Definition : 

420 quality stainless steel can be hardened by many heat treatments like high carbon steel. It contains at least 12% chromium (Cr) and this alloy is sufficient for corrosion resistance. It has good softness in annealed condition, but it has the ability to get 50 Rockwell hardness by heat treatment. For best corrosion resistance it must be hardened and gets it surface cleaned or polished. 
Martensitic stainless steels are the most suitable group for high hardness. Its weldability is poor and it usually requires a final hardening and annealing after welding. Its corrosion resistance is lower than austenitic group. The material must be efficient, and not used at subzero degrees (losses softness) and at high temperatures (losses durability). Its malleability in annealed condition is quite good. However, following hardening (especially above 30 HRC), its malleability becomes difficult.

Chemical Composition :

 Corrosion Resistance :

420 quality has a good resistance, in hardened state, to normal weather condition, food, fresh water and low alkali or acid. Its corrosion strength is low in annealed condition. Its performance is high with clean surface. Its corrosion strength is low compared to austenitic qualities. This quality is used to manufacture cutting tools, especially table knives and carving knives etc. Corrosion resistance is sufficient to withstand food waste and normal washing methods, but its long unwashed residues cause pitting.

Heat Resistance :

It intermittently provides good resistance to rusting at temperatures ranging from 1040 to 1150 degrees with air temperature. Continuously, it shows good resistance at 1150 degrees. It has a good resistance to heat stress and periodic temperature. It is usually used in the environments with sulfur dioxide gas.
It is not advisable due to continuous carbide sedimentation at temperatures between 425-860 degrees.

Heat Treating (Annealing) :

Annealing - full annealing - 840-900 degrees, it is slowly lowered to 600 degrees in the oven and then cooled in air temperature. 
Annealing process is 735-785 degrees and air cooling, hardening is heated between 980-1035 degrees, then air or oil with water is given. Oil quenching is necessary for large sections. In order to reach the specified features and hardness level in the table on mechanical features, temperature is set between 150-170 degrees. Heating limit, 425-600 degrees, should be taken into consideration.

Mechanic Features :

Physical Features :

Areas of Use :

• Forks, knives, spoons.
• Knife-edge
• Surgical tools
• Needle valve
• Scissor mouth