Reinforcing water damaged wooden fence posts, will it last, will it be strong enough?

Backgound

On a wooden fence I have several posts that are water damaged at ground level and the fence isn't holding strong anymore. The remainder of the fence is in very good condition.

I believe I can stabilise the fence with the following approach that will be cheaper to do than getting the each of the entire fence poles replaced and cemented in.

Proposed Idea

I am considering using 750mm x 75mm (2.4ft x 0.24ft) galvanised steel retaining wall posts and securing them to the existing wooden posts with galvinsed bolts (100mm x 10mm) with spring washers.

This way the 100mm bolt would be through each fence post, about 300mm (1ft) ( above ground level. 400mm (1.4ft) of the steel would be under ground and cemented in.

Question

Will this approach keep the fence strong enough? Or will the steel + bolt attached to the wood be a weakness point after a short period of time?

Is 300mm (1ft) of steel support above ground, 450mm (1.4ft) below ground enough to support the 2000mm (6.5ft) of fence post + fence above ground.

Costs

The cost of the steel is about $10 more per brand new wooden fence pole, but the effort to attach the steel is less than replacing the entire post.