Learn characteristics of main differences among galvannealed and galvanized steel. Find out about properties, applications, corrosion resistance and what coating will suit your project requirements.
The distinction between galvannealed steel and galvanized steel is important to any steel manufacturers, construction workers and any one utilizing the steel coated products. Both of the materials offer great resistance to corrosion, yet, given their specific characteristics, they are applied to various purposes. This in-depth guide is just what you need to make an informed choice as regards which type of coating can fit your particular project needs.
What is Galvanized Steel?
Galvanized steel reference Information galvanized steel; carbon steel with zinc protection added by hot-dip galvanizing. This is done by immersion of steel in molten zinc at around 860 o F (460 o C), and then a metallurgical bond is formed between zinc and the steel substrate.
Hot-dip galvanizing forms several layers of zinc-iron alloys and the outer layer is pure zinc. This zinc covering is highly corrosive resistant because of its ability to give sacrificial coverage to the underlying steel by shielding it off rusting and oxidation.
Key Characteristics of Galvanized Steel:
- Metallic shine and gleam of various bright colors
- Pure zinc outer coing
- Outstanding resistance to corrosion in the majority of environments
- Moderate bending good formability processing operations
- Normal designation but without special marking
What is Galvannealed Steel?
Galvanneal is galvanized steel and such steel is once again annealed in addition to the galvanization heat treatment. Post hot-dip galvanizing process, the steel is heated so that diffusion of alloying occurs between the molten coating of zinc and the underlying material of steel.
This extra heating changes the pure zinc covering to become a zinc-iron alloy making the resulting surface harder and more durable with improved characteristics to perform particular tasks. Galvannealed steel is such that it earned an “A” designations so as to divert it with the standard galvanized steel.
Key Characteristics of Galvannealed Steel:
- Dull, matte gray appearance
- Application of zinc-iron alloy coating all over
- High adhesion qualities of the paint
- Enhanced weldability
- Complex shapes can be formed better Enhances formability Enhanced formability Enhanced flexibility Enhanced flexibility Enhanced flexibility Enhanced ductility Enhanced ductility Enhanced ductility
Manufacturing Process Differences
The main distinction between these two kinds of steel is on the processes used to produce them once they have undergone the first stage of hot-dip galvanizing.
Galvanized Steel Process:
- Cleaning and preparations of steel
- Flux application
- Molten zinc bath galvanizing (Hot dipped galvanized)
- Finish and cooling
- Quality inspection
Galvannealed Steel Process:
- Cleaning and preparations of steel
- Flux application
- Molten zinc bath galvanizing (Hot dipped galvanized)
- Further heat treatment of annealing
- Controlled cooling
- Quality inspection
The ASTM A 653/A 653M standards are followed to produce both galvannealed and galvanized coatings and they both begin with the same process of hot dip. It is also during the annealing stage that the specific properties that makes galvannealed steel different to galvanized steel takes place.
Coating Composition and Structure
The performance difference can be explained by getting to know the composition of the coatings.
Galvanized Steel Coating:
- Outer layer: Only zinc (Eta layer)
- Middle layers: Several alloys of zinc- iron alloys
- Inboard Layer: Zinc-iron alloy Is fixed to steel base
- Total coating thickness: It is generally between 2-5 mils
Galvannealed Steel Coating:
- Even alloy of zinc-iron alloy all through the covering
- Broken and harder than pure zinc because of the formation of the zinc-iron alloying
- No zinc outer skin
- Total coating thickness: It is generally between 2-5 mils
Corrosion Resistance Comparison
Both materials are very good in protecting against corrosion although their performance is relative to the environment and the use.
Galvanized Steel Corrosion Resistance:
- Superb protection under majority of weather conditions
- Sacrificial protection is given by pure zinc outer layer
- Does well in sea conditions
- When scratched, self-healing properties are available
- The increased service life under adverse conditions
Galvannealed Steel Corrosion Resistance:
- Good corrosion resistance, but, depending on the application may be less corrosion resistant than conventional galvanized steel where the zinc-iron alloy layer could be undermined
- Barrier protection is yielded by zinc-iron alloy
- Applicable on majority areas that are indoors and moderate outdoors
- Reduced self healing capacity in comparison to galvanized steel
Paint Adhesion and Surface Preparation
Among the other major benefits of galvannealed steel is that they have better paint adhesion capabilities.
Galvannealed Steel Paint Adhesion:
- Best adhesion of paint as it has natural adhesion property
- A bit coarser pattern offers a better surface to paint sticking to it
- Low preparation of surfaces needed
- Powder coating applications suit it very well
- Perfect to use with appliances and auto parts
Galvanized Steel Paint Adhesion:
- Atomic zinc coating may be more slippery, thus not well suited to the adhesion of paint, unless it is better prepared
- Necessitates additional procedures of preparing the surface to guarantee the lifespan of its coating
- May need phosphating or etching prior to painting
- Adhesion can be potentially blocked by surface oils and oxidation
Formability and Workability
Both of the materials are characterized by good formability, which nevertheless differs due to the composition of coatings.
Galvanized Steel Formability:
- Moderate bending and forming good formability
- Zinc coating is ductile when it is pure
- May lose some coating when forming severely
- Is easy to fabricate in standard methods
Galvannealed Steel Formability:
- Being susceptible to brittleness due to increased hardness in relation to galvanized steel may restrict its applicability in any given work where flexibility is desired
- Ideal to complex forming processes
- Stronger and less subject to forming scars
- Greater insulation against coating peeling on manufacture
Welding Characteristics
Another aspect where some differences will be evident will be in regard to welding.
Galvanized Steel Welding:
- Special precaution is necessary because of zinc fumes
- Pure zinc coating may cause weld spatter to give May experience weld spatter to give
- Appropriate ventilation is vital to safety.
- And perhaps includes stripping of the coating in the weld regions
Galvannealed Steel Welding:
- More weldable in comparison to galvanized steel
- Coating using zinc-iron alloy generates few welding problems
- Reduced fume production of zinc when welding
- More quality weld and appearance
Applications and Industries
This is because galvannealed and galvanized steel will be based on need.
Galvanized Steel Applications:
- Building and structural use
- Barriers on the highway and guardrails
- Fencing and farm machinery
- Marine and coastal use
- Roofing systems and siding systems
- General fabrication with projects
Galvannealed Steel Applications:
- Electrical and mechanical parts of a vehicle
- Production of applications (freezers and refrigerators, washers, dryers)
- Equipment and ductwork in HVAC
- Manufacture of furniture and appliances
- Areas that should be painted or coated later
- Complex formed elements
Cost Considerations
Budget is a factor that may determine which materials to be used depending on what costs less.
Initial Material Costs:
- Galvannealed steel is usually 10-15 percent higher than galvanized steel
- Extra annealing contributes to costs of production
- A greater initial outlay can be compensated by savings in the process
Processing and Finishing Costs:
- Galvannealed steel lowers the costs of paint preparations
- Reduced welding prices as a result of enhanced solderability
- Less reworking and quality problems with painted jobs
- The total lifecycle cost can be in favour of galvannealed with some applications
Environmental and Safety Considerations
The two materials possess both environmental and security implications in their handling and processing.
Environmental Impact:
- The two materials are recyclable by 100%
- Zinc coated steels increase service life of steels and thus decreases replacement requirements
- Hot-dip galvanizing is an old established process that is environmentally responsible
- Galvannealed required a little more energy consumption because of annealing
Safety Considerations:
- Appropriate ventilation that must be applied when welding both materials
- Galvannealed yields less zinc fumes when welding is performed
- Generally accepted safety measures are there when dealing and processing
- No storage considerations to be considered on either material
Selection Criteria and Decision Factors
The selection of either galvannealed or galvanized steel must be done with a great deal of care bearing in mind a number of factors:
Choose Galvanized Steel When:
- The highest corrosion-resistant comes first
- One of the priorities is the cost
- Harsh environment will be applied to material
- It does not need painting or coating
- It can be formed by simple operations
Choose Galvannealed Steel When:
- There will be painting or powder coating on parts
- It needs complex forming activities
- Welding plays an important role in it
- The better is the adhesion of the paint
- Automobile or appliance application Work Working with automotive or appliance applications
Quality Standards and Specifications
The two materials are both produced to very high industry regulations that guarantee repeat quality and performance.
Applicable Standards:
- ASTM A653/A653M: Standard Specification For Steel Sheet, Zinc-Coated
- ASTM A924/A924M: Standard Specification of the General Requirements of Steel Sheet, Metallic-Coated
- ASTM A1063/A1063M: Standard Specification of Steel Sheet, Zinc- 5 %-aluminum Alloy- Coated
Quality Control Measures:
- Coating weight verification
- Adhesion testing
- Formability Bend testing
- Inspection of appearance of the surface
- Corrosion resistance test
Conclusion
It is always a matter of suitability of a galvannealed or galvanized steel to your application needs, budget and desired performance. Galvanized steel can be used in structural and outdoor assignments and has better corrosion resistance and cheaper initial costs thus use of galvanized steel is recommended where maximum protection is needed. Because it is more formable, weldable, and paint adheres well to it, galvannealed steel would be the choice when high volumes of manufactured products will need some form of finishing to follow thereafter.
Being aware of these differences, you can choose the most suitable material to complete your project and still be sure about its working and financial efficiency. Take into consideration environmental exposure, forming requirements, finishing needs, and that of total lifecycle costs in your decision.
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