Almost all kind of steel can be welded, but some mixing material steel is difficult to be welded and even can't be welded.
Engine material usually composed from mixed material that make difficult to be welded. Engine block is made by material forged to form. The mixing completely only by melted steel material together and cold in the same time.
To weld certain God need same wire material in order can be united. If you use different wire material with the object welded, the result will don't united completely.
