Angelo Fernando Padilha ◽  
Caio Fazzioli Tavares ◽  
Marcelo Aquino Martorano
Keyword(s):  
Stainless Steel ◽  
Chemical Composition ◽  
Cooling Rate ◽  
Stainless Steels ◽  
Austenitic Stainless Steels ◽  
Magnetic Method ◽  
Empirical Formulas ◽  
Delta Ferrite ◽  
Ferrite Formation ◽  
Steel Castings

The effects of chemical composition and cooling rate on the delta ferrite formation in austenitic stainless steels have been investigated. Ferrite fractions measured by a magnetic method were in the range of 0 to 12% and were compared with those calculated by empirical formulas available in the literature. The delta ferrite formation (amount and distribution) was strongly affected by the steel chemical composition, but less affected by the cooling rate. Among several formulas used to calculate the amount of delta ferrite, the best agreement was obtained with those proposed independently by Schneider and Schoefer, the latter being recommended in the ASTM 800 standard.

Tempering Response in Type 410 Stainless Steel Welds for Petrochemical Application

2020 ◽  
Author(s):  
Takuya Kusunoki ◽  
Boian Alexandrov ◽  
Benjamin Lawson ◽  
Jorge Penso ◽  
Joe Bundy
Keyword(s):  
Stainless Steel ◽  
Weld Metal ◽  
Low Cost ◽  
Postweld Heat Treatment ◽  
Base Metals ◽  
Delta Ferrite ◽  
Asme Code ◽  
Fresh Martensite ◽  
Steel Welds ◽  
Welding Consumables

Abstract Type 410 martensitic stainless steel is typically used in highly corrosive environments within petrochemical installations due to its resistance to halide stress corrosion cracking, hardenability, and low cost compared to austenitic stainless steel. However, the industry has experienced difficulties in meeting the ASME toughness, and NACE hardness requirements for wet sour services of Type 410 steel welds. Recent studies have shown that these problems are related to the wide compositional ranges of Type 410 base metals and welding consumables, leading to exceeding the A1 temperature during postweld heat treatment (PWHT) and formation of fresh martensite, and to retention of significant amount of delta ferrite in the final weld metal and heat affected zone microstructures. These studies have identified two Type 410 optimized weld metal compositions that met the specified hardness and toughness requirements. The objective of this work was to quantify the tempering response in one of the optimized welding consumables and in two Type 410 base metals. Samples of these materials were subjected to a series of PWHTs at temperatures corresponding to the lower and upper limits of the ASME code recommended temperature range (760 C and 800 °C) and at 10 °C below the A1 temperature of each material. The PWHT durations were 5 and 30 minutes, and 1, 2, and 4 hours. The hardness values related to all PWHTs performed below the corresponding A1 temperatures were used to generate Holloman–Jaffe type equations for all tested materials. As expected, the PWHTs performed above the A1 temperatures resulted in the formation of fresh martensite.

Tensile Properties of Low Nickel Austenitic Stainless Steel at Elevated Temperatures

2012 ◽  
Vol 159 ◽  
pp. 346-350
Author(s):  
Shu Min Liu ◽  
Jian Bin Zhang
Keyword(s):  
Tensile Strength ◽  
Stainless Steel ◽  
Elevated Temperatures ◽  
Peak Stress ◽  
Temperature Curve ◽  
Delta Ferrite ◽  
Cross Sectional ◽  
Different Temperatures ◽  
Increasing Temperature ◽  
Reduction Percentage

The elevated temperature short-time tensile test with the sample of casting low nickel stainless steel was conducted on SHIMADZU AG-10 at ten temperatures 300, 500, 600, 700, 800, 950, 1000, 1050, 1100, and 1250°C, respectively. The stress-strain curves with the thermal deformation at the different temperatures, the peak stress intensity-temperature curve, and the reduction percentage of cross sectional area-temperature curve were obtained. Metallographic test samples were prepared and the morphology of deforming zone was observed by optical microscopy. The experimental results show that the tensile strength of the test samples decreases with increasing temperature. From 300 to 800°C, the work harding occurred and the tensile strength increases with increasing strain. The work softening occurred and the tensile strength decreases with increasing strain at temperatures of 800 to 1250°C. The minimum value of reduction percentage was measured at 800 °C. The austenite and delta-ferrite are the main phase in the tested samples. When the tensile temperatures are increased to 1200°C, the delta-ferrite became thinner and broke down to be spheroidized.

Nitrogen Enhanced 316LN Austenitic Stainless Steel for Sodium Cooled Fast Reactors

2013 ◽  
Vol 794 ◽  
pp. 670-680 ◽  
Author(s):  
Tammana Jayakumar ◽  
A.K. Bhaduri ◽  
M.D. Mathew ◽  
Shaju K. Albert ◽  
U. Kamachi Mudali
Keyword(s):  
Stainless Steel ◽  
Austenitic Stainless Steel ◽  
Weld Metal ◽  
Nitrogen Content ◽  
Low Cycle Fatigue ◽  
Hot Cracking ◽  
Cycle Fatigue ◽  
Fast Reactors ◽  
Delta Ferrite ◽  
316Ln Ss

For the future sodium-cooled fast reactors (SFRs), which are envisaged with a design life of 60 years, nitrogen-enhanced 316LN austenitic stainless steel (SS) with improved high-temperature properties is being developed. To optimize the enhanced nitrogen content in 316LN SS, the effect of nitrogen on its tensile, creep and low cycle fatigue behavior has been investigated. For different heats of 316LN SS containing 0.07-0.22 wt% nitrogen, the tensile and creep properties increased with increase in nitrogen content, while low cycle fatigue properties peaked at 0.14 wt% nitrogen. Finally, based on the evaluation of the hot cracking susceptibility of the different heats of 316LN SS with varying nitrogen content, using the Varestraint and Gleeble hot-ductility tests, the nitrogen content for the nitrogen-enhanced 316LN SS has been optimized at a level of 0.14 wt%. The 0.14 wt% nitrogen content in this optimised composition shifts the solidification mode of the weld metal to fully austenitic region, including that due to dilution of nitrogen from the base metal, thereby increasing its hot cracking susceptibility. This necessitated development and qualification of welding electrodes for obtaining weld metal with 0.14 wt% nitrogen by optimising the weld metal chemistry so as to obtain the requisite delta ferrite content, tensile properties, and very importantly impact toughness both in the as-welded and aged conditions. Studies on localised corrosion behaviour of nitrogen-enhanced 316LN SS indicated the beneficial effect of nitrogen addition to sensitization, pitting, intergranular corrosion, stress corrosion cracking and corrosion fatigue.

Effect of Filler Alloy on Microstructure, Mechanical and Corrosion Behaviour of Dissimilar Weldment between Aisi 201 Stainless Steel and Low Carbon Steel Sheets Produced by a Gas Tungsten Arc Welding

2012 ◽  
Vol 581-582 ◽  
pp. 808-816 ◽  
Author(s):  
Chuaiphan Wichan ◽  
Srijaroenpramong Loeshpahn
Keyword(s):  
Stainless Steel ◽  
Carbon Steel ◽  
Weld Metal ◽  
Base Metal ◽  
Low Carbon Steel ◽  
Low Carbon ◽  
Delta Ferrite ◽  
Steel Sheets ◽  
Gas Tungsten Arc ◽  
Weld Metals

The joining of austenitic stainless steel (AISI 201) to low carbon steel sheets (CS) was attempted by gas tungsten arc welding (GTAW) with four types of consumables. The studied consumables were ER308L, ER309L, ER316L stainless steel wires, and AWS A5.18 carbon steel wire. The welding parameters – i.e. the current of 90 A and the welding speed of 62 mm.min-1 – were fixed in all welding operations. The microstructure of weld metal produced by stainless steel consumables consisted of delta ferrite in austenite matrix. The delta ferrite in the form of continuous dendrite was observed in weld metals produced by 308L and 309L fillers. The dendrite of delta ferrite was relatively discontinuous in weld metal produced by 316L filler. The microstructure of weld metal produced by carbon steel filler consisted of equiaxed ferrite and pearlite, similar to that of carbon steel. The corrosion behavior of weld metal was investigated by potentiodynamic method. Specimens were tested in 0.35-wt% NaCl solution saturated by laboratory air at 27°C. It was found that the corrosion potential of weld metal produced by carbon steel filler was considerably lower than those of AISI 201 base metal and weld metals welded using stainless steel consumables. Weld metals produced by stainless steel fillers –308L,309L and316L– exhibited the similar corrosion potentials as that of 201 base metal. The pitting potentials of weld metals produced by 309L, 316L fillers were higher than those of 201 base metal and weld metal produced by 308L filler respectively. It was discussed that the increase of Cr content in weld metals by using 309L filler contained with 24.791 wt% of Cr, or the addition of Cr and Mo in weld metals by using 316L filler contained with 21.347 wt% of Cr and 2 wt% of Mo, promoted the pitting corrosion resistance of weld metal to be comparable with that of Fe-17Cr-3Ni (201) base metal. An emission spectroscopy was applied to quantify the amount of elements in weld metals. By considering the contents of Cr and Mo, the pitting resistance equivalent number (PREN) of each weld metal was calculated. The discussion of the corrosion resistance of weld metals related to PREN and microstructure was made in the paper.

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