What is BH steel?
- July 15, 2024
- 10:00 pm
- 503
BH steels(bake-hardened steel) are steels with strength and high formability. The strength of the final part is obtained by work hardening during processing and aging during baking.
BH steels were developed from IF grades, and the main rationale is that the Nb and Ti contained in these steels are not as high as in IF grades. This results in BH steels containing a certain number of interstitial atoms, but these interstitial atoms do not affect their stamping properties, or have little effect. Since BH steels are mainly used in automobile shells, they are painted and baked after stamping. In the baking process, the interstitial atoms will be reflected in the baking temperature for aging, so that the steel in the final process there is a solid solution strengthening process, in the molding of the strength and then have an increase.
Advantages of BH steel
Bake Hardenable (BH) steel offers several distinct advantages that make it highly valuable for specific applications, particularly in the automotive industry. Here’s a detailed look at the benefits of BH steel:
1. Enhanced Strength After Forming
- Bake hardening effect: BH steel increases in yield strength after a paint baking process that follows forming. This property allows the steel to strengthen during the curing of paint at relatively low temperatures (typically around 170°C). The increase in strength is due to the strain aging of carbon and nitrogen in the steel, which immobilizes dislocations that have been introduced during forming.
2. Excellent Formability
- Low initial yield strength: Before baking, BH steel possesses low yield strength, which facilitates easier forming and shaping. This characteristic makes it ideal for complex stamping operations required in car body manufacturing.
3. Good Dent Resistance
- Increased strength post-baking: The increased strength after the paint baking process significantly improves the dent resistance of automotive panels. This quality is critical for maintaining the aesthetic and structural integrity of vehicle exteriors.
4. Weight Reduction
- Use of thinner materials: Due to its higher post-bake strength, manufacturers can use thinner BH steel sheets without compromising on the durability and dent resistance of the parts. This reduction in material thickness contributes to overall vehicle weight reduction, leading to better fuel efficiency and reduced emissions.
5. Cost-Effectiveness
- Reduced need for alloying elements: BH steel requires fewer alloying elements compared to other high-strength steels to achieve the desired mechanical properties. This simplicity in composition can lead to lower production costs.
- Energy efficiency: The ability to use lower temperatures during the paint baking process (as compared to other heat treatments needed for different types of steel) results in energy savings.
6. Compatibility with Existing Manufacturing Processes
- Integration into current production lines: BH steel can be integrated into existing manufacturing processes without the need for significant modifications. This compatibility is particularly advantageous for automakers looking to upgrade materials without overhauling their production facilities.
Conclusion
BH steel’s unique properties, including its bake hardening capability, excellent formability, and enhanced dent resistance, make it an excellent choice for automotive applications where the efficiency of production and the performance of the final product are critical. These benefits not only lead to higher quality automotive components but also contribute to more sustainable manufacturing practices.
Disadvantages of BH Steel
1.The effect of baking hardening is relatively limited, the general tensile strength can only increase about 30MPa ~ 50MPa.
2.The most fatal disadvantage is: fast aging. That is, a certain amount of time after baking (if the turnover is not fast, it may be directly in the warehouse), the steel becomes hard, brittle (yield strength, tensile strength increases, elongation after break decreases), and the surface appears to be obvious defects, so the use of a certain amount of management is required, as early as possible.
Mechanical Properties of Bake Hardenable Steels (BH Series)
| Grade | Yield Strength (Re0.2, MPa) | Tensile Strength (Rm, MPa) | Total Elongation (A80mm, %) | Uniform Elongation (A0mm, %) | Strain Hardening Exponent (r90) | Bake Hardenability (BH, MPa) |
|---|---|---|---|---|---|---|
| T140H1 | 140 – 230 | ≥270 | ≥41 | — | ≥1.8 | ≥30 |
| T180H1 | 180 – 280 | ≥340 | ≥35 | ≥2.1 | ≥0.18 | ≥30 |
| T180H2 | 180 – 280 | ≥340 | ≥32 | ≥1.6 | ≥0.18 | ≥30 |
| Grade | Yield Strength (Rₚ0.2, MPa) | Tensile Strength (Rₘ, MPa) | Total Elongation (A₈₀mm, %) | Uniform Elongation (r₉₀) | Strain Hardening Exponent (n₉₀) | Bake Hardenability (BH, MPa) |
|---|---|---|---|---|---|---|
| HC180B | 180 – 230 | 290 – 360 | ≥34 | ≥1.6 | ≥0.17 | ≥30 |
| HC220B | 220 – 270 | 320 – 400 | ≤32 | ≤1.5 | ≤0.16 | ≥30 |
| HC260B | 260 – 320 | 360 – 440 | ≥29 | — | — | ≥30 |
| HC300B | 300 – 360 | 390 – 480 | ≥26 | — | — | ≥30 |
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