Generally speaking, the answer to this question is “no” – or at least, not to any significant extent. The principal reason for this is that the T1 needs all of the weight it was originally designed with for rail adhesion. The T1 had a designed factor of adhesion over 4.1, which is generally considered ideal for a steam locomotive. Even though it would be possible to reduce weight by going with higher strength alloys in some applications, taking weight out would reduce the factor of adhesion, resulting in an increased propensity for wheel slip. Given the T1’s reputation, it would not be advisable to reduce factor of adhesion significantly. To counteract a sizeable weight reduction and maintain factor of adhesion, we’d need to significantly reduce the power that the locomotive was capable of, which would severely limit the locomotive’s high speed potential. We do not need to reduce weight to satisfy modern axle loading limits, so there’s little to be gained by a weight reduction program.
Another reason not to go for lightweight alloys is stiffness. Even though there is a lot of variation in strength to weight ratio among various alloys, there is almost no difference in stiffness to weight ratio. A thinner, lighter alloy will reduce stiffness, which may result in unforeseen failure modes not present in the original design due to the increased flexion.
As it is, we may need to add ballast to counteract weight loss resulting from manufacturing decisions. For example, we intend to build a fully welded boiler instead of the riveted design originally used. Even though we will be maintaining the overall size, thickness, and alloys used originally (to maintain structural stiffness of the boiler), the loss of the overlapping seams of the riveted design will result in weight loss. This will probably be in excess of any weight increase resulting from the thicker firebox needed to maintain the current federally mandated safety factor of 4.0 on boilers. (PRR Belpaire boilers were designed to a lower safety factor acceptable at that time.) Additionally, we also intend to use the Franklin Type B2 rotary cam valve gear, instead of the Type A oscillating cam gear that the T1 originally used. Our decision to use rotary cam valve gear is driven by ease of maintenance and reduced fabrication costs compared to the oscillating cam gear, but the rotary cam gear weighs about three tons less, so we may need to ballast the locomotive to maintain weight distribution.
The only area that we may elect to substitute a different material is the poppet valves. The originals were made of a high alloy steel that had some issues with durability. To improve reliability, we may investigate an alternate high strength material such as titanium. This might reduce the valve weight from approximately 4 pounds to as little as 2.5 pounds. Not a significant savings in the big picture (50 pounds total), but lighter valves will reduce reciprocating mass, which will allow for softer return springs. This will reduce the closing force on the valve seats while keeping valve float in check, which should improve reliability beyond any improvements based on alloy strength alone.
Despite its age, the T1 used a lot of very high strength and light weight alloys in its construction. The cab, boiler jacket, and streamlining were made of 6000 series aluminum, which saved about 16,000 pounds compared to a steel skin. Siderods, piston rods, crossheads, and crankpins are made from Timken high dynamic steel, which has a yield strength of 110,000 psi, and a high elongation. Spacecraft grade 7000 series aluminum was used for the crosshead shoes. Nearly all the large castings used General Steel Castings’ Nickel Steel. This nickel steel alloy had a much higher elongation than is typical in commercially available steel alloys today. Fortunately with the help of Beaver Valley Alloy and a national materials testing laboratory, The T1 Trust has been able to utilize 21st Century technology to successfully replicate General Steel Castings’ Nickel Steel.