"U.S.-Korean Social Security Agreement" 에 보면 아래와 같은 article 이 보이네요.  

https://www.ssa.gov/international/Agreement_Texts/korea.html

Article 6

The following provisions shall apply to the United States:

1. Where a person has completed at least six quarters of coverage under United States laws, but does not have sufficient periods of coverage to satisfy the requirements for entitlement to benefits under United States laws, the Agency of the United States shall take into account, for the purpose of establishing entitlement to benefits under this Article, periods of coverage which are credited under Korean laws and which do not coincide with periods of coverage already credited under United States laws.

같은 사이트에 이런 조항도 보이네요.  

https://www.ssa.gov/international/Agreement_Pamphlets/korea.html

How Benefits Can Be Paid

If you have Social Security credits in both the United States and Korea, you may be eligible for benefits from one or both countries. If you meet all the basic requirements under one country’s system, you will get a regular benefit from that country. If you do not meet the basic requirements, the agreement may help you qualify for a benefit as explained below.

• Benefits from the U.S.––If you do not have enough work credits under the U.S. system to qualify for regular benefits, you may be able to qualify for a partial benefit from the United States based on both U.S. and Korean credits. However, to be eligible to have your Korean credits counted, you must have earned at least six credits (generally one and one-half years of work) under the U.S. system. If you already have enough credits under the U.S. system to qualify for a benefit, the U.S. cannot count your Korean credits.

합산 하시게 되면 한국 국민연금 10/17 로 줄고 소셜 연금 7/17을 받게되는 걸로 알고 있습니다. 잘 알아보고 하시는게 좋겠습니다. 합산은 됩니다