Tag Archives: Tempcore

QST Atlas

When I joined Allied Steel & Wire, my first involvement was with the Tempcore process, and the qualification trials of the 40mm rebar. Over time I got to investigate the whole size range from 16mm to the upper limit of 40mm, as well as material from trials on higher strength materials, and from time to time, competitor’s material.

Wherever possible, I started to get in the habit of summarising the steel chemistry, quenching parameters, mechanical properties, the hardness profile across the bar diameter, and the corresponding microstructures, which formed part of their individual reports. And then it occurred to me that this set of summarised data could easily be compiled into what became the QST (Quench-and-Self Tempered) Atlas. Two typical examples are shown at the bottom of this blog.

The result of all these efforts ? Preciously little. It didn’t fit in any management-led scheme, it was just a metallurgist collating information of possible use for the future. The first problem was that this was in the days that all information was reported in paper copies, and the hope was that these paper copies were being held in a place where they would be consulted – optimistic ? Probably. It certainly didn’t help that this was not the days of servers, where information could be collated in a suitable format for easy analysis and wide distribution.

On top of that, the report came out when the days of the bar mill were numbered, and as such the Tempcore process was on its way out, together with any information that pertained to it.

Still, I can’t help but think that if AS&W had made better use of its metallurgists, and they were allowed to work closer with the production managers to mark the direction in which developments would lead, then this atlas might have been something that people wanted to use and peruse, with a view of making a better informed use of the Tempcore process. Maybe trials to see if the process could be sped up, or the quench flow rate modified, or the deformation pattern for each stand better understood.

In short, if all those factors had been in place, this could have represented a highlight of my career. As it was, it was all too little, too little – with as little impact as a drop in the ocean.


The Tempcore Process

For the first few years at Allied Steel & Wire, I was the development metallurgist for the Tremorfa Bar Mill, which used an interesting type of process to produce high strength reinforcement bar with the addition of alloying elements such as molybdenum or vanadium. We called it the Quench-and-Self-Tempered (QST) process, although officially its name was the Tempcore process, a process originally developed by the Centre de Recherche Métallurgique (CRM) in Liège.

The way the process works is that after a billet has been hot rolled to the correct diameter rebar it then enters a quenching chamber when still white hot, and high pressure water jets quench the bar from all directions until the outside reaches temperatures below 200°C. When the bar leaves the quenching chamber there is still enough heat left in the centre of the bar for the outside to be reheated to temperature in the order of 400°C, after which ii is allowed to cool down to room temperature on the cooling bed.

What this does to structure of the steel is that the outside turns to martensite, a hard and brittle phase of the iron-carbon diagram, during the quench, and the subsequent reheat or temper phase softens the martensite and makes it more ductile. The resulting microstructure displays various types of bainite near the surface, which gradually grades into a ferrite-pearlite structure in the centre.

My first job was to collect the data for qualification trials on the newly developed 40mm QST bar, something that went without too much of a problem as far as the mechanical properties were concerned. It did, however, run into some issues with end splitting in what had started off as the north end of the billet, where most of non-metallic inclusions congregated. Since the defect confined itself to the very ends of the bar, this turned out not to be of much importance, since an extra crop got rid of that portion of the bar.

I started investigating different types of rebar, of various dimensions and chemistry, which ultimately led to trials on a high strength type of bar which aimed to emulate Macalloy tie bars without the need for expensive alloys (I intend to have this as the topic of another blog). Unfortunately that work only came to fruition after I had left for the Contistretch process, so was not involved in subsequent approval trials.

And then came the moment when the directors of the steel plant and of the rod mill ambushed the third director, and carved up his domain amongst themselves, the bar & section mill going to the steel plant, and Tremorfa Bar Mill to the rod mill. The last I heard of it was that the bar mill was to be closed and its product range produced on the rod mill, which was to be converted into a rod-and-bar mill. Not sure what the reasoning behind it was, and how the modification of the rod mill to handle bars was effected, but presumably something must have been done to achieve the required strength without re-introducing expensive alloys in the chemistry.

All I know is that when you go on the Celsa website, there is no mention of the Tremorfa Bar Mill, and hence the Tempcore process is no longer in use in the UK. Presumably the economics must have dictated this, and presumably if the properties are acceptable, economics dictate which way the production goes.

1989-1999: The Lost Decade

When I left Iscor and South Africa in 1989, I left on a high, professionally speaking. I had been part of the Mossgas team, aimed at building an offshore platform off the coast of Mosselbay, and the steel delivery for that project was complete in my final months with Iscor. But more satisfying was my contribution to the Mossref project, where I had helped concoct the recipe which landed us the contract for the pressure vessel steels to be used in the on-shore refinery bit to the Mossgas project.

Then, back in Britain I soon found a job with Allied Steel & Wire, and even had the luxury to choose them over lesser paid offers with Inco Alloys in Hereford and British Steel in Scunthorpe. But over the next 5 years I never had the satisfaction to feel that I had substantially contributed to the welfare of the company. I did some work towards creating a high-strength Tempcore steel, but never was part of the team when it came to implementing the resulting product in tie bars.

By that time I had already moved to the Contistretch department, where the job was more of a QA nature, writing the QA manual, and trying to keep the various auditors happy. In some way of interest, but not exactly the type of job where there’s any call for your metallurgical skills. I remember a recruiter once stating that he had never managed to place anyone with AS&W, and called them “a company run by accountants, who wouldn’t know what to do with a metallurgist if their life depended on it”. And so it proved in the end. Their ambition to be the cheapest rebar producer in the UK became laughable in the face of cheap Spanish imports, and would have been absolutely nonsensical today when faced with even cheaper Chinese imports.

As mentioned elsewhere I managed to find a job with British Steel Tinplate R&D based in but not part of Welsh Labs. There the job was unsatisfactory for a number of reasons, one of which was that it called more on mechanical rather than metallurgical engineering skills. It also showed that my man management skills where I tried to use my experience in South Africa as a template did not match the work force and their expectations, and this put me off in subsequent jobs from being in charge of and responsible for the performance of other people.

But the main reason for this whole episode being unsatisfactory was that the manager in charge of Tinplate R&D was a bully and a control freak, who made many people leave when they no longer could put up with his antics. This was in the days before emails were widely available, and the fact that we were on a different site from the tinplate works in Trostre and Ebbw Vale made it easy for him to control the information going in and out of the department. And woe befell anyone who dared to go behind his back and talk to people in authority without his permission.

It was only after I had left for Ebbw Vale that I realised how unhappy and stressed I had been, when you never had a feeling of achievement and the best you could hope for was a “phew! we got out of that tight spot intact”. It’s sad that some of the people who work for you have to tell you that “it doesn’t matter what you think, because if it doesn’t match what Dave thinks, then he’ll go over your head and push his opinion through anyway”.

All I can say is: a good thing that the temporary secondment became permanent, because as soon as I was out of the pressure cooker I thought: I should have left ages ago. But how the move to Ebbw Vale became permanent is the subject of a different story.