Hardox Steel: Properties and Key Applications

Hardox Steel is a brand of wear-resistant steel produced by SSAB, known for its exceptional hardness and toughness. It is classified as a high-strength, low-alloy steel, primarily designed for applications requiring high wear resistance. The primary alloying elements in Hardox Steel include carbon (C), manganese (Mn), and boron (B), which significantly influence its mechanical properties and performance.

Comprehensive Overview

Hardox Steel is engineered to withstand extreme wear and impact, making it a preferred choice in industries such as mining, construction, and recycling. Its unique composition allows it to achieve a hardness level ranging from 450 to 700 HBW (Brinell Hardness), depending on the specific grade. The steel's microstructure is optimized for high toughness and ductility, ensuring that it can absorb energy without fracturing.

Advantages of Hardox Steel:
- High Wear Resistance: Its hardness allows it to resist abrasion and wear, extending the lifespan of components.
- Excellent Toughness: Despite its hardness, Hardox maintains good toughness, making it suitable for high-impact applications.
- Versatility: Available in various grades and thicknesses, it can be tailored to specific applications.
- Reduced Weight: Its strength-to-weight ratio allows for lighter designs without compromising performance.

Limitations of Hardox Steel:
- Cost: Higher initial material costs compared to standard steels may deter some applications.
- Weldability: While it can be welded, special considerations and filler materials are required to maintain its properties.
- Brittleness at Low Temperatures: Hardox may exhibit reduced toughness at very low temperatures, limiting its use in certain environments.

Historically, Hardox has established itself as a leader in wear-resistant steel, with a strong market presence and a reputation for quality and reliability.

Alternative Names, Standards, and Equivalents

Standard Organization	Designation/Grade	Country/Region of Origin	Notes/Remarks
UNS	S690QL	USA	Closest equivalent for high-strength applications
ASTM	A514	USA	Minor compositional differences; used in structural applications
EN	10025 S690QL	Europe	Similar properties, but may differ in toughness requirements
JIS	G3106 SM490	Japan	Comparable in strength but not specifically wear-resistant
ISO	6300	International	General classification for high-strength steels

The notes in the table highlight that while these grades may serve similar purposes, the specific wear resistance and toughness characteristics of Hardox Steel make it a superior choice for applications where these properties are critical.

Key Properties

Chemical Composition

Element (Symbol and Name)	Percentage Range (%)
C (Carbon)	0.10 - 0.30
Mn (Manganese)	0.60 - 1.60
B (Boron)	0.001 - 0.005
Si (Silicon)	0.10 - 0.50
P (Phosphorus)	≤ 0.025
S (Sulfur)	≤ 0.010

The primary alloying elements in Hardox Steel play crucial roles:
- Carbon (C): Increases hardness and strength through solid solution strengthening.
- Manganese (Mn): Enhances hardenability and toughness, contributing to the steel's overall performance.
- Boron (B): Improves hardenability and allows for finer microstructures, which enhance wear resistance.

Mechanical Properties

Property	Condition/Temper	Typical Value/Range (Metric - SI Units)	Typical Value/Range (Imperial Units)	Reference Standard for Test Method
Tensile Strength	Quenched & Tempered	1300 - 1600 MPa	188.5 - 232.0 ksi	ASTM E8
Yield Strength (0.2% offset)	Quenched & Tempered	1100 - 1400 MPa	159.5 - 203.0 ksi	ASTM E8
Elongation	Quenched & Tempered	10 - 12%	10 - 12%	ASTM E8
Hardness (HBW)	Quenched & Tempered	450 - 700 HBW	450 - 700 HBW	ASTM E10
Impact Strength	-	27 J at -40°C	20 ft-lbf at -40°F	ASTM E23

The combination of high tensile and yield strength, along with significant hardness, makes Hardox Steel suitable for applications involving heavy mechanical loading and structural integrity requirements. Its ability to maintain these properties under various conditions is critical for industries that rely on durability and performance.

Physical Properties

Property	Condition/Temperature	Value (Metric - SI Units)	Value (Imperial Units)
Density	-	7850 kg/m³	490 lb/ft³
Melting Point	-	1450 - 1520 °C	2642 - 2768 °F
Thermal Conductivity	20 °C	50 W/m·K	34.5 BTU·in/(hr·ft²·°F)
Specific Heat Capacity	-	0.46 kJ/kg·K	0.11 BTU/lb·°F
Electrical Resistivity	-	0.0000017 Ω·m	0.0000017 Ω·ft

Key physical properties such as density and thermal conductivity are significant for applications where weight and heat dissipation are critical. The density of Hardox Steel allows for strong yet lightweight designs, while its thermal conductivity ensures effective heat management in high-temperature applications.

Corrosion Resistance

Corrosive Agent	Concentration (%)	Temperature (°C/°F)	Resistance Rating	Notes
Chlorides	3-5	20-60 °C (68-140 °F)	Fair	Risk of pitting corrosion
Sulfuric Acid	10-20	20-40 °C (68-104 °F)	Poor	Not recommended
Sea Water	-	Ambient	Good	Requires protective coatings
Alkaline Solutions	-	Ambient	Fair	Risk of stress corrosion cracking

Hardox Steel exhibits varying resistance to different corrosive agents. While it performs well in sea water and mild alkaline environments, it is susceptible to pitting in chloride-rich conditions and should not be used in strong acids. Compared to other steel grades like stainless steel, Hardox's corrosion resistance is limited, making it essential to consider protective coatings or alternative materials in highly corrosive environments.

Heat Resistance

Property/Limit	Temperature (°C)	Temperature (°F)	Remarks
Max Continuous Service Temp	400 °C	752 °F	Beyond this, properties may degrade
Max Intermittent Service Temp	500 °C	932 °F	Short-term exposure only
Scaling Temperature	600 °C	1112 °F	Risk of oxidation above this temp
Creep Strength considerations	400 °C	752 °F	Begins to affect performance

At elevated temperatures, Hardox Steel maintains its strength and hardness up to a certain limit, beyond which oxidation and scaling can occur. This makes it suitable for applications involving heat, but care must be taken to avoid prolonged exposure to extreme temperatures.

Fabrication Properties

Weldability

Welding Process	Recommended Filler Metal (AWS Classification)	Typical Shielding Gas/Flux	Notes
MIG	ER70S-6	Argon + CO2 mix	Preheat recommended
TIG	ER70S-2	Pure Argon	Requires careful control
Stick	E7018	-	Post-weld heat treatment needed

Hardox Steel can be welded using various processes, but it requires specific filler materials to maintain its properties. Preheating is often recommended to prevent cracking, and post-weld heat treatment may be necessary to relieve stresses.

Machinability

Machining Parameter	Hardox Steel	AISI 1212	Notes/Tips
Relative Machinability Index	30%	100%	Harder to machine than AISI 1212
Typical Cutting Speed (Turning)	30 m/min	60 m/min	Use carbide tools for best results

Machining Hardox Steel can be challenging due to its hardness. Optimal conditions include using carbide tools and adjusting cutting speeds to avoid excessive wear on the tooling.

Formability

Hardox Steel is not as formable as lower-strength steels due to its high hardness. Cold forming is possible but may require specialized equipment and techniques to avoid cracking. Hot forming can be more effective, allowing for more complex shapes.

Heat Treatment

Treatment Process	Temperature Range (°C/°F)	Typical Soaking Time	Cooling Method	Primary Purpose / Expected Result
Quenching	800 - 900 °C / 1472 - 1652 °F	30 minutes	Air or Oil	Increased hardness and strength
Tempering	400 - 600 °C / 752 - 1112 °F	1 hour	Air	Improved toughness and ductility

Heat treatment processes such as quenching and tempering are critical for achieving the desired hardness and toughness in Hardox Steel. The metallurgical transformations during these treatments enhance the microstructure, resulting in improved mechanical properties.

Typical Applications and End Uses

Industry/Sector	Specific Application Example	Key Steel Properties Utilized in this Application	Reason for Selection (Brief)
Mining	Excavator buckets	High wear resistance, toughness	To withstand abrasive materials
Construction	Dump trucks	High strength, impact resistance	For heavy loads and durability
Recycling	Shredders	Abrasion resistance, toughness	To handle tough materials
Agriculture	Plowshares	Wear resistance, ductility	For extended service life

Other applications include:
- Material handling equipment (e.g., conveyor systems)
- Heavy machinery (e.g., bulldozers, loaders)
- Structural components in high-wear environments

Hardox Steel is chosen for these applications due to its ability to withstand harsh conditions, reducing downtime and maintenance costs.

Important Considerations, Selection Criteria, and Further Insights

Feature/Property	Hardox Steel	A514 Steel	S690QL Steel	Brief Pro/Con or Trade-off Note
Key Mechanical Property	High hardness	High strength	High toughness	Hardox excels in wear resistance
Key Corrosion Aspect	Fair resistance	Moderate resistance	Good resistance	Hardox needs protective coatings
Weldability	Moderate	Good	Fair	Special filler required for Hardox
Machinability	Challenging	Moderate	Good	Hardox requires carbide tooling
Formability	Limited	Good	Good	Hardox is less formable
Approx. Relative Cost	Higher	Moderate	Moderate	Cost may be justified by performance
Typical Availability	Widely available	Common	Common	Hardox is a well-established brand

When selecting Hardox Steel, considerations include its cost-effectiveness, availability, and specific performance requirements. While it may be more expensive than standard steels, its durability and reduced maintenance needs can lead to long-term savings. Additionally, its magnetic properties are minimal, making it suitable for applications where magnetic interference is a concern.

In summary, Hardox Steel stands out as a premier choice for applications demanding high wear resistance and toughness. Its unique properties, combined with careful consideration of fabrication and performance factors, make it a valuable material in various industries.