How to Weld T-1 Steels

the introduction of USS T1 steel. A few years ago marked the most recent major development in the long history of steel. The world's most versatile metal. Tough, strong, easily weldable. USST1 steel is today a proven engineering material. For example, in the Carina's Bridge in California, USST1 was specified for top cords, bottom cords, verticals, diagonals, gusset plates. Result, greater strength, reduced weight, easier construction. The Carina's bridge took advantage not only of USS T1's toughness and strength, but also of its weldability in the shop and field. To successfully weld T1 steel, it is only necessary to follow three basic welding rules. Use the right electrodes, the right welding heat, and the right procedure. What is the right electrode for T1 steel? It's low hydrogen. And here's why. In the extremely high heat of welding, any hydrogen which is in the electrode coating or any which may have been picked up as moisture is released. Here you see the hydrogen as a blue gas. While the metal is in the intensely hot molten state, there is no problem. for the released hydrogen is dissolved in the molten steel. But as the joint begins to cool and shrink, its capacity to hold the hydrogen is reduced. The hydrogen free to dissolve causes underbead cracks. Tough to spot because you can't see them. This underbead crack was caused by using a type E6010 electrode. A rod whose coating is often high in hydrogen. But this trouble can be avoided by using only low hydrogen electrodes of which there are several. In this case the number is E 11018 and the clue to low hydrogen coating is the number 18. Let's check a few rod classifications. E8015, E9016, and E1018. What do these numbers mean? The first two or three figures in the classification refer to the ultimate tensil strength of the deposited metal of the rod. The last two numbers are the checkpoints for low hydrogen. 15, 16, and 18. To repeat, 15, 16, and 18. Only these three numbers indicate low hydrogen coatings. Low hydrogen rods stay low in hydrogen only when they are kept free from moisture. Even the moisture in the air is easily absorbed by the rod coatings. To keep exposure to the air at a minimum, most shops open no more than a 2-hour supply of electrodes. The exposed rods are kept dry at an oven heat of 250 to 300° F. Because this temperature is above the boiling point of water, any moisture present evaporates. No moisture means the hydrogen content stays low. This reminder has been found helpful in many shops. If drying facilities are not handy to the welding operation, a portable oven can be spotted right on the job. Even when the best of care is taken, containers can become damaged. Air and moisture get at the rods, and when this happens, the safe thing to do is bake the rods dry. How long to bake them and at what temperature varies with different types. For most, 1 hour at 800° F is a good average. To review, when welding T1 steel, a low hydrogen electrode is the right electrode. The right electrode baked dry and then kept dry. When dry low hydrogen rods are used, under bead cracking presents no problem and a good weld results. Of course, this same low hydrogen rule applies to all welding procedures. With inert gas welding, be sure to order moisture-free gas. In submerged arc welding, give your flux the same treatment suggested for the rod coatings. Keep it hydrogen-free and your weld will be normal. The next vital factor is heat input. When welding USST1 steel, the right welding heat is high enough for good fusion and low enough for rapid cooling. The key phrase is rapid cooling dictated by the internal structure of T1 steel. Here is T1's normal micro structure, one of the toughest in steel. But if it is cooled too slowly, the steel loses its toughness. Even may become brittle. But because we must maintain T1's toughness, we cool it faster and USS T1 steel stays tough. Rapid cooling is the key. Another important consideration is the thickness of T1 steel. The thicker the plate, the higher the permissible heat input. The thinner the plate, the lower permissible heat input. In nearly all T1 steel welding jobs, the only preheating necessary is that required to ensure a dry surface. After all, the lower the temperature before welding, the sooner the metal cools. Now, we come to the welding process itself. Welding can generate temperatures up to 11,000° F, but by careful attention to arc speed and amperage, welding heat is easily controlled. As you know, heat input varies with the speed of arc travel. The slower the ark moves, the more heat delivered at each point. Closely related is the amperage of the ark. Because the higher the amperage, the greater the heat input. The lower the amperage, the less heat generated. We've been using words like thicker, thinner, lower, higher. For actual jobs, you need actual numbers. And here they are all on the welding heat input calculator for USST1 steel prepared by United States Steel to help you do a better job when the amps, volts, and speed of the ark are known. This circular slide rule tells you exactly how much heat you'll be putting into the joint. How will you know that a specific heat input is within safe limits? This answer is on the other side. A heat input table with suggested maximum heat units. Say your plate thickness is a/4 in. Its temperature 70° F before welding. In this case, 36 heat units are the suggested maximum. That is with 36 heat units or less. We make possible the rapid cooling which means a good tough weld. Suppose we illustrate with a job that might come your way. You want to butt weld 2/2 in plates. Assume that we use a preheat or enterpass temperature of 300° F. You check the table on your calculator. It tells you that at 300° 1/2 in plate has a suggested maximum heat input of 47 heat units. Now set the calculator at figures you might consider standard as you do in any welding job. In this case, you've selected a speed of 5 in arc travel per minute, a voltage of 25, and an amperage of 200. So you put down all the figures and make some comparisons. Your three conditions 5 in arc speed 25 volts 200 amps result in 60 heat units 13 units higher than the suggested maximum of 47. Obviously lower heat input must be worked out. You can either speed up your arc travel or lower your amps. For example, you decide to keep the amperage constant. Set 200 amps at 47 heat units. Then read off the arc speed opposite 25 volt. And you see the figure 6 and 1/4 in per minute. Now you have all your necessary information. 200 amps, 25 volts, arc speed 6 and 1/4 in. Just right for the 47 maximum heat units. You make your first pass knowing that it'll turn out just right. When you finished your first pass, your crayon shows the temperature has gone up from 300 to 400° F, 100° higher than the preheat and enterpass temperature on which your heat input calculation was based, 47 maximum heat units. An adjustment is indicated. You either lower your heat input from 47 to 40 units by lowering the amperage to 170 at the same speed or increasing the speed to 7 and 1/2 in per minute with the same number of amps. It may be best to wait for the plates to cool to the original 300° and use the original setup. There are several solutions, but whichever you choose, remember, experience has shown that a few minutes spent with this calculator will make the job easier. It is your sure guide to better welding results. It assumes the right welding heat, high enough for good fusion, and low enough for rapid cooling. Engineers and welders like yourselves who've worked with T1 steel since its introduction have come up with some good tips on speed, technique, gouging, and fillet welding. First, speed. We've already shown how too slow a speed can overheat T1 steel. An easy method of hitting the right speed is to have someone time you on several trial runs on a piece of scrap. Speed control is a must for heat control. Another tip, a straightforward stringer bead is preferred because less heat input results. The full weave technique should be avoided because the arc stays much too long at any single spot and the heat input goes beyond the maximum recommended. A stringer bead moves in a straight line, passes each point much more quickly, and keeps heat input as low as possible. When back gouging, the preferred technique is arc air gouging followed by cleanup grinding. This generates far less heat input than oxy acetylin torch gouging. Fillet weld preparation is much the same as that for butt welding. If the joint is to be preheated, it must be preheated before the tack welds are made. Dry lowhydrogen rods of a strength equivalent to the fillet weld metal are also used for the tack welds. The size of the TS must be big enough in area that they will not crack on cooling. You clean the TS before the first fillet pass to asssure a clean route. You have seen good and bad fillet welds. A bad weld has these undercuts, poor contour and bad root. Top welders try for good penetration with no undercuts. The weld is smooth, correctly contoured, and well faired in to the legs of the pieces to be joined. Because USST1 steel is so strong, additional care is necessary. When welding thick pieces, [clears throat] and if the finished weld has to be stress relieved, high strength rods such as E 100 or E10 were specified. As the weld metal cooled and contracted, it was strong enough to actually pull cracks at the toes and seriously weaken the weld. This could have been easily avoided. One way to reduce restraint caused by shrinkage is to use more ductal rods. Rods lower in strength since T-jints usually need less strength than butt joints. However, if the joint must have the higher strength rods, you can peen the weld, actually push the deposited weld metal around, thus reduce shrinkage forces, and make a weld that is free of toe cracks. Another method of avoiding cracks is to use soft steel wire as a shrink cushion. As the shrinkage pulls, the upright leg shrinks down to the bottom plate, absorbs the total contraction and prevents cracking. Machined grooves can do the same job as soft wire. Again, the weld shrinkage pulls the upright down. The grooves crush into the leg and again no toe crack. Another method is the butter weld. You locate where the fillet toe passes are to be made and put down a butter weld. Grind it down smooth and flush before the actual fillet welding. Now you'll get a solid, crack-free weld. USS T1 steel is being welded every day by those who have learned how to preserve its strength and toughness. Their experience has made this film possible. They've learned the proper use of the right electrodes, the importance of the correct welding heat, and the best in welding procedures. Procedures that work well when welding USS T1 steel to itself, to other alloy steels, to high strength steels, and to structural carbon steels. We've reproduced in this booklet all the shop experience and engineering guides shown in [music] this film. Pocket size, you can keep it handy on the job. The calculator enclosed in the back of each book is a quick source of all technical information for any job. Close attention to calculator and book will mean a successful weld of USS T1 steel every time. [music]