Revenue - Summary of Revenue by Geography (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Jun. 30, 2023	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2021
Disaggregation of Revenue [Line Items]
Net sales	$ 1,836.3	$ 2,550.3	$ 1,836.3	$ 1,475.6
Specialty Alloys Operations
Disaggregation of Revenue [Line Items]
Net sales	1,565.6	2,213.6	1,565.6	1,262.2
Performance Engineered Products
Disaggregation of Revenue [Line Items]
Net sales	344.5	433.7	344.5	259.8
Intersegment
Disaggregation of Revenue [Line Items]
Net sales	(73.8)	(97.0)	(73.8)	(46.4)
United States
Disaggregation of Revenue [Line Items]
Net sales	1,179.9	1,556.2	1,179.9	926.6
United States | Specialty Alloys Operations
Disaggregation of Revenue [Line Items]
Net sales		1,350.7	1,018.6	802.2
United States | Performance Engineered Products
Disaggregation of Revenue [Line Items]
Net sales		242.3	191.1	137.4
United States | Intersegment
Disaggregation of Revenue [Line Items]
Net sales		(36.8)	(29.8)	(13.0)
Europe
Disaggregation of Revenue [Line Items]
Net sales	253.5	437.3	253.5	242.7
Europe | Specialty Alloys Operations
Disaggregation of Revenue [Line Items]
Net sales		373.6	208.5	204.1
Europe | Performance Engineered Products
Disaggregation of Revenue [Line Items]
Net sales		81.4	58.0	46.1
Europe | Intersegment
Disaggregation of Revenue [Line Items]
Net sales		(17.7)	(13.0)	(7.5)
Asia Pacific
Disaggregation of Revenue [Line Items]
Net sales	233.9	319.5	233.9	194.4
Asia Pacific | Specialty Alloys Operations
Disaggregation of Revenue [Line Items]
Net sales		317.4	231.8	191.6
Asia Pacific | Performance Engineered Products
Disaggregation of Revenue [Line Items]
Net sales		44.5	33.1	28.6
Asia Pacific | Intersegment
Disaggregation of Revenue [Line Items]
Net sales		(42.4)	(31.0)	(25.8)
Mexico
Disaggregation of Revenue [Line Items]
Net sales	89.4	124.0	89.4	48.8
Mexico | Specialty Alloys Operations
Disaggregation of Revenue [Line Items]
Net sales		83.7	44.2	17.7
Mexico | Performance Engineered Products
Disaggregation of Revenue [Line Items]
Net sales		40.3	45.2	31.0
Mexico | Intersegment
Disaggregation of Revenue [Line Items]
Net sales		0.0	0.0	0.1
Canada
Disaggregation of Revenue [Line Items]
Net sales	41.5	60.1	41.5	32.9
Canada | Specialty Alloys Operations
Disaggregation of Revenue [Line Items]
Net sales		44.1	29.6	21.5
Canada | Performance Engineered Products
Disaggregation of Revenue [Line Items]
Net sales		16.0	11.9	11.5
Canada | Intersegment
Disaggregation of Revenue [Line Items]
Net sales		0.0	0.0	(0.1)
Other
Disaggregation of Revenue [Line Items]
Net sales	$ 38.1	53.2	38.1	30.2
Other | Specialty Alloys Operations
Disaggregation of Revenue [Line Items]
Net sales		44.1	32.9	25.1
Other | Performance Engineered Products
Disaggregation of Revenue [Line Items]
Net sales		9.2	5.2	5.2
Other | Intersegment
Disaggregation of Revenue [Line Items]
Net sales		$ (0.1)	$ 0.0	$ (0.1)