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实际上在制造无磁性护环时,冷胀形是最重要的工艺之一。神钢厂冷胀形工艺中的楔块法已经被液压胀形法所取代。液压胀形工艺的一个重要优点就在于均匀变形,必要时可以在高于200℃温度下进行液压胀形,另一个优点是对于环的不同尺寸和变形率能进行任意的胀形,也就是说能控制变形特性。为了控制变形特性,环的尺寸和被胀环的压力都按时测量,并且通过计算机控制压力。为了检查瞬时变形温度,对被胀环的表面温度也进行了监测。对于18Mn-5 Cr 钢合适的变形温度范围是350～200℃,而18Mn-18Cr 钢则是低于200℃,这可作如下解释:在18Mn-5Cr 铜中低于200℃温度下大量冷变形时将促使环的内部γ→ε相变。环内部产生的ε相使原来残余的压应力变为拉应力,引起冲击韧性和抗应力腐蚀的降低。对于18Mn-18Cr 钢,在高于200℃温度下冷变形时,应变时效将会增加应力增量,结果将引起屈强比(σ_(0·2)/σ_b)的增加。
In fact, in the manufacture of non-magnetic guard ring, cold bulging shape is one of the most important process. The wedge method in the cold-formed form of God’s steel plant has been replaced by the hydraulic bulging method. An important advantage of the hydroforming process is that it can be uniformly deformed, hydraulically expanded at temperatures above 200 ° C, if necessary, and that it has the additional advantage of being able to be arbitrarily bulged for different dimensions and deformation rates of the ring, that is to say Can control the deformation characteristics. In order to control the deformation characteristics, the size of the ring and the pressure of the expanding ring are measured on time, and the pressure is controlled by a computer. In order to check the instantaneous deformation temperature, the surface temperature of the expanded ring was also monitored. Suitable deformation temperatures for 18Mn-5Cr steel range from 350 to 200C, while 18Mn-18Cr steels are below 200C, which is interpreted as follows: Large amounts of cold deformation at temperatures below 200C in 18Mn-5Cr copper Will promote the internal ring γ → ε phase change. The ε phase generated inside the ring causes the original residual compressive stress to become tensile stress, causing a decrease in impact toughness and stress corrosion resistance. For 18Mn-18Cr steel, strain hardening will increase the stress increment at cold deformation above 200 ℃, which will result in the increase of yield ratio (σ_ (0.2) / σ_b).