Some European swords do show a degree of differential tempering and differential hardening. I don't know what technique they used though. IIRC correctly if you polish some of the swords the same way you do a JP blade, you get hamon-esque patterns:

http://www.archaeologie-online.de/magazin/fundpunkt/forschun...

Also remember that JP swords are a few hundred years more modern than what we typically think of when we think EU swords. However the Vikings had some knowledge of carbon/crucible steel making as early as 9th-10th century:

https://en.wikipedia.org/wiki/Ulfberht_swords

Masamune was like 14th century with the famous Maramasa and Kotestu being 16th century onward.