One of the main things to consider while welding is whether the metal you’re welding will become more fragile once you join it with another metal.
So does welding weakens steel? The answer is Yes, welding does make the steel weak, particularly in the heat-affected zone (HAZ), while welding at high temperatures. Welding with Cold rolled steel is usually weak.
Below are common methods that you can use to join different metals:
- Brazing
- Soldering
- Welding
Any of these three techniques you can use for joining metals. Another way to join the metal is by filling the gaps between them. The metals you will connect must be similar if you intend to use the welding method. You won’t be able to weld copper to steel. We have discussed factors that weaken steel in the article below.
Read Also: Welding Vs. Brazing
Factors Affecting the Strength of Steel
Several factors can affect the strength of welded steel, including:
- Welding techniques can result in different levels of strength in the final product. For example, some welding techniques, such as resistance welding, can have a stronger bond than others, such as gas welding.
- The parameters used during the welding process, such as temperature and pressure, can also affect the strength of the final product.
- The quality of the materials used in the welding process, such as the type of steel and the thickness of the metal, can also impact the final product’s strength.
How Does Welding Work When Two Metals are Joined?
Exposing the metal to temperature alteration via a heat transfer zone changes the metal’s physical properties causing the weakening of steel. If the metal isn’t mono-structure like glass, then temperature alteration changes it by affecting its crystalline and grain size.
MIG, laser, stir friction, and the electron beam is other welding methods you can use. High heat can also be used to apart two large metal structures. Excess heat applied to the metal decreases its strength, makes it soft, and increases elasticity. In opposition, metal can be brittle and hard.
Heat Affected Zone (HAZ)
HAZ(Heat Affected Zone) always exists while welding. Whatever occurs at the HAZ depends on the parent metal’s temperature that it’s inclined toward in the welding method and the velocity of travelling (quick or slow) of cooling not long after the weld joint has transformed into solid.
When we heat the workpiece, its gradients shrink the weld joint and damage it mechanically, resulting in tears, strains, warping, and sometimes minor fissures. However, precautionary measures like workpiece preheating, less heat output, and post-weld heat treatment can help you avoid it.
Additionally, welding fixtures like post-heating ( Oven, torch, or blanket ), quenching, or cooling it down slowly. All this depends on the method and the metal.
Welding in crucial areas or where welding failure can cause life loss must be executed by approved welders using authorized gears, following certified processes and standards by groups like AWS(American Welding Society).
Welding uncommon metals or exotic alloys requires special welding processes for that particular application and welding joint. Also, it should be certified by a professional technical welder.
Such welds need to be executed by a welder approved for that specific welding procedure as they understand the whole mechanism, materials required, joint type, and appropriate welding position. A qualified welder won’t weaken the steel by controlling the heat to the weld piece.
Weld Metal
Weld metal is usually treated as a separate part in the welded sample rather than as part of the base metal.
Weld metal region exists at the junction of two-parent components.
In fusion welding, weld metal undergoes phase change due to melting and subsequent solidification(solid to liquid and once again liquid to solid).
It contains a significant portion of filler material.
The chemical composition of weld beads may differ from that of the parent metals.
Properties of the weld metal can be improved during welding in several ways(Appropriately selecting filler composition, shielding gas)
Weld bead produces in both fusion welding and solid-state welding processes. However, it’s narrow in the solid state.
The geometry of the weld metal is characterized by three parameters, namely (i)depth of penetration,(ii)weld bead width, and (iii)reinforcement height.
Heat Affected Zone
HAZ is usually considered to be an integrated part of the base metal.
HAZ exists within the parent components surrounding the weld bead.
HAZ never melts and always remains solid, So no phase change occurs in HAZ.
It does not contain any filler material.
HAZ has the same chemical as that of parent metals.
HAZ properties don’t improve favourably during welding(its width can only be controlled to some extent).
HAZ is noticeable, particularly in fusion welding processes.HAZ is very narrow with solid-state welding and is mostly not detectable.
The only geometrical parameter of interest in the HAZ is its lateral width.
Steel Strengthening Approaches
HAZ is the only area on the steel that can be affected negatively or positively when welding. For example, if you use an appropriate filler metal, the metal area will be impacted by HAZ.
Recrystallization can’t occur on filler metal. So, it remains unchanged like the parent metal.HAZ will be only the affected area because of the factors above.
Commonly, this happens when welding with cold-rolled steel. Using this steel type makes the joint designs crucial. Besides, it will be important to factor in the pressure on the piece when welding.
Remember, the amount of heat and metal weakening are directly proportional. The higher the heat, the more quickly the metal weakens. However, using the correct heat treatment aids in correcting the post-welding defect.
Note :This blog post only covers the over of heat treatment approaches, read our seperate blog post on how to strengthen steel after welding.
How Does Heat Treatment Prevent the Weakening of Steel?
Post-weld approaches and heat treatment are among the most effective ways to strengthen the steel weld joint. They help to moderate the bainite that could occur in the HAZ.
Additionally, it prevents fissures in the metal areas if subjected to stress after some time. Correct heat treatment impacts hardness, grain size, toughness, and tensile strength. It also causes enhancement in electrical and magnetic qualities and eases strain and elasticity.
However, understanding the mechanism of heat treatment is important to get the maximum advantage. It’s not all about using a torch and allowing the metal to cool down when welding.
You need to understand and consider factors like heat temperature, the time required, and the cooling rate. Also, you need to know about the materials you will use and their effectiveness.
You can use several methods, such as natural gas, induction heating, fuel-air or oxy-fuel torches, metal bath, or electrically heated salt. However, cooling with a fan or water, sand, furnace cooling, and even air can be used.
Regulating the cooling & heating procedure is crucial to getting the desired output. These factors play a pivotal role in the weakening or strengthening steel after welding.
You won’t be able to get the desired outcome if you heat or cool too slowly or even if you apply more than the required heat. Saturating the steel throughout the heat and eventually cooling makes machining the metal easier.
Welding Effects of HSLA (High Strength Low Alloy) Steel
High Strength Low Alloy (HSLA) steel is an alloy that provides improved mechanical properties and greater resistance to atmospheric corrosion compared to carbon steel. Its application includes bridge construction, buildings, and pipelines. Besides, it is also used in automotive, shipbuilding, and other transportation applications.
However, welding HSLA steel can be more challenging than welding carbon steel as it’s higher in strength and lower in ductility. The following are some of the effects of welding on HSLA steel:
- Welding HSLA steel can cause significant changes in the microstructure and mechanical properties of the heat-affected zone (HAZ), particularly in the vicinity of the fusion line resulting in more hardness and reduced toughness which potentially causes cracking and reduced weldability.
- Preheating is often required before welding HSLA steel to reduce the cooling rate and prevent cracking in the HAZ. Preheating temperature is determined by the thickness of the material.
- HSLA steel requires special welding techniques and filler materials to ensure proper joint strength and weldability. Low-hydrogen filler metals and proper shielding gas can prevent hydrogen-induced cracking and improve weld quality.
- Post-weld heat treatment is often required for HSLA steel to reduce the residual stress caused by welding and to restore the desired mechanical properties.
FAQ’s
How strong is the welding steel?
If the joint is designed properly and carried out by an experienced welder, your weld joint will be as strong as the base it’s joining.
How does welding work on metal?
Unlike soldering and brazing, where base metal is not melted, it’s a high heat process that works with melting the base metal, usually adding filler metal.
How does welding affect yield strength?
When welding, arc voltage surges, and welding current increases solidity while decreasing yield durability. Impact toughness and ductile durability can also be impacted by it. On the other hand, if you increase welding velocity, it might increase the hardness of welds.
What factor breaks a weld?
When you try to cool the metal immediately after welding, accumulating built-up stress breaks the welds. Fracturing is a common phenomenon in weld joints, a type of stress relief that occurs by reheating the weld to a lower temperature and then allowing it to cool naturally.
Conclusion
Welding can have both positive and negative effects on steel strength. However, by choosing the right welding technique, controlling welding parameters, and using high-quality materials, you can ensure that your welded steel is strong and durable.
Whether you’re welding for construction, manufacturing, or repair, understanding the effects of welding on steel strength is critical to ensuring your success of you.
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Dave Walker
Dave Walker is a skilled welder and passionate blogger. With years of experience in welding, he has honed his craft and developed a deep understanding of the trade. In his blog, he shares his experiences, insights, and tips on welding, offering a valuable resource for fellow welders and those interested in the field. He is dedicated to promoting the importance of welding and its applications in various industries.