[Zohreh Gholami]

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Articles in this section are provided Metallurgy

[Zohreh Gholami]

ASME P-Numbers

To reduce the number of welding and brazing procedure qualifications required base metals have been assigned P-Numbers by the ASME BPVC.  Ferrous metals which have specified impact test requirements have been assigned Group Numbers within P-Numbers.

These assignments have been based on comparable base metal characteristics, such as:
     Composition
     Weldability
     Brazeability
    Mechanical Properties

Indiscriminant substitution of materials in a set of P-Numbers or Group Numbers may lead to problems or potentially failures.  Engineering assessment is necessary prior to a change in materials.

When a base metal with a UNS number Designation is assigned a P-Number, then a base metal listed in a different ASME material specification with the same UNS number shall be considered that P-Number.

The table below is a guide and is for instructive purposes only.  Anyone specifying materials or requirements should refer directly to the ASME Boiler and Pressure Vessel Code to specify materials, P-Numbers,  procedures, or other requirements and not rely on the table below.  The table below is only a rather incomplete and approximate summary of ASME data

[Zohreh Gholami]

Welding Steel Alloys

Welding Steel AlloysSteel Alloys can be divided into five groups
Carbon Steels
High Strength Low Alloy Steels
Quenched and Tempered Steels
Heat Treatable Low Alloy Steels
Chromium-Molybdenum Steels

Steels are readily available in various product forms.  To establish a proper welding procedure it is necessary to know the material properties of the steel being welded.  The American Iron and Steel Institute defines carbon steel as follows:   


Steel is considered to be carbon steel when no minimum content is specified or required for chromium, cobalt, columbium [niobium], molybdenum, nickel, titanium, tungsten, vanadium or zirconium, or any other element to be added to obtain a desired alloying effect; when the specified minimum for copper does not exceed 0.40 per cent; or when the maximum content specified for any of the following elements does not exceed the percentages noted: manganese 1.65, silicon 0.60, copper 0.60.  Carbon steels are normally classified as shown below.

Low-carbon steels contain up to 0.30 weight percent C. The largest category of this class of steel is flat-rolled products (sheet or strip) usually in the cold-rolled and annealed condition. The carbon content for these high-formability steels is very low, less than 0.10 weight percent C, with up to 0.4 weight percent Mn.  For rolled steel structural plates and sections, the carbon content may be increased to approximately 0.30 weight percent, with higher manganese up to 1.5 weight percent.

Medium-carbon steels are similar to low-carbon steels except that the carbon ranges from 0.30 to 0.60 weight percent and the manganese from 0.60 to 1.65 weight percent. Increasing the carbon content to approximately 0.5 weight percent with an accompanying increase in manganese allows medium-carbon steels to be used in the quenched and tempered condition.

High-carbon steels contain from 0.60 to 1.00 weight percent C with manganese contents ranging from 0.30 to 0.90 weight percent.

High-strength low-alloy (HSLA) steels, or microalloyed steels, are designed to provide better mechanical properties than conventional carbon steels.  They are designed to meet specific mechanical properties rather than a chemical composition.  The chemical composition of a specific HSLA steel may vary for different product thickness to meet mechanical property requirements.  The HSLA steels have low carbon contents (0.50 to ~0.25 weight percent C) in order to produce adequate formability and weldability, and they have manganese contents up to 2.0 weight percent.  Small quantities of chromium, nickel, molybdenum, copper, nitrogen, vanadium, niobium, titanium, and zirconium are used in various combinations.

Below are some typical welding considerations when welding carbon and low alloy steels
Carbon Equivalent of the Steel
Weld Cooling Rates
Solidification Cracking
Reheat Cracking
Lamellar Tearing
Hydrogen Cracking

If your company is experiencing these or other welding problems you can retain AMC to improve your weld processing.  Hire AMC to act as your welding specialist. 

[Zohreh Gholami]

Alloy Selection

Base metal and filler metal alloy selection is critical to producing good quality welds.  Proper alloy selection can reduce numerous welding problems.

Does the aluminum welding you are performing result in significant reductions in tensile strength?  Is the alloy you are using susceptible to cracking.?  Does your weld need a post welding heat treatment?  Are your processing parameters appropriate?  Can your yield be improved?  Can your weld quality be improved?  Contact us about exotic alloys or common alloys as listed below:
Commonly used Welding Alloys
Aluminum
Steel
Stainless Steel
Titanium
Nickel and Cobalt 
Magnesium
Copper
Benefits from Proper Alloy Selection
Increase weld quality and yield
Proper weld joint strength
Good corrosion and oxidation resistance
Reduction of weld and HAZ cracking
Eliminate reheat cracking
Eliminate stress corrosion cracking
Eliminate lamellar tearing
Improved weldability
Optimize dissimilar metal joints

Let AMC engineers help you identify proper base metal and filler rod alloys for your application.  Select economical, good quality welding procedures to meet your customer needs.  Let us optimize your welding procedure to improve yield, reduce rework, and reduce weld discontinuities.

Proper cleaning, processing, heat treating of your weld joint will reduce costs, reduce failures, and increase customer satisfaction.  If your company is experiencing these or other welding problems you can retain AMC to improve your weld processing.  Hire AMC to act as your welding specialist.

[Zohreh Gholami]

Aluminum Welding

Aluminum is the most difficult alloy to weld.  Aluminum oxide should be cleaned from the surface prior to welding.  Aluminum comes in heat treatable and nonheat treatable alloys.  Heat treatable aluminum alloys get their strength from a process called ageing.  Significant decrease in tensile strength can occurs when welding aluminum due to over aging.  For more information on aluminum welding processes, benefits of welding processes, welding discontinuities, or common welding problems please visit our homepage or any of the links to your left.  Take advantage of our aluminum welding experience in developing your welding processes.



Welding Aluminum Alloys
Aluminum Alloys can be divided into nine groups.

Designation    Major Alloying Element

1xxx   Unalloyed (pure) >99% Al
2xxx   Copper is the principal alloying element, though other elements (Magnesium) may be specified
3xxx   Manganese is the principal alloying element
4xxx   Silicon is the principal alloying element
5xxx   Magnesium is the principal alloying element
6xxx   Magnesium and Silicon are principal alloying elements
7xxx   Zinc is the principal alloying element, but other elements such as Copper, Magnesium, Chromium, and Zirconium may be specified
8xxx   Other elements  (including Tin and some Lithium compositions)
9xxx    Reserved for future use


Aluminum alloys are readily available in various product forms.  To establish a proper welding procedure it is necessary to know the material properties of the Aluminum alloy being welded.

Below are some of the factors affecting the welding of Aluminum.
Aluminum Oxide Coating
Thermal Conductivity
Thermal Expansion Coefficient
Melting Characteristics



Wrought Aluminum Alloys

1xxx Series.  These grades of aluminum are characterized by excellent corrosion resistance, high thermal and electrical conductivities, low mechanical properties, and excellent workability. Moderate increases in strength may be obtained by strain hardening. Iron and silicon are the major impurities.


2xxx Series.  These alloys require solution heat treatment to obtain optimum properties; in the solution heat-treated condition, mechanical properties are similar to, and sometimes exceed, those of low-carbon steel. In some instances, precipitation heat treatment (aging) is employed to further increase mechanical properties. This treatment increases yield strength, with attendant loss in elongation; its effect on tensile strength is not as great.

The alloys in the 2xxx series do not have as good corrosion resistance as most other aluminum alloys, and under certain conditions they may be subject to intergranular corrosion.  Alloys in the 2xxx series are good when some strength at moderate temperatures is desired.  These alloys have limited weldability, but some alloys in this series have superior machinability.


3xxx Series.  These alloys generally are non-heat treatable but have about 20% more strength than 1xxx series alloys. Because only a limited percentage of manganese (up to about 1.5%) can be effectively added to aluminum, manganese is used as a major element in only a few alloys.


4xxx Series. The major alloying element in 4xxx series alloys is silicon, which can be added in sufficient quantities (up to 12%) to cause substantial lowering of the melting range.  For this reason, aluminum-silicon alloys are used in welding wire and as brazing alloys for joining aluminum, where a lower melting range than that of the base metal is required.  The alloys containing appreciable amounts of silicon become dark gray to charcoal when anodic oxide finishes are applied and hence are in demand for architectural applications.


5xxx Series. The major alloying element is Magnesium and when it is used as a major alloying element or with manganese, the result is a moderate-to-high-strength work-hardenable alloy.  Magnesium is considerably more effective than manganese as a hardener, about 0.8% Mg being equal to 1.25% Mn, and it can be added in considerably higher quantities.  Alloys in this series possess relatively good welding characteristics and relatively good resistance to corrosion in marine atmospheres.  However, limitations should be placed on the amount of cold work and the operating temperatures permissible for the higher-magnesium alloys to avoid susceptibility to stress-corrosion cracking.


6xxx Series. Alloys in the 6xxx series contain silicon and magnesium approximately in the proportions required for formation of magnesium silicide (Mg2Si), thus making them heat treatable.  Although not as strong as most 2xxx and 7xxx alloys, 6xxx series alloys have relatively good formability, weldability, machinability, and relatively good corrosion resistance, with medium strength.  Alloys in this heat-treatable group are sometimes formed in the T4 temper (solution heat treated but not precipitation heat treated) and strengthened after forming to full T6 properties by precipitation heat treatment.


7xxx Series. Zinc, in amounts of 1 to 8% is the major alloying element in 7xxx series alloys, and when coupled with a smaller percentage of magnesium results in heat-treatable alloys of moderate to high strength. Usually other elements, such as copper and chromium, are also added in small quantities. Some 7xxx series alloys have been used in airframe structures, and other highly stressed parts.  Higher strength 7xxx alloys exhibit reduced resistance to stress corrosion cracking and are often utilized in an overaged temper to provide better combinations of strength, corrosion resistance, and fracture toughness.



Aluminum Welding Services
Visit our homepage for detailed information on arc welding processes, welding procedures, weld failure analysis, and expert witness testimony.  AMC can solve your companies aluminum welding procedure problems.  Hire AMC to act as your welding specialist.