Q. Our new project involves welding a 2.5-in. thick piece of AR400 steel to a 2-in. thick piece of mild steel using a 0.5-in. fillet weld, 32 in. long. The final weld will form a "T" section with a weld on both sides. We plan to weld in a horizontal position using the submerged-arc process. What filler metal do you recommend?

A. AR400 is an abrasionresistant plate with a targeted hardness of 400 HB roughly equivalent to 180 ksi in ultimate tensile strength. Generally, this material is not chosen for strength, but for wear resistance. You say you are welding the AR400 to "mild steel," which I assume has less than 70 ksi in ultimate strength. In that case, and without knowing the load requirement for the weld, E70 filler metal is a good choice for most applications. Since the weld size has a 0.5-in. leg made in the horizontal position, the weld will take three to six passes, and because it is a multiple pass weld, use a neutral flux to minimize alloy buildup and retain good ductility. A flux-wire combination of F7A2-EM12K along with a neutral flux should be adequate. The submerged arc welding process will yield deep penetration into both materials. That can be both good and bad. Given the chemistry of AR400, the weld metal could pick up some alloy from this material. Therefore, be careful to choose the correct wire diameter and current to avoid excessive penetration into the AR400. Steels like the AR400 achieve their hardness through a combination of controlled rolling practice, quenching and tempering. This means that there will be some softening in the heat affected zone of the AR400 when welded. To minimize the softening, control the preheat, interpass temperature and heat input of the welding process. Additionally, watch out for cracks resulting from restraint and rapid cooling. Considering the thickness of the materials, use a preheat and interpass temperature of 350 degrees F. Also, keep the heat input from the welding process in the 50 to 60 KJ/in. per pass range for the AR400 base metal thickness you are using. To assure low hydrogen in the weld, keep parts clean, dry and free of any contaminants such as millscale, rust and oil. In addition, proper storage and handling of welding consumables should be followed to minimize hydrogen pickup.

Q. I have been reading about plasma arc cutting. The book I have states that there are two transfer modes of generating an arc with the plasma cutting process transferred and non-transferred. The book states that the transferred mode is used for welding and cutting. My question is, can the non-transferred mode be used for plasma arc cutting?

A. In plasma cutting the nontransferred arc mode is used to start the arc or to serve as a pilot arc. In this mode the nozzle of the torch is in the electrical grounding path. This yields a consistent, short path for the arc to initiate. Due to the tremendous heating in the torch and nozzle that occurs in the nontransferred mode, both the time and current are limited. When the arc sees the preferred ground the arc transfers and enters the transferred mode. In the transferred mode the current is allowed to increase to the set value on the machine. The cutting thickness is strongly dependent on the current available at load voltage. Because of the limitations on the current in the nontransferred arc mode, cutting is generally not practical in that mode.

This column is sponsored by Penton and the Lincoln Electric Co., Cleveland. Dave Barton is a senior welding engineer in the Application Engineering Group of The Lincoln Electric Co. He oversees welding procedure development for both new technology and existing products, performs failure analyses for customers, and serves as a consultant on welding application problems. Barton has been with Lincoln Electric for 21 year. Send your questions for Mr. Barton in care of WDF by e-mail to: askdav@penton.com