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Mn-B Boron Steel
BRAND: PROMISTEEL
GRADES: 15B35H, 10B21, 20MnTiB, 50B, 15MnB
SHAPES: Wire Rod (Coil), Round Bar, Flat Bar
DELIVERY CONDITION: Hot Rolled, Spheroidize Annealed (SA)
SURFACE: Pickled & Phosphated, Black
HARDNESS: Annealed ≤180 HB (Good for Cold Heading)
FEATURE: High Hardenability at Low Cost
APPLICATION: Grade 8.8/10.9 Bolts, Track Shoes, Excavator Teeth
MOQ: 25 Tons
Mn-B Series (Manganese-Boron) steel is a specialized class of low-alloy steel designed to deliver high strength at a competitive cost. By adding a minute amount of Boron (0.0005% - 0.003%), the steel's hardenability is drastically improved without the need for expensive alloying elements like nickel or molybdenum.
Our Boron Steel (15B35 / 10B21) is the global standard for the Fastener Industry. Supplied in spheroidized annealed wire rods, it offers excellent plasticity for cold heading, yet can be heat-treated to achieve Grade 8.8, 10.9, or even 12.9 strength levels. Additionally, higher carbon grades (like 50B) are widely used for Wear Parts in construction machinery, such as track links and excavator bucket teeth.
Product Specifications & Grade Equivalents
We supply Boron Steel optimized for cold heading (CHQ) and heat treatment consistency.
Table-1
Choosing the right grade for your bolt class or wear part.
International Grade Comparison |
||||
| GB (China) | ASTM / SAE (USA) | DIN / EN (Germany) | JIS (Japan) |
Typical Application |
| 10B21 | SAE 10B21 | - | - |
Grade 8.8 / 9.8 Bolts |
| 15MnB | 15B21 | 1.5508 (17MnB3) | - |
Grade 10.9 Bolts |
| 15B35 / ML35MnB | 15B35 | 1.5530 (35MnB5) | SWRCH35K (Sim.) |
High-Strength Shafts/Bolts |
| 20MnTiB | - | - | - |
Heavy Steel Structure Bolts |
| 50B | 15B41H | 1.7176 (50MnB5) | SUP9 (Sim.) |
Track Shoes, Cutting Edges |
Table-2
The "Boron Effect" ensures deep hardening with lean alloy content.
Chemical Composition (Mass Fraction %) |
|||||
| Grade | C | Mn | B (Boron) | Ti | Si |
| 10B21 | 0.18~0.23 | 0.80~1.10 | 0.0005~0.003 | 0.01~0.04 | ≤0.10 |
| 15B35H | 0.32~0.38 | 0.80~1.10 | 0.0005~0.003 | - | 0.15~0.35 |
| 20MnTiB | 0.17~0.24 | 1.30~1.60 | 0.0005~0.0035 | 0.04~0.10 | 0.17~0.37 |
Table-3
Supplied in coil for continuous cold headers or bar for forging.
Supply Range & Formats |
|||
| Product Form | Dimensions (mm) | Delivery Condition | Surface Finish |
| Wire Rod (Coil) | Dia: 5.5 - 42.0 | Spheroidize Annealed (SA) |
Pickled & Phosphated |
| Round Bar | Dia: 16 - 150 | Hot Rolled / Annealed | Black / Peeled |
| Flat Bar | Custom Profile | Hot Rolled | Black |
Key Features and Advantages
Cold Formability
Our 10B21 and 15B35 grades are supplied with a Spheroidize Annealed structure, ensuring low yield strength and high ductility. This minimizes tool wear and cracking during the cold heading of bolt heads.
Cost-Effective Hardenability
Boron replaces more expensive alloys (like Cr, Mo, Ni). A simple Quench and Temper process yields high tensile strength equal to alloy steels.
Consistent Heat Treatment
Tightly controlled Boron and Titanium content ensures consistent hardness across large production batches.
Wear Resistance
Higher carbon boron steels (like 50B) offer excellent abrasion resistance after hardening, ideal for earthmoving ground engaging tools (G.E.T).
Typical Applications
Mn-B Series Boron Steel powers the assembly and movement of heavy machinery:
High Strength Fasteners:
- 10B21: Used for Grade 8.8 and 9.8 bolts, self-tapping screws.
- 15B35 / 20MnTiB: Used for Grade 10.9 heavy hex bolts, structural bolts, and automotive engine bolts.
Automotive Components: Steering parts, stabilization links, and seat belt mechanisms.
Construction Machinery (Undercarriage):
- Track Shoes/Links: Made from 50MnB or 25MnB profiles.
- Bucket Teeth & Cutting Edges: Requires high hardness and impact resistance.
Hand Tools: Spanners, wrenches, and sockets.
FAQ
Q1: Why use Boron Steel instead of 4140 for bolts?
A1: Cost & Process. For diameters under 30mm, Boron steel (like 15B35) can achieve the same Grade 10.9 properties as 4140 but at a significantly lower material cost. It is also easier to cold-form (cold head) than 4140, increasing production speed.
Q2: What is "Spheroidize Annealing" (SA)?
A2: It is a heat treatment that softens the steel and creates a globular carbide structure. This is essential for Cold Heading Quality (CHQ) wire. Without SA, the wire would be too hard and would crack the heading dies during bolt manufacturing.
Q3: What is 20MnTiB used for?
A3: 20MnTiB is a classic Chinese grade specifically developed for Large Hexagon Head High-Strength Bolts used in steel structure construction (bridges, skyscrapers). It offers excellent low-temperature impact toughness.
Q4: Is Boron steel weldable?
A4: Lower carbon grades (like 10B21) have good weldability. However, high carbon grades (like 50B) or heat-treated parts are difficult to weld without cracking and losing their tempered properties.
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