Inventories

Inventories at December 31, 2017 and 2016 were as follows (in millions):



	2017			2016
Raw materials and supplies	$	162.8		$	149.6
Work-in-process	955.5			837.9
Finished goods	165.0			161.7
Total inventories at current cost	1,283.3			1,149.2
Adjustment from current cost to LIFO cost basis	43.1			97.3
Inventory valuation reserves	(121.5		)	(169.0		)
Progress payments	(28.8		)	(40.5		)
Total inventories, net	$	1,176.1		$	1,037.0

Inventories, before progress payments, determined on the LIFO method were $821.2 million at December 31, 2017, and $736.3 million at December 31, 2016. The remainder of the inventory was determined using the FIFO and average cost methods, and these inventory values do not differ materially from current cost. Due to deflationary impacts primarily related to raw materials, the carrying value of the Company’s inventory as valued on LIFO exceeds current replacement cost, and based on a lower of cost or market value analysis, a net realizable value (NRV) inventory reserve is required. In applying the lower of cost or market principle, market means current replacement cost, subject to a ceiling (market value shall not exceed net realizable value) and a floor (market shall not exceed net realizable value reduced by an allowance for a normal profit margin). Impacts to cost of sales for changes in the LIFO costing methodology and associated NRV inventory reserves were as follows (in millions):



	Fiscal year ended December 31,
	2017			2016			2015
LIFO benefit (charge)	$	(54.2	)	$	(39.1	)	$	131.6
NRV benefit (charge)	54.0			39.9			(131.5		)
Net cost of sales impact	$	(0.2	)	$	0.8		$	0.1

During 2017, 2016 and 2015, inventory usage resulted in liquidations of LIFO inventory quantities, increasing cost of sales by $4.6 million, $61.5 million and $9.6 million, respectively. These inventories were carried at differing costs prevailing in prior years as compared with the cost of current manufacturing cost and purchases.

The results for fiscal years 2016 and 2015 included $17.7 million and $24.5 million, respectively, in inventory valuation charges related to the market-based valuation of titanium products. Additionally, in the third quarter of 2016, in conjunction with the indefinite idling of the Company’s Rowley, UT titanium sponge facility (see Note 16 for further explanation), an additional $11.3 million charge was taken to revalue titanium sponge inventory based on revised assessments of industrial grade titanium market conditions and expected utilization of this inventory. In December 2015, based on current market prices for non-premium quality (PQ) grades of titanium sponge, the Company recorded an additional $25.4 million charge to revalue this inventory. This charge included revised assessments of the non-PQ titanium market conditions and expected utilization of this inventory.