Revenue - Summary of Revenue by Geography (Details) - USD ($) $ in Millions	12 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2023
Disaggregation of Revenue [Line Items]
Net sales	$ 2,877.1	$ 2,759.7	$ 2,550.3
Operating
Disaggregation of Revenue [Line Items]
Net sales	2,969.0	2,854.8	2,647.3
Intersegment
Disaggregation of Revenue [Line Items]
Net sales	(91.9)	(95.1)	(97.0)
Specialty Alloys Operations
Disaggregation of Revenue [Line Items]
Net sales	2,548.7	2,432.8	2,201.5
Specialty Alloys Operations | Operating
Disaggregation of Revenue [Line Items]
Net sales	2,563.6	2,443.8	2,213.6
Specialty Alloys Operations | Intersegment
Disaggregation of Revenue [Line Items]
Net sales	(14.9)	(11.0)	(12.1)
Performance Engineered Products
Disaggregation of Revenue [Line Items]
Net sales	328.4	326.9	348.8
Performance Engineered Products | Operating
Disaggregation of Revenue [Line Items]
Net sales	405.4	411.0	433.7
Performance Engineered Products | Intersegment
Disaggregation of Revenue [Line Items]
Net sales	(77.0)	(84.1)	(84.9)
United States
Disaggregation of Revenue [Line Items]
Net sales	1,699.9	1,623.0	1,556.2
United States | Intersegment
Disaggregation of Revenue [Line Items]
Net sales	(31.2)	(29.9)	(36.8)
United States | Specialty Alloys Operations | Operating
Disaggregation of Revenue [Line Items]
Net sales	1,487.2	1,418.5	1,350.7
United States | Performance Engineered Products | Operating
Disaggregation of Revenue [Line Items]
Net sales	243.9	234.4	242.3
Europe
Disaggregation of Revenue [Line Items]
Net sales	596.2	503.8	437.3
Europe | Intersegment
Disaggregation of Revenue [Line Items]
Net sales	(21.8)	(20.9)	(17.7)
Europe | Specialty Alloys Operations | Operating
Disaggregation of Revenue [Line Items]
Net sales	545.4	449.2	373.6
Europe | Performance Engineered Products | Operating
Disaggregation of Revenue [Line Items]
Net sales	72.6	75.5	81.4
Asia Pacific
Disaggregation of Revenue [Line Items]
Net sales	344.4	391.3	319.5
Asia Pacific | Intersegment
Disaggregation of Revenue [Line Items]
Net sales	(38.9)	(44.3)	(42.4)
Asia Pacific | Specialty Alloys Operations | Operating
Disaggregation of Revenue [Line Items]
Net sales	342.1	389.4	317.4
Asia Pacific | Performance Engineered Products | Operating
Disaggregation of Revenue [Line Items]
Net sales	41.2	46.2	44.5
Mexico
Disaggregation of Revenue [Line Items]
Net sales	121.5	120.1	124.0
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	93.7	86.0	83.7
Mexico | Performance Engineered Products | Operating
Disaggregation of Revenue [Line Items]
Net sales	27.8	34.1	40.3
Canada
Disaggregation of Revenue [Line Items]
Net sales	61.2	70.1	60.1
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	50.1	56.9	44.1
Canada | Performance Engineered Products | Operating
Disaggregation of Revenue [Line Items]
Net sales	11.1	13.2	16.0
Other
Disaggregation of Revenue [Line Items]
Net sales	53.9	51.4	53.2
Other | Intersegment
Disaggregation of Revenue [Line Items]
Net sales	0.0	0.0	(0.1)
Other | Specialty Alloys Operations | Operating
Disaggregation of Revenue [Line Items]
Net sales	45.1	43.8	44.1
Other | Performance Engineered Products | Operating
Disaggregation of Revenue [Line Items]
Net sales	$ 8.8	$ 7.6	$ 9.2