I would replace the pipe with PVC just because steel (or iron) pipe gets nasty over time, and you have no way of inspecting the inside of the pipe to see how rusty / obstructed it is.

And, this might blow some minds, you can get clear PVC pipe. A little icky for normal sanitary piping around your house, but perfect for a sump pump drain - you can see what is happening inside the pipe... see if it's obstructed, water is flowing, etc.

(regular PVC pipe is white since they use the cheapest filler possible - ground up limestone).

https://www.clearpvcpipe.com/products/schedule-40-clear-pvc-pipe-1-4-in-to-12-in-size-10-ft-lengths

Here's one version of the clear quiet check valve - https://www.sumppumpsdirect.com/Zoeller-30-0041/p14772.html