ARC MAGAZINE

Which consumables are better for welding over rusty, dirty steel?

As a general rule, steel surfaces should be cleaned of any oil, grease rust and mill scale before using any type of filler metal or consumable for any arc welding process. These are all surface contaminants that can potentially adversely affect weld quality. However, sometimes complete cleaning of the steel surface cannot be performed. In these cases, the recommended consumables for “dirty” steels are those that form a slag, have deeper penetration, have a slower freezing puddle or have higher levels of silicon and manganese. Lincoln Electric has a number of consumable products that serve this purpose, including (but not limited to):

NOTE: These consumable products may be inappropriate for use because of other variables, such as the need for out-of-position welding, multiple-pass welding, applications requiring low hydrogen filler metals, etc.

What precautions should I take when welding T-1 steels?

T-1 is a quenched and tempered steel. Welding quenched and tempered steels may be difficult due to its high strength and hardenability. The base steel around the weld is rapidly heated and cooled during welding, resulting in a heat affected zone (HAZ) with high hardness. Hydrogen in the weld metal may diffuse into HAZ and cause hydrogen embrittlement, resulting in delayed underbead or toe cracking outside the weld. To minimize heat affected zone cracking, follow these steps:

• Use a low-hydrogen consumable, like a –H4 or –H2.
  
• Preheat. This slows the cooling rate.
  Note that excessive heat may anneal the base material.
• Slow cool. More time at elevated temperatures allows the dissolved hydrogen to escape.
  
• Peen the weld beads to minimize residual weld stresses.
  
• Use the lowest strength filler metal meeting design requirements. If making fillet welds, the weld can be oversized to give the specified strength.
  
• Minimize weld restraint.

What does the designator HR4 mean?

Welders accustomed to using a low hydrogen electrode with a particular classification are sometimes puzzled when they encounter electrodes with added designations such as “HR4.” Low-hydrogen electrodes are generally used in more critical applications to begin with, and their concern is understandable. However, it’s simply a case of the manufacturer providing more information on the same electrode as before.

The added characters are optional designators, permitted by the AWS classification system, to clarify the low-hydrogen characteristics of carbon steel and low alloy steel manual electrodes. Nothing in the electrodes themselves has changed.

Low hydrogen is defined as less than 16 ml per 100 grams of weld metal. This classification has now been stratified into three levels, so the added designators make it easier to quickly determine how “dry” a particular electrode is. The levels are H16, H8 and H4, corresponding to 16, 8 and 4 ml per 100 grams of weld metal. These represent the maximum diffusible hydrogen levels obtainable with a specific product.

One additional designator may also be added. This is an optional moisture-resistant designator (R), which indicates a low-hydrogen electrode’s ability to meet specific low-moisture pickup limits under controlled humidification tests. This generally indicates that the electrode’s coating has been formulated with non-hygroscopic materials and will resist picking up moisture longer than electrodes with standard low-hydrogen coatings. This can be important when welding in humid areas, since a standard coating will be affected by moisture in about two hours, while a moisture-resistant coating can be safe for use for as long as 10 hours.

When these suffixes are used, they must be imprinted on the electrode itself, in addition to appearing on the packaging. The actual AWS classification does not change when they are added, however. For example, an E7018 H4R product will still be classified as E7018, although the product is identified by the full designation.

With any low-hydrogen consumable, it is important to observe proper storage procedures. Products such as the H4R electrodes come in a hermetically sealed can. Once opened, they should be stored in a rod oven until used, since they may not meet specifications if left open in high humidity. When in doubt about low-hydrogen electrodes and their application, consult the supplier for recommendations.

What consumables should be used for weathering steel?

Core Ten steels (A242 and A588) are weathering steels commonly used for outdoor structures. These steels have a higher resistance to atmospheric corrosion than typical mild steels. Welds on these steels are often specified for similar corrosion resistance and color match.

On single-pass welds, mild steel electrodes are commonly used. There is usually enough pickup from the base metal to obtain good color match.

On multiple-pass welds, low-alloy electrodes are commonly used to obtain a good color match and similar corrosion resistance. The electrodes commonly specified include those with the suffixes –C1, –C2 and –C3.

From the welding experts at
Lincoln Electric