Abstract: The continuous cooling transition curve （CCT curve） and impact energy curve of QDH of the new hot work die steel with 0.8% Ni and without Ni were determined by thermal expansion phase change instrument and impact testing machine， and the influence of Ni on the continuous transformation law and impact energy of QDH steel were analyzed by combining the microstructure and hardness. The test results of thermal expansion curve show that Ni element can significantly reduce the critical phase transition point （Ac1， Ac3 and Ms） of QDH steel， expand the austenite phase region， shift the CCT curve to the right as a whole， reduce the critical cooling rate of pearlite from 0.03 ℃/s to less than 0.02 ℃/s， and reduce the critical cooling rate of martensitic from 0.4 ℃/s to 0.2 ℃/s， which improves the hardenability of steel. The test results of impact energy curves show that the first type of tempering brittleness and the second type of tempering brittleness of the two experimental steels are in the tempering temperature range of 350 ℃-500 ℃ and 550 ℃-620 ℃， respectively， and the impact energy of Ni-containing steel in the whole tempering temperature range is higher than that of Ni-free steel， indicating that Ni element can improve the hardenability of QDH steel and improve its toughness.

Key words: Nickel, Hot Work Die Steel, CCT Curve, Hardenability, Impact Absorbing Energy

摘要： 使用热膨胀相变仪和冲击试验机测定了含0.8%Ni和不含Ni的新型热作模具钢QDH的连续冷却转变曲线（CCT曲线）和冲击功曲线，并结合组织及硬度分析了Ni元素对QDH钢连续转变规律与冲击功的影响。热膨胀曲线测试结果表明，Ni元素可显著降低QDH钢的临界相变点（Ac1、Ac3及Ms），扩大奥氏体相区，使CCT曲线整体右移，珠光体临界冷速由0.03 ℃/s降低至0.02 ℃/s以下，马氏体的临界冷速由0.4 ℃/s降低至0.2 ℃/s，提高了钢的淬透性。冲击功曲线测试结果表明，两种实验钢均在350~500 ℃和550~620 ℃两个回火温度区间，分别出现第一类回火脆性和第二类回火脆性，其中，含Ni钢在整个回火温度区间内的冲击功均高于不含Ni钢，说明Ni元素提高QDH钢淬透性的同时也可提高其韧性。

关键词: 镍, 热作模具钢, CCT曲线, 淬透性, 冲击吸收功