Our 1045 and 4140 grade steels are both very popular options here at Capital Steel & Wire, and we often get questions related to their differences. 1045 and 4140 have distinct chemical and mechanical characteristics which make them valuable for different applications.
Chemical Makeup
It is easiest to see the differences chemical differences between 1045 and 4140 by doing a side by side comparison with a chart.
| 1045 | 4140 | |
| Iron, Fe | 98.51-98.98% | 96.79-97.78% |
| Carbon, C | 0.45% | 0.40% |
| Manganese, Mn | 0.60-0.90% | 0.75-1.00% |
| Phosphorus, P (max) | 0.04% | 0.035% |
| Sulfur, S (max) | 0.05% | 0.040% |
The carbon content of both 1045 and 4140 determines the last two digits of their grade number. The carbon content of 1040 steel is 0.40%, while 1045 has a carbon content of 0.45%. The first digit “1” identifies that they are both carbon steels, and the second digit “0” identifies that there were no modifications to the alloy. Note the higher concentration of Manganese in 4140 than 1045.
Mechanical Properties
Whether a steel is hot rolled or cold drawn determines many of the mechanical properties. The majority of 1045 and 4140 steel is purchased in cold drawn state, but we provided two graphs of both hot rolled and cold drawn mechanical properties for both 1040 and 1045.
Here is a comparison chart of 1040 and 1045 hot rolled steel mechanical properties:
| 1045 Hot Rolled | 4140 Hot Rolled | |
| Tensile Strength | 82,000 psi | 90,000 psi |
| Yield Strength | 45,000 psi | 65,000 psi |
| Elongation in 2″ | 16% | 35% |
| Reduction in Area | 40% | 40% |
| Brinell Hardness | 163 | 25 |
Here is a comparison chart of 1040 and 1045 cold drawn steel mechanical properties:
| 1045 Cold Drawn | 4140 Cold Drawn | |
| Tensile Strength | 91,000 psi | 95,000 psi |
| Yield Strength | 77,000 psi | 60,200 psi |
| Elongation in 2″ | 12% | 25% |
| Reduction in Area | 35% | 35% |
| Brinell Hardness | 179 | 197 |
Real Life Applications
4140 steel is chromium, molybdenum, manganese steel with good toughness, impact resistance and fatigue strength. 1045 has slightly increased tensile strength and yield strength numbers than 1045 as a result of a slightly higher carbon content. Also, as a result of higher carbon content, 1045 is not as easy to weld as 4140.
