Revenue - Summary of Revenue by Geography (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Jun. 30, 2026	Mar. 31, 2026	Dec. 31, 2025	Sep. 30, 2025	Jun. 30, 2025	Mar. 31, 2025	Dec. 31, 2024	Sep. 30, 2024	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2024
Disaggregation of Revenue [Line Items]
Net sales	$ 851.0	$ 811.5	$ 728.0	$ 733.7	$ 755.6	$ 727.0	$ 676.9	$ 717.6	$ 3,124.2	$ 2,877.1	$ 2,759.7
Operating
Disaggregation of Revenue [Line Items]
Net sales									3,209.8	2,969.0	2,854.8
Intersegment
Disaggregation of Revenue [Line Items]
Net sales									(85.6)	(91.9)	(95.1)
Specialty Alloys Operations
Disaggregation of Revenue [Line Items]
Net sales									2,811.7	2,548.7	2,432.8
Specialty Alloys Operations \| Operating
Disaggregation of Revenue [Line Items]
Net sales									2,826.8	2,563.6	2,443.8
Specialty Alloys Operations \| Intersegment
Disaggregation of Revenue [Line Items]
Net sales									(15.1)	(14.9)	(11.0)
Performance Engineered Products
Disaggregation of Revenue [Line Items]
Net sales									312.5	328.4	326.9
Performance Engineered Products \| Operating
Disaggregation of Revenue [Line Items]
Net sales									383.0	405.4	411.0
Performance Engineered Products \| Intersegment
Disaggregation of Revenue [Line Items]
Net sales									(70.5)	(77.0)	(84.1)
United States
Disaggregation of Revenue [Line Items]
Net sales									1,824.2	1,699.9	1,623.0
United States \| Intersegment
Disaggregation of Revenue [Line Items]
Net sales									(30.4)	(31.2)	(29.9)
United States \| Specialty Alloys Operations \| Operating
Disaggregation of Revenue [Line Items]
Net sales									1,620.3	1,487.2	1,418.5
United States \| Performance Engineered Products \| Operating
Disaggregation of Revenue [Line Items]
Net sales									234.3	243.9	234.4
Europe
Disaggregation of Revenue [Line Items]
Net sales									700.4	596.2	503.8
Europe \| Intersegment
Disaggregation of Revenue [Line Items]
Net sales									(19.0)	(21.8)	(20.9)
Europe \| Specialty Alloys Operations \| Operating
Disaggregation of Revenue [Line Items]
Net sales									652.3	545.4	449.2
Europe \| Performance Engineered Products \| Operating
Disaggregation of Revenue [Line Items]
Net sales									67.1	72.6	75.5
Asia Pacific
Disaggregation of Revenue [Line Items]
Net sales									341.2	344.4	391.3
Asia Pacific \| Intersegment
Disaggregation of Revenue [Line Items]
Net sales									(36.1)	(38.9)	(44.3)
Asia Pacific \| Specialty Alloys Operations \| Operating
Disaggregation of Revenue [Line Items]
Net sales									336.8	342.1	389.4
Asia Pacific \| Performance Engineered Products \| Operating
Disaggregation of Revenue [Line Items]
Net sales									40.5	41.2	46.2
Mexico
Disaggregation of Revenue [Line Items]
Net sales									141.8	121.5	120.1
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									118.2	93.7	86.0
Mexico \| Performance Engineered Products \| Operating
Disaggregation of Revenue [Line Items]
Net sales									23.6	27.8	34.1
Canada
Disaggregation of Revenue [Line Items]
Net sales									63.9	61.2	70.1
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									56.2	50.1	56.9
Canada \| Performance Engineered Products \| Operating
Disaggregation of Revenue [Line Items]
Net sales									7.7	11.1	13.2
Other
Disaggregation of Revenue [Line Items]
Net sales									52.7	53.9	51.4
Other \| Intersegment
Disaggregation of Revenue [Line Items]
Net sales									(0.1)	0.0	0.0
Other \| Specialty Alloys Operations \| Operating
Disaggregation of Revenue [Line Items]
Net sales									43.0	45.1	43.8
Other \| Performance Engineered Products \| Operating
Disaggregation of Revenue [Line Items]
Net sales									$ 9.8	$ 8.8	$ 7.6