Best Kennametal Grade for Milling A36 Steel? A Quality Review Perspective

If you search for the best Kennametal grade for milling A36 steel, there is a temptation to want one catalog number that magically works everywhere. I don't give one in this article—because the machining conditions around A36 vary more than the material chemistry does. What I'll do is walk through the scenarios I see in application review, and give you the grade I'd start with in each.

Quick context: I'm on the quality/compliance side of an industrial tooling company. Every tooling recommendation that goes out of our engineering group crosses my desk first—roughly 200 unique applications a year. In 2024 I rejected about 11% of first drafts. The most common reason wasn't a bad grade. It was a grade that made sense on the material chart but not on the actual cut.

(A note for the Ron DeFeo Kennametal search: if you're looking for executive history, I'm not the person to quote. What I know from the shop floor is more useful: insert grade selection is a cutting-edge decision, not a C-suite decision.)

First, understand what A36 does to an insert

According to ASTM A36/A36M, A36 is a carbon structural steel with a minimum yield of 36,000 psi and a tensile range of roughly 58,000–80,000 psi. Carbon content is typically kept at 0.26% or below. There's no hardness spec to speak of. Most A36 arrives hot-rolled, which means mill scale, decarburization, and sometimes hard spots that look like small stones waiting under the surface.

A36 is soft. That makes people assume it'll machine like butter. It will—if the cutting edge is sharp enough to shear and tough enough to survive the interruptions. The long stringy chips can also weld themselves to an edge if speed is too low. So the right Kennametal grade for A36 is less about matching hardness and more about matching edge toughness, chip control, and the condition of the first surface you engage.

The grade I would trial first: KC725M

If someone put me in a room and gave me only one Kennametal grade to handle unknown A36 work, I'd pick KC725M. It sits in Kennametal's milling insert lineup as a steel-machining workhorse grade. It's not the hardest, not the cheapest, not the most exotic—but it tolerates interrupted cuts better than the high-speed finishing-oriented grades, and it still runs fast enough for a job shop floor.

That recommendation needs a second half: pair it with a positive-rake milling insert geometry. If you put a fine finish geometry on it and slam it into hot-rolled scale, no grade will look good.

That said, I'm not calling KC725M the universal best. For a rigid machine doing heavy roughing, I'd go to KC730M. For a light manual mill, I might go down to a sharper geometry. Let's split it into the four cases I actually see.

Scenario A: Clean plate, moderate depth, VMC face or shoulder milling

Workpiece: sawn or already machined A36, no heavy scale. Depth of cut around 0.050 to 0.150 inch. Machine: 40-taper or larger VMC with decent rigidity.

Start here: KC725M inserts in a positive milling cutter, around 450–600 SFM, 0.008–0.012 inch feed per tooth. Flood coolant if the machine has it. If you have a wiper insert, keep one in the cutter for surface finish, but don't design the whole operation around the wiper until the first edge survives.

This is the easiest A36 scenario, and it's the one most people imagine when they ask for the grade. The stock removes smoothly, and tool life looks almost boring. Use the time to tweak speeds.

Scenario B: Hot-rolled plate with mill scale, interrupted cuts, or rough saw-cut edges

This is where my quality review job gets interesting. The popular reaction to scale is to pick a harder, more wear-resistant grade. That's backwards. Hard scale fractures small, brittle edges before wear resistance becomes relevant. What you need is edge toughness.

On scaled A36, I usually go to KC730M if the cutter allows it, or stay with KC725M but choose a stronger geometry and lower entry engagement. Drop speed to around 300–400 SFM on first scale contact, and keep feed up enough that the edge cuts its way under the scale instead of skidding over it. If the insert squeals or the spindle load jumps, check the edge for microchipping before you blame a speed/feed chart.

Maybe counterintuitive: a sharper-looking finishing insert can fail faster than a roughing-oriented one on scaly A36. The scale acts like an abrasive. But the bigger killer is edge breakage, not edge wear.

Scenario C: Heavy roughing on a rigid HMC or VMC

A36 has no serious hardness to limit feeds. If the machine and fixture are rigid, you can take a surprisingly aggressive cut—limited more by chip evacuation and horsepower than by workpiece condition.

For that kind of production roughing, I would not try to make KC725M do everything. KC730M is the better call for heavier loads and deeper passes. It's positioned for steel milling where the edge has to take mechanical punishment. Run it with a robust geometry and a workhorse chipbreaker. Keep the cutter arbor as short as you can.

I remember a rush order where one of our engineers wanted to use the same KC725M insert as the finish station to simplify inventory. Data looked fine on paper. But after the first roughing pass, the load meter told the real story. We changed to a dedicated roughing grade and geometry, and the cycle time dropped 19%. (Note to self: never let inventory convenience override edge loading calculations.)

Scenario D: Finishing pass, thin walls, long reach, or unstable setup

This is the other corner of A36 work: maybe you're machining a fabrication pocket, a long gusset, or a thin flange. Rigidity is poor, and the finish spec matters.

Recommendation here is still a grade from the steel milling family—often KC725M—but used in a positive, light-cutting geometry. The trick is to shear rather than push. If the part deflects, go smaller radial engagement rather than trying to feed the same width at a slower speed. That seems to be the move that works on thin A36 sections.

What I wouldn't do is pick an edge designed for aluminum and use it on A36. A36's ductility will rip a fragile edge apart if the cut isn't constant.

How to decide your scenario in 30 seconds

Ask these in order:

• Is there scale or hard spots on the first surface? If yes, lean toward a tougher edge: KC730M or KC725M with a roughing geometry, and reduce speed for the first engagement.
• Is the operation a clean CNC face mill with moderate depth? Start with KC725M in a positive geometry.
• Are you taking deep, heavy cuts on a rigid machine? Use KC730M or a dedicated roughing grade, not the finishing insert you've been testing.
• Is setup rigidity poor or finish critical? Keep KC725M but select a sharp, positive chipbreaker and limit radial engagement.

This isn't a try both and see answer. It's a decision logic based on the weakest link in the cut. On clean, rigid work, that's usually chip control. On scaled plate, it's edge breakage. On unstable setups, it's deflection.

The grade alone is not the whole quality story

I don't want to be the person who reduces an application decision to a grade code. In a quality review, grade, insert geometry, cutter body, speed, feed, and whether the previous operation left scale are a system. The best Kennametal grade for milling A36 on a clean face-mill setup can be the wrong grade on the same material milled from hot-rolled plate an hour later.

If I had to put it in one short sentence: KC725M will cover more A36 applications than any single grade I know, but the moment you see scale or deep roughing, switch to a tougher setup like KC730M and adjust the edge for the real condition.