What are low alloy steels?

When the amount of Ni, Cr, Mo, and other alloying elements is less than 10.5%, the steel is called low alloy steel. Low alloy steels range from steels with small amounts of chrome and nickel to 11/13Cr steels with 4% nickel. It makes the performance better at high temperatures and gives some corrosion resistance. Adding chrome and nickel to steel makes it more stable at high and low temperatures. This makes it popular for applications that need to work in a wide range of temperatures without getting too hot.

Making and welding with low alloy steel

When it comes to making and welding, low alloy steels can be hard to work with. The problem with weldability is that it depends on the alloy and how it is used. Each combination of alloys makes it harder to weld, so they must be treated differently. And there won’t be just one answer to these problems. The fact that each of these grades, even the ones that have been changed, needs to be fully understood in terms of its metallurgical structure and how it will be used after welding, is something that can be said about all of them. Steel with 9 percent chromium and molybdenum is a type of steel that is often used to build industrial equipment and heat exchangers. For a weld to work, there needs to be a developed welding procedure with well-thought-out heat control plans to stop a harmful phase from forming in the steel.

The Uses of Low Alloy Steel

Low-alloy steels are used for things like military vehicles, oil drilling platforms, pressure vessels and pipes, earth-moving and construction equipment, and structural steel. Low-alloy steels, like HY 80, HY 90, and HY 100 steels, are used to make submarines, bridges, ship hulls, and off-road vehicles, among other things. It has nickel, molybdenum, and chromium in it, which makes it easier to weld, stronger, and harder to cut. Most of the time, preheating and post heating are not needed to weld low-alloy steels.

Explanations of Low Alloy Steel

During production, most low-alloy steels go through heat treatment, normalizing, and tempering. You can also weld them. But welds need to be treated with heat to make sure they don’t crack.

Important reasons why low-alloy steels are better than mild steel are:

  • High yield strength
  • Able to withstand high temperatures
  • Good creep strength
  • Oxidation resistance
  • Hydrogen resistance
  • Low-temperature ductility

Because low-alloy steels are used to make thin-walled pressure vessels, they need to have a higher yield strength and creep strength. Low-alloy steels like 0.5 Mo and 12 CrMoVW are used in steam boilers, crackers, and reformers at refineries because they don’t creep as much as other steels. Low-alloy steels can only be heated to about 600°C (1112°F) at the most.

Low Alloy steel (Cr – Mo Steel) grades and suitable welding consumables

Steel categoryASTM / ASME standard  
 Low Alloy Steel PlateLow Alloy Steel PipeSMAW Electrode/ RodFlux Cored Wires
0.5%MoA204 Grade A,B,C A336 Grade F1A209 Grade T1 A335 Grade P1GL76/78A1GMX 811A1
0.5%Cr-0.5%MoA387 Grade 2 CI.1,2A213 Grade T2 A335 Grade P2GL86/88B1 
1.25%Cr-0.5%MoA387 Grade 12 Cl.1,2 A387 Grade 11 CI.1,2 A336 Grade F11A213 Grade T11, 12 A335 Grade P11, 12 A182 Grade F11GL86/88B2GMX 811B2
2.25%Cr-1.0%MoA387 Grade 22 CI.1,2 A336 Grade F22A213 Grade T22 A335 Grade P22 A182 Grade F22GL86/88B3GMX 911B3
5.0%Cr-0.5%MoA387 Grade 5 CI.1,2A335 Grade P5GL86/88B6 
9.0%Cr-1.0%MoA387 Grade 9 CI.1,2A335 Grade P9GL86/88B8 

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