There is actually.. 2 ways:

1. QEMU - but this would be unbearably slow and requires quite a bit of manual tinkering.

2. Exagear Desktop (https://eltechs.com/product/exagear-desktop/) which automates the process and runs a lot faster. It's not open source, but it does work.

Either way will allow you to run a x86 version of Linux virtually in Raspbian (or any other Raspberry Pi Linux based OS). From there onwards it's a simple matter of installing steam.

According to Legend one should be able to acchieve between Pentium III and Pentium IV speeds on the Raspberry Pi using Exagear.