| 摘要 |
A relatively low cost, high strength, high toughness bar and sheet steel, which is substantially non-susceptible to the formation of delayed surface cracks in the as-rolled condition and its method of preparation, are provided, the constitution of the steel on a percentage mass to mass basis being as follows: C = 0,21 - 0,28 Mn = 0,80 - 1,80 Cr = 1,60 - 2,10 Si = 0,35 maximum Al = 0,02 - 0,05 P and S each = 0,025 maximum Fe = the balance; the steel being characterised in that its composition is such that, upon air cooling following rolling, the transformation temperature of the steel during the cooling is at a sufficiently high level to ensure that there is sufficient thermal contraction possible after the transformation has been completed to accomodate at least the thermal expansion which had taken place during the transformation. |
