X5K Steel Springs

Munji, there are numerous forum discussions where people have talked about the new X5K steel coils. No doubt you have found them.

One has to specifically examine why a new type of steel is used in manufacturing.
Primarily, it is about lowering the cost of manufacturing.

If there are some additional advantages to the end-user, they are the only ones mentioned.

It's like the change to high-tensile sheet steel in vehicle bodies, as is pretty much the norm in vehicle construction today.
Thinner steel panels means lighter weight with more strength, so the manufacturers brag about these features.

They conveniently forget to mention the savings to them in freight costs for manufacturing, with less weight needing to be transported to the factory.
They also neglect to mention that HT steel corrodes more rapidly if the steel coating or paint is damaged.
They neglect to mention the thinner steel is more difficult to repair.

As regards the X5K springs, the end-user benefits are lighter unsprung weight, with more suspension travel, due to the thinner coil allowing tighter compression.
There is also the factor that silicon-chrome steel has greater resistance to sagging, as compared to earlier, lower-tensile steel types.

There is another important feature with the thinner, HT silicon-chrome steels - and that is one of improved hardenability due to the thinner material.

X5K is classed as a "micro-alloyed steel". MA steels end up through-hardened, when heat treated - as compared to low-alloy HT "quenched and tempered" steels - which end up with deep-depth hardening, with a softer, but very tough core.

The downsides for HT micro-alloyed steel can be an increased tendency to fracture due to the full-thickness hardening, particularly when severe conditions involving full suspension travel are involved.

Increased corrosion potential is a very real risk to HT steel, if the steel coating is damaged in any way and exposes bare steel.
Corrosion in HT steel will help initiate fractures when the steel is flexing.

The spring manufacturers have no doubt moved over to the X5K steel as an additional method of reducing their manufacturing costs.
Thinner bar means lower freight and storage costs, and easier winding on coil-winding machines.
Thinner bar also takes less heat input to reach the heat level required for heat treatment.

Seeing as the steel is made in Germany, it would suggest that the X5K steel is high quality, and the spring manufacturers have made the move to it, as much for the end-user, as they have for their own cost reduction.

A move to German-sourced steel is one move that has possibly not reduced their actual steel costs very much, if at all (in actual steel cost, and in freight cost) - so one has to have confidence it is a beneficial move.

Below is a link to a patent taken out by the Japanese on silicon-chrome steel for springs. Their spring steel also contains manganese, chrome, vanadium, nickel, boron, molybdenum and niobium - all of which are particularly good in improving steel toughness, strength and heat-treatability.
They carefully outline all the beneficial features of their spring steel, and I see no reason to argue against any of their claims.

Whether the German X5K steel uses nearly identical steel additives in their steel composition, as the Japanese spring steel is not immediately apparent, as I have found no precise composition specifications of the X5K steel - however, it's not unreasonable to assume the Germans have copied the Japanese spring steel as closely as the patent allows, without incurring lawsuits.

Patent for Japanese silicon-chrome spring steel

Micro-alloyed steel - Wikipedia

Cheers, Ron.