Expert columns

Previously, I have written about some of the energy applications Sandvik is involved in, but the overall objective for our work at strategic research is to continue the materials evolution. This, to a large extent, can be achieved by continuing to develop new problem-solving alloys.

Some months ago, I read in the newspaper that Shell was planning to invest 14 billion USD to build an export terminal for Liquid Natural Gas (LNG) in British Columbia, Canada. The reason that this project caught my eye was due to the comment made by one of the panelists in a discussion forum at the Singapore International Energy Week in 2017. He talked about the synergies of using natural gas today, with a shift to using hydrogen for the same applications in the future.

If the question were asked "what is Sandvik Materials Technology (SMT) best known for?", a large proportion of people would answer "Duplex Stainless Steels". The world of stainless steel tends not to generate too much public controversy, but I recall an ongoing argument back in the early 90’s in the letters pages of Stainless Steel World about duplex stainless steels and the role Sandvik 3RE60 played in duplex development.

From the few examples mentioned in this column, new methods of generating electricity will also require new materials solutions to deal with the environments they will work in.

When plastically deformed, traditional austenitic stainless steels with 18% chromium and 8% nickel undergo a martensitic phase transformation. This is due to the fact that the austenite phase is not thermodynamically stable at room temperature. As seen in the phase diagram in Fig 1 the phases expected at room temperature (in true equilibrium) are austenite (γ), ferrite (α) and carbides.

Owing to the unique combination of properties of stainless alloys they are indispensable in modern medicine. The required materials properties include good corrosions resistance in body fluids, biocompatibility, good strength to-weight ratio, fatigue resistance and a low magnetic susceptibility. The term biocompatibility is not well-defined but can be described in simple terms as the ability to perform adequately in a specific situation in the human body.

An Achilles heel of austenitic stainless steels is the susceptibility to stress corrosion cracking (SCC). However, when the nickel concentration exceeds about 20% considerable improvement in the resistance to stress corrosion is observed (Fig 1). Nickel-rich austenitic stainless steels (NiASS), therefore, deserve to be treated as an own family. In fact, for nickel concentrations beyond about 30% the resistance to stress corrosion is comparable to that of duplex and ferritic stainless steels.

An Achilles heel of austenitic stainless steels is the susceptibility to stress corrosion cracking (SCC). However, when the nickel concentration exceeds about 20% considerable improvement in the resistance to stress corrosion is observed (Fig 1). Nickel-rich austenitic stainless steels (NiASS), therefore, deserve to be treated as an own family. In fact, for nickel concentrations beyond about 30% the resistance to stress corrosion is comparable to that of duplex and ferritic stainless steels.

Martensite, the hardest structural component in steels, is responsible for the high hardness in many sharp edge tools. The formation of martensite is a remarkable phenomenon in materials science and smiths have known for at least 3000 years how to make use of it to produce implements such as knives, axes and ploughs. Therefore, martensite has played a crucial role in the development of our civilization.

Number three in a series of eight columns throughout 2017 on the topic of the seven families of stainless steels; their characteristics, complementary properties and the wide variety of applications from the smallest of items destined for the human body to large scale constructions in the process industry. This month features duplex stainless steels which combine the properties of austenite with the properties of ferrite.