SHIBATA : Thank you very much for your time today.
I am going to ask you Dr. ASAKURA about “Nano Powder Metal”, a popular steel material of MIZUTANI SCISSORS. To start the interview with an honest question, why does “Nano Powder Metal” cut hair so well compare with another?

ASAKURA：Well. Common cutlery and stationery scissors are actually made of extremely soft steel with its hardness HV300~HV350 (Vickers Hardness, a unit expresses the hardness of substances). “Nano Powder Metal” has HV700~HV750 besides the steel materials used for normal haircut scissors are somewhere around HV690. In this comparison, the hardness of “Nano Powder Metal” is double which is extremely hard. Its strong metallographic microstructure prevent to be nicked edge being cutting.
I don’t know if people think hair is soft but in reality, hardness of hair is quite hard, is same HV as φ100μ=0.1mm copper wire therefore a nicked edge occasionally be made with normal haircut scissors. It can be said that hairstylist and barber cut hard substance everyday.
Hard but not fragile “Nano Powder Metal” is treated by precipitation hardening that precipitates(*) carbides and increases hardness. Uniformed and fine precipitates within the microstructure produced through the process which gives long life to scissors with outstanding durability doesn’t allow nicked edge.

SHIBATA : Normally, sharp cutting edge with hard material occasionally makes nicked edge, doesn’t it?

ASAKURA : That is true.

SHIBATA : I see. The uniformed and fine precipitates allow to apply further sharp cutting edge angle for scissors.

ASAKURA : That’s right. Normally, precipitates allow to occur big protrusions however, uniformed and fine precipitates of “Nano Powder Metal” suppresses the protrusions.

SHIBATA : How it can be identified? by microscope?

ASAKURA : Yes, you can see it by microscope. Such protrusions often obstruct to apply sharp cutting edge angle.

SHIBATA : How does “Nano Powder Metal” scissors secure its hardness even though applying sharp cutting edge makes the blade thinner?

ASAKURA : It is because of using hard fundamental material and apply the best appropriated heat treatment. Theoretically, “hard materials are easily chipped”. I guess it is easy to understand glass breaks into pieces with stress. Why it happens, because of the hardness. Soft materials absorb impact and just will be dented.
The initial secret is “hardness”. However, just existing precipitates has no advantages. Existing the uniformed and fine precipitates within the microstructure ease stress and achieve well cutting and less nicked edge.
Creating precipitates requires appropriated heat treatment. Also, the composition of the microstructure too. The important thing is the proportion of ingredients that support the base of the scissors.
This is the accumulation of expertise and technical know-how of MIZUTANI Scissors, so I can’t disclose it openly, but MIZUTANI Scissors does use these materials to make scissors. It’s truly an amazing collection of technology.
 
*Precipitate: The phase has different crystal structure from the matrix phase (i.e. a carbide)