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本文选用40CrNiMoA钢以及新型高强度低碳马氏体类钢20SiMn 2 MoVA、22CrMnSiMoVA、25 SiMn 2 MoVA等材料,在不同的热处理(回火)状态下,进行了三点弯曲断裂韧性K_(IC)的测定,对40 CrNiMoA钢还进行了V形缺口夏比冲击试验(CVN)以及预制疲劳裂纹的CVN试样的冲击试验(W/A)。试验表明,对于中碳合金结构钢,在不同热处理状态下,K_(IC)值随强度指标σ_s、σ_b的增加而降低,但K_(IC)与σ_s、σ_b并不成反比关系;对于低碳合金结构钢,在低中温回火范围内,K_(IC)值随强度的增加而增加,因此,不能认为“材料强度的提高必然会导致断裂韧性的降低”是一个普遍规律,至少,它不适用于Si—Mn系列低碳马氏体类钢。40 CrNiMoA钢的尺寸因子(K_(IC)与δ、ψ的关系曲线上出现的转折说明,过高的δ、ψ对(K_(IC)/σ_s)~2作用不大,在选择材料和制定工艺时,对δ、ψ要合理要求,以利材料强度潜力的发挥。三种新型高强度低碳马氏体类钢的试验结果指出,在淬火低温回火即保持低碳马氏体组织状态时,这类钢具有较高的强度和较高的断裂韧性,与等强度的中碳合金结构钢相比,其断裂韧性值要高得多。这类钢的推广使用将在减轻产品重量,防止脆性断裂方面发挥积极作用。试验还表明,α_k、CVN值与K_(IC)随回火温度的变化有相同的走向,W/A值与K_(IC)有较密切的关系。
In this paper, 40CrNiMoA steel and new high-strength low-carbon martensitic steels such as 20SiMn 2 MoVA, 22CrMnSiMoVA, 25SiMn 2 MoVA and so on were used to study the three-point bending fracture toughness K IC at different tempering (tempering) The CrNiMoA steels were also subjected to V-notch Charpy impact test (CVN) and impact test (W / A) of pre-fatigue cracked CVN specimens. The results show that K_ (IC) value decreases with the increasing of σ_s and σ_b, but K_ (IC) is not inversely proportional to σ_s and σ_b for medium carbon alloy structural steels. For low carbon alloys Structural steel, K_ (IC) values increase with increasing strength at low and medium tempering temperatures. Therefore, it can not be considered that “the increase of material strength will inevitably lead to the decrease of fracture toughness”. It is a general rule that, at least, it does not apply Si-Mn series of low-carbon martensitic steel. The turning point on the curve of size factor (K_ (IC)) and δ, ψ of 40 CrNiMoA steel shows that the excess δ and ψ have little effect on (K_ (IC) / σ_s) Process, the δ, ψ to be reasonable requirements to facilitate the potential strength of materials to play.Three kinds of new high-strength low-carbon martensitic steel test results show that quenching low-temperature tempering that keep the low-carbon martensite state , This type of steel with high strength and high fracture toughness, and medium strength alloy structure steel, the fracture toughness value is much higher.The promotion of such steel will reduce the weight of the product, The results also showed that the changes of α_k, CVN and K_ (IC) with tempering temperature have the same trend, and the W / A value has a close relationship with K_ (IC).