Ingot segregation

When a large ingot solidifies, carbon, sulfur, and phosphorus enrich in the remaining melt and collect in the center. That's called ingot segregation. When you weld such a thing, you have different material depending on the spot: In the center it's hard and brittle and prone to cracks, outside it's softer. Before welding, you need to know where you are, best via spectral analysis. If you're in the critical area, use low-hydrogen fillers and preheat the part, then it'll be fine.