41xx steel
41xx steel is a family of SAE steel grades, as specified by the Society of Automotive Engineers. Alloying elements include chromium and molybdenum, and as a result these materials are often informally referred to as chromoly steel. They have an excellent strength to weight ratio and are considerably stronger and harder than standard 1020 steel, but are not easily welded, requiring thermal treatment both before and after welding to avoid cold cracking.
While these grades of steel do contain chromium, it is not in great enough quantities to provide the corrosion resistance found in stainless steel.
Examples of applications for 4130, 4140 and 4145 include structural tubing, bicycle frames, gas bottles for transportation of pressurized gases, firearm parts, clutch and flywheel components, and roll cages. 4150 stands out as being one of the steels accepted for use in M16 rifle and M4 carbine barrels by the United States military. These steels are also used in aircraft parts and therefore 41xx grade structural tubing is sometimes referred to as "aircraft tubing".
Properties
| Material | Condition | Tensile strength | Yield strength | Elongation at fracture, 2-inch gauge | Hardness, Rockwell |
| 4130 | Cold drawn, normalized | 20–30 | B 90–96 | ||
| 4142 | Hot rolled, annealed | 20–30 | B 90–95 | ||
| 4142 | Cold drawn, annealed | 15–25 | B 96–100 | ||
| 4150 | Hot rolled, annealed | 20–30 | B 90–96 |