Choose the Right Solid CBN Insert Grade for Cast Iron and Hardened Steel Machining
Henan UHD Ultrahard Tools Co., Ltd
2026-08-17
Procurement Decisions
Compare UHD solid CBN insert grades UBN S1, S2, S3, S4 and X3 for cast iron and hardened steel machining. Find the right grade for continuous, interrupted and heavy roughing conditions.
UHD Technical Selection Reference
Solid CBN Insert Grades for Reliable Ferrous Material Turning
A practical grade-selection reference for cast iron and hardened steel machining. UHD solid CBN inserts help manufacturers match wear resistance, thermal stability and edge toughness to actual cutting conditions.
Available grade family
S1 · S2 · S3 · S4 · X3
What Is a Solid CBN Insert?
A solid CBN insert is produced from fully sintered polycrystalline cubic boron nitride. Unlike a carbide-supported tipped insert, its cutting body is made of CBN material throughout. This construction is used in demanding ferrous-material turning where high hardness, abrasive wear, cutting heat or interrupted engagement place greater demands on the cutting edge.
Solid CBN tooling is commonly considered for cast iron, hardened steel, bearing steel, die steel and tool steel. Grade selection should not be based on workpiece material alone. The best starting point also depends on whether cutting is continuous or interrupted, the machining stage, cutting speed, depth of cut, edge preparation, insert geometry and the rigidity of the machine-toolholder system.
Grade Comparison
UBN Solid CBN Grade Overview
Use this table as an initial application reference before production validation.
| CBN Grade |
Primary Balance |
Recommended Cutting Condition |
Suitable Workpiece |
Typical Machining Stage |
| UBN S1 |
Wear resistance with impact capability |
High-speed continuous or interrupted cutting |
Alloy, gray and ductile cast iron |
Roughing and semi-finishing |
| UBN S2 |
Wear resistance and heat resistance |
High-speed continuous cutting |
Alloy, gray and ductile cast iron |
Semi-finishing and finishing |
| UBN S3 |
Impact resistance with wear resistance |
Low-speed interrupted cutting |
Hardened steel, bearing steel, die steel and tool steel |
Roughing and semi-finishing |
| UBN S4 |
Wear resistance with stable high-temperature cutting performance |
High-speed continuous cutting |
Hardened steel, bearing steel, die steel and tool steel |
Semi-finishing and finishing |
| UBN X3 |
High edge strength, impact resistance and wear resistance |
Medium-to-low speed, deep cuts or severe interruption |
High-hardness cast iron |
Heavy roughing |
A Simple Way to Narrow Down the Grade
01 · Identify the material
For cast iron, start with S1, S2 or X3. For hardened steel and related hardened ferrous materials, begin with S3 or S4.
02 · Check cutting continuity
Interrupted engagement increases edge impact. Give priority to a grade with suitable toughness for the interruption level.
03 · Define the operation
Heavy stock removal and larger depths of cut require stronger edge support; finishing usually places more emphasis on wear and heat resistance.
04 · Validate on the machine
Confirm the recommendation with the actual holder, clamping condition, machine rigidity and required tool-life target.
Recommended Starting Grades by Application
Cast Iron Machining
Choose according to speed, interruption and stock removal
UBN S1
A practical starting grade for alloy, gray and ductile cast iron in high-speed continuous or interrupted operations, particularly roughing and semi-finishing.
UBN S2
Designed for high-speed continuous cutting where semi-finishing or finishing performance is the primary objective.
UBN X3
Consider for high-hardness cast iron under heavy roughing conditions, including larger depths of cut, heavier material removal or severe interrupted cutting.
Match the edge to the interruption level
UBN S3
A suitable initial selection for low-speed interrupted cutting of hardened steel, bearing steel, die steel and tool steel in roughing or semi-finishing operations.
UBN S4
Used for high-speed continuous cutting of hardened steel where semi-finishing and finishing consistency are required.
Selection reminder: When an application combines high hardness with unstable interruption, assess edge preparation, holder rigidity and cutting parameters together with the CBN grade.
Factors That Affect Solid CBN Insert Performance
The grade is one part of a complete turning solution. A correctly selected grade may still require adjustment when the workpiece condition, cutting setup or target result changes.
- Workpiece condition: material grade, hardness, skin or scale, inclusions and surface irregularities.
- Cutting data: speed, feed rate and depth of cut should support the selected grade and operation.
- Insert configuration: ISO shape, corner radius, chip control requirement and edge honing influence cutting behavior.
- System rigidity: machine condition, toolholder overhang, clamping stability and runout affect edge reliability.
- Production target: required surface finish, dimensional consistency, cycle time and planned tool life.
- Cutting mode: continuous, light interrupted or heavily interrupted engagement requires different edge priorities.
Common ISO Formats for External Turning
Selected UHD solid CBN grades can be supplied in commonly used external-turning insert formats. Final availability depends on grade, insert geometry and the requirements of the machining application.
| ISO Designation |
L (mm) |
IC (mm) |
S (mm) |
Corner Radius R (mm) |
| RNGN120400 |
12.7 |
12.7 |
4.76 |
0 |
| SNGN120408 |
12.7 |
12.7 |
4.76 |
0.8 |
| SNGN120712 |
12.7 |
12.7 |
7.94 |
1.2 |
| SNGN090408 |
9.525 |
9.525 |
4.76 |
0.8 |
| WNGN080404 / 080408 / 080412 |
8.7 |
12.7 |
4.76 |
0.4 / 0.8 / 1.2 |
| TNGN160404 / 160408 / 160412 |
16.5 |
9.525 |
4.76 |
0.4 / 0.8 / 1.2 |
Frequently Asked Questions
Which grade should be considered for interrupted hardened steel cutting?
UBN S3 is an appropriate starting grade for low-speed interrupted cutting of hardened steel, especially in roughing and semi-finishing conditions. The actual recommendation should be verified against interruption severity and machine rigidity.
How do UBN S1 and UBN S2 differ in cast iron machining?
UBN S1 is intended for high-speed cast iron cutting that may be continuous or interrupted, with a focus on roughing and semi-finishing. UBN S2 is better aligned with high-speed continuous semi-finishing and finishing applications.
When is UBN X3 a suitable option?
UBN X3 should be considered for heavy roughing of high-hardness cast iron, particularly when the operation includes larger depths of cut, substantial stock removal, medium-to-low speeds or severe interrupted engagement.
How should I choose between UBN S3 and UBN S4?
Use S3 as the initial option for low-speed interrupted hardened steel machining. For high-speed continuous hardened steel cutting, especially semi-finishing and finishing, S4 is the more suitable starting point.
Technical Support from UHD
Request a Grade and Insert Configuration Recommendation
Henan UHD Ultrahard Tools Co., Ltd. supports global B2B manufacturers with solid CBN insert selection, ISO insert supply and non-standard tooling solutions. For a more relevant recommendation, share the details of your actual application.
Please include:
- Workpiece material and hardness
- Insert designation and machining stage
- Cutting speed, feed and depth of cut
- Continuous or interrupted cutting condition
- Machine model, holder setup and target tool life
