Segment Information, Geographic and Product Data - Summarized Financial Information by Segment (Details) - USD ($) $ in Millions	12 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2023
Segment Reporting Information [Line Items]
Consolidated net sales	$ 2,877.1	$ 2,759.7	$ 2,550.3
Cost of sales	2,108.5	2,175.4	2,213.0
Operating income	521.8	323.1	133.1
Interest expense, net	48.4	51.0	54.1
Other expense, net	6.1	60.5	6.5
Income before income taxes	467.3	211.6	72.5
Intersegment
Segment Reporting Information [Line Items]
Consolidated net sales	(91.9)	(95.1)	(97.0)
Operating income	(0.9)	1.6	(2.3)
Operating
Segment Reporting Information [Line Items]
Consolidated net sales	2,969.0	2,854.8	2,647.3
Cost of sales	2,199.8	2,272.5	2,307.9
Other segment items	143.6	137.8	128.5
Operating income	625.6	444.5	210.9
Corporate
Segment Reporting Information [Line Items]
Operating income	(102.9)	(123.0)	(75.5)
Specialty Alloys Operations
Segment Reporting Information [Line Items]
Consolidated net sales	2,548.7	2,432.8	2,201.5
Specialty Alloys Operations | Intersegment
Segment Reporting Information [Line Items]
Consolidated net sales	(14.9)	(11.0)	(12.1)
Specialty Alloys Operations | Operating
Segment Reporting Information [Line Items]
Consolidated net sales	2,563.6	2,443.8	2,213.6
Cost of sales	1,855.8	1,923.0	1,934.9
Other segment items	119.2	112.3	99.6
Operating income	588.6	408.5	179.1
Performance Engineered Products
Segment Reporting Information [Line Items]
Consolidated net sales	328.4	326.9	348.8
Performance Engineered Products | Intersegment
Segment Reporting Information [Line Items]
Consolidated net sales	(77.0)	(84.1)	(84.9)
Performance Engineered Products | Operating
Segment Reporting Information [Line Items]
Consolidated net sales	405.4	411.0	433.7
Cost of sales	344.0	349.5	373.0
Other segment items	24.4	25.5	28.9
Operating income	$ 37.0	$ 36.0	$ 31.8