Document and Entity Information - shares	6 Months Ended
	Dec. 31, 2017	Jan. 25, 2018
Document and Entity Information
Entity Registrant Name	CARPENTER TECHNOLOGY CORP
Entity Central Index Key	0000017843
Document Type	10-Q
Document Period End Date	Dec. 31, 2017
Amendment Flag	false
Current Fiscal Year End Date	--06-30
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		46,916,395
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q2