Microalloyed Strip Steel Compositions and Yield Strength
Compositions in weight percent, industrial rolling conditions and yield strength after coiling for five commercial microalloyed hot strip steels, from a low niobium C-Mn baseline to NbTiV grades that reach 599 to 638 MPa. The tables are a reference summary of a published chapter and not an Aobo Steel specification. The last table splits the measured yield strength into the part explained by grain size and solid solution and the part contributed by dislocations and carbonitride precipitation.
Compositions of the five steels
All values are weight percent, as printed. A dash means the source lists no addition of that element, and n.d. means not determined. The last column is the maximum total volume fraction available for carbonitride precipitation.
| Steel | C | Mn | Si | P | S | Al | Nb | Ti | V | N | Vf max |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Nb | 0.07 | 0.68 | 0.01 | 0.012 | 0.009 | 0.04 | 0.04 | – | – | 0.009 | 0.00045 |
| NbTi-1 | 0.05 | 0.55 | 0.02 | n.d. | n.d. | 0.02 | 0.02 | 0.06 | – | 0.006 | 0.00131 |
| NbTi-2 | 0.12 | 1.21 | 0.33 | 0.023 | 0.008 | 0.048 | 0.057 | 0.059 | – | 0.008 | 0.00166 |
| NbTi-3 | 0.11 | 1.54 | 0.28 | 0.026 | 0.007 | 0.01 | 0.04 | 0.11 | – | n.d. | 0.00261 |
| NbTiV | 0.14 | 1.38 | 0.25 | 0.018 | 0.007 | 0.07 | 0.04 | 0.04 | 0.03 | 0.008 | 0.00174 |
Source, Alloy Steel, Properties and Use (E. Morales), chapter 3, Comments About the Strengthening Mechanisms in Commercial Microalloyed Steels and Reaction Kinetics on Tempering in Low-Alloy Steels, Table 5, p. 60.
Microalloyed Strip Steel Compositions and Yield Strength, printable PDF
Two A4 pages with the five steel compositions in weight percent, the rolling conditions and the yield strength after coiling, and our contact details.
Industrial processing conditions and yield strength after coiling
Soaking, roughing, finishing and coiling temperatures are given in degrees C, thickness in millimetres and yield strength in MPa. All five steels were rolled on an industrial hot strip mill. The cooling column is printed as °C*min-1 in the source and is reproduced unchanged.
| Steel | Soaking °C | Roughing °C | Finishing °C | Cooling °C*min-1 | Coiling °C | Thickness mm | Y.S. MPa |
|---|---|---|---|---|---|---|---|
| Nb | 1150 | ≥1080 | 890 | 10 | 650 | 10 | 310 |
| NbTi-1 | 1230 | ≥1100 | 870 | 20 | 630 | 8 | 332 |
| NbTi-2 | 1150 | ≥1070 | 870 | 10 | 650 | 7 | 534 |
| NbTi-3 | 1225 | ≥1100 | 895 | 10 | 650 | 8 | 638 |
| NbTiV | 1225 | ≥1100 | 895 | 10 | 670 | 3 | 599 |
Source, Alloy Steel, Properties and Use (E. Morales), chapter 3, Comments About the Strengthening Mechanisms in Commercial Microalloyed Steels and Reaction Kinetics on Tempering in Low-Alloy Steels, Table 6, p. 60.
Where the yield strength comes from
The base yield strength is calculated from the ferrite grain size, manganese, silicon and free nitrogen in solution. The last column is the additional strengthening from dislocations and precipitation, obtained by subtracting the calculated base value from the measured yield strength. The source prints the header of the last column as Δσ( MPa, reproduced here as Δσ (MPa).
| Steel | Grain Size (µm) | σ (MPa) | Δσ (MPa) |
|---|---|---|---|
| Nb | 10.0 | 252 | 58 |
| NbTi-1 | 9.4 | 254 | 78 |
| NbTi-2 | 5.0 | 367 | 167 |
| NbTi-3 | 4.2 | 393 | 245 |
| NbTiV | 3.3 | 421 | 178 |
Source, Alloy Steel, Properties and Use (E. Morales), chapter 3, Comments About the Strengthening Mechanisms in Commercial Microalloyed Steels and Reaction Kinetics on Tempering in Low-Alloy Steels, Table 7, p. 61.
Carbon and manganese set the strength level. Steel Nb at 0.07 % C and 0.68 % Mn reached 310 MPa after coiling, while NbTi-2 at 0.12 % C and 1.21 % Mn reached 534 MPa. The three higher strength steels carry niobium with titanium, and NbTiV adds vanadium as well. For the compositions of the alloy steel grades we supply as bar, see the alloy steel composition chart.
The three higher strength steels also came off the mill thinner, at 3 to 8 mm against 10 mm for the two lower strength ones, and their ferrite grain size fell to 3.3 to 5.0 µm against about 10 µm. Grain refinement is the larger part of that gain. The additional strengthening from dislocations and precipitation runs from 58 MPa in steel Nb to 245 MPa in NbTi-3.
The steel names Nb, NbTi-1, NbTi-2, NbTi-3 and NbTiV are the identifiers used in the source chapter, not commercial grade designations. The numbers above are the figures printed in that chapter, not a purchase specification. The composition of the carbon steel grades we supply is on the carbon steel composition chart.
Composition and property data is for general reference only. Actual values vary by standard, mill, and heat number. Confirm against the material test certificate (MTC) or contact Aobo Steel.
Reference data compiled from Alloy Steel, Properties and Use (E. Morales), chapter 3, Comments About the Strengthening Mechanisms in Commercial Microalloyed Steels and Reaction Kinetics on Tempering in Low-Alloy Steels.