Impact crusher blow bars — the wear plates mounted on the rotor that hurl feed rock against the impact plates at 25–40 m/s — are the highest-wear components in an impact crusher. Traditional high-manganese steel blow bars (cast hardness only HB 179–219) depend on strong impact to work-harden, and in medium-to-low impact duty they wear fast and require frequent stoppages for changeout. High-chromium white cast iron blow bars (KmTBCr15/Cr20/Cr26) deliver HRC 58–65 as a factory final hardness — no work-hardening required — cutting wear to 60–70% of manganese steel and reducing total operating cost by approximately 30%. This guide covers the five blow-bar material grades, their hardness, toughness and selection criteria, as part of our broader mining, crushing and aggregate processing wear-parts program.
What Are Impact Crusher Blow Bars and Why Material Matters
Blow bars are the wear elements bolted to the rotor of an impact crusher (PF series). Feed material is accelerated by the rotor and flung against the blow-bar surface, then thrown against the impact plates for secondary breakage. The blow bar face simultaneously absorbs high-velocity impact (25–40 m/s typical) and abrasive sliding wear from hard rock. The material challenge is the hardness-toughness trade-off: high-chromium cast iron delivers HRC 58–65 hardness and superior wear resistance but has low impact toughness (ak 5–8 J/cm² for Cr26); martensitic alloy steel provides higher toughness (ak ≥ 15 J/cm²) at moderate hardness (HRC 48–55). No single grade is optimal for all feed materials and impact conditions — the selection must match the grade’s hardness-toughness balance to the specific duty.
Blow Bar Material Grades at a Glance
| Grade | Hardness | Impact toughness (ak) | Key property | Typical duty |
|---|---|---|---|---|
| KmTBCr15 (Cr 14–18%) | HRC 58–65 | 5–8 J/cm² | Wear + toughness balance, economical | Limestone, medium-hard feed |
| KmTBCr20 (Cr 18–23%) | HRC 58–65 | 5–8 J/cm² | Higher wear resistance | Granite, iron ore, high abrasion |
| KmTBCr26 (Cr 23–28%) | HRC 60+ | 5–8 J/cm² | Maximum wear resistance | Extreme abrasion duty |
| Martensitic alloy steel | HRC 48–55 | ≥ 15 J/cm² | High impact toughness | High impact, large feed |
| Composite casting | HRC 58–65 (face) | Steel-back toughness | Wear face + crack-resistant back | Extreme impact + wear |
Density: 7.2–7.5 g/cm³ (high-chromium iron); 7.8 g/cm³ (martensitic alloy steel). Core chemistry: C 2.0–3.0%, Cr 14–28% depending on grade. Compatible with PF-1010, PF-1210, PF-1315, PF-1520 and other impact crusher series. Blow-bar weight typically 15–220 kg depending on machine size.
KmTBCr15: The Limestone-Duty Economical Grade
KmTBCr15 (Cr 14–18%) is the economical high-chromium iron grade for blow bars processing limestone and other medium-hardness materials. After quench-and-temper heat treatment it reaches HRC 58–65 — a final hardness available from the first hour of service, with no dependence on impact work-hardening. Compared with traditional high-manganese steel blow bars (cast HB 179–219), KmTBCr15’s final hardness is over three times higher, and in medium-to-low impact limestone duty its wear rate is only 60–70% of manganese steel’s. For limestone aggregate and manufactured-sand production, Cr15 delivers the best balance of wear resistance, adequate toughness and cost. For harder feed, higher-chromium grades are required.
KmTBCr20: The Hard-Rock Balance Grade
KmTBCr20 (Cr 18–23%) is the grade for granite, iron ore and other high-abrasion feed where Cr15’s wear resistance is insufficient. The higher chromium content increases the volume fraction of hard M₇C₃ carbides in the matrix, raising wear resistance while maintaining HRC 58–65 hardness. The grade occupies the middle position in the KmTB series: more wear-resistant than Cr15, less costly than Cr26. It is the default choice for impact crushers processing mixed hard rock in aggregate and mining duty, where the feed hardness and abrasiveness demand more than the economical Cr15 grade but do not justify the premium Cr26.
KmTBCr26: Maximum Wear Resistance
KmTBCr26 (Cr 23–28%) is the top wear-resistance grade in the KmTB series, reaching HRC 60+ after heat treatment. It is specified for extreme-abrasion duty — impact crushers handling highly abrasive feed where wear life is the dominant cost driver. The high chromium content maximizes M₇C₃ carbide volume and hardness, giving the longest possible wear life in sliding-plus-impact abrasion conditions. Its limitation remains toughness: impact toughness is 5–8 J/cm² (industry typical), so it is not suited to high-impact, large-feed conditions where blow-bar fracture is a risk. For those conditions, martensitic alloy steel or composite casting is required.
Martensitic Alloy Steel: High-Impact Toughness Grade
Martensitic alloy steel blow bars (tempered condition HRC 48–55) are specified when impact toughness is the priority — high-impact duty with large, blocky feed where a high-chromium iron bar would risk fracture. With impact toughness ak ≥ 15 J/cm² (roughly double that of Cr26 iron), the martensitic steel bar absorbs heavy impacts without cracking. The trade-off is hardness: HRC 48–55 is lower than the HRC 58–65 of high-chromium iron, so wear rate is higher in sliding-abrasion duty. The grade is the correct choice when the dominant failure mode is impact fracture, not gradual wear — oversized feed, tramp metal, or very hard blocky rock that would shatter a brittle high-chromium bar.
Composite Casting: Wear Face Plus Crack-Resistant Back
Composite-casting blow bars solve the hardness-toughness trade-off by combining two materials in one component: a high-chromium iron working face (HRC 58–65) for wear resistance, metallurgically bonded to a low-alloy steel back for toughness and crack resistance. The working face delivers the same wear life as a solid high-chromium iron bar; the steel back absorbs impact that would fracture a through-hard iron bar. This is the grade for extreme combined impact-and-wear conditions — large, hard, abrasive feed where neither a solid iron bar (fracture risk) nor a solid steel bar (wear too fast) is adequate. Composite bars must be custom-manufactured to the specific duty.
Selection Summary by Application
- Limestone / medium-hard feed (low-medium impact): KmTBCr15 — economical, HRC 58–65, wear rate 60–70% of Mn steel.
- Granite / iron ore (high abrasion): KmTBCr20 — balanced wear resistance and toughness.
- Extreme abrasion (maximum wear life): KmTBCr26 — HRC 60+, longest wear life in abrasive duty.
- High impact + large blocky feed: Martensitic alloy steel — ak ≥ 15 J/cm², resists fracture.
- Extreme impact + extreme wear (combined): Composite casting — hi-Cr face for wear, steel back for toughness.
- Manufactured sand / aggregate (limestone): KmTBCr15 — best cost-to-life ratio in medium-duty.
Heat Treatment and Quality Control
Blow bars are produced by lost-foam casting (for larger pieces) or coated-sand precision casting (for medium and small pieces), with a pouring temperature of 1380–1420°C. The pre-pour double rule — furnace-front temperature measurement plus sample-block chemistry check — ensures chemical composition meets specification before pouring. Heat treatment is a quench-and-temper dual process: quenching transforms the carbide morphology from the network M₃C type to the isolated M₇C₃ type (the target microstructure for wear resistance), and tempering eliminates internal stress to preserve toughness. Different grades use different parameters — Cr15 and Cr20 emphasize toughness balance; Cr26 emphasizes hardness maximization. Martensitic alloy steel bars use dedicated quench-and-temper parameters to achieve HRC 48–55 with high impact toughness.
Quality control includes 100% hardness inspection on every bar (3 points per piece, averaged; HRC 58–65 as the pass threshold for high-chromium iron); metallographic analysis confirming M₇C₃ carbide morphology; dimensional tolerance verification — all fully traceable.
Why Huasuma for Impact Crusher Blow Bars
Huasuma’s metal casting capability offers five blow-bar materials — KmTBCr15, KmTBCr20, KmTBCr26, martensitic alloy steel and composite casting — each with independent quench-and-temper parameters. Limestone duty uses Cr15 for economy; granite duty uses Cr26 for wear life; large blocky iron ore uses martensitic steel to prevent fracture; extreme combined duty uses composite casting. Not one alloy for all duties. The quenching process transforms carbide morphology from network M₃C to isolated M₇C₃ type — verified by metallographic analysis on every piece. Pre-pour double rule (furnace-front temperature + sample-block chemistry); 100% hardness inspection (3 points averaged, HRC 58–65 threshold); metallographic analysis; dimensional tolerance verification — all completed before shipment. Composite-casting technology (hi-Cr iron working face + low-alloy steel back) is available for extreme combined impact-and-wear duty. Compatible with PF-1010, PF-1210, PF-1315 and PF-1520 impact crushers; bars can be custom-manufactured to length, thickness and mounting-hole pattern. ISO 9001 throughout; GOST compliance supported; 30 years of high-chromium iron wear-part manufacturing experience with annual capacity exceeding 10,000 tonnes and multiple batches delivered to Russian, Indian and Australian customers; 24-hour quote response; samples available for in-service validation before bulk orders.
FAQ
What is the best blow bar material for limestone crushing?
For limestone and medium-hardness feed in an impact crusher, KmTBCr15 (Cr 14–18%) is the optimum grade — HRC 58–65 final hardness with no work-hardening dependence, and wear rate only 60–70% of high-manganese steel. It delivers the best cost-to-life ratio in medium-duty limestone aggregate and manufactured-sand production.
High-chromium iron vs manganese steel blow bars — what is the difference?
High-chromium iron blow bars (HRC 58–65) achieve full hardness at the factory and do not require impact to work-harden, so they deliver consistent wear resistance in medium-to-low impact duty. Manganese steel blow bars (cast HB 179–219) require strong impact to work-harden; in low-impact limestone duty they never reach effective hardness and wear 30–40% faster. In the same duty, high-chromium iron’s comprehensive cost (replacement frequency + downtime) is approximately 30% lower.
When should I use martensitic alloy steel blow bars?
Use martensitic alloy steel (HRC 48–55, ak ≥ 15 J/cm²) when the dominant failure mode is impact fracture, not gradual wear — high-impact duty with large, blocky or hard feed, or risk of tramp metal, where a high-chromium iron bar (ak 5–8 J/cm²) would shatter. The lower hardness is the trade-off for fracture resistance.
What is a composite-casting blow bar?
A composite-casting blow bar combines a high-chromium iron working face (HRC 58–65) with a low-alloy steel back, metallurgically bonded. The face delivers the wear life of solid high-chromium iron; the steel back absorbs impact that would fracture a through-hard iron bar. It is used for extreme combined impact-and-wear conditions where neither a solid iron nor a solid steel bar is adequate.
Huasuma is a Chinese manufacturer of impact crusher blow bars in KmTBCr15/Cr20/Cr26 high-chromium white cast iron, martensitic alloy steel and composite casting for PF-series impact crushers. Blow bars supplied worldwide with GOST compliance and ISO 9001 certification. Request a quote or sample.
