Steel Weld-ability or P Number

P Number of steel is an indicator of weld-ability. The standard codes of weld-ability is refer to ASME standard that is approached to qualifying of welding procedures and welders/welding operators. For the purpose of specific toughness testing, each set of P number materials is subdivided into groups. The P Number of number materials are divided into groups 1 through 4, which loosely reflect the strength levels of the materials, as follows:

• Group 1: materials with a minimum tensile strength requirement less than 485 Mpa.
• Group 2: materials with a minimum tensile strength form 485 Mpa to less than 550 Mpa.
• Group 3: materials with a minimum tensile strength from 550 Mpa to less than 620 Mpa.
• Group 4: materials with tensile strength properties of more than 620 Mpa.

The purpose of P number is to establish qualification of material group based on weld-ability.

Effect of Chemical Composition on Weld-ability

Chemical composition of steel can affected the ability to be welding. The presence of certain chemical in the final micro-structure can effect to the weldability of steel. Weld-ability generally explain by means of a continuous transformation (CCT) diagram, which is formed by two sets of curved CCT diagram. Chemicals contain like carbon, manganese, chromium and molybdenum suppress the start of austenitic stainless steel, decomposition to lower temperature. Too much carbon contain on steel make more difficult to be welded, but contain metal like chromium, manganese or others make the steel easily to be welded. This is normal like the characteristic of metal generally.

The Quality of Welding

The characteristic of every kind of steel can different on welding apply, the increasing of temperature during welding change the crystal form, there is a limit temperature of each kind of steel to change the Chrystal form, Sometime the formed new crystal can have very bad behavior like easily to crack and even easily to corrode because of high temperature is applied during welding. So welding operator should understand the characteristic of each kind of steel and how they treat welding in order don’t break the crystal structure. Time and temperature of welding electrode will determine the quality of welding, more less a crystal structure change during welding, more better the quality of welding. The quality of welding can be seen under X-Ray, if the quality of welding is bad then the x-ray result showing porous picture. Good quality of welding will showing a solid picture of X-ray result.

Welding on Carbon Steel and Stainless Steel Result:

Here are example result of welding result on carbon steel:

carbon steel welding 1

carbon steel welding 2

The example result of welding on stainless steel:

stainless steel welding 1

stainless steel welding 2

Physical Properties of Carbon Steel

There are two properties of steel, physical properties and chemical properties of carbon steel. Physical properties of carbon steel are such as follows:

• Mean coefficient of linear thermal expansion; the ratio of the change in length to the original length at a reference temperature, To, per degree of temperature change, where To is normally room temperature. If lo is the length at To and alpha, α is the mean coefficient of linear thermal expansion, the length at temperature T, lt is given be this formula:

Lt = lo [1 + α (T – To)]

• Linear thermal expansion; the change in length over a specific temperature range per 30.5 m.
• Modulus of elasticity (E); 1. The measure of rigidity or stiffness of a material; the ratio of stress below the proportional limit to corresponding strain. 2. The slope of a stress strain curve in the range of linear proportionality of stress to strain. This known as Young’s modulus.
• Thermal conductivity; the quantity of heat transmitted, k, due to unit temperature gradient, in unit time under steady conditions in a direction normal to a surface of unit area and when the heat transfer is solely dependent on the temperature gradient.
• Thermal diffusivity; the constant in heat conduction equation describing the rate at which heat is conducted through a material. It is linked to thermal conductivity, k, specific heat, Cp, and density, , through the equation.

 Thermal diffusivity = k/Cp.⍴

• Electrical resistivity; a measure of how strongly a material opposed the flow of electric current.

Electrical resistivity = ⍴ = RA/L

• Specific heat: the amount of heat, Cp, measured in calories, required to raise the temperature of one gram of substance by one degree Celsius.
• Density: the mass per unit volume of a solid material
• Specific gravity: the ratio of the density of a substance to the density of water.
• Shear modulus (G): The ratio of shear stress to the corresponding shear strain for shear stresses below the proportional limit of the material. Value of shear modulus are usually determined by torsion testing. Shear modulus is also known as the modulus of rigidity.
• Melting point: melting point is the temperature at which a metal change from solid to liquid; temperature at which the liquid and solid are at equilibrium.
• Poisson’s Ratio: the absolute value of the ratio of transverse (lateral) strain to the corresponding axial strain resulting from uniformly distributed axial stress below the proportional limit of the material.

physical properties of carbon steel

Related Articles:

• Tensile Strength Test
• Carbon Steel Composition

Chemical Composition of Carbon Steel

Chemical composition of carbon steel are established by material specifications for each type or grade of material. The elements that are not identified should not be present in more than trace amounts except iron. Iron is the main contain of carbon steels. Other element is present in iron metal as the impurities of element, if too much the trace element will effect to the quality of the end product.

On the real product each carbon steel or metal will have vary of composition after test by heat analysis. This because when taken from the molten heat and given on the certified material test report, the actual composition of the end product might be vary due to the fluctuations that occur during solidification and processing. So for certain grade of steel will have range quality standard to anticipate this problem, and the result of product analysis will somewhat less different.






The range of steel grade in steel composition such as in alloy steel, that give the limited of carbon, manganese and silicon added in limited and varying percentages to the iron base. Even this element percentage is limited by standard, the properties of material are wide ranging. The metallurgical structure and carbon content are major contributor to the overall properties of the different carbon steel material. Steel classified as carbon steel will contain small amounts of other elements, such as chromium, molybdenum, copper, vanadium, niobium (columbium). Phosphorous and sulfur. This element usually already contain on iron as impurities elements.

Each elements that is exist in the base iron steel has some effect on the end properties of carbon steel or alloy steel and how this material will process and react to fabrication. Especially for alloy steel some element deliberately added to the base iron, with the composition depend on the grade of carbon steel. The composition of each grade is discussed in here: Steel Composition

Carbon Steel in Different Standard

Carbon steel standard in every country can be have different symbol, but they have similar classification as describe in ASME or ASTM. Carbon steel as ASME can be used as material for high pressure tank like Boiler and Pressure Vessel. Boiler and pressure vessel at room temperature can be have 40 kips per sq in (ksi) or 275 mega-pascals (Mpa) up to 100 ksi (690 Mpa). Material which can use as high pressure strength in application are very limited, material should have minimum tensile strength less than 80 ksi (550 Mpa), this material usually use high carbon steel.

Carbon steel are choose as material for any purpose because of same reason in all of user, the price, the properties and ease of fabrication. Carbon steel composition can be slightly different in each manufacturing but the limitation of their characteristic should include in the range of standard. Material specification of ASME and ASTM are similar in both chemicals and mechanical properties to those of the international specifications listed.

The table below are carbon steel standard comparative International Specifications.

comparation carbon steel standard

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Carbon Steel Grade and Application

The meaning of carbon steel in general sense is steel that contain of carbon substance inside the alloy steel. Steel itself is usually mean an iron based that contain of many kind of other substance composed them, pure iron usually contain other substance less than 2%. Carbon steel also called as plain carbon steel, ordinary steels or straight carbon steels, steel itself can contain only residual amount of element other than carbon for example silicon, aluminum, managanese and cerium. Silicon and aluminum are added into steel for deoxidation while manganese and cerium added to steel in purpose to counteract certain deleterious effect of residual sulfur. Silicon and manganese can be added in amount greater than those required strictly to meet these criteria, for example 0.60% silicon and 1.65% of manganese are accepted as the limit of carbon steel.

Carbon steel that still better for construction structure usually contain about 0.35% in order can be welded. The grade of carbon steel are divide into several type such as below:

• Low carbon steel contain below 0.15% of carbon, this steel suitable for hot worked.
• Mild Steel contain of carbon below 0.25%, this steel have somewhat higher strength near the upper carbon level. This steel better to construct of base structural steel to hold pipe lining or many other application.
• Medium carbon steels, this steel contain carbon 0.25% - 0.55%, this kind of carbon steel better for steel that used to be harden by heat treatment (quenched and tempered) to achieve yet higher strength and hardness. 
• High carbon steel

Carbon steel is the most important steel that widely used in Industrial construction and material uses. This material is used not only in many of water and steam pressure system, such as in power plants and support system. Carbon is such a powerful alloying element in steel, there are significant differences in the strength, hardness, and ductility achievable with relatively small variations in the levels of carbon in the composition. Industrial application that usually use of carbon steel like material fabrication, heat treatment, component fabrication, and fabrication process, the uses of carbon steel can in significant changes to the properties of carbon steel components.

Carbon steel in general established by coded and standards that should be implemented to achieve adequate result when working with carbon steels. Engineering division should be fulfill with this knowledge to make a decision what type of steel that should be use in there application.

See other type of Steel:

Carbon Steel

Carbon Steel Definition

It is important to clarify the meaning of carbon steel in the generic sense and in the more narrow context used in this report. The term steel is usually taken to mean an iron-based alloy containing carbon in amounts less than about 2%. Carbon steels (sometimes also termed plain carbon steels, ordinary steels, or straight carbon steels) can be defined as steels that contain only residual amounts of elements other than carbon, except those (such as silicon and aluminum) added for deoxidation and those (such as manganese and cerium) added to counteract certain deleterious effects of residual sulfur. However, silicon and manganese can be added in amounts greater than those required strictly to meet these criteria so that arbitrary upper limits for these elements have to be set; usually, 0.60% for silicon and 1.65% for manganese are accepted as the limits for carbon steel. The main component of carbon steel is Iron. This iron then mixed with other substance may other metal or Carbon to produce Carbon Steel.




The carbon steels of interest in this report are those with carbon equal to or less than about 0.35% to facilitate welding. A further distinction can be made according to carbon content. Low-carbon steels (below 0.15% carbon) contain too little carbon to benefit from hardening and are frequently used in the hot-worked or - for maximum ductility - the annealed condition. Steels of less than 0.25% carbon (often referred to as mild steel) have somewhat higher strength near the upper carbon level.

Medium-carbon steels (0.25–0.55% carbon) are often heat-treated (quenched and tempered) to achieve yet higher strength, but it is mainly the compositions below 0.35% carbon that are relevant to this report. Carbon steel is one of the most widely used materials in the industry. This material is used not only in many of the water- and steam-pressure containing systems in power plants but also in the supports for these systems. Although this report concentrates primarily on the pressure containing applications of carbon steels, it can also be a useful tool for structural carbon steel fabrication issues.

As the description implies, the primary alloying element of these iron based materials is carbon. Because carbon is such a powerful alloying element in steel, there are significant differences in the strength, hardness, and ductility achievable with relatively small variations in the levels of carbon in the composition. However, other important factors - such as material fabrication, heat treatment, component fabrication, and fabrication processes - can result in significant changes to the properties of the carbon steel components. In some cases, requirements established by codes and standards must be supplemented to achieve adequate results when working with carbon steels. It is important for the utility engineer to have access to metallurgical and properties information to aid in making decisions for projects involving carbon steels. This report is intended to provide such information on the most common boiler and piping materials used in power plants. Not all carbon steels will be covered explicitly, but the user should be able to draw relevant information needed for any required decision. The difficulties on formulate a carbon steel material is on their mixing, certain technology use for this mixing in order can make homogenize composition.

Mechanical Properties of Carbon Steel

The properties of carbon steel is perform at room temperature, on the text book usually compare to elevated temperature, what the effect to carbon steel if any temperature changes. This characteristic can draw how danger of any structure in special condition like on fire or any earth quake.

Many parameter in mechanical properties, but you just need to watch and compare of yield strength properties and tensile strength properties. There are two type of product divide that is hot rolled structural steel and structural hollow section.

There are many kind of product standard of carbon steel, in general carbon steel is coded into product standards EN 10025, EN 10210 and EN 10219. This one of the table, for the detail you must see on steel handbook.

The graph of properties each carbon steel grade as follows, yield strength is drawn with fy, and tensile strength with fu.

carbon steel properies

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Related articles about carbon steel:

• Mild Steel and Stainless Steel
• Carbon Sheet Steel
• Alloy
• Stainless Steel

Chemical Composition of Carbon Steel

Chemical Composition of Carbon Steel

The chemical compositions of carbon steel are also established by the material specifications for each type or grade of material. The elements that are not identified should not be present in more than trace amounts except iron, of course, the primary constituent of carbon steels. The quality of carbon steel depend on the production quality process, some carbon steel from certain plant can have higher price than from other plant.

Single values are minimums unless otherwise identified, and ranges are given for other elements. The UNS number is listed again for convenience and because the main criteria used to establish that identification is the chemical composition of carbon steel.

The heat analysis is given unless otherwise noted. Although this is the analysis taken from the molten heat and given on the certified material test report, the actual composition of the end product might vary in excess of the heat analysis due to fluctuations that occur during solidification and processing. The limits on the product analysis are therefore somewhat less restrictive than those of the heat analysis.

As previously discussed, the alloying that is used for the materials covered by this report is limited primarily to carbon, manganese, and silicon added in limited and varying percentages to the iron base. In spite of this limited alloying, the properties of the materials are wide-ranging.

The metallurgical structure and the carbon content are major contributors to the overall properties of the different carbon steel materials. Materials classified as carbon steel might also contain small amounts of other elements, such as chromium, nickel, molybdenum, copper, vanadium, niobium (columbium), phosphorous, and sulfur.

Each element that is added to the basic constituent of iron has some effect on the end properties of the material and how that material reacts to fabrication processes. The alloying additions are responsible for many of the differences between the various types or grades of carbon steels.

Following is a list of the elements commonly added to iron and their effects on the material, each of ingredient in carbon steel composition:

• Carbon: Carbon is the most important alloying element in steel and can be present up to 2% (although most welded steels have less than 0.5%). The carbon can exist either dissolved in the iron or in a combined form, such as iron carbide (Fe3C). Increased amounts of carbon increase hardness and tensile strength as well as response to heat treatment (hardenability). On the other hand, increased amounts of carbon reduce weldability.
• Manganese: Steels usually contain at least 0.3% manganese, which acts in a three-fold manner: it assists in deoxidation of the steel, prevents the formation of iron sulfide inclusions, and promotes greater strength by increasing the hardenability of the steel. Amounts up to 1.5% are commonly found in carbon steels.
• Silicon: Usually, only small amounts (0.2%, for example) are present in rolled steel when silicon is used as a deoxidizer. However, in steel castings, 0.35–1.0% is common. Silicon dissolves in iron and tends to strengthen it. Weld metal usually contains approximately 0.5% silicon as a deoxidizer. Some filler metals can contain up to 1.0% to provide enhanced cleaning and deoxidation for welding on contaminated surfaces. When these filler metals are used for welding of clean surfaces, the resulting weld metal strength will be markedly increased. The resulting decrease in ductility could present cracking problems in some situations.
• Sulfur: This is an undesirable impurity in steel rather than an alloying element. Special effort is made to eliminate or minimize sulfur during steelmaking. In amounts exceeding 0.05%, it tends to cause brittleness and reduce weldability. Additions of sulfur in amounts from 0.1% to 0.3% will tend to improve the machinability of steel but impair weldability. These types of steel can be referred to as freemachining.
• Phosphorus: Phosphorus is also considered to be an undesirable impurity in steels. It is normally found in amounts up to 0.04% in most carbon steels. In hardened steels, it tends to cause embrittlement. In low-alloy, high-strength steels, phosphorus can be added in amounts up to 0.10% to improve both strength and corrosion resistance, although it is not generally added for this reason in carbon steels.
• Chromium: Chrome is a powerful alloying element in steel. It is added for two principal reasons: first, it greatly increases the hardenability of steel; second, it markedly improves the corrosion resistance of iron and steel in oxidizing types of media. Its presence in some steels could cause excessive hardness and cracking in and adjacent to the weld. Stainless steels contain chromium in amounts exceeding 12%.
• Molybdenum: This element is a strong carbide former and is usually present in alloy steels in amounts less than 1.0%. It is added to increase hardenability and to elevate temperature strength.
• Nickel: Nickel is added to steels to increase their hardenability. It performs well in this function because it often improves the toughness and ductility of the steel, even with the increased strength and hardness. Nickel is frequently used to improve steel toughness at low temperatures.
• Vanadium: The addition of vanadium will result in an increase in the hardenability of steel. It is very effective in this role, so it is generally added in minute amounts. In amounts greater than 0.05%, there can be a tendency for the steel to become embrittled during thermal stress relief treatments.
• Columbium: Columbium (also called niobium), like vanadium, is generally considered to increase the hardenability of steel. However, due to its strong affinity for carbon, it can combine with carbon in the steel to result in an overall decrease in hardenability.
• Other alloying elements; Some carbon steel specifications allow additions of certain other elements, but they are not deliberately added। Other specifications might list these elements as a specified addition to the steel, but the addition would be minor in carbon steels. 

Steel that composed from many kind metal called as Alloy see here:

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