Manufacturers of high-performance components in demanding mechanical power transmission and mining applications are facing the challenge of scarcity for remelted steel. Jonas Osberg explains how ultra-clean air-melted steel is a possible alternative material for bearings, rollers and gears
Recent changes in the supply chain for remelted steel mean that buyers are now facing long lead times for orders. Waiting times can be as long as two years with no flexibility to vary order quantity or dimensions. This presents a risk to production continuity for original equipment manufacturers (OEMs). To overcome this, it may be worth reviewing whether ultra-clean air-melted steel is a suitable alternative.
Traditionally, remelted steel is used to make components that need to face demanding conditions over a long service life. The remelting process produces ultra-clean steel by reducing the number and size of non-metallic inclusions. In turn, this improves fatigue strength because inclusions can act as tiny stress-raisers over many loading cycles. This eventually leads to failure from metal fatigue.
To avoid this, engineers first integrated remelted steel into design specifications 60 years ago – and some of these design standards remain in place today. However, there have been huge improvements in air-melted steel quality over this time.
This creates an opportunity for OEMs to maintain security of supply, shortening lead time and achieving greater flexibility by sourcing an ultra-clean air-melted steel with the same performance of remelted steel. Today’s best air-melted steels can match remelted steels produced under electro-slag remelting (ESR) and even some vacuum arc remelting (VAR) processes. It is not currently possible for air-melting metallurgy to achieve the standard of vacuum induction melted VAR (VIM VAR) steels that are used in aerospace.
The key to switching to an air-melted product is that it needs to have the same cleanness as traditional remelted steels, as well as having tight control over the shape of inclusions. The process of rolling steel into bar tends to elongate the inclusions at the same time as the steel itself.
However, high-performance power transmission components need isotropic performance. This means that they must have the same mechanical and fatigue performance under loading from any axis. This requires inclusions to be approximately spherical in shape – and this is a key feature of our isotropic quality (IQ) steels. This makes them a feasible alternative as remelted steel is becoming harder to source.
Challenging Specifications
The challenge when switching from a remelted steel to a modern, high-quality air-melted alternative is that the former are often enshrined in company and product specifications. By setting minimum standards for materials, these documents act as insurance policies for performance of mechanical systems. Therefore, the requirements in these standards are often set by the end-customer and trickle down the supply chain.
Once a business has gone through the process of evaluating and approving a material, it will only consider alternatives in the face of significant risk or disruption in the market. This is particularly true for safety-critical or performance-critical components.
The availability crunch in remelted steel is a risk that threatens manufacturing continuity. Therefore, it may be worth challenging company standard specifications, especially as air-melt metallurgy has experienced up to 60 years of development since the core of some specifications were first developed.
Even though IQ-Steel has similar properties to remelted products, OEMs need to build their own technical case and challenge customers before they can consider it as a potential replacement.
A starting point for building a case is to review laboratory data on high-performance air-melted steel and review the underlying technical requirements in the company specifications. In our testing, we found close alignment in the hardness and fatigue strength between IQ-Steel and remelted ESR and VAR steels. The most significant difference we found was in visual appearance under the microscope – and this was due to differing microsegregation between samples.
However, OEMs will always need to perform their own testing and evaluation, which is why we can provide samples of material.
Commercial Factors
Having similar performance and a significantly shorter lead time can help to avoid supply chain risk. However, IQ-Steel also provides further commercial advantages.
Depending on the dimensions required, our minimum order quantity (MOQ) is as small as 5-12 tonnes, compared with 20-30 tonnes for remelted steels. In addition, air-melted steel is less costly than remelted steel, which is a nice additional benefit in critical applications where cost is less important than performance.
A further benefit is that ultra-clean air-melted steel will always have a lower carbon footprint than remelted steel. Until the industry completely eliminates emissions from production, the second melting process will always have a bigger environmental impact than a single melt.
Read the technical report ‘Developing a lighter, stronger and cleaner air-melt steel for critical applications’ here
