How can warm steel and wood merge together?

I need to describe the manufacturing of japanese knives. I struggle with the step when the steel blade is put together with the wooden handle.
Here are some pictures from the video <https://www.youtube.com/watch?v=j2L_Ku47afo> (at 6'42"):


[![Merging between warm steel and wood](https://i.stack.imgur.com/RAeDK.png)](https://i.stack.imgur.com/RAeDK.png)


After putting the hot blade inside the handle, you can see that the steel immediately cools down and after hitting the handle with a hammer, the two pieces are merged. I've been told that the welding could not function between two different materials, especially not wood. **Could you please explain me how those two materials merge together in this situation please ?**


Thanks in advance for your answers !


**EDIT:**


1. Sorry if this doesn't seem directly related to chemistry, I was more interested of what happened in the molecular scale than the physic reactions, if you think about a better forum to ask this do not hesitate to tell it to me;
2. For those who can't see the picture or the video, the blacksmith has made a very long, thin end to the steel blade which he has warmed up until it becomes orange and then he puts it inside the wooden handle (which has a drilled hole). After he did this you can see smoke going out the handle, and finally the blacksmith hits the handle with a hammer (in the direction of the length).




A common press fit , no chemistry involved. Most commonly used for files (in US). All my files (old) use this same press fit, I believe newer files have plastic handles. The use of heat to custom shape the hole for the tang is a good modification. A smaller pilot hole can be used because it will be enlarged to the right size by burning. This likely gives a tighter fit compared to a larger round hole


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