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		6 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Jun. 30, 2020
Revenue from Contract with Customer [Abstract]
Consolidated net sales	$ 348.8	$ 573.0	$ 702.1	$ 1,158.4
Operating (Loss) Income:
Consolidated operating (loss) income	(89.0)	55.0	(137.8)	114.8
Depreciation and Amortization:
Consolidated depreciation and amortization	28.6	30.5	59.6	61.0
Capital Expenditures:
Consolidated capital expenditures	26.6	46.7	59.9	94.3
Total Assets:
Consolidated total assets	3,043.9		3,043.9		$ 3,227.2
Corporate
Operating (Loss) Income:
Consolidated operating (loss) income	(70.6)	(21.9)	(97.1)	(41.0)
Depreciation and Amortization:
Consolidated depreciation and amortization	1.0	1.3	2.7	2.6
Capital Expenditures:
Consolidated capital expenditures	9.8	16.4	19.3	32.6
Total Assets:
Consolidated total assets	510.0		510.0		428.9
Intersegment
Revenue from Contract with Customer [Abstract]
Consolidated net sales	(6.4)	(16.0)	(15.7)	(31.1)
Operating (Loss) Income:
Consolidated operating (loss) income	0.4	0.2	0.4	0.2
Depreciation and Amortization:
Consolidated depreciation and amortization	0.1	(0.2)	0.1	(0.5)
Capital Expenditures:
Consolidated capital expenditures	0.0	0.0	0.0	0.0
Total Assets:
Consolidated total assets	(13.9)		(13.9)		(9.2)
Specialty Alloys Operations | Operating
Revenue from Contract with Customer [Abstract]
Consolidated net sales	300.4	483.0	601.1	974.1
Operating (Loss) Income:
Consolidated operating (loss) income	(11.6)	76.3	(30.2)	157.3
Depreciation and Amortization:
Consolidated depreciation and amortization	23.3	23.2	46.5	46.8
Capital Expenditures:
Consolidated capital expenditures	15.7	24.9	37.4	50.1
Total Assets:
Consolidated total assets	2,088.7		2,088.7		2,259.0
Performance Engineered Products | Operating
Revenue from Contract with Customer [Abstract]
Consolidated net sales	54.8	106.0	116.7	215.4
Operating (Loss) Income:
Consolidated operating (loss) income	(7.2)	0.4	(10.9)	(1.7)
Depreciation and Amortization:
Consolidated depreciation and amortization	4.2	6.2	10.3	12.1
Capital Expenditures:
Consolidated capital expenditures	1.1	$ 5.4	3.2	$ 11.6
Total Assets:
Consolidated total assets	$ 459.1		$ 459.1		$ 548.5