AISI 420 Stainless Steel Pipe Tubing Description:

ASTM A276 420 1.4021 Stainless Steel Type 420 Stainless Steel provides both outstanding corrosion resistance and exceptional wear resistance. To obtain the best possible strength and wear resistance, oil quenching alloy 420 at a temperature between 1800° F and 1950° F. Alloy 420 Stainless Steel is commonly used in dental and surgical instruments, cutlery, plastics molds, pump shafts, steel balls, and numerous hand tool.

Because of its air hardening properties, type 420 Stainless Steel is not often welded, although, it is possible. When welded with stainless steel type 420, preheat the steel to a temperature between 300° F and 400° F. After welding, temper the work piece at temperature for two hours. When hot working, it is recommended to gradually raise the temperature to 1400° F and then gradually raise the temperature to anywhere from 2000° F to 2200° F. While working, avoid letting the work temperature drop below 1600° F by frequently reheating the steel. To prevent cracking, furnace cool the work piece slowly after working. Any extreme cold forming will cause alloy 420 Stainless Steel to crack, but it can endure minor cold work.

Grade 420 stainless steel is a higher carbon version of 410; like most non-stainless steels it can be hardened by heat treatment. It contains a minimum of 12 per cent chromium, just sufficient to give corrosion resistance properties. It has good ductility in the annealed condition but is capable of being hardened up to Rockwell Hardness 50HRC, the highest hardness of the 12 percent chromium grade. Best corrosion resistance is when the metal is hardened and surface ground or polished.
Related grades to 420 are high carbon high hardness martensitic stainless steel such as the 440 series and also variations to 420 containing molybdenum (for increased corrosion resistance), sulphur (for increased machinability) or vanadium (for higher hardness). A slightly higher carbon version of 420 is the non-standard grade 420C.
Martensitic stainless steel are optimised for high hardness, and other properties are to some degree compromised. Fabrication must be by methods that allow for poor weldability and usually also allow for a final harden and temper heat treatment. Corrosion resistance is lower than the common austenitic grades, and their useful operating temperature range is limited by their loss of ductility at sub-zero temperatures and loss of strength by over-tempering at elevated temperatures.

These properties are specified for bar product in ASTM A276. Similar but not necessarily identical properties are specified for other products such as stainless plate and forging in their respective specifications.

420 Stainless Steel Chemical Composition:

Table 1. Chemical Composition for ASTM A276 420 stainless steel

Grade	–	C	Mn	Si	P	S	Cr	Mo	Ni	N
420	min. max.	0.15 –	– 1.00	– 1.00	– 0.040	– 0.030	12.0 14.0	–	–	–

ASTM A176: Standard Specification for Stainless and Heat-Resisting Chromium Steel Plate, Sheet, and Strip

ASTM A276: Standard Specification for Stainless Steel Bars and Shapes

ASTM A959: Standard Guide for Specifying Harmonized Standard Grade Compositions for Wrought Stainless Steel

420 Stainless Steel Mechanical Properties:

Typical mechanical properties for grade 420 stainless steels are given in table 2.
Table 2.Mechanical properties of 420 grade stainless steel

Tempering Temperature (°C)	Tensile Strength (MPa)	Yield Strength0.2% Proof (MPa)	Elongation (% in 50mm)	Hardness Brinell (HB)	Impact Charpy V (J)
Annealed *	655	345	25	241 max	–
204	1600	1360	12	444	20
316	1580	1365	14	444	19
427	1620	1420	10	461	#
538	1305	1095	15	375	#
593	1035	810	18	302	22
650	895	680	20	262	42

420 Stainless Steel Physical Properties:

Typical physical properties for annealed grade 420 stainless steel are given in table 3.
Table 3. Physical properties of 420 grade stainless steel in the annealed condition

Grade	Density (kg/m³)	Elastic Modulus (GPa)	Mean Coefficient of Thermal Expansion(mm/m/°C)			Thermal Conductivity(W/m.K)		Specific Heat 0-100°C(J/kg.K)	Electrical Resistivity (nW.m)
			0-100°C	0-315°C	0-538°C	at 100°C	at 500°C
420	7750	200	10.3	10.8	11.7	24.9	–	460	550

420 Stainless Steel Grade Specification Comparison:

Approximate grade comparisons for 420 stainless steels are given in table 4.
Table 4. Grade specifications for 420 grade stainless steel

Grade	UNS	BS	BS	EN	EN	Swedish	Japanese
–	No.		EN		Name	SS	JIS
420	S42000	420S37	56C	1.4021	X20Cr13	2303	SUS 420J1

420 Stainless Steel Possible Alternative Grades:

Possible alternative grades to grade 420 stainless steels are given in table 5.
Table 5. Possible alternative grades to 420 grade stainless steel

Grade	Why it might be chosen instead of 420
410	Only a lower hardened strength is needed.
416	High machinability is required, and the lower hardened strength and lower corrosion resistance of 416 is acceptable.
440C	A higher hardened strength or hardness than can be obtained from 420 is needed.
“specials”	Variations of 420 are available to special order. These offer higher hardness, corrosion resistance and machinability for particular applications.

420 Stainless Steel Corrosion Resistance:

Grade 420 has good resistance in the hardened condition to the atmosphere, foods, fresh water and mild alkalies or acids. Corrosion resistance is lower in the annealed condition.
Performance is best with a smooth surface finish. Less corrosion resistant than the austenitic grades and also less than 17% chromium ferritic alloys such as Grade 430; 420 also has slightly lower resistance than grade 410.
This grade is commonly used for cutlery – particularly blades of table knives and for some carving knives and similar. The corrosion resistance is sufficient to resist attack by food and normal washing methods, but prolonged contact with unwashed food residues can result in pitting.

420 Stainless Steel Heat Resistance:

Not recommended for use in temperatures above the relevant tempering temperature, because of reduction in mechanical properties. The scaling temperature is approximately 650°C.

420 Stainless Steel Heat Treatment

Annealing – Full anneal – 840-900°C, slow furnace cool to 600°C and then air cool.
Process Anneal – 735-785°C and air cool.
Hardening – Heat to 980-1035°C, followed by quenching in oil or air. Oil quenching is necessary for heavy sections. Temper at 150-370°C to obtain a wide variety of hardness values and mechanical properties as indicated in the accompanying table.
The tempering range 425-600°C should be avoided.

420 Stainless Steel Welding

Pre-heat to 150-320°C and post-heat at 610-760°C. Grade 420 coated welding rods are recommended for high strength joints, where a post-weld hardening and tempering heat treatment is to be carried out.
If parts are to be used in the “as welded” condition, a ductile joint can be achieved by using Grade 309 filler rod. AS 1554.6 pre-qualifies welding of 420 with Grade 309 rods or electrodes.

420 Stainless Steel Machining

In the annealed condition this grade is relatively easily machined, but if hardened to above 30HRC machining becomes more difficult. Free machining grade 416 is a very readily machined alternative.

420 Stainless Steel Applications:

Typical applications include:
• Cutlery
• Knife Blades
• Surgical Instruments
• Needle Valves

• Shear Blades