Al对热挤压模具钢 SDAH13连续冷却转变规律的影响

采用热膨胀仪测定Al质量分数分别为0.77%和1.43%以及无Al的热挤压模具钢SDAH13的连续冷却转变曲线,并结合光学显微镜、扫描电镜及显微硬度仪分析Al元素对SDAH13钢相变点、连续转变规律、组织以及硬度的影响.结果表明：Al元素显著提高SDAH13钢的Ac1、Ac3和Ms点,降低淬火残留奥氏体含量,同时扩大铁素体及奥氏体两相区.在1060℃奥氏体化温度下,Al元素对SDAH13钢贝氏体相变的临界冷速(0.30℃·s-1)无明显影响,但使贝氏体相区变宽,Al质量分数分别为0.77%和1.43%的SDAH13钢的珠光体相变的临界冷速(0.05℃·s-1和0.3℃·s-1)均高于无Al的SDAH13钢的临界冷速(0.02℃·s-1),且Al质量分数为1.43%的SDAH13钢在0.02~0.08℃·s-1冷速下出现先共析铁素体组织. Al的加入还使SDAH13钢淬火硬度有所降低.

Effect of Al on the continuous cooling transformation characteristic of hot extrusion die steel SDAH13

The continuous cooling transformation ( CCT) diagrams of SDAH13 hot extrusion die steels with different mass fractions of Al (0. 77% and 1. 43%) and without Al were measured by dilatometry. The effects of Al on the CCT diagrams, microstructure and hardness of SDAH13 steels were studied by optical microscopy, scanning electron microscopy ( SEM) and Vickers hardness test. The results show that the phase transformation temperature points ( Ac1 , Ac3 and Ms) of SDAH13 steels significantly increase, the contents of retained austenite in the quenched steels decrease, and theα-γmulti-phase region expands with the increase in mass fraction of Al. However, when austenited at 1060℃, Al has no obvious influence on the critical cooling rate (0. 30℃·s-1 ) of bainite transforma-tion, but bainite phase region broadens. Meanwhile, the critical cooling rates of pearlite transformation of SDAH13 steels with the Al content of 0. 77% and 1. 43% are 0. 05℃·s-1 and 0. 3℃·s-1, respectively, which are higher than the critical cooling rate (0. 02℃·s-1 ) of pearlite transformation of SDAH13 steel without Al. Pro-eutectoid ferrite appears at the cooling rate from 0. 02℃·s-1 to 0. 08℃·s-1 when the mass fraction of Al reaches 1. 43%. Nevertheless, the quenched hardness decreases with Al addition.