Business Segments - Schedule of results of operation, depreciation and amortization, capital expenditures and total assets by reportable segments (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019	Jun. 30, 2019
Net Sales:
Consolidated net sales	$ 585.4	$ 609.9	$ 1,743.8	$ 1,738.8
Operating Income (Loss):
Consolidated operating income	58.7	73.2	173.5	173.6
Depreciation and Amortization:
Consolidated depreciation and amortization	31.2	30.8	92.2	90.9
Capital Expenditures:
Consolidated capital expenditures	49.7	49.0	144.0	130.7
Total Assets:
Consolidated total assets	3,429.4		3,429.4		$ 3,187.8
Corporate
Operating Income (Loss):
Consolidated operating income	(17.8)	(17.3)	(58.8)	(51.5)
Depreciation and Amortization:
Consolidated depreciation and amortization	1.8	1.2	4.4	3.6
Capital Expenditures:
Consolidated capital expenditures	11.3	9.4	43.9	23.6
Total Assets:
Consolidated total assets	311.3		311.3		192.5
Intersegment
Net Sales:
Consolidated net sales	(11.3)	(17.1)	(42.4)	(50.0)
Operating Income (Loss):
Consolidated operating income	0.4	0.3	0.6	1.5
Depreciation and Amortization:
Consolidated depreciation and amortization	(0.2)	(0.2)	(0.5)	(0.5)
Capital Expenditures:
Consolidated capital expenditures	0.0	(0.3)	(0.1)	(1.1)
Total Assets:
Consolidated total assets	(12.9)		(12.9)		(18.7)
Specialty Alloys Operations | Operating
Net Sales:
Consolidated net sales	488.1	498.3	1,462.2	1,435.4
Operating Income (Loss):
Consolidated operating income	76.4	73.6	233.7	195.3
Depreciation and Amortization:
Consolidated depreciation and amortization	23.1	23.8	69.8	71.3
Capital Expenditures:
Consolidated capital expenditures	34.1	24.6	84.3	66.0
Total Assets:
Consolidated total assets	2,448.7		2,448.7		2,349.2
Performance Engineered Products | Operating
Net Sales:
Consolidated net sales	108.6	128.7	324.0	353.4
Operating Income (Loss):
Consolidated operating income	(0.3)	16.6	(2.0)	28.3
Depreciation and Amortization:
Consolidated depreciation and amortization	6.5	6.0	18.5	16.5
Capital Expenditures:
Consolidated capital expenditures	4.3	$ 15.3	15.9	$ 42.2
Total Assets:
Consolidated total assets	$ 682.3		$ 682.3		$ 664.8