D2 vs H13 vs HSS vs Carbide: Blade Steel for Plastic Recycling

 

If you run a shredder, granulator or pelletizing line, you've probably had the same debate: "Just order D2, it's cheap and works for everything." Or the opposite: "Let's go full carbide and stop worrying about wear." Both views sound simple. Neither works well for every plastic recycling job. The wrong blade steel for plastic recycling doesn't just wear out faster-it shows up as extra fines, unstable pellet size, emergency stops and a higher cost per ton.

 

 

At SHJ KNIFE, we design & manufacturing recycling blades every day and see this pattern across many plants. Some lines overuse D2 tool steel blades and struggle on high-temperature PET or filled compounds. Others upgrade everything to carbide and then fight chipping and high tooling cost. This article pulls those lessons together into a clear framework. We'll walk through where D2 still makes the most sense, when H13 pelletizer knives or HSS granulator blades give a better return, and in which extreme cases carbide recycling blades are really worth it-so you can choose blade steel with data and process conditions in mind, not guesswork.

 

3. When D2 Still Works Best

4. When to Upgrade to H13

5. When High-Speed Lines Need HSS

6. When You Really Need Carbide

7. Blade Steel Selection by Application Scenario

8. Cost per Ton – A Simple Way to Compare Options

9. How SHJ KNIFE Supports Your Blade Steel Decisions

 

 

 

 

Every plastic recycling plant watches three numbers: throughput, quality and cost per ton. Blade steel touches all three.

If you choose a steel that wears too fast, the edge rounds early. Shredders start to tear instead of cut. Granulators produce more fines and dust. Pelletizers struggle to hold pellet length and create tails. Operators then slow the line, push more amps or stop more often for regrinds and blade changes.

 

On the other hand, if you choose an "overkill" steel everywhere, you may lock in high tooling costs without a clear gain. Some lines can hit their targets with standard D2 tool steel blades. Others really need H13, HSS or carbide only on the most critical machines. The trick is to match blade steel for plastic recycling to the real process, not to a one-size-fits-all rule.

 

 

 

 

 

Many plants start with D2 and never leave it. That choice sometimes comes from habit, but D2 does have a clear role.

 

D2 tool steel blades work well in standard PP and PE recycling. Typical jobs include bottle flakes, film offcuts, sprues and runners, and general production scrap. Shredders, granulators and some pelletizers can all run D2 in these conditions with a good balance between tool life and cost.

If your line runs moderate temperatures, modest fillers and stable loads, D2 often stays the most economical blade steel for plastic recycling. You may not gain much by jumping to HSS or carbide in these areas. Instead, you can focus on good heat treatment, correct hardness, proper sharpening and correct blade gaps.

 

 

Use D2 as your "default" when:

 

• You process clean, low- to medium-filled PP/PE.
• Machine speed is moderate.
• Blade changes do not cause major downtime.

 

When you see early wear in D2, look first at contamination, clearances and sharpening. Only then consider a jump in steel grade.

 

 

 

 

Some lines run hotter and push blades far beyond D2's comfort zone. PET and PVC are good examples. Hot die face pelletizing also punishes the cutting edge with thermal shock.

 

H13 pelletizer knives and H13 die face cutters handle these conditions better. H13 belongs to the hot-work steel family. It keeps strength and toughness at elevated temperatures and resists cracking from thermal cycling.

 

 

You should look at H13 when:

 

• You cut PET or PVC at high melt temperature.
• You run hot die face systems where the blade touches hot melt and a hot die plate.
• You see edge cracking or early failure on D2 blades near the die.

 

H13 does not always wear as slowly as D2 under pure abrasion. However, in hot and unstable temperature zones, it often survives where D2 fails. That extra robustness can save you many unplanned stops on your pelletizer head.

 

 

 

 

 

Some recycling and compounding plants push speed very hard. High shaft rpm, heavy regrind and tight schedules leave little room for frequent blade changes. In these cases, HSS granulator blades or HSS pelletizer knives often make more sense.

 

High speed steel holds its hardness at higher temperatures and under heavier cutting loads than standard tool steel. It gives you a sharp edge that stays stable for longer cycles, especially when you keep the sharpening and mounting under control.

 

 

Consider HSS if:

 

• Your granulator runs at high rpm and handles a lot of daily volume.
• Your strand pelletizer runs fast and you want to stretch the time between knife changes.
• You see that D2 blades dull too quickly even with clean material.

 

HSS costs more than D2, but you can justify it when each blade change stops a key line or when labor and downtime dominate your total cost.

 

 

 

 

 

Carbide recycling blades sit at the extreme end of the spectrum. They deliver the highest wear resistance but do not like shock or abuse. You reach for carbide when the material attacks every other steel. These cases often include:

 

sources from：https://wihometals.com/tungsten-carbide-steel-vs-carbon-tool-steel/

 

• Glass-fiber reinforced compounds (GF PP, GF PA, etc.).
• High mineral loading (CaCO₃, talc and similar).
• High recycled content with unknown hard contaminants.

 

In these jobs, carbide pelletizer knives or carbide-tipped granulator blades can hold edge shape for long campaigns. You gain fewer blade changes, more stable product and a clearer cost per ton.

However, carbide does not forgive misuse. Incorrect mounting, very hard impact or tramp metal can chip the edge. You also need more care during sharpening and handling.Carbide makes sense when:

 

• You already tried D2, H13 or HSS and still see very short blade life.
• Your process runs valuable, abrasive compounds with strict quality demands.
• You can support careful handling and controlled process conditions.

 

Use carbide as a targeted upgrade for difficult machines, not a blanket solution across the whole plant.

 

 

 

 

 

 

A simple way to decide on blade steel for plastic recycling is to look at the process step and the material together. Here is a practical view.

 

1. Plastic Recycling + Pelletizing Lines

 

Typical flow: shredder → granulator → extruder → pelletizer.

 

✳Shredder Blades

• Many lines use D2 or other alloy steels.
• If you process mostly light plastics and packaging, D2 often works.
• If you crush thicker parts or mixed materials, consider tougher alloys rather than higher hardness.

 

✳Granulator blades / crusher knives

• Start with D2 for standard bottle, film and regrind jobs.
• Move to HSS granulator blades if speed and throughput are very high and wear still dominates your cost.

 

✳Pelletizer knives / Die Face Cutters

• Use D2 for standard PP/PE pellets at moderate temperature.
• Switch to H13 pelletizer knives for PET, PVC and hot die face systems.

 

2. Engineering Plastics and Compounds

 

Compounding plants handle PA, PBT, POM and many specialty materials. Filler content and glass fiber percentages often run high.

 

✳Granulators

• HSS granulator blades often offer the best balance between wear and toughness.
• For very abrasive compounds, consider carbide-tipped designs.

 

✳Pelletizers

• Use H13 near hot dies or where melt temperature fluctuates.
• Consider carbide edges for the most abrasive, glass-filled compounds.

 

3. High Recycled Content and High Fillers

 

Recycling plants that re-pelletize high recycled content or high fillers see a lot of variability. Contamination and wear can both rise.

• Use D2 or HSS for most shredding and grinding.
• Upgrade critical pelletizers or high-load granulators to carbide recycling blades where tests show a clear gain in tool life.

 

A short trial on one machine often reveals if a higher steel grade really reduces total cost, or only moves cost from downtime into tooling.

 

 

 

 

The best blade steel for plastic recycling is not always the one with the longest life or the lowest price per blade. It is the one that brings down total cost per ton over time.

You can think in three parts:

 

1. Blade cost

• Purchase price of D2, H13, HSS or carbide blades.

 

2. Changeover and sharpening cost

• Labor time, machine downtime, setup and adjustments.

 

3. Process impact

• Lost throughput when blades dull.
• Off-spec product, extra fines and rework.

 

For some lines, D2 wins because blades cost less and changes do not hurt much. For other lines, HSS or carbide wins because each stop costs more than the premium steel.

 

A simple exercise can help:

 

• Track current blade life and changeover time on one machine.
• Estimate cost per hour of downtime.
• Test a higher-grade blade and log the same numbers.

 

With that data, you can compare real cost per ton instead of judging by blade price alone.

 

 

 

 

Blade steel choice does not need to stay a guessing game. You can treat it as an engineering decision.

 

SHJ KNIFE supplies plastic recycling machine blades across all three key process steps: shredder, granulator and pelletizer. Our team works with D2 tool steel blades, H13 pelletizer knives, HSS granulator blades and carbide recycling blades on a daily basis. We see how each grade behaves with different polymers, fillers and line layouts.When you share your material list, current blade life and basic machine data, we can:

 

• Suggest a realistic starting grade for your shredders, granulators and pelletizers.
• Help you build a simple standard for blade steel by application, not just by machine brand.
• Design blades that match your geometry, including OEM-compatible dimensions for many common recycling and pelletizing lines.

 

If you want to review your current blade setup, start with one machine or one process step. Look at real data, compare D2, H13, HSS and carbide in that context, and then roll the result across the rest of the plant. With the right blade steel for plastic recycling, your line can run cleaner, longer and with a more predictable cost per ton.