Revenue - Summary of Revenue by End-use Markets (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
Specialty Alloys Operations
Disaggregation of Revenue [Line Items]
Net sales	2,548.7	2,432.8	2,201.5
Performance Engineered Products
Disaggregation of Revenue [Line Items]
Net sales	328.4	326.9	348.8
Operating
Disaggregation of Revenue [Line Items]
Net sales	2,969.0	2,854.8	2,647.3
Operating | Specialty Alloys Operations
Disaggregation of Revenue [Line Items]
Net sales	2,563.6	2,443.8	2,213.6
Operating | Performance Engineered Products
Disaggregation of Revenue [Line Items]
Net sales	405.4	411.0	433.7
Intersegment
Disaggregation of Revenue [Line Items]
Net sales	(91.9)	(95.1)	(97.0)
Intersegment | Specialty Alloys Operations
Disaggregation of Revenue [Line Items]
Net sales	(14.9)	(11.0)	(12.1)
Intersegment | Performance Engineered Products
Disaggregation of Revenue [Line Items]
Net sales	(77.0)	(84.1)	(84.9)
Aerospace and Defense
Disaggregation of Revenue [Line Items]
Net sales	1,768.6	1,538.8	1,290.7
Aerospace and Defense | Operating | Specialty Alloys Operations
Disaggregation of Revenue [Line Items]
Net sales	1,679.6	1,449.9	1,214.6
Aerospace and Defense | Operating | Performance Engineered Products
Disaggregation of Revenue [Line Items]
Net sales	104.0	111.1	108.0
Aerospace and Defense | Intersegment
Disaggregation of Revenue [Line Items]
Net sales	(15.0)	(22.2)	(31.9)
Medical
Disaggregation of Revenue [Line Items]
Net sales	351.2	375.6	301.6
Medical | Operating | Specialty Alloys Operations
Disaggregation of Revenue [Line Items]
Net sales	243.7	282.4	213.8
Medical | Operating | Performance Engineered Products
Disaggregation of Revenue [Line Items]
Net sales	166.8	144.9	123.4
Medical | Intersegment
Disaggregation of Revenue [Line Items]
Net sales	(59.3)	(51.7)	(35.6)
Energy
Disaggregation of Revenue [Line Items]
Net sales	200.3	185.8	163.3
Energy | Operating | Specialty Alloys Operations
Disaggregation of Revenue [Line Items]
Net sales	193.2	177.2	151.6
Energy | Operating | Performance Engineered Products
Disaggregation of Revenue [Line Items]
Net sales	7.1	8.6	11.6
Energy | Intersegment
Disaggregation of Revenue [Line Items]
Net sales	0.0	0.0	0.1
Transportation
Disaggregation of Revenue [Line Items]
Net sales	113.3	149.1	185.0
Transportation | Operating | Specialty Alloys Operations
Disaggregation of Revenue [Line Items]
Net sales	105.8	141.3	178.5
Transportation | Operating | Performance Engineered Products
Disaggregation of Revenue [Line Items]
Net sales	7.9	8.2	7.5
Transportation | Intersegment
Disaggregation of Revenue [Line Items]
Net sales	(0.4)	(0.4)	(1.0)
Industrial and Consumer
Disaggregation of Revenue [Line Items]
Net sales	359.5	415.3	487.2
Industrial and Consumer | Operating | Specialty Alloys Operations
Disaggregation of Revenue [Line Items]
Net sales	341.3	393.0	455.1
Industrial and Consumer | Operating | Performance Engineered Products
Disaggregation of Revenue [Line Items]
Net sales	35.3	40.3	60.6
Industrial and Consumer | Intersegment
Disaggregation of Revenue [Line Items]
Net sales	(17.1)	(18.0)	(28.5)
Distribution
Disaggregation of Revenue [Line Items]
Net sales	84.2	95.1	122.5
Distribution | Operating | Specialty Alloys Operations
Disaggregation of Revenue [Line Items]
Net sales	0.0	0.0	0.0
Distribution | Operating | Performance Engineered Products
Disaggregation of Revenue [Line Items]
Net sales	84.3	97.9	122.6
Distribution | Intersegment
Disaggregation of Revenue [Line Items]
Net sales	$ (0.1)	$ (2.8)	$ (0.1)