For almost all metals, the key thing is grain and crystalline structure [1]. Different cooling rate create different properties hence why katanas are made with

For almost all metals, the key thing is grain and crystalline structure [1]. Different cooling rate create different properties hence why katanas are made with half of it shielded when quenched. A big part of this (and alloys) is the grain size and the abundance of dislocations in the structure. But I am not entirely sure what the article is suggesting either. I'm not sure if it's lowering the cooling rate to create better grain structure or by increasing the water temperature decreases the microfractures in the grain boundaries (like hydrogen embrittlement). [1] https://www.twi-global.com/technical-knowledge/faqs/faq-what-are-the-microstructural-constituents-austenite-martensite-bainite-pearlite-and-ferrite https://www.twi-global.com/technical-knowledge/faqs/faq-what...