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420 STANDARD VALUES
C
Si
Mn
P
S
Cr
X46Cr13
50 HRC - 55 HRC
max. 241HB
100MnCrW4
57-62 HRC
max. 229 HB
420 PHYSICAL PROPERTIES
420 stainless steel has, in its annealed condition, good ductility and can, when hardened, reach a hardness of min. 469 BHN (50 HRC). As a martensitic stainless steel 420 is optimized for its high hardness, while other properties are compromised to some degree. 420 loses ductility at sub-zero temperatures and is in comparison to austenitic steels less corrosion resistant, has poor weldability and loses strength when over-tempered at elevated temperatures.
420 TECHNICAL PROPERTIES
Typically the density of 420 stainless steel is 0.278 lb/in3 (7.7g/cm3) at room temperature.
The yield strength shows how much stress can be applied to a material before it plastically deforms. Beyond this point it does not return to its original form when the stresses have been removed.The material deforms permanently or breaks past that point.
The range for the stainless steel 420 is between 74.4 to 200 KSI (512.9 - 1378.9 MPa).
The heat conductivity for the 420 stainless steel is at 30 W/(m*K) (208 BTU/(h-ft*°F)) at room temperature.
| 10-6m/(m • K) | At a temperature of |
|---|---|
| 10.5 | 68 - 212°F |
| 11.0 | 68 - 392°F |
| 11.5 | 68 - 572°F |
| 12.0 | 68 - 752°F |
| 12.0 | 68 - 932°F |
The specific heat capacity of the 420 stainless steel at room temperature is at 0.46 J/g-°C (0.109 BTU/lb-°F). This value shows how much heat is needed to heat 1lb of material by 1 Fahrenheit.
| Value | At a temperature of |
|---|---|
| 0.55 (Ohm*mm²)/m | 68°F |
The relationship between stress and strain of steel is being described in the modulus of elasticity (Young’s Modulus) and can be found in the table below with the according values and temperatures.
| Value | At a temperature of |
|---|---|
| 31183 KSI | 68°F |
| 30748 KSI | 392°F |
| 29732 KSI | 572°F |
| 27557 KSI | 752°F |
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420 PROCEDURE
During quenching the 420 stainless steel undergoes the phase transformation from austenite to martensite. Quick cooling can achieve a higher hardness, the quicker the material is cooled down the more martensite form whereas a slow cooling of this material may leave some austenite or other phases behind. Rapid cooling though has its risks too, it may introduce stresses that can lead to quench cracking and may cost the parts its toughness.
To reach a variety of hardness values and mechanical properties, heat the work piece to 300 - 1292°F (150 - 700°C) and cool in still air. For optimal corrosion resistance and mechanical properties, the temperature range of 797-1112°F (425-600°C) should be avoided.
Tempering this steel grade at low temperatures will achieve a higher hardness, while higher temperatures improve the toughness but will decrease the hardness.
Reduced impact toughness might be the result of temper embrittlement which might occur when tempering in a range of 800 - 1100°F (425 - 595°C).
To reach a variety of hardness values and mechanical properties, heat the work piece to 300 - 1292°F (150 - 700°C) and cool in still air. For optimal corrosion resistance and mechanical properties, the temperature range of 797-1112°F (425-600°C) should be avoided.
Tempering this steel grade at low temperatures will achieve a higher hardness, while higher temperatures improve the toughness but will decrease the hardness.
Reduced impact toughness might be the result of temper embrittlement which might occur when tempering in a range of 800 - 1100°F (425 - 595°C).
This diagram shows the micro changes at different temperatures which are important during heat treatment. They show the optimum condition for the hardening, annealing and normalizing process.
This diagram shows the structural changes at micro level over time at a constant temperature. It shows at what temperature and after what time different phases, e.g., perlite, martensite or bainite start to build.
420 SURFACE TREATMENT
When contemplating a surface treatment the finish and intended application should be taken in consideration. Some surface finishes can impact properties needed, if corrosion resistance is a needed property, a surface treatment that enhances the natural corrosion resistance should be chosen.
Below are some examples for possible surface treatments.
This process is an impact treatment where multiple high velocity shots are blasted onto the material surface leaving small indentations removing stress risers. It makes the surface more resistant and can prevent fatigue and stress corrosion failure.
Note: Protective gear like goggles, masks, helmets, gloves and protective clothing should be worn and adequate ventilation or dust extraction should be provided.
Appropriate guards to prevent shot spillage should be in place, equipment regularly maintained and shot should be free from contaminants.
Abrasive particles like glass or ceramic beads are blasted against the surface to remove contaminants like rust, paint or scale and to promote a uniform matt finish.
Note: Care has to be taken during this process as the process produces dust and small parts might be propelled back. Protective gear like masks, helmets and protective clothing should be worn and adequate ventilation or dust extraction should be provided.
420 PROCESSING
420 stainless steel machines similar to some high carbon steels and creates tough stringy chips.
Annealed the material is, to some extent, easier to machine than in its hardened condition.
EDM can be used to achieve various surface finishes but is mainly used to produce intricate shapes, small details and complex geometries in hard material. As the 420 is at the higher end of hardness EDM can be used successfully. Care with electrodes, dielectric fluid and cutting speeds should be taken with finish and applications in mind.
Slowly heat the workpiece to a temperature of about 1472°F (800°C), then more rapidly to 1922-2084°F (1050-1140°C). Forging should be done in the temperature range of 2012-1472°F (1100-800°C), then slowly cool in the furnace, dry ash or materials that will promote slow cooling.
While forging has its advantages, like grain refinement, elimination of porosity, better directional strength and an improved microstructure to name just a few, it has some disadvantages as well. Forging can, especially in its hardened condition, be hard on tool wear, form an oxide scale that needs to be removed after forging, and may require a heat treatment after forging. Forging is reduced to the more rough shapes compared to casting, machining or EDM.
As an air-hardening steel the 420 stainless steel is rarely welded.
If welding cannot be avoided, preheat to 300-400°F (149-204°C) before welding, then anneal 6-8 hours at a temperature of 1350-1450°F (732-788°C) followed by air cooling. To retain its mechanical properties, if fillers are required, the filler should be similar to the base material.
420 APPLICATION OPTIONS
Due to the combination of high hardness, corrosion and wear resistance and polishability the 420 stainless steel can be used for applications like razor blades, dental and surgical instruments, plastic molds, and machine, valve and firearm parts.
• Medical technology
• Plastic molds
• Synthetic resin mold tools
• Die casting tools
• Cutting tools
• Machine knives
• Scraper blades
• Surgical instruments
• Measuring tools
• Ice-skates
420 CONCLUSION
- Corrosion resistant cold work steel
- Plastic mold steel
- Martensite
- Good machinability
- Magnetizable
- Hardenable
- Polishable
- Low distortion through hardener
- High hardness acceptance
- Good wear resistance
- Poor weldability
420 ALTERNATIVES
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420 DATASHEET
Download the technical data sheet in PDF format here.
The data shown here has been compiled with the greatest diligence and is regularly updated with regard to the correctness and completeness of its content. The content is indicative only and should not be taken as a warranty of specific properties of the product described or a warranty of suitability for a particular purpose. All information presented is given in good faith and no liability will be accepted for actions taken by third parties in reliance on this information. ABRAMS Industries reserves the right to change or amend the information given here in full or parts without prior notice.