Revenue - Summary of Revenue by Geography (Details) - USD ($) $ in Millions	12 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2022
Disaggregation of Revenue [Line Items]
Net sales	$ 2,759.7	$ 2,550.3	$ 1,836.3
Intersegment
Disaggregation of Revenue [Line Items]
Net sales	(95.1)	(97.0)	(73.8)
Specialty Alloys Operations | Operating
Disaggregation of Revenue [Line Items]
Net sales	2,443.8	2,213.6	1,565.6
Performance Engineered Products | Operating
Disaggregation of Revenue [Line Items]
Net sales	411.0	433.7	344.5
United States
Disaggregation of Revenue [Line Items]
Net sales	1,623.0	1,556.2	1,179.9
United States | Intersegment
Disaggregation of Revenue [Line Items]
Net sales	(29.9)	(36.8)	(29.8)
United States | Specialty Alloys Operations | Operating
Disaggregation of Revenue [Line Items]
Net sales	1,418.5	1,350.7	1,018.6
United States | Performance Engineered Products | Operating
Disaggregation of Revenue [Line Items]
Net sales	234.4	242.3	191.1
Europe
Disaggregation of Revenue [Line Items]
Net sales	503.8	437.3	253.5
Europe | Intersegment
Disaggregation of Revenue [Line Items]
Net sales	(20.9)	(17.7)	(13.0)
Europe | Specialty Alloys Operations | Operating
Disaggregation of Revenue [Line Items]
Net sales	449.2	373.6	208.5
Europe | Performance Engineered Products | Operating
Disaggregation of Revenue [Line Items]
Net sales	75.5	81.4	58.0
Asia Pacific
Disaggregation of Revenue [Line Items]
Net sales	391.3	319.5	233.9
Asia Pacific | Intersegment
Disaggregation of Revenue [Line Items]
Net sales	(44.3)	(42.4)	(31.0)
Asia Pacific | Specialty Alloys Operations | Operating
Disaggregation of Revenue [Line Items]
Net sales	389.4	317.4	231.8
Asia Pacific | Performance Engineered Products | Operating
Disaggregation of Revenue [Line Items]
Net sales	46.2	44.5	33.1
Mexico
Disaggregation of Revenue [Line Items]
Net sales	120.1	124.0	89.4
Mexico | Intersegment
Disaggregation of Revenue [Line Items]
Net sales	0.0	0.0	0.0
Mexico | Specialty Alloys Operations | Operating
Disaggregation of Revenue [Line Items]
Net sales	86.0	83.7	44.2
Mexico | Performance Engineered Products | Operating
Disaggregation of Revenue [Line Items]
Net sales	34.1	40.3	45.2
Canada
Disaggregation of Revenue [Line Items]
Net sales	70.1	60.1	41.5
Canada | Intersegment
Disaggregation of Revenue [Line Items]
Net sales	0.0	0.0	0.0
Canada | Specialty Alloys Operations | Operating
Disaggregation of Revenue [Line Items]
Net sales	56.9	44.1	29.6
Canada | Performance Engineered Products | Operating
Disaggregation of Revenue [Line Items]
Net sales	13.2	16.0	11.9
Other
Disaggregation of Revenue [Line Items]
Net sales	51.4	53.2	38.1
Other | Intersegment
Disaggregation of Revenue [Line Items]
Net sales	0.0	(0.1)	0.0
Other | Specialty Alloys Operations | Operating
Disaggregation of Revenue [Line Items]
Net sales	43.8	44.1	32.9
Other | Performance Engineered Products | Operating
Disaggregation of Revenue [Line Items]
Net sales	$ 7.6	$ 9.2	$ 5.2