420RM Stainless Steel - DIN 1.4122 - X39CrMo17-1 - Data

Where can the stainless steel 420RM be used?

The 420RM stainless steel has a good combination of mechanical properties and corrosion resistance which lends itself in applications like cutting tools, mechanical components, pump and valve parts, surgical and dental instruments, the food industry as well as for machine parts. As a martensitic steel it can be hardened to a high level to provide good wear resistance and a long lasting cutting edge. Care should be taken when exposing the material to environments with chlorides and extreme pH levels.

Is the 420RM a stainless steel?

Yes, with a mass fraction of 15.5 - 17.5% of chromium the 420RM is a stainless steel.

Is the 420RM corrosion resistant?

To be classified as corrosion resistant the material grade has to have a minimum of 10.5% of chromium, with a chromium content of 15.5 - 17.5% of chromium this means the 420RM is a corrosion resistant steel. 

General corrosion

In moderately corrosive environments, with low chloride ion concentrations, the 420RM shows good corrosion resistance, this is increased further with the addition of molybdenum but without further protection against corrosion, e.g. cathodic protection, this steel is not suitable for sea water. Due to its high chromium content this stainless steel grade does offer a corrosion resistance to organic and citric acids. Corrosion resistance can further be enhanced if the surface is finely ground or polished.

Is  the 420RM stainless steel magnetizable?

As a martensitic stainless steel the 420RM can be magnetized which may be advantageous for some applications and is suitable for magnetic clamping.

Heat treatment of stainless steel 420RM

Annealing 420RM stainless steel

Heat the material uniformly to a temperature of 138 - 1508°F (750 - 820°C) and hold for 2 to 4 hours. Following this, finish the process by a slow cooling in the furnace or in air.

Stress relieving 420RM stainless steel

Uniformly heat the parts to a temperature of 1112 - 1202°F (600 - 650°C), follow this with a cooling in the furnace.

Hardening stainless steel 420RM

Slowly and uniformly heat the work pieces to a temperature of 1796 - 1940°F (980 - 1060°C) hold and quench.

Quenching stainless steel 420RM

The chosen quenching medium depends on the complexity and size of the workpiece to avoid warping and/or cracking.

• Air
• Oil
• Salt- or polymer bath

Tempering stainless steel 420RM

Heat the material to a tempering range of 1202 - 1382°F (650 - 750°C) then cool in air.

Care must be taken to temper the material as soon as possible after hardening to avoid possible cracking. 

Dimensional changes for the 420RM stainless steel

Like all metals the 420 RM does expand and contract during heating and cooling as well as when stress relieving or during phase changes. Care has to be taken during those processes that the material does not distort.

Surface treatment for stainless steel 420RM

Though already corrosion resistant the 420RM can be surface treated to enhance the corrosion resistance further or enhance wear resistance for longer tool live as well as for aesthetic appeal. Following are a few examples of surface treatments for the 420RM stainless steel.

Passivation of the 420RM stainless steel

This process removes free iron from the surface with nitric and citric acids. It enhances the base material by overlaying it with a thin layer of chromium oxide.

Nitriding the 420 RM stainless steel

Nitriding introduces nitrogen into the surface of the material which creates a harder surface (case) and enhances wear resistance and fatigue life.

Physical Vapor Deposition/Chemical Vapor Deposition coating the 420RM

PVD and CVP deposit a thin film over the surface of the material which can enhance wear resistance and corrosion resistance.

Carburizing 420RM stainless steel

To promote a harder surface and improve wear resistance this process introduces carbon into the surface of the 420RM.

Black oxide coating, brushing and polishing

Black oxide coating leaves the material with a non-reflective, matt black finish which can add a slight corrosion resistance.

Brushing and polishing will leave a satin finish which is, like black oxide coating, aesthetically appealing but may also reduce product adhesion to the surface. By polishing, minute groves might be smoothed out which will give contaminants less room to attach and create a starting point to corrosion for example. 

Machinability of the 420RM stainless steel

Forging stainless steel 420RM

Slowly preheat the parts to a temperature of 1472°F (800°C), then more rapidly heat to 2108 - 2156°F (1150 - 1180°C). Forging is done in the temperature range of 2156 - 1742°F (1180 - 950°C), do not let the temperature drop below 1742°F (950°C). Cool the parts in the furnace, dry ash or similar materials promoting slow cooling.

Welding stainless steel 420RM

420RM is not normally welded. If welding is necessary the steel should be preheated to a temperature range of 572 - 752°F (300 - 400°C). Since a large proportion of non-tempered martensite form in the heat affected zones, it is necessary to temper the material after. As during the tempering treatment, the martensite of the rest of the workpieces are being over-tempered, it is advisable to follow the hardening and tempering processes as stated above.

As in the tempering step, it is important to commence with the heat treatment as close as possible to finishing the welding process to reduce the possibility of cracking.

Wear resistance of stainless steel 420RM

The wear resistance for the 420RM stainless steel is 3 on a scale where 1 is low and 6 is high.

Tensile strength for the stainless steel 420RM

Stainless steel 420RM has a tensile strength of approx. 159.5 KSI on delivery (0.145 KSI = 1MPa). In order to reach this value, a tensile test is performed to show how much force is needed to stretch or elongate a sample before it breaks.

Yield strength 420RM stainless steel

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. 

For stainless steel 420RM the yield strength is approx. 79.8 KSI (500 MPa).

Working hardness for 420RM stainless steel

The working hardness for the AISI 420 stainless steel is in a range of 277 - 456 BHN (30 - 48 HRC).

Specific heat capacity of 420RM stainless steel

The specific heat capacity of the 420 stainless steel at room temperature is at 0.43 J/g-°C (0.103 BTU/lb-°F). This value shows how much heat is needed  to heat 1lb of material by 1 Fahrenheit.

Continuous TTT-diagram for stainless steel 420RM

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.

Isothermal TTT-diagram for stainless steel 420RM

The following diagram shows the structural changes at micro levels over time at a constant temperature. It shows at what temperatures the different phases, e.g., perlite, martensite and bainite start to form.

420RM stainless steel properties

Steel Density for 420RM stainless steel

Typically the density of stainless steel 420 RM is 0.278 lb/in3 (7.7g/cm3) at room temperature.

Thermal conductivity of stainless steel 420RM

The heat conductivity for the 420RM stainless steel is at 29 W/(m*K) (201 BTU/(h-ft*°F)) at room temperature. 

Thermal expansion coefficient

The following table shows expansion or contraction at various temperatures, which may be very important for high temperature works or when working with high temperature changes.

Specific electrical resistivity of stainless steel 420RM

You can find the temperature dependent material constant (Resistivity) in the following table. The electrical conductivity is the reciprocal value of the specific resistance.

Is the 420RM stainless steel a knife steel?

The 420RM has good corrosion resistance, high hardness after heat treatment and good wear resistance and toughness. These properties will give a knife a sharp edge with good edge retention and chipping or breaking resistance. The 420RM can be used for knife making due to those well balanced properties.

Conclusion

With a good balance between corrosion resistance, performance, mechanical properties and durability the 420RM stainless steel is a good choice when a high hardness, toughness and wear resistance is necessary for knives or machine parts for example. Environment should be considered as the 420RM may show limitations to its corrosion resistance in chlorides and extreme pH levels.

Datasheet for stainless steel 420RM

As a steel supplier we provide you with the datasheet for stainless steel 420RM in PDF format.

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