ASTM A193
Grade B8ML4CuN
UNS S31730 Bolts
Understanding This Highly Specific Grade
B8ML4CuN sits alongside B8CLNCuB at the far specialized end of the ASTM A193 stainless bolting family — a designation most fastener buyers won’t encounter in routine procurement, built for a narrow, often project-specific set of requirements rather than general corrosion-resistant bolting. As with that grade, every letter here corresponds to a genuine compositional decision: M for molybdenum-bearing base chemistry, L for low carbon, Cu for a deliberate copper addition, and N for a nitrogen addition. The “4” preceding CuN is part of this specific grade’s formal ASTM designation and, based on general naming conventions in this family, most likely relates to a specific composition or property variant defined within the standard rather than a percentage figure — this is worth confirming directly against the standard text.
The molybdenum-bearing, low-carbon logic follows the same general principle covered on our B8MLN/B8MLNA grade page — a 316-type base gives genuine chloride and pitting resistance, while low carbon addresses weld-decay risk.
The copper and nitrogen additions, and the exact meaning of the “4” in this designation, are the genuinely specialized part of this grade, and because this is used for a narrow set of specific, often customer- or project-driven applications, we recommend confirming the exact composition limits, mechanical property requirements, and intended service condition directly against the current ASTM A193 standard text or your project specification before finalizing an order.
Akbar Fasteners Pvt. Ltd. exports to over 50 countries, and we’re glad to manufacture to this specification once the exact composition and property requirements from your project or the governing standard are confirmed, verified under our ISO 9001:2015 quality system.
An Honest Note on This Specific Grade
B8ML4CuN is a considerably less common designation than the general ASTM A193 grades we cover elsewhere on this site, and published, detailed reference material on its precise composition limits and typical service applications is genuinely limited compared to more widely used grades. We manufacture to this specification when a customer provides the exact composition and property requirements — either from the current ASTM A193 standard text or a project-specific data sheet — rather than relying on general description alone. If you’re specifying this grade, please share the governing document with your inquiry so we can confirm manufacturability accurately.
Where This Designation Typically Comes From
Project-Specific Specification
Typically called out by name on a specific project drawing or purchase specification, not chosen from a general catalog.
Inherited Molybdenum Benefits
Shares the same 316-type chloride and pitting resistance logic as B8MLN/B8MLNA.
Additional Micro-Alloying Control
Copper and nitrogen additions specified deliberately for reasons defined by the governing project standard.
Verified Against Your Governing Document
We manufacture to the composition and property requirements you provide, confirmed before production.
What Each Part of the Name Signals
Molybdenum-Bearing
316-type base chemistry, consistent with the chloride and pitting resistance logic used across the B8M family.
Controlled Low Carbon
Carbon content controlled to a low band, consistent with the low-carbon logic used across the B8L family.
Copper Micro-Alloy
Deliberate copper addition, specified for a purpose defined by the governing standard or project spec.
Nitrogen Addition
Controlled nitrogen addition, generally for strength gain, confirmed per the governing standard.
B8ML4CuN Specification Approach
Shared Elements With B8MLN/B8MLNA
- Base Type Molybdenum-Bearing Austenitic
- Carbon Low, Controlled Band
- Nitrogen Controlled Addition
- Chromium/Nickel/Mo Per Governing Standard
What Makes This Grade Different
- Copper Confirmed to Project Spec
- Designation Suffix “4” Confirmed to Standard Text
- UNS Designation S31730
- Mechanical Properties Confirmed Per Order
Our Order Process for B8ML4CuN
- Step 1 Confirm Governing Document
- Step 2 Verify Composition Limits
- Step 3 Manufacture & Test to Spec
- Step 4 Issue Full Documentation
Application Context
A specification this specific is generally driven by a particular project or customer standard, not a general application category.
Specialized Chemical Process Equipment
with defined composition needs
High-Value Custom Fabrication
tied to a governing standard
Marine & Offshore Infrastructure Projects
standards and specifications
Engineering-Specified Critical Bolting
is dictated by design engineering
Standard Export Documentation
Prepared as standard practice once composition and property requirements are confirmed for your order.
Mill Test Certificate (MTC)
Heat number, chemical composition, and mechanical property verification for every lot.
Chemical Composition Report
Confirms actual composition, including copper and nitrogen content, against your confirmed specification.
Certificate of Conformance
Confirms the shipment matches the purchase order specification in full.
Certificate of Origin (COO)
Confirms India as country of manufacture for destination customs purposes.
NABL Accredited Test Reports
Independent mechanical and chemical testing available on request for critical applications.
Commercial Invoice & Packing List
Itemized value, Incoterm, and detailed carton/weight breakdown for customs clearance.
Internationally Recognised Standards Coverage
Related Fastener Grades & Materials
ASTM A193 Grade B8MLN / B8MLNA
Our molybdenum-bearing, nitrogen-enhanced grade family without the copper addition.
View B8MLN / B8MLNA →ASTM A193 Grade B8CLNCuB
Our other genuinely niche copper-modified grade, based on 347LN instead of 316-type.
View B8CLNCuB →SS 316 / 316H / 316L Fasteners
Our broader 316 family guide, covering the base marine-grade logic this specialty grade builds on.
View SS 316 Guide →Stainless Steel Fasteners Manufacturer India
Our broader stainless steel fastener manufacturing capability across all major grades.
View SS Manufacturer Guide →Have the Governing
Specification for This Grade?
Share your project standard or the ASTM A193 edition you’re working to, and we’ll confirm manufacturability, composition, and mechanical property alignment before quoting. Akbar Fasteners Pvt. Ltd. responds within 24 hours.
Sales: +91 724 0000 733 · Support: +91 800 9315 333 · sales@akbarfasteners.in