Självlegering/Tolerance of recycled elements
Optimising retained alloy elements in new steel sheet products
Project leader: Margareta Nylén, Corrosion and Metals Research Institute
Introduction
Good environmental practice necessitates the recycling and re-use of all materials as well as the optimal use of raw materials. This project aims to find ways of obtaining the maximum benefit out of the accompanying alloy elements that arise from ores or recycled iron so that these can be retained and used to their best advantage. Swedish iron ores contain significant levels of both vanadium (V) and phosphorus (P) while scrap often contains manganese (Mn), nickel (Ni), chromium (Cr) or molybdenum (Mo). All these elements can be valuable alloys. In current practice, many alloy elements are lost or intentionally removed during steel-making which represents a loss of value and may even result in further environmental problems in disposing of the contaminated by-products.
Goals
General
- Seek and identify advantages from ‘self-alloying'from scrap
- Identify and avoid the problems that can arise from the mixed feed-stock.
- Evaluate the potential of V-microalloyed steels that could be produced via LD converter as a basis for new high strength cold rolled sheets
- Identify and evaluate other products that could be developed by utilising retained elements from ore or scrap
Industrial
To evidence the value of an increased acceptance level for rest elements in final steel products through increased flexibility in the choice of scrap grades and the possibility to use less expensive raw materials for example in the production of steel sheet.
Environmental
To decrease the consumption of vanadin and titan by 44 tons/year and 35 tons/year respectively in the production of carbon steel. To use the high V-P product of project 88031 and to increase the acceptance level for copper in the production of steel sheet.
Work plan
The project will make use of existing knowledge and experience to identify how alloy elements arising from ore or scrap can best be utilised singly or in combination to provide desirable properties in the product materials. The development of new steel products in this way must go hand-in-hand with developments in smelting technology.
Task 1 - Feasibility study
The first stage of the work will be to investigate how the alloy elements that can be retained in steels after re-melting with today's or feasible future processes can be utilised to obtain special user properties. Steel compositions that are not standard today may still provide interesting properties in a cost-effective manner. In effect, one is aiming to convert elements that are perceived as impurities in the scrap into useful alloy elements. Together with process modification where necessary, this will enable special new high performance products to be developed.
Task 2 - New high strength sheet steel based on V alloying
The high vanadium content of Swedish ores means that there is a good potential for recovering this micro alloy element. Vanadium is a powerful strengthening agent, especially when in combination with nitrogen. MEFOS is working, in the frame of the "Steel eco-cycle" project, on a new method for recovering of V from LD slag. The material obtained has a high P content together with V, and a quote V/P around 15-20. Increasing the V/P ratio to 50-100, in order to match today's specifications in steel sheet production may be difficult and costly. However, P is widely used as an addition to certain sheet steels where it improves strength with minimum detriment to formability. Thus it is very important to study the effect of (and the possibility of tolerating) a higher P content in steel sheets micro-alloyed with V. Such a study will probably make possible the use of the product obtained at MEFOS without needing V-P separation.
Steel compositions with respect to V, P and C that can be achieved metallurgical will be laboratory processed by simulated hot rolling and coiling. Different strengthening mechanisms will be investigated including precipitation hardening with VN, dual-phase and back-annealing. In this way the down-stream processing will be optimised with respect to the chemical composition of the steel.
It is unlikely that this type of product could form a major part of steel production in a foreseeable future but on the basis of it becoming a significant niche product with a volume of 100 ktons/year, the value in V-alloy cost alone would amount to 20 MSEK.
There is also an interest (from SSAB) in replacing part of the Nb and Ti which is used today in micro alloyed steels in the range 300-500 MPa with V. Doing that would increase the volume of V calculated here.
Finally, the effect of a higher P content together with V in tool steels, for the same reason as for construction steel, would be of interest to study.
Task 3 - Evaluation of low carbon steel sheets containing Cu and Ni
Based on the results from Task 1 and preliminary studies conducted at KIMAB, low carbon steel sheets containing Cu and Ni were selected for laboratory production and evaluation, including tension tests, light-optical microscopy, texture measurements and chemical analysis. This work, in cooperation with SSAB Tunnplåt, was done as a master thesis work in 2006. It demonstrated the possibility of tolerating higher Cu and Ni contents than in the actual production without deterioration of formability and mechanical properties.
Deliverables for 2004-2008
Planned user deliverables
- Information to the steel-making industry to define the combinations of retained elements that will be acceptable in new product types
- Defined conditions for processing regarding modifications of the process route to avoid problems and to provide optimal properties for the end-user (e.g. strength, corrosion and wear resistance).
- Information to the engineering industry, to demonstrate that these products will meet market requirements and are economically viable.
Planned scientific deliverables
- Contribution to product design rules for optimum re-use of the metal at the end of the product's life.
Deliverables for 2004-2005
R & D activities | Status |
Survey of valuable alloy elements, today often lost in recycling and production | Collaboration with KTH started - to determine possible levels of vanadium that can be retained during steelmaking . RFCS application (SAFS) submitted to extend the scope of the present project |
Proposal for new scrap-based steel product | Use of copper contamination to improve deep-drawability and ageing resistance in cold rolled and annealed sheet steel |
Deliverables for 2006
R & D activities | Status |
Feasibility study
| A literature survey about the opportunities and dangers of using residual elements in steel was carried out, with focus on low carbon low alloyed steels. Visits and discussions were conducted with five Swedish steel producers, to define the problem areas and opportunities concerning the different elements in recycled materials. Both studies were used as a basis for choosing Cu containing low carbon steel sheets for further evaluation. Preliminary version of the reports in June 2006. Publication November 2006. |
Cu and Ni in LC steel sheets
| A master thesis work was carried out. Low carbon steel sheets containing up to 0.3 % Cu and 0.3 % Ni were investigated in a lab.scale in collaboration with SSAB Borlänge. Promising results were obtained, showing that higher levels of residuals may be tolerated in this type of steel. Publication of the master thesis work in November 2006. |
Retained V alloying | A detailed project plan was set up in collaboration with SsAB (Luleå and Borlänge) and MEFOS. The experiments aim among others to demonstrate the possibility of using the semi-product from project 88031 containing high levels of V and P. |
Deliverables for 2007
R & D activities | Status |
Retained V alloying, evaluation A detailed project plan is set up in collaboration with SSAB (Luleå and Borlänge) and MEFOS. The experiments aim among others to demonstrate the possibility of using the semiproduct from project 88031 containing high levels of V and P. Sample production and laboratory testing to be started January 2007.
| Six alloys containing high levels of V and P, simulating the semi-produt fromproject 88031, were cast. Samples were prepared for testing. Laboratory simulation of hot rolling and coiling was done using a compression testing equipment and a furnace. One coiling temperature (500 °C) was chosen from preliminary optimisation tests. Tensile testing specimen were thereafter machined from the tested materials, and tensile tests were performed. Finally, the specimen were prepared metallografically and observed with light optical microscope. No decreasing of the mechanical properties was observed with increasing P halt, which is a promising result.
|
Deliverables for 2008
R & D activities | Status |
| Final report |
Fragmentering
/Shredding
... är en teknik som används för sönderdelning av skrot innan det smälts om till nytt stål. Genom att utveckla tekniken att finfördela skrotet kan variationerna i dess samman-sättning minskas och dess densitet ökas. Detta innebär att stålindustrin vid omsmältning av skrotet kan reducera både sitt elbehov och sina utsläpp av koldioxid.
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Laseranalys
/Laser analysis
... är en teknik som nu utvecklas för snabb bestämning av skrotets metallinnehåll. Stålindustrin väntas här få tillgång till en teknologi som kan komma att reducera behovet av jungfruliga metaller vid användning av skrot för tillverkning av nytt stål.
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Skrotflödet i samhället
/Recycling of steel
... är trots den höga återvinningsgraden föga dokumenterat. Med bättre kunskaper skapas förutsättningar för ökad återvinning och bättre styrning av skrotsorter för optimerad skrot-användning. Stålindustrin får möjlighet att effektivisera sin energianvänd-ning, stora ekonomiska värden tas till vara och miljöbelastningen minskar.
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Ytrening av skrot
/Surface cleaning of scrap
... är en teknik som skall bredda användningen av färg- och metallbelagt skrot som råvara till ett ökat antal stålsorter. För stålindustrin innebär användning av ytrenat och förvärmt skrot att både energi-användning och koldioxidutsläpp kan reduceras. Dessutom kan den avdrivna zinkbeläggningen komma att återanvändas inom zinkindustrin.
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Vanadinutvinning
/Recovery of Vanadium
Det finns låga halter av vanadin i svensk järnmalm. Genom utveckling av metoder för utvinning av vanadinet får en redan exploaterad naturresurs ett ökat miljövärde.
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Ökat metallutbyte vid smältning av stål/New melting processes EAF
... är teoretiskt möjligt genom metallurgisk manipulering under smältförloppet. Målet är att skapa sådana förhållanden att metaller överförs till stålet i stället för till slaggen. Detta innebär minskat behov av jungfruliga metaller, samtidigt som slaggen kan ges nya användnings-områden.
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Återvinning av slagg
/New slag systems EAF
... är tekniskt möjligt genom utveckling av nya metoder för lakning av olika metaller ur slagger, t.ex vanadin, och behandling av slagger så de kan användas som t.ex isoleringsmaterial eller cementråvara. Vissa slagger kan också användas som ny slaggbildare i stålprocessen, vilket minskar behovet av ny kalk. Återvinning av slagg miinskar både behovet av deponering och förbrukningen av nya naturresurser vid ståltillverkningen.
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Bevarande av alla ämnen i skrotet
/Tolerance of recycled elements
... är en teoretisk studie som skall söka klarlägga hur dessa kan nyttjas för att ge den färdiga stålproduktens önskade egenskaper. Om sådan "självlegering" blir praktisk möjlig kan de metalliska ämnen som finns i skrotet, och som normalt avlägsnas i processen, bevaras i det nya stålet. Detta innebär att förlusten av metaller ur stålets kretslopp kan reduceras.
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Nya höghållfasta stålprodukter
/Optimisation of hot rolling
... är ett forskningsprojekt som skall identifiera de processparametrar som vid värmning och valsning har störst inverkan på materialegenskaperna. De nya rönen kan ge stålindustrin möjligheter att med ökad precision framställa nya avancerade stålsorter och samtidigt minska förbrukningen av fossila bränslen.
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Metoder för lättare stålkonstruktioner
/High strength steel structures
...ska för avancerade höghållfasta stål utmynna i att stålets egenskaper kopplas till produkternas användning och återvinning ur ett livscykelperspektiv. Genom denna metodutveckling kan stål-, bygg- och verkstadsindustrin få nya infallsvinklar på användandet av stål som både kan minska behovet av jungfruliga metaller och reducera emissionerna vid såväl tillverkning som användning av produkterna.
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Miljövärderingsanalyser
/Environmental evaluation
I. Methodology for evaluation of environmental impact
...ska påvisa Stålkretsloppets miljövärde med beaktande av ekologiska, tekniska och sociala faktorer. Miljövärderingar ger forskare, industri, användare och samhället i övrigt möjlighet att värdera såväl stålets nytta för miljön som dess belastning på miljön ur ett livscykelperspektiv. En metod som gör miljövärderingar tillgängliga för objektiva beslut.
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II. Conjoint analysis as a decision tool for evaluation of environmental performance of for instance experts and consumers preferences
... tar fram en metod för att mäta olika experters och andra intressenters attityder till och värdering av komplexa miljöfrågor.
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