将A视为B，其中的“视为”主要是你已经知道A不是B，例如：我将她视为我的妈妈 将A看成B，其中的“看成”表示你不知道B不是A ，有将A 错认为B 的意思

“视为” has in some way the same meaning as “看成” , but more official, here is an example: 我把他视为我最大的敌人。 我把他看成（是）我最大的敌人。 （I see him as my biggest enemy.） In this case both sentences mean the same thing. And as for me it just feels more natural to put a “是 ”after “看成”. It wouldn't be wrong if you don't do it. And here’s a situation they could not be exchanged: 我把他看成了你。 In this case “看成” means you took sth or someone wrong as another thing or person. You mistook A as B by seeing which is “看”. There is also a “听成”，which means you mistook A as B by hearing. I hope my explanation could help you.

视为经常用于政府 和权威，政治上的准确! 看成就是普通人说的话！