ASSESSMENT OF THE EFFECT OF CARBON ON PERFORMANCE PROPERTIES AND THE MICROSTRUCTURE OF ROLL STEEL

This paper concentrates on studying the effect of carbon on performance properties of 150KhNM roll steel grade. The introduction contains a brief literature review on the effect of the roll alloy chemistry on performance and mechanical properties of mill rolls. Besides, it demonstrates the relevance of the presented studies. The paper describes the effect of chemical elements, such as manganese, niobium, vanadium, nickel on the microstructure and mechanical properties of mill rolls. It also classifies alloying elements by their effect on polymorphic transformation temperatures and shows carbide-forming elements increasing such property. We also considered the effect of the carbide phase on hypereutectoid steel. The paper contains carbide compounds that may be formed in steels, and their classification. It describes the mechanism of the effect of the carbide phase on performance properties of steel castings. The second part of the paper presents a research procedure and briefly describes materials used for the research and laboratory and analytical equipment. The third part of the paper presents the research results. It describes the effect of carbon in a broad range on service durability of hypereutectoid roll steel in conditions of wear at room and elevated (400 ºС) temperatures. Besides, we determined the effect of carbon on the roll alloy microstructure and analyzed relations between the microstructure and performance properties of hypereutectoid roll steel. The conclusion of the paper summarizes the results and contains the references used for an analytical review.

Development of Ductile Irons for High-Temperature Applications: Characterization in the As-Cast and Oxidized States

Ductile iron alloyed with molybdenum and different levels of aluminium and silicon was cast to determine the proper combination of elements to increase the temperature range of operation. Four alloys containing 1.5wt.% molybdenum and different combinations of aluminium and silicon (i.e. 3.5Si-3.0A1, 4.5Si-2.0Al and 4.5Si-3.0Al) were cast at 1350, 1400 and 1450⁰C into step blocks. The effects of alloy chemistry, pouring temperature and casting thickness in the as-cast and oxidized conditions were studied. Results from the as-cast condition show that graphite morphology (i.e., size, count and sphericity) improved with lower Si/Al ratios and intermediate pouring temperatures. Higher silicon and lower aluminium contents accompanied by intermediate pouring temperatures reduced the onset of surface and sub-surface defects. Results from the oxidized condition show that maximum oxidation resistance was achieved in alloys containing higher aluminium and silicon contents. This also increased the critical α-ferrite to γ-austenite phase transformation temperature range.

Development of Ductile Irons for High-Temperature Applications: Characterization in the As-Cast and Oxidized States

Ductile iron alloyed with molybdenum and different levels of aluminium and silicon was cast to determine the proper combination of elements to increase the temperature range of operation. Four alloys containing 1.5wt.% molybdenum and different combinations of aluminium and silicon (i.e. 3.5Si-3.0A1, 4.5Si-2.0Al and 4.5Si-3.0Al) were cast at 1350, 1400 and 1450⁰C into step blocks. The effects of alloy chemistry, pouring temperature and casting thickness in the as-cast and oxidized conditions were studied. Results from the as-cast condition show that graphite morphology (i.e., size, count and sphericity) improved with lower Si/Al ratios and intermediate pouring temperatures. Higher silicon and lower aluminium contents accompanied by intermediate pouring temperatures reduced the onset of surface and sub-surface defects. Results from the oxidized condition show that maximum oxidation resistance was achieved in alloys containing higher aluminium and silicon contents. This also increased the critical α-ferrite to γ-austenite phase transformation temperature range.

Development of Bulk Metallic Glasses and their Composites by Additive Manufacturing - Evolution, Challenges and a Proposed Novel Solution

Bulk metallic glasses (BMGs) and their composites (BMGMCs) have emerged as competitive materials for structural engineering applications exhibiting superior tensile strength, hardness along with very large elastic strain limit. However, they suffer from lack of ductility and subsequent low toughness due to the inherent brittleness of the glassy structure which makes them amenable to failure without appreciable yielding. Various mechanisms and methods have been proposed to counter this effect out of which, recently Additive Manufacturing has gained widespread attention. It is proposed that additive manufacturing can overcome these difficulties in single step due to inherent existence of very high cooling rate in the process which is essential for glass formation. This, when coupled with careful selection of alloy chemistry is proposed to be the best solution to fabricate near net shape parts in a single step with excellent properties. In this report, an effort has been made to describe one possible route to achieve this. Solidification processing employing carefully selected inoculants based on edge to edge matching technique along with the carefuly controlled inoculation procedure is proposed to reflect upon enhanced mechanical properties. It is hypothesized that number density, size and distribution of ductile crystalline phase would best be able to improve microstructure and hence properties. This is meant to be controlled by manipulating type, size and the amount of inoculants. The proposed methodology is claimed to bear maximum potential.

Mechanical and Electrochemical Coupled Pitting Behavior of 2219 Aluminum Alloy: A Theoretical and Experimental Study

This study attempts to provide a theoretical estimate coupled with an analysis of the measured data to predict pitting damage of an aluminum alloy 2219 under the conjoint influence of mechanical load and corrosive environment. In accordance with the basic principle of crater growth coupled with the synergistic influences of mechanical and chemical effects, the law governing the presence and growth of corrosion pits was studied. Based on the concept of microscopic damage mechanics, porosity as a damage variable was introduced and the resulting model for estimating the reduction in elastic modulus of the material that has experienced observable damage due to pitting was established. Accelerated corrosion tests and uniaxial tensile tests are carried out, and a research-grade microscope coupled with a laser range finder was used to study the formation, presence, and growth of the pits with time. It was found that the corrosion pit in the chosen aluminum alloy can be simulated as a semi-ellipsoid, and the relationship between the depth of the pit and applied stress is an exponential function. This enabled in establishing the influence of alloy chemistry on nature, extent, and severity of damage due to pitting. The macroscopic morphology of the damaged specimens after corrosion was carefully observed and analyzed. The influence of time of exposure to the environment and applied load on damage due to pitting was verified. A comparison between the calculated results and experimental data reveals an overall correctness of the method developed and discussed in this paper.