USN100 and BN91 CBN Insert Selection for HRC55–70 Surface-Hardened Alloy Hard Turning
UHD provides selection guidance and cutting parameter ranges for hard turning Stellite, nickel-based, and iron-based overlay alloys at HRC55–70 using USN100 Integral Brazed CBN Insert Series for roughing and BN91 Full Face CBN Insert Series for finishing.
Hard turning surface-hardened overlay alloys is not simply a matter of selecting a CBN grade. Stellite, nickel-based, and iron-based weld overlays at HRC55–70 can combine high hardness with uneven heat-affected zones, porosity, inclusions, unmelted areas, and hard spots. These conditions create fluctuating cutting loads that can affect edge integrity, process stability, and tool-change planning.
For this application, UHD (Henan UHD Ultrahard Tools Co., Ltd) recommends separating roughing and finishing objectives: use the USN100 Integral Brazed CBN Insert Series where interrupted cutting and overlay defects create impact risk, and use the BN91 Full Face CBN Insert Series for stable, continuous finishing operations that require controlled wear behavior and repeatable production cycles.
Why HRC55–70 Overlay Alloy Turning Requires a Process-Based Choice
Hardfacing and weld-overlay components are commonly found in remanufactured rolls, valve sealing surfaces, screws, wear plates, rings, sleeves, and other high-wear parts. Although the overlay may be specified within a hardness range, the actual cutting condition can vary significantly across the workpiece.
Hardness and structure variation
Changes between the overlay, substrate, and heat-affected zone can cause variations in cutting force and edge loading.
Defect-related impact
Porosity, slag inclusions, weld beads, and hard particles may turn an apparently continuous cut into an intermittent impact condition.
Different roughing and finishing targets
Roughing prioritizes resistance to chipping and edge failure, while finishing focuses on stable wear, dimensional control, and predictable tool replacement.
USN100 and BN91: Defined Roles in the Hard-Turning Process
ROUGHING / IMPACT-PRONE CUTTING
The UHD USN100 series is an integral brazed, double-sided indexable CBN insert solution for roughing overlay alloys where defects, interrupted engagement, or uneven stock can expose the cutting edge to impact.
- Recommended for rough stock removal and larger remaining allowance.
- Suitable when porosity, inclusions, weld irregularity, or hard spots are present.
- Helps place the higher-risk material-removal stage before finishing.
- Supports a process focus on edge integrity and reduced abnormal interruptions.
FINISHING / CONTINUOUS CUTTING
The UHD BN91 series is a full-face CBN insert solution for finishing operations under stable, continuous cutting conditions, where consistent wear progression and a manageable tool-change point are important.
- Recommended for finishing passes with small and uniform allowance.
- Best suited to stable, continuous engagement after roughing risk has been reduced.
- The larger CBN cutting area is appropriate for continuous hard-turning requirements.
- Supports the establishment of repeatable finishing cycles and tool-life monitoring.
Reference Selection and Starting Cutting Parameters
The ranges below are practical starting windows for HRC55–70 Stellite, nickel-based, and iron-based overlay alloy turning. Final settings should be adjusted according to machine rigidity, workholding, workpiece diameter, overlay thickness, stock uniformity, cutting continuity, and the observed wear pattern.
| Operation |
Typical Condition |
Recommended UHD Series |
Vc |
f |
ap |
Primary Selection Objective |
| Roughing |
Porosity, inclusions, uneven weld surface, interrupted or impact-prone cutting |
USN100 Integral Brazed CBN Insert Series |
40–80 m/min |
0.10–0.25 mm/rev |
0.5–2.0 mm |
Manage impact and reduce chipping or insert damage risk during stock removal |
| Finishing |
Stable and continuous cutting, uniform finishing allowance |
BN91 Full Face CBN Insert Series |
60–120 m/min |
0.05–0.20 mm/rev |
0.1–0.5 mm |
Support stable wear behavior, dimensional consistency, and controlled cycle planning |
Application note: Begin near the lower end of the applicable parameter window during initial trials. Confirm edge condition, vibration, wear mode, and dimensional trend before increasing cutting speed or feed.
Three Questions for Fast Insert Selection
- 1 Is the operation roughing or finishing?
For roughing, large allowance, or an objective of safely removing unstable overlay material, prioritize USN100. For finishing with dimensional and surface-quality control as the main objective, prioritize BN91.
- 2 Is cutting continuous or interrupted?
Visible weld beads, steps, cavities, or recurring hard spots indicate a more interrupted condition and favor USN100. A uniform surface with continuous tool engagement is the appropriate condition for BN91 finishing.
- 3 How controllable is the overlay quality?
For repair parts or overlays with unavoidable defects, use USN100 to address risk earlier in the process. For consistent batch parts with controlled material quality, BN91 can be introduced for stable finishing performance.
A Repeatable Introduction Process for Production
1. Collect application data
Confirm overlay system, HRC range, thickness, heat-treatment condition, defect condition, workpiece geometry, machine type, and clamping method.
2. Divide roughing and finishing
Allocate uneven stock and impact risk to the USN100 roughing stage, then reserve a stable and uniform allowance for BN91 finishing.
3. Establish a conservative baseline
Start within the reference windows and assess vibration, edge condition, wear location, and finished-part dimensional movement.
4. Set tool-change criteria
Record machining time or parts per edge, wear appearance, and size trend to define a practical, repeatable replacement point.
What to Check When Performance Is Unstable
| Observed Condition |
Review First |
Process Direction |
| Chipping, notch damage, or insert loss during stock removal |
Interrupted cutting level, overlay defects, workholding, uneven allowance, and overly aggressive ap or f |
Use USN100 for the impact-prone stage and stabilize the roughing pass before advancing parameters. |
| Unpredictable finish size or surface marks |
Remaining allowance consistency, cutting continuity, vibration, and edge wear progression |
Create a more uniform finishing condition and evaluate BN91 under stable continuous engagement. |
| Frequent variation between similar workpieces |
Overlay quality, runout, fixture repeatability, and actual hardness or defect distribution |
Document the material and setup variables; do not evaluate insert performance only by unit price or isolated cycle results. |
Application Boundary and UHD Technical Support
This guidance is intended for hard turning HRC55–70 surface-hardened Stellite, nickel-based, and iron-based overlay alloys. It does not replace material-specific tooling strategies for non-ferrous metals, austenitic stainless steels such as 304 or 316, or low-hardness steels.
Machine rigidity, clamping stability, runout, stock distribution, cutting interruption, and dry or coolant conditions all influence final performance. UHD supports B2B customers with application information, insert selection, parameter-window recommendations, and a structured approach from trial cutting to repeatable production use.
