I can't say I've ever heard of the use of chromium or chromium like elements being used in Chinese swords. There doesn't seem to be any major sources of chromium in China that I could find. This doesn't mean that there aren't some small sources or that they could have traded it in from India or something.

However, mercury (derived from cinnabar) was used quite plentifully throughout Chinese history in alchemy and metallurgy. Mercury has been used as part of the process of working silver for centuries. According to the text Shangqing han xiang jianjian tu, written by the Daoist master Sima Chengzhen, the best powerful ritual swords used by Daoists were made of silver and worked with mercury and cinnabar. It's possible that the use of these chemicals with silver would have created blades that had very tarnish resistant properties.

The most famous untarnished Chinese blade, the Sword of Goujian, is bronze sword with traces of iron, lead, sulfur and arsenic. It's pristine state is mostly attributed to being well sealed in its scabbard though.