What Is 420 Stainless Steel? Hardness, Composition and Applications

420 stainless steel (AISI 420, UNS S42000) is a hardenable martensitic stainless steel with a minimum chromium content of about 12 percent. It offers high strength, good polishability and the ability to reach very high hardness, typically up to roughly 50 HRC, after quenching and tempering. Unlike the austenitic 300-series grades it is magnetic in every condition, and it is normally selected where wear resistance and edge-holding ability matter more than maximum corrosion resistance.

What Is 420 Stainless Steel?

420 is the general-purpose martensitic stainless steel. It combines a moderate chromium level of 12 to 14 percent with a comparatively high carbon range of 0.15 to 0.40 percent. The carbon is the key to its behaviour: on heating into the austenite region and then quenching, the structure transforms to hard martensite, and a subsequent tempering treatment trades a small amount of hardness for useful toughness.

Because it is a straight chromium grade without molybdenum or nickel additions, its corrosion resistance is moderate. It performs acceptably in clean atmospheric, fresh water, mild organic and many food-contact environments, but it is not the right choice for chlorides, seawater or hot mineral acids. The grade is fully magnetic, readily machinable in the annealed condition and capable of taking a very fine polish, which is why it dominates the cutlery and instrument sectors.

Equivalent Grades and Standards

420 is one of the most widely standardized stainless steels, and the various national designations are frequently quoted side by side on enquiry documents.

Standard	Equivalent grade
AISI / ASTM	Type 420 (ASTM A276, A182, A240 where applicable)
UNS	S42000
EN / DIN	EN 1.4021, X20Cr13
JIS	SUS420J1 and SUS420J2
GB (China)	20Cr13, formerly designated 2Cr13

The two Japanese variants differ only in carbon level. SUS420J1 sits at the lower end of the carbon range and is easier to machine and tougher, while SUS420J2 carries more carbon and therefore hardens to a higher figure after heat treatment, at the cost of some ductility and weldability. The Chinese grade 20Cr13 corresponds closely to SUS420J1; where higher hardness is required the higher-carbon 30Cr13 grade is used.

Chemical Composition of 420 Stainless Steel

Typical analysis for 420 is given below. Balance of the composition is iron plus residual elements.

Element	Content (%)	Effect
C	0.15 - 0.40	Controls hardness and hardenability
Cr	12.0 - 14.0	Corrosion resistance and hardenability
Mn	1.00 max	Deoxidation
Si	1.00 max	Deoxidation
P	0.04 max	Residual, kept low for toughness
S	0.03 max	Residual, kept low for machinability balance

The rising carbon content improves hardenability and the attainable hardness, but it also consumes chromium in the form of carbides and therefore reduces corrosion resistance relative to austenitic grades such as 304 and 316. It is important to note that 420 contains no molybdenum; claims that molybdenum improves its corrosion resistance are incorrect, and buyers should look for molybdenum-bearing grades such as 316 or 440C where added pitting resistance is genuinely needed.

Mechanical Properties After Hardening and Tempering

Property	Typical value
Tensile strength	700 - 1000 MPa
Yield strength (0.2% offset)	about 500 MPa
Hardness, hardened and tempered	up to 50 HRC
Elongation	about 15%
Magnetic behaviour	Magnetic in all conditions
Hardness, annealed condition	about 235 HBW max

Hardening is carried out by austenitizing in the range of roughly 980 to 1060 degrees C followed by an oil or air quench. Tempering between about 200 and 350 degrees C retains the highest hardness for cutting edges, while tempering near 600 to 650 degrees C produces a tougher, lower-hardness condition suited to shafts, stems and structural parts. Tempering should be avoided in the intermediate range around 400 to 550 degrees C, where a loss of toughness and corrosion resistance is commonly observed.

How 420 Compares with 304, 316 and 440

Feature	420 (Martensitic)	304 / 316 (Austenitic)	440A / 440C
Corrosion resistance	Moderate	Good to excellent	Good to high
Hardness potential	Up to about 50 HRC	Not hardenable by heat treatment	Up to 60 HRC or above
Magnetic	Yes	No	Yes
Weldability	Limited, preheat advisable	Excellent	Poor
Carbon	0.15 - 0.40%	0.08% max	440A about 0.6% to 440C about 1.2%
Typical use	Cutlery, tools, shafts, valves	Kitchenware, tanks, marine hardware	Bearings, premium blades

Against 316, the trade is straightforward: 316 brings outstanding chloride and chemical resistance but stays soft, while 420 brings hardness and wear resistance but only basic corrosion protection. Against 304, 420 offers hardenability and lower cost but gives up weldability and general-purpose corrosion performance. Against 440C, 420 offers easier machining and better toughness in some sections, while 440C wins clearly on ultimate hardness and edge retention.

Typical Applications of 420 Stainless Steel

Cutlery, kitchen knives, scissors and blades that must hold an edge

Surgical and dental instruments, orthopaedic tools and parts requiring repeated disinfection

Valve stems, trim and seats, pump shafts, spindles and fasteners

Plastic moulds, dies, measuring tools and wear-resistant machine parts

Chemical machinery bearings and bushings with light corrosive duty

Decorative and non-food-contact surface hardware that needs a high polish

Frequently Asked Questions

Q: Is 420 stainless steel food safe?
Yes, in normal kitchen use. 420 is widely used for knife blades and cutting tools and is regarded as suitable for food contact, provided it is kept clean and dry. It is not molybdenum-bearing, so it should not be relied on for long contact with salty, acidic or chloride-rich foods where a 316 surface would last longer.

Q: Is 420 stainless steel magnetic?
Yes, it is magnetic in all conditions. Its martensitic crystal structure makes it strongly ferromagnetic whether it is supplied annealed, hardened or tempered, which also makes it easy to identify on site with a magnet.

Q: Can 420 stainless steel be hardened?
Yes. It is austenitized at roughly 980 to 1060 degrees C, quenched in oil or air, and then tempered. Hardness can reach about 50 HRC, and the tempering temperature is selected according to whether maximum edge hardness or greater toughness is required.

Q: Is 420 stainless steel easy to grind and sharpen?
Its main practical quality is that it takes and restores a keen edge easily, which is why it dominates budget and mid-range cutlery. Ceramic honing rods handle it effectively, and it responds well to conventional grinding wheels and belts without excessive loading.

Q: Which is better, 316 or 420 stainless steel?
They solve different problems. Choose 316 for marine, medical or chemical environments where corrosion resistance is the priority. Choose 420 for cutting tools, mechanical parts and components that need high hardness and wear resistance rather than maximum corrosion protection.

Q: Does 420 stainless steel contain molybdenum?
No. Standard 420 is a straight chromium martensitic steel with 12 to 14 percent chromium, 0.15 to 0.40 percent carbon and no deliberate molybdenum addition. Where molybdenum-bearing corrosion resistance is required, a different grade such as 316 or 440C should be selected.