Stainless Steel 420
| Chemical Analysis | |
|---|---|
| C | Carbon 0.15 min |
| Mn | Manganese 1.00 max |
| P | Phosphorus 0.040 max |
| S | Sulfur 0.030 max |
| Si | Silicon 1.00 max |
| Cr | Chromium 12.00 – 14.00 |
General Characteristics of Stainless Steel 420
This is another basic hardenable stainless steel, with higher strength, hardness and wear resistance than type 410.
Applications of Stainless Steel 420
This alloy is used for cutlery and surgical instruments, scissors etc., valves, gears, shafts, cams, pivots etc. It may also be used at moderately elevated temperatures for valve parts, springs. It should not be used at sub-zero temperatures where heavy stresses are involved.
Forging Stainless Steel 420
Preheat to 1400/1500ºF (760/815ºC), then heat to 2000/2200ºF (1100/1205ºC) and forge. Ideally forgings should be cooled in a furnace held at 1550ºF (845ºC), but if this is not possible in warm dry lime or ashes. Air cooling after forging may cause cracking. Anneal after forging, but cool to room temperature before annealing. Do not forge below 1650ºF (900ºC).
Heat Treatment
Annealing
For maximum softness heat to 1550/1650ºF (840/900ºC) and cool slowly in furnace, to give an approximate hardness of 179 BHN.
As an intermediate or process anneal, heat to 1350/1450ºF (730/790ºC) and furnace or air cool to give an approximate hardness of 196 BHN.
Hardening
Heat to 1850/1950ºF (1010/1065ºC) and quench in warm oil.
Tempering
For maximum hardness and corrosion resistance, tempering should be carried out between 300/400ºF (150/205ºC) followed by air cooling. This will give a hardness of approximately Rc 52.
To ensure maximum corrosion resistance, this alloy should not be tempered over 800ºF (430ºC).
Machinability
Because of its higher carbon content, type 420 machines somewhat like a high-carbon tool steel, giving tough, stringy chips. Easier machining, if machinability is of prime importance, will be obtained from the free-machining type 420, but at the expense of certain other properties.
Weldability
This air-hardening grade is seldom welded. Satisfactory welds might be obtained by preheating to 300/400ºF (150/205ºC) followed by a 6-8 hour anneal at 1350/1450ºF (730/790ºC) and air cooling. If weld properties are important then a 420 filler rod should be used; if not a 309 filler rod is satisfactory.
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