S136 Steel: Properties and Key Applications in Molding

S136 steel, also known as stainless mold steel, is a high-performance tool steel primarily used in the manufacturing of molds and dies. Classified as an austenitic stainless steel, S136 is characterized by its high corrosion resistance, excellent polishability, and good machinability. The primary alloying elements in S136 include chromium (Cr), nickel (Ni), and molybdenum (Mo), which contribute significantly to its properties.

Comprehensive Overview

S136 steel is designed for applications requiring high wear resistance and corrosion protection. Its composition typically includes around 13% chromium, 0.3% carbon, and 1% molybdenum, which enhance its hardness and toughness. The steel is often used in the production of molds for plastic injection, where the ability to withstand high temperatures and corrosive environments is critical.

Advantages:
- Corrosion Resistance: S136 exhibits excellent resistance to rust and corrosion, making it suitable for use in humid or chemically aggressive environments.
- High Hardness: The steel can achieve high hardness levels, which is beneficial for wear resistance in mold applications.
- Polishability: S136 can be polished to a high finish, which is essential for aesthetic applications and reducing friction in mold surfaces.

Limitations:
- Cost: S136 is generally more expensive than other tool steels due to its alloying elements and processing requirements.
- Weldability: While it can be welded, special precautions must be taken to avoid cracking and ensure proper joint integrity.

Historically, S136 has gained popularity in the mold-making industry due to its superior performance compared to traditional carbon steels. Its unique properties have positioned it as a preferred choice for high-quality molds, particularly in the plastic industry.

Alternative Names, Standards, and Equivalents

Standard Organization	Designation/Grade	Country/Region of Origin	Notes/Remarks
UNS	S13600	USA	Closest equivalent to AISI 420
AISI/SAE	AISI 420	USA	Minor compositional differences
ASTM	ASTM A681	USA	Specification for stainless tool steels
EN	EN 1.2083	Europe	Equivalent grade with similar properties
JIS	JIS SUS420J2	Japan	Similar corrosion resistance but different mechanical properties

The table above highlights various standards and equivalents for S136 steel. Notably, while AISI 420 is often considered an equivalent, it may not provide the same level of corrosion resistance or polishability, which are critical in mold applications.

Key Properties

Chemical Composition

Element (Symbol and Name)	Percentage Range (%)
C (Carbon)	0.30 - 0.40
Cr (Chromium)	12.0 - 14.0
Ni (Nickel)	0.5 - 1.0
Mo (Molybdenum)	0.5 - 1.0
Mn (Manganese)	1.0 max
Si (Silicon)	1.0 max
P (Phosphorus)	0.03 max
S (Sulfur)	0.03 max

The primary alloying elements in S136 steel play crucial roles:
- Chromium: Enhances corrosion resistance and hardness.
- Nickel: Improves toughness and ductility.
- Molybdenum: Increases hardness and resistance to pitting corrosion.

Mechanical Properties

Property	Condition/Temper	Test Temperature	Typical Value/Range (Metric)	Typical Value/Range (Imperial)	Reference Standard for Test Method
Tensile Strength	Annealed	Room Temp	600 - 800 MPa	87 - 116 ksi	ASTM E8
Yield Strength (0.2% offset)	Annealed	Room Temp	400 - 600 MPa	58 - 87 ksi	ASTM E8
Elongation	Annealed	Room Temp	10 - 15%	10 - 15%	ASTM E8
Hardness (HRC)	Annealed	Room Temp	30 - 40 HRC	30 - 40 HRC	ASTM E18
Impact Strength	Annealed	-20°C	30 - 50 J	22 - 37 ft-lbf	ASTM E23

The mechanical properties of S136 steel make it suitable for applications involving significant mechanical loading. Its high tensile strength and yield strength ensure structural integrity under stress, while its elongation indicates good ductility, allowing for deformation without fracture.

Physical Properties

Property	Condition/Temperature	Value (Metric)	Value (Imperial)
Density	Room Temp	7.8 g/cm³	0.282 lb/in³
Melting Point/Range	-	1400 - 1450 °C	2552 - 2642 °F
Thermal Conductivity	Room Temp	25 W/m·K	14.5 BTU·in/(hr·ft²·°F)
Specific Heat Capacity	Room Temp	500 J/kg·K	0.12 BTU/lb·°F
Electrical Resistivity	Room Temp	0.72 µΩ·m	0.0000013 Ω·in

Key physical properties such as density and melting point are significant for processing and application. The relatively high melting point allows S136 to maintain its integrity at elevated temperatures, making it suitable for high-temperature applications.

Corrosion Resistance

Corrosive Agent	Concentration (%)	Temperature (°C/°F)	Resistance Rating	Notes
Chlorides	3-10	20-60 / 68-140	Good	Risk of pitting
Acids	10-20	20-40 / 68-104	Fair	Susceptible to stress corrosion cracking
Alkaline Solutions	5-15	20-60 / 68-140	Excellent	Resistant to alkaline environments
Atmospheric	-	-	Excellent	Good for outdoor applications

S136 steel demonstrates excellent resistance to various corrosive environments, particularly in alkaline solutions. However, it is susceptible to pitting corrosion in chloride-rich environments and stress corrosion cracking in acidic conditions. Compared to other grades like AISI 420 and AISI 440C, S136 offers superior corrosion resistance, particularly in humid and chemically aggressive settings.

Heat Resistance

Property/Limit	Temperature (°C)	Temperature (°F)	Remarks
Max Continuous Service Temp	300	572	Suitable for prolonged exposure
Max Intermittent Service Temp	400	752	Short-term exposure only
Scaling Temperature	600	1112	Risk of oxidation beyond this temp
Creep Strength Considerations	400	752	Begins to degrade at this temp

S136 steel maintains its mechanical properties at elevated temperatures, making it suitable for applications involving heat. However, care must be taken to avoid prolonged exposure to temperatures above 300 °C, as this can lead to oxidation and degradation of the material.

Fabrication Properties

Weldability

Welding Process	Recommended Filler Metal (AWS Classification)	Typical Shielding Gas/Flux	Notes
TIG	ER 308L	Argon	Preheat recommended
MIG	ER 308L	Argon + CO2 mix	Post-weld heat treatment advised

S136 steel can be welded using standard processes like TIG and MIG. However, preheating is recommended to minimize the risk of cracking. Post-weld heat treatment can help relieve stresses and improve the overall integrity of the weld.

Machinability

Machining Parameter	S136 Steel	AISI 1212	Notes/Tips
Relative Machinability Index	70	100	Moderate machinability
Typical Cutting Speed	30 m/min	50 m/min	Adjust for tool wear

S136 steel has moderate machinability compared to benchmark steels like AISI 1212. Optimal cutting speeds and tooling should be employed to achieve the best results, and care must be taken to avoid excessive heat generation during machining.

Formability

S136 steel exhibits good formability, allowing for both cold and hot forming processes. However, due to its high hardness, care should be taken to avoid work hardening during cold forming. Recommended bend radii should be adhered to in order to prevent cracking.

Heat Treatment

Treatment Process	Temperature Range (°C/°F)	Typical Soaking Time	Cooling Method	Primary Purpose / Expected Result
Annealing	800 - 850 / 1472 - 1562	1 - 2 hours	Air	Softening, improving machinability
Hardening	1000 - 1100 / 1832 - 2012	30 minutes	Oil	Increasing hardness
Tempering	200 - 300 / 392 - 572	1 hour	Air	Reducing brittleness

Heat treatment processes significantly affect the microstructure and properties of S136 steel. Annealing softens the material, enhancing machinability, while hardening increases hardness and wear resistance. Tempering is crucial to reduce brittleness and improve toughness.

Typical Applications and End Uses

Industry/Sector	Specific Application Example	Key Steel Properties Utilized in this Application	Reason for Selection
Automotive	Injection molds for bumpers	High hardness, corrosion resistance	Durability and longevity
Consumer Goods	Molds for household items	Excellent polishability, wear resistance	Aesthetic finish and performance
Medical Devices	Surgical instrument molds	Corrosion resistance, biocompatibility	Safety and hygiene

Other applications include:
- Molds for electronic components
- Food processing equipment
- Aerospace components

S136 steel is chosen for these applications due to its unique combination of hardness, corrosion resistance, and ability to achieve a high-quality finish, making it ideal for both functional and aesthetic requirements.

Important Considerations, Selection Criteria, and Further Insights

Feature/Property	S136 Steel	AISI 420	AISI 440C	Brief Pro/Con or Trade-off Note
Key Mechanical Property	High hardness	Moderate hardness	High hardness	S136 offers better corrosion resistance than AISI 420
Key Corrosion Aspect	Excellent	Good	Fair	S136 is superior in corrosive environments
Weldability	Moderate	Good	Poor	S136 requires careful welding practices
Machinability	Moderate	Good	Poor	AISI 420 is easier to machine
Formability	Good	Fair	Poor	S136 can be formed with care
Approx. Relative Cost	High	Moderate	Moderate	S136 is more expensive due to alloying elements
Typical Availability	Moderate	High	High	S136 may not be as readily available as AISI 420

When selecting S136 steel, considerations include cost-effectiveness, availability, and specific application requirements. Its unique properties make it suitable for high-performance applications, but the higher cost and moderate machinability may limit its use in some scenarios. Understanding the trade-offs between S136 and alternative grades is crucial for optimal material selection in engineering applications.