Cover Page - USD ($)	12 Months Ended
	Jun. 30, 2021	Aug. 13, 2021	Dec. 31, 2020
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Jun. 30, 2021
Current Fiscal Year End Date	--06-30
Document Transition Report	false
Entity File Number	1-5828
Entity Registrant Name	CARPENTER TECHNOLOGY CORPORATION
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	23-0458500
Entity Address, Address Line One	1735 Market Street
Entity Address, Address Line Two	15th Floor
Entity Address, City or Town	Philadelphia
Entity Address, State or Province	PA
Entity Address, Postal Zip Code	19103
City Area Code	610
Local Phone Number	208-2000
Title of 12(b) Security	Common Stock, $5 Par Value
Trading Symbol	CRS
Security Exchange Name	NYSE
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 1,398,479,325
Entity Common Stock, Shares Outstanding		48,067,164
Documents Incorporated by Reference	Selected portions of the Company's fiscal year 2021 definitive Proxy Statement are incorporated by reference into Part III of this Report.
Entity Central Index Key	0000017843
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
Amendment Flag	false