CHT 400 Steel: Properties and Key Applications

CHT 400 Steel is a high-performance alloy steel known for its exceptional mechanical properties and versatility in various engineering applications. Classified as a medium-carbon alloy steel, CHT 400 is primarily composed of iron, carbon, and a variety of alloying elements that enhance its strength, toughness, and wear resistance. The key alloying elements in CHT 400 include chromium, molybdenum, and nickel, which contribute to its overall performance characteristics.

Comprehensive Overview

The fundamental nature of CHT 400 Steel is defined by its medium carbon content, which typically ranges from 0.30% to 0.50%. This carbon content provides a balance between strength and ductility, making it suitable for applications requiring both toughness and hardness. The addition of chromium enhances corrosion resistance and hardenability, while molybdenum improves strength at elevated temperatures and contributes to overall toughness. Nickel further enhances toughness and impact resistance, particularly in low-temperature environments.

Advantages and Limitations

Advantages (Pros)	Limitations (Cons)
High strength-to-weight ratio	Susceptible to stress corrosion cracking
Excellent wear resistance	Requires careful heat treatment to achieve desired properties
Good machinability	Limited corrosion resistance compared to stainless steels
Versatile for various applications	May require protective coatings in harsh environments

CHT 400 Steel holds a significant position in the market due to its balance of properties, making it a popular choice in industries such as automotive, aerospace, and manufacturing. Its historical significance lies in its ability to meet the demanding requirements of modern engineering applications, providing reliable performance in critical components.

Alternative Names, Standards, and Equivalents

Standard Organization	Designation/Grade	Country/Region of Origin	Notes/Remarks
UNS	G41400	USA	Closest equivalent to AISI 4140
AISI/SAE	4140	USA	Minor compositional differences to be aware of
ASTM	A829	USA	Specification for alloy steel plates
EN	42CrMo4	Europe	Equivalent with slight variations in composition
JIS	SCM440	Japan	Similar properties, often used in automotive applications

The table above highlights various standards and equivalents for CHT 400 Steel. While these grades may be considered equivalent, subtle differences in composition and processing can significantly affect performance. For instance, AISI 4140 may have slightly different mechanical properties due to variations in heat treatment practices, which can influence the selection for specific applications.

Key Properties

Chemical Composition

Element (Symbol and Name)	Percentage Range (%)
C (Carbon)	0.30 - 0.50
Cr (Chromium)	0.90 - 1.20
Mo (Molybdenum)	0.15 - 0.25
Ni (Nickel)	0.40 - 0.70
Mn (Manganese)	0.60 - 0.90
Si (Silicon)	0.15 - 0.40
P (Phosphorus)	≤ 0.035
S (Sulfur)	≤ 0.040

The primary role of the key alloying elements in CHT 400 Steel is as follows:

• Carbon (C): Enhances hardness and strength through heat treatment.
• Chromium (Cr): Improves corrosion resistance and hardenability.
• Molybdenum (Mo): Increases strength at elevated temperatures and enhances toughness.
• Nickel (Ni): Provides improved toughness and impact resistance, especially in low temperatures.

Mechanical Properties

Property	Condition/Temper	Test Temperature	Typical Value/Range (Metric)	Typical Value/Range (Imperial)	Reference Standard for Test Method
Tensile Strength	Quenched & Tempered	Room Temp	850 - 1000 MPa	123 - 145 ksi	ASTM E8
Yield Strength (0.2% offset)	Quenched & Tempered	Room Temp	600 - 800 MPa	87 - 116 ksi	ASTM E8
Elongation	Quenched & Tempered	Room Temp	15 - 20%	15 - 20%	ASTM E8
Reduction of Area	Quenched & Tempered	Room Temp	50 - 60%	50 - 60%	ASTM E8
Hardness (Rockwell C)	Quenched & Tempered	Room Temp	28 - 34 HRC	28 - 34 HRC	ASTM E18
Impact Strength (Charpy V-notch)	Quenched & Tempered	-20°C	30 - 50 J	22 - 37 ft-lbf	ASTM E23

The combination of these mechanical properties makes CHT 400 Steel suitable for applications requiring high strength and toughness, such as in structural components, gears, and heavy machinery. Its ability to withstand high stress and impact loads makes it a preferred choice in demanding environments.

Physical Properties

Property	Condition/Temperature	Value (Metric)	Value (Imperial)
Density	-	7.85 g/cm³	0.284 lb/in³
Melting Point	-	1425 - 1540 °C	2600 - 2800 °F
Thermal Conductivity	20 °C	45 W/m·K	31 BTU·in/h·ft²·°F
Specific Heat Capacity	-	460 J/kg·K	0.11 BTU/lb·°F
Electrical Resistivity	-	0.00065 Ω·m	0.00038 Ω·in
Coefficient of Thermal Expansion	20 - 100 °C	12 × 10⁻⁶ /°C	6.67 × 10⁻⁶ /°F

The practical significance of the physical properties of CHT 400 Steel includes:

• Density: Affects the weight and structural design of components.
• Thermal Conductivity: Important for applications involving heat dissipation.
• Specific Heat Capacity: Influences thermal management in high-temperature applications.

Corrosion Resistance

Corrosive Agent	Concentration (%)	Temperature (°C)	Resistance Rating	Notes
Chlorides	3 - 10	20 - 60	Fair	Risk of pitting
Sulfuric Acid	10 - 30	20 - 50	Poor	Not recommended
Sea Water	-	20 - 40	Good	Moderate resistance
Alkaline Solutions	5 - 20	20 - 60	Fair	Susceptible to stress corrosion cracking

CHT 400 Steel exhibits moderate corrosion resistance, particularly in environments with chlorides and alkaline solutions. It is susceptible to pitting and stress corrosion cracking, especially in chloride-rich environments. Compared to stainless steels like 304 or 316, CHT 400's corrosion resistance is limited, making it less suitable for applications where exposure to corrosive agents is a concern.

In comparison to other grades, such as AISI 4140, CHT 400 may show similar resistance in certain environments but may not perform as well in highly corrosive conditions. The choice between these grades should consider the specific environmental conditions and the required performance characteristics.

Heat Resistance

Property/Limit	Temperature (°C)	Temperature (°F)	Remarks
Max Continuous Service Temp	400	752	Suitable for prolonged exposure
Max Intermittent Service Temp	500	932	Short-term exposure only
Scaling Temperature	600	1112	Risk of oxidation at higher temps
Creep Strength considerations begin around	450	842	Performance may degrade at elevated temps

At elevated temperatures, CHT 400 Steel maintains good mechanical properties, making it suitable for applications involving heat. However, it is essential to monitor service temperatures to avoid oxidation and degradation of material properties. The steel's performance can be compromised if exposed to temperatures beyond its limits for extended periods.

Fabrication Properties

Weldability

Welding Process	Recommended Filler Metal (AWS Classification)	Typical Shielding Gas/Flux	Notes
MIG	ER70S-6	Argon + CO2 mixture	Preheat recommended
TIG	ER80S-Ni	Argon	Requires post-weld heat treatment
Stick	E7018	-	Good for thicker sections

CHT 400 Steel is generally weldable, but care must be taken to avoid cracking. Preheating is often recommended to minimize the risk of thermal stress. Post-weld heat treatment can help relieve residual stresses and improve toughness in the weld area.

Machinability

Machining Parameter	CHT 400 Steel	AISI 1212	Notes/Tips
Relative Machinability Index	60	100	Moderate machinability
Typical Cutting Speed	30 m/min	50 m/min	Adjust based on tooling

CHT 400 Steel exhibits moderate machinability, requiring appropriate tooling and cutting speeds to achieve optimal results. The use of high-speed steel or carbide tools is recommended for effective machining.

Formability

CHT 400 Steel can be formed through both cold and hot processes. Cold forming is feasible but may lead to work hardening, necessitating careful control of bend radii and forming techniques. Hot forming is preferred for complex shapes, allowing for better ductility and reduced risk of cracking.

Heat Treatment

Treatment Process	Temperature Range (°C)	Typical Soaking Time	Cooling Method	Primary Purpose / Expected Result
Annealing	600 - 700	1 - 2 hours	Air or water	Softening, improved ductility
Quenching	800 - 900	30 minutes	Oil or water	Hardening, increased strength
Tempering	400 - 600	1 hour	Air	Reducing brittleness, improving toughness

The heat treatment processes for CHT 400 Steel involve critical metallurgical transformations. Quenching increases hardness by transforming the microstructure to martensite, while tempering reduces brittleness and enhances toughness. Proper heat treatment is essential to achieve the desired balance of mechanical properties.

Typical Applications and End Uses

Industry/Sector	Specific Application Example	Key Steel Properties Utilized in this Application	Reason for Selection
Automotive	Gears and shafts	High strength, toughness	Durability under load
Aerospace	Structural components	Lightweight, high strength	Performance in extreme conditions
Manufacturing	Machine tools	Wear resistance, machinability	Precision and longevity

Other applications of CHT 400 Steel include:

• Oil and gas: Components in drilling equipment.
• Construction: Structural beams and supports.
• Heavy machinery: Parts requiring high wear resistance.

The selection of CHT 400 Steel in these applications is driven by its ability to withstand high stress and provide reliable performance in demanding environments.

Important Considerations, Selection Criteria, and Further Insights

Feature/Property	CHT 400 Steel	AISI 4140	AISI 4340	Brief Pro/Con or Trade-off Note
Key Mechanical Property	High strength	Moderate	High strength	CHT 400 offers a balance of strength and toughness
Key Corrosion Aspect	Fair	Good	Fair	CHT 400 is less resistant than stainless steels
Weldability	Moderate	Good	Moderate	Requires preheat and post-weld treatment
Machinability	Moderate	Good	Fair	CHT 400 is easier to machine than AISI 4340
Formability	Good	Fair	Fair	CHT 400 can be formed effectively
Approx. Relative Cost	Moderate	Moderate	Higher	Cost-effective for high-performance applications
Typical Availability	Common	Common	Less common	CHT 400 is widely available in various forms

When selecting CHT 400 Steel, considerations include cost-effectiveness, availability, and specific performance requirements. Its moderate corrosion resistance and good weldability make it suitable for a range of applications, while its mechanical properties ensure reliability under load. The choice between CHT 400 and alternative grades should be based on the specific demands of the application, including environmental conditions and mechanical loading requirements.

In summary, CHT 400 Steel is a versatile medium-carbon alloy steel that offers a unique combination of strength, toughness, and wear resistance, making it a preferred choice in various engineering applications. Its properties and performance characteristics should be carefully evaluated against application requirements to ensure optimal selection.