| 摘要 |
Steel, which is especially useful for making plastic injection moulds, has the composition (by wt.) 0.03-0.25% C, 0-0.2% Si, 0-0.9% Mn, 1.5-5% Ni, 0-18% Cr, 0.05-1% Mo + one half W, 0-0.3% S, 0.05-3% each of Al and/or Cu, optionally 0-0.3% each of one or more of V, Nb, Zr, Ta and Ti, optionally 0-0.3% each of one or more of Pb, Se, Te and Bi, balance Fe and impurities (especially nitrogen). The composition satisfies the relationships (I) and (II): Kth=3.8 x C+9.8 x Si+3.3 x Mn+2.4 x Ni+ alpha x Cr+1.4 x (Mo+ one half W) ≤ 15 (I) where alpha = 1.4 if the Cr content is less than 8% and alpha = 0 if the Cr content is ≥ 8%; Tr=3.8 x C+1.07 x Mn+0.7 x Ni+0.57 x Cr+1.58 x (Mo+ one half W)+kB ≥ 3.1 (II) where kB = 0.8 the B content is 0.0005-0.015%; otherwise kB = 0; and if the Cr content is ≤ 5%, then composition satisfies relationship (III): Kth divided by Tr = ≤ 3 (III) Also claimed are (i) a block of the above steel which has a characteristic dimension (d) of ≥ 20 mm and which has, at all points, a tempered martensitic, bainitic or martensitic-bainitic structure of hardness greater than 350 HB; and (ii) a welding wire of the above steel. |
