Final Report Summary - SINT-NAS (Sintering Behavior in Steels containing New Alloying Systems)
SINT-NAS is a research project aimed to define the optimum conditions for processing advanced steel compositions by the Powder Metallurgy (PM) route.
Powder Metallurgy is a cost-effective process which allows manufacturing near net-shape metallic products by die pressing metal powder into the desired shape and then consolidating the material by sintering at elevated temperatures. Compared to equivalent manufacturing techniques, powder metallurgy presents the advantage of being a Sustainable Manufacturing Process that provides an efficient use of the raw material (around 98% material-utilization rate), reduces the number of steps needed to produce a part, lowers the average energy consumption on each step, and also reduces the overall gas emissions during the process. Structural ferrous parts represent more than 80% of the total European PM parts production (around 228 ktonnes), and approximately 70-85% of these ferrous parts are consumed by the automotive industry. The inherent porosity of the PM steel components (typically around 10%) is frequently regarded as detrimental. However, for the automotive sector, it can be turned out into an advantage because it can provide a significant weight reduction. Considering that some of the most important applications of PM are found in the heaviest parts of the vehicles (e.g. the engine and the transmission box), an expansion in the use of PM parts can bring a significantly positive effect for the environment.
The low environmental impact of the PM process and its potential for increasing fuel efficiency (e.g. by reducing the engine weight) are the driving forces for the development of this technology. But the growth of the PM-steels usage -particularly in the automotive sector- has nowadays increasingly demanding requirements, the most critical ones being to provide: high cost effectiveness of the part compared to competing technologies, high level of material performance, as well as very close dimensional tolerances.
The advances needed to achieve simultaneously these three requirements can be made by stimulating the research on innovative alloying systems that allow a lower-cost production combined with the achievement of a higher level of properties. The need for alloying alternatives is also motivated by the high volatility in the price of the traditional alloying elements used in PM (Cu, Ni and Mo), the recycling problems resulting from the use of Cu and the fact that fine Ni powders have recently been regarded as carcinogenic.
Cheaper and more efficient alloying elements are Cr, Mn and Si, widely used in the production of wrought steel parts (the main competitor of PM). However, these elements present much higher affinity for oxygen than the traditional Cu, Ni and Mo, which is a very important limitation for the PM technology since the high specific surface area available in the powder particles makes them more reactive in contact with the surrounding atmosphere.
Here, the master alloy (MA) concept provides many advantages. A master alloy is a powder that contains all of the alloying elements in a combined form and is designed to be mixed in small amounts with the base iron powder in such way that the final composition of the steel is achieved after sintering. The combination of oxygen sensitive alloying elements with other elements with less oxygen affinity (such as Fe) provides protection against oxidation, the compressibility of the base powder is maintained, and the distribution of alloying elements can be promoted by designing the composition of the master alloy to form a liquid phase during sintering.
The main objective of SINT-NAS is to define the optimum conditions for processing Mn-Si sintered steels through the master alloy route, providing enough experimental data to show the potential robustness of the final product/process. The achievement of this main goal was undertaken by successively addressing three partial objectives
Objective 1: Identify the oxidation/reduction processes in different atmospheres: critical temperatures, reducing/oxidizing agents, reduction/oxidation reactions (thermodynamic and kinetic viability).
Objective 2: Identify the optimal conditions for sintering: maximization of mechanical properties and minimization of production costs.
Objective 3: Evaluate the product robustness and provide sintering guidelines
The fulfillment of the project was addressed by successively undertaking three Work Packages (WP): WP1, WP2 and WP3. A fourth work package WP4 was devoted to the Dissemination Strategy and was carried out during the whole extension of the project.
Work Package 1 (WP1): Identification of Oxidation/Reduction Mechanisms
Task 1.1: Materials Selection
Task 1.2 Evaluation of the effect of the master alloy composition
Task 1.3 Evaluation of the effect of the base powder composition
Task 1.4 Evaluation of the effect of the delubrication process
Task 1.5 Summarize reactions, study the kinetic and thermodynamic viability and identify the possible cross effects
Work Package 2 (WP2): Optimization of Sintering Conditions
Task 2.1: Selection of Materials and Sintering Conditions
Task 2.2: Effect of Sintering Conditions on Mechanical Properties
Task 2.3: Effect of Sintering Conditions on Densification and Dimensional control
Task 2.4: Summarize, compare and provide global conclusions
Work Package 3 (WP3): Evaluation of the robustness in the final product
Task 3.1: Define Sintering Conditions and produce different batches
Task 3.2: Evaluate Mechanical and Physical Properties
Task 3.3: Evaluate the sensitivity of the final product to sintering conditions
Work Package 4 (WP4): Dissemination strategy
Task 4.1: Exploitation Plan
Task 4.2: Dissemination Activities
SINT-NAS represents an important step-forward for implementing the use of master alloys containing novel alloying elements (such as Cr, Mn and Si) in sintered steels, particularly due to the following outcomes from the project:
- An insight on the chemistry of the sintering process. The chemical reactions occurring during sintering have been traditionally ignored because the alloying elements used (usually Cu, Ni, Mo) have an oxygen-affinity similar to that of iron. Here., the peculiarities of such chemical phenomena when considering the use of oxygen-sensitive elements such as Cr, Mn and Si have been thoroughly assessed and are critical for identifying the sintering conditions needed to successfully sinter these "tricky" materials
- It has been found that the particular chemical composition of the master alloy plays an important role, and therefore the optimum sintering conditions depend on the specific master alloy composition used. Some of the technological parameters that can be adapted to optimize the final properties of steels containing Fe-Mn-Si-(Cr) master alloys are: delubrication cycles, heating rates, composition of the atmosphere and sintering temperature.
- One of the main advantages of using master alloys is the possibility of designing their composition to form a liquid phase that enhances the distribution of the alloying elements and the sintering mechanisms. In this situation, the properties of the liquid-solid-atmosphere interactions are of critical importance, in particular: the character of the liquid/solid interaction (dissolutive or not dissolutive) and the presence of oxygen sensitive alloying elements determine the dimensional changes and the microstructural evolution.
- The use of novel atomization techniques provide a very favorable scenario for the use of master alloy powders. Master alloy powders produced by Ultra High Pressure water atomization present very suitable morphologies, oxygen contents and particle sizes. The properties of steels containing such master alloys are similar or better than those obtained with commercially available powders.
Besides, SINT-NAS has an impact on several aspects that will directly contribute to European excellence and competitiveness:
• Contributing in the creation of a Greener Europe: PM offers more effective use of the material (more than 98% material utilization rate), less energy consumption per part-produced, fewer numbers of steps in the production, and also an overall reduction in CO emissions. Increasing the amount of PM parts in the automobile would not only offer a reduction in costs, but would also make the way towards more sustainable manufacturing practices.
• Promoting a Smarter Economy. The possibility of reinforcing the competitiveness of the Powder Metallurgy Industry in Europe through the optimization of process and costs aimed in this research project is an excellent example of how the “development of knowledge” can be the most powerful tool for pushing up the European Economy.
• Promoting Academia-Industry partnerships and Technology Transfer. The studies carried out in these project always considered the need to meet the industrial needs. The results from the project promoted a high interest from the industry and the transference of knowledge to the European industries has been very successful.
• Helping to increase the presence of women in positions of high responsibility in specific areas with almost exclusively masculine participation. This fellowship provided the female applicant with a unique scientific profile in the Powder Metallurgy field, where there is an enormous lack in feminine representation.
More information about SINT-NAS can be found at the webpage: https://www.cta.tuwien.ac.at/division_chemical_technologies/powdermetallurgy/sint_nas/
Powder Metallurgy is a cost-effective process which allows manufacturing near net-shape metallic products by die pressing metal powder into the desired shape and then consolidating the material by sintering at elevated temperatures. Compared to equivalent manufacturing techniques, powder metallurgy presents the advantage of being a Sustainable Manufacturing Process that provides an efficient use of the raw material (around 98% material-utilization rate), reduces the number of steps needed to produce a part, lowers the average energy consumption on each step, and also reduces the overall gas emissions during the process. Structural ferrous parts represent more than 80% of the total European PM parts production (around 228 ktonnes), and approximately 70-85% of these ferrous parts are consumed by the automotive industry. The inherent porosity of the PM steel components (typically around 10%) is frequently regarded as detrimental. However, for the automotive sector, it can be turned out into an advantage because it can provide a significant weight reduction. Considering that some of the most important applications of PM are found in the heaviest parts of the vehicles (e.g. the engine and the transmission box), an expansion in the use of PM parts can bring a significantly positive effect for the environment.
The low environmental impact of the PM process and its potential for increasing fuel efficiency (e.g. by reducing the engine weight) are the driving forces for the development of this technology. But the growth of the PM-steels usage -particularly in the automotive sector- has nowadays increasingly demanding requirements, the most critical ones being to provide: high cost effectiveness of the part compared to competing technologies, high level of material performance, as well as very close dimensional tolerances.
The advances needed to achieve simultaneously these three requirements can be made by stimulating the research on innovative alloying systems that allow a lower-cost production combined with the achievement of a higher level of properties. The need for alloying alternatives is also motivated by the high volatility in the price of the traditional alloying elements used in PM (Cu, Ni and Mo), the recycling problems resulting from the use of Cu and the fact that fine Ni powders have recently been regarded as carcinogenic.
Cheaper and more efficient alloying elements are Cr, Mn and Si, widely used in the production of wrought steel parts (the main competitor of PM). However, these elements present much higher affinity for oxygen than the traditional Cu, Ni and Mo, which is a very important limitation for the PM technology since the high specific surface area available in the powder particles makes them more reactive in contact with the surrounding atmosphere.
Here, the master alloy (MA) concept provides many advantages. A master alloy is a powder that contains all of the alloying elements in a combined form and is designed to be mixed in small amounts with the base iron powder in such way that the final composition of the steel is achieved after sintering. The combination of oxygen sensitive alloying elements with other elements with less oxygen affinity (such as Fe) provides protection against oxidation, the compressibility of the base powder is maintained, and the distribution of alloying elements can be promoted by designing the composition of the master alloy to form a liquid phase during sintering.
The main objective of SINT-NAS is to define the optimum conditions for processing Mn-Si sintered steels through the master alloy route, providing enough experimental data to show the potential robustness of the final product/process. The achievement of this main goal was undertaken by successively addressing three partial objectives
Objective 1: Identify the oxidation/reduction processes in different atmospheres: critical temperatures, reducing/oxidizing agents, reduction/oxidation reactions (thermodynamic and kinetic viability).
Objective 2: Identify the optimal conditions for sintering: maximization of mechanical properties and minimization of production costs.
Objective 3: Evaluate the product robustness and provide sintering guidelines
The fulfillment of the project was addressed by successively undertaking three Work Packages (WP): WP1, WP2 and WP3. A fourth work package WP4 was devoted to the Dissemination Strategy and was carried out during the whole extension of the project.
Work Package 1 (WP1): Identification of Oxidation/Reduction Mechanisms
Task 1.1: Materials Selection
Task 1.2 Evaluation of the effect of the master alloy composition
Task 1.3 Evaluation of the effect of the base powder composition
Task 1.4 Evaluation of the effect of the delubrication process
Task 1.5 Summarize reactions, study the kinetic and thermodynamic viability and identify the possible cross effects
Work Package 2 (WP2): Optimization of Sintering Conditions
Task 2.1: Selection of Materials and Sintering Conditions
Task 2.2: Effect of Sintering Conditions on Mechanical Properties
Task 2.3: Effect of Sintering Conditions on Densification and Dimensional control
Task 2.4: Summarize, compare and provide global conclusions
Work Package 3 (WP3): Evaluation of the robustness in the final product
Task 3.1: Define Sintering Conditions and produce different batches
Task 3.2: Evaluate Mechanical and Physical Properties
Task 3.3: Evaluate the sensitivity of the final product to sintering conditions
Work Package 4 (WP4): Dissemination strategy
Task 4.1: Exploitation Plan
Task 4.2: Dissemination Activities
SINT-NAS represents an important step-forward for implementing the use of master alloys containing novel alloying elements (such as Cr, Mn and Si) in sintered steels, particularly due to the following outcomes from the project:
- An insight on the chemistry of the sintering process. The chemical reactions occurring during sintering have been traditionally ignored because the alloying elements used (usually Cu, Ni, Mo) have an oxygen-affinity similar to that of iron. Here., the peculiarities of such chemical phenomena when considering the use of oxygen-sensitive elements such as Cr, Mn and Si have been thoroughly assessed and are critical for identifying the sintering conditions needed to successfully sinter these "tricky" materials
- It has been found that the particular chemical composition of the master alloy plays an important role, and therefore the optimum sintering conditions depend on the specific master alloy composition used. Some of the technological parameters that can be adapted to optimize the final properties of steels containing Fe-Mn-Si-(Cr) master alloys are: delubrication cycles, heating rates, composition of the atmosphere and sintering temperature.
- One of the main advantages of using master alloys is the possibility of designing their composition to form a liquid phase that enhances the distribution of the alloying elements and the sintering mechanisms. In this situation, the properties of the liquid-solid-atmosphere interactions are of critical importance, in particular: the character of the liquid/solid interaction (dissolutive or not dissolutive) and the presence of oxygen sensitive alloying elements determine the dimensional changes and the microstructural evolution.
- The use of novel atomization techniques provide a very favorable scenario for the use of master alloy powders. Master alloy powders produced by Ultra High Pressure water atomization present very suitable morphologies, oxygen contents and particle sizes. The properties of steels containing such master alloys are similar or better than those obtained with commercially available powders.
Besides, SINT-NAS has an impact on several aspects that will directly contribute to European excellence and competitiveness:
• Contributing in the creation of a Greener Europe: PM offers more effective use of the material (more than 98% material utilization rate), less energy consumption per part-produced, fewer numbers of steps in the production, and also an overall reduction in CO emissions. Increasing the amount of PM parts in the automobile would not only offer a reduction in costs, but would also make the way towards more sustainable manufacturing practices.
• Promoting a Smarter Economy. The possibility of reinforcing the competitiveness of the Powder Metallurgy Industry in Europe through the optimization of process and costs aimed in this research project is an excellent example of how the “development of knowledge” can be the most powerful tool for pushing up the European Economy.
• Promoting Academia-Industry partnerships and Technology Transfer. The studies carried out in these project always considered the need to meet the industrial needs. The results from the project promoted a high interest from the industry and the transference of knowledge to the European industries has been very successful.
• Helping to increase the presence of women in positions of high responsibility in specific areas with almost exclusively masculine participation. This fellowship provided the female applicant with a unique scientific profile in the Powder Metallurgy field, where there is an enormous lack in feminine representation.
More information about SINT-NAS can be found at the webpage: https://www.cta.tuwien.ac.at/division_chemical_technologies/powdermetallurgy/sint_nas/