关于镀硬铬时的氢脆问题

关于镀硬铬时的氢脆问题

1. 氢脆的定义

氢脆是钢中溶解的氢聚合成氢分子, 造成应力集中, 超过钢材的强度极限, 并在钢材上形成小裂纹, 也称为白斑. 氢脆主要发生在低合金高强钢上, 不锈钢及弹性件. 氢脆的主要原因是表面处理. 电镀、氮化等零件处理过程中产生的氢气渗入金属内部，导致晶格排列紊乱. , 产生失真, 导致内应力增大, 使金属或涂层变脆, 并造成零件断裂或涂层剥落. 正在进行中, 氢脆需要满足两个条件: 该金属的氢含量较高; 有一定的外力.

由于氢脆引起磁滞开裂的特点, 零部件的使用性能受到严重影响, 并且存在较大的安全隐患. 所以, 在零件的设计和加工中, 特别是在高压下工作的液压元件, 需要严格控制.

2. 脱氢脆化处理的适用范围及程序

并非所有金属在表面处理时都会产生氢脆. 根据研究数据和实践, 氢脆主要发生在零件表面处理后的以下材料中.
(1) 拉伸强度981N/mm2以上的热处理碳钢和合金钢零件 (或硬度高于38HRC).
(2) 弹簧钢零件 (包括钢琴线, 油回火钢丝, 和高碳钢丝) 硬度370HV以上.
(3) 抗拉强度1236N/mm2以上的马氏体不锈钢制品 (或36HRC或以上) 经受热处理.
目前处理中, 引起氢脆的主要工艺是酸洗, 电镀, 氮化, 和电解. 上述工序在加工零件表面时, 将产生氢气并渗透到零件中, 导致氢脆.

3. 氢脆案例分析

液压产品一般需要在高压下工作, 并且有些部件承受的力更大. 当零件吸收氢气时, 他们会在弱点上崩溃. 阀芯是空心的. 由于功能需求, 中空部分需要用单向阀密封. , 阀芯在高压下工作, 要求单向阀的配合部位具有较强的抗冲击性和韧性. 同时, 为了满足一定的耐磨要求, 很多厂家都选择这种阀芯表面镀铬处理, 并要求镀层较厚, 但由于镀铬工艺的电流效率较低, 电镀时间长，渗氢严重.

4. 氢脆的措施及预防

消除零件因吸附氢而产生的氢脆, 一般选择干燥工艺, 干燥过程一般分为:
(1) 一般干燥处理, 干燥温度200℃左右.
(2) 低温干燥处理, 干燥温度低于180℃.
干燥方法如下:
(1) 干燥处理最好在氢吸附过程后立即进行, 最长不超过4h.
(2) 干燥处理的时间和温度按附表要求进行. 原则, 治疗必须一次性完成. 治疗开始后, 它不能被打断. 持续维护并在规定时间内完成.
(3) 镀层剥离后重新电镀的情况, 或者在电镀后施加另一电镀层的情况, 脆化过程两次以上, 当干燥处理从初始工序到最终工序的时间在4h以内时, 仅进行最后一步后的干燥处理, and the others can be omitted.

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In the design and processing of parts, hydrogen embrittlement should also be prevented in advance. 例如, the materials that are prone to hydrogen embrittlement can be properly heated, shot peened or vibrated before surface treatment, so that the hydrogen on the workpiece can escape , The stress is released and hydrogen embrittlement is reduced; on the premise of meeting the performance, try to use processes with less hydrogen permeation, such as surface treatment degreasing, rust removal, ETC。, and chemical degreasing, cleaning agents or solvents can be used. Oil: When removing rust and scale, use sand blowing to remove rust as much as possible. If pickling is used, it is necessary to add corrosion inhibitors in the pickling solution.

5. concluding remarks

Generally speaking, the greater the strength of the material, the greater the sensitivity to hydrogen embrittlement. In addition to the hardness, the following points should be considered comprehensively:
(1) The use safety factor of parts, the parts with high safety importance should be strengthened to remove hydrogen treatment.
(2) Parts with small cross-sectional areas, such as small springs, thinner springs, ETC.
(3) With notched parts that are prone to stress concentration.
Hydrogen embrittlement in the surface treatment process is extremely harmful. The requirement for hydrogen embrittlement is a clear concept that technicians must make when designing and processing. Appropriate measures should be taken according to different parts and usage conditions to achieve the purpose of eliminating hydrogen embrittlement.