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Optimal Composition Window of Type 410 Welding Consumables and Base Metals for Hydro-processing Applications

Stone, David Joseph
http://orcid.org/0000-0003-0191-6785
http://rave.ohiolink.edu/etdc/view?acc_num=osu149270477418846

Abstract Details

2017, Master of Science, Ohio State University, Welding Engineering.
Typically found in highly corrosive environments within the petrochemical industry, martensitic stainless steels are primarily selected over the more expensive austenitic stainless steels for their increased hardenability and resistance to halide stress corrosion cracking. Recently, unexpected high hardness and a loss of toughness has been experienced in both the weld metal and heat affected zone (HAZ) of hydro processing components fabricated with Type 410 steel. This has made it difficult to meet the hardness and toughness requirements set by ASME, API, and NACE. These unpredictable properties have been related to the large composition window of Type 410 steels, which can lead to exceeding the A1 temperature during post weld heat treatment (PWHT) resulting in formation of fresh martensite, and/or retention of significant amount of delta ferrite in the weld metal and HAZ. To address this problem, a two stage study was conducted to determine elemental effects on the A1 temperature (stage one) and retention of delta ferrite, (stage two) in Type 410 welding consumables and base metals. The results from both stages were then used in conjunction to develop a refined composition window that would avoid formation of fresh martensite during PWHT in the ASME specified temperature range while maintaining below 20% volume fraction of delta ferrite. In the frame work of stage one, a hypothesis of exceeding the A1 temperature during PWHT within the ASME specification\ was evaluated using CALPHAD based software ThermoCalcTM. Using a model based design of experiment (DOE) approach over eight alloying elements, compositional effects on the A1 temperature range in Type 410 steel and weld metal could be predicted with reduced number of simulations within ThermoCalcTM software. This was done using a resolution V surface response design included the effects of interactions. By developing and running simulations of 82 theoretical compositions of a ¼ factorial DOE within ThermoCalcTM, it was found that is possible for the A1 temperature range in Type 410 steel to expand below and above the ASME recommended PWHT temperature range of 760°C to 800°C. This presents a large risk of forming fresh martensite during post weld heat treatment. Both nitrogen, not specified by AWS, and copper, not specified by either AWS or ASTM, were also found to significantly lower the A1 temperature. Through regression analysis, elemental effects on the A1 temperature were quantified and a formula and a corresponding diagram that predict the A1 temperature of alloys within the Type 410 steel composition range were developed. Validation of the developed formula was performed using single sensor differential thermal analysis (SS-DTA and dilatometry with both commercially available and custom made alloys. Stage two examined both the composition and cooling rate effects on retention of delta ferrite through a developed simulation model of the ferrite to austenite phase transformation using the kinetic based software DICTRA. The developed model was used in conjunction with a DOE simulating 17 theoretical compositions at 3 separate cooling rates. This was done to predict the amount of retained delta ferrite as a function of both composition and cooling rate. It was found that a volume fractions or retained delta ferrite could reach up to 80% depending on the composition. The effect of cooling rate on the retention of delta ferrite was also found to be dependent on solidification mode. Reduction of ferrite was found with both rapid cooling rates that promote an FA solidification mode and with slower cooling rates that promote an F solidification mode, following a near equilibrium transformation path. Results from simulations were used to develop a predictive formula for the amount of retained delta ferrite in Type 410 steel and weld metal. Predictions of retained delta ferrite made with the developed formula were compared with predictions made with the Balmforth diagram using the 17 theoretical compositions. It was found that predictions made with the developed formula at cooling rate of 15°C/sec and predictions with the Balmforth diagram were statistically the same. Validation was then performed through point count analysis over 9 custom made alloys. The newly developed predictive formula was found to overestimate the volume fraction of delta ferrite when using rapid cooling rates. However, at slower cooling rates, predictions made with the developed formula were comparable with the volume fraction of retained delta ferrite found through point count analysis within the custom made alloys. From both the stage one and two results, a methodology for optimization of the Type 410 steel composition range was developed. This was done through a basic MatLab script, iterating millions of theoretical compositions through the predictive equations for the A1 temperature and for the volume fraction of retained delta. By visually graphing the output of this script, smaller compositional windows were found that had a high probability of having the combined attributes of a low retention of delta ferrite, below 20%, and an A1 temperature above 800°C. This produced a total of 4 composition windows at 4 different carbon levels.
Boian Alexandrov, Dr. (Advisor)
Carolin Fink, Dr (Committee Member)
201 p.
Engineering; Materials Science
410; stainless steel; delta ferrite; A1 temperature; model based DOE; ThermoCalc; simulation; martensitic; oil and gas industry; Hydro-processing; arc welding; GTAW; SMAW;

Recommended Citations

Citations

  • Stone, D. J. (2017). Optimal Composition Window of Type 410 Welding Consumables and Base Metals for Hydro-processing Applications [Master's thesis, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu149270477418846

    APA Style (7th edition)

  • Stone, David. Optimal Composition Window of Type 410 Welding Consumables and Base Metals for Hydro-processing Applications. 2017. Ohio State University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu149270477418846.

    MLA Style (8th edition)

  • Stone, David. "Optimal Composition Window of Type 410 Welding Consumables and Base Metals for Hydro-processing Applications." Master's thesis, Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu149270477418846

    Chicago Manual of Style (17th edition)

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This open access ETD is published by The Ohio State University and OhioLINK.