Computers and Technology
Submitted By KrimsonChin
Types and Uses
Steel is often classified by its carbon content: a high-carbon steel is serviceable for dies and cutting tools because of its great hardness and brittleness; low- or medium-carbon steel is used for sheeting and structural forms because of its amenability to welding and tooling. Alloy steels, now most widely used, contain one or more other elements to give them specific qualities. Aluminum steel is smooth and has a high tensile strength. Chromium steel finds wide use in automobile and airplane parts on account of its hardness, strength, and elasticity, as does the chromium-vanadium variety. Nickel steel is the most widely used of the alloys; it is nonmagnetic and has the tensile properties of high-carbon steel without the brittleness. Nickel-chromium steel possesses a shock resistant quality that makes it suitable for armor plate. Wolfram (tungsten), molybdenum, and high-manganese steel are other alloys. Stainless steel, which was developed in England, has a high tensile strength and resists abrasion and corrosion because of its high chromium content.
Steel guide - Steel classification
Steel may be classified in categories
Steel can be subdivided into different categories which represent different chemical composition standards. Due to the large variety of categories and grades only a few kinds can be introduced below.
Sorted steel rods
Carbon steel is a simple kind of steel which can be hardened. Carbon steel contains between 0.5 and 1.7 percent carbon.
Alloyed steel has a specific composition and contains a particular percentage of Vanadium, Molybdenum and other elements. Many products are made of alloyed steel, i.e. gearings and axles of automobiles.
Alloys which contain cobalt or tungsten are used to produce permanent magnets.
Stainless Steel contains chromium, nickel and other alloys which prevent corrosion of the steel even under harsh conditions like high humidity or exposure to corroding acids.
Chromium increases the hardness of steel whereas nickel increases the toughness. An alloy with 25% nickel can be pulled to twice the length without breaking. V2A-Steel contains for example 71% iron, 20% chromium, eight percent nickel and 0.2% carbon, silicon and manganese respectively.
Stainless Steel can be used for pipes and tanks of oil refineries or in chemically engineered processes. Surgical instruments and other medical equipment is made of stainless steel, too.
A variety of tools and the cutting or forming parts of machines can be made of tool steel.
Tool steel contains tungsten, molybdenum and other alloys which increase toughness and hardness as well as wear-resistance.
Material properties required for design
The properties that need to be considered by designers when specifying steel construction products are:
END OF STEEL
Uses of Soil:
1. Soil is used in agriculture, where it serves as the primary nutrient base for the plants. Soil resources are critical to the environment, as well as to food and fiber production. Soil provides minerals and water to plants. Soil is used to make plants grow healthy. The types of soil used in agriculture (among other things, such as the purported level of moisture in the soil) vary with respect to the species of plants that are cultivated.
2. Soil is used in constructions and arts. Soil material is a critical component in the mining and construction industries. Soil serves as a foundation for most construction projects. Massive volumes of soil can be involved in surface mining, road building, and dam construction. Earth sheltering is the architectural practice of using soil for external thermal mass against building walls. Soil is used to make pots.
3. Soil play an important role in filtrating and purifying water. After coming down as precipitation, much of the rain water is percolated through the many horizons of a soil profile and renamed as groundwater. As the water moves through different areas such as wetlands, forests, and riparian zones many pollutants are removed. Pollutants such as viruses, oils, metals, excess nutrients, and sediments are filtered out by the soil and surrounding organisms.
4. Waste management often has a soil component. Landfills use soil for daily cover. Septic drain fields treat septic tank effluent using aerobic soil processes.
5. Organic soils, especially peat, serve as a significant fuel resource.
Soil Classification concerns the grouping of soils with a similar range of properties (chemical, physical and biological) into units that can be geo-referenced and mapped. Soils are a very complex natural resource, much more so than air and water.
Soils contain all naturally occurring chemical elements and combine simultaneously solid, liquid and gaseous states. Moreover, the number of physical, chemical and biological characteristics and their combinations are nearly endless. No wonder then that many different approaches have been proposed to come to a sensible grouping of different soils. Also soil classification systems were developed for different purposes :
Soil Taxonomy to interpret soil surveys;
The FAO Legend for representing the global distribution and geography of soils;
WRB to facilitate correlations between different soil classification systems
One can distinguish three different stages to illustrate the development of soil classification systems. Early soil classification systems (Russian, USDA 1938) focused on the environment and the soil forming factors to classify soils in zonal soils (in which the pedogenesis was mainly determined by climate and vegetation) and azonal and intrazonal (in which pedogenesis was mainly determined by parent material and time of development). The difference between azonal and intrazonal soils was made on the basis of soil profile development. A later development focused on the processes occurring in the soil itself (such as ferallitisation, salinization, leaching and accumulation etc…). These processes were roughly characterized by soil properties. A good example of the latter approach is the French classification system (CPCS, 1967). Modern soil classification started with the publication of the 7th Approximation of the USDA Soil Taxonomy, where precisely defined and quantified soil properties as such, or in combination, were used to define “diagnostic soil horizons”.
Physical Properties of Soil
Permeability (the rate at which water moves through the soil) and Water-Holding Capacity(WHC; the ability of a soils micropores to hold water for plant use) are affected by * The amount, size and arrangement of pores * Macropores control a soil’s permeability and aeration. * Micropores are responsible for a soil’s WHC
Porosity is in turn affected by * Soil texture * Soil structure * Compaction * Organic matter
Soil texture (the relative proportions of sand, silt, and clay) is important in determining the water-holding capacity of soil: 1. Fine-textured soils hold more water than coarse-textured soils but may not be ideal 2. Medium-textured soils (loam family) are most suitable for plant growth
- Sands are the largest particles and feel gritty
- Silts are medium-sized and feel soft, silky, or floury
- Clays are the smallest sized particles and feel sticky and are hard to squeeze.
- Relative size perspective: Sand (house) > Silt > Clay (penny)
Four main types of soil structure (the arrangement of aggregates in a soil): * Platy - common with puddling or ponding of soils * Prismatic (columnar) – common in subsoils in arid and semi-arid regions * Blocky – common in subsoils especially in humid regions * Granular (crumb) – common in surface soils with high organic matter content
Properties of soil particle size | Sand | Silt | Clay | Porosity | mostly large pores | small pores predominate | small pores predominate | Permeability | rapid | low to moderate | slow | Water holding capacity | limited | medium | very large | Soil particle surface | small | medium | very large |
Soil Compaction destoys the quality of the soil because it restricts rooting depth and decreases pore size. The effects are more water-filled pores less able to absorb water, increasing runoff and erosion, and lower soil temperatures. To reduce compaction: * Add organic matter * Make fewer trips across area * Practice reduced-till or no-till systems * Harvest when soils are not wet