Low Temperature Impact Properties of 1.4418 Martensitic Stainless Steel
Published: December 22, 2025 | Category: Technical Blog | By FUSHUN METAL
Table of Contents
1. Introduction
With the rapid development of the liquefied natural gas (LNG) industry, the demand for high-performance cryogenic storage and transportation equipment has grown significantly. Austenitic stainless steels such as 304, 304L, 316, and 316L have been widely used in LNG low-temperature storage and transportation applications (below -160°C) due to their excellent cryogenic properties and corrosion resistance.
However, these austenitic stainless steels generally suffer from low strength and poor wear resistance. Components made from these materials that bear heavy loads often experience severe wear, which limits the overall service life of the equipment.
“Martensitic stainless steel can achieve higher strength and wear resistance through heat treatment strengthening, while maintaining superior corrosion resistance due to its Cr and Ni content.”
The 1.4418 is a German-grade martensitic stainless steel that obtains a martensite/ferrite microstructure through heat treatment strengthening. This steel exhibits excellent comprehensive properties and is widely used in shipbuilding, petrochemical, and other mechanical industries. However, since this steel grade has no corresponding domestic equivalent, performance data is relatively scarce, especially regarding low-temperature toughness data for LNG applications.
This article presents research conducted by a certain research institution on the impact properties of 1.4418 martensitic stainless steel at different temperatures, providing practical guidance for industrial applications.
2. Test Materials and Methods
2.1 Material Composition
The test material was 1.4418 martensitic stainless steel forgings. The chemical composition is shown in the table below:
| C | Ni | Si | Mn | P | S | Cr | Mo | N |
|---|---|---|---|---|---|---|---|---|
| 0.0483 | 5.1042 | 0.1786 | 0.725 | 0.0253 | 0.0033 | 16.199 | 0.9086 | 0.0179 |
Table 1: Chemical composition of 1.4418 martensitic stainless steel (wt%)
2.2 Heat Treatment Process
The 1.4418 martensitic stainless steel forgings were subjected to quenching and tempering heat treatment with the following parameters:
- Quenching: 950°C × 5 hours, oil cooling
- Tempering: 600°C × 2 hours, air cooling
2.3 Test Methodology
Impact tests were conducted according to the GB/T 229-2007 standard (Metallic materials – Charpy pendulum impact test method). The tests were performed at the following temperatures:
Test Temperatures: 25°C (room temperature), 0°C, -40°C, -65°C, -90°C, -115°C, -140°C, -165°C, and -196°C
The equipment and procedures included:
- JB-300 impact testing machine with automatic sample feeding low-temperature environmental test chamber
- Temperature control through regulated liquid nitrogen flow into the environmental chamber
- Samples held at target temperature for 30 minutes before testing
- Three samples tested at each temperature, with average values reported
- Scanning electron microscopy (SEM) analysis of fracture surfaces
3. Low Temperature Impact Performance Results
The variation of impact absorption energy with temperature for 1.4418 martensitic stainless steel reveals several important characteristics:
| Temperature (°C) | Impact Absorption Energy (J) | Change from RT (%) | Characteristics |
|---|---|---|---|
| 25 (RT) | 81 | — | Excellent ductility |
| 0 to -90 | Slight decrease | Minimal | Stable performance |
| -115 | ~50 | -38.27% | First significant drop |
| -140 | Similar to -115°C | ~-40% | Transition zone |
| -165 | 27 | -66.67% | Ductile-brittle transition |
| -196 | 22 | -72.84% | Brittle fracture region |
Table 2: Impact absorption energy of 1.4418 stainless steel at different temperatures
“The test results indicate that 1.4418 martensitic stainless steel possesses relatively high low-temperature impact performance. Particularly in the temperature range above -90°C, the impact performance is minimally affected by temperature.”
Key Observations
Stable Performance Region (25°C to -90°C)
The impact absorption energy shows minimal variation across this temperature range, demonstrating excellent cryogenic stability for moderate low-temperature applications.
Transition Region (-115°C to -140°C)
A notable decrease in impact energy occurs at -115°C (38.27% reduction), though the material still retains certain plastic deformation characteristics.
Brittle Region (-165°C and below)
Significant ductile-brittle transition occurs with the impact energy dropping to 27 J. However, complete brittle fracture was not observed throughout the entire test temperature range.
4. Fracture Surface Analysis at Different Temperatures
Scanning electron microscopy (SEM) analysis was conducted at 500× and 2000× magnification to reveal the fracture mechanisms at different temperatures. The analysis focused on temperatures where significant changes in impact energy were observed: -90°C, -115°C, -140°C, -165°C, and -196°C.
4.1 Room Temperature Fracture (25°C)
At room temperature, 1.4418 martensitic stainless steel exhibits typical ductile fracture characteristics. The fracture morphology consists of dimples of various sizes and tear ridges. After quenching and tempering, the microstructure contains martensite and ferrite phases. The martensite matrix contains carbide particles of different sizes, while the ferrite phase acts as a plastic phase that impedes crack propagation, thereby inhibiting rapid crack growth and improving the steel’s plasticity.
4.2 Fracture at -90°C
At -90°C, the impact fracture remains predominantly dimple-dominated, still exhibiting plastic deformation characteristics overall. However, compared to room temperature:
- The number of small-sized dimples and tear ridges is relatively reduced
- Large-sized dimples are fewer in number and shallower in depth
- Some cleavage fracture features begin to appear, correlating with the slight decrease in impact energy
4.3 Fracture at -115°C
Significant Change: The fracture surface shows obvious cleavage fracture characteristics. The large-sized dimples observed at room temperature have essentially transformed into cleavage features. The fracture consists of brittle slip platforms and a small amount of layered fracture surfaces, presenting an uneven brittle cleavage platform. However, at 2000× magnification, tear ridges and small-sized dimples can still be observed around the cleavage surfaces, indicating that the steel still possesses certain plastic characteristics at this temperature.
4.4 Fracture at -140°C
The fracture morphology at -140°C is relatively consistent with that at -115°C, with only a reduction in the number of local tear ridges. This explains the relatively stable impact energy values between these two temperatures.
4.5 Fracture at -165°C and -196°C
Critical Transition: At -165°C, the cleavage fracture characteristics become more pronounced. The tear ridges and small-sized dimples between cleavage surfaces are significantly reduced, and a large number of cleavage platforms appear. This indicates that the fracture mechanism at this temperature is predominantly cleavage fracture, marking a clear ductile-brittle transition. The fracture morphology at -196°C is consistent with that at -165°C, similarly exhibiting cleavage fracture characteristics.
| Temperature | Dominant Fracture Mode | Key Features |
|---|---|---|
| 25°C | Ductile (Dimple) | Various dimple sizes, tear ridges, second-phase particles visible |
| -90°C | Predominantly Ductile | Dimple-dominated with some cleavage features emerging |
| -115°C | Mixed Mode | Obvious cleavage with residual tear ridges and small dimples |
| -140°C | Mixed Mode | Similar to -115°C with fewer tear ridges |
| -165°C | Cleavage (Brittle) | Extensive cleavage platforms, minimal ductile features |
| -196°C | Cleavage (Brittle) | Typical cleavage fracture characteristics |
Table 3: Summary of fracture characteristics at different temperatures
5. Key Conclusions
Based on the comprehensive cryogenic impact testing and fracture analysis of 1.4418 martensitic stainless steel, the following conclusions can be drawn:
Conclusion 1: Superior Performance Above -90°C
1.4418 martensitic stainless steel exhibits excellent low-temperature impact performance in the temperature range above -90°C. As the temperature decreases, the impact absorption energy shows minimal reduction. At -115°C, the low-temperature impact absorption energy decreases by 38.27% compared to room temperature, representing the first significant drop, yet the material still retains certain plastic deformation characteristics. At -165°C, the impact absorption energy decreases significantly by 66.67% compared to room temperature, indicating a clear ductile-brittle transition.
Conclusion 2: Fracture Mechanism Evolution
In the temperature range above -90°C, 1.4418 martensitic stainless steel predominantly exhibits dimple fracture. When the temperature drops to -115°C, obvious cleavage fracture appears, but a significant number of small-sized dimples and tear ridges still exist between cleavage surfaces. When the temperature continues to decrease to -165°C and below, the fracture mechanism transitions to typical cleavage fracture characteristics.
Practical Application Guidance from FUSHUN METAL
- Optimal Operating Range: For applications requiring high strength and wear resistance with good toughness, 1.4418 is well-suited for operating temperatures above -90°C.
- Caution Zone (-90°C to -140°C): Applications in this range should carefully consider safety factors and may require additional testing specific to the application conditions.
- LNG Applications: For ultra-low temperature LNG applications (below -160°C), alternative materials such as austenitic stainless steels may be more appropriate despite their lower strength.
- Heat Treatment: The quenching and tempering process (950°C/5h oil quench + 600°C/2h air cool) is critical for achieving optimal properties.
6. Frequently Asked Questions
Q: What is the impact absorption energy of 1.4418 martensitic stainless steel at room temperature?
At room temperature (25°C), 1.4418 martensitic stainless steel exhibits an impact absorption energy of 81 J, demonstrating excellent toughness characteristics. This value remains relatively stable throughout the temperature range from room temperature to -90°C.
Q: At what temperature does 1.4418 steel undergo ductile-brittle transition?
The 1.4418 martensitic stainless steel undergoes a significant ductile-brittle transition at -165°C, where the impact absorption energy drops to 27 J, representing a 66.67% decrease from room temperature values. The first notable decrease in impact performance occurs at -115°C with a 38.27% reduction.
Q: Is 1.4418 martensitic stainless steel suitable for LNG applications?
1.4418 martensitic stainless steel demonstrates superior low temperature impact performance in the temperature range above -90°C, making it suitable for certain cryogenic applications. However, for ultra-low temperature LNG applications below -160°C, careful consideration is required due to the ductile-brittle transition behavior. For such extreme conditions, austenitic stainless steels like 304L or 316L may be more appropriate choices.
Q: What is the recommended heat treatment for 1.4418 martensitic stainless steel?
The recommended quenching and tempering heat treatment includes: quenching at 950°C for 5 hours with oil cooling, followed by tempering at 600°C for 2 hours with air cooling. This heat treatment produces a martensite/ferrite dual-phase microstructure that provides the optimal balance of strength, wear resistance, and toughness.
Q: What are the main advantages of 1.4418 over austenitic stainless steels?
Compared to austenitic stainless steels like 304 and 316L, 1.4418 martensitic stainless steel offers higher strength and better wear resistance through heat treatment strengthening, while maintaining good corrosion resistance due to its Cr (16.2%) and Ni (5.1%) content. This makes it ideal for components that bear heavy loads where austenitic grades would experience excessive wear, thereby improving overall equipment service life.
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