Welding

All high strength HS 100 and abrasion resistant HS 400, HS 450 and HS 500 steel plate can be welded by all the common processes provided low hydrogen weld material is used and the appropriate preheat temperatures are followed. Low heat input welding methods should be used, such as metal-arc, gas-shielded and multiple pass submerged arc welding. In this way, good mechanical properties can be retained in the heat affected zones. High heat input welding processes which generate heat input exceeding 90 KJ/in. (3.5 KJ/mm) should be avoided.

We have provided further information on welding below. Many steel mills also provide welding guidelines and recommendations for their products. ThyssenKrupp Steel provides the following information:

Welding N-A-XTRA
Welding XAR
Preheat Temperatures N-A-XTRA
Preheat Temperatures XAR
Consumables N-A-XTRA
Consumables XAR

Weldability
Carbon equivalent (CE) is a basis for evaluating weldability. A lower CE indicates better weldability. Less weldable (or more hardenable) steels have a higher risk of hydrogen induced cold cracking and therefore require precautionary steps such as preheating and low hydrogen practices to reduce that risk. There are various formulas for calculating carbon equivalent values. The world's leading producers of heat treated plate recommend using the International Institute of Welding (IIW) formula (or the Dearden & O'Neil formula):
CE = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15
Working Temperature & Preheating
High strength and abrasion resistant steel can sometimes be welded with the steel at room temperature without the risk of hydrogen cracking, particularly for thin plates. However, when single plate thickness is 0.75" or above, some preheating above room temperature is generally required. Most mills provide detailed preheating recommendations for their products. When comparing recommendations, be sure to check the heat input. If the heat input is 25-30 KJ/in (0.9-1.1 KJ/mm), for example, the preheat temperature would typically be higher than if the heat input was 50-70 KJ/in. (1.9-2.7 KJ/mm), sometimes by as much as 100C (210F).  When quenched and tempered steels are welded, a soft zone forms near the fusion limit. The width of the soft zone varies with heat input. If the heat input remains low, the soft zone should not affect the strength of the welded joint. For thicknesses below 0.375" (9.5mm), heat input should generally not exceed 28 KJ/in. (1.1 KJ/mm).  

Preheat and interpass temperatures should be maintained during welding by using a gas burner, heating blankets or, when the temperature is reached, by using the welding heat itself. Temperatures should be measured on both sides of the plate (for example, by using temperature crayons or heat guns). Under conditions of severe restraint, for tack welding, or in damp weather conditions, preheat temperatures would typically be increased.

Consumables
An undermatching weld metal is often desirable. Consumables that produce softer weld metal are cheaper and, because of their lower alloy content, are less hardenable than those producing a higher strength weld metal. In addition, consumables that produce softer weld metal are capable of deforming plastically more readily while the weld is cooling, thereby reducing the restraint on the joint. The filler material can be the same as for A572-50 or similar, such as AWS E7018 type. For butt welds where the joint strength must be equal to that of the parent plate, consider using electrodes such as AWS E11018.

Quenched and tempered steel can easily be welded together with other steels having a corresponding basic analysis. In such cases, consumables that match the softer steel grades should generally be chosen. However, only filler metals and processes that result in low hydrogen levels may be used. In addition, consumables must be stored in a manner that prevents the absorption of moisture. If there is any risk that moisture has been absorbed, the consumables must be discarded or redried in compliance with the manufacturer's instructions. Covered electrodes should be thoroughly dried to ensure that the hydrogen content does not exceed 10mL/100 g weld metal.

Joint Preparation

For good welding results, it is important to keep crack-promoting hydrogens away from the weld joint. Make sure the joint is clean and use only dry consumables. The joints should be prepared in the same manner as for ordinary steels by means of gas cutting or machining. All impurities on or adjacent to the joint (such as scale, rust, oil, paint and moisture) must be removed prior to welding. These impurities contain hydrogen sources and may cause cracking. A good close fit between the members of the joint is essential to minimize the stresses and thereby reduce the risk of cracking. The risk is greatest for initial, often smaller, weld passes.

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