Metal materials

6. Metal materials

Metals are the substances which have a number of specific features: brilliance, high thermal and electrical conductance.

T he iron-carbon alloys - steels (up to 2.14 % C) and cast-irons (2.14-6.67 % C) are widely used in modern technique, particularly in construction. Their specific weight is up to 95-97 % in the general volume of metals used in metal structures. Cast-irons and steels are the basic representatives of the ferrous metals. Aluminium, magnesium, zinc, as well as their alloys belongs to the nonferrous metals.

Metal materials in construction are mainly used as various products: plates, angled, double-T and channel-shaped sections (shapes, bars), pipes.

The production of the light steel structures made of the economic sections of rolled metals and low-alloy high-strength steel is increased. Mass of the light structures is less in 4-6 times than the ordinary steel structures; working hours diminish approximately at 30 %.

The application of the alloys based on light nonferrous metals, especially aluminum is enlarged (Fig.6.1). The external wall panels, structures of counter ceilings and partitions, window frames, doors, stained glasses, jalousies and others are made on the base of aluminum alloys. Aluminium alloys structures have less weight (2.7-2.9 t/m³), better fire-resistance, seismic resistance, cold resistance and durability in comparison with structural steel and approach to its strength.

6.1. Metal materials in construction

Iron-carbon alloys. The composition and structure, assignment and the most characteristic technical properties are the basic classification peculiarities of iron-carbon alloys.

Depending on composition and structure, cast-irons are divided into two basic groups: grey and white. In grey cast-irons a carbon is contained mainly as graphite, in white – as cementite (Fe₃C). The fracture dark grey in color is characteristic for the first one, and lusterless white – for the second one.

Grey cast-iron has good castability unlike the white cast-iron that has high hardness and fragility. The sanitary products, pipes, floors, tubing for tunnels and other products are made of grey cast-iron. The grey cast-iron can be graded depending on tensile strength. For example, its grades accordingly ASTM is given below.

ASTM Grade	Class 20	Class 30	Class 35	Class 40
Tensile Strength (PSI103)	20-27	24-34	30-40	40-45
Brinell Hardness	201 Max	223 Max	241 Max	262 Max

Note: 1 Pa= 145,04×10⁻⁶ PSI.

Addition of the special admixtures to the liquid grey cast-iron before pouring, allows to get modified, in particular, high-strength cast-iron. It is alloyed by chrome, nickel, molybdenum, titanium, aluminum to produce the cast-iron with the special properties: heat-resistant, frictionproof, anticorrosive etc.

White iron is assigned, mainly, for its processing into steel and malleable cast-iron production. Malleable cast-iron differs from the grey one with the enhanced plasticity, good processability. It is manufactured by the protracted heating (annealing) of white cast-iron at the temperature 760-980°C. The malleable cast-iron can be graded depending on tensile strength, yield strength and elongation. For example, grades accordingly ASTM is given below.

ASTM Grade	60-40-18	60-45-12	80-55-06	100-70-03	120-90-02
Tensile Strength (PSIx103)	60 Min	65 Min	80 Min	100 Min	120 Min
Yield Strength (PSIx103)	40 Min	45 Min	55 Min	70 Min	90 Min
Elongation (%)	18 Min	12 Min	6 Min	3 Min	2 Min

Cast-irons with the special properties are used in such cases, when the cast, except of strength, should be resistant to the wearing, corrosion etc.

Steels are divided according to their composition into carbon and alloyed steels. Carbon steels, except of iron and carbon, contain the admixtures of row of chemical elements which are brought with the raw materials or predefined by the features of production. There are distinguished low (to 0.3% C), intermediate-alloy (0.3–0.5% C) and high-alloy (over 0.5% C) steels. Alloyed steels contain along with ordinary admixtures some alloying ones, which are specially included elements - chrome (Cr), nickel (Ni), molybdenum (Mo), tungsten (W), silicon (Si), manganese (Mn), copper (Cu), phosphorus (P), titan (Ti), vanadium (V), nitrogen (N), niobium (Nb), aluminum (Al).

According to the assignment steels are divided into structural, tool and special steels.

S tructural carbon steel which contains 0.65-0.70% of the carbon is mainly applied for the building structures. At increasing the carbon content from 0.65 to 1.35% and manganese content up to 0.4% tool steel is obtained; at diminishing carbon to 0.2% - steel for the deep-drawing; with raised sulphur and phosphorus content - automatic steel which is used mainly for fixings production (bushings, nuts, screws etc.).

Strength and hardness of steels grow with the increasing of carbon content, but plasticity and weldability reduce (Fig 6.2). Carbon steel, fully deoxidized after melting, is called killed steel, partly deoxidized – semi-killed steel and unkilled steel. Killed steel hardens without noticeable gas emission. It have better strength properties, but at the same time less output of metal at rolling and higher cost in comparison with semi-killed and unkilled steels.

By quality there are carbon steels of ordinary quality and high-quality steels. Steel of ordinary quality is applied for production of building structures, fittings, pipes etc. There are applied steels with normalized composition and mechanical properties.

T here are different grades systems for steel in different countries. Definition of steel grade normally represents combination of letters and numbers, representing the composition and the most important steel properties. For example, in USA there are used several definitions of metals and alloys related to the standardization organizations: AISI, ACI, ANSI, ASTM, etc. In the wide-spread systems of definitions AISI (American Iron and Steel Institute) carbon and alloyed steels, as a rule, are determined by four numbers. For carbon steels there are 4 groups of grades: 10ХХ, 11ХХ, 12ХХ, 15ХХ. The first two numbers determine the number of steels group, and the last two – average content of carbon in the steel, multiplied per 100. Thus steel 1045 relates to the group 10ХХ of qualitative structural steels (unsulfonated, with Mn content lеss than 1%) and contains about 0.45% of carbon. Along with four numbers in the names of steels there also can occur the letters. Letters M and E are placed before the name of the steel, which means that the steel is purposed for production of irresponsible section steel (letter M) or smelting in the electric furnace (letter E). In the end of the name there can be present letter H, which determines that hardenability is the characteristic feature of the steel.

Grading system of steels in Europe is given in Fig.6.3 and Table 6.1, 6.2.

Table 6.1

Group 1. Mechanical properties of steel

Letter	Leading symbol	Additional symbol for steels
		Group 1	Group 2
S G - cast steel work placed before, if required	Structural steels   E.g S355J0 Properties:  Minimal yield stress (N/mm2) (three numbers).	Fracture energy (in Joules) tests 27 J     40 J     60 J      C JR        KR      LR     +20  J0       K0        L0         0  J2        K2       L2       -20  J3        K3       L3       -30  J4        K4       L4       -40  J5        K5       L5       -50  J6        K6       L6        -60 M= thermal mechanical deformed   N= normalized  Q= heat-treated  G= other properties, if required with 1 or 2 numbers	C= with special ductility in cold state  F= for forging  L= for low temperatures  M= thermal-mechanically deformed N= normalized  Q= heat-treated  S= for shipbuilding  T= for tubes  W= weather resistant
B	Reinforcing steel E.g: B500N  Properties: Yield stress (N/mm2) (three numbers).	N= normal elongation  H= high elongation  G= other properties, if required with 1 or 2 numbers	Letter and number,  if required
Y	Hot-rolled steels for prestressed structures For example: Y1770C  Properties: Minimal temporary resistance (N/mm2) (four numbers, zero before is possible).	С= cold-drawn wire  H= hot-rolled or prestressed bars Q= heat-treat wire S= thin cable  G= other properties, if required with 1 or 2 numbers

Table 6.2

Group 2. Chemical composition of steels

Letter		Leading symbol		Additional symbol for steels
				Group 1		Group 2
C G - cast steel work  placed before, if required	Alloy-free steels with average content of Mn < 1%.  E.g.: С35Е4  Carbon content: (up to three numbers = 100  average content of С of the assigned range		Е= specified maximum content SR= specified range of content SD= for wire drawing  С= specific ductility in cold state  W= for welding wire  G= other properties, if required with 1 or 2 numbers		Additional symbols are not provided
G - cast steel work  placed before, if required	Alloys-free steels with content of Mn > 1%, E.g.: 28Mn6  Carbon content: (up to three numbers = 100  average content С of assigned range.		Alloying elements:  Letters = symbols for characterization of alloying elements.  Numbers = separated, correspond to the average content of element, multiplied on the following factor.  Element                    Factor Cr, Co, Mn, Ni, Si,                 4 Al, Be, Cu, Mo, Nb, Pb, Ta, Ti, V, Zr     10 Ce, N, P, S                          100 B                                       1000

Carbon high-quality steel have an enhanced cleanness, the limits of carbon content are restricted, sulphur content should not exceed 0.04%; the phosphorus content should be the same. Depending on deoxidation degree these steels permanent can be killed or unkilled.

For low-alloy structural steels depending on the assured characteristics, categories are set which differ by the testing conditions on the impact strength.

Selecting the degree of responsibility and conditions of performance of steel structures the grades of steel and category of their delivery are taken into consideration.

Nonferrous metals alloys. For the production of aluminum alloys, foil, cable and electrically conductive elements aluminum of technical cleanness, containing 0.15-1% admixtures is used. Aluminum alloys are divided into two groups: 1 - alloys which are deformed, from which by rolling, pressing, dragging, forging and punching the various products and mouldings are obtained; 2- alloys which are assigned for making of production. The most typical aluminum alloys which are deformed (as duralumin) contain 2.2-5.2% Cu, up to 1.75% Mg, up to 1% Si, up to 1% Fe and up to 1% Mn. The grades of duralumin are signed with the letter D with a subsequent digit - conditional number of alloy with the increasing of which its mechanical strength increases. A commonly duralumin contains 4.4% copper, 1.5% magnesium, 0.6% manganese and 93.5% aluminum by weight. Typical yield strength is 450 MPa, with variations depending on the composition and temper. Although the addition of copper improves strength, it also makes these alloys sensitive to corrosion. For sheet products, corrosion resistance can be greatly enhanced by metallurgical bonding of a high-purity aluminum surface layer. Among castings aluminum alloys silumins are the most widespread alloys of aluminum with silicon, which is added in amount of 4-13%. Among the advantages of silumin is its high corrosion resistance, making it useful in humid environments.

Except of the aluminum alloys, copper alloys – brass and bronze, are applied in construction. Zinc is a basic alloying element (to 45%) in brass, and tin, aluminum, silicon and other elements are in bronze. At marking bronze and brass their composition is specified.

Magnesium alloys belong to the lightest structural materials (magnesium density is 1.7 g/cm³). The same as aluminum alloys, they are divided into alloys which are deformed and casting. Low density in combination with high strength and corrosive resistance are also characteristic for titanic alloys.

M etal products. Steel structures are produced of the rolled products and also of the formed and welded sections (Fig. 6.4).

Rolled products are the most widely used, divided into four groups: steel shape, sheet steel, special types of rolled metal, pipes. Various reticular and whole structures are assembled from the rolling sections: columns, beams, bunkers, masts, towers, pipelines, reservoirs etc.

The steel shape includes the sections of popular demand (round, square, L-steel, channels, I-beams) and sections of the special assignments (rails and others). The L-steel, I sections and channels are widely used in construction.

The angle sections are divided into two types: equal and unequal. The lightest angle sections have sizes 20×20 mm and thickness 3 mm (20×3), and the heaviest - correspondingly 250×250 and 30 mm (250×30).

The double-T sections and channel are selected by the numbers which correspond to their height in millimeters. The numbers of I sections vary from 10 to 60, channels - from 5 to 40. The I sections are rolled with long up to 19 m, channels – up to 18 m. They are applied mainly as beams which work on a bend and axle loading. Channels differ from the I sections with the moved wall to the edge of shelves. The form of channels simplifies assembling to their walls of other elements. Channels are widely used as the roof beams of industrial buildings.

In the last years metallurgical industry started to supply ight-weight I-beams, the main distinguishing feature of which are thinner walls.

Steel depending on the thickness of sheets is divided onto the plate steel (4-16 mm), sheet steel (0.2-4 mm), universal wide strip steel (4-60 mm), slabs (60 - 200 mm), roll and corrugated steel.

The sheet steel is in the form of the plates 8500 mm in width and up to 12 m in length. Steel sheets up to 40 mm thick are the most widely used in construction. Steel plates have length up to 4 m, width – 600-1400 mm. They are applied at production of bent slender sections and formed construction bent slender sections production. Manufacturing of bent sections enables to simplify substantially production technology of details and save up to 10% of metal. Shaped boarding is used for arranging of light and comfortable at the assembling roof.

The basic type of the rolled metal for construction is reinforcing bar (rebar). Rebar, or reinforcing bar, is a common steel bar, and is commonly used in reinforced concrete and reinforced masonry structures. It is usually made of carbon steel, and has ridges for better mechanical anchoring into the concrete. (Fig. 6.5).

Rebar is available in different grades and specifications that vary in yield strength, ultimate tensile strength, chemical composition, and percentage of elongation.

The grade designation is equal to the minimum yield strength of the bar in ski (1000 phi) for example grade 60 rebar has minimum yield strength of 60 ski. Rebar is typically manufactured in grades 40, 60, and 75.

Common specifications (accordingly ASTM) are:

- A 615 Deformed and plain carbon-steel bars for concrete reinforcement

- A 706 Low-alloy steel deformed and plain bars for concrete reinforcement

- A 955 Deformed and plain stainless-steel bars for concrete reinforcement

- A 996 Rail-steel and axle-steel deformed bars for concrete reinforcement

H istorically in Europe, rebar is made of mild steel material with yield strength of approximately 250 N/mm². Modern rebar is made of high-yield steel, with yield strength more typically 500 N/mm². Rebar can be supplied with various grades of ductility, with the more ductile steel capable of absorbing considerably greater energy when deformed - this can be of use in design to resist the forces from earthquakes for example.

Most grades of steel used in rebar are suitable for welding, which can be used to bind several pieces of rebar together. However, welding can reduce the fatigue life of the rebar, and as a result rebar cages are normally tied together with wire. Grade ASTM A706 is suitable for welding without damaging the properties of the steel. Besides fatigue concerns welding rebar has become less common in developed countries due to the high labor costs of certified welders. Steel for prestressed concrete may not be welded absolutely.

When welding or wire-tying rebar is impractical or uneconomical a mechanical connection or rebar coupler can be used to connect two or more bars together. These couplers are popular in precast concrete construction at the joints between members and to reduce rebar congestion in highly reinforced areas.

The metal pipes are widely used for the erection of towers, masts and other grillworks. The metal pipes are applied for the pressure pipings, to the pipelining in out-of-the-way places, and also when the use of pipes made of other material is impossible. The steel pipes are applied in pipelines with the power pressure more than 1.5 MPa, cast-iron - more than 1.2 MPa. Stand-pipes are subjected to the hydraulic pressure (P), MPa which is calculated by a formula:

, (6.1)

where S– minimum thickness of wall, mm; _q – permissible stress; D_int– internal diameter of pipe, mm.

Depending on the production method they are divided into the seamless hot-drawn and cold-drawn and electric-welded with longitudinal or spiral seam pipes.

The steel electric-welded pipes with internal cement-sand and external bituminous or other coating are widely applied for water transporting at the operating pressure up to 2 MPa for the reclamation work. The type of the steel pipes with anticorrosive coating is galvanized thin-walled pipes. They are applied for placing of the pipelines of the irrigative systems with pressure 0.8-1.5 MPa.

Along with the round welded pipes for steelworks square and rectangular welded pipes are applied.

Besides the steel, elements made of aluminum alloys as sheet products, bent and pressed sections are utilized in construction. Pressing enables to get aluminum sections, not only similar to steel ones but also other including comparatively complicated by shape.

Metal, assigned for the erection of building structures, is kept in stacks accordingly to its type, size and grade. It is palletized on the metal or wooden plates. For the aluminum products storage only the wooden plates are used. The wooden plates are saturated by the special mixture and dye with the paints to prevent the electrochemical corrosion of metal.

For storage of pipes, round and square steel the metallic shelvings are set which prevent the stack breakage.