The welding ability or Weldability is considered as the ability of a material to be welded under the suitably designed conditions of construction imposed in specific to perform satisfactorily in structure and intended service.
Definition of weldability
Weldability is the ability of a material to be welded by a process, under given conditions to perform satisfactorily at the desired service.
Weldability of materials
-Weldability can be defined as the property of a material that indicates the ease of joining metals together by a given welding process. This means that metals with good weldability can be readily welded to give satisfactory performance in the fabricated structure.
metals and their alloys with sufficient weldability must meet the following requirements:
- Compatibility of strength, toughness, and unchanged corrosion resistance after welding.
- Sound weld quality even with high dilution.
- Should not be embrittled when stress relieving
Characteristics of weldability
Some of the essential factors involved and affect weldability are as follows:
Metallurgical compatibility is the ability to join metals and their alloys, within the degree of dilution encountered in a specific process. without producing harmful components or steps.Mr. MUBASSIR I. GHONIYA of Mechanical Engineering.
Mechanical soundness is also an influencing factor and is required to meet rigidity requirements and general engineering standards.
The serviceability factors of resulting welded joints like:
It may concern the ability of the welded structure by a specific process, to work under low and high temperatures, impact loads, etc.
Factor affecting weldability
Several factors can influence the weldability of metals. such as the welding procedure(welding process, base metal properties, joint design, consumables, surface conditions), Metallurgy of materials, etc.
Effect of alloying elements
Alloying elements influence the hardenability of the heat-affected zone, The elements that have the greatest effect on the hardenability of steel are Si, C, V, Ni, Mn, Mo,andCr, etc,
The effect of these alloying elements on controlling the tendency to form heat affected zone martensite, and thus cold cracking may be expressed as carbon equivalent(CE)
=%C+%Mn/4 +%Ni/20 +%Cr/10+%Cu/40-%Mo/50-%V/10
- It may increase or decrease the hardenability of the metal.
- The precipitate from age-hardiness.
- Aluminum, vanadium, titanium, zirconium, and nitrogen act as grain refiners in carbon and alloy steels.
- Reduce segregation, control the tensile-to-brittle transformation temperature, Produce, substitutional alloys and strengthen the metal by solid solution hardening.
- Increase mechanical properties by lattice distortion(eg, carbon and boron, from interstitial alloys with steels
- Formation of carbides.
- Provide deoxidation of molten metal without loss of primary alloying elements(eg, titanium, zirconium, aluminum, silicon, etc., have an affinity for oxygen than iron and thus act as deoxidizers in carbon and low alloy steels).
The purpose of weldability testing is to collect such information about the behavior of the material during welding that it is possible to establish the correct welding condition. These tests provide useful information like heat treatment of the materials, energy input, Joint design preparation, etc.
These tests may be classified as theoretical tests, simulated tests, or actual welding tests.
An example of the theoretical weldability test can be as follows:
Member of notched bend specimens can be austenitized at 1150 degrees centigrade and at calculated rates to duplicate the expected hardness of the HAZ. If specimens can be bent through 10-20℃, they are considered sufficiently ductile for most applications.
A simulated test may involve heating and cooling a metal specimen over a thermal cycle exacting like that found in a particular weld.
Actual welding test
Actual welding tests may be of two types:
Fabrication weldability tests that determine the susceptibility of the welded joint(welding defects) to cracking .these tests are Hot cracking tests.,Root cracking tests and Hydrogen induced cracking tests.
Service weldability tests
Service weldability tests measure mechanical properties which are considered essential for the satisfactory performance of the welded joint during service. These tests are:
tensile, hardness, and bend tests.Impact tests.fatigue tests.corrosion tests.creep tests, etc.