Judging the quality of a product by its magnetism can be a mistake, especially with so many developments taking place in the world of stainless steel, writes Neil Hargate, business manager – service division at Aperam.
"Magnetic stainless steel for my food preparation counter did you say? No thanks — it’s cheap, poor quality and will rust!”
You’ve probably overheard this type of conversation, or even had this type of conversation, at a catering equipment exhibition or in a buying situation. ‘Bad mouthing’ magnetic stainless steel — which is also known as ferritic stainless steel — in the catering sector has taken place for a considerable time and is sometimes used to criticise another equipment manufacturer’s product as being low grade.
It is worth understanding some basics about why stainless steel can be magnetic and that the property of magnetism has no relationship whatsoever with quality or stainless steel’s ability to resist corrosion. On the contrary, using magnetic ferritic stainless steel can truly add value through lowering cost and, very importantly, stabilising the cost of catering equipment.
Stainless steel has been used in catering environments for many years and it is the reference standard in a professional kitchen. The definition of a steel being stainless and rust resistant is that it must have a minimum of 11% content of chromium.
This level of chromium content enables a chromium oxide layer to form on the surface of steel which protects the steel from the environment and constantly repairs itself — so the steel becomes stainless or corrosion resistant. Regular washing of the surface using non chloride-based cleaners is sufficient to keep the steel stainless and looking like new.
There are in fact two principle types of stainless steel used in catering, both of which contain chromium for corrosion resistance. One of these stainless steels also contains nickel and is generally known as grade 304 austenitic stainless steel. The other, which contains no nickel, is typically known as grade 430 ferritic stainless steel.
Grade 430 ferritic stainless steel is magnetic, as in fact is all of the family of ferritic stainless steels. In fact, grade 430 probably accounts for 60% of the stainless steel used in catering equipment while grade 304 accounts for the balance.
There is a myth in the industry that the content of nickel gives grade 304 austenitic material superior corrosion resistance in a catering environment, but this is not the case because steels are stainless because of their chromium content, not their nickel content.
In a catering environment, nickel content adds no benefit to corrosion resistance — it only adds cost. Being a material which is traded on the London Metal Exchange, Nickel has volatile pricing and in the past four years it has experienced periods when its price has tripled. The expensive and volatile nature of nickel makes 304 austenitic stainless steel more expensive and over time it has a very unstable cost.
So what about magnetism? Well, it is simply the atomic structure that dictates whether stainless steels are magnetic or not. Adding nickel changes the atomic structure, which makes it non magnetic. This atomic structure has no bearing on corrosion resistance. A similar yet striking comparison is graphite and diamond. They are essentially the same materials but with different atomic structures!
Magnetism can, in fact, be a very useful property in catering equipment. Such things as magnetic signs and labels can be attached to equipment — where they can be used for everything from identifying a patient’s meal in a hospital to advertising an establishment’s name. The ability to fix a thermocouple to a piece of equipment, store cooking utensils or close doors are all things which make use of the magnetic properties of ferritic stainless steels
In recent years, magnetic ferritic stainless steels have been developed, which has enabled nickel containing stainless steels like 304 to be replaced.
This has allowed customers to significantly reduce their purchase price of stainless steel and, very importantly, stabilise their cost for the future.
Approximately five years ago, Aperam developed a magnetic ferritic stainless steel focused on replacing the need for expensive 304 grade in the catering sector.
The steel developed is called K41 and provides the necessary level of corrosion resistance and quality to substitute grade 304 for commercial catering equipment.
In terms of cost saving, K41 today gives an average 35% saving in raw material. It has also provided a much more stable cost whereas grade 304 stainless steel has shown 50% movement in raw material cost during 2011. It is worth pointing out that during the production of ferritic stainless steels such as K41, the carbon dioxide emissions are significantly less when compared with austenitic stainless steel such as grade 304. Therefore, ferritic stainless steel like K41 has much better green credentials.
K41 has been well accepted by catering equipment suppliers, with more than 30,000 tonnes being delivered to this sector since 2007. The spread of countries and customers who are now using this grade is wide and covers both Europe and countries which are based further afield.
In terms of equipment, K41 is being used in food preparation tables, storage cupboards, extraction canopies and cooking units and has been a real success.
The cost saving and stable cost benefits of K41 have most recently been taken up by countries outside of the UK, however there is no reason why the same benefits and advantages cannot be successfully used by the UK catering sector.