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Interrelations of compositions, transformation kinetics, morphology, and mechanical properties of alloy steels

Description: The strong influence of the fine-scale microstructural features on mechanical properties has become increasingly evident during the past decade. This is particularly true for fracture toughness of quenched and tempered alloy steels. Large differences in microstructure can be produced by isothermal, rather than athermal, treatments in the bainite and upper martensite temperature ranges. The kinetics of transformation as well as the kinds and volume fractions of transformation products can be varied over wide ranges by relatively small changes in chemical composition. The effects of the common alloying elements on transformation kinetics, both separately and in various combinations were determined experimentally. The synergistic effects of individual elements added as pairs of elements were not predictable from a knowledge of the effects of the individual elements. Isothermal treatments, coupled with variations in the kinds and amounts of alloying elements, produced different morphologies, compositions, and volume fractions of the transformation products. The effects of such microstructural differences on tensile properties, fracture toughness, and fatigue characteristics were evaluated. Beneficial effects were found, such as substantial increases in fracture toughness, with small changes in alloy content or with heat treatments that differed from those conventionally used.
Date: March 1, 1977
Creator: Parker, E. R.
Partner: UNT Libraries Government Documents Department

Low alloy steels for thick wall pressure vessels. Yearly report, October 1, 1976--September 30, 1977

Description: A summary is presented of progress during the first year of a program to modify current ferrous alloys and develop new low-alloy steels that can be field-fabricated into large-diameter, thick-walled pressure vessels for commercial coal gasifiers. Determination of design criteria for the pressure vessel steels, incorporating information gained through review of the literature and gained through interaction with industry, national laboratory personnel, and research contractors is described. Work has been performed to verify that simulation techniques lead to good reproducibility. This work has required evaluating commercially-produced material and small ingot material. Primary program effort has been placed on carrying out studies in modified commercial alloy systems to direct scaled-up investigations. Transformation behavior, microstructural characterization and mechanical property assessment have been determined for several modified alloys. Emphasis has been placed on Mn-Mo-Ni steels, A533 types, and Cr-Mo steels, A-542-type. Initial compositions for complete thick-section characterization have been determined. Work on the third system, Ni-Cr-Mo steels (A543-type) has focused on embrittlement susceptibility, with composition modifications having been selected for studying this phenomenon. Work on eutectoid steels has been undertaken on an associated fundamental studies program. These studies have been aimed at identifying useful alloy systems.
Date: January 1, 1977
Creator: Horn, R.M.; Parker, E.R. & Zackay, V.F.
Partner: UNT Libraries Government Documents Department

Wear resistant alloys for coal handling equipment. Progress report, January 1--September 30, 1977

Description: The in-service operating conditions of coal transport and fragmentation equipment involve various combinations of dry or liquid slurry abrasion, impact loading, and temperatures that may vary from ambient to elevated (500/sup 0/F--1000/sup 0/F). Both 2-body and 3-body abrasive wear can be encountered. The published literature contains little information on testing materials under the various abrasive conditions that are of concern, especially 3-body wear. However, a number of tests were identified which may serve to provide wear data under different service conditions. A dry abrasive wear tester, to be used for screening alloys, was constructed. A review of the alloy steel literature was completed and was used to select low-alloy and secondary hardening steel compositions for screening. Initial screening criteria included the stipulation of a hardness of R/sub c/55 with an impact toughness of around 15 ft lbs or a fracture toughness of 80 KSI..sqrt..in., depending on the application being considered. Several of the steels that were evaluated to date appeared to meet these criteria. A systematic development of secondary hardening steels has been evolved and it has been shown that good combinations of strength and toughness were achieved through proper composition and microstructural control. These higher alloyed steels appear to be suited for long-term, elevated-temperature service. The lower alloy Cr-Ni-Mo and Cr-Si-Mo steels investigated also exhibited good combinations of strength and toughness and may be suitable for ambient temperature use.
Date: January 1, 1977
Creator: Bhat, M.S.; Zackay, V.F. & Parker, E.R.
Partner: UNT Libraries Government Documents Department

Development of nickel-free austenitic stainless steels for ambient and cryogenic applications

Description: A series of alloys have been developed as possible replacements for some austenitic stainless steels. These alloys utilized a Mn substitution for Ni and a reduced Cr concentration from the 18% ordinarily found in the AISI 300 series stainless steels to a concentration of 13%. The base system studied was an alloy containing Fe-16%Mn-13%Cr while other elements added included small additions of N, Si and Mo. A range of microstructures was produced from the alloying additions. The base composition had a triplex (fcc, hcp, bcc) structure while the most highly modified compositions were fully austenitic. Mechanical testing included tensile testing and Charpy V-notch testing conducted at various temperatures between -196/sup 0/C to 23/sup 0/C. Excellent combinations of strength and ductility were obtained (40--65 ksi yield strength, 100--125 ksi ultimate strength, 45--75% elongation and 60--80% reduction of area) at room temperature. Upper shelf energies in Charpy V-notch testing were as high as 185 ft-lbs with a ductile-brittle transition temperature (DBTT) of -160/sup 0/C. Analysis of fracture surfaces determined that alloys without interstitials had no transition in the mode of failure between room temperature and liquid nitrogen temperature. Results of an ASTM sensitization corrosion test, where the experimental alloys were compared to 347 stainless steel, indicated that the alloys were not susceptible to intergranular attack.
Date: February 1, 1978
Creator: Haddick, G.T.; Thompson, L.D.; Parker, E.R. & Zackay, V.F.
Partner: UNT Libraries Government Documents Department

Low alloy steels that minimize the hydrogen-carbide reaction. Final technical report, October 1, 1978-September 30, 1979. Part I

Description: This report presents results obtained during the first year of a research program to investigate important metallurgical parameters that control the reactions of hydrogen with carbides in steels. Preliminary work included a detailed literature review of th phenomenon of decarburization and methane bubble formation in steels and a suitable experimental technique for investigating hydrogen attack in laboratory conditions was established. Detailed microstructural-mechanical property evaluations were carried out on two series of alloys; the first was based on a plain carbon steel to which binary and ternary alloy additions were made to vary the carbide structure and morphology and assess these effects on the observed hydrogen attack resistance. The second group of steels consisted of commercial Mn-Mo-Ni (A 533 B) and Cr-Mo (A 542 type) steels and their alloy modifications, with a view towards developing steels with improved hydrogen attack resistance.
Date: January 1, 1979
Creator: Kar, R. J.; Parker, E. R. & Zackay, V. F.
Partner: UNT Libraries Government Documents Department