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1.前言 阻碍高强度钢实用化的因素之一,是起因 于内部破坏的长期疲劳特性的降低。如图1所 示,高温回火的碳素钢和低合金钢的10~7次疲 劳强度(疲劳极限σ_W)与抗拉强度σ_B呈直线关 系,σ_W=0.53σ_B。但是,如果抗拉强度超过 1200MPa,疲劳极限呈饱和倾向。这是相对于低 强度一方来说为表面破坏,而在高强度方面显 然原因是以夹杂物之类为起点的内部破坏。以 前,疲劳极限的评价大致以10~7次作为标准;然 而当发现内部破坏,疲劳强度在10~7次以上的
1. Introduction One of the factors hindering the practical use of high-strength steels is the reduction of long-term fatigue characteristics due to internal damage. As shown in Fig. 1, the fatigue strength (fatigue limit σ_W) of 10-7 times of high temperature tempered carbon steel and low alloy steel is in a linear relationship with the tensile strength σ_B, σ_W = 0.53σ_B. However, if the tensile strength exceeds 1200 MPa, the fatigue limit tends to be saturated. This is a surface failure with respect to the low strength side, whereas the obvious reason for the high strength is the internal failure starting from inclusions and the like. In the past, the assessment of fatigue limit was based on a criterion of 10 to 7 times; however, when internal failure was found, the fatigue strength was 10 to 7 times or more