## 3 Results
### Forecast of SIUS and Scrap  
SIUS have exhibited a continuous growth trend, as shown in Figure 9. The total SIUS in Henan Province reached 642.42 Mt in 2030 and are projected to reach 802.99 Mt by 2060, with the average annual growth rate declining from 10% in 2023 to 5% in 2060, indicating a gradual saturation trend. Among the five downstream sectors, the building sector remains the most significant source of SIUS. The SIUS of the building sector increased from 332.62 Mt in 2023 to 519.25 Mt in 2060, accounting for 65% of the total SIUS. The machinery sector is the second-largest source of SIUS. It has increased from 97.37 Mt in 2023 to 131.61 Mt in 2060. The other three sectors (infrastructure, transportation, and domestic appliances) account for a small proportion of the total SIUS and together are projected to account for 19% of the total by 2060.  
Henan Province will have mature steel stocks because the decline in population will cause the supply of end-of-life scrap and steel consumption to be at a similar level. In quantitative terms, the shift toward a circular economy featuring a closed-loop steel system will be attainable by that time [44].  
Figure 8: Decomposition of e (MS, GDP).  
Figure 9: SIUS from 2023 to 2060 in Henan Province.  
Scrap steel currently boasts the highest recycling rate among metal products [45] and is the only renewable resource capable of replacing iron ore. It is also a crucial raw material in the Scrap-EAF (Electric Arc Furnace) route in the iron and steel industry. Recycling scrap steel not only reduces energy consumption [46; 47; 48] and pollutant emissions [49; 50] but also contributes to the green development of the whole industry.  
Figure 10a illustrates the total available recyclable scrap steel in Henan Province from 2023 to 2060. Over this period, the total available scrap steel resources are projected to increase from 11.05 Mt to 19.48 Mt. The respective proportions of HS and PS in the total recyclable scrap resources will drop from 15% in 2023 to 5% in 2060 and from 19% to 6%. This trend reflects technological advancements that have reduced waste during steel manufacturing. Depreciated scrap steel has always been a key source of recyclable scrap steel resources. By 2060, the amount of depreciated scrap steel is anticipated to reach 17.96 Mt, representing 88% of the total recyclable scrap steel. Adequate scrap resources are the key prerequisite for the steel industry to realize green and low-carbon transformation.  
Figure 10b shows the distribution of depreciated scrap steel in the main downstream sectors of the iron and steel industry. In the composition of depreciated scrap steel sources, the building sector has consistently been the dominant contributor, significantly influencing the overall trend of depreciated scrap steel. The proportion of depreciated scrap steel is projected to rise from 61% in 2023 to 67% in 2060. The machinery sector is the second-largest contributor, with the amount of depreciated scrap steel reaching 2.42 Mt by 2060, accounting for 14% of the total. The transportation sector s experiencing the fastest growth in depreciated scrap steel, with an average annual increase of 5%. This indicates that the transportation sector is undergoing rapid development, which requires frequent maintenance, upgrades, or reconstruction, thereby generating more scrap steel.  
The sustainable development policy encourages industries to substitute environmentally friendly materials. Adequate secondary steel resources, which are renewable and environmentally friendly, are essential for the steel industry to realize its green and low-carbon transformation.