EFFECTS OF CHEMISTRY ON STEEL PROPERTIES TUTORIALS

CHEMISTRY EFFECT ON STEEL PROPERTIES
What Are The Chemical Effects On Steel?


Chemical composition determines many characteristics of steels important in construction applications. Some of the chemicals present in commercial steels are a consequence of the steel making process. Other chemicals may be added deliberately by the producers to achieve specific objectives. Specifications therefore usually require producers to report the chemical composition of the steels.

During the pouring of a heat of steel, producers take samples of the molten steel for chemical analysis. These heat analyses are usually supplemented by product analyses taken from drillings or millings of blooms, billets, or finished products. ASTM specifications contain maximum and minimum limits on chemicals reported in the heat and product analyses, which may differ slightly.

Principal effects of the elements more commonly found in carbon and low-alloy steels are discussed below. Bear in mind, however, that the effects of two or more of these chemicals when used in combination may differ from those when each alone is present. Note also that variations in chemical composition to obtain specific combinations of properties in a steel usually increase cost, because it becomes more expensive to make, roll, and fabricate.

Carbon is the principal strengthening element in carbon and low-alloy steels. In general, each 0.01% increase in carbon content increases the yield point about 0.5 ksi. This, however, is accompanied by increase in hardness and reduction in ductility, notch toughness, and weldability, raising of the transition temperatures, and greater susceptibility to aging.

Hence limits on carbon content of structural steels are desirable. Generally, the maximum permitted in structural steels is 0.30% or less, depending on the other chemicals present and the weldability and notch toughness desired.

Aluminum, when added to silicon-killed steel, lowers the transition temperature and increases notch toughness. If sufficient aluminum is used, up to about 0.20%, it reduces the transition temperature even when silicon is not present.

However, the larger additions of aluminum make it difficult to obtain desired finishes on rolled plate. Drastic deoxidation of molten steels with aluminum or aluminum and titanium, in either the steel making furnace or the ladle, can prevent the spontaneous increase in hardness at room temperature called aging. Also, aluminum restricts grain growth during heat treatment and promotes surface hardness by nitriding.

Boron in small quantities increases hardenability of steels. It is used for this purpose in quenched and tempered low-carbon constructional alloy steels. However, more than 0.0005 to 0.004% boron produces no further increase in hardenability. Also, a trace of boron increases strength of low-carbon, plain molybdenum (0.40%) steel.

Chromium improves strength, hardenability, abrasion resistance, and resistance to atmospheric corrosion. However, it reduces weldability. With small amounts of chromium, low-alloy steels have higher creep strength than carbon steels and are used where higher strength is needed for elevated-temperature service. Also chromium is an important constituent of stainless steels.

TYPES OF BRICKS USED IN CIVIL STRUCTURAL ENGINEERING CONSTRUCTION BASICS

BRICKS USED IN CIVIL STRUCTURAL CONSTRUCTION BASIC INFORMATION
What Are The Different Type of Bricks Used In Construction?


Brick is obtained by moulding good clay into a block, which is dried and then burnt. This is the oldest building block to replace stone.

Manufacture of brick started with hand moulding, sun drying and burning in clamps. A considerable amount of technological development has taken place with better knowledge about to properties of raw materials, better machinaries and improved techniques of moulding drying and burning.

The size of the bricks are of 90 mm × 90 mm × 90 mm and 190 mm × 90 mm × 40 mm. With mortar joints, the size of these bricks are taken as 200 mm × 100 mm × 100 mm and 200 mm × 100 mm × 50 mm.


Types of Bricks
Bricks may be broadly classified as:
(i) Building bricks
(ii) Paving bricks
(iii) Fire bricks

(iv) Special bricks.
(i) Building Bricks: These bricks are used for the construction of walls.
(ii) Paving Bricks: These are vitrified bricks and are used as pavers.
(iii) Fire Bricks: These bricks are specially made to withstand furnace temperature. Silica bricks belong to this category.
(iv) Special Bricks: These bricks are different from the commonly used building bricks with respect to their shape and the purpose for which they are made. Some of such bricks are listed below:
(a) Specially shaped bricks
(b) Facing bricks
(c) Perforated building bricks
(d) Burnt clay hollow bricks
(e) Sewer bricks
( f ) Acid resistant bricks.

(a) Specially Shaped Bricks: Bricks of special shapes are manufactured to meet the requirements of different situations. Some of them are shown in Fig. 1.3.

(b) Facing Bricks: These bricks are used in the outer face of masonry. Once these bricks are provided, plastering is not required. The standard size of these bricks are 190 × 90 × 90 mm or 190 × 90 × 40 mm.

(c) Perforated Building Bricks: These bricks are manufactured with area of perforation of 30 to 45 per cent. The area of each perforation should not exceed 500 mm2. The perforation should be uniformly distributed over the surface. They are manufactured in the size 190 × 190 × 90 mm and 290 × 90 × 90 mm.

(d) Burn’t Clay Hollow Bricks: Figure 1.4 shows a burnt clay hollow brick. They are light in weight. They are used for the construction of partition walls. They provide good thermal insulation to buildings. They are manufactured in the sizes 190 × 190 × 90 mm, 290 × 90 × 90 mm and 290 × 140 × 90 mm. The thickness of any shell should not be less than 11 mm and that of any web not less than 8 mm.

e) Sewer Bricks: These bricks are used for the construction of sewage lines. They are manufactured from surface clay, fire clay shale or with the combination of these. They are manufactured in the sizes 190 × 90 × 90 mm and 190 × 90 × 40 mm. The average strength of these bricks should be a minimum of 17.5 N/mm2 . The water absorption should not be more than 10 per cent.

( f ) Acid Resistant Bricks: These bricks are used for floorings likely to be subjected to acid attacks, lining of chambers in chemical plants, lining of sewers carrying industrial wastes etc. These bricks are made of clay or shale of suitable composition with low lime and iron content, flint or sand and vitrified at high temperature in a ceramic kiln.