The designation you refer to is probably ASTM A565 Grade 616, which is a 422 stainless steel. This is a martensitic stainless steel for elevated temperature service.
This is a weldable alloy. However, could you please provide specific service details? The reason for my asking is for the proper selection of filler metal. For service temperatures below 1000 deg F, an Inconel or Ni base filler metal would work.
AISI Type 422 will require a 500 deg F preheat, and stress relief that could result in warpage to a finished product.