UV Construction Materials
UV Assembly Technology
The UV will be assembled at a dry dock. After manufacturing and delivery of components to the assembly point, they will install embedded framed structures, where the tanks will be mounted in tiers, followed by the filling up of the first tier with the syntactic material. The syntactic material will be poured into a special casing. Simultaneously with the filling up of the casing, they will assemble power units and mount a work tool.
When the assembly is completed, the dock will be filled with water, and the UV will be removed from the dock. The Vehicle will be assembled near the mining point, and the assembled UV will be towed directly to the mining point.
Why did the team choose the syntactic material as a composite material for buoyancy elements? The main reasons for the application of hollow glass microspheres (HGM) to form the composites is the necessity to reduce the material density and therefore the weight of elements made from it. The composites with low density made on the basis of HGMs are conventionally in wide use for the construction of deep-sea machines (as well as for the buoyancy elements and for molding of high-strength elements of those deep-sea machines). The utilization of glass microspheres in making polyester pressmaterials of SMCs (sheet molding compounds) and BMCs (bulk molding compounds) makes it possible to substantially reduce their density (from 1.8 gr/cm3 to 1.3 gr/cm3) while preventing material impairment of resilience and strength properties of composites. Table 1 shows the comparative analysis of properties of foamed plastic and HGM-based (syntactic) composite materials. The immense superiority of resilience and strength properties of syntactic materials as compared to foamed plastic offers the engineers essentially new possibilities.
Table 1. Properties of foamed plastic and HGM-based composite materials.
Table 2. Glass microsphere properties.
Development of low-cost high-tension alloyed steel
In order to form the UV structural elements, we also needed high-tension alloyed steel. The majority of known high-tension steels (strength level σв> 1,500 МPa), for example, martensite-ageing, TRIP-steels and others, usually contain expensive highly rare components in a large amount: 4-11% Ni, 2-5% Mo, and some of them - 2-9% Co. This fact to some extent holds back wide manufacture of this type of steel. Lately, the problem of preservation of the said components has become increasingly relevant in the world. That is why our team has found a substitute for previously used materials, which would completely satisfy all technical requirements to the construction of the UV.
The objective of this work was the creation and testing of new high-tension nickel-free metastable steels whose properties are highly competitive with expensive analogues – based on the study of the impact of reduced chrome content on phase conversions, structure and properties.
Thus, we used new nickel-free chrome-manganese steel compounds containing 2-8% of chrome (see Table 3)
Table 3. Chrome-manganese steels chemical composition
The steels were melted out in basic induction furnaces and cast into cakes with the weight of ~15 kg. The cakes were forged to make rods with the section of 11х11 mm, from which, upon annealing, they made the samples for various studies. In the course of this study, our specialists applied differentially thermal, dilatometric, magnetometric, and metallographic methods. The testing of properties was carried out in case of stretching (GOST 1497-84), torsion (GOST 3565-78), impact bending of the samples with a U-notch (GOST 9454-78). The attrition tests under the condition of sliding friction between two metals were conducted at МИ-1М machine. The relative wear resistance (s) was determined as the benchmark weight loss (annealed steel 45) to the sample weight loss ratio within the same time period (20 min.).
The introduction into the steel of a small amount of vanadium ensures the preservation of fine grains due to formation of hardly soluble VC carbides.
The C30Cr2Mn6Si2V steel after quenching at 1,000оС contains 80-82% of martensite and retained austenite (Аret.). Besides, the structure of all the steel under consideration comprises of small amount (4-5%) of carbides, (Fe,Cr)3C, VC, whose content changes in case of thermal treatment.
By predominant content of phases, the developed steels belong to the following structural classes: C30Cr2Mn6Si2V – martensite-austenite, C30Cr4Mn6Si2V and C30Cr6Mn6Si2V – austenite-martensite, and C30Cr8Mn6Si2V – austenite. The martensite in the studied steels mostly has rack-type (packet-like) structure. The Аret. looks as interlayers between martensite racks, or in case of its high content (ca 50 %) – in the form of separate grains (fields). We found dispersive not dissolved carbide particles in the steel structures. The austenite in the steel structure is metastable; and, in case of deformation, it converts to martensite. As a result of development of the deformation induced martensitic transformation, in the tested portion of broken samples due to torsion of the studied steels, we discovered the occurrence of the deformation martensite. In whole, it has packet-like structure, however, it distinguishes itself for increased density of dislocations and a great number of dispersed carbides that are likely to have deposited as a result of continuous dynamic deformation ageing in the course of studies. In the deformed grains of the remainder austenite (not converted) of C30Cr8Mn6Si2V steel we noticed a great number of slip lines, twins and defects.
Mechanical properties of the developed steels are determined by the initial (after thermal treatment) phase structure and development of deformation induced martensitic transformation.
Thus, the highest set of strength and plastic properties: av=1,910 МPa, G0.2=1,460 МPa; 8=16%; у=60%, was obtained in C30Cr2Mn6Si2V steel containing a small amount of Аret..
The results allow considering new steels as a promising high-tension material to replace highly rare and expensive alloys used to manufacture various parts for dedicated equipment, armor, and some types of tools.