420HC Stainless Steel: Properties and Key Applications

420HC Stainless Steel is a high-carbon stainless steel that falls under the martensitic classification. This steel grade is primarily alloyed with chromium (around 13-15%) and carbon (approximately 0.4-0.5%), which significantly influence its properties. The presence of chromium provides corrosion resistance, while carbon enhances hardness and strength.

Comprehensive Overview

420HC stainless steel is known for its excellent hardness and wear resistance, making it a popular choice for applications requiring durability. Its martensitic structure allows it to be hardened through heat treatment, resulting in a material that can achieve high levels of strength and toughness.

Key Characteristics:
- Corrosion Resistance: While not as resistant as austenitic stainless steels, 420HC offers decent resistance to oxidation and corrosion in mild environments.
- Hardness: It can reach hardness levels of up to 58 HRC after heat treatment, making it suitable for cutting tools and blades.
- Toughness: The steel maintains good toughness, which is essential for applications that experience impact or shock loading.

Advantages:
- High hardness and wear resistance.
- Good edge retention, making it ideal for knives and cutting tools.
- Moderate corrosion resistance suitable for various environments.

Limitations:
- Limited corrosion resistance compared to higher alloyed stainless steels.
- Can be challenging to machine due to its hardness.
- Requires careful heat treatment to achieve desired properties.

Historically, 420HC has been utilized in various applications, including cutlery, surgical instruments, and industrial blades, establishing its position in the market as a reliable choice for high-performance applications.

Alternative Names, Standards, and Equivalents

Standard Organization	Designation/Grade	Country/Region of Origin	Notes/Remarks
UNS	S42000	USA	Closest equivalent to AISI 420 with higher carbon content.
AISI/SAE	420HC	USA	High carbon variant of AISI 420.
ASTM	A276	USA	Standard specification for stainless steel bars and shapes.
EN	1.4021	Europe	Equivalent grade in European standards.
JIS	SUS420J2	Japan	Similar properties but with slightly different composition.

The differences between these grades often lie in their carbon content and heat treatment responses, which can affect hardness, toughness, and corrosion resistance. For instance, while SUS420J2 has lower carbon content, it may offer better corrosion resistance but at the expense of hardness.

Key Properties

Chemical Composition

Element (Symbol and Name)	Percentage Range (%)
C (Carbon)	0.40 - 0.50
Cr (Chromium)	13.00 - 15.00
Mn (Manganese)	1.00 max
Si (Silicon)	1.00 max
P (Phosphorus)	0.04 max
S (Sulfur)	0.03 max

The primary alloying elements in 420HC stainless steel are chromium and carbon. Chromium enhances corrosion resistance and hardness, while carbon increases strength and wear resistance. Manganese and silicon are included to improve hardenability and toughness.

Mechanical Properties

Property	Condition/Temper	Test Temperature	Typical Value/Range (Metric - SI Units)	Typical Value/Range (Imperial Units)	Reference Standard for Test Method
Tensile Strength	Annealed	Room Temp	520 - 700 MPa	75 - 102 ksi	ASTM E8
Yield Strength (0.2% offset)	Annealed	Room Temp	350 - 500 MPa	51 - 73 ksi	ASTM E8
Elongation	Annealed	Room Temp	12 - 20%	12 - 20%	ASTM E8
Hardness	Quenched & Tempered	Room Temp	54 - 58 HRC	54 - 58 HRC	ASTM E18
Impact Strength	Quenched & Tempered	-20°C	30 J	22 ft-lbf	ASTM E23

The mechanical properties of 420HC stainless steel make it suitable for applications that require high strength and hardness. Its tensile strength and yield strength indicate its ability to withstand significant loads, while the hardness values suggest excellent wear resistance. The impact strength, although lower than some other grades, is adequate for many applications.

Physical Properties

Property	Condition/Temperature	Value (Metric - SI Units)	Value (Imperial Units)
Density	Room Temp	7.75 g/cm³	0.28 lb/in³
Melting Point/Range	-	1450 - 1510 °C	2642 - 2750 °F
Thermal Conductivity	Room Temp	25.4 W/m·K	17.5 BTU·in/(hr·ft²·°F)
Specific Heat Capacity	Room Temp	500 J/kg·K	0.12 BTU/lb·°F
Electrical Resistivity	Room Temp	0.74 µΩ·m	0.74 µΩ·in
Coefficient of Thermal Expansion	Room Temp	16.0 x 10⁻⁶ /K	8.9 x 10⁻⁶ /°F

The density of 420HC indicates a relatively heavy material, which contributes to its durability. The melting point suggests good thermal stability, while the thermal conductivity and specific heat capacity indicate moderate heat transfer properties. The electrical resistivity is typical for stainless steels, making it suitable for various electrical applications.

Corrosion Resistance

Corrosive Agent	Concentration (%)	Temperature (°C/°F)	Resistance Rating	Notes
Chlorides	3-10	20-60 / 68-140	Fair	Risk of pitting corrosion.
Acids (HCl)	10-20	20-40 / 68-104	Poor	Not recommended for strong acids.
Alkaline Solutions	5-10	20-60 / 68-140	Good	Moderate resistance.
Atmospheric	-	-	Good	Performs well in mild environments.

420HC stainless steel exhibits moderate corrosion resistance, particularly in atmospheric conditions and alkaline environments. However, it is susceptible to pitting corrosion in chloride-rich environments and should be avoided in applications involving strong acids. Compared to austenitic grades like 304 or 316, 420HC has lower corrosion resistance but offers superior hardness.

Heat Resistance

Property/Limit	Temperature (°C)	Temperature (°F)	Remarks
Max Continuous Service Temp	400 °C	752 °F	Suitable for intermittent use.
Max Intermittent Service Temp	500 °C	932 °F	Limited oxidation resistance.
Scaling Temperature	600 °C	1112 °F	Risk of scaling at high temps.

At elevated temperatures, 420HC stainless steel maintains its strength but may experience oxidation and scaling. It is not recommended for continuous service above 400 °C due to potential degradation of mechanical properties.

Fabrication Properties

Weldability

Welding Process	Recommended Filler Metal (AWS Classification)	Typical Shielding Gas/Flux	Notes
TIG	ER420	Argon	Preheat recommended.
MIG	ER420	Argon + CO2	Requires careful control.
Stick	E420	-	Not ideal for thick sections.

420HC stainless steel can be welded, but care must be taken to avoid cracking. Preheating is often recommended to minimize thermal stress. Post-weld heat treatment can also improve the toughness of the weld.

Machinability

Machining Parameter	420HC	AISI 1212	Notes/Tips
Relative Machinability Index	50%	100%	Requires sharp tools and slow speeds.
Typical Cutting Speed	30 m/min	60 m/min	Adjust based on tooling and setup.

Machining 420HC can be challenging due to its hardness. It is advisable to use high-speed steel or carbide tools and to maintain lower cutting speeds to achieve optimal results.

Formability

420HC stainless steel is not highly formable due to its high carbon content and resulting hardness. Cold forming is possible but may lead to work hardening, requiring careful control of bend radii and forming processes.

Heat Treatment

Treatment Process	Temperature Range (°C/°F)	Typical Soaking Time	Cooling Method	Primary Purpose / Expected Result
Annealing	800 - 900 / 1472 - 1652	1-2 hours	Air	Reduce hardness, improve ductility.
Quenching	1000 - 1100 / 1832 - 2012	30 minutes	Oil or Air	Achieve high hardness.
Tempering	150 - 200 / 302 - 392	1 hour	Air	Reduce brittleness, enhance toughness.

Heat treatment processes significantly affect the microstructure and properties of 420HC. Quenching increases hardness, while tempering helps relieve stresses and improve toughness.

Typical Applications and End Uses

Industry/Sector	Specific Application Example	Key Steel Properties Utilized in this Application	Reason for Selection (Brief)
Cutlery	Kitchen knives	High hardness, edge retention	Excellent for sharp blades.
Medical	Surgical instruments	Corrosion resistance, hardness	Sterilizable and durable.
Industrial	Cutting tools	Wear resistance, toughness	Long-lasting performance.

Other applications include:
- Scissors and shears
- Industrial blades
- Fasteners and fittings

420HC is chosen for these applications due to its excellent hardness and wear resistance, which are critical for tools and instruments that require sharp edges and durability.

Important Considerations, Selection Criteria, and Further Insights

Feature/Property	420HC	AISI 440C	AISI 304	Brief Pro/Con or Trade-off Note
Key Mechanical Property	High hardness	Higher hardness	Lower hardness	440C offers better hardness but less toughness.
Key Corrosion Aspect	Moderate resistance	Fair	Excellent	304 is better for corrosive environments.
Weldability	Moderate	Poor	Good	304 is easier to weld.
Machinability	Challenging	Moderate	Good	304 is easier to machine.
Formability	Low	Low	Moderate	304 can be formed more easily.
Approx. Relative Cost	Moderate	Higher	Lower	420HC is cost-effective for its properties.
Typical Availability	Common	Less common	Very common	304 is widely available.

When selecting 420HC stainless steel, consider its balance of hardness and corrosion resistance. While it is not as corrosion-resistant as austenitic grades, its hardness makes it suitable for applications where wear resistance is critical. Additionally, its availability and cost-effectiveness make it a practical choice for many industries.

In summary, 420HC stainless steel is a versatile material that offers a unique combination of hardness, wear resistance, and moderate corrosion resistance, making it suitable for a wide range of applications, particularly in cutlery and industrial tools.