塑料模具钢大型预硬化模块的研究

系统研究了LF+VD精炼工艺、钢锭模设计、氩气保护浇注工艺、大型钢锭高温扩散工艺、锻造工艺、淬火工艺及高温回火工艺等因素对718钢大型预硬化模块材料纯净度和硬度均匀性的影响规律。结果显示：LF和VD精炼过程中炉渣碱度分别保持在3.5～4.0和3.0～3.5，精炼后钢中wS]控制到0.003%，TO]为12×10-6；28t钢锭模尾锥形状和入口倒角优化设计后，尾部夹杂废品率由6.81%降低到1.55%；通过试验确定氩气流量按4～8 m3/h控制；大型钢锭高温扩散后，模块低倍组织的偏析和硬度偏差分别由≤3.0级和≤5.0HRC提高到≤2.0级和≤3.5HRC；采用FM法代替平砧拔长，模块低倍组织疏松和超声波探伤检验分别由≤3.0级和C/d提高到≤2.0级和D/d；采用水-空控时淬火和电加热回火炉回火对规格为650 mm×1 080 mm的模块进行预硬化处理，模块横断面硬度偏差≤3.5HRC。

Research on Large-Size Pre-Hardened Mould Blocks of Plastic Mould Steels

The effect of relative process specifications such as LF＋VD melting process,ingot mold design,argon protective casting process,high temperature homogenizing process and forging process for heavy ingots,quenching process and high temperature tempering process for mould blocks on material purity and hardness uniformity were systematically investigated.The test results show that,sulfur content can be controlled as low as 0.005%,and total oxygen content as low as 12×10-6 if slag basicity of LF and VD were kept within 3.5~4.0 and 3.0~3.5 respectively;rejection rate caused by inclusions at ingot bottom was reduced from 6.81% to 1.55% by optimizing the design of the 28 t ingot mold bottom taper shape and ingate chamfering;it was confirmed by argon protective casting test that argon flow rate should be controlled at 4~8 m3/h;the macro segregation and hardness deviation were improved from ≤ grade 3.0 and ≤ 5.0HRC to ≤ grade 2.0 and ≤ 3.5HRC respectively by adopting high temperature homogenizing process;the macro porosity and the ultrasonic testing result was improved from ≤ grade 3.0 and C/d to ≤ grade 2.0 and D/d respectively by applying FM forging method instead of drawing by flat anvil;the hardness deviation on the cross section of 650 mm×1 080 mm mould blocks was ≤ 3.5HRC by pre-hardening treatment（water-air alternatively timed quenching ＋ high temperature tempering by electrical heating furnace）.