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常用帶電作業(yè)承力工具材料的疲勞特性

Fatigue characteristics of common live working tool materials

金屬材料的疲勞特性：影響金屬材料疲勞特性的因素很多，除受成分、夾雜物和熱處理的影響外，還有其他因素。

Fatigue characteristics of metal materials: there are many factors that affect the fatigue characteristics of metal materials, besides the influence of composition, inclusions and heat treatment, there are other factors.

金屬材料表面加工、尺寸和應(yīng)力集中的影響：工具部件承受彎曲和扭轉(zhuǎn)載荷時(shí)表面應(yīng)力大，疲勞破壞多數(shù)自表面開(kāi)始。粗糙的表面狀態(tài)相當(dāng)于存在很多微缺口，由缺口應(yīng)力集中而導(dǎo)致疲勞強(qiáng)度降低。表面越粗糙，疲勞強(qiáng)度降低得越嚴(yán)重。有圓角、油孔和螺紋鍵槽等缺口的部件，因應(yīng)力集中導(dǎo)致部件疲勞強(qiáng)度降低。缺口越尖銳應(yīng)力越集中，疲勞強(qiáng)度降低越嚴(yán)重。

The influence of surface processing, dimension and stress concentration of metal materials: the surface stress of tool parts under bending and torsion load is the largest, and most of the fatigue damage starts from the surface. The rough surface state is equivalent to the existence of many micro notches, which lead to the reduction of fatigue strength due to the stress concentration of the notches. The rougher the surface is, the more serious the fatigue strength is. The fatigue strength of parts with round corner, oil hole, thread keyway and other notches is reduced due to stress concentration. The sharper the notch, the more concentrated the stress, the more serious the fatigue strength reduction.

部件表面鍍層對(duì)其疲勞強(qiáng)度也有影響：工具表面鍍層主要是鉻（Cr）和鎳（Ni），鍍這兩種金屬時(shí)造成疲勞極限大為降低的主要原因是鍍層中產(chǎn)生很大的殘余拉應(yīng)力。由于鍍層中存在很多微細(xì)龜裂紋，它作為缺口使應(yīng)力集中。如30CrMo材料未鍍前的疲勞極限為72.5MPa。鍍0.25mm厚的Cr后，其疲勞極限則為50.6MPa，僅為鍍前的68%。

The coating on the surface of parts also has some influence on its fatigue strength: the coating on the surface of tools is mainly chromium (CR) and nickel (Ni). The main reason for the great reduction of fatigue limit caused by the plating of these two metals is the large residual tensile stress in the coating. Because there are many micro tortoise cracks in the coating, it acts as a notch to make the stress concentration. For example, the fatigue limit of 30CrMo material before plating is 72.5mpa. After plating 0.25mm Cr, the fatigue limit is 50.6mpa, only 68% of that before plating.

熱處理對(duì)其疲勞強(qiáng)度的影響：通過(guò)加熱、保溫和冷卻等步驟來(lái)調(diào)整金屬內(nèi)部組織，改善材料性能的技術(shù)手段，稱(chēng)為熱處理。熱處理可分為退火、亞火、回火和淬火等。退火即隨爐冷卻，亞火即空氣冷卻，淬火即用水突然冷卻，回火即再加溫。退火和亞火可提高機(jī)械性能，降低硬度，提高塑性和內(nèi)應(yīng)力，淬火是為了得到高硬度和高耐磨性，以得到強(qiáng)度與塑性的良好配合，回火是為了防止淬火引起的內(nèi)應(yīng)力和脆性。

The influence of heat treatment on its fatigue strength: the technical means to adjust the internal structure of metal and improve the performance of material through heating, heat preservation and cooling, is called heat treatment. Heat treatment can be divided into annealing, sub fire, tempering and quenching. Annealing is cooling with furnace, sub fire is cooling with air, quenching is cooling suddenly with water, tempering is heating again. Annealing and tempering can improve mechanical properties, reduce hardness, improve plasticity and eliminate internal stress. Quenching is to obtain high hardness and high wear resistance, so as to obtain a good combination of strength and plasticity. Tempering is to prevent internal stress and brittleness caused by quenching.