How do I ask him to try bondage without freaking him out?

I would try to warm the waters a bit. My husband dropped a few hits to like my hand pined down, then he showed me a few pics here and there. and even once showed me a video. by the end I was ready to go.

Slowly ease into it with less intimidating things first. Like bondage tape or a padded/soft material hand cuffs.

get some free handcuffs and let him use it on you

Mention it casually and gauge reaction. Hell, you could even mention something about "50 Shades of Grey" and see his reaction. I finally found out my wife was wanting what I'd been wanting the whole time by subtle hints she mentioned while reading a book similar.

I had mine read 50 shades and we just ordered a BUNCH of bondage toys

Suggest something light like handcuffs or blindfold, and if he's game, do more.

I forced it on him. We got into an argument and he tried going to bed instead of talking to me. So I brought out my bondage straps (which he didn't know I had at the time) and quickly tied him up. Talking definitely turned into something else

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I agree with the previous posters, start with trying something small like a blindfold and soft handcuffs and if he's okay with it then slowly add more. That's how I did it with my partner. I think if I would've started with "hey, why don't we try some bondage?" from the start he might not have been very open minded about the idea.

I think you need to talk about it outside the bedroom first. Then discuss something you want to do, then look at it (pics and stuff), then try it, then evaluate. The last part is really important. Talk about what happened and about what you liked and did not like. Then if you both enjoyed it and want more just repeat the steps. I would not just try it out without talking to him. I would also not suggest 50 shades of grey. Some people like it, I do not. I do not think it is very kink positive and makes it seem wrong, when being kinky is not a problem.