How to Tell If Your H13 Steel Is Really ESR

A customer running an aluminum extrusion plant in Brazil recently ran into a problem that shows up more often than most buyers realize. He purchased what was labeled as ESR H13 tool steel from a supplier, put it into production, and found that the dies performed almost the same as ordinary non-ESR H13. Service life, wear resistance, and toughness all landed in the same range he had seen from conventional material before. He suspected the steel was never electroslag remelted at all. Still, he had no way to prove it, and a supplier will rarely admit to mislabeling material without hard evidence in front of them.

This situation is common in the tool steel trade because ESR adds real cost to production, and the temptation to sell conventional steel under an ESR label is strong when buyers cannot verify the claim themselves. The good news is that ESR leaves physical evidence in the steel that cannot be faked. Once you know what to look for, distinguishing genuine ESR H13 from conventional H13 becomes a matter of testing rather than trust.

Why ESR Should Perform Differently in the First Place

Electroslag remelting is a secondary refining process. A consumable electrode is melted through a reactive liquid slag, and the resulting steel solidifies progressively from the bottom of the mold upward. This directional solidification is what gives ESR steel its advantages over conventional air-melted or electric furnace steel. If a batch of H13 labeled as ESR shows no improvement in die life or toughness compared to standard H13, the most likely explanation is that the material never went through the ESR process, or went through a poor quality version of it that failed to deliver the expected refinement.

What to Check in the Macrostructure

Genuine ESR ingots solidify without the central shrinkage cavities and porosity that commonly appear in conventional ingots. A hot acid deep etch test on a cross section will expose this difference clearly. Conventional single-melt steel typically reveals centerline inclusions, check marks, and porosity under this test, while authentic ESR material shows a dense, uniform surface free of these defects. ESR steel is also free of the macrosegregation that shows up in conventional ingots, where carbon and alloy content can vary noticeably from the center of the cross section to the edge. In true ESR H13, this kind of segregation is virtually absent.

What to Check in the Microstructure

The faster and more uniform solidification of ESR produces a finer grain structure and tighter secondary dendrite arm spacing. In H13 specifically, interdendritic spacing at the center of a conventional ingot typically falls in the 700 to 800 micrometer range. In comparison, a properly processed ESR ingot brings this down to somewhere in the 450 to 500 micrometer range. Exact figures shift with ingot diameter and sampling location, so these numbers are a useful reference range rather than a fixed pass or fail line. Carbide banding is another marker. ESR steel shows much less banding, along with smaller and more evenly distributed eutectic carbides. This finer, more uniform carbide structure is a large part of why ESR H13 responds better to tratamento térmico and holds up better under repeated thermal cycling in extrusion dies.

What to Check in Cleanliness

ESR slag filters out oxide inclusions, silicates, and sulfides as molten metal droplets pass through it during remelting. A microscopic cleanliness rating under ASTM E-45 will often place standard electric furnace steel in the 2.0 to 2.5 range for thick sulfide and silicate inclusions. In contrast, genuine ESR steel commonly comes in at 1.0 or lower, often showing no thick inclusions at all. These ranges shift depending on the starting cleanliness of the electrode. Whether secondary refining such as ladle furnace or vacuum degassing was applied before ESR, so they should be read as typical ranges rather than fixed thresholds. Sulfur content tells a similar story. ESR generally cuts sulfur levels by 50 to 70 percent compared to the starting material, and well-controlled slag chemistry can bring it down toward 0.002 percent. However, the exact reduction depends on electrode sulfur content and slag design. A mill certificate showing sulfur content in line with ordinary H13 is still a strong signal that the ESR claim does not hold up.

What to Check in Mechanical Behavior

Because ESR removes macrosegregation and aligns the internal structure, the resulting steel is close to isotropic, meaning properties measured across the material are nearly the same as properties measured along its length. In conventional steel, transverse ductility and toughness usually fall well short of longitudinal values. Properly produced ESR H13 commonly reaches a transverse-to-longitudinal tensile strength and elongation ratio in the range of 0.90 or higher, with an impact toughness ratio often above 0.78. However, the exact figures move with forging ratio and heat treatment condition. Fatigue testing reinforces this pattern. Genuine ESR steel consistently endures more stress cycles before failure than air-melted steel of the same grade, which directly explains why real ESR H13 dies should outlast conventional ones in extrusion service.

What to Check on the Ingot Surface

If you have access to the ingot before it is forged or rolled, surface condition is one of the easiest checks available. The water-cooled mold used in ESR freezes a thin layer of solid slag between the mold wall and the solidifying steel, which leaves the ingot with a clean, smooth surface that needs no grinding before hot working. Conventional ingots almost always require surface conditioning first—a rough, unrefined surface on material sold as ESR is worth questioning.

Turning Suspicion Into Evidence

For a buyer who already suspects a batch was mislabeled, the practical path forward is to request a hot acid etch photo, an ASTM E-45 cleanliness report, and a sulfur content figure from the mill certificate, then compare those numbers against the expected ESR ranges above. Any one of these checks on its own is useful. Together, they turn a suspicion based on die performance into a documented case that a supplier cannot easily argue against.

This is also why traceability matters as much as the ESR claim itself. At Aobo Steel, every batch we source as ESR H13 is fully traceable back to the mill that produced it, and comes with mill test reports covering sulfur content and inclusion ratings rather than a label alone. Genuine ESR refining adds real cost at the mill level, which is reflected in price. Our ESR H13 typically runs 300 to 350 US dollars per ton above non-ESR H13, and that price gap is one more piece of evidence buyers can use. Material priced the same as conventional H13 but sold as ESR is unlikely to have actually gone through the process, since no mill absorbs that extra refining cost for free.

For extrusion die buyers who have been burned by underperforming material before, this combination of documentation and honest pricing is often the difference between guessing and knowing what you are actually putting into your dies.