NM550 & NM600 Wear-Resistant Steel Plate

Product Overview

NM550 and NM600 are the top two grades of the Chinese quenched and tempered wear plate series, produced to GB/T 24186-2022 and supplied at 520 – 580 HBW and 570 – 640 HBW respectively. They are handled on one page because they are chosen for the same reason and carry the same constraints: they are the grades you specify when a liner is still wearing out too fast at a lower hardness and the cost of changing it is high.

These are thin-section grades. Maximum supply thickness is 80 mm for NM550 and 50 mm for NM600, against 150 mm for NM400. That is a consequence of how far the hardness can be pushed through the section before the core properties fall away, and it means neither grade should be specified for heavy structural liner work above those thicknesses.

Applied in the right place, the payoff is measurable. The mill quotes NM600 at a tensile strength above 1,800 MPa, hardness from HBW 570, low-temperature impact of ≥ 20 J at −40 °C, and a 6t → 90° cold bending capability — so it tolerates impact as well as abrasion, which is what separates a wear plate from a hard but brittle one.

Expect to pay for that in fabrication. Both grades need a preheat of 150 – 180 °C for flame cutting from 20 mm, both need preheat for welding below 40 mm, and both cut, drill and mill at the lowest speeds in the series. Neither should be selected on hardness alone if the part is complex to make.

How we supply it differently: plate is sourced from first-tier Chinese mills, and can leave China cut and nested to your drawing, edge-milled, rolled or drilled, and shot blasted to Sa 2.5 with a weldable shop primer. On the two grades where a careless flame cut is most likely to leave a crack in a wear-critical edge, having cutting, edge milling and heat control done in one controlled sequence is the part of the supply that protects the part you are buying.

Mechanical Properties & Hardness

Figures are the mill’s guaranteed values for NM550E. Tensile strength, elongation and impact energy are performance requirements: where they are not specified in the contract, only Brinell hardness is guaranteed, so state them on the order if your incoming inspection is going to test for them.

Chemical Composition (Ladle Analysis, % Max)

The low phosphorus and sulphur ceilings are the point of the grade: the mill’s clean-steel practice holds P at or below 40 ppm, S at or below 10 ppm and H at or below 1.2 ppm in production, which is what keeps the cold-cracking sensitivity and the brittle-to-ductile transition temperature down.

Carbon Equivalent & Weldability

CEQ = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15. These are the mill ceilings for grades ordered to a high-weldability requirement; the actual figure for your heat is on the mill certificate.

Supply Range

Tighter widths and shorter lengths are available as cut-to-size or as nested parts to drawing. Longer plate than 24,000 mm is not rolled in this series.

Typical Applications

• Hard-rock crusher liners — Wear surfaces where a 500 HBW liner is still replaced too often.
• Chute, hopper and bin liners — High-tonnage transfer points in mining, quarrying and sinter plants.
• Grizzly bars, screen decks and wear strips — Thin sections carrying continuous coarse abrasion.
• Excavator and loader wear plate — Bottom and side wear protection on high-hour machines.
• Where replacement is expensive — Components whose change-out cost, not material cost, drives the specification — the case these grades exist for.

Choose NM550 where you need a step beyond NM500 but still want 80 mm of section available; choose NM600 for the thinnest, hardest liner in the most aggressive duty, where impact is present as well as abrasion.

If the part is complex to fabricate, or thicker than 50 mm is needed, reconsider NM450 or NM500 — in those cases the extra hardness is usually bought with fabrication risk rather than with wear life.

Fabrication: Cutting & Forming

Cutting methods compared

Laser gives the tightest tolerance but the narrowest thickness window; oxy-fuel takes the widest range of thickness at the loosest tolerance; plasma sits between them. Water jet is the only method that introduces no heat at all.

Maximum flame cutting speed

Maximum recommended flame cutting speed in mm/min. The mill datasheet lists a ceiling only from the thickness at which preheat control becomes necessary; thinner plate is cut at higher speed.

Preheat before cutting

Preheat by flame or electric mat, and heat the cut line uniformly — local overheating is as damaging as no preheat at all. As a general rule, when the shop temperature is below 5 °C and the plate is over 20 mm, preheat before cutting regardless of grade.

• Cut clean. Mill scale, rust and oil all degrade cut quality. Clean the cut line on both faces before cutting, and clear the cutting area top and bottom.
• Tune the process, do not just run it. Nozzle size, gas pressure, cutting method and speed have to be set to the grade and thickness in front of you. Hot cutting — flame, plasma or laser — is the correct method for these grades when it is set up properly.
• Watch narrow cut-offs. Where the part being cut off is narrower than about 200 mm, the cutting heat can soften it through its width. Where that matters, use underwater plasma arc cutting, underwater laser cutting or water jet cutting — the water jet is a cold cut with no heat-affected zone and no local softening at all.
• Shearing. Plate below about 10 mm can be sheared. As the grade gets harder, shear stress and tool wear rise, so blade clearance has to be increased and the blade kept hard, sharp and slightly radiused at the corners.
• Slow cooling helps. Where cutting cracks are a concern, keeping the still-warm cut parts together and covering them so they cool slowly reduces the risk.

Fabrication: Drilling, Milling & Boring

The mill does not tabulate separate drilling data for NM550 and NM600. Start from the NM500 figures and reduce, and expect to use solid or replaceable carbide tooling with rigid clamping and a steady 8 – 10 % emulsion supply.

• Milling. Face milling at %s with a hard-coated carbide blade and 0.10 – 0.12 mm per tooth. Use climb milling: it makes thinner chips, puts a small tensile stress on the tool, and the downward cutting force presses the plate onto the table, so the cut is stable and tool wear is low.
• Threads. %s
• Boring. Rough bore first, then finish bore, with a hard-coated carbide blade at about 120 m/min and 0.08 mm per revolution.
• Tool life. Machining data published for wear-resistant plate assumes rigid clamping and a continuous coolant supply. If you get vibration, reduce overhang and cutting speed before you change the tool.

Welding

Minimum preheating temperature, gas-shielded welding, in °C. Preheat depends strongly on thickness, so the table is a floor, not a target.

• Groove preparation. Prepare grooves mechanically wherever possible. Where flame cutting is used, leave machining allowance and then remove the heat-affected zone and oxides by milling, planing or grinding. Narrow grooves — I type, narrow V or U — reduce filler metal and heat input; a groove angle of 30° to 50° is suggested.
• Cleanliness. Clean the groove edges and at least 50 mm either side, and grind out moisture, oil, grease and other contamination. Use a stainless steel brush or a grinding wheel.
• Dry the consumables. Stick electrodes must be dried at 300 – 350 °C for two hours before use; welding flux at 200 – 300 °C for one hour.
• Preheat properly. Whole-plate heating gives better results than local heating. Where local heating is used, the groove and the material 100 mm either side of it must all reach the specified temperature. Electric heating mats or flame heating are both acceptable.
• Why it matters. These grades have a relatively high carbon equivalent, are sensitive to hydrogen, and are prone to cold cracking and to heat-affected-zone softening. Correct preheat, correct consumables and a controlled heat input are what prevent both.

Grade Comparison: NM360 – NM600

The harder the grade, the better the resistance to sliding abrasion — and the harder it is to cut, form, drill and weld. The hardest plate is not automatically the cheapest answer: price the whole cycle, including the fabrication step, before you specify.

International Equivalent Grades

Cross-references are indicative only. They are based on nominal hardness and delivery condition, they are not a statement of equivalence, and grades are not interchangeable between makers — always confirm the actual data sheet for the plate you are offered, including the CEQ and the impact temperature.

Processing & Delivery Services

Tell us the application and the drawing rather than just the grade, and we will quote the plate together with the cutting, forming, machining and surface preparation that gets it to your site ready to fit.

Ordering & Documentation

To quote accurately we need: grade, thickness × width × length (or a nesting drawing), quantity, hardness acceptance range if you are sampling, edge condition (sheared, flame cut or machined), surface condition (bare, blasted, or blasted and primed), destination port and required delivery date.

Every shipment is supplied with a mill test certificate traceable to heat number and plate identification. Where the contract does not specify tensile strength, elongation or impact energy, the mill guarantees Brinell hardness only — so if those properties matter for your acceptance, state them on the order.

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