Effects of alloying elements on the weldability of metals
When welding metals with various alloying elements (Molybdenum, Silicon, Chromium, etc.), various problems may arise that directly affect the quality of the resulting weld (cracks, pores, non-welds, etc.) due to:
- Metallurgical,
- Lower melting phases,
- Different physical properties.
In order to avoid difficulties and problems, it is necessary to know very well how this, or that alloying element affects the weldability of the metal. Knowledge of the influence of alloying elements on the weldability of various steels will contribute to a better understanding of welding processes.
| Alloying Element | Effect on Weldability |
|---|---|
| Carbon | Can increase susceptibility to cracking, particularly in high-carbon steels. Preheating and post-weld heat treatment may be required. |
| Chromium | Improves corrosion resistance but can decrease weldability due to increased hardness and susceptibility to hot cracking. Preheating and controlled cooling may be necessary. |
| Nickel | Enhances toughness and resistance to cracking. Generally improves weldability, but high nickel content can lead to hot cracking. |
| Molybdenum | Improves high-temperature strength but can decrease weldability due to increased hardness and cracking susceptibility. Preheating and post-weld heat treatment may be necessary. |
| Vanadium | Enhances strength and hardness but can decrease weldability due to increased cracking susceptibility. Preheating and post-weld heat treatment may be required. |
| Titanium | Can improve weldability by reducing grain growth and preventing embrittlement. Titanium alloys are generally weldable with proper techniques. |
| Aluminum | Can decrease weldability due to oxide formation, which requires proper cleaning and shielding. Aluminum alloys may require specialized welding techniques. |
| Copper | Can decrease weldability due to cracking and porosity. Precautions like preheating and filler metal selection are needed for copper alloys. |
| Sulphur | Increases susceptibility to hot cracking. Low-sulphur content is preferred for better weldability. |
| Phosphorus | Increases brittleness and susceptibility to cracking. Low-phosphorus content is preferred for improved weldability. |
| Silicon | Can increase fluidity and penetration but may result in increased porosity. Proper cleaning and shielding gases are necessary. |
Carbon
Is one of the most significant chemical elements in steels. The carbon content in steels affects strength, hardenability, toughness, weldability.
In low-carbon steels (carbon less than 0.25%), weldability is practically not impaired. With an increase in the carbon content, weldability deteriorates sharply, since in the HAZ zones a large number of hardening structures arise that cause cracks.
With a high content of carbon in the filler material, the likelihood of pore formation increases.
Manganese
Manganese is a good deoxidizer as well toughness enhancer above sub-zero temperature. Electrodes or wire must be alloyed with higher manganese when welding in a CO2 welding gas shielding.
With the content of manganese in the metal up to 0.8%, the welding process is not complicated. With an increase in the steel content (1.8% -2.5%), there is a danger of hydrogen cracking (cold cracks), because manganese contributes to the appearance of brittle structures (hardening).
With an increased content of manganese (11-16%), during welding there is an intense burnout of this substance.
Silicon
Silicon is like manganese, is a good deoxidizer. With a small amount of silicon (up to 0.03%), weldability does not affect. With a silicon content of 0.8-1.5%, weldability deteriorates due to the increased fluidity of silicon steel and the formation of refractory silicon oxides. With a high content of silicon, due to increased fluidity, the appearance of hot cracks is especially dangerous.
Chromium
chromium content of steels contributes to an increase in corrosion resistance. But, when welding steels, chromium carbides are formed, which increase the hardness in the HAZ (heat affected zone).
Nickel
The nickel content in steels contributes to an increase in toughness, which is especially important when steels operate at low temperatures.
Also, nickel helps to increase the ductility, strength of steel and grain refining. At the same time, the weldability of steel does not deteriorate. But, due to the high price of this alloying element, the use is limited by economic considerations.
Molybdenum
The content of molybdenum in steels increases the strength capacity at high temperatures. It prevents oxidation of the alloy at elevated temperature. On the other hand, molybdenum contributes to the formation of cracks in the HAZ and the weld metal as it increases weld hardness.
Tungsten
The content of tungsten in steels dramatically increases the hardness of steel and its performance at high temperatures (red resistance). On the other hand, tungsten complicates the welding process and actively oxidizes. Tungsten present in metal reduces the weldability of the material.
Vanadium
The content of vanadium in steels dramatically increases the hardenability of steel. Due to hardenability, as well as due to the oxidation of vanadium, the weldability of steels deteriorates.
Titanium’s
Titanium is used as an alloying element due to its high corrosion resistance and thermal stabilization of stainless steel. Titanium and niobium are added to stainless steel to bind carbon and thus prevent sensitization.
The use of niobium, similar to titanium, is due to its high corrosion resistance. When welding steels, niobium contributes to the formation of hot cracks.
