一、前言 近年来国内外研究表明,低碳马氏体是高强度和良好的塑性、韧性结合的一种组织状态同时还有低的脆性转变温度、在静载,疲劳及多种载荷之下,其缺口敏感性和过载敏感性均较低,这些特点引起工程技术部门的重视。目前,国内外使用最多的超高强度钢中,低合金的是4340、300-M,高合金的是马氏体时效钢,强度级别可达到1760-2400Mpa(180—245kg/mm~2),K_(IC)可达到2940—3430N/mm~(3/2)(300—350kg/mm~(3/2))以上。4340、300—M等钢种因含碳量高,亚结构是孪晶,强度虽然很高,但韧性差,通过超高 I. Introduction In recent years, domestic and foreign studies have shown that low-carbon martensite is a combination of high strength and good ductility, toughness and a state of tissue with low brittle transition temperature, static load, fatigue and a variety of loads , The notch sensitivity and overload sensitivity are low, these features caused by engineering and technical departments attention. At present, the most commonly used ultra-high strength steel at home and abroad, the low-alloy is 4340,300-M, high-alloy is martensitic steel, the strength level can reach 1760-2400Mpa (180-245kg / mm ~ 2) K_ (IC) can reach 2940-3430N / mm ~ (3/2) (300-350kg / mm ~ (3/2)) above. 4340,300-M and other steel because of high carbon content, substructure is twin, the intensity is high, but the toughness is poor, through the ultra-high